Phase transition behavior of (K,Na)NbO3-based high-performance lead-free piezoelectric ceramic composite with different phase compositions depending on Na fraction

The structures of the main (K1-xNax)NbO3 perovskite in a high-performance lead-free piezoelectric ceramic composite (K1-xNax)(0.86)Ca0.04Li0.02-Nb0.85O3-delta-K0.85Ti0.85Nb1.15O5-BaZrO3-MgO-Fe2O3 (x = 0.52 and 0.70) with trace amounts of LiMgFeTiO4 inverse spinel and (Li, K)(2)(Mg, Fe, Ti, Nb)(6)O-13 layered structure have been investigated by transmission electron microscopy (TEM) and synchrotron powder X-ray diffractometry (XRD) with varying temperatures. The bright-field TEM images have shown tetragonal 90 degrees-domain contrasts at 80 and 40 degrees C, and the XRD profile has been simulated by adding an average structure of two differently oriented tetragonal structures bound by a 90 degrees-domain wall for the x = 0.52 sample. Aggregates of tilted NbO6 nanodomains have been observed in a high-resolution TEM image, and the crossover of P4mm-Amm2 features from 60 to 20 degrees C and diffuse 2 x 2 x 2 superlattice reflections of the tilted NbO6 Imm2 structure have been observed in XRD data for the x = 0.70 sample. (C) 2018 The Japan Society of Applied Physics