Aluminum nitride (AlN) is considered one of the most desirable materials for integrated circuits and electronic packaging substrates. However, raw AlN powder reacts easily with water, forming Al(OH)₃ or AlOOH on the surface and hindering the development of an aqueous tape-casting process for preparing AlN ceramic substrates. In this study, hydrolyzed polymaleic anhydride (HPMA) was used to modify AlN powder, which has good water solubility and dispersibility. The AlN powder was modified with 5 wt% HPMA remained stable in water for at least 90 h under magnetic stirring condition and 24 h under ball milling condition, indicating that HPMA-modified AlN powder has good resistance to hydrolysis. The action mechanism of HPMA is revealed. Firstly, –COOH of the HPMA polymer and the oxide layer on the surface of the AlN powder underwent a dehydration condensation reaction to form a compound. Secondly, long chains of the polymer further coated the surface of the AlN powder, forming an anti-hydration layer with a thickness of about 7.0 nm on the surface of the AlN particles. In addition, AlN green sheets were successfully prepared by aqueous tape casting using the HPMA-modified AlN powder without additional dispersants. Subsequently, AlN ceramic substrates were obtained by sintering at 1750 ℃ for 4 h under an N₂ atmosphere with a pressure of 0.2 MPa. The relative density and thermal conductivity were tested to be 97.3% and 122 W/(m·K), respectively.

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.