Structural Phase Transition and Metallization of Nanocrystalline Rutile Investigated by High-Pressure Raman Spectroscopy and Electrical Conductivity

The pressure-induced photoconductivity enhancement of black-TiO2

The pressure-induced enhancement of the optoelectronic properties of black-TiO2 nanocrystals is presented. The underlying mechanisms are elucidated by comparing the behavior with that of white-TiO2. The disordered layer in black-TiO2 contributes to the enhanced photoconductivity, while the crystal structure dominates in relation to photoconductivity variations. Our findings provide valuable insights for gaining a fundamental understanding of black-TiO2.

Electron Microscope Study of the Pressure-Induced Phase Transformation and Microstructure Change of TiO2 Nanocrystals

Microstructure transformation of materials under compression is crucial to understanding their high-pressure phase transformation. However, direct observation of the microstructure of compressive materials is a considerable challenge, which impedes the understanding of the relations among phase transformation, microstructure, and material properties. In this study, we used transmission Kikuchi diffraction and transmission electron microscopy to intuitively characterize pressure-induced phase transformation and microstructure of TiO2. We observed the changes of twin boundaries with increasing pressure and intermediate phase TiO2-I of anatase transformed into TiO2-II (α-PbO2 phase) for the first time. The following changes occur during this transformation: anatase (diameter of ∼100 nm) → anatase twins 60° along the [110] zone axis → intermediate TiO2-I twins 60° along the [010] zone axis → TiO2-II twins 90° along the [010] zone axis. These results directly reveal the crystallographic relation among these structures, enhancing our understanding of the phase transformation in TiO2 nanocrystals.

Pressure-Induced Structural Phase Transition and Metallization of CrCl3 under Different Hydrostatic Environments up to 50.0 GPa

High-pressure structural, vibrational, and electrical transport properties of CrCl₃ were investigated by means of Raman spectroscopy, electrical conductivity, and high-resolution transmission electron microscopy under different hydrostatic environments using the diamond anvil cell in conjunction with the first-principles theoretical calculations up to 50.0 GPa. The isostructural phase transition of CrCl₃ occurred at 9.9 GPa under nonhydrostatic conditions. As pressure was increased up to 29.8 GPa, CrCl₃ underwent an electronic topological transition accompanied by a metallization transformation due to the discontinuities in the Raman scattering and electrical conductivity, which is possibly belonging to a typical first-order metallization phase transition as deduced from first-principles theoretical calculations. As for the hydrostatic condition, a ∼2.0 GPa pressure delay in the occurrence of two corresponding transformations of CrCl₃ was observed owing to the different deviatoric stress. Upon decompression, we found that the phase transformation from the metal to semiconductor in CrCl₃ is of good reversibility, and the obvious pressure hysteresis effect is observed under different hydrostatic environments. All of the obtained results on the structural, vibrational, and electrical transport characterizations of CrCl₃ under high pressure can provide a new insight into the high-pressure behaviors of representative chromium trihalides CrX₃ (X = Br and I) under different hydrostatic environments.

Some Remarks on the Electrical Conductivity of Hydrous Silicate Minerals in the Earth Crust, Upper Mantle and Subduction Zone at High Temperatures and High Pressures

As a dominant water carrier, hydrous silicate minerals and rocks are widespread throughout the representative regions of the mid-lower crust, upper mantle, and subduction zone of the deep Earth interior. Owing to the high sensitivity of electrical conductivity on the variation of water content, high-pressure laboratory-based electrical characterizations for hydrous silicate minerals and rocks have been paid more attention to by many researchers. With the improvement and development of experimental technique and measurement method for electrical conductivity, there are many related results to be reported on the electrical conductivity of hydrous silicate minerals and rocks at high-temperature and high-pressure conditions in the last several years. In this review paper, we concentrated on some recently reported electrical conductivity results for four typical hydrous silicate minerals (e.g., hydrous Ti-bearing olivine, epidote, amphibole, and kaolinite) investigated by the multi-anvil press and diamond anvil cell under conditions of high temperatures and pressures. Particularly, four potential influence factors including titanium-bearing content, dehydration effect, oxidation−dehydrogenation effect, and structural phase transition on the high-pressure electrical conductivity of these hydrous silicate minerals are deeply explored. Finally, some comprehensive remarks on the possible future research aspects are discussed in detail.

Effects in Band Gap for Photocatalysis in TiO2 Support by Adding Gold and Ruthenium

One of the key features of a nano catalyst for photocatalysis is the band gap, because, through its analysis, the potential of the catalyst can be determined. In this investigation, the impact on the band gap of different catalysts made by the sol–gel method, compared with TiO2 P25 Sigma-Aldrich, showing the effect of using gold or ruthenium as a metal supported on TiO2, with two different dosage percentages of 1 and 3 percent, was analysed. Additionally, two oxidation states of the catalyst, the reduced form and the oxidized form of the metal, were used to see the effect on the band gap. The experiments show that the gold addition has a higher beneficial effect on the band gap for the UV region (ultra violet region), and the ruthenium addition has a higher beneficial effect for the UV/visible region. The preferred oxidation state for the band gap was the oxidized state. The characterisation of the catalyst provided an insight into the relation between the band gap and the catalyst itself.