FT-IR spectra of ZrHEDP samples are presented in Fig. and are confirmed as the same as ZrHEDPs in previous reports. Figure (c) represents the FT-IR spectra of the synthesized ZrHEDPs around approximately 1060 cm -1 due to PO3 stretching (P-O). As for the spectra of the ZrHEDP with higher P/Zr values, the P-O shifted to higher wavenumbers. The wavenumbers of the P-O in the ZrHEDP with P/Zr = 1.8, 2.5, 2.8, and 3.0 were 1052, 1058, 1058, and 1061 cm -1 , respectively.