High-Pressure Neutron Powder Diffraction Study of ε-CL-20: A Gentler Way to Study Energetic Materials

Abstract

High-pressure studies have been performed on the ε-form of the powerful explosive CL-20. Hydrostatic compression over the pressure range 0-12 GPa has been monitored using synchrotron powder X-ray diffraction. The potential effects of X-ray radiation damage were observed and circumvented through a follow-up compression study over the pressure range 0-7 GPa using neutron powder diffraction. This second study revealed smooth compression behaviour, and the absence of any phase transitions. Intermolecular interaction energies as obtained using PIXEL calculations did not show any discontinuity upon application of pressure. An isothermal equation of state has been determined, and the high-pressure response is supported by dispersion-corrected DFT calculations. Inelastic neutron scattering (INS) (experimental and simulated) spectra for the ε-form are in excellent agreement.

Effect of synchrotron X-ray radiation damage on phase transitions in coordination polymers at high pressure

“…Metal-organic frameworks and coordination polymers principally show reductions in volume upon X-ray radiation damage, which may be linked to their amorphization process. However, in the case of molecular compounds, an increase in volume is more typically observed with increasing X-ray irradiation, as measured for Br(collidine) 2 ClO 4 glycinium phosphite, the energetic molecule 2,4,6,8,10,12-hexanitrohexaazaisowurtzitane and [M(1,5-cyclooctadiene)Cl] 2 catalysts with M = Ir + or Rh + (Morgan et al, 2018;Bogdanov et al, 2021;Konar et al, 2020;Fernando et al, 2021). The impact of radiation on structural behaviour is again highlighted for Br(collidine) 2 ClO 4 , where diffuse scattering disappears upon increased X-ray exposure (Morgan et al, 2018).…”

“…With the increasing use of third-and fourth-generation synchrotrons, the impact of radiation damage in small-molecule crystallographic research has gained greater importance (Christensen et al, 2019). Radiation damage is especially critical for in-situ and time-resolved studies, where the sample is investigated as a function of various external conditions, and is measured multiple times (Konar et al, 2020). It then becomes important to separate the possible effects from exposure to X-ray irradiation and the behaviour of the sample due to the applied stimulus, such as temperature or pressure.…”

High-Pressure Structural Behavior of para-Xylene

“…26 The continued validation of increasingly sophisticated dispersion models has demonstrated that the DFT plus dispersion (DFT-D) model not only can reproduce experimentally determined hydrostatic compression behavior but can also be used to guide experimental endeavors. 25 The objectives of this research effort were therefore as follows: (i) to perform the first high-pressure neutron diffraction study on perdeuterated p-xylene to solve the highpressure phase, (ii) to reproduce the pressure-induced crystallization on hydrogenous p-xylene inside a DAC and to compare the high-pressure single-crystal structure with the neutron powder data; (iii) to explore the ability of modern DFT models to predict the hydrostatic compression behavior, and (iv) to obtain accurate pressure−volume equations of state.…”

“…Moreover, it has been shown that neutron techniques cause much less radiation damage for molecular materials. 24,25 To further complement our experimental findings, we performed first-principles simulation as well. Density functional theory (DFT) has demonstrated a remarkable ability to predict the evolution of structures with pressure, particularly when weak dispersion forces are accounted for.…”

“…Therefore, the accurate location of hydrogen (D) positions can be obtained from neutron diffraction on the deuterated sample. Moreover, it has been shown that neutron techniques cause much less radiation damage for molecular materials. , …”