Andrault D, Fiquet G, Guyot F, Hanfland M
D. Andrault, Laboratoire des Geomateriaux, Institut de Physique du Globe, Paris 75252, France. G. Fiquet, Laboratoire de Geologie, Ecole Nationale Superieure de Lyon, Lyon 69364, France. F. Guyot, Laboratoire de Mineralogie-Cristallographie,
Science. 1998 Oct 23;282(5389):720-4. doi: 10.1126/science.282.5389.720.
A Rietveld structural analysis of stishovite, with angle-dispersive x-ray diffraction synchrotron source at the European Synchrotron Radiation Facility, confirmed a CaCl2 form of stishovite distortion at 54 +/- 1 gigapascals but confirmed no further phase transformation up to 120 gigapascals. The deviatoric stress that is usually encountered at such pressures was relaxed after yttrium-aluminum-garnet-laser heating. A single Birch-Murnaghan equation of state fits volumes of stishovite and a CaCl2 form, showing that the tetragonal distortion occurs without a substantial change in volume. At the 54-gigapascal transition, the pressure-induced lattice modifications were similar to those found in a Landau-type temperature-induced transition. It is proposed that, above the transition pressure, the critical temperature increases above 300 kelvin, so that the lower entropy form becomes stable.
利用欧洲同步辐射装置的角散射X射线衍射同步辐射源对斯石英进行的里特维尔德结构分析证实，在54±1吉帕斯卡的压力下，斯石英呈现出CaCl₂形式的畸变，但在高达120吉帕斯卡的压力下未发现进一步的相变。钇铝石榴石激光加热后，在这种压力下通常遇到的偏应力得到了缓解。一个单一的Birch-Murnaghan状态方程拟合了斯石英和CaCl₂形式的体积，表明四方畸变发生时体积没有实质性变化。在54吉帕斯卡的转变点，压力诱导的晶格变化与在朗道型温度诱导转变中发现的变化相似。有人提出，在转变压力以上，临界温度升高到300开尔文以上，从而使熵较低的形式变得稳定。
