Transparent electro-optic (EO) oxide ceramics are known for their rapid EO effects. EO ceramics have several advantages over single-crystals, including variable size and shape, controllable chemical composition, superior mechanical properties, and low cost. Synthesis of high-performance transparent EO ceramics requires high purity of raw materials, high density, homogeneous composition, uniform grain size, and relatively wide bandgap. Powder synthesis and sintering are two of the critical steps involved in the fabrication of highly transparent EO ceramics. Using high-activity precursor powders has been effective in fabricating high-density ceramics that demonstrate excellent EO performance. The sintering process plays a crucial role in achieving this result, and currently, there are several sintering methods available for producing high-density ceramics, including hot-pressing, hot isostatic pressing, and spark plasma sintering. This review summarizes the recent progress in materials and processes used to develop transparent EO ceramics, including those based on lead zirconate titanate, lead magnesium niobate-lead titanate, and lead-free potassium sodium niobate. In addition, several novel applications of transparent EO ceramics, including light shutters, spectral filters, optical memory, as well as image storage and displays are reviewed. In the end, the review concludes with a discussion of future trends and perspectives.

There has been a surge of research interest in the promising lead-free potassium−sodium niobate (KNN)-based ceramics, applications of which could be significantly promoted by improving thermal stability of piezoelectricity. Besides, endowing the KNN-based ceramics with photoluminescence property by rare-earth-ion doping can make them more completive lead-free counterparts in potential applications such as novel multifunctional sensing devices. Herein, a novel KNN-based ceramic material doped with Eu was elaborately designed to simultaneously obtain enhanced temperature-stable piezoelectricity and good luminescence property. By the introduction of diffused phase transition and the modulation of unit cell distortion, a large piezoelectric strain coefficient (d^*₃₃) with a small variation (590±59 pm/V) over a wide temperature range (from room temperature to 110 ℃) was realized. The optimal composition also exhibited a considerable piezoelectric coefficient (d₃₃) with small fluctuation (330±33 pC/N) from 20 to 80 ℃. In addition to the enhanced temperature-stable piezoelectricity, the luminescence of these ceramics was slightly enhanced with the elevation of BaZrO₃ (BZ) doping contents, which could be attributed to the increased compositional disorder and the decreased unit cell distortion of the matrix material. Moreover, an optical characteristic was more prominent at ultra-low temperatures. This work unprecedentedly provides a novel paradigm for the design of multifunctional KNN-based ceramics with enhanced temperature-stable piezoelectricity and good luminescence property, revealing the great potential of the rare-earth-element-doped KNN material for future applications in the novel multifunctional devices.