The low-frequency Young modulus and internal friction in Pb-Ca and Pb-Zr titanate ceramics

Measurements of the elastic moduli of Ca-modified lead titanate ceramics, as a function of temperature, have been made for frequencies in the range 0.2-20 Hz and for poling fields in the range 0-90 kV cm(-1), using the three-point bending method. The results indicate that there are extrinsic contributions to the elastic modulus due to microstructure and polarization processes in the samples, with the contribution of microstructure greater than that of the polarization state, We found a relaxational behaviour of the elastic modulus due to thermal fluctuations with large relaxation limes. Induced by order-parameter fluctuations in the phase transition and to the diffusive character of the ferro-paraelectric transitions that; take place in materials of these compositions, Comparisons with very low-frequency behaviour of PZT ceramics are made and the results are discussed on the basis of the existent theoretical models dealing with thermal fluctuations at the ferro-paraelectric phase transition.