Bulk, dense, nanocrystalline yttrium aluminum garnet by consolidation of amorphous powders at low temperatures and high pressures

Amorphous Al2O3-37.5% Y2O3 powders, prepared using spray pyrolysis followed by partial or complete thermal decomposition, were hot-pressed at 315degrees-640degreesC and 500 or 750 MPa uniaxial pressure. Hot pressing of fully decomposed amorphous powder at 450degrees-640degreesC at pressures up to 750 MPa led to densification (up to 96%) as well as nanocrystallization of yttrium aluminum garnet (YAG). When the pressure was applied during heating, instead of after reaching the final temperature, higher relative densities resulted. Fully crystalline starting powder did not densify. The low true density of the amorphous phase (3.1 g.cm(-3)) was believed to be responsible for the densification through enhanced ionic mobilities.