Pressure Distribution Investigation in Silicon Oil Compressed in Diamond Anvil Cell

Diamond anvil cell (DAC) is a kind of widely used static-high-pressure device. Benefitting from its wide pressure range, excellent optical applicability and convenience of use, DAC provides a tremendous boost to the development of high-pressure science. However, at high pressures, factors like solidification of pressure transmitting medium may cause destruction of the hydrostatic pressure condition in the DAC sample chamber, leading to the generation of pressure gradients. In this work, a new method of using the technique of picosecond ultrasonics to investigate acoustic signal distribution at various locations within the sample chamber was proposed, which can analyze the pressure distribution via the acoustic observations. Limitations in the continuity of signal acquisition, sample selection, etc. can be overcome in this experimental technique, which could be built and manipulated in an ordinary laboratory. Here, pressure gradient in silicon oil was carried out under compression using this technique, and the results revealed that the pressure gradient in the sample chamber increased from 1.3×10⁻⁴ GPa/μm at 1 GPa to 5.3×10⁻² GPa/μm at 30 GPa. In addition, the anomalous change of standard deviation of the pressure distribution was analyzed by combining it with in-situ Raman spectroscopy, then the possible phase transitions of silicone oil at high pressures were discussed.