Crystal Chemistry of RE₆Mg_xCd_23–xPb [0.6(1) ≤ x ≤ 3.2(1); RE = La and Ce]. New Mixed‐Metal Derivatives of the RE₆Cd₂₃T Phases (T = Group 14/15/16 Element)

Abstract

Synthesis and crystal structure determinations are reported for six quaternary phases with the general formula RE6MgxCd23–xPb [RE = La, Ce; 0.6(1) ≤ x ≤ 3.2(1)]. These compounds were prepared by high temperature reactions of the elements in sealed Nb tubes. As revealed by powder and single‐crystal X‐ray diffraction, their crystal structures are of the cubic Zr6Zn23Si system (cF120, Fm3m, Z = 4), itself an interstitially filled variant of the Th6Mn23 structure type. Rather than distributing equally across the entire Cd23 sub‐structure, Mg displayed a tendency to accumulate at specific sites (most notably 4a); charge differences between sites within the sub‐structure, as revealed by computational methods, are the likeliest explanation.