Kinetics and formation mechanism of yttrium aluminum garnet from an amorphous phase prepared by the sol–gel method

Isothermal crystallization kinetics was studied for Y3Al5O12 obtained from amorphous dispersed phases based on aggregately stable sols of yttrium aluminum hydroxides. To describe the formation of yttrium aluminum garnet from the amorphous phases, a mathematical model involving intermediate Y4Al2O9 and YAlO3 phases has been proposed. From the obtained experimental data on the phase composition of the crystallizing system, kinetic parameters of the crystallization process were determined, which allowed us to propose a probable mechanism of YAG crystallization from hydrosols of various composition. The actual mechanism of garnet formation depends not just on the temperature treatment conditions of the amorphous phase, but also on the type of the precursors. The optimization of the time–temperature regimes of YAG crystallization allowed preparation of samples with required properties. Thus, the sol–gel method involving sols of high stability towards aggregation is shown to be promising for the production of high-quality powders and optical ceramics of yttrium aluminum garnet.