Amorphous Polymorphs

In analogy with polymorphism in crystalline materials it has been suggested that some materials, when subjected to suitable pressure-temperature conditions, may also exhibit distinct amorphous phases. The early evidences of polyamorphism were found in simple systems such as ice, quartz and silicon. In this context the network structures that exhibit pressure-induced amorphization are interesting from the point of view of polyamorphism. Recent in-situ high pressure Raman scattering and synchrotron x-ray diffraction studies on negative thermal expansion material zirconium tungstate have revealed an amorphous to amorphous transition at 19 GPa. The transition was identified for the discontinuities in the structural parameters such as position and height of the first peak of the structure factor and that in the tungstate internal vibrational mode frequency. Another compound, vanadium pentaoxide could also exhibit polyamorphism as it turns amorphous at 40 GPa and it also forms a glass during melt-quenching.