Solid-state structural chemistry at high pressure using x-ray synchrotron radiation diffraction techniques.

Energy dispersive X-ray diffraction with synchrotron radiation has been used to probe the room temperature, high pressure phase diagrams of several inorganic compounds. A review of the publications for high pressure X-ray diffraction at synchrotron sources is given. The techniques, theory, apparatus and errors of high pressure X-ray diffraction are discussed. A spectroscopic system used to enable pressure calibration is refined and its merits discussed. The calibration of this instrument against an NaC1 standard is presented. CuGeO3 undergoes two phase transitions at 73 kbar and 110 kbar respectively. The effect of pressure on the Jahn-Teller distortion around copper is discussed. The first high pressure polymorph of hafnia (beginning at 26 kbar) is shown to be iso-structural with that of zirconia. A mechanism for the transition is offered. The effect of pressure on the series of iso-structural vanadates MVO3 (M = K, Rb, Cs, NH4) reveals phase transitions in KVO3 and RbVO3 at 27 and 40 kbar respectively. Models for the transitions are offered. Intuitive expectations of an increase in compressibilities with an increase in cation size are not realised. NH4VO3 transforms to an amorphous phase at 47 kbar. A full structural model for (COD)PtNPhS(O)2NPh is offered with an R- factor of 2.54%. A discussion of ring-puckering in this and similar systems is given. An improved structural model for powdered hafnia is offered. High resolution synchrotron techniques are used in combination with Rietveld refinement methods. A discussion of the structure is given.