Phase composition and structure of grain boundary of oversintered Y3Al5O12 ceramics

Phase composition and microstructures of grain boundary of oversintered yttrium aluminum garnet （Y3Al5O12, YAG） ceramics by vacuum sintering at 1 850 ℃ were investigated. For synthesizing YAG, grain boundary is a key factor for YAG ceramics. The morphology of grain boundary was observed by SEM, TEM and its composition was analyzed by EDS. It is identified that the grain boundary is composed of a-AI2O3 and yttrium aluminum perovskite （YAP, YAlO3） eutectics. At the edge of YAG crystal grain, YAG phase is decomposed into perovskite YAP and α-Al2O3 during high temperature sintering. Due to refractive indexes of YAP and α-Al2O3 phases in wide grain boundary are different from those of YAG, the transmittance of oversintered YAG ceramics is lower than that of YAG ceramics sintered at 1 750 ℃.