Material properties of piezoceramics at elevated temperatures

The material properties of different piezoelectric ceramics were studied at elevated temperatures using the resonance method. Specifically the behavior of the longitudinal and transverse charge coefficients, dielectric constant, compliance coefficient and coupling coefficient were investigated. The modes studied were the length expander modes with the field both parallel and perpendicular to the strain and the materials under investigation were PZT (Navy II), Lead Metaniobate and Bismuth Titanate. All the samples studied were from the same manufacturing batch. The measured values of the charge coefficient at room temperature were compared with those obtained through direct methods (d33 meter and laser interferometer) and were found to compare well. Each material is affected differently by temperature changes, though all show a general increase in the charge coefficient with an increase in temperature. The increase in values of the charge coefficient is seen to be mainly due to the increase in the dielectric constant with very little influence from the mechanical coupling and compliance, except close to the Curie temperature where the coupling coefficient goes to zero. Bismuth Titanate has the widest temperature range however, based on a temperature scale normalized by the Curie Temperature PZT Navy II and Lead Metaniobate show the more stable material properties.