Thermoelectric properties of the new tellurides SrSc2Te4 and BaSc2Te4 in comparison to BaY2Te4

The two new ternary scandium tellurides SrSc2Te4 and BaSc2Te4 were prepared by heating the elements at temperatures between 800 °C and 900 °C under vacuum. Both compounds crystallize in the CaFe2O4 type, space group Pnma, Z = 4, with lattice dimensions of a = 13.1795(17) Å, b = 4.2323(7) Å, c = 15.367(2) Å, V = 857.2(2) Å3 for SrSc2Te4, and a = 13.292(2) Å, b = 4.2694(7) Å, c = 15.523(3) Å, V = 880.9(2) Å3 for BaSc2Te4. The structures comprise a three-dimensional network of edge- and corner-sharing ScTe6 octahedra. The Sr and Ba cations are located in linear channels, surrounded by eight Te atoms forming bicapped trigonal prisms. SrSc2Te4 and BaSc2Te4 are electron-precise materials exhibiting common oxidation states, Sr2+, Ba2+, Sc3+, and Te2−. We calculated the band gaps to be 0.1 eV for SrSc2Te4 and 0.2 eV for BaSc2Te4. At room temperature, both materials exhibit a high Seebeck coefficient and low electrical conductivity.