THE IMPACT OF ATOMS HETEROVALENT SUBSTITUTION ON THE STRUCTURE OF An+1BnO3n+1 TYPE COMPOUNDS

Abstract

The regularities of impact heterovalent substitutions of atoms A- and B-positions on the slab perovskite-like structure of A_n+1B_nO_3n+1 type compounds were determined based on the analysis of structure Sr_2-xLn_xB^IV_1-xB^III_xO₄ and Sr_3-xLn_xB^IV_2-xB^III_xO₇ (Ln = La, Pr, Nd, Sm, B^III = In, Sc, B^IV = Ti, Sn) types ompounds and phases. It was established that the inclusion of REE and indium atoms in the single- and double-slab structures of compounds Sr_n+1B^IV_nO_3n+1 leads to increase the degree of  interblockpolyhedra AO₉ and octahedra BO₆ deformation and a decrease the distance between adjacent perovskite-like blocks. Increase the degree of deformation of AO₉interblockpolyhedra leads to increase in the tension in the interblock slab of Sr_2-xLn_xB^IV_1-xIn_xO₄ and Sr_3-xLn_xB^IV_2-xIn_xO₇ slab perovskite-like structure and the reduction of the distance between the two-dimensional perovskite-like blocks brings the structure of their two-dimensional slab perovskite-like structure closer to the structure of thermodynamically much more stable three-dimensional structures. The simultaneous combined action of these factors gradually destabilizes the slab perovskite-like structure and limits the region of its existence in the Sr_2-xLn_xB^IV_1-xIn_xO₄ and Sr_3-xLn_xB^IV_2-xIn_xO₇ series (in particular, it explains the absence of SrNdInO₄ and SrLn₂In₂O₇ (Ln = La – Sm) with slab perovskite-like structure). The significant influence of heterovalent substitution of atoms in slab perovskite-like structure of A_n+1B_nO_3n+1 type compounds on the structure of newly formed phases provides grounds for using this type of substitution for further targeted regulation of structure-sensitive properties of materials based on A_n+1B_nO_3n+1 type compounds with slab perovskite-like structure.