Piezoelectricity offers an electromechanical coupling that is widely utilized in transducer applications. There has been a consistent demand for transparent piezoelectric materials for optoelectrical applications. Therefore, despite the inherent tradeoff between the transparency and the piezoelectricity, numerous strategies have been explored to develop the transparent piezoelectric materials. Nonetheless, the most transparent piezoelectric materials developed to date is either a single crystal or materials that achieve transparency via hot-press sintering, limiting its industrial applicability. Therefore, we introduce a novel piezoelectric material that ensures transparency through co-doping and pressureless sintering of polycrystalline ceramics. In this study, we employed a compositional optimization approach to enhance the synergistic effect between the transparency and the piezoelectric properties of 0.71Pb(Mg_1/3Nb_2/3)O₃–0.29PbTiO₃ (PMN–0.29PT) ceramics. By utilizing the tape casting process for mass production and large-area manufacturing, our Pb_0.913La_0.0145Sm_0.0145(Mg_1/3Nb_2/3)_0.71Ti_0.29O₃ (TP2.9) ceramics exhibited over 60% transparency and large piezoelectric coefficient (d₃₃) of 1104 pC/N. This material holds considerable promise for a wide range of industrial applications in both the optical and electronic domains.

Among the unresolved issues in the study of relaxor ferroelectrics is the role of freezing temperature, across which the dynamics of polarization reversal in relaxor ferroelectrics changes. The presence of this freezing temperature is best manifested by the appearance of a double polarization hysteresis loop just above the freezing temperature. Given that the polarization pinching evolving into a double hysteresis starts well below the freezing temperature, there exists a transient temperature regime between the nonergodic and the ergodic relaxor states. To clarify the role of the freezing temperature on the pinching, the polarization reversal near the freezing temperature of relaxor (Pb_1-xLa_x)(Zr_1-yT_y)_1-x/4O₃ (PLZT) was monitored using three in situ electric field methods: electrocaloric effect, neutron diffraction, and transmission electron microscopy. We demonstrate that the pinching results from a two-step process, 1) domain detexturization in the ferroelectric state and 2) miniaturization of domains. This observation explains the recently reported gap between the depolarization temperature T_d and the ferroelectric-to-relaxor transition temperature T_F-R in lead-free relaxors. We further show that T_d and T_F-R, which have long been considered identical in lead-based relaxors, are not the same. The current study suggests that the mismatch between T_d and T_F-R is an inherent feature in both lead-based and lead-free relaxor ferroelectrics.