Light-permissive piezoelectrics: advances in Pb-based transparent ceramics and crystals for next-generation devices

Transparent piezoelectric materials that combine optical clarity with strong electromechanical coupling are gaining attention for their applications in integrated photonic, acoustic, and biomedical technologies. Among these, lead-based perovskites-particularly Pb(Zr,Ti)O₃ (PZT) and its derivatives-stand out for their tunable properties and high performance. Historically, achieving both high piezoelectric performance and optical clarity in the same material has been challenging, as ferroelectric domain walls and grain boundaries that enhance piezoelectricity tend to scatter light. Lanthanum (La) co-doped PLZT ceramics have achieved visible light transmittance exceeding 60% through the combination of ultrafine grain engineering and high-density sintering. Meanwhile, advanced processing methods such as hot-forging, pressureless sintering, and wafer bonding have enabled the fabrication of translucent PZT ceramics, thin films, and large single crystals. Solid-state-grown PZT single crystals exhibit excellent piezoelectric coefficients (e.g., d₃₃ > 2000 pC N^-1), supporting their use in high-efficiency devices. Transparent ultrasonic transducers now offer greater than 80% optical transmission and wide acoustic bandwidths, rivalling conventional systems. While single crystals exhibit higher strain responses (∼1.97%) compared to ceramics (∼0.76%), ceramics offer advantages in terms of processability and compositional flexibility. Together, these advances underscore the potential of transparent PZT-based materials to enable multifunctional devices that bridge the gap between optics and acoustics. This review examines the synthesis, structure-property relationships, and diverse applications of transparent PZT ceramics and single crystals, with a focus on their potential future integration in energy harvesting, wearable electronics, and next-generation optoelectronic systems.