On the possibility of isomorphic substitutions in ferroelectrics with the perovskite -and pseudoilmenite - type structure

The present paper deals with a crystallochemical analysis of the possibilities of isomorphic substitution of atoms in the ferroelectrics (Na, Li) NbO3 and LiNbO3 with a perovskite- and pseudoilmenite-type structure, respectively. As the arguments we used dimension, electronegativity, electron structure and symmetry of valent orbitals of the substituted and substituting atoms. The solid solutions (SS) of binary systems on the basis of LiNbO3 (or NaNbO3) and iso- and nonisostructural components and also the compositions of (Na, Li) NbO3 and lithium metaniobate (LMN) modified with n-valent (n = 1 - 6) elements were chosen as the objects of the present study. Diagrams of solubilities for substitutions in the A- or B- sublattice of (Na, Li)NbO3 and LiNbO3 were constructed. The original experimental results and the bibliographical data confirming the correctness of the analysis a presented.