2 research outputs found
Cyclic Phase Transition from Hexagonal to Orthorhombic Then Back to Hexagonal of EuF<sub>3</sub> 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 EuF<sub>3</sub> nanocrystals. Under hydrostatic compression,
the hexagonal EuF<sub>3</sub> 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
EuF<sub>3</sub> partly transforms to orthorhombic at 70 MPa, then
the orthorhombic EuF<sub>3</sub> 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–NO<sub>2</sub> 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