Studies on imperfection and phase transformation in crystalline minerals

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The research on imperfection and phase transformation in crystalline minerals started in 1995 and has been undertaken ever since. The subjects of the research are (1) to prepare a system for analyzes of diffuse scattering, (2) to equip our diffraction system with monochromators and new detect in order to direct the system suitable for measurements of diffuse scattering, and (3) to measure diffuse scattering of some materials and to analyze the measured data. The results obtained up to the present and the research being in progress are as follows.On the first subject, prof.Rahman of the university of Hannover, Germany, proposed us to collaborate with each other on analyzes of the diffuse scattering found in diffraction patterns of akermanite group on which we have worked in these several years. Prof.Rahman had developed a powerful system to simulate and reconstruct diffuse scattering by computers and wanted to adapt his system to our problems. In 1996 we have started our collaboration t … More o adapt the system for analyzes of incommensurate structures and then to simulate diffuse scattering observed in the diffraction patters of akermanite group minerals. One of the investigators of this research is still working in the University of Hanover on these problems.On the second subject, we have constructed a system to measure diffuse scattering. Crystal monchromators (graphite and Si) were installed on a high-power X-ray generator (12kW) and a Weissenberg camera equipped with a cassette for'Imaging plate' was newly developed. The system is working for measurement of diffuse scattering now.On the third subject, we have determined the incommensurate structures of akermanite [Ca_2MgSi_2O_7] and of akermanite solid solution [Ca_2 (Mg, Fe) Si_2O_7] with the description in five-dimensional space. A paper of a crystal-chemical discussion of the incommensurate structure of the latter has been submitted to a journal. Results of the simulation of the diffuse scattering was presented to the annual meeting of German Crystallographic Association in 1997 at Hamburg. Since samples of akermanite solid solution include some domains with different retardation under a microscope, we measured diffuse scatterings from different domains with synchrotron radiation and we are analysing them now. We are also making simulation of the diffuse scattering by a molecular orbital method in order to clarify the origin of the incommensurate modulation, and we could get preliminary results. On dehydration products of hydro-oxides of Al and Fe, our investigator is analysing the diffuse scattering at the University of Hannover now. Less