Crystallization of Y3Al5O12 garnet from deep undercooled melt effect of the Al-Ga substitution

Melts of garnet Y3Al5O12 and compositions lying on both sides of this compound were rapidly cooled in contactless conditions by using an aerodynamic levitation device coupled with a CO2 laser. The crystallized phases were analyzed at room temperature by XRD and 27Al MAS NMR. As the temperature reached by the supercooled melt decreases, the solidification was shown to lead successively to a mixture of YAlO3 and Al2O3, a monophasic garnet type structure and a glass. The formation of Y3Al5O12 starts at about 920 °C under the melting temperature and only 50 °C above the glass transition temperature. The solidification behaviour of liquid Y3Al5−xGaxO12 (x = 0.5, 1) was similar. Results clearly show the difficulties of garnet to nucleate. They are consistent with a rapid increase of the melt viscosity in the temperature range just above the formation of glass.