X-ray Rietveld and 57Fe Mössbauer studies of epidote and piemontite on the join Ca2Al2Fe3+Si3O12(OH)–Ca2Al2Mn3+Si3O12(OH) formed by hydrothermal synthesis
X-ray Rietveld and 57Fe Mössbauer studies of epidote and piemontite on the join Ca2Al2Fe3+Si3O12(OH)–Ca2Al2Mn3+Si3O12(OH) formed by hydrothermal synthesis
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DOI：
10.2138/am.2010.3418
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发表时间：
2010-08
影响因子：
3.1
通讯作者：
M. Nagashima;M. Akasaka
中科院分区：
文献类型：
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作者：
M. Nagashima;M. Akasaka
用X射线Rietveld和57Fe穆斯堡尔方法研究了Ca2Al2Fe3+qMn3+1-qSi3O12.5合成绿帘石/蒙脱石中Fe3+和Mn3+在八面体M1、M2和M3位上的分布及其对晶体结构的影响。以Q=1.0、0.75、0.5和0.25为起始原料，在200-400 Mpa、500℃的压力下，利用标准冷封压力容器，将绿辉石和膨润土晶化为几乎单一的相。用Mn_2O_3-MnO_2缓冲液生产足以维持Fe~(3+)和Mn~(3+)的₂。Rietveld精化收敛到拟合度范围从1.21到1.60。在此温度下，Σ(Fe~(3+)+Mn~(3+))对八面体晶位的择优取向为M3>；M1(>；>；M2)。Σ(Fe3++Mn3+)的Kd=[(Fe3++Mn3+)/Al]M1/[(Fe3++Mn3+)/Al]M3，(0.0 5~0.13)分别与单独的Mn3+和Fe3+与Al3+的Kd值相近。但M1和M3的Kd=(Fe3+/Mn3+)M1/(Fe3+/Mn3+)M3的Kd值随Fe3+总：Mn3+总比例的不同而变化。在Fe3+含量大于0.4个原子/摩尔单位(APFU)和Mn3+>0.6APFU的绿帘石中，Fe3+对M1的选择性强于Mn3+。在Fe3+含量为0.12，Mn3+含量为0.73-0.78的沸石中，Mn3+对M1的选择性大于Fe3+。单独的Mn3+和Fe3+的位置占有率由各自的Kd值和相应的绿帘石和云母中的Mn3+和Fe3+浓度决定。晶胞参数的变化表明，Al-↔-Fe~(3+)取代引起的线性变化和Al-↔-Mn~(3+)取代引起的非线性变化共同作用。
Abstract Fe3+ and Mn3+ distributions on octahedral M1, M2, and M3 sites in synthetic epidote/piemontite from Ca2Al2Fe3+q Mn3+1-qSi3O12.5 starting material and their effects on the crystal structure were investigated using X-ray Rietveld and 57Fe Mössbauer methods. Epidote and piemontite were crystallized as almost single phases from q = 1.0, 0.75, 0.5, and 0.25 starting materials at Pfluid of 200-400 MPa and a temperature of 500 °C, using standard cold-seal pressure vessels. The Mn2O3-MnO2 buffer was used to produce fO₂ adequate to maintain Fe3+ and Mn3+. The Rietveld refinements converged to goodness-of-fit ranges from 1.21 to 1.60. At this temperature, site preferences of Σ(Fe3++Mn3+) for octahedral sites are M3>M1(>>M2). KD values of Σ(Fe3++Mn3+), where KD = [(Fe3++Mn3+)/Al]M1/[(Fe3++Mn3+)/Al]M3, (0.05-0.13) are similar to those of individual Mn3+ and Fe3+ vs. Al3+, respectively. However, the KD values of Fe3+ and Mn3+ for M1 and M3, where KD = (Fe3+/Mn3+)M1/(Fe3+/Mn3+)M3, vary with Fe3+ Total:Mn3+ Total ratios. In epidote with Fe3+ content larger than 0.4 atoms per formula unit (apfu) and Mn3+ < 0.6 apfu, Fe3+ has a stronger preference for M1 than Mn3+. In piemontite with 0.12 Fe3+ and 0.73-0.78 Mn3+ apfu, the preference of Mn3+ for M1 is greater than that of Fe3+. The site occupancies of individual Mn3+ and Fe3+ are governed by the individual KD values and the Mn3+ and Fe3+ concentrations in corresponding epidote and piemontite. Variations of the unit-cell parameters indicate the combined result of linear variation due to Al ↔ Fe3+ substitution and nonlinear variation due to Al ↔ Mn3+ substitution.