Effects of One-Dimensional Pressure on the Properties of Several Transducer Ceramics

The effects of one-dimensional pressure parallel to the polar axis of piezoelectric ceramics have been investigated for a cobalt-modified barium titanate, NRE-4, two strontium-modified lead zirconate titanates, AM-97 and PZT-4, and a niobium-modified lead zirconate titanate, PZT-5. Pressures up to 10 000 psi had little permanent effect on the polarization and coupling factors of AM-97 and PZT-4 but permanently reduced those of NRE-4 and PZT-5. The low-field permittivity decreased initially and then increased with increasing pressure for all materials. At fields up to 3 kV/cm on AM-97 and PZT-4, the permittivity and dielectric loss increased severely with pressures to 10 000 psi; the field dependence decreased to approximately constant values independent of the magnitude of the pressure after several hundred hours. Similar measurements on NRE-4 showed that the changes with pressure and time were not so severe. Changes in the high-field permittivity and loss due to hydrostatic pressure superimposed on a one-dimensional bias pressure were small, provided that the bias pressures were applied to the ceramics at least one week before the hydrostatic pressure. Changes resulting from one-dimensional pressure are explained in relation to domain processes. Implications for underwater-transducer design are discussed.