High pressure behavior of adamantane is investigated up to pressures of 26 GPa at ambient temperature using Raman spectroscopy. A detailed study of changes in the Raman spectrum of the C–H stretching modes across the disorder–order transition around 0.5 GPa is reported. Pressure dependence of the internal mode frequencies suggest two more subtle transitions around 2.8 GPa and 8.5 GPa, respectively, which are reversible. Evolution of spectra at higher pressures show evidence for another structural transition above 24 GPa.
Results of the low frequency dielectric constant
(ε), dielectric loss and x-ray powder diffraction (XRD) measurements on orthorhombic
Al2(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
Al2(WO4)3. Another monoclinic
modification of Al2(WO4)3
is also observed from our XRD studies at 3.4 GPa.
Al2(WO4)3
amorphizes above a pressure of 18 GPa, and this pressure induced amorphization is
attributed to the lack of thermal activation for decomposition.
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