Site Preference of Metal Atoms in Gd5–xMxTt4 (M = Zr, Hf; Tt = Si, Ge)

Abstract Zirconium and hafnium were incorporated into the Gd 5 Ge 4 and Gd 5 Si 4 parent compounds in order to study the metal‐site occupation in the M 5 X 4 magnetocaloric phases ( M = metals; X = p elements) family. The Gd 5– x Zr x Ge 4 phases adopt the orthorhombic Sm 5 Ge 4 ‐type (space group Pnma ) structure for x ≤ 1.49 and the tetragonal Zr 5 Si 4 ‐type ( P 4 1 2 1 2) structure for x ≥ 1.77. The Gd 5 –x Hf x Si 4 compounds crystallize in the orthorhombic Gd 5 Si 4 ‐type ( Pnma ) structure for x ≤ 0.41 and the Zr 5 Si 4 ‐type structure for x ≥ 0.7. In both systems, single‐crystal X‐ray diffraction reveals that the Zr/Hf atoms preferentially occupy the slab‐surface M 2 and slab‐center M 3 sites, both of which have a significantly larger Zr/Hf population than the slab‐surface M 1 site. The metal‐site preference, i.e. the coloring problem on the three metal sites, is discussed considering geometric and electronic effects of the local coordination environments. The analysis of the metal‐site occupation in Gd 5– x Zr x Ge 4 and Gd 5 –x Hf x Si 4 as well as other metal‐substituted M 5 X 4 systems suggests that both geometric and electronic effects can be used to explain the metal‐site occupation.