Pressure-induced drastic collapse of a high oxygen coordination shell in quartz-like α-GeO2
Pressure-induced drastic collapse of a high oxygen coordination shell in quartz-like α-GeO2
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DOI：
10.1088/1367-2630/16/2/023022
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发表时间：
2014-02-13
影响因子：
3.3
通讯作者：
Chen, Dongliang
中科院分区：
文献类型：
--
作者：
Dong, Juncai;Zhang, Xiaoli;Chen, Dongliang
利用扩展x射线吸收精细结构谱，采用多重散射分析方法，采用单晶金刚石砧细胞和多毛细半透镜相结合的方法，研究了四面体网状石英α - geo2中锗周围的局部结构演变。随着压力的增加，第一壳层Ge-O键的距离略有缩小，而第三壳层Ge-O键的距离则急剧减小。在7-14 GPa范围内，当第3壳层Ge-O键距离落在第2壳层Ge-O键距离的范围内时，第1壳层Ge-O键距离缓慢延长，这是由配位引起的，从4倍增加到6倍。此外，这些特征伴随着四面体间Ge-O-Ge角的闭合和两个四面体内O-Ge-O角的打开，其拓扑结构令人惊讶地呈现出沿c轴的螺旋手性，这与角连接的GeO4四面体的双螺旋相反。这些结果表明，石英和类石英材料中的高压相变可能与结构不稳定性有关，这种不稳定性是由最近的阴离子壳的剧烈坍塌驱动的，这与高对称性阴离子亚晶格的出现是一致的。我们的发现为类石英氧化物的致密化机制提供了重要的见解，这将对我们理解各种后石英晶体相的亚稳态和压力诱导非晶化具有广泛的意义。
With the combination of a single crystal diamond anvil cell and a polycapillary half-lens, the local structural evolution around germanium in tetrahedrally networked quartz-like alpha-GeO2 has been investigated using extended x-ray absorption fine structure spectroscopy of up to 14 GPa by multiple-scattering analysis method. While the first shell Ge-O bond distances show a slight contraction with increasing pressure, the third shell Ge-O bond distances are found to decrease dramatically. The sluggish lengthening of the first shell Ge-O bond distances, initiated by coordination increase from fourfold to sixfold, occurs in the 7-14 GPa range just when the third shell Ge-O bond distances fall in the region of the second shell Ge-Ge bond distances. Moreover, these features are accompanied by the closing of intertetrahedral Ge-O-Ge angles and the opening of two intratetrahedral O-Ge-O angles, whose topological configuration surprisingly exhibits a helical chirality along the c axis that is opposite to the double helices of the corner-linked GeO4 tetrahedra. These results suggest that the high-pressure phase transitions in quartz and quartz-like materials could be associated with a structural instability that is driven by the drastic collapse of the next-nearest-neighbour anion shell, which is consistent with the emergence of high-symmetry anion sublattice. Our findings provide crucial insights into the densification mechanisms of quartz-like oxides, which would have broad implications for our understanding of the metastability of various post-quartz crystalline phases and pressure-induced amorphization.