Single-crystal Pb[(Zn13/Nb23/)0.93Ti0.07]O3 (PZNT 93/7) for highly reliable ultrasonic transducers

Piezoelectric single crystals of Pb[(Zn₁3/Nb₂3/)_0.93Ti_0.07]O₃ (PZNT 93/7) 40 mm in diameter were grown with PbO flux by the solution Bridgman method. The prerequisites for the growth of PZNT 93/7 single crystals are higher melting temperature, a longer melting time than Pb[(Zn₁3/Nb₂3/)_0.91Ti_0.09]O₃ (PZNT 91/9), and the addition of ZnO. The pyrochlore pellets of PZNT 93/7 are more stable than those of PZNT 91/9. The Curie temperature is 155-175°C and the temperature corresponds to the rhombohedral-tetragonal phase change, T_rt, is higher than 100°C for PZNT 93/7 single crystals. T_rt corresponds to the degradation boundary temperature of the electromechanical coupling coefficient, k₃₃, and also of the dielectric constant. The sensitivity degradation of ultrasonic transducers using PZNT 93/7 single crystals can be avoided up to a high temperature of about 100°C. Although the piezoelectric properties of single crystals of PZNT 91/9 are excellent, it has become clear that the electromechanical coupling coefficient, k₃₃, and other properties degrade drastically above about 80°C. Therefore, our results indicate that PZNT 93/7 has good potential for application in the mass production of ultrasonic transducers.