Mercouri G. Kanatzidis

The ternary and quaternary selenides, β-CsBi₃Se₅, Rb₂CdBi₆Se₁₁, CsAg_0.5Bi_3.5Se₆, CsCdBi₃Se₆, Rb₂Ag_1.5Bi_7.5Se₁₃, and Cs₂Ag_1.5Bi_7.5Se₁₃, are all members of the new homologous series A₂[M_5+nSe_9+n] and crystallize in structures related to each other in a systematic way; these compounds are mid gap semiconductors and are of interest as thermoelectric materials.

The Zintl phase, Yb₈Ge₃Sb₅ exhibits a complex lattice response and an abrupt negative thermal expansion below 15 K – subtle structural changes before and after the transition are consistent with temperature-induced electron transfer from (to) Yb 4f bands to (from) Sb 5p and Ge 4p bands.

Sb₄Te₃ and Sb₈Te₉ are members of the homology (Sb₂Te₃)_m·(Sb₂)_n, with structures consisting of Sb₂- and Sb₂Te₃-type slabs stacked along [001]; electrical conductivity and thermopower are reported for several members of this family.

Derivatives of β-K₂Bi₈Se₁₃ are an interesting series of materials for thermoelectric investigations due to their very low thermal conductivity and highly anisotropic electrical properties. Up to now substitutions on the Bi and alkali metal sites have been studied in order to tune the thermoelectric properties. In this work, the thermoelectric properties of the sulfur-substituted K₂Bi₈Se_13−xS_x (0<x<13) are presented with respect to Seebeck coefficient, the electrical and thermal conductivity as a function of temperature. Seebeck coefficient measurements showed the n-type character of all members while electrical conductivity shows higher values compare to the other solid solution series of the same type. The lattice thermal conductivity is affected due to the Se/S disorder. The temperature dependence of the figure-of-merit ZT shows that these materials have potential for high temperatures applications with promising thermoelectric performance.