Ingenieurwissenschaften und zugeordnete Tätigkeiten
Filtern
Erscheinungsjahr
- 2022 (2)
Dokumenttyp
Sprache
- Englisch (2)
Referierte Publikation
- ja (2) (entfernen)
Schlagworte
- DFT (1)
- Energetic Materials (1)
- Energetic materials (1)
- Gandolfi method (1)
- Phase transition (1)
- Structural dynamics (1)
- Thermal expansion (1)
- Variable temperature (1)
- X-ray diffraction (1)
Organisationseinheit der BAM
Variable-temperature single-crystal diffraction experiments treated with the Gandolfi method reveal the detailed temperature evolution of the unit-cell dimensions, structural transformations and the phase co-existence of the energetic material FOX-7. Two first-order phase transitions are observed accompanied by abrupt changes in volume and unit-cell dimensions. The thermal expansion is found to be linear for all three phases, albeit highly anisotropic. Moreover, the experimental thermal expansion coefficients differ from those predicted from literature atomistic simulations.
Highly anharmonic thermal vibrations may serve as a source of structural instabilities resulting in phase transitions, chemical reactions and even the mechanical disintegration of a material. Ab initio calculations model thermal motion within a harmonic or sometimes quasi-harmonic approximation and must be complimented by experimental data on temperature-dependent vibrational frequencies. Here multi-temperature atomic displacement parameters (ADPs), derived from a single-crystal synchrotron diffraction experiment, are used to characterize low-frequency lattice vibrations in the alpha-FOX-7 layered structure. It is shown that despite the limited quality of the data, the extracted frequencies are reasonably close to those derived from inelastic scattering, Raman measurements and density functional theory (DFT) calculations. Vibrational anharmonicity is parameterized by the Grüneisen parameters, which are found to be very different for in-layer and out-of-layer vibrations.