Pb(Zn1/3Nb2/3)O3/PbTiO3 single-crystal piezoelectrics for ultrasonic transducers

The Pb(Zn_1/3Nb_2/3)O₃ (PZN)/PbTiO₃ (PT) solid solution has been grown in single crystal form. The dielectric and piezoelectric properties have been determined over a wide range of compositions. Longitudinal coupling constants in this system can be maintained at near 90% for a wide range of relative permittivities, allowing a 'designer dielectric' approach to ultrasonic transducer design. The piezoelectric transducer model developed by Kimholtz, Leedom and Matthaei (KLM) was employed to first optimize transducer design points, and then to study the behavior of these materials as operational transducers. Two types of transducers were modeled and contrasted to conventional materials, a 50 MHz single element designed for ultrasound backscatter microscopy and a 5 MHz phased array element. These two transducer designs are representative of the wide range of properties available in this system by carefully choosing a composition. Extremely high piezoelectric coupling coefficients (k₃₃ greater than 94%) and a range of dielectric constants (3000 - 5000) have been observed in these systems on the rhombohedral side of the morphotropic phase boundary (MPB). Relatively low dielectric constants (approximately 1000) and high thickness mode coupling (kt greater than 63%) were observed as typical of tetragonal formulations. A prototype single element transducer at 35 MHz was fabricated from PZN/8% PT and compared, in pulse/echo mode, to a PZT-5H transducer similar design.