Fig. 3 shows the SEM image of the s

Fig. 3 shows the SEM image of the sample with the autoclave and sintering temperatures of 280 and 1300 ˚C, respectively. A dense microstructure was observed. The grains were equiaxed, although the templates were platelike, anisotropically shaped particles. This suggests a grain growth occurred for the sample. This result is consistent with a previous study on a templated grain growth.[11] Similar dense microstructures were observed for other samples. The average grain size calculated from the images as well as the density is listed in Table 1. As a result of the hydrothermal treatment, an exaggerated grain growth was suppressed. The grain size was about 2 µm and it did not strongly depend on the autoclave temperature.