Tetragonal-to-tetragonal phase transition in lead-free (K_xNa_1-x)NbO₃ (x = 0.11 and 0.17) crystals

Lead free piezoelectric crystals of (K_xNa_1-x)NbO₃ (x = 0.11 and 0.17) have been grown by the modified Bridgman method. The structure and chemical composition of the obtained crystals were determined by X-ray diffraction (XRD) and electron probe microanalysis (EPMA). The domain structure evolution with increasing temperature for (K_xNa_1-x)NbO₃ (x = 0.11 and 0.17) crystals was observed using polarized light microscopy (PLM), where distinguished changes of the domain structures were found to occur at 400 °C and 412 °C respectively, corresponding to the tetragonal to tetragonal phase transition temperatures. Dielectric measurements performed on (K_0.11Na_0.89)NbO₃ crystals exhibited tetragonal to tetragonal and tetragonal to cubic phase transitions temperatures at 405 °C and 496 °C, respectively.