Место издания:Littoral-Cote d’Opale University Calais, France
Номер статьи:OP-VC08
Аннотация:Lead-free perovskite oxides based on ferroelectrics (K0.5Na0.5)NbO3 (KNN), BaTiO3 (BT), and ferroelectric-relaxor (Na0.5Bi0.5)TiO3 (NBT) are being intensively studied in order to replace widely used toxic Pb-based ones. These oxides are promising for applications in capacitors, piezoelectrics, electrocaloric and other devices. We studied influence of donor and acceptor dopants on structure, microstructure, and dielectric properties of compositions from Morphotropic Phase Boundary (MPB) in the KNN-BT and NBT-BT systems additionally modified with overstoichiometric additives KCl, NaCl, LiF, ZnO и CuO. Ceramic samples were prepared by the two-step solid-state reaction method and were characterized using complex of physico-chemical methods: X-ray Diffraction, Scanning Electron Microscopy, Second Harmonic Generation, and Dielectric Spectroscopy. Unit cell parameters changes were observed in modified compositions depending on radii of substituting cations. Ferroelectric phase transitions at 400 – 700 K were observed. Phase transitions near ~ 400 K in NBT-based compositions revealed typical relaxor behavior related to the presence of polar nanoregions in a nonpolar matrix. Additionally, effects of dielectric relaxation caused by formation of oxygen vacancies due to possible defficiency in the A-sites and/or by the presence of cations with mixed valency in the B-sites of perovskite lattice were observed at temperatures > 700 K. The compositions characterized by increased values of dielectric permittivity at the room temperature and spontaneous polarization were revealed confirming prospect of their functional properties improvement.
