High-temperature X-ray diffraction and Raman scattering studies of Ba-doped (Na0.5Bi0.5)TiO3 Pb-free piezoceramics

The structural changes in (100 - x)Na0.5Bi0.5TiO3-xBaTiO(3) (0 <= x <= 10) ceramics were investigated as a function of composition and temperature by X-ray diffraction and Raman spectroscopy. As Ba concentration increases, the structure changed from rhombohedral to tetragonal (x > 6.5) across a morphotropic phase boundary like phase coexistence at x similar to 5.5, which is further evidenced by phonon anomalies observed in composition-dependent Raman spectra. On heating, the disappearance of peak splits in {111} (x <= 5) and {200} (x >= 6.5) Bragg peaks and the changes in their 2 theta-positions indicated temperature-driven structural changes: ferroelectric to antiferroelectric (approximate to T-d, depolarization temperature) at 220 degrees C and antiferroelectric to paraelectric (rhombohedral to tetragonal) at 320 degrees C. In addition, Raman spectral analysis suggested that at elevated temperatures, two tetragonal phases with slightly different space groups coexisted at x >= 6.5 and most of the phase transition temperatures shifted towards left with increasing x. (C) 2013 Elsevier B. V. All rights reserved.