| Using a variety of diamond anvil cells, in conjunction with x-ray diffraction, Raman and Fourier Transform Infrared (FTIR) spectroscopy, nanocrystalline ZnS, TiO2, SiC, Ag and the negative thermal expansion (NTE) materials: HfV2O7, ZrV2O7, is studied under high pressure.; To study the pressure-induced changes of HfV2O7, energy dispersive synchrotron based x-ray diffraction is performed up to 41.7 GPa. X-ray diffraction indicates that HfV2O7 undergoes two phase transitions between 0--42 GPa, the first occurring at 3.7 +/- 0.3 GPa. The second is indicated by a gradual loss of the intensity of the Bragg peaks, suggesting pressure-induced amorphization, and is not complete even at 41.7 GPa.; The room temperature Raman and infrared spectra of ZrV2O 7 are observed up to pressures of 12 GPa and 5.7 GPa respectively. Average mode Gruneisen parameters are calculated for the Raman and infrared active modes. Changes in the spectra under pressure indicate a phase transition at ∼1.6 GPa which is consistent with the previously observed alpha (cubic) to beta (pseudo-tetragonal) phase transition, and changes in the spectra at ∼4 GPa are consistent with an unquenchable transformation to an amorphous structure.; Different samples of nanocrystalline ZnS and bulk ZnS are studied under ambient conditions using Raman spectroscopy. High pressure Raman spectroscopy is carried out on nanocrystalline ZnS of mixed wurtzite and sphalerite structure. It is found that there is a phase transition from zinc blende to the rock salt structure occurred around 16 GPa.; Nanocrystalline TiO2 with particle size of 5 nm is studied using Raman spectroscopy. Pressure induced amorphization was observed around 18 GPa.; To study the particle-size dependence of the bulk modulus, energy dispersive x-ray diffraction is performed up to 50 and 35 GPa on 15 and 30 nm of nanocrystalline silver, respectively.; Room temperature x-ray diffraction studies are performed up to 45 GPa pressure on nanocrystalline beta-SiC with average particle sizes 10, 20 and 50 nm. It is found that compressibility of 3C-SiC has a complicated dependence on particle size. |
