Variation of the oxygen content and point defects in olivines, (Fex Mg1−x)2SiO4, 0.2 ≤ x ≤ 1.0
Variation of the oxygen content and point defects in olivines, (Fex Mg1−x)2SiO4, 0.2 ≤ x ≤ 1.0
复制标题
橄榄石中氧含量和点缺陷的变化，(Fex Mg1−x)2SiO4, 0.2 ≤ x ≤ 1.0
DOI：
10.1007/s00269-002-0283-1
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发表时间：
2002
影响因子：
1.4
通讯作者：
R. Dieckmann
中科院分区：
文献类型：
--
作者：
T. Tsai;R. Dieckmann
用热重法研究了0.2≤x≤1.0的橄榄石（FexMg1−x）2SiO4中氧含量的变化规律。在1130°C和1200°C时，测量了氧活度变化引起的质量变化，作为氧活度和阳离子组成的函数。在测量过程中，样品与含有CO， CO2和N2的气体直接接触，并且在样品堆底部的几个点也与SiO2直接接触。通过拟合实验数据的质量变化方程推导热力学利用点缺陷,这是显示为橄榄石0.2≤≤0.2 x 1.0≤1130°C和x 0.7≤1200°C氧活动范围内调查,观测到的氧气含量变化与阳离子空缺和Fe3 +离子M网站和Fe3 +离子在硅网站多数缺陷如果认为只有三种类型的点缺陷发生在大多数缺陷。考虑了不同的情况，封闭体系，考虑到ξ=[Si]/([Si]+[Fe]+[Mg])不一定等于1/3，橄榄石与SiO2或辉石处于平衡状态。本研究中观察到的氧含量变化明显小于先前文献报道的变化。有人提出，这些差异与早期研究中用作样品支架的贵金属容器中铁的溶解和/或二次相的存在有关。
Abstract The variation of the oxygen content in olivines, (FexMg1−x)2SiO4, with 0.2 ≤ x ≤ 1.0, was investigated by thermogravimetric measurements. Mass changes occurring upon oxygen activity changes were measured as a function of oxygen activity and cationic composition at 1130 and 1200 °C. During the measurements the samples were in direct contact with gases containing CO, CO2 and N2 and, at a few spots at the bottom of the sample stack, also with SiO2. By fitting experimental data of mass changes to equations derived using point defect thermodynamics, it was shown for olivines with 0.2 ≤ x ≤ 1.0 at 1130 °C and 0.2 ≤ x ≤ 0.7 at 1200 °C within the oxygen activity ranges investigated that the observed variations in the oxygen contents are compatible with cation vacancies and Fe3+ ions on M sites and Fe3+ ions on silicon sites as majority defects if it is assumed that only three types of point defects occur as majority defects. Different cases were considered, closed systems, taking into account that ξ=[Si]/([Si]+[Fe]+[Mg]) is not necessarily equal to 1/3, and olivines in equilibrium with SiO2 or pyroxenes. The oxygen content variations observed in this study are significantly smaller than those reported previously in the literature. It is proposed that these differences are related to the dissolution of Fe into noble metal containers used as sample holders in earlier studies and/or to the presence of secondary phases.