X-ray diffraction reveals two structural transitions in szomolnokite
X-ray diffraction reveals two structural transitions in szomolnokite
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DOI：
10.2138/am-2022-8147
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发表时间：
2022-04
影响因子：
3.1
通讯作者：
O. Pardo;V. Dobrosavljevic;T. Perez;W. Sturhahn;Zhenxian Liu;G. Rossman;J. Jackson
中科院分区：
文献类型：
--
作者：
O. Pardo;V. Dobrosavljevic;T. Perez;W. Sturhahn;Zhenxian Liu;G. Rossman;J. Jackson
摘要在地球、火星和太阳系的冰冷卫星上的各种环境中，已经发现和研究了水合硫酸盐。含水含硫相的地下存在，在任何程度上都需要更好地了解它们在压力下的热力学和弹性性质。端元的实验和计算数据是缺乏的，需要准确地模拟含水，含硫的行星内部。在这项工作中，高压X射线衍射（XRD）和同步辐射傅里叶变换红外光谱（FTIR）测量szomolnokite（FeSO 4·H2O）分别高达83和24 GPa。该研究发现，在5.0（1）和6.6（1）GPa之间，szomolnokite发生单斜-三斜（C2/c到P1）结构相变，在12.7（3）和16.8（3）GPa之间发生以前未知的三斜-单斜（P1到P21）结构相变。通过XRD图谱中出现明显的反射来识别高压转变，该反射不能归因于与P1 β相解离相关的第二相，并且其特征还在于结构内的H2O键合增加。我们为我们的数据中确定的三个相中的每一个相拟合了三阶Birch-Murnaghan状态方程，并重新拟合了已发表的数据，以比较szomolnokite，水镁矾（MgSO 4·H2O）和红柱石（Na 2 Mg（SO 4）2·4 H2O）的弹性参数。在环境压力下，szomolnokite比blödite压缩性低，比kieserite压缩性高，但在7 GPa时，szomolnokite和kieserite具有大致相同的体积模量，而blödite的体积模量在20 GPa时仍低于这两个相。这些结果表明，索钼石的高压单斜相的稳定性和结构内的水保持在行星内部深处发现的压力。
Abstract Hydrated sulfates have been identified and studied in a wide variety of environments on Earth, Mars, and the icy satellites of the solar system. The subsurface presence of hydrous sulfur-bearing phases to any extent necessitates a better understanding of their thermodynamic and elastic properties at pressure. End-member experimental and computational data are lacking and are needed to accurately model hydrous, sulfur-bearing planetary interiors. In this work, high-pressure X-ray diffraction (XRD) and synchrotron Fourier-transform infrared (FTIR) measurements were conducted on szomolnokite (FeSO4·H2O) up to ~83 and 24 GPa, respectively. This study finds a monoclinic-triclinic (C2/c to P1̅) structural phase transition occurring in szomolnokite between 5.0(1) and 6.6(1) GPa and a previously unknown triclinic-monoclinic (P1̅ to P21) structural transition occurring between 12.7(3) and 16.8(3) GPa. The high-pressure transition was identified by the appearance of distinct reflections in the XRD patterns that cannot be attributed to a second phase related to the dissociation of the P1̅ phase, and it is further characterized by increased H2O bonding within the structure. We fit third-order Birch-Murnaghan equations of state for each of the three phases identified in our data and refit published data to compare the elastic parameters of szomolnokite, kieserite (MgSO4·H2O), and blödite (Na2Mg(SO4)2·4H2O). At ambient pressure, szomolnokite is less compressible than blödite and more than kieserite, but by 7 GPa both szomolnokite and kieserite have approximately the same bulk modulus, while blödite’s remains lower than both phases up to 20 GPa. These results indicate the stability of szomolnokite’s high-pressure monoclinic phase and the retention of water within the structure up to pressures found in planetary deep interiors.