Influence of the modification methods on the crystal structure and macroresponses of the multicomponent ferroelectric media based on sodium-potassium niobates

The superstoichiometrical and stoichiometrical modification of the solid solutions (SS) of the multi- element system 0.98(Na$_{0.54}$K$_{0.46}$)(Nb$_{0.9}$Ta$_{0.1}$)O$_3$–0.02LiSbO$_3$ by plain (MnO$_2$, CuO) and combined (MnO$_2$+NiO, Bi$_2$O$_3$+Fe$_2$O$_3$) oxides was studied. The samples were obtained by two-stage solid-phase synthesis followed by sintering using conventional ceramic technology. Based on the analysis of X-ray studies, it was established that the initial solid solution has an orthorhombic symmetry with a monoclinic perovskite cell R(M). The modification of it, both stoichiometrical and superstoichiometrical, with the specified modifiers, leads to the appearance of a second, tetragonal phase inside the orthorhombic R(M) phase, i. e., transfers the solid solution to the morphotropic phase transition region. With both modification schemes, the density of the modified ceramics increases compared to the density of the original solid solution; at the same time in the superstoichiometrically modified solid solutions, the stability of the structure to small fluctuations in composition was revealed. The compositions with superstoichiometrical modification by MnO$_2$ and Bi$_2$O$_3$+Fe$_2$O$_3$ oxides have high-quality piezoelectric parameters and can be recommended for applications in microwave technology.