High-temperature structural behavior of a stuffed derivative of α-quartz, Mg0.5AlSiO4, has been investigated using in situ synchrotron-based angle-dispersive powder X-ray diffraction (XRD) from 299 to 1273 K. Rietveld analysis of the XRD data indicates that the framework of Mg0.5AlSiO4 remains isostructural with α-quartz throughout the temperature range tested. As in α-quartz, unit-cell parameters a and c and cell volume V of Mg0.5AlSiO4 increase with increasing temperature, primarily due to progressive tilting of [(Al,Si)O4] tetrahedra along the a axes. However, the rates of increase in the cell parameters and the rate of decrease in the tetrahedral tilt angle (δ) are much smaller for Mg0.5AlSiO4 than for α-quartz. This behavior can be attributed to the occupancy of Mg2+ over the octahedral channel sites in the α-quartz-type framework, effectively hindering the [(Al,Si)O4] tetrahedral tilting. As a result, the α- to β-quartz phase transformation, which exists in silica at 846 K, does not occur in Mg0.5AlSiO4 up to 1273 K, and probably beyond, to its melting point.

中文翻译：

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α-石英填充衍生物 Mg0.5AlSiO4 在高温下的结构行为：原位同步加速器 XRD 研究

使用基于原位同步加速器的角色散粉末 X 射线衍射 (XRD) 从 299 到 1273 K 研究了 α-石英填充衍生物 Mg0.5AlSiO4 的高温结构行为。 XRD 数据的 Rietveld 分析表明 Mg0.5AlSiO4 的骨架在整个测试温度范围内与 α-石英保持同构。与α-石英一样，Mg0.5AlSiO4 的晶胞参数 a 和 c 以及晶胞体积 V 随着温度升高而增加，这主要是由于 [(Al,Si)O4] 四面体沿 a 轴逐渐倾斜。然而，Mg0.5AlSiO4 的电池参数增加率和四面体倾斜角 (δ) 的减少率比 α-石英小得多。这种行为可归因于 Mg2+ 在 α-石英型框架中的八面体通道位点上的占据，有效地阻止了 [(Al,Si)O4] 四面体倾斜。因此，在 846 K 时存在于二氧化硅中的 α- 到 β-石英相变在 Mg0.5AlSiO4 中不会发生，直至 1273 K，甚至可能超过其熔点。