ANISOTROPY IN PIEZOELECTRIC PROPERTIES OF MODIFIED LEAD TITANATE CERAMICS

Lead titanate ceramics modified with samarium and calcium exhibit large anisotropy in electromechanical coupling factors. The planar coupling factor in these materials shows a strong temperature dependence passing through a minimum near room temperature, whereas the thickness coupling factor remains practically constant. To explain this behavior, the material coefficients d//3//1, S//1//1**E, and epsilon //3//3**T characteristic for the planar coupling mode were investigated as a function of temperature ( minus 180 degree to 100 degree C) for samples poled at different electric fields (10 to 90 kv/cm). All material coefficients must be considered as complex quantities to describe the piezoelectric resonance in these ceramics.