INTENSITY ANALYSIS FOR HIGH PRESSURE POWDER DIFFRACTION USING DIAMOND ANVIL CELLS. H. Fujihisa, K. Aoki, H. Yamawaki, and M. Sakashita, National Institute of Materials and Chemical Research, 1-1 Higashi, Tsukuba, Ibaraki 305, Japan

An angle dispersive powder x-ray diffraction experiment with an image plate (IP) and a diamond anvil cell has greatly improved data quality1, which allows us to get an accurate structure including atomic parameters under pressure. The use of the synchrotron beam is recommended to get high angular resolution and sufficient intensity in powder patterns. The IP makes it possible to remove geometrical error easily on computer and to generate a 2theta versus intensity pattern.

Then we can determine atomic parameters by the Rietveld or the least-square methods. A powder pattern of which structure is fully known also gives electron density distribution map. The limiting number of the observed peaks causes termination errors in both maps of the traditional Fourier synthesis and the previous maximum entropy method (MEM)2. To overcome this problem, we have developed a new MEM for high pressure experiments3 which can reduce the termination errors by the same theory as the difference synthesis.

References

1. O. Shimomura, K. Takemura, H. Fujihisa, Y. Fujii, Y. Ohishi, T. Kikegawa, Y. Amemiya, and T. Matsushita: Rev. Sci. Instrum. 63, 967 (1992).

2. M. Sakata and M. Sato: Acta Cryst. A46, 263 (1990).

3. H. Fujihisa, Y. Fujii, K. Takemura, O. Shimomura, R. J. Nelmes, M. I. McMahon: Proc. 4th workshop of IUCr HPG, Tsukuba 1995.