Recent development of the Maximum Entropy Method (MEM) in crystallography is described on 3 aspects. Firstly, in order to solve the negative scattering problem in the treatment of neutron diffraction data, the MEM equation is derived as a function of the nuclear densities instead of scattering length densites. Secondly, a new algorithm is developed to carry out the MEM calculation effectively. The MEED computer program based on the new algorithm can perform the same MEM calculation typically a few hundreds times faster than the old version of the MEM program, MEMTARO. Thirdly, the anharmonicities of Be is determined from the MEM nuclear density map obtained by using single crystyal neutron diffraction data.
Electron spectro-microscope equipped with a parallel-EELS is a powerful tool for elemental analyses as well as an investigation of electronic structures on a local specimen area. The present paper shows an application of this method to organic crystals. Electron energy-loss near-edge structures (ELNES) observed on the carbon and the nitrogen K-edges of the chlorinated Cu-phthalocyanine and poly GeO-phthalocyanine were measured as a function of irradiation dose. From an analysis of the change of ELNES peaks, a sitedependent process in the radiation damage was proposed, which was realized due to the localized property of an inner-shell electron excitation.
Pressure effect on the cation distribution in olivine (Mg, Fe) 2SiO4 was detected through heating and quenching experiments under high pressures, combined with single crystal X-ray structure refinements under atmospheric pressure. The distribution coefficient KD [= (Fe/Mg) M1/ (Fe/Mg) M2] in the mantle olivine increases with depth by the effects of both pressure and temperature. The KD at the depth of 400 km is evaluated to be larger than 2.2, in contrast to 0.9-1.2 of natural samples available at the surface of the Earth.
Precise knowledge about the atomic geometries of surfaces is the basis for understanding surface properties such as electronic structure and adsorption processes of molecules. The dynamic analysis of intensity vs. energy (IV) curves of low-energy electron diffraction is the most powerful method for determining the surface geometries of crystal surfaces. The disadvantage of this method is that it requires a rather long CPU time to calculate IV curves. When we treat complex surface structures with many atoms in a surface unit cell, we must carry out calculations using many possible surface structural models while changing their structural parameters, and compare the calculated spectra with experimental ones. The recently developed tensor LEED method drastically reduces these timeconsuming calculations. This paper briefly reports on the characteristic features and advantages of tensor LEED compared to the canventional method. Some examples of the application of this mathod to the determination of surface structures are also reported.
Can metallic hydrogen be craeted? Pursuing the goal of making metallic hydrogen, high-pressure scientists have developped various new experimental techniques. Single-crystal synchrotron x-ray diffraction of solidified gases is one of such techniques. Recent structural studies of dense solid He demonstrate that the P-T conditions accessible to single-crystal X-ray diffraction measurement is extended to 20 GPa and 40K.