Mechanical and Electromechanical Properties of PMN-PT Single Crystals for Naval Sonar Transducers

Single crystals in the relaxor-ferroelectric lead magnesium niobate (PMN)-lead titanate (PT) system provide significant advantage for underwater sonar transducers. Compared to lead zirconate titanate ceramics, the large electromechanical coupling factor provides significant increases in transducer bandwidth. The superior strain energy density generates higher source level across the band, and the lower Young´s modulus allows considerably smaller transducers. These payoffs occur even when PMN-PT crystals are subject to navy relevant conditions such as uniaxial mechanical compressive stresses up to 42 MPa, electric fields up to 1.2 MV/m, and a range of temperatures from 5 to 50degC. This research will provide insight into the impact of navy relevant electric fields and mechanical stress conditions on the cracking and failure of the piezocrystals. The compressive, flexural, and tensile strength of PMN-PT crystal will be reported and discussed with respect to mechanical stress conditions in a typical naval transducer. The dielectric constant, piezoelectric coefficient, Young´s modulus, electromechanical coupling factor and energy density under large signal quasi-static conditions will be discussed from the perspective of the implications for sonar projector design and performance.