Temperature dependence of piezoelectric properties of Ca-substituted PbTiO3 ceramics and composites

A study is presented on the thermal behaviour of the thickness, Kt, and planar, Kp, electromechanical coupling factors of Ca-substituted PbTiO3 ceramics with Ca/Pb ratios of 24/76 and 35/65 and their composites. Glass was used as a matrix material so as to obtain composites able to work at higher temperatures than those with an organic matrix. In ceramics it is shown that the thermal behaviour of the electromechanical anisotropy (Kt/Kp) depends strongly on microtexture, due mainly to variations of Kp whereas Kt varies slightly. In PTC24/76 the planar electromechanical coupling coefficient vanishes between 100° and 200°C, for less dense ceramic; for higher densities Kp has values of 2 - 6 % in the same interval. In PTC35/65 composites Kp is very low, sometimes unmeasurable, and Kt/Kp is further enhanced. Permittivity is significantly lower than in the ceramic and there is also a moderate reduction in density. These properties make glass matrix composites potencially attractive in ultrasonic transducer applications.