Time-resolved Raman spectroscopy for monitoring the structural evolution of materials during rapid compression.

Rapid compression experiments performed using a dynamic diamond anvil cell (dDAC) offer the opportunity to study compression rate-dependent phenomena, which provide critical knowledge of the phase transition kinetics of materials. However, direct probing of the structure evolution of materials is scarce and so far limited to the synchrotron based x-ray diffraction technique. Here, we present a time-resolved Raman spectroscopy technique to monitor the structural evolutions in a subsecond time resolution. Instead of applying a shutter-based synchronization scheme in previous work, we directly coupled and synchronized the spectrometers with the dDAC, providing sequential Raman data over a broad pressure range. The capability and versatility of this technique are verified by in situ observation of the phase transition processes of three rapid compressed samples. Not only the phase transition pressures but also the transition pathways are reproduced with good accuracy. This approach has the potential to serve as an important complement to x-ray diffraction applied to study the kinetics of phase transitions occurring on time scales of seconds and above.

Note: a novel method to measure the deformation of diamond anvils under high pressure.

A novel and simple method based on optical-fiber frequency domain interferometer to measure the deformation of diamond anvils under high pressure is presented. The working principle and application examples are given in this paper. The deformation of diamond anvils is obtained up to 37.7 GPa, our results verify that the deformation has an obvious difference between uploading and downloading at a given pressure, the maximum difference is up to 4.5 µm at 18.8 GPa, and the cupping effect is observed directly.

Pressure-induced structural phase transition and equation of state of LiTaO3.

Using in situ high-pressure x-ray diffraction and ab initio techniques, a high-pressure structure of LiTaO3 has been determined to be an orthorhombic phase with the space group Pnma. At ambient temperature, the transition pressure from the R3c phase (the ordinary phase at ambient pressure and temperature) to the Pnma phase is about 33.0 GPa and the phase transition is reversible. This phase transition can be reproduced qualitatively by ab initio calculations, but with a lower transition pressure of 19.9 GPa. The equation of state of LiTaO3 is also reported.