Synthesis, crystal structure and physical properties of the solid solutions Ca_14–x RE_xCdSb₁₁ (RE = La–Nd, Sm, Gd–Yb,x ≈ 0.85±0.15)

This article presents new antimonides represented with the general formula Ca_14–xRE_xCdSb₁₁ (RE=La–Nd, Sm, Gd–Yb, x ≈ 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 I4₁/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 Yb^2+/3+ state is apparent. Furthermore, the measured charge transport properties suggest small bandgap degenerate semiconductor-like behavior and suitability for thermoelectrics.