12058-86-5Relevant articles and documents
Structures and transport properties of metastable solid solutions (NaSbTe2)1-x(GeTe)x
Schwarzmüller, Stefan,Yang, Fangshun,Oeckler, Oliver
, p. 774 - 779 (2019)
In contrast to the solid solution series (LiSbTe2)1-x(GeTe)x, compounds with compositions (NaSbTe2)1-x(GeTe)x are not thermodynamically stable at room temperature, but can be obtained as metastable phases by quenching melts with x ≤ 0.5. For x > 0.5 and in slowly cooled melts, samples are inhomogeneous. Despite the metastability, the lattice parameters of (NaSbTe2)1-x(GeTe)x show a Vegard-like behavior. The limited tendency toward forming solid solutions is due to the fact that the ionic radius of Na+ is much larger than that of Ge2+ or Li+ and thus the lattice parameter of NaSbTe2 (a = 6.32 ?) being significantly larger than that of LiSbTe2 (a = 6.11 ?). Measurements of transport properties revealed an increasing Seebeck coefficient with increasing GeTe content. Electrical and thermal conductivities of all members of the series (NaSbTe2)1-x(GeTe)x with x ≤ 0.5 are low with ~15 mS cm?1 and 0.5 W m?1 K?1, respectively, which is consistent with the inherently low electrical conductivity of NaSbTe2. Nevertheless, this model system explains both the low thermoelectric performance of other chalcogenides with high Na contents and the widely recognized potential of Na as doping agent in thermoelectric materials.
Weak itinerant ferromagnetism and electronic and crystal structures of alkali-metal iron antimonides: NaFe4Sb12 and KFe 4Sb12
Leithe-Jasper,Schnelle,Rosner,Baenitz,Rabis,Gippius,Morozova,Borrmann,Burkhardt,Ramlau,Schwarz,Mydosh,Grin,Ksenofontov,Reiman
, p. 1 - 12 (2004)
The synthesis, chemical, structural, and magnetic properties of alkali-metal compounds with filled-skutterudite structure, NaFe 4Sb12 and KFe4Sb12, are described. X-ray and neutron diffraction and elemental analysis established the crystal structure without defects and disorder on the cation site. The temperature and pressure dependence of the cubic unit cell of NaFe4Sb12 and the displacement parameter of Na are investigated. The electronic structure is calculated by density functional methods (LMTO, FPLO). Quantum chemical calculations (electron localization function) reveal the covalent character of both Fe-Sb and Sb-Sb interactions. Electronic structure calculations within the local density approximation exhibit a band ferromagnetic ground state and predict a half-metallic behavior. In contrast to isostructural alkaline-earth compounds (CaFe4Sb12 and BaFe4Sb12), the alkali-metal skutterudites are itinerant electron ferromagnets with small magnetic moments (≈0.25 μB/Fe atom) and TC≈=85 K. Yet the paramagnetic moments of all four compounds are between 1.5 μB and 1.7 μB per Fe atom, indicating similar Stoner factors. Temperature-dependent 57Fe and 121Sb Moessbauer spectroscopies confirm the ferromagnetic state in the sodium compound with very small hyperfine fields at the iron and antimony sites.