Characterization of lead-free ceramics on the base of sodium-bismuth titanate and sodium-potassium niobate via PFM local probes
E.D. Politova1, G.M. Kaleva1, N.V. Golubko1, A.V. Mosunov1, N.V. Sadovskaya1, D.A. Kiselev2, A.M. Kislyuk2, S. Yu. Stefanovich1,3, P.K. Panda4
1L.Ya.Karpov Institute of Physical Chemistry, Vorontsovo pole str. 10, Moscow 105064 Russia,
2National University of Science and Technology “MISiS”, Leninskii pr. 4, Moscow 119991 Russia,
3Lomonosov Moscow State University, Leninskie gory 1, Moscow 119992 Russia,
4National Aerospace Laboratories, Kodihalli, Bangalore-560017 India
Lead-free piezoelectric oxide materials are being intensively studied in order to replace widely used Pb-based ones during last ten years. We studied influence of cation substitutions on stoichiometry, structure parameters, dielectric, ferroelectric, and piezoelectric properties of ceramics based on (Na0..5Bi0.5)TiO3 (NBT) and (K0.5Na0.5)NbO3 (KNN) perovskites.
The samples were characterized using the X-ray Diffraction, Scanning Electron Microscopy (SEM), Second Harmonic Generation (SHG), Dielectric Spectroscopy, and Atomic Force Microscopy in Piezorespone Force Microscopy mode (PFM) methods.
Ceramic samples in systems (Na0.5Bi0.5)TiO3 - BaTiO3 (NBT-BT) and (K0.5Na0.5)NbO3 – BaTiO3 (KNN-BT) with compositions close to Morphotropic Phase Boundaries (MPB) were prepared by the two-step solid-state reaction method at temperatures of 900 – 1500 K. The samples were additionally modified by small amounts of Li2O, MnO2, Ni2O3, and Fe2O3 (1-5 mol.%) oxides.
Changes in the unit cell volume of the KNN- and NBT-based ceramics observed correlate with cation substitutions. Ferroelectric phase transitions near ~ 400 K and ~ 550 K (NBT) and at ~700 K (KNN) were revealed in the dielectric permittivity versus temperature curves of ceramics studied. Ferroelectric phase transitions near ~ 400 K (NBT) revealed typical relaxor-type behavior confirming presence of polar nanoregions in a nonpolar matrix.
Remnant hysteresis loops were received for separate grains in the samples using switching spectroscopy PFM method. In PFM nucleation of a single domain occurs under a sharp tip, and the PFM signal follows the development of domains at a single location. Local PFM hysteresis loops for the samples studied were observed indicating ferroelectric polarization switching at nanoscale. Increase in the spontaneous polarization value was proved for modified ceramics using the SHG method.
Finally, non monotonous changes of the dielectric parameters εrt, tanδrt and maximum effective local d33 values were observed in modified BNT- and KNN-based compositions, thus confirming their prospects for new lead-free materials development.
The work was supported by the Russian Foundation for Basic Research (Project 16-53-48009).