Microstructure and piezoelectric properties of AC poled relaxor-PbTiO₃ perovskite single crystals

High-performance perovskite relaxor-PbTiO₃ (relaxor-PT) piezoelectric single crystals (SCs) fabricated by the melt-growth Bridgeman method have been widely used in medical ultrasound imaging devices as probes and in high-performance underwater equipment since around 2000. To improve the piezoelectric properties of these SCs, the use of alternating-current poling (ACP) instead of conventional DC poling has been widely adopted since 2018. Macro- and microstructural observations by scanning electron microscopy (SEM) are the best way to easily confirm the relationship between electrical properties and macro- and microstructure. After optimal ACP, fine 109º domain layers of 0.5 to several m parallel to the electrodes have been obtained, contributing to 10-100% improvement in dielectric constant and piezoelectric constant. Relaxor-PT SCs fabricated by the solid state crystal growth method with self-poring, excellent composition uniformity and machinability, high piezoelectric performance, and the low acoustic impedance due to the inclusion of spherical micropores in the SCs are also discussed.