We report an anomalous phase transition in compressed In2Se3. The high-pressure studies indicate that In2Se3 transforms to a new isosymmetric R-3m structure at 0.8 GPa whilst the volume collapses by ∼7%. This phase transition involves a pressure-induced interlayer shear glide with respect to one another. Consequently, the outer Se atoms of one sheet locate into the interstitial sites of three Se atoms in the neighboring sheets that are weakly connected by van der Waals interaction. Interestingly, this interlayer shear glide changes the stacking sequence significantly but leaves crystal symmetry unaffected. This study provides an insight to the mechanisms of the intriguing isosymmetric phase transition.
The significant conductivity enhancement of semiconductor BiOI up to 19.2 GPa has provided an example of the directed regulation of the electrical properties of BiOX layered materials using controllable pressure.
The inhomogeneity in pressure inside the sample chamber of a diamond anvil cell (DAC) poses a major challenge to the accurate measurement of the properties of materials under high pressures, especially when the pressure medium solidifies under compression or is prohibited in the experiment. In this paper, the authors systematically investigate the pressure gradient in a DAC sample chamber and its evolution over time with changes in temperature. The results show that pressure gradients were formed along both the radial and the axial directions upon compression, and gradually decayed with time and increasing temperature. After a period of relaxation at room temperature, the pressure gradient along the axial direction gradually decayed and a new equilibrium was established. A similar process was observed along the radial direction but required a longer period before reaching equilibrium. Appropriate heating of the sample can cut the relaxation time to the order of tens of minutes and smoothen the pressure gradient in both directions. The electrical properties of olivine were significantly different when the measurements were conducted before and after relaxation was complete, indicating that the relaxation in pressure is essential for acquiring reliable data in a DAC under high pressures.
Temperature induced pressure drift in the diamond anvil cell (DAC) is a major issue in high-pressure high-temperature experiments. It is commonly acknowledged that these drifts originate from multiple factors, but no systematic descriptions have been made so far. By introducing an internal water-cooling system in the DAC, we have performed a systematic investigation into temperature induced pressure drifts to reveal the mechanism behind them and to find a proper experimental procedure to achieve minimal pressure variation in DAC’s heating experiment. It is revealed in this experiment that pressure variation during heating processes originates from multiple temperature related factors of the DAC. The variation itself can be considered as a rebalancing process of the compression forces on the sample chamber initiated by the disturbance caused by temperature elevation. It is possible to suppress pressure variation by maintaining the temperature of the DAC body at room temperature to ensure the consistency of compression on the sample chamber. At the same time, the best procedure for the heating experiments is to properly pre-heat the sample chamber equipped with the internal water-cooling system before performing the in situ measurements on the temperature-related properties at the pressurized and heated conditions. Our discovery provides a reliable procedure for the sample heating process in the DAC and helps resolve the complex mystery of the influence of the combination of pressure and temperature in high-pressure high-temperature experiments.
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