| The research presented in this thesis focuses on the structural studies and the high pressure behavior of oxide negative thermal expansion (NTE) materials that can be classified as framework materials.;The first two chapters are devoted to TaO2F which adopts the ReO3-type cubic structure. Our studies under pressure revealed a rather complicated high pressure behavior for this deceivingly simple compound. The diffraction measurements at variable temperature and high pressure indicated that pressure had a significant effect on the linear coefficient of thermal expansion of TaO2F. In the remainder of the thesis, compounds that belong to the Sc2(WO4)3 family were examined. High-pressure in-situ powder diffraction studies were conducted on Zr2(WO4)(PO4)2, Zr2 (MoO4)(PO4)2, Hf2(WO 4)(PO4)2, and Sc2(WO4) 3 in order to investigate the effects of pressure on the coefficients of thermal expansion, existence of phase transitions, phase transition pressures and structural changes occurring upon phase transitions. |
