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Single crystals of SrAl_2Si_2 were synthesized by reaction of the elements in an aluminum flux at 1000 °C. SrAl_2Si_2 is isostructural to CaAl2Si2 and crystallizes in the hexagonal space group P–3m1 (90 K, a=4.1834 (2), c=7.4104 (2) A, Z=1, R1=0.0156, wR2=0.0308). Thermal analysis shows that the compound melts at 1020 °C. Low-temperature resistivity on single crystals along the c-axis shows metallic behavior with room temperature resistivity value of 7.5 mΩ cm. High-temperature Seebeck, resistivity, and thermal conductivity measurements were made on hot-pressed pellets. The Seebeck coefficient shows negative values in entire temperature range decreasing from −78 μV K^(−1) at room temperature to −34 μV K^(−1) at 1173 K. Seebeck coefficients are negative indicating n-type behavior; however, the temperature dependence is consistent with contribution from minority p-type carriers as well. The lattice contribution to the thermal conductivity is higher than for clathrate structures containing Al and Si, approximately 50 mW cm^(−1) K, and contributes to the overall low zT for this compound.

In the quest for alternative energy sources, hydrogen has long been touted as one of the most likely candidates to replace fossil fuels, provided practical solutions for its storage and transport can be found. Clathrate hydrates, amongst other nano-porous materials, have shown remarkable potential for hydrogen storage, adsorbing up to 7.5%wt H, albeit in extreme pressure and temperature conditions [1]. Upon crystallising, these compounds form a three-dimensional host matrix where guest atoms can be accommodated within distinct polyhedral “cages”. Recent work exhibited a sodium silicide clathrate NaxSi46, consisting of a silicon matrix with two distinct Na guest sites, labelled 2a and 6d, stable at room temperature and with promising hydrogen encapsulation properties [2]. Magic angle spinning nuclear magnetic resonance was initially used to show that in the growth conditions specific to this work some of the 6d sites were Na-deficient and H-rich.

The temperature dependence of the magnetization in two new compounds is presented and compared with Ca14MnBi11. One of the new compounds, Sr14MnBi11, orders ferromagnetically and the other, Ba14MnBi11, is an antiferromagnet at low T. The Curie-Weiss constants C and Θ, found above the ordering temperatures, imply that Mn has four unpaired electrons in each compound and that the near neighbor magnetic coupling in each compound is ferromagnetic, even for antiferromagnetic Ba14MnBi11. For each of these compounds the low temperature high field moment is consistent with the Mn having about 2.5 unpaired electrons.

Two compounds, BaT4Sb12 (T = Fe, Ru), have been synthesized using high temperature methods. These compounds crystallize in the cubic LaFe4P12 structure type. Two methods are described for the synthesis of BaFe4Sb12. Single crystals of BaFe4Sb12 can be prepared by reacting BaSb, Fe, and Sb in a 1:4:18 (Ba:Fe:Sb) molar ratio (method I). Single crystal X-ray diffraction data (room temperature, a = 9.200(3) A) for BaFe4Sb12 prepared by Method I were refined (cubic, Im 3 (No. 204), Z = 2, R = 1.96%, Rw = 1.73% for 179 independent reflections). BaFe4Sb12 can also be prepared in ≥80% yield from the reaction of stoichiometric amounts of Ba2Sb3, FeSb2, and Sb (method II). Low temperature (130 K, a = 9.188(2)) single crystal X-ray diffraction data on BaFe4Sb12 crystals produced from Method II were also measured and refined (R = 2.29%, Rw = 2.45% for 179 independent reflections). The structure of BaFe4Sb12 will be compared to that of the LaFe4Sb12 and CoSb3.

Rare-earth transition metal compounds Yb_(14)Mn_(1−x)Zn_xSb_(11), isostructural with Ca_(14)AlSb_(11), have been prepared using a metal flux growth technique for thermoelectric property measurements (with x = 0.0, 0.2, 0.3, 0.4, 0.7, 0.9, and 1.0). Single-crystal X-ray diffraction and electron microprobe analysis data indicate the successful synthesis of a solid-solution for the Yb_(14)Mn_(1−x)Zn_xSb_(11) structure type for 0 0.4. High-temperature (298 K–1275 K) measurements of the Seebeck coefficient, resistivity, and thermal conductivity were performed on hot-pressed, polycrystalline samples. As the concentration of Zn increases in Yb_(14)Mn_(1−x)Zn_xSb_(11), the Seebeck coefficient remains unchanged for 0 ≤ x ≤ 0.7 indicating that the free carrier concentration has remained unchanged. However, as the nonmagnetic Zn^(2+) ions replace the magnetic Mn^(2+) ions, the spin disorder scattering is reduced, lowering the resistivity. Replacing the magnetic Mn^(2+) with non magnetic Zn^(2+) provides an independent means to lower resistivity without deleterious effects to the Seebeck values or thermal conduction. Alloying the Mn site with Zn reduces the lattice thermal conductivity at low temperatures but has negligible impact at high temperatures. The reduction of spin disorder scattering leads to an ∼10% improvement over Yb_(14)MnSb_(11), revealing a maximum thermoelectric figure of merit (zT) of ∼1.1 at 1275 K for Yb_(14)Mn_(0.6)Zn_(0.4)Sb_(11).

Lanthanum doping of the high-temperature p-type thermoelectric material Yb_(14)MnSb_(11) enhances the figure of merit zT through carrier concentration tuning. This is achieved by substituting La^(3+) on the Yb^(2+) site to reduce the free hole concentration as expected from the change in valence. The high-temperature transport properties (Seebeck coefficient, electrical resistivity, Hall mobility, and thermal conductivity) of Yb_(13.6)La_(0.4)MnSb_(11) are explained by the change in carrier concentration using a simple rigid parabolic band model, similar to that found in Yb_(14)Mn_(1−x)A_(lx)Sb_(11). Together, use of these two dopant sites enables the partial decoupling of electronic and structural properties in Yb_(14)MnSb_(11)-based materials.

Layered d-metal pnictide oxides are a unique class of compounds which consists of characteristic d-metal pnictide layers and metal oxide layers. More than 100 of these layered compounds, including the recently discovered Fe-based superconducting pnictide oxides, can be classified into 9 structure types. These structure types and the chemical and physical properties of the characteristic d-metal pnictide layers and metal oxide layers of the layered d-metal pnictide oxides are reviewed and discussed. Furthermore, possible approaches to design new superconductors based on these layered d-metal pnictide oxides are proposed., 29 pages including 6 tables and 2 figures

The effect of Y 2 O 3 -stabilized ZrO 2 (YSZ) particle size on composite YSZ -(La 0 . 8 5 Sr 0 . 1 5 ) 0 . 9 8 MnO 3 (LSM) cathode microstructure and performance was examined. Two nanocrystalline YSZ powders were compared withdifferent particle size and surface areas; a commercial powder with ∼100 nm particles and 11 m 2 /g surface area and a synthesized YSZ powder with ∼10 nm particles and 124 m 2 /g surface area. The LSM phase of the composite was the same in both systems. Anode supported single cells were fabricated and the electrochemical performances measured. The cathode microstructures for the high surface area YSZ composites were examined as a function of sintering temperature and compared to the lower surface area YSZ composite cathode sintered at 1150 °C. The larger surface area YSZ was prepared using a novel epoxide initiated sol-gel synthesis, followed by aerogel processing. The aerogels were characterized with TEM, SEM, BET surface area analysis, and powder XRD.

A hydrogen-encapsulated inorganic clathrate, which is stable at ambient temperature and pressure, has been prepared in high yield. Na5.5(H2)2.15Si46 is a sodium-deficient, hydrogen-encapsulated, type I silicon clathrate. It was prepared by the reaction between NaSi and NH4Br under dynamic vacuum at 300 °C. The Rietveld refinement of the powder X-ray diffraction data is consistent with the clathrate type I structure. The type I clathrate structure has two types of cages where the guest species, in this case Na and H2, can reside: a large cage composed of 24 Si, in which the guest resides in the 6d crystallographic position, and a smaller one composed of 20 Si, in which the guest occupies the 2a position. Solid-state 23Na, 1H, and 29Si MAS NMR confirmed the presence of both sodium and hydrogen in the clathrate cages. 23Na NMR shows that sodium completely fills the small cage and is deficient in the larger cage. The 1H NMR spectrum shows a pattern consistent with mobile hydrogen in the large cage. 29Si NMR ...

We investigated the effect of Cd and Hg doping on the first order superconducting (SC) transition and the high field-low temperature SC state of CeCoIn$_5$ by measuring the specific heat of CeCo(In$_{\rm 1-x}$Cd$_{\rm x}$)$_5$ with x=0.0011, 0.0022 and 0.0033 and CeCo(In$_{\rm 1-x}$Hg$_{\rm x}$)$_5$ with x=0.00016, 0.00032, and 0.00048 at temperatures down to 0.1 K and fields up to 14 T. Cd substitution rapidly suppresses the cross-over temperature $T_{\rm 0}$, where the superconducting transition changes from second to first order, to $T$=0 K with x=0.0022 for $H\parallel$ [100], while it remains roughly constant up to x=0.0033 for $H\parallel$ [001]. The associated anomaly of the proposed FFLO state in Hg-doped samples is washed out by x=0.00048, while remaining at the same temperature, indicating high sensitivity of that state to impurities. We interpret these results as supporting the non-magnetic, possibly FFLO, origin of the high field - low temperature state in CeCoIn$_5$.

The phase Y{sub 10}I{sub 13}C{sub 2} is synthesized by the reaction at {approximately} 800{degree}C of powdered Y and YI{sub 3} with impure Y{sub 2}O{sub 3}, the vital carbon component resulting from incomplete decomposition of the yttrium oxalate precursor. The phase has not been obtained from more conventional carbon sources. The identity of carbon as the interstitial is supported by these syntheses, microprobe analyses of Y{sub 10}I{sub 13}C{sub 2} vs Y{sub 6}I{sub 7}C{sub 2}, and both the occupancy and the dimensions of the yttrium cavity in which carbon occurs. The phase occurs in space group C2/m, Z = 2; a = 21.317 (6) {angstrom}; c = 19.899 (5) {angstrom}; {beta} = 97.40 (2){degree}; R/R{sub w} = 3.3%/3.9% for 838 independent reflections with 2{theta} {le} 50{degree} (Mo K{alpha}). The compound consists of centered Y{sub 6}I{sub 12}C- and empty Y{sub 6}I{sub 8}-type clusters condensed by edge sharing into commensurate double and single chains, respectively. The chains are further cross-linked by additional iodine atoms. The two chain types are very similar to those known individually in the phases Y{sub 6}I{sub 7}C{sub 2} and Y{sub 4}Cl{sub 6} and are presumably metallic and semiconducting, respectively. The Y{sub 4}I{sub 6} chain is the first iodide example ofmore » condensed Y{sub 6}X{sub 8}-type clusters. This feature appears to be stabilized in this structure by a sterically less demanding means of bridging these chains between sheets of a Y{sub 6}I{sub 7}C{sub 2}-like arrangement. 30 refs., 3 figs., 3 tabs.« less

There are a wide variety of ternary compounds, AxMyXz, where A = alkali or alkaline earth metal, M = semimetal or main group element and X = pnictide, that have been synthesized. For example the compounds Ba3AlSb3, Ca3AlSb3, Ca3AlSb3 and Ca5Al2Sb6 have been synthesized and their structures can be understood via the Zintl formalism which can be simply stated as the octet rule for all atoms. The structures can be generally formulated as A− + [(MX)−] so that the anionic units in these examples may be written as: (Al2Sb6)12-; (AlSb3)6- chains; a (Al2Sb6)10- network; and [(AlSb9- 4) + 4Sb3- + Sb7- 3). The Zintl concept has also been applied to ternary transition metal compounds such as the lanthanum transition metal pnictides and ternary transition metal chalcogenides. These structures and their related properties can be understood in terms of cations and complex polyatomic anionic units. The Zintl concept, as it applies to ternary pnictide compounds, will be presented and its extension to ternary tra...

Sodium intercalation compounds of YbOCI have been synthesized by reaction of Na-NH3 solutions with YbOCI (SmSI structure type). These materials have been characterized by powder X-ray diffraction and optical spectroscopy. An increase in the basal plane separation of ∼3 A indicates that cointercalation of NH3 occurs. Optical spectroscopy data show the appearance of two new absorption bands upon intercalation and is consistent with the reduction of Yb3+ to Yb2+. Synthesis, structure and optical properties of these new materials is discussed.

Magnetic susceptibility and electrical resistivity measurements have been made on the Zintl compound, Cal4MnBi11, for temperatures between 6 K and 300 K. The magnetic data are consistent with high spin Mn+3 for T < 100 K and a ferromagnetic transition is observed at ∼56 K. Although the Mn+3 ion has four unpaired spins in the paramagnetic regime, the ferromagnetic moment is considerably reduced. Resistivity data also display a transition at approximately 56 K.

The magnetic, thermal, and transport properties of single crystals of the narrow gap semiconductor Ce3Au3Sb4 have been studied. Transport data are consistent with an exponential activation and variable range hopping at low temperatures, which is characteristic of weak disorder and localization. The specific heat and the magnetic susceptibility data suggest the existence of a large density of states of localized states in the gap. The physics is then different from standard Kondo insulators. From its unique physical properties, we propose a three band model valence, conduction, and f bands with weak disorder that explains most of the experimental findings.

Single crystals of BaAl2Si2 were grown from an Al molten flux and characterized using single-crystal X-ray diffraction at 10 and 90 K and neutron diffraction at room temperature. BaAl2Si2 crystallizes with the α-BaCu2S2 structure type (Pnma), is isostructural with α-BaAl2Ge2, and is an open 3D framework compound, where Al and Si form a covalent cagelike network with Ba2+ cations residing in the cages. BaAl2Si2 has a unit cell of a = 10.070(3) A, b = 4.234(1) A, and c = 10.866(3) A, as determined by room-temperature single-crystal neutron diffraction (R1 = 0.0533, wR2 = 0.1034). The structure as determined by single-crystal neutron and X-ray diffraction (10 and 90 K) indicates that BaAl2Si2 (Pnma) is strictly isostructural to other (α)-BaCu2S2-type structures, requiring site specificity for Al and Si. Unlike BaAl2Ge2, no evidence for an α to β (BaZn2P2-type, I4/mmm) phase transition was observed. This compound shows metallic electronic resistivity and Pauli paramagnetic behavior.

This study describes a new stable inorganic clathrate compound encapsulating hydrogen in the Si cage structure. In this work, the characterization of the new type-I Si clathrate, Na6(H2)2Si46, is illustrated. Na6(H2)2Si46 was prepared from NaSi and NH4X (X = Cl and Br) under dynamic vacuum at 300 oC. Rietveld refinement of powder X-ray diffraction data was consistent with the clathrate type-I structure. Solid-state 1 H, 29 Si and 23 Na MAS NMR confirmed the presence of both hydrogen and sodium in the clatharte cages. 23 Na NMR indicated that the guest sites are not fully occupied by Na. In order to validate the structure and investigate the Na content, the synthesized particles were examined using spherical aberration (Cs) corrected VG HB501 scanning transmission electron microscope (STEM) operated at 100 kV. Fig. 2 shows a high-angle annular dark-field (HAADF) image taken along [100] with the convergence semi-angle of 20 mrad and collection semi-angle of 70-210 mrad. Image calculation was made with Kirkland’s code [3] with the thickness of 21 nm and defocus value of 22.5 nm. The calculated image inserted in Fig. 2 is in good agreement with the experimental one. The ring pattern and the center of the ring correspond to the Si24 cage and the 6d sites, respectively. When observed along [100], the 6d sites are aligned in an atomic column which is apart from the nearest columns by 0.23 nm so that the Na occupancy in the 6d sites can be determined by comparing the experimental intensity profiles with calculated ones. Fig. 3 shows an averaged experimental image using 2dx software [4] and calculated images with different Na occupancies in the 6d sites as well as intensity profiles along the line X-Y. The peak intensity at the

Single crystals of AxBa8-xAl14Si31 (A = Sr, Eu) were grown using a molten Al flux technique. Single-crystal X-ray diffraction confirms that AxBa8-xAl14Si31 (A = Sr, Eu) crystallize with the type I clathrate structure, and phase purity was determined with powder X-ray diffraction. Stoichiometry was determined to be Sr0.7Ba7.3Al14Si31 and Eu0.3Ba7.7Al14Si31 by electron microprobe analysis. These AxBa8-xAl14Si31 phases can be described as framework-deficient clathrate type I structures with the general formula, AxBa8-xAlySi42-3y/4[]4-1/4y. DSC measurements indicate that these phases melt congruently at 1413 and 1415 K for Sr0.7Ba7.3Al14Si31 and Eu0.3Ba7.7Al14Si31, respectively. Temperature-dependent resistivity indicates metallic behavior, and the negative Seebeck coefficient indicates transport processes dominated by electrons as carriers. Thermal conductivity of these phases remains low with Sr0.7Ba7.3Al14Si31 having the lowest values.

By converting waste heat into electricity and improving the efficiency of refrigeration systems, thermoelectric devices could play a significant role in solving today's energy problems. Increasing the thermoelectric efficiency (as measured by the thermoelectric material's figure-of-merit, zT) is critical to the development of this technology. Complex Zintl phases, in particular, make ideal candidates for thermoelectric materials because the necessary "electron-crystal, phonon-glass" properties can be engineered with an understanding of the Zintl chemistry. A recent example is the discovery that Yb(14)MnSb(11), a transition metal Zintl compound, has twice the zT as the material currently in use at NASA. This perspective outlines a strategy to discover new high zT materials in Zintl phases, and presents results pointing towards the success of this approach.

A series of core/shell CdSe/Zn1-xMnxS nanoparticles were synthesized for use in dual-mode optical and magnetic resonance (MR) imaging techniques. Mn2+ content was in the range of 0.6−6.2% and varies with the thickness of the shell or amount of Mn2+ introduced to the reaction. These materials showed high quantum yield (QY), reaching 60% in organic solvent. Water-soluble nanoparticles were obtained by capping the core/shell particles with amphiphilic polymer, and the QY values in water reached 21%. These materials also demonstrated high relaxivity with r1 values in the range of 11−18 mM-1 s-1 (at room temperature, 7 T). Both optical and MR imaging were performed on nanoparticles in aqueous solution and applied to cells in culture. The results showed that the QY and manganese concentration in the particles was sufficient to produce contrast for both modalities at relatively low concentrations of nanoparticles.

Large samples (6–8 g) of Yb11Sb10 and Ca11Sb10 have been synthesized using a high-temperature (1275–1375 K) flux method. These compounds are isostructural to Ho11Ge10, crystallizing in the body-centered, tetragonal unit cell, space group I4/mmm, with Z=4. The structure consists of antimony dumbbells and squares, reminiscent of Zn4Sb3 and filled Skutterudite (e.g., LaFe4Sb12) structures. In addition, these structures can be considered Zintl compounds; valence precise semiconductors with ionic contributions to the bonding. Differential scanning calorimetry (DSC), thermogravimetry (TG), resistivity (ρ), Seebeck coefficient (α), thermal conductivity (κ), and thermoelectric figure of merit (zT) from room temperature to at minimum 975 K are presented for A11Sb10 (A=Yb, Ca). DSC/TG were measured to 1400 K and reveal the stability of these compounds to ∼1200 K. Both A11Sb10 (A=Yb, Ca) materials exhibit remarkably low lattice thermal conductivity (∼10 mW/cm K for both Yb11Sb10 and Ca11Sb10) that can be attributed to the complex crystal structure. Yb11Sb10 is a poor metal with relatively low resistivity (1.4 mΩ cm at 300 K), while Ca11Sb10 is a semiconductor suggesting that a gradual metal–insulator transition may be possible from a Ca11−xYbxSb10 solid solution. The low values and the temperature dependence of the Seebeck coefficients for both compounds suggest that bipolar conduction produces a compensated Seebeck coefficient and consequently a low zT.

Single crystals of AxBa8-xAl14Si31 (A = Sr, Eu) were grown using a molten Al flux technique. Single-crystal X-ray diffraction confirms that AxBa8-xAl14Si31 (A = Sr, Eu) crystallize with the type I clathrate structure, and phase purity was determined with powder X-ray diffraction. Stoichiometry was determined to be Sr0.7Ba7.3Al14Si31 and Eu0.3Ba7.7Al14Si31 by electron microprobe analysis. These AxBa8-xAl14Si31 phases can be described as framework-deficient clathrate type I structures with the general formula, AxBa8-xAlySi42-3y/4[]4-1/4y. DSC measurements indicate that these phases melt congruently at 1413 and 1415 K for Sr0.7Ba7.3Al14Si31 and Eu0.3Ba7.7Al14Si31, respectively. Temperature-dependent resistivity indicates metallic behavior, and the negative Seebeck coefficient indicates transport processes dominated by electrons as carriers. Thermal conductivity of these phases remains low with Sr0.7Ba7.3Al14Si31 having the lowest values.

We report the phase transfer of hydrophobic CdSe/Zn 1-x Mn x S quantum dots (QDs) into water by encapsulation with octylamine-modified poly(acrylic acid) (PAA). CdSe/Zn 1-x Mn x S QDs are of interest as multimodality biological probes where the photoluminescence and magnetic relaxivity can be tuned independently. Different percentages of the carboxyl groups in PAA were grafted with octylamine molecules and the modified PAA was used for capping CdSe/Zn 1-x Mn x S QDs to make them water soluble. We investigated the optical properties and the solubility of the CdSe/Zn 1-x Mn x S QDs in water. It was found that the PAA with a modification percentage of ~ 45% resulted in soluble CdSe/Zn 1-x Mn x S QDs with the highest quantum yield (QY) in water of approximately 20%. The QY of CdSe/Zn 1-x Mn x S QDs in water was lower than the initial measurement in chloroform and dropped in the initial stages of phase transfer, stabilizing at 20%. Hydrodynamic size of the polymer encapsulated CdSe/Zn 1-x Mn x S QDs in water was evaluated by dynamic light scattering (DLS). The smallest average hydrodynamic diameter of ~ 30 nm was achieved when the molecular ratio of QDs to PAA for capping was 1 nanomole of QDs to 24 micromole of monomer unit.

Fluorescent silicon nanomaterials have initiated great interest for their potential biological applications. In this paper, we report the synthesis of water-soluble, luminescent silicon nanoparticles with high quantum yield. The surfaces of the Si nanoparticles were capped by hydrophobic or hydrophilic organic molecules that passivate and protect the silicon particles from oxidation. The as-synthesized silicon nanoparticles displayed strong photoluminescence in the blue region of the visible spectrum. The attached organic molecules conveyed both water solubility and high stability, and coating had little adverse effect on the optical properties of nanoparticles. These results have major implications towards using colloidal silicon nanoparticles effectively in biological fluorescence imaging.

A molten Al flux method was used to grow single crystals of the type I clathrate compound Ba8Al14Si31. Single-crystal neutron diffraction data for Ba8Al14Si31 were collected at room temperature using the SCD instrument at the Intense Pulsed Neutron Source, Argonne National Laboratory. Single-crystal neutron diffraction of Ba8Al14Si31 confirms that the Al partially occupies all of the framework sites (R1 = 0.0435, wR2 = 0.0687). Stoichiometry was determined by electron microprobe analysis, density measurements, and neutron diffraction analysis. Solid-state 27Al NMR provides additional evidence for site preferences within the framework. This phase is best described as a framework-deficient solid solution Ba8Al14Si31, with the general formula, Ba8AlxSi42-3/4x[]4-1/4x ([] indicates lattice defects). DSC measurements and powder X-ray diffraction data indicate that this is a congruently melting phase at 1416 K. Temperature-dependent resistivity reveals metallic behavior. The negative Seebeck coefficient indicat...

Single crystals of Y b14−xCexMnSb11 were grown from tin metal as a flux solvent with a maximum Ce incorporation of 0.6. The phases with x ∼ 0.1–0.6 crystallize in the tetragonal Ca14AlSb11 structure type with I41/acd space group. In this structure type, there are 4 crystallographically unique Yb sites and the structure can be described according to the Zintl concept as containing 14Y b2+ + [MnSb4]9− + [Sb3]7− + 4Sb3−. For x > 0.3, Ce is incorporated on specific Yb sites in the structure as a function of x, initially at x = 0.3 on the Yb(2) site followed by Yb(4) at higher values of x. These sites have the largest volume as indicated by Hirshfeld surface analysis of chemical bonding. As Ce content is increased, the ferromagnetic ordering temperatures decrease and effective paramagnetic moments increase. The magnetic ordering temperatures decrease from the undoped TC of 50 K until x ∼ 0.4, where the lowest TC of 39 K is reached. As the additional electron introduced by Ce3+ fills the hole associated with [MnSb4]9−, the screening of the Mn moments is reduced. This leads to an increase in overall moment attributed to Mn in addition to the moment from the Ce3+ f electron. Increasing Ce content also leads to an increase in electrical resistivity, an expected effect from reducing the carrier concentration.

The magnetization and resistivity of single crystals of the ferromagnetic compound Sr14MnSb11 are measured as functions of magnetic field, temperature, and crystal orientation. The uniform magnetic susceptibility is used to identify TC=39 K. The ferromagnetic state is found to have a hard axis (c axis) anisotropy. The resistivity data place the compound in the class of colossal magnetoresistance (CMR) materials such as Ca-doped LaMnO3. The data are also compared to the related CMR material Eu14MnSb11.

HRTEM image of a single Ge nanocrystal. The image has been rotationally filtered to improve clarity. The lattice fringes imaged are for Ge 〈111〉, with a d spacing of 3.27 A. Reaction between the Zintl salt NaGe and GeCl4 is shown to produce Ge nanocrystals. The reaction proceeds readily in refluxing diglyme at ambient pressure. The nanocrystals produced may be surface-terminated by reaction with RLi or RMgBr and demonstrate quantum confinement.

Powder samples of the type I clathrate phases, with the proposed stoichiometry Ba8Al16Si30 and Eu2Ba6Al16Si30, were synthesized using direct reaction of stoichiometric amounts of the elements. Rietveld refinement of powder X-ray diffraction data is consistent with the clathrate type I structure. Composition, microstructure, and thermoelectric property measurements were made on hot-pressed pellets. Stoichiometry of the Ba8Al16Si30 sample was determined from microprobe data to be Ba8Al14Si31, close to the deficient framework solid solution of the general formula, Ba8AlxSi42-3/4x[]4-1/4x (x = 14; [], open square indicates lattice defect). In the case of the rare-earth-substituted compound, microprobe analysis of the microstructure indicates that it is not single phase, but contains multiple components, most of the general clathrate stoichiometry. The majority phase has the stoichiometry EuBa7Al13Si32. Both phases show conductivity typical of heavily doped semiconductors with negative Seebeck coefficients. Th...

Powder samples of the type I clathrate phases, with the proposed stoichiometry Ba8Al16Si30 and Eu2Ba6Al16Si30, were synthesized using direct reaction of stoichiometric amounts of the elements. Rietveld refinement of powder X-ray diffraction data is consistent with the clathrate type I structure. Composition, microstructure, and thermoelectric property measurements were made on hot-pressed pellets. Stoichiometry of the Ba8Al16Si30 sample was determined from microprobe data to be Ba8Al14Si31, close to the deficient framework solid solution of the general formula, Ba8AlxSi42-3/4x[]4-1/4x (x = 14; [], open square indicates lattice defect). In the case of the rare-earth-substituted compound, microprobe analysis of the microstructure indicates that it is not single phase, but contains multiple components, most of the general clathrate stoichiometry. The majority phase has the stoichiometry EuBa7Al13Si32. Both phases show conductivity typical of heavily doped semiconductors with negative Seebeck coefficients. Th...

Homogeneous, nanocrystalline La1-xSrxMnO3 (LSM) powders, with x ∼ 0.15, were synthesized with the epoxide addition sol−gel method. Through this simple technique, sol−gel materials were prepared from methanolic solutions of metal chlorides without the need for alkoxides, polymeric gel agents, or elaborate reaction schemes. The gels were dried in ambient conditions, resulting in mesoporous xerogels with networked nanostructures interconnecting particulate regions. Calcination of the dried gels resulted in the crystallization of single-phase LSM by 700 °C, after decomposition of intermediate hydroxide, chloride, and oxychloride compounds. SEM analysis indicated that the calcined powders were nanocrystalline and consisted of discrete particles, free of hard agglomeration. The average crystallite size and equivalent spherical diameter determined from XRD line broadening and BET analysis, respectively, were in good agreement with the SEM results (∼100 nm). The activation energies for the electronic conductivity...

Thermoelectric materials provide a key solution to energy problems through the conversion of heat into electrical energy. We report that the complex Zintl compound, Yb14MnSb11, breaks a 2-decade stagnation in high-temperature (>900 K), p-type materials development for thermoelectric power generation. This material achieves quadrupled efficiency and virtually doubled figure of merit over the current state-of-the-art, SiGe, thus earmarking it superior for thermoelectric applications in segmented devices. Yb14MnSb11 represents the first complex Zintl phase with substantially higher figure of merit and efficiency than any other competing materials, opening a new class of thermoelectric compounds with remarkable chemical and physical properties.

Measurements of specific heat, magnetic susceptibility, electrical resistivity, and penetration depth have been performed on $\mathrm{Ce}\mathrm{Co}{\mathrm{In}}_{5\ensuremath{-}x}{\mathrm{Sn}}_{x}$ $(0\ensuremath{\leqslant}x\ensuremath{\leqslant}0.24)$ single crystals. The suppression of superconductivity and the decrease of the specific heat jump at ${T}_{c}$, $\ensuremath{\Delta}C∕{T}_{c}$, with increasing Sn concentration, and the power-law temperature dependence of penetration depth are consistent with impurity scattering calculated within the Abrikosov-Gorkov formalism indicating $d$-wave superconductivity in $\mathrm{Ce}\mathrm{Co}{\mathrm{In}}_{5\ensuremath{-}x}{\mathrm{Sn}}_{x}$. The non-Fermi liquid behavior [$C∕T\ensuremath{\sim}\ensuremath{-}\mathrm{ln}\phantom{\rule{0.2em}{0ex}}T$ and $\ensuremath{\rho}(T)\ensuremath{\sim}T$] observed in the normal state in zero magnetic field is quite robust against Sn substitution (and a variety of other tuning parameters), suggesting quantum criticality involving itinerant $f$-electrons in this system.

In situ high-resolution transmission electron microscopy (HRTEM) was used to investigate the effect of heating on an organo-Ge polymer/nanoparticle composite material containing 4-8 nm diameter alkyl-terminated Ge nanoparticles. The product was obtained from the reduction of GeCl4 with Na(naphthalide) with subsequent capping of the -Cl surface with n-butyl Grignard reagent. The in situ HRTEM micrographs show that the product undergoes significant changes upon heating from room temperature to 600 degrees C. Two pronounced effects were observed: (i) Ge nanoparticles coalesce and remain crystalline throughout the entire temperature range, and (ii) the organo-Ge polymer acts as a source for the in situ formation of additional Ge nanoparticles. The in situ-formed Ge nanoparticles are approximately 2-3 nm in diameter. These in situ-formed nanoparticles (2-3 nm) are so dense that, together with the original ones, they build up an almost continuous crystalline film in the temperatures between 300 and 500 degrees C. Above 480 degrees C, melting of the in situ formed Ge nanoparticles (2-3 nm) is observed, while nanoparticles greater than 5 nm remain crystalline. After cooling to room temperature, the 2-3 nm Ge nanoparticles recrystallized.

Single crystals of a new Zintl compound, EuIn2P2, were grown from indium metal as a flux solvent. The compound crystallizes in the hexagonal P6(3)/mmc space group with a unit cell of a = 4.0829(6) A, c = 17.595(4) A, and Z = 2. It contains alternating Eu2+ layers and [In2P2]2- layers. This compound is paramagnetic at high temperatures with a magnetic transition at 24 K. In the magnetically ordered state, it shows large magnetic anisotropy. The temperature-dependent resistivity of this compound suggests interaction between conduction electrons and local spins. Negative colossal magnetoresistance of up to −398% (MR = {[ρ(H) − ρ(0)]/ρ(H)} × 100%) at 5 T is observed at 24 K.

The framework-deficient clathrate phases Ba7.5Al13Si29 and Eu0.27Ba7.22Al13Si29 were prepared using a molten Al flux. Single-crystal X-ray diffraction confirmed the two phases to be clathrate type ...

We report the synthesis of high quality ZnS nanoparticles using sulfur and zinc acetate as the S and Zn source, respectively. It was found that sulfur and zinc acetate could be easily dissolved in the mixture of trioctylphosphine oxide (TOPO) and hexadecylamine (HDA) at a temperature of about 65°C and ZnS nanoparticles were generated at temperatures above 150°C. These reactive species of sulfur and zinc were also used for an epitaxial growth of ZnS shell around a CdSe core. The formation of ZnS nanoparticles was confirmed by powder X-ray diffraction (XRD). Particle size and size distribution were studied by transmission electron microscopy (TEM). Optical properties were characterized by a combination of UV-vis and photoluminescence (PL) spectroscopy. The PL quantum yield of the CdSe/ZnS nanoparticles reached about 66% compared with the dye, Rhodamine 6G (R6G). The present synthetic strategy is a "greener" and simpler synthetic scheme due to the use of air-stable and environmentally benign reagents of sulfur and zinc acetate instead of air-sensitive ones such as dimethylzinc and bis(trimethylsilyl) sulfide.

Phosphorus containing and octyl-terminated silicon nanoparticles (NPs) are generated by a solution reduction route under room temperature conditions for the first time and characterized by TEM, HRTEM, EDX, 1H/13C/31P NMR, EPR, and PL spectroscopy, then annealed to form a thin film with phosphorus doping confirmed by microprobe elemental analyses.

Fe/Au nanoparticles have been chemically synthesized through a reverse micelle reaction and investigated by both conventional and synchrotron based x-ray diffraction and by magnetic and Moessbauer spectral studies. The powder x-ray diffraction patterns reveal both the presence of crystalline alpha-iron and gold and the absence of any crystalline iron oxides or other crystalline products. First-order reversal curves, along with the major hysteresis loops of the Fe/Au nanoparticles have been measured as a function of time in order to investigate the evolution of their magnetic properties. The iron-57 Moessbauer spectra of both uncoated iron nanoparticles and the Fe/Au nanoparticles have been measured at 78 and 295 K and indicate that two major iron containing components are present, namely the expected alpha-iron and the unexpected amorphous Fe1-xBx alloy; several poorly crystallized ordered iron(III) oxide components as well as paramagnetic iron(II) and iron(III) components are also observed. These results indicate that the Fe-core/Au-shell nanoparticles synthesized through reverse micelles are far more complex that had been believed., 31 pages, 1 table, 8 figures, to appear in Chemistry of Materials

A new rare earth metal Zintl phase, Eu(3)In(2)P(4), was synthesized by utilizing a metal flux method. The compound crystallizes in the orthorhombic space group Pnnm with the cell parameters a = 16.097(3) A, b = 6.6992(13) A, c = 4.2712(9) A, and Z = 2 (T = 90(2) K, R1 = 0.0159, wR2 = 0.0418 for all data). It is isostructural to Sr(3)In(2)P(4). The structure consists of tetrahedral dimers, [In(2)P(2)P(4/2)](6-), that form a one-dimensional chain along the c axis. Three europium atoms interact via a Eu-Eu distance of 3.7401(6) A to form a straight line triplet. Single-crystal magnetic measurements show anisotropy at 30 K and a magnetic transition at 14.5 K. High-temperature data give a positive Weiss constant, which suggests ferromagnetism, while the shape of susceptibility curves (chi vs T) suggests antiferromagnetism. Heat capacity shows a magnetic transition at 14.5 K that is suppressed with field. This compound is a semiconductor according to the temperature-dependent resistivity measurements with a room-temperature resistivity of 0.005(1) Omega m and E(g) = 0.452(4) eV. It shows negative magnetoresistance below the magnetic ordering temperature. The maximum magnetoresistance (Deltarho/rho(H)) is 30% at 2 K with H = 5 T.

A new rare earth metal Zintl phase, Eu(3)In(2)P(4), was synthesized by utilizing a metal flux method. The compound crystallizes in the orthorhombic space group Pnnm with the cell parameters a = 16.097(3) A, b = 6.6992(13) A, c = 4.2712(9) A, and Z = 2 (T = 90(2) K, R1 = 0.0159, wR2 = 0.0418 for all data). It is isostructural to Sr(3)In(2)P(4). The structure consists of tetrahedral dimers, [In(2)P(2)P(4/2)](6-), that form a one-dimensional chain along the c axis. Three europium atoms interact via a Eu-Eu distance of 3.7401(6) A to form a straight line triplet. Single-crystal magnetic measurements show anisotropy at 30 K and a magnetic transition at 14.5 K. High-temperature data give a positive Weiss constant, which suggests ferromagnetism, while the shape of susceptibility curves (chi vs T) suggests antiferromagnetism. Heat capacity shows a magnetic transition at 14.5 K that is suppressed with field. This compound is a semiconductor according to the temperature-dependent resistivity measurements with a room-temperature resistivity of 0.005(1) Omega m and E(g) = 0.452(4) eV. It shows negative magnetoresistance below the magnetic ordering temperature. The maximum magnetoresistance (Deltarho/rho(H)) is 30% at 2 K with H = 5 T.

We report the chemical synthesis of Fe-core/Au-shell nanoparticles by a reverse micelle method, and the investigation of their growth mechanisms and oxidation-resistant characteristics. The core-shell structure and the presence of the Fe & Au phases have been confirmed by transmission electron microscopy, energy dispersive spectroscopy, X-ray diffraction, Mossbauer spectroscopy, and inductively coupled plasma techniques. Additionally, atomic-resolution Z-contrast imaging and electron energy loss spectroscopy (EELS) in a scanning transmission electron microscope (STEM) have been used to study details of the growth processes. The Au-shell grows by nucleating on the Fe-core surface before coalescing. The magnetic moments of such nanoparticles, in the loose powder form, decrease over time due to oxidation. The less than ideal oxidation-resistance of the Au shell may have been caused by the rough Au surfaces. However, in the pressed pellet form, electrical transport measurements show that the particles are fairly stable, as the resistance of the pellet does not change appreciably over time., 21 pages, 4 figures, Chemistry of Materials, in press

Eu3InP3has been prepared as large single crystals with an indium flux reaction. The structure of the new compound is isotypic to Sr3InP3and crystallizes in the orthorhombic space group Pnma with unit cell dimensions of a = 12.6517(15) Å, b = 4.2683(5) Å, and c = 13.5643(14) Å (Z = 4, T = 140 K, R1 = 0.0404, wR2 = 0.0971 for all data). The structure consists of one-dimensional chains of corner-shared distorted [InP2P2/2]6-tetrahedra separated by rows of Eu2+ions. Two of the three crystallographically distinct europium sites have a short Eu(1)-Eu(2) distance of 3.5954(7) Å, which yields Eu-Eu dimers. The Eu-P bond distances range from 2.974(2) to 3.166(2) Å. The temperature dependence of the conductivity indicates that Eu3InP3is a small band gap semiconductor. Both magnetization and Eu-151 Mössbauer spectral measurements indicate that the europium in Eu3InP3is divalent and that at least two magnetic transitions occur. Magnetization studies reveal magnetic transitions at 14, 10.4, and ∼5 K. These transitions are also observed in heat capacity studies of Eu3InP3. The Mössbauer spectra indicate that the two europium sites are ordered at 12 K and that all three europium sites are ordered at 8 K. © 2005 American Chemical Society.