The Microstructural Dependence of Piezoelectric Properties in PbTiO3 Ceramics

The grain size dependence of lattice constants (a and c), dielectric constant ([straight epsilon]/[straight epsilon]0), dissipation factor (tanδ), electromechanical coupling factors (κt and κp), and mechanical quality factor (QM) was investigated in ceramics with the compositions of 0.99[sm middot]Pb1-XLa2X/3TiO3+0.01[sm middot]MnO2 with X=0.05 (grain size=0.37-1.32μm) and X=0.10 (grain size=0.30-1.14μm). With decreasing grain size, c/a (lattice constant ratio), tanδ (of non-poled), κt/κp (anisotropy of coupling factor), and QM decreased, while [straight epsilon]/[straight epsilon]0 (of both non-poled and poled) increased. When poled, tanδ showed little grain size dependence. A close correlation was observed between the lattice constant ratio and the dielectric constant for all the materials, and the grain size dependence of these properties has been attributed mainly to the effect of internal stress in grains. The grain size dependence of tanδ may be interpreted on the basis of the effect of grain size on the motion of do-main boundaries. The values of QM-1 and tanδ did not agree with the relationship, QM-1∝tanδ, usually observed in ferroelectric materials. This is possibly explained in terms of the ceramic structure-dependent component of inner friction (QM-1), which becomes significant with decreasing grain size.