IMF2017

Lead-free ferroelectric materials on the base of (Na_0.5Bi_0.5)TiO₃ (NBT) and (K_0.5Na_0.5)NbO₃ (KNN) are being intensively studied in order to replace widely used Pb-based ones. In this work, effects of modification of compositions by donor and acceptor dopants in the A- and B-sites of perovskite lattice and over stoichiometric additives on structure, dielectric and ferroelectric properties of ceramics in the (K_0.5Na_0.5)NbO₃ (KNN), (Na_1/2Bi_1/2)TiO₃ - BaTiO₃ (NBT-BT) and (Na_1/2Bi_1/2)TiO₃ - BaTiO₃ - Bi(Mg_1/2Ti_1/2)O₃ (NBT-BT-BMT) systems have been studied. Ceramic samples were prepared by the two-step solid-state reaction method at temperatures of 970–1470 K. The samples were characterized using the X-ray Diffraction, Scanning Electron Microscopy, Second Harmonic Generation (SHG), and Dielectric Spectroscopy methods. Ferroelectric phase transitions were revealed at ~ 350 - 400 K and at ~ 550 K (NBT-based) and at ~700 K (KNN) in the dielectric permittivity versus temperature curves. Phase transitions near 350-400 K revealed typical relaxor-type behavior attributed to the presence of polar nanoregions in a nonpolar matrix. Increase in the spontaneous polarization value was observed in modified ceramics using the SHG method. At the room temperature, non monotonous changes of the dielectric parameters were observed in modified compositions studied. The results obtained confirmed prospects of new lead-free materials development by modification of KNN- and NBT-based compositions close to the MPB by aliovalent cation substitutions.