Katja M. Kleinke

Thermoelectric performance of NiyMo3Sb7−xTex(y≤0.1, 1.5≤x≤1.7)

Mo3Sb7−xTex is a high temperature thermoelectric material, reported to reach figure of merit (ZT)=0.8 at 1023 K. Various p-type samples of NiyMo3Sb7−xTex were prepared with y≤0.1 and 1.5≤x≤1.7 via high temperature reactions at 993 K. Adding transition metal atoms into the empty cube formed by Sb atoms significantly alters the band structure and thus the thermoelectric properties. Electronic band structure calculations indicate that adding Ni slightly increases the charge carrier concentration, while higher Te content causes a decrease. Thermoelectric properties were determined on pellets densified via hot pressing at 993 K. Seebeck as well as electrical and thermal conductivity measurements were performed up to 1023 K. The highest ZT value thus far was obtained from a sample of nominal composition Ni0.06Mo3Sb5.4Te1.6, which amounts to 0.93 at 1023 K.

Thermoelectric properties of the quaternary chalcogenides BaCu5.9STe6 and BaCu5.9SeTe6.

These quaternary chalcogenides are isostructural, crystallizing in a unique structure type comprising localized Cu clusters and Te(2)(2-) dumbbells. With less than six Cu atoms per formula unit, these materials are p-type narrow-gap semiconductors, according to the balanced formula Ba(2+)(Cu(+))6Q(2-)(Te(2)(2-))3 with Q = S, Se. Encouraged by the outstanding thermoelectric performance of Cu(2-x)Se and the low thermal conductivity of cold-pressed BaCu(5.7)Se(0.6)Te(6.4), we determined the thermoelectric properties of hot-pressed pellets of BaCu(5.9)STe(6) and BaCu(5.9)SeTe(6). Both materials exhibit a high Seebeck coefficient and a low electrical conductivity, combined with very low thermal conductivity below 1 W m(-1) K(-1). Compared to the sulfide-telluride, the selenide-telluride exhibits higher electrical and thermal conductivity and comparable Seebeck coefficient, resulting in superior figure-of-merit values zT, exceeding 0.8 at relatively low temperatures, namely, around 600 K.

HfMoSb4, the first nonmetallic early transition metal antimonide

HfMoSb4, isostructural with the isoelectronic NbSb2, exhibits nonmetallic properties, as predicted via electronic structure calculations made before the actual discovery of HfMoSb4.

Distorted Sb chains in the interlayer region of the antimonide-selenide MoSb2Se

MoSb2Se can be prepared by annealing the elements in the stoichiometric ratio in a sealed silica tube between 600 °C and 750 °C. MoSb2Se forms its own structure type, comprising MoSbSe layers that are topologically equivalent to the layers of β-MoTe2. The MoSbSe layers are interconnected to a truly three-dimensional structure by additional interlayer Sb atoms, which are covalently bonded to the Sb atoms of the surrounding MoSbSe layers. Large pseudo-octahedral voids remain between the interlayer Sb atom chains. A superstructure is formed creating alternating short and long Sb–Sb bonds along the b axis, as confirmed via electronic structure calculations. Large voids remain present between the interlayer Sb chains. MoSb2Se is metallic with small negative Seebeck coefficients.