Salamat, N.; (2010) High pressure solid state chemistry of C-N-H and Ti-N systems. Doctoral thesis , UCL (University College London).

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Abstract

This thesis presents the use of molecular precursors for the synthesis of solid-state materials through the application of extreme conditions. The main tool for the exploration of these materials was the diamond anvil cell which generated static pressures of up to 85 GPa. Combined with the use of highpower lasers, it provides a powerful and efficient technique for high-pressurehigh- temperature synthesis of solid-state materials. The work presented here is an investigation into the synthesis and recovery of new materials within two solid-state systems, C-N-H and Ti-N-O. Crystallographic analysis of these systems is a challenging process, made more difficult by their relatively light elemental composition and the use of the diamond anvil cell. In both cases a systematic experimental and analytical strategy was adopted to enable the extraction of the best data possible, both qualitatively and statistically. Two C-N-H systems were investigated: C2N3H and C6N9H3.HCl. Synchrotron X-ray diffraction and Raman scattering data are reported for the new dense tetrahedrally bonded phase C2N3H with a defective wurtzite structure. This is synthesised by laser heating from an organic precursor, dicyandiamide, C2N4H4 at high-pressure in a diamond anvil cell. This work confirms the structure deduced in previous work from electron diffraction experiments on samples recovered to ambient conditions. The graphitic layered compound C6N9H3.HCl was subjected to pressures up to 70 GPa in a diamond anvil cell and its structural behaviour was examined using synchrotron X-ray diffraction. The use of laser heating experiments revealed the synthesis of a new carbon nitride phase which is recoverable to ambient conditions. The second group of systems explored was those based on Ti-O-N. Amorphous or nano-crystalline precursors were used to attempt the synthesis of Ti3N4. The high-pressure and temperature behaviour of these materials was examined using synchrotron X-ray diffraction and Raman spectroscopy, in a laser-heated diamond anvil cell. In addition, the high-pressure studies of Ti2.85O4N, a recently discovered titanium oxynitride phase, are reported here up to 70 GPa. Using synchrotron angle dispersive techniques two high-pressure phases are observed and an attempt to elucidate these structures are reported.

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