Calcium Substitution in Rare-earth Metal Germanides with the Gd5Si4 Type Structure

Abstract

An extended series of rare-earth metal calcium germanides have been synthesized and structurally characterized. The compounds have the general formula RE5−xCaxGe4 (1.5<x<3.6; RE=rare-earth metal; Ce, Nd, Sm, Tb−Lu) and their structures have been established from single-crystal X-ray diffraction methods. They crystallize with the Gd5Si4-type in the orthorhombic space group Pnma (No. 62; Z=4; Pearson symbol oP36), where the germanium atoms are interconnected into two kinds of Ge2-dimers, formally [Ge2]6−. These studies show that Ca can be successfully incorporated into the host RE5Ge4 structure, whereby trivalent rare-earth metal atoms can be substituted by divalent calcium atoms. Rare-earth metal and calcium atoms are arranged in distorted trigonal prisms and cubes, centered by either Ge or Ca atoms. On one of the metal sites, the substitution is preferential and in 9 out of the 10 refined structures, the Wyckoff site 4c is found almost exclusively occupied by Ca. On the other two metal sites the substitution patterns appear to be governed by the mismatch between the size of the RE3+ and Ca2+ ions. This work further demonstrates the ability for the Gd5Si4 structure type to accommodate the substitution of a non-magnetic element while maintaining the global structural integrity.