Melting behavior of SiO2 up to 120 GPa
Melting behavior of SiO2 up to 120 GPa
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DOI：
10.1007/s00269-019-01077-3
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发表时间：
2020-01
影响因子：
1.4
通讯作者：
D. Andrault;G. Morard;G. Garbarino;M. Mezouar;M. Bouhifd;Tatsuhiko Kawamoto
中科院分区：
文献类型：
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作者：
D. Andrault;G. Morard;G. Garbarino;M. Mezouar;M. Bouhifd;Tatsuhiko Kawamoto
液态硅酸盐的结构通常被描述为各种原子实体的统计混合物，其相对丰度可以随压力、温度和组成而变化。不幸的是，这种观点仍然主要是理论上的，由于缺乏实验报告的硅酸盐熔体结构，特别是在压力下。我们对SiO2端元进行了X射线衍射，以探测高达~ 120 GPa和7000 K的熔化曲线以及高达~ 80 GPa的熔体结构。我们证实了陡峭的增加的熔融曲线以上~ 14 GPa时，斯铁云母变得稳定柯石英在亚固相线条件下，与约80 K/GPa的斜率。然后，在45 GPa和5400 K附近，熔化曲线显著变窄，这种效应很可能反映了SiO2熔体结构的致密化。扩散X-射线散射的信号是兼容的Si配位数从4到6的变化沿着熔化曲线，在与以前的作品报告了类似的演变过程中的SiO2玻璃的冷压缩。由于有限的压力范围内（在10至20 GPa），其中的熔化曲线改变其斜率，我们推测一个困难的共存四面体SiO 4和八面体SiO 6在SiO2熔体在高压下。
The structure of liquid silicates is commonly described as a statistical mixture of various atomic entities with relative abundances that can vary with pressure, temperature, and composition. Unfortunately, this view remains largely theoretical due to scarce experimental reports on the silicate melt structure, in particular under pressure. We performed X-ray diffraction of the SiO2end member to probe the melting curve up to ~ 120 GPa and 7000 K, and the melt structure up to ~ 80 GPa. We confirm the steep increase of the melting curve above ~ 14 GPa when stishovite becomes stable over coesite in subsolidus conditions, with a slope of about 80 K/GPa. Then, around 45 GPa and 5400 K, the melting curve flattens significantly, an effect most likely reflecting the densification of the SiO2melt structure. The signal of diffuse X-ray scattering is compatible with a change of the Si coordination number from 4 to 6 along the melting curve, in agreement with previous works reporting a similar evolution during the cold compression of SiO2glass. Because of the limited pressure range (within 10 to 20 GPa) in which the melting curve changes its slope, we speculate a difficult coexistence of tetrahedral SiO4and octahedral SiO6units in SiO2melt at high pressures.