Kinetic Study on the Crystal Structure Transformation by Time-resolved Measurement of X-ray Diffraction

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Research of the crystal structure and texture of the minerals are necessary for understanding the dynamical phenomena in earth sciences. A new analytical system is designed for the observation of the crystal structure change in the process of the phase transformations, decomposition, melting, recrystallizaton in response to the variation of the physical, conditions, pressure and temperature and stress surround the earth materials. For these research we have developed the following new systems :(1) Angular dispersive measurement for time-resolved diffraction study A new system for time-resolved studies under pressure was composed of four-circle diffractometer with a position sensitive detector having an working angular region of 120^ﾟ and of computer aided measurement and control system. A high photon count efficiency is a large advantage for high pressure X-ray diffraction studies.(2) High pressure apparatus A diamond anvil with an oil-pressure controller was installed on the four-circ … More le diffractometer set on the rotated anode X-ray generator. Pressure was finely controlled by a sensor and measured by the ruby fluorescence method and equation state of internal standard sample of NaCl based on the compressibility.Result 1. Kinetics of polymorphic transition of GeO_2 from hexagonal (quartz-type P321, z=3) to tetragonal (rutile type P4/mmm, z=2) various temperatures under pressure. (1) Hexagonal GeO_2 was transformed to the amorphous phase at 7GPa and 62ﾟC but easily transformed to rutile structure at 85^ﾟC and 0.6GPa. The amorphous phase was successively retained up to 25GPa at room temperature. (2) Full width half maximums (FWHM) of the diffraction peaks became linearly broadened due to reducing crystallite size, indicating the enhancement of the finer-domain. Integrated diffraction intensities were decreased with pressure. (3) A local structure around Ge ion in the quenched amorphous phase was analyzed by EXAFS and Raman spectra at room condition. It was elucidated that amorphous phase was partly composed of 6-fold coordinated Ge ions and that the structure was quite different from that of melted-glass. (4) The amorphous phase was confirmed to be thermodynamically metastable.2. Dehydration Process of Ca (OH) _2 and Mg (OH) _2A time-resolved observation of the dehydration process was undertaken by energy dispersive diffraction using tungsten rotated anode X-ray and synchrotron radiation. The in situ measurements of the spectra up to 900^ﾟC were carried out by intrinsic Ge SSD in the energy range 10keV-40kev. Integrated intensities obtained by the profile fitting provide the mass ratio of oxide products to hydrates. Less