From the Ternary Phase Ca 14 Zn 1+δ Sb 11 (δ ≈ 0.4) to the Quaternary Solid Solutions Ca14–xRExZnSb11 (RE = La–Nd, Sm, Gd, x ≈ 0.9). A Tale of Electron Doping via Rare-Earth Metal Substitutions and the Concomitant Structural Transformations

In this work, the ternary compound Ca14Zn1.37(1)Sb11 and its six rare-earth metal substituted derivatives Ca14–xRExZnSb11 (RE = La–Nd, Sm, Gd; x ≈ 0.90±0.06) have been synthesized and structurally characterized by single-crystal X-ray diffraction methods. All com-pounds formally crystallize in the tetragonal Ca14AlSb11 structure type (space group $I$41$/ acd$, No. 142, $Z$ = 8). The crystal structure of Ca14Zn1.37(1)Sb11 subtly differs from the structure of the remaining six, as well as from the structure of the archetype, due to the presence of a partially occupied interstitial Zn position. The extra zinc atom is needed in this structure to alleviate the unfavorable number of valence electrons in the imaginary Ca14ZnSb11. Electron doping, via substitution of RE3+ ions on Ca2+ sites is shown as an alternative route to achieve electron balance in these Zn-based analogs of the Ca14AlSb11 structure, which does not require the in-corporation of interstitial atoms. Electrical resistivity measurements done on single-crystalline samples are in agreement with the notion that Ca14–xRExZnSb11 behave as either bad metals or heavily-doped semi-conductors. Magnetization measurements show Curie-Weiss paramagnetic behavior related to the local-moment magnetism of the RE3+ ions.