57 results on '"Svilen Bobev"'
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2. Observation of Anomalously High Seebeck Coefficients in the Family of Zintl Phase Semiconductors Ca10RECdSb9 (RE = Rare-Earth Metal)
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Michael O. Ogunbunmi and Svilen Bobev
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General Chemical Engineering ,Materials Chemistry ,General Chemistry - Published
- 2022
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3. Giant Thermoelectric Power Factor Anisotropy in PtSb1.4Sn0.6
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Yu Liu, Zhixiang Hu, Michael O. Ogunbunmi, Eli Stavitski, Klaus Attenkofer, Svilen Bobev, and Cedomir Petrovic
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Inorganic Chemistry ,Condensed Matter - Materials Science ,Condensed Matter - Strongly Correlated Electrons ,Strongly Correlated Electrons (cond-mat.str-el) ,Materials Science (cond-mat.mtrl-sci) ,FOS: Physical sciences ,Physical and Theoretical Chemistry - Abstract
We report giant anisotropy in thermoelectric power factor ($S^2\sigma$) of marcasite structure-type PtSb$_{1.4}$Sn$_{0.6}$. PtSb$_{1.4}$Sn$_{0.6}$, synthesized using ambient pressure flux growth method upon mixing Sb and Sn on the same atomic site, is a new phase different from both PtSb$_2$ and PtSn$_2$ that crystallize in the cubic $Pa\bar{3}$ pyrite and $Fm\bar{3}m$ fluorite unit cell symmetry, respectively. Giant difference in $S^2\sigma$ for heat flow applied along different principal directions of the orthorhombic unit cell mostly stems from anisotropic Seebeck coefficients. more...
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- 2022
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4. Synthesis of Type II Ge and Ge–Si Alloyed Clathrates Using Solid-State Electrochemical Oxidation of Zintl Phase Precursors
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Andrew Dopilka, Alexander Ovchinnikov, Amanda Childs, Svilen Bobev, Xihong Peng, and Candace K. Chan
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Inorganic Chemistry ,Physical and Theoretical Chemistry - Abstract
Germanium clathrates with the type II structure are open-framework materials that show promise for various applications, but the difficulty of achieving phase-pure products via traditional synthesis routes has hindered their development. Herein, we demonstrate the synthesis of type II Ge clathrates in a two-electrode electrochemical cell using Na more...
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- 2022
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5. Structural Complexity and Tuned Thermoelectric Properties of a Polymorph of the Zintl Phase Ca2CdSb2 with a Non-centrosymmetric Monoclinic Structure
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Michael O. Ogunbunmi, Sviatoslav Baranets, and Svilen Bobev
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Inorganic Chemistry ,Physical and Theoretical Chemistry - Published
- 2022
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6. On the Effects of Aliovalent Substitutions in Thermoelectric Zintl Pnictides. Varied Polyanionic Dimensionality and Complex Structural Transformations─The Case of Sr3ZnP3 vs Sr3AlxZn1–xP3
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Sviatoslav Baranets, Adam Balvanz, Gregory M. Darone, and Svilen Bobev
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General Chemical Engineering ,Materials Chemistry ,General Chemistry - Published
- 2022
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7. Synthesis and Transport Properties of the Family of Zintl Phases Ca3RESb3 (RE = La–Nd, Sm, Gd–Tm, Lu): Exploring the Roles of Crystallographic Disorder and Core 4f Electrons for Enhancing Thermoelectric Performance
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Michael O. Ogunbunmi, Sviatoslav Baranets, and Svilen Bobev
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General Chemical Engineering ,Materials Chemistry ,General Chemistry - Published
- 2021
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8. Two Polymorphs of BaZn2P2: Crystal Structures, Phase Transition, and Transport Properties
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Michael O. Ogunbunmi, Adam Balvanz, Sviatoslav Baranets, and Svilen Bobev
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Inorganic Chemistry ,Crystallography ,Phase transition ,Tetragonal crystal system ,Chemistry ,Band gap ,Seebeck coefficient ,Phase (matter) ,Orthorhombic crystal system ,Crystal structure ,Physical and Theoretical Chemistry ,Single crystal - Abstract
The novel α-BaZn2P2 structural polymorph has been synthesized and structurally characterized for the first time. Its structure, elucidated from single crystal X-ray diffraction, indicates that the compound crystallizes in the orthorhombic α-BaCu2S2 structure type, with unit cell parameters a = 9.7567(14) A, b = 4.1266(6) A, and c = 10.6000(15) A. With β-BaZn2P2 being previously identified as belonging to the ThCr2Si2 family and with the precedent of structural phase transitions between the α-BaCu2S2 type and the ThCr2Si2 type, the potential for the pattern to be extended to the two different structural forms of BaZn2P2 was explored. Thermal analysis suggests that a first-order phase transition occurs at ∼1123 K, whereby the low-temperature orthorhombic α-phase transforms to a high-temperature tetragonal β-BaZn2P2, the structure of which was also studied and confirmed by single-crystal X-ray diffraction. Preliminary transport properties and band structure calculations indicate that α-BaZn2P2 is a p-type, narrow-gap semiconductor with a direct bandgap of 0.5 eV, which is an order of magnitude lower than the calculated indirect bandgap for the β-BaZn2P2 phase. The Seebeck coefficient, S(T), for the material increases steadily from the room temperature value of 119 μV/K to 184 μV/K at 600 K. The electrical resistivity (ρ) of α-BaZn2P2 is relatively high, on the order of 40 mΩ·cm, and the ρ(T) dependence shows gradual decrease upon heating. Such behavior is comparable to those of the typical semimetals or degenerate semiconductors. more...
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- 2021
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9. Structural Uniqueness of the [Nb(As5)2]5– Cluster in the Zintl Phase Cs5NbAs10
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Sviatoslav Baranets, Alexander Ovchinnikov, Svilen Bobev, and Olga Dmitrenko
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010304 chemical physics ,Band gap ,Atom (order theory) ,010402 general chemistry ,Ring (chemistry) ,01 natural sciences ,0104 chemical sciences ,chemistry.chemical_compound ,Crystallography ,Zintl phase ,chemistry ,0103 physical sciences ,Cluster (physics) ,Physical and Theoretical Chemistry ,Electronic band structure ,Cyclopentane ,Monoclinic crystal system - Abstract
The structure of the novel Zintl phase, Cs5NbAs10, is reported for the first time. This compound crystallizes in the monoclinic P21/c space group (no. 14) with eight formula units per cell. The structure represents a unique atomic arrangement, constituting a new structure type with Wyckoff sequence e32. The most important structural element is the unprecedented [Nb(As5)2]5- cluster anion, formed by a Nb atom enclosed between two As5 rings. These nonaromatic cyclic species, formally [As5]5-, adopt an envelope conformation similar to that of cyclopentane. To date, it is only the second example of an [As5]5- ring with this conformation, reported in an inorganic solid-state compound. The bonding characteristics of the [Nb(As5)2]5- cluster and the [As5]5- rings are thoroughly investigated using first-principles methods and discussed. Electronic band structure calculations on Cs5NbAs10 suggest that this compound is a semiconductor with an estimated band gap of ca. 1.4 eV. more...
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- 2021
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10. Complex Structural Disorder in the Zintl Phases Yb10MnSb9 and Yb21Mn4Sb18
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Sviatoslav Baranets, Svilen Bobev, and Alexander Ovchinnikov
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Inorganic Chemistry ,Diffraction ,Crystallography ,Ternary numeral system ,010405 organic chemistry ,Chemistry ,Phase (matter) ,Crystal structure ,Physical and Theoretical Chemistry ,010402 general chemistry ,01 natural sciences ,0104 chemical sciences - Abstract
A systematic investigation of the ternary system Yb–Mn–Sb led to the discovery of the novel phase Yb10MnSb9. Its crystal structure was characterized by single-crystal X-ray diffraction and found to... more...
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- 2021
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11. Ultralow Thermal Conductivity and High Thermopower in a New Family of Zintl Antimonides Ca10MSb9 (M = Ga, In, Mn, Zn) with Complex Structures and Heavy Disorder
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Alexander Ovchinnikov, Svilen Bobev, Sevan Chanakian, and Alexandra Zevalkink
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Materials science ,General Chemical Engineering ,Analytical chemistry ,Flux ,02 engineering and technology ,General Chemistry ,010402 general chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,0104 chemical sciences ,Thermal conductivity ,Seebeck coefficient ,Materials Chemistry ,0210 nano-technology - Abstract
A new family of Zintl antimonides with the approximate composition Ca10MSb9 (M = Ga, In, Mn, Zn) has been obtained via two synthetic approaches: (1) using Sb as a flux and (2) using the conventiona... more...
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- 2021
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12. Caught in Action. The Late Rare Earths Thulium and Lutetium Substituting Aluminum Atoms in the Structure of Ca14AlBi11
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Sviatoslav Baranets and Svilen Bobev
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Lanthanide ,Crystal chemistry ,chemistry.chemical_element ,General Chemistry ,Crystal structure ,Biochemistry ,Catalysis ,Lutetium ,Metal ,Crystallography ,Colloid and Surface Chemistry ,Thulium ,chemistry ,Main group element ,Zintl phase ,visual_art ,visual_art.visual_art_medium - Abstract
Described are two unprecedented cases, where the rare earth metals Tm and Lu partially substitute Al atoms in the structure of the Zintl phase Ca14AlBi11. These are the first examples within this large family where lanthanides replace the atoms of a main group element. Such crystal chemistry has never been observed before in other materials with the same structure. The uniqueness of this finding is also amplified by the fact that the rare earth metal atoms in the crystal structure are tetrahedrally coordinated, which is another remarkable trait of the new Tm- and Lu-substituted compounds. more...
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- 2020
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13. New n-Type Zintl Phases for Thermoelectrics: Discovery, Structural Characterization, and Band Engineering of the Compounds A2CdP2 (A = Sr, Ba, Eu)
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Elif Ertekin, Svilen Bobev, Jiaxing Qu, Adam Balvanz, Prashun Gorai, and Sviatoslav Baranets
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Materials science ,General Chemical Engineering ,02 engineering and technology ,General Chemistry ,Crystal structure ,010402 general chemistry ,021001 nanoscience & nanotechnology ,Thermoelectric materials ,01 natural sciences ,0104 chemical sciences ,Characterization (materials science) ,Crystallography ,Chemical bond ,Band engineering ,Thermoelectric effect ,Materials Chemistry ,0210 nano-technology - Abstract
Zintl phases, owing to their complex crystal structures and intricate chemical bonding, have recently been recognized as promising candidates for thermoelectric (TE) applications. Band engineering,... more...
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- 2020
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14. Understanding the Amorphous Lithiation Pathway of the Type I Ba8Ge43 Clathrate with Synchrotron X-ray Characterization
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Andrew Dopilka, Amanda Childs, Candace K. Chan, and Svilen Bobev
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Electrode material ,Materials science ,General Chemical Engineering ,Clathrate hydrate ,X-ray ,02 engineering and technology ,General Chemistry ,010402 general chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,Synchrotron ,0104 chemical sciences ,law.invention ,Characterization (materials science) ,Amorphous solid ,Crystallography ,law ,Materials Chemistry ,0210 nano-technology - Abstract
Tetrel (Tt = Si, Ge, and Sn) clathrates have highly tunable host–guest structures and have been investigated as novel electrode materials for Li-ion batteries. However, there is little understandin... more...
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- 2020
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15. Observation of an Unexpected n-Type Semiconducting Behavior in the New Ternary Zintl Phase Eu3InAs3
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Sviatoslav Baranets, Svilen Bobev, and Kalpna Rajput
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Diffraction ,Materials science ,General Chemical Engineering ,02 engineering and technology ,General Chemistry ,010402 general chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,0104 chemical sciences ,Crystallography ,Zintl phase ,Materials Chemistry ,0210 nano-technology ,Ternary operation ,Flux (metabolism) - Abstract
The ternary arsenides Eu3InAs3 and Sr3InAs3 have been obtained by reactions of the elements in In flux at 1373 K. Structure elucidation by single-crystal X-ray diffraction reveals that Eu3InAs3 and... more...
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- 2020
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16. Tunable Magnetic Exchange between Rare-Earth Metal 5d and Iron 3d States: A Case Study of the Multiple Magnetic Transitions in Gd6FeBi2 and the Solid Solutions Dy6–xGdxFeBi2 (1 ≤ x ≤ 5) with Curie Temperatures in the Range 120–350 K
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Wei He, Svilen Bobev, Yong-Mook Kang, Jey-Jau Lee, Jiliang Zhang, and Tonghan Yang
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Diffraction ,Range (particle radiation) ,Materials science ,Condensed matter physics ,General Chemical Engineering ,Rare earth ,Physics::Optics ,02 engineering and technology ,General Chemistry ,010402 general chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,0104 chemical sciences ,Metal ,Magnetization ,visual_art ,Magnet ,Materials Chemistry ,visual_art.visual_art_medium ,Curie ,0210 nano-technology ,Solid solution - Abstract
In this paper, the room-temperature magnet Gd6FeBi2 was comprehensively characterized by means of temperature-dependent single-crystal X-ray diffraction, magnetization measurements, and experimenta... more...
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- 2020
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17. Computational Design of Thermoelectric Alloys Through Optimization of Transport and Dopability
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Adam Balvanz, Sviatoslav Baranets, Prashun Gorai, Svilen Bobev, and Jiaxing Qu
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Materials science ,Optimization problem ,business.industry ,Process Chemistry and Technology ,Alloy ,Electronic structure ,engineering.material ,Thermoelectric materials ,Engineering physics ,Condensed Matter::Materials Science ,Mechanics of Materials ,Photovoltaics ,Lattice (order) ,Thermoelectric effect ,engineering ,Density functional theory ,General Materials Science ,Electrical and Electronic Engineering ,Material properties ,business - Abstract
Alloying is a common technique to optimize the functional properties of materials for thermoelectrics, photovoltaics, energy storage etc. Designing thermoelectric (TE) alloys is especially challenging because it is a multi-property optimization problem, where the properties that contribute to high TE performance are interdependent. In this work, we develop a computational framework that combines first-principles calculations with alloy and point defect modeling to identify alloy compositions that optimize the electronic, thermal, and defect properties. We apply this framework to design n-type Ba2(1-x)Sr2xCdP2 Zintl thermoelectric alloys. Our predictions of the crystallographic properties such as lattice parameters and site disorder are validated with experiments. To optimize the conduction band electronic structure, we perform band unfolding to sketch the effective band structures of alloys and find a range of compositions that facilitate band convergence and minimize alloy scattering of electrons. We assess the n-type dopability of the alloys by extending the standard approach for computing point defect energetics in ordered structures. Through the application of this framework, we identify an optimal alloy composition range with the desired electronic and thermal transport properties, and n-type dopability. Such a computational framework can also be used to design alloys for other functional applications beyond TE. more...
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- 2021
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18. Bismuth as a Reactive Solvent in the Synthesis of Multicomponent Transition-Metal-Bearing Bismuthides
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Alexander Ovchinnikov and Svilen Bobev
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Bearing (mechanical) ,010405 organic chemistry ,Chemistry ,Inorganic chemistry ,chemistry.chemical_element ,010402 general chemistry ,01 natural sciences ,0104 chemical sciences ,law.invention ,Liquid bismuth ,Bismuth ,Inorganic Chemistry ,Solvent ,Transition metal ,law ,Melting point ,Physical and Theoretical Chemistry ,Solubility - Abstract
Employment of liquid bismuth (Bi) allows the facile single-crystal growth of compounds containing elements with high melting points, provided that these elements have reasonably high solubility in Bi. Utilization of the Bi flux approach yielded two new ternary bismuthides, SrNi more...
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- 2019
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19. New n-type Zintl Phases for Thermoelectrics: Discovery, Structural Characterization and Band Engineering of the Compounds A2CdP2 (A = Sr, Ba, Eu)
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Prashun Gorai, Adam Balvanz, Elif Ertekin, Sviatoslav Baranets, Svilen Bobev, and Jiaxing Qu
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Materials science ,Zintl phase ,Chemical physics ,Thermoelectric effect ,Doping ,Orthorhombic crystal system ,Crystal structure ,Isostructural ,Thermoelectric materials ,Characterization (materials science) - Abstract
Zintl phases, owing to their complex crystal structures and intricate chemical bonding, have recently been recognized as promising candidates for thermoelectric (TE) applications. Band engineering, including band convergence has been shown to be an effective way to enhance the thermoelectric performance of such materials. In this work, a series of emerging TE materials, the isostructural Zintl phases with the general formula A2CdP2 (A = Sr, Ba, Eu) are presented for the first time. Their structures, established from single-crystal X-ray diffraction methods, show them to crystallize with the orthorhombic Yb2CdSb2 structure type, with first-principles calculations on phase stability confirming that Ba2CdP2 and Sr2CdP2 are thermodynamically stable. Computationally, it was found that both Ba2CdP2 and Sr2CdP2 have the potential to exhibit high n-type TE performance (0.6 and 0.7 relative to the n-type PbTe, a reference TE material). To optimize the TE performance, band engineering strategies, including isovalent substitution and cation mutations, were investigated. From the band engineering of Ba2CdP2 via isovalent substitution of Sr on a single Ba site, leading to the quaternary composition SrBaCdP2, it can be suggested that increasing the conduction band valley degeneracy is an effective way to improve the n-type TE performance by three-fold. Moreover, first-principles defect calculations reveal that both Ba2CdP2 and SrBaCdP2 are n-type dopable, adding these compounds to a small list of rare n-type dopable Zintl phases. The band engineering strategies used in this work are equally applicable to other TE materials, either for optimization of existing TE materials or designing new materials with desired properties. more...
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- 2020
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20. Experimental and Computational Study of the Lithiation of Ba8AlyGe46–y Based Type I Germanium Clathrates
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J. Mark Weller, Candace K. Chan, Xihong Peng, Svilen Bobev, Andrew Dopilka, and Ran Zhao
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Diffraction ,Work (thermodynamics) ,Materials science ,Clathrate hydrate ,chemistry.chemical_element ,Germanium ,02 engineering and technology ,010402 general chemistry ,021001 nanoscience & nanotechnology ,Electrochemistry ,01 natural sciences ,0104 chemical sciences ,Amorphous solid ,Anode ,chemistry ,Transmission electron microscopy ,Physical chemistry ,General Materials Science ,0210 nano-technology - Abstract
In this work, we investigate the electrochemical properties of Ba8AlyGe46–y (y = 0, 4, 8, 12, 16) clathrates prepared by arc-melting. These materials have cage-like structures with large cavity volumes and can also have vacancies on the Ge framework sites, features which may be used to accommodate Li. Herein, a structural, electrochemical, and theoretical investigation is performed to explore these materials as anodes in Li-ion batteries, including analysis of the effect of the Al content and framework vacancies on the observed electrochemical properties. Single-crystal X-ray diffraction (XRD) studies indicate the presence of vacancies at the 6c site of the clathrate framework as the Al content decreases, and the lithiation potentials and capacities are observed to decrease as the degree of Al substitution increases. From XRD, electrochemical, and transmission electron microscopy analysis, we find that all of the clathrate compositions undergo two-phase reactions to form Li-rich amorphous phases. This is ... more...
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- 2018
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21. Synthesis, and Crystal and Electronic Structures, of the Titanium-Rich Bismuthides AE3Ti8Bi10 (AE = Sr, Ba, Eu)
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Alexander Ovchinnikov and Svilen Bobev
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Magnetic moment ,010405 organic chemistry ,Chemistry ,Crystal structure ,010402 general chemistry ,01 natural sciences ,Chemical formula ,0104 chemical sciences ,Inorganic Chemistry ,Crystal ,Pearson symbol ,Crystallography ,Octahedron ,Chemical bond ,Substructure ,Physical and Theoretical Chemistry - Abstract
Three isotypic compounds with the chemical formula AE3Ti8Bi10 (AE = Sr, Ba, Eu) have been obtained via both high-temperature solid state and flux growth reactions. Their crystal structure, representing a new type (space group P63/mmc, Pearson symbol hP42), features an open framework composed of interlinked TiBi5 square pyramids and TiBi6 octahedra. The Ti–Bi substructure is penetrated by infinite columns of face-sharing AE6 polyhedra centered by Bi atoms. First-principle calculations and physical property measurements indicate metallic behavior and absence of localized magnetic moments on the Ti atoms. Analysis of the chemical bonding reveals strong Ti–Bi and Ti–Ti bonds. The latter demonstrate classic two-center, as well as multicenter, interactions. more...
- Published
- 2018
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22. Rare-Earth Metal Substitutions in Ca9–xRExMn4Sb9 (RE = La–Nd, Sm; x ≈ 1). Synthesis and Characterization of a New Series of Narrow-Gap Semiconductors
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Svilen Bobev and Yi Wang
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Diffraction ,Materials science ,General Chemical Engineering ,02 engineering and technology ,General Chemistry ,Narrow-gap semiconductor ,010402 general chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,0104 chemical sciences ,Characterization (materials science) ,Metal ,Crystallography ,Group (periodic table) ,Electrical resistivity and conductivity ,visual_art ,Materials Chemistry ,visual_art.visual_art_medium ,Orthorhombic crystal system ,Isostructural ,0210 nano-technology - Abstract
This paper details the synthesis and the structural characterization of the new antimonides with general formulas Ca9–xRExMn4Sb9 (RE = La, Ce, Pr, Nd, and Sm; x ≈ 1). The synthesis of these phases was accomplished by both high temperature reactions of the respective elements and by Pb-flux experiments. The structures were determined by single-crystal X-ray diffraction methods. All title compounds are isostructural and crystallize with the orthorhombic space group Pbam (No. 55). The structure is similar, but not isotypic to Ca9Mn4Bi9 (same space group; Pearson code oP44). On the basis of that, Ca9–xRExMn4Sb9 can be considered as new derivatives of this structure type, presenting the first examples of rare-earth metal substitutions within the “9-4-9” family of compounds. Electrical resistivity measurements confirm the successful electron doping, achieved by the aliovalent replacement of Ca2+ with RE3+ cations in the structure, leading to the emergence of narrow band-gap semiconducting behavior. Temperature-... more...
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- 2018
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23. Intricate Li–Sn Disorder in Rare-Earth Metal–Lithium Stannides. Crystal Chemistry of RE3Li4–xSn4+x (RE = La–Nd, Sm; x < 0.3) and Eu7Li8–xSn10+x (x ≈ 2.0)
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Svilen Bobev, Sheng-Ping Guo, Nian-Tzu Suen, and James Hoos
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010405 organic chemistry ,Crystal chemistry ,chemistry.chemical_element ,Crystal structure ,Electronic structure ,010402 general chemistry ,01 natural sciences ,0104 chemical sciences ,Inorganic Chemistry ,Crystallography ,Homologous series ,chemistry.chemical_compound ,chemistry ,Lithium ,Orthorhombic crystal system ,Physical and Theoretical Chemistry ,Valence electron ,Ternary operation - Abstract
Reported are the syntheses, crystal structures, and electronic structures of six rare-earth metal-lithium stannides with the general formulas RE3Li4- xSn4+ x (RE = La-Nd, Sm) and Eu7Li8- xSn10+ x. These new ternary compounds have been synthesized by high-temperature reactions of the corresponding elements. Their crystal structures have been established using single-crystal X-ray diffraction methods. The RE3Li4- xSn4+ x phases crystallize in the orthorhombic body-centered space group Immm (No. 71) with the Zr3Cu4Si4 structure type (Pearson code oI22), and the Eu7Li8- xSn10+ x phase crystallizes in the orthorhombic base-centered space group Cmmm (No. 65) with the Ce7Li8Ge10 structure type (Pearson code oC50). Both structures can be consdered as part of the [RESn2] n[RELi2Sn] m homologous series, wherein the structures are intergrowths of imaginary RESn2 (AlB2-like structure type) and RELi2Sn (MgAl2Cu-like structure type) fragments. Close examination the structures indicates complex occupational Li-Sn disorder, apparently governed by the drive of the structure to achieve an optimal number of valence electrons. This conclusion based on experimental results is supported by detailed electronic structure calculations, carried out using the tight-binding linear muffin-tin orbital method. more...
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- 2018
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24. Synthesis of 1T, 2H, and 6R Germanane Polytypes
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Wolfgang Windl, Shishi Jiang, Yaxian Wang, Svilen Bobev, Michael R. Scudder, Maxx Q. Arguilla, Nicholas D. Cultrara, and Joshua E. Goldberger
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Diffraction ,Materials science ,Band gap ,General Chemical Engineering ,Stacking ,chemistry.chemical_element ,Germanium ,02 engineering and technology ,General Chemistry ,010402 general chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,Thermal expansion ,0104 chemical sciences ,Crystallography ,chemistry ,Zintl phase ,Lattice (order) ,Materials Chemistry ,0210 nano-technology ,Germanane - Abstract
Polytypism, or the ability for materials to crystallize with different stacking sequences, often leads to fundamentally different properties in families of two-dimensional materials. Here, we show that is possible to control the polytype of GeH, a representative two-dimensional material that is synthesized topotactically by first controlling the polytype sequence of the precursor Zintl phase. 1T, 2H, and 6R GeH can be prepared by the topotactic deintercalation of 1T EuGe2, 2H α-CaGe2, and 6R β-CaGe2, respectively. The 6R and 1T GeH polytypes exhibit remarkably similar properties and feature band gaps of 1.63 and 1.59 eV, respectively. However, the 2H CaGe2 precursor forms due to the incorporation of small amounts of In flux in the germanium lattice, which is retained when converted to GeH. Consequently, 2H GeH has a reduced band gap of 1.45 eV. Finally, temperature dependent diffraction of 6R GeH shows a negative coefficient of thermal expansion along the a-axis and a positive coefficient of thermal expan... more...
- Published
- 2018
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25. Anodes for Lithium-Ion Batteries Based on Type I Silicon Clathrate Ba8Al16Si30 - Role of Processing on Surface Properties and Electrochemical Behavior
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Lakshmi Krishna, Candace K. Chan, Ting Yang, Hangkun Jing, Svilen Bobev, J. Mark Weller, and Ran Zhao
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Materials science ,Silicon ,Inorganic chemistry ,Clathrate hydrate ,chemistry.chemical_element ,02 engineering and technology ,010402 general chemistry ,021001 nanoscience & nanotechnology ,Electrochemistry ,01 natural sciences ,0104 chemical sciences ,Anode ,symbols.namesake ,chemistry ,Impurity ,symbols ,General Materials Science ,Lithium ,Particle size ,0210 nano-technology ,Raman spectroscopy - Abstract
Type I silicon clathrates based on Ba8AlySi46-y (8 < y < 12) have been studied as potential anodes for lithium-ion batteries and display electrochemical properties that are distinct from those found in conventional silicon anodes. Processing steps such as ball-milling (typically used to reduce the particle size) and acid/base treatment (used to remove nonclathrate impurities) may modify the clathrate surface structure or introduce defects, which could affect the observed electrochemical properties. In this work, we perform a systematic investigation of Ba8AlySi46-y clathrates with y ≈ 16, i.e, having a composition near Ba8Al16Si30, which perfectly satisfies the Zintl condition. The roles of ball-milling and acid/base treatment were investigated using electrochemical, X-ray diffraction, electron microscopy, X-ray photoelectron and Raman spectroscopy analysis. The results showed that acid/base treatment removed impurities from the synthesis, but also led to formation of a surface oxide layer that inhibited ... more...
- Published
- 2017
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26. The Ternary Alkaline-Earth Metal Manganese Bismuthides Sr2MnBi2 and Ba2Mn1–xBi2 (x ≈ 0.15)
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Sheng-Qing Xia, Bayrammurad Saparov, Alexander Ovchinnikov, and Svilen Bobev
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Condensed matter physics ,chemistry.chemical_element ,02 engineering and technology ,Manganese ,Crystal structure ,Electronic structure ,010402 general chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,Magnetic susceptibility ,0104 chemical sciences ,Degenerate semiconductor ,Inorganic Chemistry ,Crystallography ,chemistry ,Orthorhombic crystal system ,Physical and Theoretical Chemistry ,Isostructural ,0210 nano-technology ,Ternary operation - Abstract
Two new ternary manganese bismuthides have been synthesized and their structures established based on single-crystal X-ray diffraction methods. Sr2MnBi2 crystallizes in the orthorhombic space group Pnma (a = 16.200(9) A, b = 14.767(8) A, c = 8.438(5) A, V = 2018(2) A3; Z = 12; Pearson index oP60) and is isostructural to the antimonide Sr2MnSb2. The crystal structure contains corrugated layers of corner- and edge-shared [MnBi4] tetrahedra and Sr atoms enclosed between these layers. Electronic structure calculations suggest that Sr2MnBi2 is a magnetic semiconductor possessing Mn2+ (high-spin d5) ions, and its structure can be rationalized within the Zintl concept as [Sr2+]2[Mn2+][Bi3-]2. The temperature dependence of the resistivity shows behavior consistent with a degenerate semiconductor/poor metal, and magnetic susceptibility measurements reveal a high degree of frustration resulting from the two-dimensional nature of the structure. The compositionally similar Ba2Mn1-xBi2 (x ≈ 0.15) crystallizes in a very different structure (space group Imma, a = 25.597(8) A, b = 25.667(4) A, c = 17.128(3) A, V = 11253(4) A3; Z = 64; Pearson index oI316) with its own structure type. The complex structure boasts Mn atoms in a variety of coordination environments and can be viewed as consisting of two interpenetrating 3D frameworks, linked by Bi-Bi bonds. Ba2Mn1-xBi2 can be regarded as a highly reduced compound with anticipated metallic behavior. more...
- Published
- 2017
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27. Ba and Sr Binary Phosphides: Synthesis, Crystal Structures, and Bonding Analysis
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Svilen Bobev, Alexander I. Boldyrev, Alexander S. Ivanov, Kirill Kovnir, Hua He, and Juli-Anna Dolyniuk
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Inorganic Chemistry ,Crystallography ,Octahedron ,Chemical bond ,Chemistry ,Vacancy defect ,Orthorhombic crystal system ,Electronic structure ,Crystal structure ,Physical and Theoretical Chemistry ,Isostructural ,Monoclinic crystal system - Abstract
Synthesis, crystal structures, and chemical bonding are reported for four binary phosphides with different degrees of phosphorus oligomerization, ranging from isolated P atoms to infinite phosphorus chains. Ba3P2 = Ba4P(2.67)□(0.33) (□ = vacancy) crystallizes in the anti-Th3P4 structure type with the cubic space group I4̅3d (no. 220), Z = 6, a = 9.7520(7) Å. In the Ba3P2 crystal structure, isolated P(3-) anions form distorted octahedra around the Ba(2+) cations. β-Ba5P4 crystallizes in the Eu5As4 structure type with the orthorhombic space group Cmce (no. 64), Z = 4, a = 16.521(2) Å, b = 8.3422(9) Å, c = 8.4216(9) Å. In the crystal structure of β-Ba5P4, one-half of the phosphorus atoms are condensed into P2(4-) dumbbells. SrP2 and BaP2 are isostructural and crystallize in the monoclinic space group P2₁/c (no. 14), Z = 6, a = 6.120(2)/6.368(1) Å, b = 11.818(3)/12.133(2) Å, c = 7.441(2)/7.687(2) Å, β = 126.681(4)/126.766(2)° for SrP2/BaP2. In the crystal structures of SrP2 and BaP2, all phosphorus atoms are condensed into ∞(1)P(1-) cis-trans helical chains. Electronic structure calculations, chemical bonding analysis via the recently developed solid-state adaptive natural density partitioning (SSAdNDP) method, and UV-vis spectroscopy reveal that SrP2 and BaP2 are electron-balanced semiconductors. more...
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- 2015
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28. Synthesis, Structure, Thermoelectric Properties, and Band Gaps of Alkali Metal Containing Type I Clathrates: A8Ga8Si38 (A = K, Rb, Cs) and K8Al8Si38
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Hua He, Susan M. Kauzlarich, Frank E. Osterloh, Jing Zhao, Svilen Bobev, and Fan Sui
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Materials science ,Band gap ,General Chemical Engineering ,Inorganic chemistry ,Clathrate hydrate ,Analytical chemistry ,Spark plasma sintering ,General Chemistry ,Atmospheric temperature range ,Alkali metal ,Electrical resistivity and conductivity ,Seebeck coefficient ,Thermoelectric effect ,Materials Chemistry - Abstract
A series of alkali metal containing compounds with type I clathrate structure, A8Ga8Si38 (A = K, Rb, Cs) and K8Al8Si38, were synthesized and characterized. Room temperature lattice parameters of A8Ga8Si38 (A = K, Rb, Cs) and K8Al8Si38 were determined to be 10.424916(10), 10.470174(13), 10.535069(15), and 10.48071(2) A, respectively. The type I clathrate structure (cubic, Pm3n) was confirmed for all phases, and in the case of K8Al8Si38 and K8Ga8Si38, the structures were also refined using synchrotron powder diffraction data. The samples were consolidated by Spark Plasma Sintering (SPS) for thermoelectric property characterization. Electrical resistivity was measured by four probe AC transport method in the temperature range of 30 to 300 K. Seebeck measurements from 2 to 300 K were consistent with K8Al8Si38 and K8Ga8Si38 being n-type semiconductors, while Rb8Ga8Si38 and Cs8Ga8Si38 were p-type semiconductors. K8Al8Si38 shows the lowest electrical resistivity and the highest Seebeck coefficient. This phase a... more...
- Published
- 2015
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29. Quaternary Pnictides with Complex, Noncentrosymmetric Structures. Synthesis and Structural Characterization of the New Zintl Phases Na11Ca2Al3Sb8, Na4CaGaSb3, and Na15Ca3In5Sb12
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Yi Wang, Svilen Bobev, and Stanislav S. Stoyko
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Inorganic Chemistry ,Crystallography ,Group (periodic table) ,Chemistry ,Inorganic chemistry ,Tetrahedron ,Orthorhombic crystal system ,Structure type ,Physical and Theoretical Chemistry ,Characterization (materials science) ,Monoclinic crystal system - Abstract
Three new Zintl phases, Na11Ca2Al3Sb8, Na4CaGaSb3, and Na15Ca3In5Sb12, have been synthesized by solid-state reactions, and their structures have been determined by single-crystal X-ray diffraction. Na11Ca2Al3Sb8 crystallizes with its own structure type (Pearson index oP48) with the primitive orthorhombic space group Pmn21 (No. 31). The structure is best viewed as [Al3Sb8]15– units of fused AlSb4 tetrahedra, a novel type of Zintl ion, with Na+ and Ca2+ cations that solvate them. Na4CaGaSb3 also crystallizes in its own type with the primitive monoclinic space group Pc (No. 7; Pearson index mP36), and its structure boasts one-dimensional [GaSb3]6– helical chains of corner-shared GaSb4 tetrahedra. The third new compound, Na15Ca3In5Sb12, crystallizes with the recently reported K2BaCdSb2 structure type (space group Pmc21; Pearson index oP12). The Na15Ca3In5Sb12 structure is based on polyanionic layers made of corner-shared InSb4 tetrahedra. Approximately one-sixth of the In sites are vacant in a statistical man... more...
- Published
- 2015
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30. Structural Variability versus Structural Flexibility. A Case Study of Eu9Cd4+xSb9 and Ca9Mn4+xSb9 (x ≈ 1/2)
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Sheng-Qing Xia, Zhen Wu, Svilen Bobev, Xiao-Cun Liu, and Xutang Tao
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Inorganic Chemistry ,Crystallography ,Stereochemistry ,Chemistry ,Group (periodic table) ,Differential thermal analysis ,Orthorhombic crystal system ,Structure type ,Physical and Theoretical Chemistry ,Isostructural ,Type (model theory) ,Ternary operation ,Unit (ring theory) - Abstract
The focus of this article is on the synthesis and structural characterization of the new ternary antimonides Eu(9)Cd(4+x)Sb(9) and Ca(9)Mn(4+x)Sb(9) (x ≈ (1)/2). Although these compounds have analogous chemical makeup and formulas, which may suggest isotypism, they actually belong to two different structure types. Eu(9)Cd(4.45(1))Sb(9) is isostructural with the previously reported Eu(9)Zn(4.5)Sb(9) (Pbam), and its structure has unit cell parameters a = 12.9178(11) Å, b = 23.025(2) Å, and c = 4.7767(4) Å. Ca(9)Mn(4.41(1))Sb(9) crystallizes in the orthorhombic space group Pnma with unit cell dimensions a = 12.490(2) Å, b = 4.6292(8) Å, and c = 44.197(8) Å and constitutes a new structure type. The two structures are compared and contrasted, and the structural relationships are discussed. Exploratory work aimed at the arsenic-based analogues of either type led to the identification of Ca(9)Zn(4.46(1))As(9), forming with the latter structure [a = 11.855(2) Å, b = 4.2747(8) Å, and c = 41.440(8) Å]. Differential thermal analysis and electrical resistivity measurements, performed on single crystals of Ca(9)Zn(4+x)As(9), indicate high thermal stability and semiconducting behavior. Magnetic susceptibility measurements on Eu(9)Cd(4+x)Sb(9) samples confirm the expected Eu(2+) ([Xe]4f(7)) ground state. more...
- Published
- 2014
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31. Structural Modulations in the Rare-Earth Metal Digermanides REAl1–xGe2 (RE = Gd–Tm, Lu, Y; 0.8 < x < 0.9). Correlations between Long- and Short-Range Vacancy Ordering
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Svilen Bobev, Yingmin Wang, and Jiliang Zhang
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Inorganic Chemistry ,Diffraction ,Pearson symbol ,Crystallography ,Electron diffraction ,Condensed matter physics ,Chemistry ,Superlattice ,Vacancy defect ,Orthorhombic crystal system ,Physical and Theoretical Chemistry ,Selected area diffraction ,Superstructure (condensed matter) - Abstract
Rare-earth metal aluminum germanides with the general formula REAl(1-x)Ge(2) (RE = Gd, Tb, Dy, Ho, Er, Tm, Lu, and Y) have been synthesized by direct fusion of the corresponding elements. The structures have been studied by single-crystal X-ray diffraction and selected-area electron diffraction (SAED). The average structure represents a randomly "stuffed" variant of the orthorhombic ZrSi(2) structure type, also known as the CeNi(1-x)Si(2) type (Pearson symbol oC16; space group Cmcm). The SAED patterns for selected members of the family suggest the coexistence of commensurate and incommensurate structural modulations. The most prominent model for long-range vacancy ordering is the Tb(4)FeGe(8) type (Pearson symbol mP26; space group P21/n), which is the commensurate 4-fold superstructure of CeNi(1-x)Si(2) (x = (3)/4). Short-range correlations cause additional deviations in the 4-fold superlattice. These results shed more light on the structural complexity as a function of the aluminum vacancies and size of the rare-earth metal. Magnetic susceptibility measurements are presented and discussed. The measured ordering temperatures and calculated ones based on empirical rules and Ruderman-Kittel-Kasuya-Yosida interactions are shown to be in close agreement. more...
- Published
- 2014
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32. Synthesis and Structural Characterization of RE7Zn21Tt2 (RE = La–Nd; Tt = Ge, Sn, and Pb): New Structure Type Among the Polar Intermetallic Phases
- Author
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Svilen Bobev and Nian-Tzu Suen
- Subjects
Inorganic Chemistry ,Pearson symbol ,Magnetization ,Crystallography ,Group (periodic table) ,Magnetism ,Chemistry ,Intermetallic ,Orthorhombic crystal system ,Electronic structure ,Physical and Theoretical Chemistry ,Ternary operation - Abstract
Reported are 11 new ternary phases with the general formula RE7Zn21Tt2 (RE = La-Nd; Tt = Ge, Sn, and Pb), synthesized from the respective elements by reactions at high temperature. Their structures, established on the basis of single-crystal and powder X-ray diffraction work, are shown to be a new structure type with the orthorhombic space group Pbam (No. 55, Pearson symbol oP60). This complex atomic arrangement features condensed polyhedra made up of Zn atoms, interspersed by Ge, Sn, or Pb atoms in trigonal-planar coordination. The structure bears resemblance with the La3Al11 and the LaRhSn2 structure types, which are compared and discussed. Temperature dependent dc magnetization measurements confirm RE(3+) ground states for all rare-earth elements, and the expected local-moment magnetism due to the partial filling of their 4f states for RE(3+) = Ce(3+), Pr(3+), and Nd(3+). Theoretical considerations of the electronic structure based on the tight-binding linear muffin-tin orbital (TB-LMTO-ASA) method are also presented: the calculations support the experimental observation of a small, but not negligible, homogeneity range in RE7Zn(21+x)Tt(2-x) (x0.5). The partial substitution of the tetrel atoms by the electron-poorer Zn appears to be an important attribute, leading to an optimal valence electron concentration and, thereby, to the overall electronic stability of the crystal structure of this family of polar intermetallics. more...
- Published
- 2013
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33. Copper and Zinc Substitutions in Clathrates of Tin: Synthesis, Structural Characterization, and Physical Properties of A8Cu2.67Sn43.33 and A8Zn4Sn42 (A = K, Rb, Cs) with the Type-I Structure
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Marion C. Schäfer and Svilen Bobev
- Subjects
Materials science ,General Chemical Engineering ,chemistry.chemical_element ,General Chemistry ,Zinc ,Crystal structure ,Thermoelectric materials ,Alkali metal ,Copper ,Crystallography ,Dodecahedron ,chemistry ,Electrical resistivity and conductivity ,Materials Chemistry ,Tin - Abstract
Reported are two series of tin-based clathrates—A8Cu2.67Sn43.33 and A8Zn4Sn42 (A = K, Rb, Cs)—crystallizing in the cubic type-I structure. The six new compounds have been obtained in quantitative yields and have been characterized by single-crystal X-ray diffraction. Copper and zinc randomly substitute tin on only one of the three framework sites, 6c, while the remaining two sites 16i and 24k are exclusively occupied by tin. The alkali metals reside in the two types of cages in the structure—the 20-atom dodecahedra and the 24-atom tetrakaidecahedra. According to the structure refinements, both cages are completely filled; in the bigger tetrakaidecahedron, the smaller K and Rb atoms are displaced off its center, whereas the larger Cs atoms are located at the center. These findings are presented and discussed; preliminary results from measurements of the Seebeck coefficients (300–500 K) and the electrical resistivity (100–400 K) are presented as well. more...
- Published
- 2013
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34. New Polar Intermetallic Phases RE2Zn5Tt (RE = La–Nd; Tt = Sn and Pb): Synthesis, Structure, Chemical Bonding, and Magnetic Properties
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Svilen Bobev and Nian-Tzu Suen
- Subjects
Inorganic Chemistry ,Pearson symbol ,Magnetization ,Crystallography ,Paramagnetism ,Chemical bond ,Chemistry ,Intermetallic ,Orthorhombic crystal system ,Crystal structure ,Electronic structure ,Physical and Theoretical Chemistry - Abstract
Reported are the synthesis, crystal structure, electronic structure, and magnetic properties of a series of zinc-rich ternary phases with formulas RE2Zn5Tt (RE = La-Nd; Tt = Sn and Pb). The structures of these compounds have been established by single-crystal and powder X-ray diffraction. They crystallize in the orthorhombic space group Cmcm (No. 63, LaRhSn2 structure type, Pearson symbol oC32). The most prominent structural feature is the trigonal-planar coordination of the Sn(Pb) atoms; the latter interconnect layers of Zn atoms to comprise a complex [Zn5Tt] polyanionic framework. The structural relationships between the structure of the title compounds and the EuIn4, La3Al11, and YIrGe2 structure types are highlighted. Temperature-dependent DC magnetization measurements indicate Pauli-like paramagnetism for La2Zn5Sn, while Ce2Zn5Sn, Pr2Zn5Sn, and Nd2Zn5Sn display Curie-Weiss behavior in the high-temperature regime. At cryogenic temperatures, the magnetic responses of Ce2Zn5Sn, Pr2Zn5Sn, and Nd2Zn5Sn appear to deviate from the Curie-Weiss law; however, no magnetic orderings could be observed down to 5 K. Theoretical considerations of the electronic structure on the basis of the tight-binding linear muffin-tin orbital (TB-LMTO-ASA) method are also presented and discussed. more...
- Published
- 2013
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35. Tin Clathrates with the Type II Structure
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Marion C. Schäfer and Svilen Bobev
- Subjects
Colloid and Surface Chemistry ,chemistry ,Polymer chemistry ,Inorganic chemistry ,chemistry.chemical_element ,General Chemistry ,Tin ,Alkali metal ,Biochemistry ,Catalysis - Abstract
For a very long time, Ba(16)Ga(32)Sn(104) has been the sole representative of tin clathrates with the type II structure. Herein, we present several new members of this structural family: Cs(8)Ba(16)Ga(39.7(3))Sn(96.3(3)), Rb(9.9(5))Ba(13.3(2))Ga(36.4(3))Sn(99.6(3)), and K(2.0(4))Ba(14.0(4))Ga(30.4(2))Sn(105.6(4)). The successful synthesis of these novel compounds was facilitated through the use of alkali and alkaline-earth metals, which selectively fill the available cages. more...
- Published
- 2013
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36. Synthesis, Crystal Chemistry, and Magnetic Properties of RE7Li8Ge10 and RE11Li12Ge16 (RE = La–Nd, Sm): New Members of the [REGe2]n[RELi2Ge]m Homologous Series
- Author
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Sheng-Ping Guo, Yaho Jung, Tae-Soo You, and Svilen Bobev
- Subjects
Diffraction ,Crystal chemistry ,Inorganic chemistry ,Structure type ,Inorganic Chemistry ,Magnetization ,Homologous series ,chemistry.chemical_compound ,Paramagnetism ,Crystallography ,chemistry ,Group (periodic table) ,Orthorhombic crystal system ,Physical and Theoretical Chemistry - Abstract
Eight new rare-earth metal–lithium–germanides belonging to the [REGe2]n[RELi2Ge]m homologous series have been synthesized and structurally characterized by single-crystal X-ray diffraction. The structures of the title compounds can be rationalized as linear intergrowths of imaginary RELi2Ge (MgAl2Cu structure type) and REGe2 (AlB2 structure type) slabs. The compounds with general formula RE7Li8Ge10 (RE = La–Nd, Sm), i.e., [REGe2]3[RELi2Ge]4, crystallize in the orthorhombic space group Cmmm (No. 65) with a new structure type. Similarly, the compounds with general formula RE11Li12Ge16 (RE = Ce–Nd), i.e., [REGe2]5[RELi2Ge]6, crystallize in the orthorhombic space group Immm (No. 71) also with its own structure type. Temperature-dependent DC magnetization measurements indicate Curie–Weiss paramagnetism in the high-temperature regime and hint at complex magnetic ordering at low temperatures. The measured effective moments are consistent with RE3+ ground states in all cases. The experimental results have been co... more...
- Published
- 2012
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37. Synthesis, Structure, Chemical Bonding, and Magnetism of the Series RELiGe2 (RE = La–Nd, Sm, Eu)
- Author
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Johnpierre Paglione, Shanta Saha, Richard L. Greene, Nian-Tzu Suen, Tae-Soo You, and Svilen Bobev
- Subjects
Chemistry ,Crystal chemistry ,Parent structure ,chemistry.chemical_element ,Inorganic Chemistry ,Metal ,Pearson symbol ,Paramagnetism ,Crystallography ,Chemical bond ,Group (periodic table) ,visual_art ,visual_art.visual_art_medium ,Lithium ,Physical and Theoretical Chemistry - Abstract
This article focuses on the synthesis and the crystal chemistry of six members of a series of rare-earth metal based germanides with general formula RELiGe(2) (RE = La-Nd, Sm, and Eu). The structures of these compounds have been established by single-crystal X-ray diffraction (CaLiSi(2) structure type, space group Pnma, Z = 4, Pearson symbol oP16). The chemical bonding within this atomic arrangement can be rationalized in terms of anionic germanium zigzag chains, conjoined via chains of edge-shared LiGe(4) tetrahedra and separated by rare-earth metal cations. The structure can also be viewed as an intergrowth of AlB(2)-like and TiNiSi-like fragments, or as the result of the replacement of 50% of the rare-earth metal atoms by lithium in the parent structure of the REGe monogermanides. Except for LaLiGe(2) and SmLiGe(2), the remaining four RELiGe(2) phases exhibit Curie-Weiss paramagnetism above about 50 K. In the low temperature regime, the localized 4f electrons in CeLiGe(2), PrLiGe(2), and SmLiGe(2) order ferromagnetically, while antiferromagnetic ordering is observed for NdLiGe(2) and EuLiGe(2). The calculated effective magnetic moments confirm RE(3+) ground states in all cases excluding EuLiGe(2), in which the magnetic response is consistent with Eu(2+) configuration (J = S = 7/2). The experimental results have been complemented by tight-binding linear muffin-tin orbital (TB-LMTO) band structure calculations. more...
- Published
- 2011
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38. Mixed Cations and Structural Complexity in (Eu1−xCax)4In3Ge4 and (Eu1−xCax)3In2Ge3—The First Two Members of the Homologous Series A2[n+m]In2n+mGe2[n+m] (n, m = 1, 2, ...∞; A = Ca, Sr, Ba, Eu, or Yb)
- Author
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Tae-Soo You, Svilen Bobev, and Paul H. Tobash
- Subjects
Intermetallic ,Mineralogy ,Inorganic Chemistry ,Pearson symbol ,Metal ,Homologous series ,chemistry.chemical_compound ,Crystallography ,chemistry ,visual_art ,visual_art.visual_art_medium ,Orthorhombic crystal system ,Physical and Theoretical Chemistry ,Electronic band structure ,Monoclinic crystal system - Abstract
Reported are the synthesis and the structural characterization of two members of a new homologous series of polar intermetallic compounds, which exist only with mixed alkaline-earth and rare-earth metal cations. Crystals of (Eu(1-x)Ca(x))(4)In(3)Ge(4) (0.35(1) more...
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- 2010
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39. New Manganese-Bearing Antimonides and Bismuthides with Complex Structures. Synthesis, Structural Characterization, and Electronic Properties of Yb9Mn4+xPn9 (Pn = Sb or Bi)
- Author
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Svilen Bobev and Sheng-Qing Xia
- Subjects
Dopant ,General Chemical Engineering ,chemistry.chemical_element ,General Chemistry ,Electronic structure ,Manganese ,Metal ,Crystallography ,Transition metal ,chemistry ,visual_art ,Materials Chemistry ,visual_art.visual_art_medium ,Orthorhombic crystal system ,Isostructural ,Ternary operation - Abstract
Reported are structure and property studies on a series of isostructural compounds with general formulas Yb9Mn4+xSb9 (x ≈ 0.2), A9Mn4+xBi9 (A = Ca and Yb; x ≈ 0), and the Zn-substituted derivatives Yb9(Mn,Zn)4+xSb9 (0 < x < 0.4). They have been synthesized from the corresponding elements by high-temperature reactions, and their structures have been established by single-crystal X-ray diffraction. Despite being nearly stoichiometric phases, whose average crystallographic arrangement can be described with the orthorhombic Ca9Mn4Bi9 type structure (space group Pbam, No. 55), these ternary materials exist within narrow homogeneity ranges, whereupon an interstitial site is partially occupied by the transition metal. Electronic structure calculations confirm that the “empty” A9Mn4Sb9 or A9Mn4Bi9 structures are electron deficient, making them suitable hosts for small dopant atoms. The expected poorly metallic behavior is evidenced from temperature-dependent resistivity data gathered from single-crystals. Magneti... more...
- Published
- 2009
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40. Synthesis, Structure, and Bonding of the Zintl Phase Ba3Cd2Sb4
- Author
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Bayrammurad Saparov, Svilen Bobev, and Sheng-Qing Xia
- Subjects
education.field_of_study ,Inorganic chemistry ,Population ,Context (language use) ,Inorganic Chemistry ,Crystal ,Crystallography ,chemistry.chemical_compound ,Zintl phase ,chemistry ,Group (periodic table) ,Ternary compound ,Physical and Theoretical Chemistry ,education ,Electronic band structure ,Monoclinic crystal system - Abstract
Reported are the synthesis of the new ternary compound Ba3Cd2Sb4 and its structure determination by single-crystal X-ray diffraction. Ba3Cd2Sb4 crystallizes with the monoclinic space group C2/m (No. 12); unit cell parameters a = 17.835(2) A, b = 4.8675(5) A, c = 7.6837(7) A, and beta = 112.214(1) degrees; Z = 4. Its structure can be viewed as made of Ba2+ cations and [Cd2Sb4] double chains that are interconnected through Sb-Sb bonds to form 2D infinity2[Cd2Sb4]6- layers. The bonding arrangement in Ba3Cd2Sb4 can also be derived from other known structure types that feature similar fragments, such as TiNiSi, Ca3AlAs3, and Ca5Al2Sb6. Tight-binding linear muffin-tin-orbital band structure calculations are presented as well and show that the constituent elements have closed-shell configurations, indicative of Ba3Cd2Sb4 being a Zintl phase with poor metallic behavior. Crystal orbital Hamilton population analyses on selected atomic interactions in this structure are discussed within the context of the site preference, manifested in the mixed-cation compounds and Ba3-xAxCd2Sb4, where A = Ca, Sr, Eu, and Yb. more...
- Published
- 2008
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41. Structure and Properties of a New Family of Nearly Equiatomic Rare-Earth Metal-Tin-Germanides RESn1+xGe1−x (RE = Y, Gd−Tm): an Unusual Example of Site Preferences Between Elements from the Same Group
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John J. Meyers, Joe D. Thompson, Filip Ronning, Svilen Bobev, Paul H. Tobash, Gary DiFilippo, and John L. Sarrao
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Materials science ,General Chemical Engineering ,Rare earth ,Structure (category theory) ,chemistry.chemical_element ,Mineralogy ,General Chemistry ,Metal ,Crystallography ,chemistry ,Group (periodic table) ,visual_art ,Materials Chemistry ,visual_art.visual_art_medium ,Tin ,Stoichiometry - Abstract
Seven nearly stoichiometric compounds with general formulas RESn1+xGe1−x (RE = Y, Gd−Tm; x ≈ ±0.15) have been synthesized from the corresponding elements using high-temperature reactions and molten... more...
- Published
- 2008
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42. Structure and Properties of Gd3Ge4: The Orthorhombic RE3Ge4 Structures Revisited (RE = Y, Tb−Tm)
- Author
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Namjung Hur, Paul H. Tobash, Svilen Bobev, John L. Sarrao, Gary DiFilippo, and Joe D. Thompson
- Subjects
Inorganic Chemistry ,Paramagnetism ,Magnetization ,Crystallography ,chemistry ,Atom ,chemistry.chemical_element ,Antiferromagnetism ,Germanium ,Context (language use) ,Orthorhombic crystal system ,Physical and Theoretical Chemistry ,Magnetic susceptibility - Abstract
The new binary compound Gd(3)Ge(4) has been synthesized and its structure has been determined from single-crystal X-ray diffraction. Gd(3)Ge(4) crystallizes in the orthorhombic space group Cmcm (No. 63) with unit cell parameters a = 4.0953(11) A, b = 10.735(3) A, c = 14.335(4) A, and Z = 4. Its structure can be described as corrugated layers of germanium atoms with gadolinium atoms enclosed between them. The bonding arrangement in Gd(3)Ge(4) can also be derived from that of the known compound GdGe (CrB type) through cleavage of the (infinity)(1)[Ge(2)] zigzag chains in GdGe and a subsequent insertion of an extra germanium atom between the resulting triangular fragments. Formally, these characteristics represent isotypism with the Er(3)Ge(4) type (Pearson's oC28). However, re-examination of the crystallography in the whole RE(3)Ge(4) series (RE = Y, Tb-Tm) revealed discrepancies and called into question the accuracy of the originally determined structures. This necessitated a new rationalization of the bonding, which is provided in the context of a comparative discussion concerning both the original and revised structure models, along with an analysis of the trends across the series. The temperature dependence of the magnetic susceptibility of Gd(3)Ge(4) shows that it is paramagnetic at room temperature and undergoes antiferromagnetic ordering below 29 K. Magnetization, resistivity, and calorimetry data for several other members of the RE(3)Ge(4) family are presented as well. more...
- Published
- 2007
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43. Interplay between Size and Electronic Effects in Determining the Homogeneity Range of the A9Zn4+xPn9 and A9Cd4+xPn9 Phases (0 ≤ x ≤ 0.5), A = Ca, Sr, Yb, Eu; Pn = Sb, Bi
- Author
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Sheng-Qing Xia and Svilen Bobev
- Subjects
Chemistry ,General Chemistry ,Electronic structure ,Electron deficiency ,Biochemistry ,Magnetic susceptibility ,Catalysis ,Crystallography ,Colloid and Surface Chemistry ,Transition metal ,Electronic effect ,Orthorhombic crystal system ,Isostructural ,Valence electron - Abstract
Seven cadmium- and zinc-containing Zintl phases, A9Zn(4+x)Pn9 and A9Cd(4+x)Pn9 (0 < or = x < or = 0.5), A = Ca, Sr, Yb, Eu; Pn = Sb, Bi, have been synthesized, and their structures have been determined by single-crystal X-ray diffraction. All compounds are isostructural and crystallize in the centrosymmetric orthorhombic space group Pbam (no. 55, Z = 2), and their structures feature tetrahedra of the pnicogens, centered by the transition metal. The tetrahedra are not isolated but are connected through corner sharing to form ribbons, which are separated by the divalent cations. The occurrence of a small phase width and its variation across this family of compounds has been systematically studied by variable temperature crystallography, resistivity, and magnetic susceptibility measurements, and these results have been reconciled with electronic structure calculations performed using the tight-binding linear muffin-tin orbital (TB-LMTO-ASA) method. These analyses of the crystal and electronic structure indicate that the polyanionic subnetwork requires 19 additional electrons, whereas only 18 electrons are provided by the cations. Such apparent "electron deficiency" necessitates the presence of an interstitial atom in order for an optimal bonding to be achieved; however, an interplay between the sizes of the cations and anions and the total valence electron concentration (governed by the stoichiometry breadth) is suggested as a possible mechanism for achieving structure stability. The structural relationship between these and some known structures with two-dimensional layers are discussed as well. more...
- Published
- 2007
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44. Cation−Anion Interactions as Structure Directing Factors: Structure and Bonding of Ca2CdSb2 and Yb2CdSb2
- Author
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Sheng-Qing Xia and Svilen Bobev
- Subjects
Diffraction ,Chemistry ,Point reflection ,Structure (category theory) ,General Chemistry ,Space (mathematics) ,Biochemistry ,Catalysis ,Ion ,Crystallography ,Colloid and Surface Chemistry ,Group (periodic table) ,Tetrahedron ,Orthorhombic crystal system - Abstract
Two new transition-metal-containing Zintl phases, Ca2CdSb2 and Yb2CdSb2, have been synthesized by flux reactions, and their structures have been determined by single-crystal X-ray diffraction. Yb2CdSb2 crystallizes in the noncentrosymmetric orthorhombic space group Cmc21 (No. 36, Z = 4). Ca2CdSb2 crystallizes in the centrosymmetric orthorhombic space group Pnma (No. 62, Z = 4). Despite the similarity in their chemical formulas and unit cell parameters, the structures of Yb2CdSb2 and Ca2CdSb2 are subtly different: Ca2CdSb2 has a layered structure built up of infinite layers of CdSb4 tetrahedra connected through corner-sharing. These layers are stacked in an alternating AA-1AA-1 sequence along the direction of the longest crystallographic axis (A denotes a layer; A-1 stands for its inversion symmetry equivalent), with Ca2+ cations filling the space between them. The structure of Yb2CdSb2 features the very same [CdSb2]4- layers of CdSb4 tetrahedra, which because of the lack of inversion symmetry are stacked in an AAAA-type fashion and are separated by Yb2+ cations. Electronic band structure calculations performed using the TB-LMTO-ASA method show a small band gap at the Fermi level for Ca2CdSb2, whereas the gap closes for Yb2CdSb2. These results suggest narrow gap semiconducting and poorly metallic behavior, respectively, and are confirmed by resistivity and magnetic susceptibility measurements. The structural relationship between these new layered structure types and some well-known structures with three-dimensional four-connected nets are discussed as well. more...
- Published
- 2007
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45. Vacancy Ordering in SmGe2-x and GdGe2-x (x = 0.33): Structure and Properties of Two Sm3Ge5 Polymorphs and of Gd3Ge5
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John L. Sarrao, Namjung Hur, Svilen Bobev, Paul H. Tobash, Daniel Lins, and Joe D. Thompson
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Inorganic Chemistry ,Magnetization ,Crystallography ,Chemistry ,Vacancy defect ,Intermetallic ,Antiferromagnetism ,Orthorhombic crystal system ,Crystal structure ,Physical and Theoretical Chemistry ,Isostructural ,Heat capacity - Abstract
The crystal structures and the magnetic properties of three new binary rare-earth intermetallic phases are reported. alpha-Sm3Ge5 and beta-Sm3Ge5 and Gd3Ge5 have been prepared from the corresponding elements through high-temperature reactions using the flux-growth method. The structures of the three compounds have been established using single-crystal X-ray diffraction: alpha-Sm3Ge5 crystallizes with its own type in the hexagonal space group P2c (No. 190) with cell parameters a = 6.9238(11) A, c = 8.491(3) A, and Z = 2, whereas beta-Sm3Ge5 adopts the face-centered orthorhombic Y3Ge5 type with space group Fdd2 (No. 43) and with cell parameters a = 5.8281(6) A, b = 17.476(2) A, c = 13.785(2) A, and Z = 8. The orthorhombic Gd3Ge5 with cell parameters a = 5.784(2) A, b = 17.355(6) A, and c = 13.785(5) A is isostructural with beta-Sm3Ge5. The structures of the title compounds can be described as AlB(2) and alpha-ThSi2 derivatives with long-range ordering of the germanium vacancies. Temperature-dependent DC magnetization (5-300 K) measurements show evidence of antiferromagnetic ordering below ca. 30 and 10 K for alpha-Sm3Ge5 and beta-Sm3Ge5, respectively. Gd3Ge5 undergoes two successive magnetic transitions below ca. 15 and 11 K. The temperature dependence of the resistivity and heat capacity of Gd3Ge5 are discussed as well. more...
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- 2006
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46. Unusual Mn−Mn Spin Coupling in the Polar Intermetallic Compounds CaMn2Sb2 and SrMn2Sb2
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Justin Merz, Joe D. Thompson, Ana Lima, Veronika Fritsch, John L. Sarrao, Richard Dronskowski, Michael Gillessen, and Svilen Bobev
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Inorganic Chemistry ,Crystallography ,Ferromagnetism ,Magnetic structure ,Magnetoresistance ,Electrical resistivity and conductivity ,Chemistry ,Intermetallic ,Electronic structure ,Physical and Theoretical Chemistry ,Isostructural ,Magnetic field - Abstract
Large single-crystals of two polar intermetallic phases, CaMn2Sb2 and SrMn2Sb2, have been grown using In or Sn as metal fluxes and characterized by single-crystal X-ray diffraction. The two compounds are isostructural and crystallize with the CaAl2Si2 structure (space group P3m1, No. 164) with unit cell parameters determined at 120(2) K of a = 4.5204(6) angstroms, c = 7.456(2) angstroms and a = 4.5802(17) angstroms, c = 7.730(5) angstroms for CaMn2Sb2 and SrMn2Sb2, respectively. Temperature- and field-dependent dc- and ac-magnetization measurements suggest complex magnetic ordering of the Mn moments below ca. 250 and 35 K for CaMn2Sb2 and below ca. 265 K for SrMn2Sb2. Resistivity measurements reveal metallic-like temperature dependence with rho(290) = 40 m omega cm for CaMn2Sb2 and rho290 = 100 m omega cm for SrMn2Sb2 with negligible magnetoresistance at 5 K in applied magnetic fields up to 10 kOe. Spin-polarized DFT electronic structure calculations confirm the metallic-like properties and provide further evidence for a magnetic structure where Mn atoms form two magnetic sublattices with ferromagnetic coupling within them and strong antiferromagnetic coupling between them. more...
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- 2006
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47. Crystal Growth, Structural, and Property Studies on a Family of Ternary Rare-Earth Phases RE2InGe2 (RE = Sm, Gd, Tb, Dy, Ho, Yb)
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Svilen Bobev, John L. Sarrao, Paul H. Tobash, and Joe D. Thompson, Ana Lima, and Daniel Lins, and M. F. Hundley
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Materials science ,General Chemical Engineering ,chemistry.chemical_element ,Crystal growth ,General Chemistry ,Crystallography ,Magnetization ,Paramagnetism ,Tetragonal crystal system ,chemistry ,Electrical resistivity and conductivity ,Materials Chemistry ,Antiferromagnetism ,Ternary operation ,Indium - Abstract
A series of new rare-earth indium−germanides RE2InGe2 (RE = Sm, Gd, Tb, Dy, Ho, Yb) have been prepared from the corresponding elements through high-temperature reactions using an excess of indium as flux. Single-crystal and powder X-ray diffraction studies showed that these ternary phases crystallize in the tetragonal space group P4/mbm, Z = 2, Pearson's symbol tP10, and represent new members of the Mo2FeB2 family (an ordered ternary variant of the U3Si2 structure type). The temperature dependence of the dc magnetization (5−300 K) indicates that the RE2InGe2 (RE = Sm−Ho) compounds order magnetically below ca. 60 K, whereas Yb2InGe2 exhibits Pauli-like temperature-independent paramagnetism. Isothermal magnetization, electrical resistivity, and calorimetry measurements are presented as well and confirm the existence of ordered antiferromagnetic states at low temperatures. The structural trends and the evolution of the magnetic properties are also discussed. more...
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- 2005
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48. Probing the Limits of the Zintl Concept: Structure and Bonding in Rare-Earth and Alkaline-Earth Zinc-Antimonides Yb9Zn4+xSb9 and Ca9Zn4.5Sb9
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Joe D. Thompson, Svilen Bobev, Susan M. Kauzlarich, Marilyn M. Olmstead, John L. Sarrao, and Haakon Hope
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Inorganic Chemistry ,Crystallography ,Alkaline earth metal ,Transition metal ,Zintl phase ,Chemistry ,chemistry.chemical_element ,Orthorhombic crystal system ,Crystal structure ,Zinc ,Crystallite ,Physical and Theoretical Chemistry ,Isostructural - Abstract
A new transition metal Zintl phase, Yb(9)Zn(4+x)Sb(9), was prepared by high-temperature flux syntheses as large single crystals, or by direct fusion of the corresponding elements in polycrystalline form. Its crystal structure was determined by single-crystal X-ray diffraction. Its Ca-counterpart, hitherto known as Ca(9)Zn(4)Sb(9), and the presence of nonstoichiometry in it were also studied. Yb(9)Zn(4+x)Sb(9) was found to exist in a narrow homogeneity range, as suggested from the crystallographic data at 90(3) K (orthorhombic, space group Pbam (No. 55), Z = 2): (1) a = 21.677(2) A, b = 12.3223(10) A, c = 4.5259(4) A, R1 = 3.09%, wR2 = 7.18% for Yb(9)Zn(4.23(2))Sb(9); (2) a = 21.706(2) A, b = 12.3381(13) A, c = 4.5297(5) A, R1 = 2.98%, wR2 = 5.63% for Yb(9)Zn(4.380(12))Sb(9); and (3) a = 21.700(2) A, b = 12.3400(9) A, c = 4.5339(4) A, R1 = 2.75%, wR2 = 5.65% for Yb(9)Zn(4.384(14))Sb(9). The isostructural Ca(9)Zn(4.478(8))Sb(9) has unit cell parameters a = 21.830(2) A, b = 12.4476(9) A, and c = 4.5414(3) A (R1 = 3.33%, wR2 = 5.83%). The structure type in which these compounds crystallize is related to the Ca(9)Mn(4)Bi(9) type, and can be considered an interstitially stabilized variant. Formal electron count suggests that the Yb or Ca cations are in the +2 oxidation state. This is supported by the virtually temperature-independent magnetization for Yb(9)Zn(4.5)Sb(9). Electrical resistivity data show that Yb(9)Zn(4.5)Sb(9) and Ca(9)Zn(4.5)Sb(9) are poor metals with room-temperature resistivity of 10.2 and 19.6 mOmega.cm, respectively. more...
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- 2004
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49. Instabilities in the Linear Sb Atom Chain of the New Binary Antimonide Ti11-xSb8-y
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Svilen Bobev and Holger Kleinke
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Crystallography ,Materials science ,Heteronuclear molecule ,Annealing (metallurgy) ,General Chemical Engineering ,Lattice (order) ,Antimonide ,Atom ,Materials Chemistry ,General Chemistry ,Isostructural ,Stoichiometry ,Homonuclear molecule - Abstract
The new binary antimonide Ti11-xSb8-y was prepared from directly reacting the elements in stoichiometric ratios, either by melting the reaction mixture in an arc furnace or by annealing it in a resistance furnace above 1000 °C. Ti11-xSb8-y is a nonstoichiometric compound with a small phase range that cannot be prepared with the idealized Ti:Sb ratio of 11:8. Ti10.84(3)Sb7.74(1) crystallizes in the Cr11Ge8 type, isostructural with (Zr,V)11Sb8: space group Pnma, lattice dimensions a = 1462.28(9) pm, b = 559.72(4) pm, c = 1764.4(1) pm, V = 1.4441(2) nm3 (Z = 4). One can describe this type as an intergrowth of distorted fragments of the NiAs and W5Si3 types. In addition to the dominating heteronuclear Ti−Sb bonds, the structure of Ti11-xSb8-y comprises several homonuclear Ti−Ti and Sb−Sb bonding interactions. Short bonds of alternating 276 and 284 pm occur in a linear nonclassical chain of mainly Sb atoms (i.e., 87% Sb and 13% Ti). According to our experiments, the incorporation of Ti atoms into this chain, ... more...
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- 2003
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50. Nd2Ba2CaZn2Ti3O14.4: A New High Dielectric Constant Oxide Having a Disordered (Cubic) Perovskite Structure
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G. N. Subbanna, Svilen Bobev, Ashok K. Ganguli, and Pika Jha
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Permittivity ,Materials science ,Rietveld refinement ,General Chemical Engineering ,Neutron diffraction ,Analytical chemistry ,Mineralogy ,General Chemistry ,Dielectric ,Crystal structure ,Electron diffraction ,Materials Chemistry ,Dielectric loss ,High-κ dielectric - Abstract
A new oxide of the formula Nd2Ba2CaZn2Ti3O14.4 has been successfully prepared by a high-temperature ceramic route at 1200 degreesC. The title compound crystallizes in a cubic structure with a = 3.94263(7) Angstrom (space group = Pm (3) over barm, wRp = 0.0305, Rp, = 0.0192) as obtained from Rietveld refinement of powder neutron diffraction data. X-ray and electron diffraction studies also confirm the absence of any ordering of the cations. The titlen compound has a high dielectric constant of 59 at 100 kHz and a very small frequency coefficient of the dielectric constant (depsilon/dF = 1.26 x 10(-6) Hz(-1)). The dielectric loss is 0.0047 at 100 kHz, which also shows very minor variation with frequency. The temperature-dependence studies show an increase in dielectric constant and dielectric loss over the temperature range 35-300 degreesC. more...
- Published
- 2003
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