Electrostrictive materials

Abstract

Two types of electrostrictive materials will be described: (1) relaxor ferroelectrics with diffuse phase transitions, and (2) antiferroelectric ceramics with a field‐induced ferroelectric phase. Transducers made from relaxor ferroelectrics such as lead magnesium niobate (PMN) and lead zinc niobate (PZN) are operated above Tc in a broad transition range characterized by the presence of nanometer‐size microdomains that impart large electromechanical coupling coefficients to the ceramic. These relaxor materials show no piezoelectric effect under ac drive because of the absence of any net spontaneous polarization, but microdomain fluctuations give rise to large electrostrictive strains (∼10−3) with no hysteresis. Under dc bias, PMN ceramics show piezoelectric d33 coefficients as large as 1500 pC/N, three times those of PZT. The second type of electrostrictive transducer is based on a field‐induced phase change from an antiferroelectric structure to a ferroelectric phase. Ceramics in the PbZrO3‐PbTiO3‐PbSnO3 ternary system are used as bistable transducers for digital motions where shape‐memory hysteresis can be an advantage. Other uses for electrostrictive transducers include adaptive optic systems, micropositioners, and smart transducers in which the size of the piezoelectric coefficient can be adjusted with a dc bias field.