The MEM Charge density studies from multi high resolution synchrotron powder X-ray diffraction data.

Applied Physics, Nagoya University* Structural Materials Science Laboratory, Riken**
â—‹Eiji Nishibori* Shinobu Aoyagi* Kenichi Kato* Masaki Takata** Makoto Sakata*

Maximum Entropy Method (MEM) has been widely used for charge studies by X-ray powder diffraction experiments in the materials science field. The MEM is a method for statistical deduction of diffraction data. The MEM density study always requires accurate data with high counting statistics. It is normally difficult to collect high counting statistics in high angular regions in powder data. In order to improve counting statistics of powder diffraction data, we have been developing the both experimental and analytical techniques based on multi powder diffraction data. In this study, we report the MEM charge density studies of Silicon and Diamond from the multi powder diffraction data.
The multi powder data for silicon and diamond were collected at SPring-8, BL02B2. We measured two dataset for one sample at one temperature point. One of the dataset was measured in normal procedure. Another dataset was measured for improvement of counting statistics for high-order reflections.
These data sets were simultaneously analysed. The structure factors for MEM analysis were extracted. The MEM charge densities of silicon and diamond were determined from the extracted structure factors. The covalent bonds of silicon and diamond were clearly revealed by the MEM charge densities. The charge density at bond mid-point is coincided with various theoretical calculations within 0.1 e/ Å-3. The present results show that the multi powder data method is appropriate for accurate charge density by MEM.