Anomalous density, sound velocity, and structure of pressure-induced amorphous quartz

Abstract

The study of quartz and other silica systems under pressure is one of the most prolific domains of research over the past 50 years because of their applications in material science and fundamental relevance to planetary interiors. The characterization of the amorphous state is essential for the comprehension of pressure-induced amorphization of minerals, the metamorphism observed in shocked materials, and the study of melt structures under pressure. Here, we measured in situ, under static compression the density, sound velocities, and electronic structure of quartz as it passes through its pressure-induced amorphization transition. The transition pressure could be derived from the abrupt increase in density and sound velocity at 24 GPa, and from strong changes in the silicon L 2,3 edge and oxygen K edge between 22 and 27 GPa observed in x-ray Raman scattering data, confirming previous results from x-ray diffraction. Above this pressure, our data show an anomalous behavior in density, sound velocity, and electronic fine structure compared to the cold compressed glass and other silica polymorphs. The pressure-induced amorphous quartz has a lower density relative to that of the compressed glass, consistent with the lower average coordination inferred from a different signature in the Si L 2,3 and O K electronic absorption edges measured by x-ray Raman scattering spectroscopy. This behavior sheds light on the pressure limit of tetrahedral units in SiO 2 components and the existence of polyamorphism in network-forming materials, and highlights the possibility to discriminate between different amorphous states with x-ray Raman scattering spectroscopy.

Atomic surface of quartz glass induced by photocatalytic green chemical mechanical polishing using the developed SiO2@TiO2 core–shell slurry

“…This leads to the excitation of TiO 2 from the valence band to the conduction band, resulting in the generation of free electrons. 39,40 Simultaneously, positively charged holes are formed in the valence band, leading to the generation of more ˙OH radicals, 36 as shown in eqn (2) and (3).TiO 2 + hν → h + + e − H 2 O + h + → ˙OH + H 2 …”

“…The quartz glass is composed of 99.9% SiO 2 . 36 In the case of single-abrasives, TiO 2 exhibits a relatively low hardness of 6–6.5 when used for abrasives. Consequently, TiO 2 is unable to rapidly remove the reaction layer, resulting in relatively poor mechanical polishing efficiency.…”

“…9(b) . The quartz glass surfaces before and after polishing exhibited clear absorption peaks at 460 cm −1 , 605 cm −1 , 36 794 cm −1 , and 1050 cm −1 . Among them, the band at 460 cm −1 corresponds to the bending vibration peak of the silicon–oxygen bond, while the bands at 605 cm −1 and 1070 cm −1 correspond to the stretching vibration peaks of the silicon–oxygen bond.…”