On the Extended Series of Quaternary Zintl Phases Ca13REMnSb11 (RE = La–Nd, Sm, Gd–Dy)

Abstract

Eight new compounds with a general formula Ca14–xRExMnSb11 (RE = La–Nd, Sm, Gd–Dy; x ≈ 1) were synthesized by the molten flux method and their structures were established via single‐crystal X‐ray diffraction. The overarching goal of this study was to investigate the effect of electron doping, via substitution of RE3+ at Ca2+ sites, on the crystal structure and physical properties of Ca14MnSb11, which is a candidate for thermoelectric applications. All studied phases are isostructural, and crystallize in the tetragonal body‐centered space group I41/acd (Ca14AlSb11 structure type, Pearson index tI208). The structure is made up of MnSb410– tetrahedra, randomly mixed Ca2+ and RE3+ cations, Sb3– anions, and linear Sb37– polyanions. Comprehensive structural work confirms high rare‐earth metal content with Ca2+/RE3+ randomly mixed on all four cation sites, with the caveat that the larger RE atoms (La–Nd) prefer to occupy the Ca2 site, while the smaller RE atoms (Sm, Gd, Tb, and Dy) preferably occupy the Ca1 site. Nearly phase‐pure polycrystalline samples have been synthesized using solid‐state reactions, and have been used for physical property measurements. The resistivities of the bulk Ca14–xRExMnSb11 (RE = La–Nd, Sm, Gd; x ≈ 1) samples reveal semiconducting behavior, consistent with the notion of electron doping in the parent p‐type Ca14MnSb11 material. Magnetic susceptibilities suggest complex magnetic ordering at temperatures below ca. 50 K, likely originating from coupling between two or more magnetic sub‐lattices.