Gadolinium gallium garnet liquid phase epitaxy and the physical chemistry of garnet molten solutions

Gadolinium gallium garnet, GGG, growth and dissolution are studied by a liquid phase epitaxy, LPE, technique using a molten solution of x Gd2O3, y Ga2O3, p PbO and b moles B2O3, where p = 83.53 to 96.6 and b = 7.5 to 0. Ratios of x : y range from 3 : 5 (the stoichiometric value) to 3 : 75, while x is varied from 0.309 to 1.875. This GGG system yields garnet over a broad range, including stoichiometric Gd3Ga5O12 and provides an ideal experimental system for testing garnet growth-dissolution and solubility models. Measuring both growth rates, f{hook}+, and dissolution rates, f{hook}-, allows the accurate determination of liquidus temperatures where f{hook}+ = f{hook}- = 0. Garnet liquidus data fit an Arrhenius-type temperature-dependent solubility product if these ionic solutions are considered to have only a quarter of their Pb active and to contain gadolinium borate chemical complexes. In other words, high thermodynamic activities exist for Gd and especially for Ga. A simple ionic solution model does not adequately describe these solutions. © 1982.