Rare-Earth Metal Substitutions in Ca_9–<i>x</i><i>RE</i>_<i>x</i>Mn₄Sb₉ (<i>RE</i> = La–Nd, Sm; <i>x</i> ≈ 1). Synthesis and Characterization of a New Series of Narrow-Gap Semiconductors

This paper details the synthesis and the structural characterization of the new antimonides with general formulas Ca9–x­REx­Mn4Sb9 (RE = La, Ce, Pr, Nd, and Sm; x ≈ 1). The synthesis of these phases was accomplished by both high temperature reactions of the respective elements and by Pb-flux experiments. The structures were determined by single-crystal X-ray diffraction methods. All title compounds are isostructural and crystallize with the orthorhombic space group Pbam (No. 55). The structure is similar, but not isotypic to Ca9­Mn4Bi9 (same space group; Pearson code oP44). On the basis of that, Ca9–x­REx­Mn4Sb9 can be considered as new derivatives of this structure type, presenting the first examples of rare-earth metal substitutions within the “9-4-9” family of compounds. Electrical resistivity measurements confirm the successful electron doping, achieved by the aliovalent replacement of Ca2+ with RE3+ cations in the structure, leading to the emergence of narrow band-gap semiconducting behavior. Temperature-dependent magnetization measurements indicate paramagnetic behavior and complex magnetic interactions.