XRD results indicated all of the ZrHEDP samples are in amorphous states. On the other hand, the centre carbon bound to two phosphorous in HEDP has a sp 3 hybrid orbital, twisting the whole HEDP structure. It eventually disturbs keeping the layer-by-layer structure, which could be the origin of the amorphous state. In this case, it is difficult for both phosphoric acid groups of HEDP to be fixed in zirconium layers due to steric hindrance, and either of the two readily becomes movable -PO3H2.