Acoustic emission in ferroelectric lead titanate ceramics: origin and recombination of microcracks

Abstract

Lead titanate doped with niobium forms solid solutions of the type Pb_1-x/2(Ti_1-xNb_x)O₃ where x = 0.02 and 0.05. The ferroelectric Curie temperature of these solid solutions is around 465° C, compared to 490° C for PbTiO₃ at the cubic-tetragonal phase change. The lattice distortions at and below the Curie temperature generate internal stresses, leading to microcraking. The microcracking in lead titanate ceramics is detected by acoustic emission methods as a function of heating to and cooling from various temperatures upto 800° C. From this study it is concluded that microcracking is primarily triggered by the sudden lattice parameter changes at the Curie temperature on cooling and that it is enhanced by the anisotropic thermal expansion below the transition. The healing of microcracks is a gradual process and escapes direct detection by the acoustic emission methods. An indication of the recombination of microcracks on heating has been obtained by the total number of acoustic emission counts in samples cooled from various temperatures and also from fixed temperatures after different periods.