Phase transitions in Al2(WO4)3:: high pressure investigations of low frequency dielectric constant and crystal structure

Results of the low frequency dielectric constant (e), dielectric loss and x-ray powder diffraction (XRD) measurements on orthorhombic Al-2(WO4)(3) under pressure are reported. The dielectric constant and the dielectric loss both show a sharp peak at about 0.5 GPa, indicating a ferroelastic phase transformation. This phase is found to be identical to the low temperature monoclinic phase of Al-2(WO4)(3). Another monoclinic modification of Al-2(WO4)(3) is also observed from our XRD studies at 3.4 GPa. Al-2(WO4)(3) amorphizes above a pressure of 18 GPa, and this pressure induced amorphization is attributed to the lack of thermal activation for decomposition.