Effects of surface layers on the physical properties of lanthanum doped lead zirconate titanate ceramic

Dielectric measurements in the temperature range of -20°C to 160°C have been performed on lanthanum doped lead zirconate titanate ceramic samples with rough ground, polished and chemically etched surfaces. It is found that the dielectric constants, dielectric loss, polarization and pyroelectric coefficient are the smallest in the ground samples and the largest in the etched samples. The difference is very pronounced near the permittivity maximum temperature Tmax. The measured dielectric constant was found to depend on sample thickness in the ground and polished samples but not in samples with etched surfaces. The results are explained in terms of a simple surface layer model. A nonferroelectric layer is produced during lapping, which has a dielectric constant of the order of 100 and the capacitance of this layer in the investigated temperature range is 0.2-0.7 u,F/cm2. Through post-annealing, the contributions from the nonferroelectric nature of this surface layer and from the two dimensional tensile stress generated by lapping were also separated and quantified.