The XRD patterns of the specimens prepared by CSP at 200 °C with yttrium nitrate solution are presented in Fig. 4. Although no second phase is observed in the 1YN specimen, the coexistence of the second phases Y4O(OH)9NO3 and Y(OH)3 is evident in the 5YN and 10YN specimens, and Y4O(OH)9NO3 alone is detected in the 20YN specimen. This indicates that the dissolved yttrium nitrate is transformed into Y4O(OH)9NO3 and Y(OH)3 during the CSPprocess. In addition, as the amount of yttrium nitrate increased, the peak intensity of Y4O(OH)9NO3 increased while that of Y(OH)3 decreased.