EFFECT OF ISOVALENT SUBSTITUTION OF EUROPIUM WITH DYSPROSIUM ON THE SLAB STRUCTURE OF SrEu2−xDyxSc2O7 SCANDATES

Abstract

The dimensions of the phase region with a slab perovskite-like structure in the SrEu_2−xDy_xSc₂O₇ system were determined: 0 ≤ х ≤ 0.5 and the crystal structure of the SrEu_2−xDy_xSc₂O₇ phases with x = 0.25 and 0.5 was determined using a program based on Rietveld algorithms for multiphase samples. It was established that SrEu_2−xDy_xSc₂O₇ samples with x = 0.25 and 0.5 contain two polymorphic modifications with a slab perovskite-like structure: a modification with rhombic syngonia (sp. group Fmmm) and modification with tetragonal syngonia (sp. group I4/mmm). The basis of the slab structure of both modifications of SrEu_2−xDy_xSc₂O₇ are two-dimensional perovskite-like blocks with a thickness of two slabs of deformed ScO₆ octahedra, which connected by vertices. A slab of (Eu,Dy)O₉ polyhedra is located between the blocks and the blocks are connected to each other by bonds —O—(Eu,Dy)—O—. It was established that the increase in the content of dysprosium atoms in SrEu_2−xDy_xSc₂O₇ leads to an increase in the degree of deformation of LnO₉ interblock polyhedra and a decrease in the Ln—O₂ interblock distance. This transformation of the structure destabilizes the interblock space and is one of the main factors in the destruction of the slab perovskite-like structure of SrEu_2−xDy_xSc₂O₇ phases at x > 0.5 and leads to the impossibility of SrDy₂Sc₂O₇ scandate existence.