FT-IR results showed that P-O vibration in the ZrHEDP shifts to high wavenumbers when the P/Zr is large (Fig. )). A higher wavenumber for the P-O indicates a higher energy state, i.e., a more unstable bond of -PO3H2. It is identical to the case that the H-bond is weakened by acid-acid interactions. The acid-acid interaction does not originate if acids do not concentrate to some extent. Then, the large amounts of -PO3H2