Synthesis, crystal structure and physical properties of the solid solutions Ca14-xRExCdSb11 (RE=La-Nd, Sm, Gd-Yb, x≈0.85±0.15)

This article deals with the new antimonides represented with the general formula Ca14-xRExCdSb11 (RE=La-Nd, Sm, Gd-Yb, x approximate to 0.85 +/- 0.15). The 12 studied compounds constitute a nearly complete series of rare-earth metal substituted variants of the ternary Ca14CdSb11 phase. All have been synthesized from the respective elements, employing high-temperature reactions under molten flux conditions. The structures have been fully characterized by single-crystal X-ray diffraction methods. All materials crystallize in the tetragonal Ca14AlSb11 structure type (space group I4(1)/acd, No. 142, Z=8). Rare-earth element atoms randomly substitute Ca atoms on the four available crystallographic sites, with a noted preference for the Ca2 site in case of the light (La-Nd) rare-earth elements and the Ca1 site in case of the heavier (Sm, Gd-Yb) ones. The electronic structure calculations and resistivity measurements indicate title compounds as degenerated semiconductors. Magnetization measurements at varied temperature show Curie-Weiss paramagnetic behavior consistent with local-moment magnetism due to the 3+ ground state for the rare-earth metal ions. In the case of the Yb-containing sample, a mixed-valence Yb2+/3+ state is apparent. The measured charge transport properties suggest small bandgap degenerate semiconductor-like behavior and suitability for thermoelectrics.