Cation distribution and interatomic interactions in oxides with heterovalent isomorphism: III. Complex aluminates LnCaAlO(4) (Ln = Y, La, Nd, Gd, Ho,Er, Yb)

The heterovalent isomorphism of Ln(3+) and Ca2+ cations in stoichiometric L nCaAlO(4) oxides was studied. The X-ray diffractometry of the intensity of Lane background modulations revealed a positive short-range ordering in Ln( 3+) and Ca2+ distribution over points of one structural site common for bot h ions, which results in formation of stable Ln(3+)-Ca2+ couples in adjacen t nine-coordinate oxygen polyhedra. The degree of ordering and the intercha nge 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.