After field cooling (FC) alternating current poling (ACP), we investigated the dielectric and piezoelectric properties of [001]_pc-oriented 0.24Pb(In_1/2Nb_1/2)O₃ (PIN)-0.46Pb(Mg_1/3Nb_2/3)O₃ (PMN)- 0.30PbTiO₃ (PT) (PIMN-0.30PT) single crystals (SCs), which were manufactured by continuous- feeding Bridgman (CF BM) within morphotropic phase boundary (MPB) region. By ACP with 4 kV_rms/cm from 100 to 70 ℃, the PIMN-0.30PT SC attained high dielectric permittivity $({\epsilon }_{33}^T\text{/}{\epsilon }_0)$ of 8330, piezoelectric coefficient (d₃₃) of 2750 pC/N, bar mode electromechanical coupling factor k₃₃ of 0.96 with higher phase change temperature (T_pc) of 103 ℃, and high Curie temperature (T_C) of 180 ℃. These values are the highest ever reported as PIMN-xPT SC system with T_pc > 100 ℃. The enhancement of these properties is attributed to the induced low symmetry multi-phase supported by phase analysis. This work indicates that FC ACP is a smart and promising method to enhance piezoelectric properties of relaxor-PT ferroelectric SCs including PIMN-xPT, and provides a route to a wide range of piezoelectric device applications.

The effects of alternating current poling (ACP) at 80 ℃ on electrical properties of [001]-oriented 0.72 Pb(Mg_1/3Nb_2/3)O₃-0.28PbTiO₃ (PMN-28PT) single crystals (SCs) have been investigated. The square-wave ACP SCs poled at high voltage (HV, 5 kV_rms/cm) occasionally showed large fluctuations and low opposite values of piezoelectric coefficient (d₃₃ = ± 1370 pC/N) in one plate. This revealed spurious-mode vibrations (SMV) of impedance spectrum. However, after depolarizing and repolarizing the sample with a sine-wave ACP at low voltage (LV, 3.5 kV_rms/cm), the d₃₃ enhanced to be 1720 pC/N (+26%) and did not exhibit large fluctuation or opposite values in one plate any more. The impedance spectrum became clean and the abnormal SMV disappeared. We proposed four possible mechanisms of the SMV, and speculate that the main cause maybe by macro-scale sub-domain structure and/or phase change in the main domain structure and/or phase in the SC plate due to the specific poling conditions not eternal mechanical damage of PMN-PT SCs. This study will be useful to realize a high d₃₃ and improve other properties of PMN-PT ACP SC ultrasonic transducers without any SMV for high-frequency medical imaging equipment.