Structure Analysis by X-ray Powder Diffraction under High Pressure

@A diamond anvil cell (DAC) is a handy device that can generate pressure over 100 GPa and is applicable to Raman,infrared, and x-ray measurements. However, it needs special techniques to overcome difficuities due to its small sample volume and its mechanical limitation of a signal aperture. Our new DAC uses boron carbide (B₄C) backing plates because of a wide cornical aperture up to 90 degrees. This allows us to obtain higher resolution in x-ray structure analyses. The x-ray powder diffraction technique with an imaging plate detector is now widely used in various experimental fields including high pressure research. We developed a computer program named PIP capable of converting two-dimensional powder image to one-dimensional pattern. The aim of this program is to prepare easily and quickly one-dimensional diffraction patterns available for structure analysis such as the Rietveld method. Powder preparations and diffraction measurements should be done with care, especially for high pressure experiments, to make intensity analyses reliable. Structure analyses for high pressure data also require special techniques to avoid a misindexing and an over-parameterization problem. High quality intensity data are applicable not only to structure analyses but also to electron density analyses by the maximum entropy method.