High pressure-high temperature studies on superhard materials

In this thesis research, a laser heating facility was built on the micro-Raman and Photoluminiscence (PL) spectrometer at Physics Department of University of Alabama at Birmingham (UAB). Details of design and operation of the laser heating facility are described in this dissertation. Combined with the diamond anvil cell technique, high pressure high temperature (HPHT) environments were created in the lab. In situ Raman/PL studies on the sample at HPHT environments were performed. Accurate temperature measurements by Raman spectroscopy and Blackbody radiation were carried out in the laser heating experiments.; Optical measurement of pressures by Sm:YAG pressure marker was extended to 304 GPa in this research, well beyond the 200 GPa limit of using ruby as the traditional pressure marker. Pressure induced disorder and laser induced recrystallization in Sm:YAG were also observed.; The superhard materials studied in this research are SiC, BN, and diamond.; We report the first measurement of the Raman spectra of 6H-SiC to 95 GPa, and of 4H-SiC to 66 GPa at ambient temperature. The lattice dynamics quantities such as the Born effective charge {dollar}esbsp{lcub}T{rcub}{lcub}*{rcub}{dollar} and mode Gr"uneisen parameter {dollar}gamma{dollar} are derived and used to predict the stability of the SiC crystal structures.; We discovered the zincblende cubic BN to rhombohedral BN phase transition by laser heating at ambient pressure. In situ Raman spectroscopic measurement provided the accurate parameters, such as the transition temperature (at 1800 {dollar}pm{dollar} 40 K), and the temperature dependence of the Raman modes from cubic and rhombohedral phases of boron nitride.; In the ultrapure synthetic diamonds, we observed a strong photoluminiscence band induced by the stress at high pressures. The low nitrogen impurity level in this diamond allows us to measure for the first time the stress dependence of the fluorescence peak in the diamond.; The laser heating facility and the diamond anvil cell provide us powerful methods to open up the field of HPHT studies. The bright future of this field is enlightened by the present encouraging results on superhard materials.