Effects of High Static Stress on the Piezoelectric Properties of Transducer Materials

Piezoelectric ceramic elements in high-power acoustic transducers are subjected to high static as well as dynamic stress. This is particularly true of well-matched transducers operating in deep water, since the static stress in the piezoelectric element may be several times the water pressure. The present study was undertaken in an effort to determine the effects of static compressive stress on the piezoelectric properties of two commercial lead titanate zirconate compositions, PZT-4 and PZT-5, and of two barium-titanate compositions, commercial Ceramic B (a barium calcium titanate), and the composition 88 wt% barium titanate, 12 wt% lead titanate (BaPb12Ti). The permanent effects of stress exposure, determined at zero stress after exposure to a given stress, were found to be more severe with stress parallel to the polar axis than with perpendicular stress, as expected. Under maintained stress, however, the effects of perpendicular stress are more severe. PZT-4 and BaPb12Ti, generally better suited for use as radiating transducers, show effects dependent upon exposure time but independent of the number of stress cycles. Ceramic B and PZT-5 show effects dependent upon the number of stress cycles and less dependent upon the total period of stress exposure. Of the compositions tested, PZT-4 and BaPb12Ti were least affected by high static stress, suffering relatively little from exposure to stress as high as 15 000 psi. Of these two compositions. PZT-4 has markedly higher coupling (k33∼0.64 compared to 0.365) and therefore offers higher transducer bandwidth.