High‐pressure torsion of SiO <sub>2</sub> quartz sand: Phase transformation, optical properties, and significance in geology
Qing Wang, Kaveh Edalati, Ikuro Fujita, Motonori Watanabe, Tatsumi Ishihara, Zenji Horita
Abstract
Abstract Phase transformation and optical properties of silica (silicon dioxide, SiO 2 ) quartz sand under high pressure/temperature has been of interest in geology and optical physics for many years. In this study, besides high pressure/temperature, high plastic strain is simultaneously applied to the quartz sand by high‐pressure torsion (HPT) processing. The material shows oxygen vacancy formation and transformation to (a) a denser nanocrystalline quartz phase, (b) a high‐temperature amorphous phase and (c) a high‐pressure coesite phase. These structural and microstructural changes lead to light absorbance, electron spin resonance, photoluminscence and photocatalytic activity, while these changes are enhanced by increasing strain. This study introduces a possible pressure‐temperature‐strain‐based mechanism for the formation of naturally observed vacancies and coesite phase in SiO 2 ‐based minerals and sands.