ИСТИНА

Abstract Lead-free oxide materials are being intensively studied in order to replace widely used Pb-based ones because of environmental problems caused by toxic lead. Among the most promising, oxides with perovskite structure based of ferroelectrics BaTiO3 (BT), (K0.5Na0.5)NbO3 (KNN) and ferroelectric-relaxor (Na0.5Bi0.5)TiO3 (NBT) are being considered. We studied effects of donor and acceptor dopants on structure, microstructure, and functional properties of compositions from Morphotropic Phase Boundary in the KNN-BT and NBT-BT systems. Ceramic samples were prepared by the two-step solid-state reaction method and characterized using the X-ray Diffraction, Scanning Electron Microscopy, Second Harmonic Generation, Dielectric Spectroscopy, and Piezorespone Force Microscopy methods. Changes in the unit cell volume were observed in the modified compositions correlating with radii of substituting cations. Ferroelectric phase transitions at temperatures 400 - 700 K were revealed in the KNN-BT and NBT-BT systems. Phase transitions near ~ 400 K in NBT-based compositions reveal typical relaxor behavior related to the presence of polar nanoregions in a nonpolar matrix. At temperatures > 700 K effects of dielectric relaxation caused by formation of oxygen vacancies due to deficiency in the A-sites and/or presence of cations with mixed valency in the B-sites of perovskite lattice were observed. Local PFM hysteresis loops observed for KNN- and NBT-based samples indicated to ferroelectric polarization switching at nanoscale. In the KNN-BT samples effective d33 piezoelectric coefficient values reached 300 pm/V. The results obtained confirmed prospects of new lead-free materials development by modification of the KNN- and NBT-based compositions. The work was supported by RFBR (Projects 16-53-48009, 17-03-00542, 18-03-00372). ( https://www.scientificfederation.com/condensed-matter-physics-2018/scientific-program.php#event-schedule-accordion-content-day-01-s120 )