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1. Investigation and field effect tuning of thermoelectric properties of SnSe2 flakes

Author

Pallecchi, I., Caglieris, F., Ceccardi, M., Manca, N., Marre', D., Repetto, L., Schott, M., Bilc, D. I., Chaitoglou, S., Dimoulas, A., and Verstraete, M. J.

Subjects
Condensed Matter - Materials Science, Condensed Matter - Mesoscale and Nanoscale Physics
Abstract

The family of Van der Waals dichalcogenides (VdWDs) includes a large number of compositions and phases, exhibiting varied properties and functionalities. They have opened up a novel electronics of two-dimensional materials, characterized by higher integration and interfaces which are atomically sharper and cleaner than conventional electronics. Among these functionalities, some VdWDs possess remarkable thermoelectric properties. SnSe2 has been identified as a promising thermoelectric material on the basis of its estimated electronic and transport properties. In this work we carry out experimental meas-urements of the electric and thermoelectric properties of SnSe2 flakes. For a 30 micron thick SnSe2 flake at room temperature, we measure electron mobility of 40 cm^2 V^-1 s^-1, a carrier density of 4 x 10^18 cm^-3, a Seebeck coefficient S around -400 microV/K and thermoelectric power factor around 0.35 mW m^-1 K^-2. The comparison of experimental results with theoretical calculations shows fair agreement and indicates that the dominant carrier scattering mechanisms are polar optical phonons at room temperature and ionized im-purities below 50 K. In order to explore possible improvement of the thermoelectric properties, we carry out reversible electrostatic doping on a thinner flake, in a field effect setup. On this 75 nm thick SnSe2 flake, we measure a field effect variation of the Seebeck coefficient of up to 290 % at low temperature, and a corresponding variation of the thermoelectric power factor of up to 1050 %. We find that the power factor increases with the depletion of n-type charge carriers. Field effect control of thermoelectric transport opens perspectives for boosting energy harvesting and novel switching technologies based on two-dimensional materials., Comment: in press on Physical Review Materials

Published
2023
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2. Interstitial Transition Metal Doping in Hydrogen Saturated Silicon Nanowires

Author

Durgun, E., Bilc, D. I., Ciraci, S., and Ghosez, Ph.

Subjects
Condensed Matter - Materials Science
Abstract

We report a first principles systematic study of atomic, electronic, and magnetic properties of hydrogen saturated silicon nanowires (H-SiNW) which are doped by transition metal (TM) atoms placed at various interstitial sites. Our results obtained within the conventional GGA+U approach have been confirmed using an hybrid functional. In order to reveal the surface effects we examined three different possible facets of H-SiNW along [001] direction with a diameter of ~2nm. The energetics of doping and resulting electronic and magnetic properties are examined for all alternative configurations. We found that except Ti, the resulting systems have magnetic ground state with a varying magnetic moment. While H-SiNWs are initially non-magnetic semiconductor, they generally become ferromagnetic metal upon TM doping. Even they posses half-metallic behavior for specific cases. Our results suggest that H-SiNWs can be functionalized by TM impurities which would lead to new electronic and spintronic devices at nanoscale., Comment: 22 pages, 9 figures

Published
2012

3. Frustration of tilts and A-site driven ferroelectricity in KNbO_3-LiNbO_3 alloys

Author

Bilc, D. I. and Singh, D. J.

Subjects
Condensed Matter - Materials Science
Abstract

Density functional calculations for K_{0.5}Li_{0.5}NbO_3 show strong A-site driven ferroelectricity, even though the average tolerance factor is significantly smaller than unity and there is no stereochemically active A-site ion. This is due to the frustration of tilt instabilities by A-site disorder. There are very large off-centerings of the Li ions, which contribute strongly to the anisotropy between the tetragonal and rhombohedral ferroelectric states, yielding a tetragonal ground state even without strain coupling., Comment: 4 pages, 5 figures

Published
2008
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4. Hybrid exchange-correlation functional for accurate prediction of the electronic and structural properties of ferroelectric oxides

Author

Bilc, D. I., Orlando, R., Shaltaf, R., Rignanese, G. -M., Íñiguez, Jorge, and Ghosez, Ph.

Subjects
Condensed Matter - Materials Science
Abstract

Using a linear combination of atomic orbitals approach, we report a systematic comparison of various Density Functional Theory (DFT) and hybrid exchange-correlation functionals for the prediction of the electronic and structural properties of prototypical ferroelectric oxides. It is found that none of the available functionals is able to provide, at the same time, accurate electronic and structural properties of the cubic and tetragonal phases of BaTiO$_3$ and PbTiO$_3$. Some, although not all, usual DFT functionals predict the structure with acceptable accuracy, but always underestimate the electronic band gaps. Conversely, common hybrid functionals yield an improved description of the band gaps, but overestimate the volume and atomic distortions associated to ferroelectricity, giving rise to an unacceptably large $c/a$ ratio for the tetragonal phases of both compounds. This super-tetragonality is found to be induced mainly by the exchange energy corresponding to the Generalized Gradient Approximation (GGA) and, to a lesser extent, by the exact exchange term of the hybrid functional. We thus propose an alternative functional that mixes exact exchange with the recently proposed GGA of Wu and Cohen [Phys. Rev. B 73, 235116 (2006)] which, for solids, improves over the treatment of exchange of the most usual GGA's. The new functional renders an accurate description of both the structural and electronic properties of typical ferroelectric oxides., Comment: 13 pages, 4 figures, 7 tables

Published
2008
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5. Scanning Tunneling Microscopy of Defect States in the Semiconductor Bi$_2$Se$_3$

Author

Urazhdin, S., Bilc, D., Tessmer, S. H., Mahanti, S. D., Kyratsi, Theodora, and Kanatzidis, M. G.

Subjects
Condensed Matter - Materials Science
Abstract

Scanning tunneling spectroscopy images of Bi$_2$Se$_3$ doped with excess Bi reveal electronic defect states with a striking shape resembling clover leaves. With a simple tight-binding model we show that the geometry of the defect states in Bi$_2$Se$_3$ can be directly related to the position of the originating impurities. Only the Bi defects at the Se sites five atomic layers below the surface are experimentally observed. We show that this effect can be explained by the interplay of defect and surface electronic structure., Comment: 4 pages, 4 figures

Published
2001
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7. Synthesis, crystal structure and thermoelectric properties of a new metal telluride Ba3Ag3InTe6

Author

Lee, M.-Y., Bilc, D. I., Symeou, E., Lin, Y.-C., Liang, I.-C., Kyratsi, Theodora, Hsu, K. F., and Kyratsi, Theodora [0000-0003-2916-1708]

Subjects
Materials science, Band gap, 02 engineering and technology, Crystal structure, 010402 general chemistry, 021001 nanoscience & nanotechnology, 01 natural sciences, 0104 chemical sciences, Inorganic Chemistry, Crystallography, chemistry.chemical_compound, chemistry, Telluride, Thermoelectric effect, Density of states, Orthorhombic crystal system, Direct and indirect band gaps, 0210 nano-technology, Electronic band structure
Abstract

A new metal telluride Ba3Ag3InTe6 was synthesized by a solid-state reaction at 650 °C. Crystal data: Orthorhombic, Cmc21, a = 4.5669(3) Å, b = 27.9366(16) Å, c = 13.3819(8) Å, V = 1707.3(2) Å3, and Z = 4. This compound adopts a new two-dimensional structure constructed by AgTe4 and InTe4 tetrahedra and Ba2+ cations. The edge-sharing AgTe4 tetrahedra form a puckered layer of [Ag3Te4]5- and the corner-sharing InTe4 tetrahedra form a zig-zag chain of [InTe2]- that dangles from both edges of the layer. The band gap determined by UV-vis-NIR absorption spectra is estimated to be around 0.48 eV. This compound is a p-type semiconductor with high Seebeck coefficients of 325-334 μV K-1 in an entire temperature range of 320-400 K. The electrical conductivity of 9.4 S cm-1 and the thermal conductivity of 0.35 W mK-1 give a ZT value of 0.11 at 400 K. The electronic band structure reveals a direct band gap at the Γ point of the face centered primitive Brillouin zone. The density of states (DOS) analysis shows that the p-type hole transport is mostly achieved through the layer consisting of AgTe4 tetrahedra. © 2017 the Partner Organisations. 4 1458 1464 1458-1464

Published
2017

8. Syntheses, crystal Structures and electronic Structures of new metal chalcoiodides Bi2CuSe3I and Bi6Cu3S10I

Author

Liang, I.-C., Bilc, D. I., Manoli, M., Chang, W.-Y., Lin, W.-F., Kyratsi, Theodora, Hsu, K. F., and Kyratsi, Theodora [0000-0003-2916-1708]

Subjects
Electronic structure, Materials science, Geometry, 02 engineering and technology, Crystal structure, 010402 general chemistry, 01 natural sciences, Electronic band structure, Inorganic Chemistry, Electric conductivity, Temperature range, Materials Chemistry, Electrical conductivity, Physical and Theoretical Chemistry, P type semiconductor, Valence (chemistry), Seebeck coefficient, Density of states, 021001 nanoscience & nanotechnology, Condensed Matter Physics, Bonding interactions, Three-dimensional structure, 0104 chemical sciences, Electronic, Optical and Magnetic Materials, Energy gap, Crystallography, Octahedron, Thermal conductivity, Diffuse reflectance spectrum, Metal chalcoiodide, Ceramics and Composites, Orthorhombic crystal system, Solid state reactions, 0210 nano-technology, Density of state, Monoclinic crystal system
Abstract

Two new metal chalcoiodides were synthesized by solid-state reactions at 400 °C. Crystal Data: Bi2CuSe3I, 1, monoclinic, C2/m, a=14.243(2) Å, b=4.1937(7) Å, c=14.647(2) Å, β=116.095(2)°, V=785.7(2) Å3, and Z=4 Bi6Cu3S10I, 2, orthorhombic, Pnma, a=17.476(2) Å, b=4.0078(4) Å, c=27.391(2) Å, V=1918.5(3) Å3, and Z=4. Compound 1 adopts a three-dimensional structure formed by two alternative layers, which consist of BiSe5 square pyramids, BiSe4I2 octahedra, CuSe4 tetrahedra, and CuSe2I2 tetrahedra. Compound 2 possesses a new open framework built up of BiS5 square pyramides, BiS6 octahedra, BiS8 polyhedra, and CuS4 tetrahedra where I- anions are uniquely trapped within the tunnels. Both electronic structures reveal that bismuth and chalcogenide orbitals dominate the bandgaps. The Cu d and I p states contribute to the top of valence bands, in which the distribution of I orbitals may correspond to the relative bonding interactions in 1 and 2. The optical bandgaps determined by the diffuse reflectance spectra are 0.68 eV and 0.72 eV for 1 and 2, respectively. 1 is a p-type semiconductor with high Seebeck coefficients of 460-575 μV/K in the temperature range of 300-425 K. The electrical conductivity is 0.02 S/cm at 425 K for the undoped sample. The thermal conductivity is 0.22 W/mK at 425 K. © 2015 Elsevier Inc. All rights reserved. 234 1 8 1-8

Published
2016

11. Local structure and influence of bonding on the phase-change behavior of the chalcogenide compounds K1−xRbxSb5S8

Author

Wachter, J. B., Chrissafis, K., Petkov, V., Malliakas, C. D., Bilc, D. I., Kyratsi, Theodora, Paraskevopoulos, K. M., Mahanti, S. D., Torbrügge, T., Eckert, H., Kanatzidis, M. G., and Kyratsi, Theodora [0000-0003-2916-1708]

Subjects
Electronic band structure calculations, Phase transition, Pair distribution function analyses, Phase change behavior, Ionic bonding, Crystal structure, Non volatile memory, law.invention, Thermodynamic properties, Inorganic Chemistry, Differential scanning calorimetry, law, Materials Chemistry, Physical and Theoretical Chemistry, Crystallization, Chemistry, Glasses, Potassium compounds, Condensed Matter Physics, Electronic, Optical and Magnetic Materials, Crystallography, Non-volatile memory, Thermal conductivity, Phase transitions, Raman spectroscopy, Ceramics and Composites, Melting point, Glass, Glass transition, Solid solution
Abstract

KSb5S8 and its solid solution analogs with Rb and Tl were found to exhibit a reversible and tunable glass→crystal→glass phase transition. Selected members of this series were analyzed by differential scanning calorimetry to measure the effect of the substitution on the thermal properties. The solid solutions K1-xRbxSb5S8 exhibited clear deviations in melting and crystallization behavior and temperatures from the parent structure. The crystallization process of the glassy KSb5S8 as a function of temperature could clearly be followed with Raman spectroscopy. The thermal conductivity of both glassy and crystalline KSb5S8 at room temperature is ∼0.40 W/m K, among the lowest known values for any dense solid-state material. Electronic band structure calculations carried out on KSb5S8 and TlSb5S8 show the presence of large indirect band-gaps and confirm the coexistence of covalent Sb-S bonding and predominantly ionic K(Tl)⋯S bonding. Pair distribution function analyses based on total X-ray scattering data on both crystalline and glassy K1-xRbxSb5S8 showed that the basic structure-defining unit is the same and it involves a distorted polyhedron of "SbS7" fragment of ∼7 Å diameter. The similarity of local structure between the glassy and crystalline phases accounts for the facile crystallization rate in this system. © 2006 Elsevier Inc. All rights reserved. 180 420 431 420-431

Published
2007

13. Electronic structure of K 2Bi 8Se 13

Author

Bilc, D. I., Mahanti, S. D., Kyratsi, Theodora, Chung, D. Y., Kanatzidis, M. G., Larson, P., and Kyratsi, Theodora [0000-0003-2916-1708]

Subjects
crystal structure, ab initio calculation, energy transfer, X ray powder diffraction, potassium, article, anisotropy, semiconductor, electric conductivity, bismuth, chalcogen, chemical bond, temperature dependence, selenium, density functional theory
Abstract

K 2Bi 8Se 13 belongs to a class of complex chalcogenides that shows potential for superior thermoelectric performance. This compound forms in two distinct phases, α and β. The β phase, which has several sites with mixed K/Bi occupancy, is a better thermoelectric. To understand the origin of this difference between the two phases we have carried out electronic structure calculations within ab initio density functional theory using the full potential linearized augmented plane wave (FLAPW) method. Both the local spin density approximation (LSDA) and the generalized gradient approximation (GGA) were used to treat the exchange and correlation potential. The spin-orbit interaction (SOI) was incorporated using a second variational procedure. The α phase is found to be a semiconductor with an indirect LSDA/GGA band gap of 0.38 eV/0.46 eV compared to 0.76 eV for the observed direct optical gap. For the β phase we have chosen two different ordered structures with extreme occupancies of K and Bi atoms at the "mixed sites." The system is found to be a semimetal for both the ordered structures. To incorporate the effect of mixed occupancy we have chosen a 1 × 1 × 2 supercell with an alternative K/Bi occupancy at the mixed sites. The system is a semiconductor with an indirect LSDA/GGA band gap of 0.32 eV/0.41 eV. We find that the mixed occupancy is crucial for the system to be a semiconductor because the Bi atoms at the mixed sites stabilize the p orbitals of the nearest-neighbor Se atoms by lowering their energy. We also find a strong anisotropy in the effective mass near the conduction band minimum, with the smallest effective mass along the mixed K/Bi chains (parallel to the c axis). This large anisotropy suggests that β-K 2Bi 8Se 13 has a great potential for an n-type thermoelectric. ©2005 The American Physical Society. 71

Published
2005

14. Surface effects in layered semiconductors Bi2Se3 and Bi2Te3

Author

Urazhdin, S., Bilc, D. I., Mahanti, S. D., Tessmer, S. H., Kyratsi, Theodora, Kanatzidis, M. G., and Kyratsi, Theodora [0000-0003-2916-1708]

Subjects
Condensed Matter::Materials Science
Abstract

Scanning tunneling spectroscopy of Bi2Se3 and Bi2Te3 layered narrow gap semiconductors reveals finite in-gap density of states and suppressed conduction in the energy range of high valence-band states. Electronic structure calculations suggest that the surface effects are responsible for these properties. Conversely, the interlayer coupling has a strong effect on the bulk near-gap electronic structure. These properties may prove to be important for the thermoelectric performance of these and other related chalcogenides. © 2004 The American Physical Society. 69

Published
2004

15. Scanning tunneling microscopy of defect states in the semiconductor (formula presented)

Author

Urazhdin, S., Bilc, D. I., Tessmer, S. H., Mahanti, S. D., Kyratsi, Theodora, Kanatzidis, M. G., and Kyratsi, Theodora [0000-0003-2916-1708]

Abstract

Scanning tunneling spectroscopy images of (formula presented) doped with excess Bi reveal electronic defect states with a striking shape resembling clover leaves. With a simple tight-binding model, we show that the geometry of the defect states in (formula presented) can be directly related to the position of the originating impurities. Only the Bi defects at the Se sites five atomic layers below the surface are experimentally observed. We show that this effect can be explained by the interplay of defect and surface electronic structure. © 2002 The American Physical Society. 66 1 4 1-4

Published
2002

16. Electroresistance Effect in Ferroelectric Tunnel Junctions with Symmetric Electrodes

Author

Bilc, D. I., Novaes, Frederico D., Íñiguez, Jorge, Ordejón, Pablo, Ghosez, Philippe, Bilc, D. I., Novaes, Frederico D., Íñiguez, Jorge, Ordejón, Pablo, and Ghosez, Philippe

Abstract

Understanding the effects that govern electronic transport in ferroelectric tunnel junctions (FTJs) is of vital importance to improve the efficiency of devices such as ferroelectric memories with nondestructive readout. However, our current knowledge (typically based on simple semiempirical models or first-principles calculations restricted to the limit of zero bias) remains partial, which may hinder the development of more efficient systems. For example, nowadays it is commonly believed that the tunnel electroresistance (TER) effect exploited in such devices mandatorily requires, to be sizable, the use of two different electrodes, with related potential drawbacks concerning retention time, switching, and polarization imprint. In contrast, here we demonstrate at the first-principles level that large TER values of about 200% can be achieved under finite bias in a prototypical FTJ with symmetric electrodes. Our atomistic approach allows us to quantify the contribution of different microscopic mechanisms to the electroresistance, revealing the dominant role of the inverse piezoelectric response of the ferroelectric. On the basis of our analysis, we provide a critical discussion of the semiempirical models traditionally used to describe FTJs. © 2012 American Chemical Society.

Published
2012

17. Hybrid exchange-correlation functional for accurate prediction of the electronic and structural properties of ferroelectric oxides

Author

UCL - FSA/MAPR - Département des sciences des matériaux et des procédés, Bilc, D. I., Orlando, R., Shaltaf, Riad, Rignanese, Gian-Marco, Iniguez, Jorge, Ghosez, Ph., UCL - FSA/MAPR - Département des sciences des matériaux et des procédés, Bilc, D. I., Orlando, R., Shaltaf, Riad, Rignanese, Gian-Marco, Iniguez, Jorge, and Ghosez, Ph.

Abstract

Using a linear combination of atomic orbitals approach, we report a systematic comparison of various density functional theory (DFT) and hybrid exchange-correlation functionals for the prediction of the electronic and structural properties of prototypical ferroelectric oxides. It is found that none of the available functionals is able to provide, at the same time, accurate electronic and structural properties of the cubic and tetragonal phases of BaTiO3 and PbTiO3. Some, although not all, usual DFT functionals predict the structure with acceptable accuracy, but always underestimate the electronic band gaps. Conversely, common hybrid functionals yield an improved description of the band gaps, but overestimate the volume and atomic distortions associated with ferroelectricity, giving rise to an unacceptably large c/a ratio for the tetragonal phases of both compounds. This supertetragonality is found to be induced mainly by the exchange energy corresponding to the generalized gradient approximation (GGA) and, to a lesser extent, by the exact exchange term of the hybrid functional. We thus propose an alternative functional that mixes exact exchange with the recently proposed GGA of Wu and Cohen [Phys. Rev. B 73, 235116 (2006)] which, for solids, improves over the treatment of exchange of the most usual GGA's. The new functional renders an accurate description of both the structural and electronic properties of typical ferroelectric oxides.

Published
2008

24. Electronic structure ofK2Bi8Se13

Author

Bilc, D. I., primary, Mahanti, S. D., additional, Kyratsi, T., additional, Chung, D. Y., additional, Kanatzidis, M. G., additional, and Larson, P., additional

Published
2005
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33. <f>REAu3Al7 (RE=rare earth)</f>: new ternary aluminides grown from aluminum flux

Author

Latturner, S.E., Bilc, D., Ireland, J.R., Kannewurf, C.R., Mahanti, S.D., and Kanatzidis, M.G.

Subjects
*TERNARY alloys, *FLUX (Metallurgy)
Abstract

A series of ternary aluminide intermetallics with a new structure type were formed from the reaction of gold and rare-earth metals in aluminum flux. The REAu3Al7 structure was obtained with all rare earths RE with the exception of La and Eu. These materials crystallize in the rhombohedral space group R-3c, with unit cell parameters a=8.0922(6) A˚ and c=21.066(2) A˚ for PrAu3Al7 as an example. The variation in cell edges with rare-earth size is regular with the exception of the Yb analogue. The possible mixed valency indicated by this result was confirmed by magnetic susceptibility measurements. Density functional theory-based band structure calculations on YbAu3Al7 indicate the ytterbium f-orbitals are located just below the Fermi level, further supporting the mixed valence description of this material. [Copyright &y& Elsevier]

Published
2003
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34. Crystal Growth, Thermoelectric Properties, and Electronic Structure of AgBi<INF>3</INF>S<INF>5</INF> and AgSb<INF>x</INF><INF></INF>Bi<INF>3</INF><INF>-</INF><INF>x</INF><INF></INF>S<INF>5</INF> (x = 0.3)

Author

Kim, J.-H., Chung, D.-Y., Bilc, D., Loo, S., Short, J., Mahanti, S. D., Hogan, T., and Kanatzidis, M. G.

Abstract

The compound AgBi3S5 (I) (synthetic pavonite) and its solid solution AgSbxBi3-xS5 (x = 0.3) (II) were prepared by direct combination of elemental Ag, Bi, Sb, and S. They crystallize in the monoclinic space group C2/m with a = 13.345(3) Å, b = 4.0416(8) Å, c = 16.439(3) Å, and β = 94.158(3)° for I and a = 13.302(4) Å, b = 4.0381(11) Å, c = 16.388(5) Å, and β = 94.347(5)° for II. The Bridgman technique was used to grow bulk crystals of these materials. The crystal structure refinements, physicochemical properties, and thermoelectric properties of these materials are presented. The thermoelectric power for AgBi3S5 and AgSb0.3Bi2.7S5 showed −64 and −98 μV/K, respectively, with room-temperature electrical conductivity of 489 and 260 S/cm. The thermal conductivity for both compounds at room temperature was measured to be very low at ~1 W/m·K, respectively. Electronic band structure calculations for AgBi3S5 suggest the importance of silver d-states to the charge transport and also indicate the presence of an indirect energy gap.

Published
2005

35. Quaternary Intermetallics Grown from Molten Aluminum:  The Homologous Series Th<INF>2</INF>(Au<INF>x</INF><INF></INF>Si<INF>1</INF><INF>-</INF><INF>x</INF><INF></INF>)[AuAl<INF>2</INF>]<INF>n</INF><INF></INF>Si<INF>2</INF> (n = 1, 2, 4)

Author

Latturner, S. E., Bilc, D., Mahanti, S. D., and Kanatzidis, M. G.

Abstract

An appropriate combination of Th or ThO2 with Au and Si in liquid aluminum has resulted in the formation of three new quaternary intermetallic compounds. All three materials grow as large platelike crystals and have structure types that define a new homologous series. Th2AuAl2Si3 is tetragonal, I41/amd, with unit cell parameters a = 4.2119(4) Å and c = 36.165(5) Å. Th2Au3Al4Si2 and Th2Au5Al8Si2 both crystallize in the orthorhombic space group Cmmm, with cell parameters a = 4.266(1) Å, b = 23.574(8) Å, and c = 4.249(1) Å and a = 4.2612(8) Å, b = 35.661(7) Å, and c = 4.2487(8) Å, respectively. The Th2(AuxSi1-x)[AuAl2]nSi2 structures feature planes of parallel infinite zigzag silicon chains alternating with slabs of antifluorite type AuAl2. The AuAl2 slabs increase in thickness going from Th2AuAl2Si3 (n = 1) to Th2Au5Al8Si2 (n = 4). All three materials show temperature independent Pauli paramagnetism and metallic conductivity. Band structure calculations were carried out on each compound using density functional theory (full potential LAPW method), and the details of the density of states have been correlated with the observed data.

Published
2002
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42. ChemInform Abstract: Quaternary Intermetallics Grown from Molten Aluminum: The Homologous Series Th2(AuxSi1‐x) [AuAl2]nSi2(n = 1, 2, 4).

Author

Latturner, S. E., Bilc, D., Mahanti, S. D., and Kanatzidis, M. G.

Abstract

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Published
2002
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43. Local structure and influence of bonding on the phase-change behavior of the chalcogenide compounds K1− x Rb x Sb5S8

Author

Wachter, J.B., Chrissafis, K., Petkov, V., Malliakas, C.D., Bilc, D., Kyratsi, Th., Paraskevopoulos, K.M., Mahanti, S.D., Torbrügge, T., Eckert, H., and Kanatzidis, M.G.

Subjects
*CHALCOGENIDES, *INORGANIC compounds, *CHEMICAL structure, *CHEMICAL reactions
Abstract

Abstract: KSb5S8 and its solid solution analogs with Rb and Tl were found to exhibit a reversible and tunable glass→crystal→glass phase transition. Selected members of this series were analyzed by differential scanning calorimetry to measure the effect of the substitution on the thermal properties. The solid solutions K1− x Rb x Sb5S8 exhibited clear deviations in melting and crystallization behavior and temperatures from the parent structure. The crystallization process of the glassy KSb5S8 as a function of temperature could clearly be followed with Raman spectroscopy. The thermal conductivity of both glassy and crystalline KSb5S8 at room temperature is ∼0.40W/mK, among the lowest known values for any dense solid-state material. Electronic band structure calculations carried out on KSb5S8 and TlSb5S8 show the presence of large indirect band-gaps and confirm the coexistence of covalent Sb-S bonding and predominantly ionic K(Tl)⋯S bonding. Pair distribution function analyses based on total X-ray scattering data on both crystalline and glassy K1− x Rb x Sb5S8 showed that the basic structure-defining unit is the same and it involves a distorted polyhedron of “SbS7” fragment of ∼7Å diameter. The similarity of local structure between the glassy and crystalline phases accounts for the facile crystallization rate in this system. [Copyright &y& Elsevier]

Published
2007
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44. R3Au(6+x)Al26T (R = Ca, Sr, Eu, Yb; T = early transition metal): a large family of compounds with a stuffed BaHg11 structure type grown from aluminum flux.

Author

Latturner SE, Bilc D, Mahanti SD, and Kanatzidis MG

Abstract

A collection of new quaternary intermetallic compounds with a cubic, stuffed BaHg(11) structure type has been synthesized by the combination of a divalent rare earth or alkaline earth metal R, an early transition metal T, and gold in an excess of molten aluminum. Structural characterization of these R(3)Au(6+x)Al(26)T compounds by powder and single crystal X-ray diffraction indicates that the unit cell varies with the radii of the early transition metal T and the rare earth/alkaline earth R as expected. The element T (where T = group 4, 5, 6, and 7 element) appears to be responsible for the stabilization of up to 43 different members of the R(3)Au(6+x)Al(26)T family of compounds. Varying amounts of disorder and trends in partial occupancies of the Au stuffed site--the site that is vacant in the parent compound BaHg(11)--are also indicated by the diffraction studies of this family of compounds. Magnetic susceptibility data reveals that the transition metal atoms in these materials do not possess local magnetic moments. For the magnetic rare earth containing materials, the europium compounds undergo a ferromagnetic transition at 10 K, and the ytterbium analogues show mixed valent behavior. Band structure calculations also support a mixed valent state for Yb in these compounds.

Published
2009
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45. Ferrimagnetism in EuFe4Sb12 due to the interplay of f-electron moments and a nearly ferromagnetic host.

Author

Krishnamurthy VV, Lang JC, Haskel D, Keavney DJ, Srajer G, Robertson JL, Sales BC, Mandrus DG, Singh DJ, and Bilc DI

Abstract

We combine x-ray magnetic circular dichroism spectroscopy at Fe L2,3 edges, at Eu M4,5 edges, x-ray absorption spectroscopy (XAS) investigation of Eu valence, and local spin density calculations, to show that the filled skutterudite Eu0.95Fe4Sb12 is a ferrimagnet in which the Fe 3d moment and the Eu2+ 4f moment are magnetically ordered with dominant antiferromagnetic coupling. From Eu L3 edge XAS, we find that about 13% of the Eu have a formal valence of 3+. We ascribe the origin of ferrimagnetism at a relatively high transition temperature TC of 85 K in Eu0.95Fe4Sb12 to f-electron interaction with the nearly ferromagnetic [Fe4Sb12]2.2- host lattice.

Published
2007
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46. Frustration of tilts and A-site driven ferroelectricity in KNbO3-LiNbO3 alloys.

Author

Bilc DI and Singh DJ

Abstract

Density functional calculations for K(0.5)Li(0.5)NbO(3) show strong A-site driven ferroelectricity, even though the average tolerance factor is significantly smaller than unity and there is no stereochemically active A-site ion. This is due to the frustration of tilt instabilities by A-site disorder. There are very large off centerings of the Li ions, which contribute strongly to the anisotropy between the tetragonal and rhombohedral ferroelectric states, yielding a tetragonal ground state even without strain coupling.

Published
2006
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47. Intermetallic compounds with near Zintl phase behavior: RE2Zn3Ge6 (RE = La, Ce, Pr, Nd) grown from liquid indium.

Author

Salvador JR, Bilc D, Gour JR, Mahanti SD, and Kanatzidis MG

Abstract

A series of compounds has been discovered while investigating reactions of rare earth, transition metals, and Ge in excess indium. These compounds, RE2Zn3Ge6 (RE = La, Ce, Pr, Nd), are isostructural, crystallizing in the orthorhombic space group Cmcm with lattice parameters a = 5.9691(9) angstroms, b = 24.987(4) angstroms, and c = 5.9575(9) angstroms for La2Zn3Ge6, a = 5.9503(5) angstroms, b = 24.761(2) angstroms, and c = 5.9477(5) angstroms for the Ce analogue, a =5.938(2) angstroms, b = 24.708(8) angstroms, and c = 5.936(2) angstroms for Pr2Zn3Ge6, and a = 5.9094(7) angstroms, b = 24.619(3) angstroms, and c = 5.9063(5) angstroms for the Nd analogue. The structure is composed of PbO-like ZnGe layers and ZnGe4 cage layers and is related to the Ce4Zn8Ge(11-x) structure type. The bonding in the system can be rationalized using the Zintl concept resulting in a material that is expected to be a valence precise semiconductor, although its behavior is more consistent with it being a semimetal, making it an intermediate case. The results of band structure calculations and magnetic measurements of these compounds are discussed.

Published
2005
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48. On the lamellar compounds CuBiP(2)Se(6), AgBiP(2)Se(6) and AgBiP(2)S(6). Antiferroelectric phase transitions due to cooperative Cu(+) and Bi(3+) ion motion.

Author

Gave MA, Bilc D, Mahanti SD, Breshears JD, and Kanatzidis MG

Subjects
Crystallography, X-Ray, Electrochemistry methods, Ions chemistry, Models, Molecular, Phase Transition, Semiconductors, Sulfur chemistry, Surface Properties, Temperature, Bismuth chemistry, Copper chemistry, Inorganic Chemicals chemistry, Phosphorus chemistry, Selenium chemistry, Silver chemistry
Abstract

CuBiP(2)Se(6), AgBiP(2)Se(6), and AgBiP(2)S(6) were prepared from the corresponding elements. CuBiP(2)Se(6) and AgBiP(2)Se(6) crystallize in the space group R with a = 6.5532(16) A and c = 39.762(13) A for CuBiP(2)Se(6) and a = 6.6524(13) A and c = 39.615(15) A for AgBiP(2)Se(6). AgBiP(2)S(6) crystallizes in the triclinic space group P with a = 6.3833(13) A, b = 7.1439(14) A, c = 9.5366(19) A, alpha = 91.89(3) degrees , beta = 91.45(3) degrees , gamma = 94.05(3) degrees . CuBiP(2)Se(6) was found to exhibit a temperature-dependent antiferroelectric ordering of the Cu(+) and Bi(3+) ions in the lattice. An intermediate and a fully ordered structure were refined at 173 and 97 K, respectively. Electronic band and total energy calculations at the DFT level clearly suggest that the antiferroelectric model is energetically favored over the paraelectric and hypothetical ferrielectric models. This phase transition can be classified as a second-order Jahn-Teller distortion. The antiferroelectric state of CuBiP(2)Se(6) is an indirect gap semiconductor. The compounds were characterized with differential thermal analysis and solid-state UV/vis diffuse reflectance spectroscopy. Generalized implications regarding the expected ferroelectric behavior of compounds in the CuMP(2)Se(6) system (M = trivalent metal) are discussed.

Published
2005
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49. Tb4FeGe8 grown in liquid gallium: trans-cis chains from the distortion of a planar Ge square net.

Author

Zhuravleva MA, Bilc D, Pcionek RJ, Mahanti SD, and Kanatzidis MG

Abstract

The ternary germanide Tb4FeGe8 was obtained from Ga flux reactions. The crystal structure studied with single-crystal X-ray diffraction revealed the existence of an orthorhombic average substructure (Cmcm, Z=1) with cell parameters a = 4.1118(14) A, b=15.844(5) A, and c=3.9885(15) A. The refinement [I > 2sigma(I)] converged to final residuals R1/wR2 = 0.0363/0.0893. The average structure (CeNiSi2-type) consists of a 3D [Fe1/4Ge2] framework where Ge atoms form a square net and Fe atoms reside alternatively above and below it with only 1/4 occupation probability. X-ray and electron diffraction studies showed a modulation in the Ge net. The modulated structure was refined based on a 4-fold monoclinic supercell (P2(1)/n) with parameters a = 5.7315(11) A, b = 15.842(3) A, c = 11.438(2) A, and beta = 91.724(4) degrees with R1/wR2 = 0.0643/0.1735 and uncovered a severe distortion of the Ge square net. The Ge atoms are displaced to form an array of cis-trans chains. The Ge-Ge distances within these chains are distinctively bonding, whereas those between the chains are nonbonding. Results of the electronic structure calculations and magnetic measurements are also reported. The structural distortions found in Tb4FeGe8 cast a doubt onto the correctness of many of the reported REM1-xGe2 disordered compounds and call for reinvestigation.

Published
2005
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50. Resonant states in the electronic structure of the high performance thermoelectrics AgPbmSbTe2+m: the role of Ag-Sb microstructures.

Author

Bilc D, Mahanti SD, Quarez E, Hsu KF, Pcionek R, and Kanatzidis MG

Abstract

Ab initio electronic structure calculations based on gradient corrected density-functional theory were performed on a class of novel quaternary compounds AgPb(m)SbTe(2+m), which were found to be excellent high temperature thermoelctrics with a large figure of merit ZT approximately 2.2 at 800 K. We find that resonant states appear near the top of the valence and bottom of the conduction bands of bulk PbTe when Ag and Sb replace Pb. These states can be understood in terms of modified Te-Ag(Sb) bonds. The electronic structure near the gap depends sensitively on the microstructural arrangements of Ag-Sb atoms, suggesting that large ZT values may originate from the nature of these ordering arrangements.

Published
2004
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