The grain boundary structure and oxygen tracer diffusion in transparent yttrium aluminum garnet (YAG) ceramics varying from 2% excess of Y 2 O 3 to 0.5% excess of Al 2 O 3 were studied. The characterization of the specimens is as follows: (i) For the Y 2 O 3 ‐excess specimen, a second phase (yttrium aluminum perovskite: YAP) containing silicon in the grain boundary was found, (ii) For the Al 2 O 3 ‐excess specimen, both aluminum‐rich particles (alumina) and a silicon‐rich segregant layer were observed in the grain boundary. The volume diffusion of the oxygen tracer is little influenced by the excess composition. In contrast, the grain boundary diffusion of the oxygen tracer is suppressed in the Y 2 O 3 ‐excess specimens, compared to Al 2 O 3 ‐excess specimens. These differences are thought to result from the chemical reaction between the second phase and the intergranular liquid phase during the sintering.
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Sakaguchi et al. (1996) studied this question.
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