Phase transition behavior of (K,Na)NbO 3 -based high-performance lead-free piezoelectric ceramic composite with different phase compositions depending on Na fraction

The structures of the main (K 1− x Na x )NbO 3 perovskite in a high-performance lead-free piezoelectric ceramic composite (K 1− x Na x ) 0.86 Ca 0.04 Li 0.02 Nb 0.85 O 3−δ –K 0.85 Ti 0.85 Nb 1.15 O 5 –BaZrO 3 –MgO–Fe 2 O 3 ( x = 0.52 and 0.70) with trace amounts of LiMgFeTiO 4 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°-domain contrasts at 80 and 40 °C, and the XRD profile has been simulated by adding an average structure of two differently oriented tetragonal structures bound by a 90°-domain wall for the x = 0.52 sample. Aggregates of tilted NbO 6 nanodomains have been observed in a high-resolution TEM image, and the crossover of P 4 mm – Amm 2 features from 60 to 20 °C and diffuse 2 × 2 × 2 superlattice reflections of the tilted NbO 6 Imm 2 structure have been observed in XRD data for the x = 0.70 sample.