辉石结构与相变的第一性原理研究

发布时间：2018-05-03 21:23

本文选题：第一性原理 + 辉石　；参考：《高压物理学报》2017年02期

【摘要】：利用第一性原理方法研究了Mg端员辉石(MgSiO3)低压相(Pbca、P2_1/c)和高压相(C2/c、P2_1ca)在不同压力下(0~30GPa)的结构。首先计算得到了不同压力下各相的晶胞体积,并由状态方程拟合得到了体积模量,结果显示在零温零压条件下Pbca和P2_1/c(低压单斜相)的体积模量相近,C2/c的体积模量最大(比Pbca的大3%),而P2_1ca作为高压相其体积模量却比Pbca小很多。其次分析了Mg端员辉石3个轴向的压缩性,发现C2/c相的c轴比a轴难压缩,与前人研究的透辉石(MgCaSi2O6)的表现相反。P2_1/c、C2/c、P2_1ca的链角随着压力的增大而减小;Pbca其中一种链角的变化趋势和其他3个相一样,而另一种链角先随着压力的增大而减小,在达到7GPa后开始增大,可能表示相的不稳定或开始相变。最后通过研究不同相之间的焓值差,讨论了Mg端员辉石在低温高压下可能存在的相变情况。
[Abstract]:The structures of the low pressure phase Pbcao 2 / c) and the high pressure phase C 2 / C 2 C 2 1 Ca) of mg terminal pyroxene MgSiO 3 are studied by using the first principle method under different pressures. The cell volume of each phase is calculated at different pressures, and the bulk modulus is obtained by fitting the equation of state. The results show that at zero temperature and zero pressure, the volume modulus of Pbca and P21 / c (low pressure monoclinic phase) is similar to that of C2 / c (3% larger than that of Pbca), while the volume modulus of P2_1ca as high pressure phase is much smaller than that of Pbca. Secondly, the compressibility of mg end member pyroxene is analyzed. It is found that the C axis of C 2 / c phase is more difficult to compress than that of a axis. The chain angle of Pbca decreases with the increase of pressure, and the change trend of one chain angle is the same as that of the other three phases, while the other chain angle decreases with the increase of pressure. The increase of 7GPa may indicate the instability of phase or the beginning of phase transition. Finally, the phase transition of mg terminal pyroxene at low temperature and high pressure is discussed by studying the enthalpy difference between different phases.
【作者单位】：中国科学院计算地球动力学重点实验室;中国科学院大学地球科学学院;
【基金】：国家自然科学基金(41274091,41674089)
【分类号】：O469

【相似文献】