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Polymorphic phase transition mechanism of compressed coesite

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Polymorphic phase transition mechanism of compressed coesite

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Abstract

 

Silicon dioxide is one of the most abundant natural compounds. Polymorphs of ​SiO2 and their phase transitions have long been a focus of great interest and intense theoretical and experimental pursuits. Here, compressing single-crystal coesite ​SiO2 under hydrostatic pressures of 26–53 GPa at room temperature, we discover a new polymorphic phase transition mechanism of coesite to post-stishovite, by means of single-crystal synchrotron X-ray diffraction experiment and first-principles computational modelling. The transition features the formation of multiple previously unknown triclinic phases of ​SiO2 on the transition pathway as structural intermediates. Coexistence of the low-symmetry phases results in extensive splitting of the original coesite X-ray diffraction peaks that appear as dramatic peak broadening and weakening, resembling an amorphous material. This work sheds light on the long-debated pressure-induced amorphization phenomenon of ​SiO2, but also provides new insights into the densification mechanism of tetrahedrally bonded structures common in nature.

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