The crystal structure and spectral properties of bulk MoS 2 were investigated at high pressures up to 51 GPa using a diamond anvil cell with synchrotron radiation in addition to high temperature X-ray diffraction and high pressure Raman spectroscopic analysis. While the crystal structure of MoS 2 is stable on increasing temperature, results of high pressure experiments show a pressure-induced isostructural hexagonal distortion to a 2H a -hexagonal P6 3 /mmc phase around 26 GPa as predicted by theoretical calculations reported earlier. The 2H a -hexagonal phase coexists with the ambient 2H c phase up to 51 GPa, the highest pressure achieved in our experiments. The Raman data obtained in our high pressure experiments show consistent changes in the vibrational modes. Furthermore, the diffraction data obtained for the shocked MoS 2 to pressures 8 GPa is found to be structurally resilient.

Usually two modes of arc attachment to cathodes for high intensity discharge (HID) lamps are observed, the spot mode for high pressure, low currents and large electrode diameters and the diffuse mode for the opposite conditions. Recently, a very constricted attachment to cathodes was observed both in real HID lamps and in Bochum's model lamp. In the model lamp, the extremely constricted arc attachment was observed in argon and xenon atmosphere at a pressure p = 0.26 MPa and for currents I = 1-6 A. Whereas the global electrode temperature and the cathode fall of the diffuse and the spot mode differ only slightly, the extremely constricted arc attachment (so-called `super spot mode') is associated with a significantly decreased global electrode temperature at similar parameters. The reduction in electrode temperature implies low cathode falls and low electrode losses, respectively. Scanning electron micrographs show that the surface structure of the electrodes has substantial influence on the mode of cathodic arc attachment.

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The reaction mechanism and kinetics of the thermal decomposition of uranium dinitride/uranium sesquinitride to uranium mononitride under inert atmosphere at elevated temperature were studied. An increase in the lattice parameter of the UN(2)/alpha-U(2)N(3) phase was observed as the reaction temperature increased, corresponding to a continuous removal of nitrogen. Electron density calculations for these two compounds using XRD powder patterns of the samples utilizing charge-flipping technique were performed for the first time to visualize the decrease in nitrogen level as a function of temperature. Complete decomposition of UN(2) into alpha-U(2)N(3) at 675 degrees C and the UN formation after a partial decomposition of alpha-U(2)N(3) at 975 degrees C were also identified in this study. The activation energy for the decomposition of the UN(2)/alpha-U(2)N(3) phase into UN, 423.8 +/- 0.3 kJ/mol (101.3 kcal/mol), was determined under an inert argon atmosphere and is reported here experimentally for the first time.

Ion irradiation experiments and atomistic simulations were used to demonstrate that irradiation-induced lattice swelling in a complex oxide, Lu2Ti2O7, is due initially to the formation of cation antisite defects. X-ray diffraction revealed that cation antisite formation correlates directly with lattice swelling and indicates that the volume per antisite pair is approximately 12  Å3. First principles calculations revealed that lattice swelling is best explained by cation antisite defects. Temperature accelerated dynamics simulations indicate that cation Frenkel defects are metastable and decay to form antisite defects.