Phase transition in sol-gel-derived Na-modified PLZT ceramics

Complex compounds of Na-modified PLZT, Pb-0.92(La1-zNaz)(0.08)(Zr0.60Ti0.40 )((0.98+0.04z))O-3 (z = 0 0. 0.1, 0.3, 0.5 and 0.7 mol%) (PLNZT) were synth esized by the sol-gel technique. Preliminary structural analysis of the mat erials from room-temperature XRD data shows that the materials are of tetra gonal structure. Detailed dielectric studies of these materials as a functi on of temperature (30-350 degrees C) at 10 kHz reveal broad maxima at their respective transition temperatures (T-c). The degree of disorder or diffus ivity (gamma) lies between 1 and 2 for all the compounds studied, indicatin g that there is disorder in the system. The remanent polarization (P-r) and coercive field (E-c) determined from the P-E hysteresis loops of the compo unds were found to be quadratic and linear functions of temperature respect ively, suggesting that a second-order phase transition occurs in them. Meas urements of pyroelectric and piezoelectric coefficients provided some usefu l device parameters.