A₂B₂O₇ system compounds, which usually present three phase structures mainly based on the ionic radius ratios of r_A and r_B (r_A/r_B), have been studied for potential applications in many fields, such as thermal barrier coatings, luminescence powders, fast-ion conductors, photocatalysts, and matrices for immobilization of highly active radionuclides. Since 2005, La₂Hf₂O₇ was fabricated into transparent ceramics and much more attentions were paid on A₂B₂O₇ transparent ceramics for new applications. In this review, the development of A₂B₂O₇ system transparent ceramics was described. The structure characteristics, powder synthesis method, and sintering techniques of the final A₂B₂O₇ transparent ceramics were summarized. After that, the mostly reported A₂Hf₂O₇, A₂Zr₂O₇, and A₂Ti₂O₇ system transparent ceramics were systematically introduced. The potential application fields and future development trends were also discussed, focusing on scintillators, optical elements, and other luminescent materials

The Ce-doped (Gd, Y)₃Al₅O₁₂ transparent ceramics with Gd³⁺ content of 0 to 80 mol% were fabricated using a solid-state sintering method under vacuum. Their phase compositions and structure parameters were checked by X-ray diffraction (XRD). Optical and luminescence characteristics were investigated and thoroughly discussed by transmittance, absorption spectra and luminescence examination. The Gd³⁺ ions were found of great importance to the band structure of crystal and energy state of Ce³⁺ in the garnet ceramics. Balanced Gd³⁺ admixture into the YAG lattice provided excellent color coordinates and CRI for the phosphor for warm white light illumination. This study provides an efficient approach to tailor the luminescence of the garnet phosphors.

Alumina green bodies were shaped by slip casting under a strong magnetic field. Alumina ceramics were obtained by hot isostatic pressing (HIP) at 1275°C and pressureless sintering at above 1700°C, respectively. HIP-sintered alumina, with in-line transmittance of 52% at 600nm and 82% at 2μm, showed a sub-micrometer grain microstructure and a slight grain orientation. However, XRD results demonstrated the grains of pressureless sintered alumina sintered at >1700°C oriented along c-axis, and texture microstructure was observed by SEM. It indicated that magnetic field assisted slip casting produced “seeds” of grain orientation, and orientation degree that could achieve depended on the sintering temperature.