Structure and vibration spectra of strontium and magnesium oxalates at high pressure

ABSTRACT

We report theoretical and experimental investigations on the structures of strontium and magnesium oxalates, and corresponding Raman spectra at high pressure. These systems have shown progress in the generation of CO₂ and in the synthesis of energetic doped polymeric carbon monoxide after X-ray irradiation and simultaneous application of high pressure. Density functional perturbation theory (DFT) was used to calculate the zone center optical phonons in monoclinic and triclinic strontium oxalate, and the ambient triclinic phase of magnesium oxalate. Vibration modes were also determined in terms of atomic displacements for both compounds. The simulations were compared to experimental Raman spectra in an effort to elucidate the details of the phase transition between monoclinic and triclinic phases. Additional phonon dispersion calculations of the compounds were performed to gain better insight into the dynamic phase stability in strontium and magnesium oxalates under high pressure.

Keywords:

• X-ray diffraction
• energetic materials
• vibrational spectroscopy

Acknowledgements

We thank Jennifer Ciezak-Jenkins for discussions, and Victor Milman from Dassault Systèmes BIOVIA for help with details of CASTEP calculations.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

This work was supported in part by a grant of Computer Time from the DOD High Performance Computing Modernization Program at the ARL, NAVY, AFRL and ERDC DOD supercomputing resource centers [portions of this work were performed at HPCAT (sector 16), advanced photon source (APS), Argonne National Laboratory. HPCAT operations are supported by DOE-NNSA’s Office of Experimental Sciences. The advanced photon source is a U.S. Department of Energy (DOE) Office of Science User Facility operated for the DOE Office of Science by Argonne National Laboratory under contract no. DE-AC02-06CH11357.