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

Diffraction studies at extreme pressure-temperature conditions encounter intrinsic difficulties due to the small access angle of the diamond anvil cell and the high background of the diffraction peaks. Energy-dispersive x-ray diffraction is ideal for overcoming these difficulties and allows the collection and display of diffracted signals on the order of seconds, but is limited to one-dimensional information. Materials at high pressures in diamond anvil cells, particularly during simultaneous laser heating to temperatures greater than 3000 K often form coarse crystals and develop preferred orientation, and thus require information in a second dimension for complete analysis. We have developed and applied a diamond cell rotation method for in situ energy-dispersive x-ray diffraction at high pressures and temperatures in solving this problem. With this method, we can record the x-ray diffraction as a function of chi angle over 360 degrees, and we can acquire sufficient information for the determination of high P-T phase diagrams, structural properties, and equations of state. Technical details are presented along with experimental results for iron and boron. (C) 2001 American Institute of Physics.