Ce₄(P_1-<i>_x</i>Si<i>_x</i>)_3-<i>_z</i>: A First Example for the Stabilization of the Anti-Th₃P₄ Type Structure by Substitution in the Non-Metal Substructure

A first rare-earth phosphide silicide Ce4(P1-xSix)3-z and its analogues with La, Pr, and Nd were synthesized and characterized. The compounds crystallize in the anti-Th3P4 structure type. The cerium compound shows a mixed occupation of the 12a site with Si and P and possesses a wide homogeneity range with respect to x and z variation. The electronic configuration of Ce, deduced from magnetic susceptibility and X-ray absorption spectroscopy data, remains 4f 1 (Ce3+) independently from x and z. The cerium valence and the phase stability region are discussed employing electronic band-structure calculation and chemical bonding analysis with electron localization function. Atomic interactions are shown to remain nearly unchanged, while the change of the excess electron concentration with P/Si substitution is considered to play the main role for the stabilization of the structural motif.