Cation Distribution and Interatomic Interactions in Oxides with Heterovalent Isomorphism: III. Complex Aluminates LnCaAlO_4 (Ln = Y, La, Nd, Gd, Ho, Er, Yb)

摘要

The heterovalent isomorphism of Ln~(3+) and Ca~(2+) cations in stoichiometric LnCaAlO_4 oxides was studied. The X-ray diffractometry of the intensity of Laue background modulations revealed a positive short-range ordering in Ln~(3+) and Ca~(2+) distribution over points of one structural site common for both ions, which results in formation of stable Ln~(3+)-Ca~(2+) couploes in adjccent nine-coordinate oxygen polyhedra. The degree of ordering and the interchange energy estimated in the quasichemical approximation depend both on the effective cationic charges and on the number of unpaired f electrons of the lanthanide atom.