The Activation Energy of the Back Transformation of Silicate Perovskite to Enstatite
The Activation Energy of the Back Transformation of Silicate Perovskite to Enstatite
复制标题
硅酸盐钙钛矿向顽火辉石逆转变的活化能
DOI：
10.1029/gm039p0243
复制
发表时间：
2013
期刊：
影响因子：
--
通讯作者：
R. Jeanloz
中科院分区：
文献类型：
--
作者：
E. Knittle;R. Jeanloz
在零压力下测量了钙钛矿结构中的(Mg0.9Fe0.1)SiO3向顽辉石结构反向转变的活化能。活化能为 70 (±20) kJ/摩尔，与许多其他硅酸盐的蠕变、扩散和相变值相比很小。我们认为，这种转变可能是通过中心镁离子（或相应的空位）穿过钙钛矿结构十二面体表面的四个氧离子的移动来激活的。根据高温下 Mg-O 键振动振幅的简单谐波模型，预计 Mg 离子的这种迁移性会在活化能为 60 kJ/摩尔（根据我们的测量）和活化体积接近 1 cm−1/摩尔的情况下发生。硅酸盐钙钛矿的活化能值较小的含义如下：1）地球中的钙钛矿相变不应存在动力障碍； 2）任何位于地球表面的捕虏体中的硅酸盐钙钛矿都会在地质上短暂的时间内（3-100年）恢复为顽火辉石，因此最大限度地减少了在地球表面发现这种高压相作为天然样本的机会。
The activation energy for the back transformation of (Mg0.9Fe0.1) SiO3in the perovskite structure to the enstatite structure has been measured at zero pressure. The activation energy is 70 (±20) kJ/mole, small in comparison with values for creep, diffusion and phase transitions in many other silicates. We suggest that the transition may be activated by movement of the central Mg ion (or the corresponding vacancy) through the four oxygen ions of the dodecahedral face of the perovskite structure. From a simple harmonic model of the amplitudes of vibration of Mg‐O bonds at elevated temperature, this mobility of the Mg ions is expected to occur with an activation energy of 60 kJ/mole (in accord with our measurement) and an activation volume near 1 cm−1/mole. Implications of the small value of the activation energy for silicate perovskite are as follows: 1) there should be no kinetic hindrance to the perovskite phase transition in the earth; 2) any silicate perovskite emplaced on the earth's surface in a xenolith would revert to enstatite in a geologically brief time (3–100 years), therefore minimizing the chances of finding this high‐pressure phase as a natural sample on the earth's surface.