A far from equilibrium state developed from pulse poling for high performance piezoelectric transducers

Creating a piezoelectric or pyroelectric material from a ferroelectric material requires aligning its ferroelectric domains to achieve a remanent polarization. This complex process involves nucleating/growing domain structures and inducing a macroscopic, non-centrosymmetric symmetry under an applied electric field. For many years, this process has not received significant attention. Typically, DC fields are applied at elevated temperatures to align the domain states, balancing the depolarization and screening fields in a metastable state that is still near equilibrium. In contrast, the pulse poling (PP) strategy uses field pulses much faster than the time it takes for depolarization and bulk screening processes to occur. This instability allows the PP of relaxor ferroelectric (RFE) crystals and textured ceramics to induce a new far-from-equilibrium (FFE) state, which has enhanced properties compared to conventional DC poling. RFE crystals are of interest because it is known that poling them in specific directions creates engineered domain structures that provide giant piezoelectric properties with low hysteretic losses. By applying PP to RFE crystals in the < 001 > direction, significant changes in the electromechanical properties within the FFE state were observed, which opens new high-performance opportunities for these materials in transducer applications. This review outlines the property enhancements with PP and their origins while modeling the properties with a phenomenological thermodynamic approach. The properties are discussed with respect to transducer applications and benchmarked to other traditional poling strategies. Mn: PMN-PIN-PT, Mn: PMN-PZT, and Sm: PMN-PIN-PT are primarily used as model systems to demonstrate enhanced electromechanical performance with PP over other conventional poling strategies. Given the new concepts discussed in this paper, there is also a future research section at the end of the paper to drive the innovation beyond this initial work.