Isothermal pressure-volume equations of state of beta HMX (octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine) at temperatures of 30, 100, and 140°C under both hydrostatic and nonhydrostatic compressions have been obtained using synchrotron angle-dispersive x-ray diffraction experiments. The samples were heated to the isotherm temperature and compressed up to 5.8GPa. At all temperatures HMX remained in the beta phase up to 5.8GPa. However, at 140°C upon decompression to ambient from nonhydrostatic pressures above 4GPa, HMX underwent a phase transition to the delta phase. The same transition was seen upon decompression to ambient from hydrostatic compression; however, parts of the sample remain in the β phase, resulting in a mixed-phase sample. The diffraction data were analyzed to yield unit-cell dimensions at each pressure, and further analyzed to yield thermal expansion, bulk modulus, and the pressure derivative of the bulk modulus.

Structural changes in 1,1-diamino-2,2-dinitroethylene (DADNE, FOX-7) compressed to high pressure in diamond anvil cells were investigated using angle-dispersive x-ray diffraction analysis, Raman spectroscopy, and optical polarizing microscopy. The x-ray results show several changes above 1 GPa. When the x-ray data are indexed according to the ambient-pressure structure, DADNE shows anisotropic compression, with higher compression along the b axis than along the a or c axis. An ambient-temperature isothermal equation of state of DADNE was generated from these data. In addition, the experimentally obtained Raman spectra were matched with vibrational normal modes calculated using quantum chemistry calculations. The shifts in vibrational modes indicate changes in H-wagging vibrations with pressure.

The effect of pressure to 5.6 GPa on the structure of ammonium perchlorate (AP, NH4ClO4) was investigated at room temperature using X-ray diffraction studies and IR and Raman spectroscopy. Two phase transitions were observed. Under hydrostatic conditions, the first transition starts at about 0.9 GPa with the appearance of a few new diffraction peaks and a discontinuity in the pressure-induced shifts of certain Raman frequencies. This transition is most likely a molecular change in AP due to “freezing” of freely rotating NH4 units, similar to effects at low temperature. The second transition starts at 2.9 GPa with a drop in diffraction intensity followed by a new pattern of diffraction peaks by 3.0 GPa. This transition is also characterized by another discontinuity in the Raman shifts and the emergence of two new Raman modes. The phase above 3.0 GPa is stable to 5.6 GPa. The P−V data to 0.9 GPa obtained from X-ray diffraction measurements were used to calculate a bulk modulus of 15.2 ± 0.3 GPa for the ambient-pressure phase.

The phase stability of epsilon hexanitrohexaazaisowurtzitane at high pressure and temperature was investigated using synchrotron angle-dispersive x-ray diffraction experiments. The samples were compressed at room temperature using a Merrill-Bassett diamond anvil cell. For high-temperature compression experiments a hydrothermal diamond anvil cell developed by Bassett was used. Pressures and temperatures of around 5 GPa and 175°C, respectively, were achieved. The epsilon phase was determined to be stable under ambient pressure to a temperature of 120°C. A phase transition to the gamma phase was seen at 125°C and the gamma phase remained stable until thermal decomposition above 150°C. Pressure-volume data for the epsilon phase at ambient and 75°C were fitted to the Birch-Murnaghan formalism to obtain isothermal equations of state.

CuS, or covellite (hexagonal symmetry), was compressed in a diamond anvil cell at room temperature up to a pressure of 45 GPa, and studied using x rays from both a Mo Kα source and a synchrotron. The x-ray diffraction spectrum of CuS disappears by about 18 GPa. The presence of Cu fluorescence lines in all spectra and the reappearance of diffraction lines upon decompression confirm that CuS undergoes reversible pressure-induced amorphization at this pressure. A third-order Birch–Murnaghan equation of state fit to the diffraction data below 11 GPa yields a bulk modulus of 89±10 GPa with a pressure derivative of −2±2 for covellite. Further compression up to 45 GPa shows three to four diffraction lines of very low intensity, implying some high pressure ‘‘ordering’’ of the amorphous phase. The Raman spectra obtained indicate that the changes in structure are probably due to the twisting or the distortion of covalently bonded CuS4–CuS4 units in different directions.