Effective factors in the kinetics of pressure-induced transformation.

石英-辅酶转化的动力学在4GPa和650、750和850℃下被调查，使用石英单晶体和丰富的样品。光学微观观测，用于部分转化的单晶体样本，以指示在石英颗粒和生长的表面上的coesite heterogeneously nucleates。Coesite的增长率是晶体学取向的独立性。“不相干的颗粒-边界核和界面-控制增长的机制似乎在转变期间运行。”“Coesite rims的厚度增加了线性地作为时间的一个功能和增长率明显取决于温度。”The activation energy for growth of coesite is determined as 85 （±11） kJ/mol and this value is significantly small in comparison with that determined for powdered samples.Synchrotron x-ray powder diffraction studies were performed on Ca（OH）y D22 y D2 and Mg（OH）y D22 y D2 under room temperature pressuriization to 10.4 GPa and 16.0 GPa， respectively。我们在日本KEK的光子工厂使用了钻石铁砧电池技术和数据，收集了BL-18 C的成像板探测器。C轴比A轴要温和得多，而且，C/a比率的降低与压力有关。在压缩曲线中没有明显的不连续性。O原子的原子位置（1/3， 2/3， z），已经成功地利用Rietveld分析的X射线粉末差异模式。In Mg（OH）イイD22イエD2， a change of compression mechanism is observed at 11 GPa。However， in Ca（OH）イイD22イエD2， it is concluded that the shortening of the interlayer spacing controlls compression below the amorphization pressure and no change of compression mManagement ism has occurred。It has been reported that H disorder occurs at a pressure in Mg（OH）イイD22イエD2 and the present results clearly suggest that the H disorder has great influence on the compression behavior。

The kinetics of the quartz-coesite transformation were investigated at 4 GPa and 650, 750 and 850℃ using quartz single crystal and powdered samples. Optical microscopic observations for partly transformed single crystal samples indicate that the coesite heterogeneously nucleates on the surface of the quartz grain and grows into the interior. The growth rate of coesite is independent of crystallographic orientations. The mechanism of incoherent grain-boundary nucleation and interface-controlled growth seems to operate during the transformation. The thickness of the coesite rims increases linearly as a function of time and the growth rate clearly depends on temperature. The activation energy for growth of coesite is determined as 85 (±11) kJ/mol and this value is significantly small in comparison with that determined for powdered samples.Synchrotron x-ray powder diffraction studies were performed on Ca(OH)ィイD22ィエD2 and Mg(OH)ィイD22ィエD2 under room temperature pressurization to 10.4 GPa and 16.0 GPa, respectively. We used the diamond anvil cells technique and the data were collected with an imaging plate detector at BL-18C in Photon Factory at KEK, Japan. The c-axis is much softer than the a-axis and, thus, the c/a ratio decreases with pressure. There is no remarkable discontinuity in the compression curves. The atomic position of O atoms, (1/3, 2/3, z), has been successfully refined using Rietveld analysis of x-ray powder diffraction patterns. In Mg(OH)ィイD22ィエD2, a change of compression mechanism is observed at 11GPa. However, in Ca(OH)ィイD22ィエD2, it is concluded that the shortening of the interlayer spacing controls compression below the amorphization pressure and no change of compression mechanism has occurred. It has been reported that H disorder occurs at a pressure in Mg(OH)ィイD22ィエD2 and the present results clearly suggest that the H disorder has great influence on the compression behavior.