Effects of microstructure on the dielectric properties of lanthana substituted PbTiO₃ and Pb (Zr, Ti) O₃-ceramics

The effect of grain size on unit-cell dimensions and dielectric properties has been studied in ceramic lanthana-substituted leadtitanate and leadtitanate-zirconate mixed crystals of the general composition Pb_1−αxLa_xZr_yTi_1−yO_{3+x(1.5−α)}. The influence of grain size has been investigated in the range from 0.6μm–10μm and can be distinguished from other microstructural influences by its effect on dielectric properties. A decrease of the grain size leads to a decrease of the maximum of the dielectric constant ε′ at the “Curie” temperature T_c′, while the value of T_c′ shifts to a lower temperature and the ε′-T curve (phase transition) becomes broadened. The results can be discussed in terms of a distribution of internal compression stresses spreading around an average value which increases with decreasing grain size.