Single-crystal Pb[(Zn/sub 1/3/Nb/sub 2/3/)/sub 0.93/Ti/sub 0.07/]O/sub 3/ (PZNT 93/7) for highly reliable ultrasonic transducers

Abstract

Piezoelectric single crystals of Pb[(Zn/sub 1/3/Nb/sub 2/3/)/sub 0.93/Ti/sub 0.07/]O/sub 3/ (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[(Zn/sub 1/3/Nb/sub 2/3/)/sub 0.91/Ti/sub 0.09/]O/sub 3/ (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/spl deg/C and the temperature corresponds to the rhombohedral-tetragonal phase change, T/sub rt/, is higher than 100/spl deg/C for PZNT 93/7 single crystals. T/sub rt/ corresponds to the degradation boundary temperature of the electromechanical coupling coefficient, k/sub 33/, 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/spl deg/C. Although the piezoelectric properties of single crystals of PZNT 91/9 are excellent, it has become clear that the electromechanical coupling coefficient, k/sub 33/, and other properties degrade drastically above about 80/spl deg/C. Therefore, our results indicate that PZNT 93/7 has good potential for application in the mass production of ultrasonic transducers.