Constitution peculiarities of the five-layer structure of isomophically substituted phases of CaLn4−xLnIxTi5O17 type

Abstract

The crystal layer of CaPr₃GdTi₅O₁₇ perovskite-like structure (LPS) is determined by X-ray powder diffraction (sp. gr. P2₁/b, a = 0.7671(3) nm, b = 3.145(1) nm, c = 0.5444(2) nm, γ = 96.99(2)º, R_B = 0.086). The basic details of the crystallochemical mechanism of isomorphic replacement of REE atoms in LPS CaLn₄Ti₅O₁₇ are established. The character of the localization of Ca, Ln, and Ln^I atoms in LPS CaLn_4−xLn^I_xTi₅O₁₇ does not depend on the symmetry of a crystal lattice. As for Ca and REE atoms, the partial ordering with primary localization of Ca atoms at the center and in the intermediate layers of perovskite-like blocks is typical. REE atoms are on the boundaries of blocks, and Ln^I atoms are orderly located only on the boundaries of blocks.