Distribution of Cr3+ between octahedral and tetrahedral sites in synthetic blue and green (CaMgSi2O6)95(CaCrAlSiO6)5 diopsides
Distribution of Cr3+ between octahedral and tetrahedral sites in synthetic blue and green (CaMgSi2O6)95(CaCrAlSiO6)5 diopsides
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DOI：
10.1180/mgm.2019.1
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发表时间：
2019-02
影响因子：
2.7
通讯作者：
M. Akasaka;Yohei Takasu;M. Handa;M. Nagashima;M. Hamada;T. Ejima
中科院分区：
文献类型：
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作者：
M. Akasaka;Yohei Takasu;M. Handa;M. Nagashima;M. Hamada;T. Ejima
研究了[CaMgSi 2 O 6（Di）]95[CaCrAlSiO 6（CrAlTs）]5（mol.%）玻璃中蓝色和绿色透辉石中Cr ~（3+）的分布。确定使用Rietveld精修的X射线衍射数据，以评估通过光学光谱分析公布的结果，并澄清Cr 3 +-Al 3+分布之间的八面体M1和四面体T网站上的晶体结构的影响。起始材料是在800°C下从玻璃中结晶2天的Di 95 CrAlTs 5-透辉石。在800°C和1000°C下持续7天的另外19天之后，透辉石保持蓝色。通过在1200 ℃下加热3天，蓝色透辉石逐渐变为蓝绿色，7天后变为绿色。合成相的化学计量组成，证实了电子探针分析。通过Rietveld方法细化的Cr占位率导致M1和T部位的部位人群：M1[Mg0.95Cr0.030（4）Al0.020]T[Si1.950Cr0.020Al0.030]和M1[Mg0.95Cr0.037（4）Al0.020]T[ www.example.com ] 13]T[Si1.950Cr0.013Al0.037]（每6个氧）分别为蓝色透辉石在800和1000°C：M1[Mg0.95Cr0.042（3）Al0.008]T[Si1.950Cr0.008Al0.042]，用于120 ℃下的蓝绿色透辉石0 °C下3天;和M1[Mg 0.95 Cr 0.049（3）Al 0.001]T[Si1.950Cr0.001Al0.049]对于绿色透辉石在1200 ℃下7天。这种Cr和Al分布影响八面体和四面体配位多面体的体积和位置畸变：蓝色透辉石的TO 4四面体体积（2.251-2.258 μ 3）大于绿色透辉石（2.237 3）;前者的M1 O 6八面体体积（11.74-11.77 μ 3）小于后者（11.86 3）;蓝色透辉石中的TO 4四面体（=1.006; σθ（泰特）2 = 24.37-24.69）比绿色透辉石的畸变小（= 1.007; σθ（泰特）2 = 27.94），前者的M_1O_6八面体（=1.006; σθ（oct）2 = 20.39-21.13）比后者（= 1.005; σθ（oct）2 = 17.58）畸变更大。
Abstract The distribution of Cr3+ ions in blue and green diopsides crystallised from a glass with the composition [CaMgSi2O6 (Di)]95[CaCrAlSiO6 (CrAlTs)]5 (mol.%) was determined using Rietveld refinement of X-ray diffraction data in order to evaluate published results by optical spectroscopic analysis, and to clarify the influence of Cr3+–Al3+ distribution between the octahedral M1 and tetrahedral T sites on the crystal structure. The starting material was Di95CrAlTs5-diopside crystallised from glass at 800°C for 2 days. After another 19 days at 800°C and 1000°C for 7 days, the diopsides remained blue. The blue diopside gradually changed to bluish green by heating at 1200°C for 3 days and to green after 7 days. The stoichiometric compositions of the synthesised phases were confirmed by electron microprobe analysis. The Cr occupancies refined by the Rietveld method resulted in the site populations in the M1 and T sites: M1[Mg0.95Cr0.030(4)Al0.020]T[Si1.950Cr0.020Al0.030] and M1[Mg0.95Cr0.037(4)Al0.013]T[Si1.950Cr0.013Al0.037] (per 6 oxygens) for the blue diopsides at 800 and 1000°C, respectively: M1[Mg0.95Cr0.042(3)Al0.008]T[Si1.950Cr0.008Al0.042] for the bluish green diopside at 1200°C for 3 days; and M1[Mg0.95Cr0.049(3)Al0.001]T[Si1.950Cr0.001Al0.049] for the green diopside at 1200°C for 7 days. Such Cr and Al distributions effect the volumes and site distortions of the octahedral and tetrahedral coordination polyhedra: the TO4 tetrahedron volumes of the blue diopsides (2.251–2.258 Å3) are larger than that of the green diopside (2.237 Å3); the M1O6 octahedron volumes of the former (11.74–11.77 Å3) are smaller than that of the latter (11.86 Å3); the TO4 tetrahedra in the blue diopside ( =1.006; σθ(tet)2 = 24.37–24.69) are less distorted than that of the green diopside ( = 1.007; σθ(tet)2 = 27.94); the M1O6 octahedra in the former ( =1.006; σθ(oct)2 = 20.39–21.13) are more distorted than that of the latter ( = 1.005; σθ(oct)2 = 17.58).