Thermodynamic properties of anhydrous and hydrous wadsleyite, β−Mg2SiO4
Thermodynamic properties of anhydrous and hydrous wadsleyite, β−Mg2SiO4
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DOI：
10.1080/08957959.2013.806498
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发表时间：
2013-08
影响因子：
2
通讯作者：
S. Jahn;R. Rahner;E. Dachs;M. Mrosko;M. Koch‐Müller
中科院分区：
文献类型：
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作者：
S. Jahn;R. Rahner;E. Dachs;M. Mrosko;M. Koch‐Müller
瓦兹利石，β - Mg₂SiO₄，是一种重要的高压矿物，可能在地球的过渡带中充当水的汇聚处。在这项研究中，我们首先通过实验以及第一性原理模拟确定了常压下无水瓦兹利石的热容和熵。在298 K时测得的标准熵S⁰为86.7(11) J/(mol·K)。然后，进行了扩展模拟以探究压力和水合作用对这些热力学性质的影响。研究了几种氢掺入结构模型的稳定性，并使用能量最低的结构推导出了在常压以及15 GPa下，标称含水量为1.6和3.3 wt%的含水瓦兹利石的振动熵和热容。考虑到对构型熵的估算，预计在常压下，含水量为1.6和3.3 wt%的含水瓦兹利石的S⁰比无水瓦兹利石的S⁰分别高约3.5和5 J/(mol·K)。
Wadsleyite, β-Mg2SiO4, is an important high pressure mineral that may act as a sink of water in the Earth's transition zone. In this study, we first determine the heat capacity and entropy of anhydrous wadsleyite at ambient pressure both experimentally and by first principles simulations. The measured standard entropy S0 at 298 K is 86.7(11) J/(mol K). Then, extended simulations are performed to explore the effect of pressure and hydration on these thermodynamic properties. The stability of several structural models of hydrogen incorporation is investigated and the lowest energy structures are used to derive the vibrational entropy and the heat capacity of hydrous wadsleyite with a nominal content of 1.6 and 3.3 wt% H2O at an ambient pressure and at 15 GPa. Considering an estimation of the configurational entropy, S0 of hydrous wadsleyite with 1.6 and 3.3 wt% H2O is predicted to be about 3.5 and 5 J/(mol K) higher than that of anhydrous wadsleyite at the ambient pressure.