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Understanding the structural properties and chemical bonding in complex multinary chalcogenides is highly valuable, as it provides vital information for controlling their physical properties to suit various technological applications. We report on the structural, thermal, and electronic properties of PbCuBiS 3 by incorporating an experimental and theoretical investigation of this material. Analysis of the experimental temperature-dependent heat capacity and thermal conductivity data show that weak bonding and strong lattice anharmonicity give rise to ultralow thermal conductivity. Chemical bonding information obtained from the density functional theory electronic calculations reveal significant antibonding interactions that underscore the dominant role of the Cu-S tetrahedra on occupied antibonding states, as well as a highly distorted Pb/Bi-S environment inducing weak bonding and strong lattice anharmonicity. This study broadens our understanding of the structure-property relationships for this material, and can be useful for developing this and similar chalcogenide materials for potential applications of interest. [Display omitted] [ABSTRACT FROM AUTHOR]

Polycrystalline quaternary chalcogenides with compositions Cu 1.1 Cd 1.8 In 1.1 Te 4 , Cu 1.3 Cd 1.9 In 0.8 Te 4 , Cu 1.2 Zn 1.8 InTe 4 and Cu 1.2 Zn 1.6 In 1.2 Te 4 were synthesized by reacting the constituent elements and subsequent solid state annealing followed by densification by hot-pressing in order to investigate the transport properties with varying compositions, and therefore carrier densities. The thermal conductivity of these compositions, as well as stoichiometric CuZn 2 InTe 4 and CuCd 2 InTe 4 , are reported for the first time. In addition to the thermal conductivity, resistivity, Seebeck coefficient and compositional stability measurements are also discussed. These materials are p-type semiconductors with very low thermal conductivity values. The potential for improved thermoelectric performance is also discussed. [ABSTRACT FROM AUTHOR]

The title compound is synthesized by kinetically controlled thermal decomposition of a precursor, NaSi + NaAlSi (obtained from the elements reacted at 923 K for 34 h in a tungsten crucible) mixed with CsCl (1023 K, 9 h). [ABSTRACT FROM AUTHOR]

Gallium doped Cu 2 ZnSnSe 4 quaternary chalcogenides with and without excess Cu were synthesized by elemental reaction and densified using hot pressing in order to investigate their high temperature transport properties. The resistivity, ρ , and Seebeck coefficient, S , for these materials decrease with increased Ga-doping while both mobility and effective mass increase with Ga doping. The power factor ( S 2 /ρ ) therefore increases with Ga-doping however the highest thermoelectric figure of merit ( ZT = 0.39 at 700 K) was obtained for the composition that had the lowest thermal conductivity. Our results suggest an approach for optimizing the thermoelectric properties of these materials and are part of the continuing effort to explore different quaternary chalcogenide compositions and structure types, as this class of materials continues to be of interest for energy-related applications. [ABSTRACT FROM AUTHOR]

A hydrothermal approach was employed to efficiently synthesize SnSe nanorods. The nanorods were consolidated into polycrystalline SnSe by spark plasma sintering for low temperature electrical and thermal properties characterization. The low temperature transport properties indicate semiconducting behavior with a typical dielectric temperature dependence of the thermal conductivity. The transport properties are discussed in light of the recent interest in this material for thermoelectric applications. The nanorod growth mechanism is also discussed in detail. [ABSTRACT FROM AUTHOR]

The synthesis and processing of different compositions and structure types is of fundamental importance, although challenging in many cases with inorganic clathrate-II compositions representing one such example. Herein we report on the synthesis and structural properties investigation of phase pure clathrate-II (Fd 3 ¯ m) Rb 12.9 Si 136. Temperature-dependent structural data and analyses revealed lattice anharmonicity in this inorganic clathrate. Moreover, the selective synthesis of either clathrate-I (Rb 6.8 Si 46 , Pm 3 ¯ n) or clathrate-II (Rb 12.9 Si 136) was achieved by varying the processing temperature. Our results are compared to that of other silicon clathrates. Atomic structure and temperature dependent lattice parameter for Rb 12.9 Si 136. [Display omitted] • Phase pure clathrate-II Rb 12.9 Si 136 was synthesized for the first time. • Temperature dependent structural analyses allowed for determination of the coefficient of thermal expansion. • We demonstrated the selective synthesis of phase pure clathrate-I and clathrate-II compositions with processing temperature. [ABSTRACT FROM AUTHOR]

The madocite Pb 17 (Sb 0.75 As 0.25 ) 16 S 41 was synthesized by reaction of binary compounds and densified using hot pressing. The optical band-gap, thermal stability, and temperature-dependent heat capacity and thermal conductivity are reported for the first time. The thermal properties are evaluated using the Debye model. The findings in this work lay the foundation for a more detailed understanding of the physical properties of this material, and is part of the continuing effort in investigating materials with new compositions that possess low thermal conductivity for potential low-cost thermal barrier coating and energy-related applications. [ABSTRACT FROM AUTHOR]

We report on the synthesis and low temperature transport properties of rhombohedral derivatives of the cubic skutterudite CoSb3, namely Co4-xFexGe6Se6 with x = 0, 1, 1.5. Rietveld refinement and elemental analyses were used to identify the structure and stoichiometry of the compositions. The thermal conductivity was investigated by employing the Debye model with different phonon-scattering parameters. This investigation demonstrates that Fe substitution is feasible in these skutterudite derivatives and can significantly affect the transport properties as compared with Co4Ge6Se6. [ABSTRACT FROM AUTHOR]

A new stannite phase was synthesized and its temperature dependent transport properties were investigated. Cu2CdSnTe4 possesses strong p-type conduction, while the temperature dependence of the thermal conductivity exhibits typical dielectric behavior. Electronic structure calculations allowed for a description of the transport characteristics in terms the energy band structure, density of states, and Fermi surface. The potential for thermoelectric applications is also discussed. [ABSTRACT FROM AUTHOR]

Abstract: Partially Yb-filled Fe substituted polycrystalline p-type skutterudites with nominal compositions Yb x Co2.5Fe1.5Sb12, with varying filler concentrations x, were synthesized by reacting the constituent elements and subsequent solid state annealing, followed by densification by hot-pressing. The compositions and filling fractions were confirmed with a combination of Rietveld refinement and elemental analysis. Their thermoelectric properties were evaluated from 300 to 800K. The Seebeck coefficients for the specimens increase with increasing temperature and plateau at around 750K. The thermal conductivity decreases with increasing Yb filling fraction, and bipolar conduction becomes evident and increases at elevated temperatures. A maximum ZT value of 0.8 was obtained at 750K for Yb0.47Co2.6Fe1.4Sb12. The thermoelectric properties and potential for further optimization are discussed in light of our results. [Copyright &y& Elsevier]

Systematic dc magnetization studies using the Banerjee criterion, Kouvel-Fisher, and magnetocaloric effect methods provide physical insights into the origin of the magnetic anomaly and the tunneling effect of europium on the ferromagnetic ordering in Eu8Ga16Ge30 type-I clathrates. We show that Eu8Ga16Ge30 undergoes a second-order magnetic transition (SOMT) at TC ~ 35 K, resulting from the magnetic interaction between the Eu2+ ions at the Eu2 sites, followed by a secondary magnetic transition at TL ~ 10 K (indicated as a magnetic anomaly in previous studies), as a result of the magnetic interaction between the Eu2+ ions at the Eu1 and Eu2 sites. The critical exponent β = 0.388 is close to that predicted from the three-dimensional Heisenberg model (β = 0.365), while the critical exponent γ = 0.956 is close to that predicted from the mean-field model (γ = 1). The substitution of Sr2+ for Eu2+ retains the SOMT but largely reduces the transition temperatures (TC ~ 15 K and TL ~ 5 K), with the critical exponents β = 0.521 and γ = 0.917 close to those predicted from the mean-field model (β = 0.5 and γ = 1). These results point to the important fact that the tunneling of Eu2+ between the four equivalent sites in the tetrakaidecahedral cage tends to prevent the occurrence of a long-range ferromagnetic ordering in the type-I clathrate materials. [ABSTRACT FROM AUTHOR]

The chemistry of new materials and the effects of chemical substitutions on physical properties continues to be of intense interest as it directly affects many technological fields. The synthesis and temperature dependent transport properties of GdTe 1.62 Se 0.18 were investigated revealing polaronic transport upon simple alloying with selenium. Temperature-dependent resistivity and thermopower measurements indicate strong electron-phonon coupling, as compared to the few other chalcogenides that display such transport. In addition, the low thermal conductivity is intrinsic for this material, and a result of the stacking arrangement in the crystal structure as well as of a statistical disordered Te 2 2– anion. Image, graphical abstract [ABSTRACT FROM AUTHOR]

Partially filled polycrystalline p-type skutterudites of nominal compositions Yb x Co3FeSb12 were synthesized and their thermoelectric properties characterized. The compositions and filling fractions were confirmed with a combination of Rietveld refinement and elemental analysis. The thermoelectric properties were evaluated from 300 K to 810 K. The Seebeck coefficient and resistivity increase while the thermal conductivity decreases with increasing Yb content. A maximum ZT value of 0.85 was obtained at 810 K. This work is part of a continuing effort to enhance the thermoelectric properties of p-type skutterudites, as this class of materials continues to be of interest for thermoelectrics applications. (© 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [ABSTRACT FROM AUTHOR]

Large-volume, phase-pure synthesis of BC8 silicon (I a 3, c I 16) has enabled bulk measurements of optical, electronic, and thermal properties. Unlike previous reports that conclude BC8-Si is semimetallic, we demonstrate that this phase is a direct band gap semiconductor with a very small energy gap and moderate carrier concentration and mobility at room temperature, based on far- and midinfrared optical spectroscopy, temperature-dependent electrical conductivity, Seebeck and heat capacity measurements. Samples exhibit a plasma wavelength near 11 µ m, indicating potential for infrared plasmonic applications. Thermal conductivity is reduced by 1-2 orders of magnitude depending on temperature as compared with the diamond cubic (DC-Si) phase. The electronic structure and dielectric properties can be reproduced by first-principles calculations with hybrid functionals after adjusting the level of exact Hartree-Fock (HF) exchange mixing. These results clarify existing limited and controversial experimental data sets and ab initio calculations. [ABSTRACT FROM AUTHOR]

The article presents a study which determines the crystal growth and preparation of Na24Si136 or intermetallic clathrates. The study utilized various conventional synthesis techniques in the preparation and crystal growth of intermetallic clathrates. It determined that spark plasma treatment is the first step for the synthesis and crystal growth of intermetallic clathrate.

We reveal the specific structural and bonding features that result in anisotropic thermal transport for CsPbBr 3 by directional single-crystal measurements and elucidate the bases for the low Debye temperature and speed of sound. This work enhances the research on perovskites and reveals the structural features governing the thermal properties.

We investigate the temperature and magnetic field-dependent electrical and thermal properties of Eu 2.2 Ga 11 Sn 35 , revealing a change in electronic structure and an increase in magnetoresistance with increasing field, as well as the origin of magneto-suppressed thermal conductivity of this unconventional inorganic clathrate-I material with very low cation concentration.

Quaternary chalcogenides continue to be of interest for a variety of technological applications, with physical properties stemming from their structural complexity and stoichiometric variation. In certain structure types, partial vacancies on specific lattice positions present an opportunity to investigate electrical and thermal properties in light of these lattice defects. In this work, we investigated the structural, thermal, and electronic properties of CuInSnSe 4 , a material that belongs to a relatively unexplored class of quaternary chalcogenides with a defect adamantine crystal structure. First-principles calculations together with experimental measurements revealed a chalcopyrite-like structure with inherent vacancies and characteristic s-p and p-d orbital hybridizations in the electronic structure of the material. Cation disorder and lattice anharmonicity result in very low thermal conductivity with values significantly lower than those for related compositions. This work reveals the fundamental physical properties of a previously uninvestigated quaternary chalcogenide and may aid investigations of similar as well as other quaternary chalcogenide compositions.

We elucidate the thermal properties of superionic conductors, which are of intense current interest for solid-state battery applications. The temperature-dependent thermal properties of superionic NaSbS 2 were investigated by analyses of appropriate models revealing that a predominant contribution to thermal transport above the Debye temperature is from thermal diffusion.

Single crystals of the quaternary chalcogenide BaCuGdTe 3 were obtained by direct reaction of elements allowing for a complete investigation of the intrinsic electrical and thermal properties of this previously uninvestigated material. The structure was investigated by high-resolution single-crystal synchrotron X-ray diffraction, revealing an orthorhombic crystal structure with the space group Cmcm. Although recently identified as a semiconductor suitable for thermoelectric applications from theoretical analyses, our electrical resistivity and Seebeck coefficient measurements show metallic conduction, the latter revealing strong phonon-drag. Temperature dependent hole mobility reveals dominant acoustic phonon scattering. Heat capacity data reveal a Debye temperature of 183 K and a very high density of states at the Fermi level, the latter confirming the metallic nature of this composition. Thermal conductivity is relatively high with Umklapp processes dominating thermal transport above the Debye temperature. The findings in this work lay the foundation for a more detailed understanding of the physical properties of this and similar multinary chalcogenide materials, and is part of the continuing effort in investigating quaternary chalcogenide materials and their suitability for use in technological applications.

The structural, thermal, and electronic properties of Ba 2 MnSe 3 were investigated. Analysis of the low-temperature heat capacity revealed a low Debye temperature and a low average speed of sound that, together with the bonding in this material, result in a low thermal conductivity over a relatively large temperature range. Density functional theory and calculated electron localization were employed to investigate the electronic structure and bonding. Absorption and photoluminescence spectroscopy measurements corroborated our calculations and revealed a direct band gap of 1.75 eV. This study expands on our understanding of the physical properties of this material and reveals previously unascertained properties, the knowledge of which is imperative for any potential application of interest.

The thermal properties of Ba 3 Cu 2 Sn 3 Se 10 were investigated by measurement of the thermal conductivity and heat capacity. The chemical bonding in this diamagnetic material was investigated using structural data from Rietveld refinement and calculated electron localization. This quaternary chalcogenide is monoclinic ( P 2 1 / c ), has a large unit cell with 72 atoms in the primitive cell, and a high local coordination environment. The Debye temperature (162 K) and average speed of sound (1666 m s -1 ) are relatively low with a very small electronic contribution to the heat capacity. Ultralow thermal conductivity (0.46 W m -1 K -1 at room temperature) is attributed to the relatively weak chemical bonding and intrinsic anharmonicity, in addition to a large unit cell. This work is part of the continuing effort to explore quaternary chalcogenides with intrinsically low thermal conductivity and identify the features that result in a low thermal conductivity.

Quaternary chalcogenides continue to be of interest due to the variety of physical properties they possess, as well as their potential for different applications of interest. Investigations on materials with the sphalerite crystal structure have only recently begun. In this study we have synthesized sulfur-based sphalerite quaternary chalcogenides, including off-stoichiometric compositions, and investigated the temperature-dependent electronic, thermal and structural properties of these materials. Insulating to semiconducting transport is observed with stoichiometric variation, and analyses of heat capacity and thermal expansion revealed lattice anharmonicity that contributes to the low thermal conductivity these materials possess. We include similar analyses for CuZn 2 InSe 4 and compare these sphalerite quaternary chalcogenides to that of zinc blende binaries in order to fully understand the origin of the low thermal conductivity these quaternary chalcogenides possess.

Structural, electrical, and thermal properties of CdSnAs 2 , with analyses from temperature-dependent transport properties over a large temperature range, are reported. Phase-pure microcrystalline powders were synthesized that were subsequently densified to a high-density homogeneous polycrystalline specimen for this study. Temperature-dependent transport indicates n -type semiconducting behavior with a very high and nearly temperature independent mobility over the entire measured temperature range, attributed to the very small electron effective mass of this material. The Debye model was successfully applied to model the thermal conductivity and specific heat. This work contributes to the fundamental understanding of this material, providing further insight and allowing for investigations into altering this and related physical properties of these materials for technological applications.

The synthesis, electronic structure and temperature dependent transport properties of polycrystalline Cu 1+x Mn 2-x InTe 4 (x = 0, 0.2, 0.3) are reported for the first time. These quaternary chalcogenides were synthesized by direct reaction of the elements, followed by solid state annealing and hot press densification. The thermal conductivity is low for all specimens and intrinsic to the material system. Furthermore, the off-stoichiometry specimens illustrate the sensitivity of the transport properties to stoichiometry, with a greater than two-orders-of magnitude increase in carrier concentration with increased Cu content. First principles calculations of the electronic structure are also reported, and are in agreement with the experimental data. This fundamental investigation shows the potential towards further optimization of the electrical properties that, in addition to the intrinsically low thermal conductivity, provides a basis for further research into the viability of this material system for potential energy-related applications.

Thermoelectricity allows direct conversion between heat and electricity, providing alternatives for green energy technologies. Despite these advantages, for most materials the energy conversion efficiency is limited by the tendency for the electrical and thermal conductivity to be proportional to each other and the Seebeck coefficient to be small. Here we report counter examples, where the heavy fermion compounds Yb TM 2 Zn 20 ( TM = Co, Rh, Ir) exhibit enhanced thermoelectric performance including a large power factor ( PF = 74 μW/cm-K 2 ; TM = Ir) and a high figure of merit ( ZT = 0.07; TM = Ir) at 35 K. The combination of the strongly hybridized electronic state originating from the Yb f -electrons and the novel structural features (large unit cell and possible soft phonon modes) leads to high power factors and small thermal conductivity values. This demonstrates that with further optimization these systems could provide a platform for the next generation of low temperature thermoelectric materials.

We report on the structural, chemical, electrical, and thermal properties of n-type polycrystalline NbFeSb synthesized by induction melting of the elements. Although several studies on p-type conduction of this half-Heusler composition have recently been reported, including reports of relatively high thermoelectric properties, very little has been reported on the transport properties of  n-type compositions. We combine transport property investigations together with short- and long-range structural data obtained by Mössbauer spectroscopy of iron-57 and antimony-121 and by neutron total scattering, as well as first-principles calculations. In our investigation, we show that n-type conduction can occur from antiphase boundaries in this material. This work is intended to provide a greater understanding of the fundamental properties of NbFeSb as this material continues to be of interest for potential thermoelectric applications.

Tin clathrate-II framework-substituted compositions are of current interest as potential thermoelectric materials for medium-temperature applications. A review of the literature reveals different compositions reported with varying physical properties, which depend strongly on the exact composition as well as the processing conditions. We therefore initiated an approach whereby single crystals of two different (K,Ba) 16 (Ga,Sn) 136 compositions were first obtained, followed by grinding of the crystals into fine powder for low temperature spark plasma sintering consolidation into dense polycrystalline solids and subsequent high temperature transport measurements. Powder X-ray refinement results indicate that the hexakaidecahedra are empty, K and Ba occupying only the decahedra. Their electrical properties depend on composition and have very low thermal conductivities. The structural and transport properties of these materials are compared to that of other Sn clathrate-II compositions.

Quaternary chalcogenides, particular compounds with the stannite structure-type, are of interest for thermoelectrics applications however tellurium-containing compositions have not been extensively investigated. We report on the synthesis and high temperature thermoelectric properties of p-type stannites Cu2.2Zn0.8SnSe4-xTex (x = 0.1, 0.2, 0.3, and 0.4). The compositions for each specimen were confirmed with a combination of Rietveld refinement and elemental analysis. Hall measurements indicate that holes are the dominant charge carriers in these materials. The electrical resistivity shows little temperature dependence up to 500 K and then increases with increasing temperature. The thermal conductivity decreases with increasing temperature with no indication of increase at higher temperatures suggesting a minimal bipolar diffusion effect in the thermal conductivity although these materials possess relatively small band-gaps as compared to that of other stannite compositions. A maximum ZT value of 0.56 was obtained at 700 K for Cu2.2Zn0.8SnSe3.7Te0.3 due to a relatively high Seebeck coefficient and low thermal conductivity.