In piezoelectric ceramic lead zirconate titanate (PZT) dielectric loss and mechanical loss are coupled. So, in PZT ceramics used as power transducers, the high mechanical lossresults in an increasing of the temperature which contributes to reducing the intensity of polarization. Moreover, Young's modulus is very sensitive to phase transitions and polarization level.
In the present report, the Young's modulus E(T) and the mechanical loss Q-1(T) are measured in order to study phase transitions and temperature-induced depolarization. The temperature range is 100 K to 700 K. Two classes of doped PZT ceramics are tested: the Navy 1 and the Navy 3. These two classes are used mainly for power transducer applications.
Two phase transitions are easily observed by two anomalies on the E(T) curves: rhombohedral to tetragonal (TR-T), and tetragonal to cubic (Tc). The tetragonal phase is located between 2S0 K and 590 K for the Navy 1 class, and located between 180 K and 520 K for the Navy 3 class. The phase transition TR-T induces a smooth decrease of mechanical loss, but a very high mechanical loss peak corresponds to the phase transition Tc.
Moreover, the E(T) and Q-1(T) curves allow the study of the influences of thermal cycles on the polarization of the material: before annealing of poled specimens, the Young's modulus is higher, and the mechanical loss is lower than those in unpoled specimens. After annealing of poled specimens, the Young's modulus is reduced and mechanical loss is increased. However, the Young's modulus of annealed specimens remains still higher than in unpoled specimens through the temperature range of both ferroelectric and paraelectric phases.