@article{Chen2026, 
author = {Xingtao Chen and Yijun Shen and Zhouru Kong and Qinbiao Nan and Dahan Liu and Lixin Yu and Jun Wang and Jianqi Qi and Tiecheng Lu},
title = {Unravelling the H2O-assisted high-pressure sintering mechanism: A route to highly transparent cubic alumina ceramics},
year = {2026},
journal = {Journal of Advanced Ceramics},
volume = {15},
number = {5},
pages = {9221291},
keywords = {optical properties, transparent ceramics, γ-Al2O3, transient liquid phase, high-pressure sintering},
url = {https://www.sciopen.com/article/10.26599/JAC.2026.9221291},
doi = {10.26599/JAC.2026.9221291},
abstract = {Transparent cubic alumina (γ-Al2O3) ceramics are promising optical materials but are challenging to densify without phase transformation or cracking. Herein, we report a novel H2O-assisted high-pressure sintering (HPS) strategy that enables the fabrication of highly transparent, crack-free γ-Al2O3 ceramics at temperatures as low as 300 °C. By combining GPa-level pressures (0.8–5 GPa) with precisely controlled H2O concentrations (5–75 wt%) as a transient solvent, we achieve near-theoretical densities (> 99%) and exceptional optical transmittance (> 80% in the visible range). Systematic investigation reveals a non-monotonic dependence of densification and transparency on H2O content, with an optimal concentration of ~15 wt% under 5 GPa. Microstructural and spectroscopic analyses correlate superior optical quality with a pore-free, nanocrystalline microstructure and the absence of secondary phases. Crucially, through integrated first-principles calculations and ab initio molecular dynamics simulations, we unravel the atomic-scale mechanism. Namely, under high pressure, H2O dissociates at the particle interface, with the resultant H+ forming Al–H bonds and OH− incorporating into interstitial lattice sites. This process stabilizes a hydroxyl-cubic aluminate (HAl2O4)-like structure, which not only facilitates stress-free densification via an enhanced dissolution–precipitation pathway but also effectively relieves internal stresses that typically cause cracking in pressure-only sintering. This work provides a fundamental mechanistic understanding of the synergistic role of H2O and ultra-high pressure in low-temperature ceramic consolidation, establishing a generalizable route to transparent nanocrystalline ceramics that are otherwise inaccessible via conventional thermal sintering.}
}