Two-dimensional energy dispersive x-ray diffraction at high pressures and temperatures

Diffraction studies at extreme pressure-temperature conditions encounter in trinsic difficulties due to the small access angle of the diamond anvil cel l and the high background of the diffraction peaks. Energy-dispersive x-ray diffraction is ideal for overcoming these difficulties and allows the coll ection and display of diffracted signals on the order of seconds, but is li mited to one-dimensional information. Materials at high pressures in diamon d anvil cells, particularly during simultaneous laser heating to temperatur es greater than 3000 K often form coarse crystals and develop preferred ori entation, and thus require information in a second dimension for complete a nalysis. We have developed and applied a diamond cell rotation method for i n situ energy-dispersive x-ray diffraction at high pressures and temperatur es in solving this problem. With this method, we can record the x-ray diffr action as a function of chi angle over 360 degrees, and we can acquire suff icient information for the determination of high P-T phase diagrams, struct ural properties, and equations of state. Technical details are presented al ong with experimental results for iron and boron. (C) 2001 American Institu te of Physics.