Pressure-Induced Reverse Reaction of the Photochemical Decomposition of Germanium Tetraiodide Molecular Crystal

GeI₄ molecular crystal and its solution in cyclohexane were irradiated by lasers of different wavelengths to investigate the critical wavelength for photochemical decomposition of GeI₄. We have observed that 633 nm laser can photochemically decompose GeI₄, exceeding the previously reported wavelength limit of 514 nm. XPS spectra indicate that GeI₄ is photochemically decomposed into Ge₂I₆ and I₂; unlike GeBr₄, Ge²⁺ (GeI₂) cannot be found in the photochemical reaction products. Raman spectra measurement of GeI₄ under high pressure up to 24 GPa show that Raman signals of Ge₂I₆ and I₂ vanish at 0.5 to 1.7 GPa. This finding clearly shows that high pressure can effectively reverse the photochemical decomposition of GeI₄ and influence the direction of the solid-state reaction, which is usually found on gas-phase reactions

Cyclic Phase Transition from Hexagonal to Orthorhombic Then Back to Hexagonal of EuF₃ While Loading Uniaxial Pressure and under High Temperature

The structure and photoluminescence properties are investigated under high pressure and high temperature for pure orthorhombic and hexagonal EuF₃ nanocrystals. Under hydrostatic compression, the hexagonal EuF₃ remains stable at pressures up to 26 GPa. Under nonhydrostatic compression, a cyclic phase transition from hexagonal to orthorhombic and then back to hexagonal is observed for the first time. When loading uniaxial compression, the pure hexagonal EuF₃ partly transforms to orthorhombic at 70 MPa, then the orthorhombic EuF₃ transforms to hexagonal at about 3 GPa, and the transition is completed at about 10 GPa. The cyclic phase transition is also observed during the heating process; the hexagonal transforms to orthorhombic at 550 °C and then to hexagonal at 855 °C. The content phase diagrams are obtained under high pressure and at high temperature

Pressure-Induced Conformer Modifications and Electronic Structural Changes in 1,3,5-Triamino-2,4,6-trinitrobenzene (TATB) up to 20 GPa

To probe the behavior of structural evolution and optical properties in solid energetic material TATB, X-ray diffraction (XRD) and Raman and absorption spectroscopy were performed under high pressure up to 20 GPa. The absorption edge shifts to red, and the color significantly varies with increasing pressure for TATB. The XRD patterns under high pressure indicate that TATB maintains the triclinic structure within this pressure range. An electronic structural change is observed at ∼5 GPa, resulting from the modification of conformers of TATB, which is associated with the rotation of nitro and amino groups under high pressure. The current experimental results clarified the absence of phase transition below 20 GPa and confirmed that the pressure-induced color change originates from the enhancing conjugation of π orbital due to the shorting C–NO₂ bonds and the rotation of nitro groups with increasing pressure. The third-order Birch–Murnaghan equation of state is obtained up to 16.5 GPa, which is helpful for calculating researchers to verify the correctness of their models