Metastable silica high pressure polymorphs as structural proxies of deep Earth silicate melts.,Nature Communications

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Metastable silica high pressure polymorphs as structural proxies of deep Earth silicate melts.
Nature Communications ( IF 14.7 ) Pub Date : 2018-11-15 , DOI: 10.1038/s41467-018-07265-z
E Bykova _{1,

2} , M Bykov _{2,

3} , A Černok _{2,

4} , J Tidholm ₅ , S I Simak ₅ , O Hellman _{5,

6} , M P Belov ₃ , I A Abrikosov ₅ , H-P Liermann ₁ , M Hanfland ₇ , V B Prakapenka ₈ , C Prescher _{8,

9} , N Dubrovinskaia ₁₀ , L Dubrovinsky ₂

Affiliation

Photon Sciences, Deutsches Elektronen-Synchrotron (DESY), Notkestraße 85, 22607, Hamburg, Germany.
Bayerisches Geoinstitut, University of Bayreuth, Universitätsstraße 30, 95440, Bayreuth, Germany.
Materials Modeling and Development Laboratory, National University of Science and Technology 'MISIS', Leninsky Avenue 4, 119049, Moscow, Russia.
School of Physical Sciences, The Open University, Walton Hall, Milton Keynes, MK7 6AA, UK.
Department of Physics, Chemistry and Biology, Linköping University, SE-581 83, Linköping, Sweden.
Department of Applied Physics and Materials Science, California Institute of Technology, 1200 East California Boulevard, Pasadena, California, 91125, USA.
European Synchrotron Radiation Facility (ESRF), 6 Rue Jules Horowitz, 38000, Grenoble, France.
Center for Advanced Radiation Sources, University of Chicago, 5640 South Ellis Avenue, Chicago, Illinois, 60637, USA.
Institute of Geology and Mineralogy, Universität zu Köln, Zülpicher Straße 49b, 50674, Köln, Germany.
Material Physics and Technology at Extreme Conditions, Laboratory of Crystallography, University of Bayreuth, Universitätsstraße 30, 95440, Bayreuth, Germany.

Modelling of processes involving deep Earth liquids requires information on their structures and compression mechanisms. However, knowledge of the local structures of silicates and silica (SiO₂) melts at deep mantle conditions and of their densification mechanisms is still limited. Here we report the synthesis and characterization of metastable high-pressure silica phases, coesite-IV and coesite-V, using in situ single-crystal X-ray diffraction and ab initio simulations. Their crystal structures are drastically different from any previously considered models, but explain well features of pair-distribution functions of highly densified silica glass and molten basalt at high pressure. Built of four, five-, and six-coordinated silicon, coesite-IV and coesite-V contain SiO₆ octahedra, which, at odds with 3^rd Pauling's rule, are connected through common faces. Our results suggest that possible silicate liquids in Earth's lower mantle may have complex structures making them more compressible than previously supposed.

中文翻译：

亚稳二氧化硅高压多晶型物作为深层地球硅酸盐熔体的结构代表。

涉及地球深层液体的过程建模需要有关其结构和压缩机制的信息。_{然而，对于深部地幔条件下硅酸盐和二氧化硅（SiO 2} ）熔融的局部结构及其致密化机制的了解仍然有限。在这里，我们报告了使用原位单晶 X 射线衍射和从头计算模拟的亚稳态高压二氧化硅相柯石英 IV 和柯石英 V 的合成和表征。它们的晶体结构与以前考虑的任何模型都截然不同，但很好地解释了高压下高致密化石英玻璃和熔融玄武岩的配对分布函数的特征。柯石英-IV 和柯石英-V 由四配位、五配位和六配位硅构成，包含 SiO _{6八面体，它们通过公共面连接，这与}^第三鲍林规则不一致。我们的结果表明，地球下地幔中可能存在的硅酸盐液体可能具有复杂的结构，使其比之前认为的更容易压缩。

更新日期：2018-11-15

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