Enhanced co-solubilities of Ca and Si in YAG (Y3Al5O12)

Official URL: http://dx.doi.org/10.1002/pssc.200778902

General garnet structure (Ia3-d) is a forgiving host and can accommodate cations of varying sizes and valence states. Studies on highly yttrium doped alumina ceramics with Ca and Si contamination indicated that YAG precipitates in the ceramic had a propensity to allow simultaneous incorporation of small amounts of Ca and Si impurities in their structure. In this study, using chemical synthesis techniques it was shown that YAG can accommodate up to approximately 8 cation % Ca+2 and Si+4 (i.e. Ca+2/Y+3 and Si+4/Y+3) if they are incorporated together. Equilibrium conditions are established by calcining samples at 900 C for 2 hours and cooling the samples to room temperature in the furnace. Disappearing-phase method and energy dispersive X-ray spectroscopy (EDS) were used to determine solubility and co-solubility limits. Beyond the solubility limit phase separation occurred and three crystalline yttrium aluminate phases (YAG, YAP (yttrium aluminate perovskite, YAlO3), YAM (yttrium aluminate monoclinic, Y4Al2O9)) were observed. It is believed that the excess Ca and Si above co-solubility limit precipitate out in the form of an x-ray amorphous anorthite-like glass in the system.