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Abstract
We performed the first high-pressure study of melamine using X-ray Raman spectroscopy (XRS) up to ∼17 GPa in a diamond anvil cell at ambient temperature. We utilized the 16 ID-D undulator beamline at the Advanced Photon Source for the X-ray source. The observed diminishment of the 1s→π* peak as well as other changes in the XRS spectra with pressure suggest the possibility of intra- and inter-molecular bonding changes due to two phase changes in the investigated pressure range or hybridization changes of atomic orbitals in the material with pressure. We also performed a complementary X-ray powder diffraction study of neat melamine up to 24 GPa observing at least two phase transitions with pressure. Pressure cycling indicated that the phase transitions were reversible. Density-functional theory calculations performed on the system at ambient and low pressure show a high level of agreement with the experiments.
Acknowledgements
We thank Stas Sinogeikin of HP-CAT for aid in the X-ray diffraction measurements. We thank Dr Allen L. Johnson for aid in the measurements. We thank Prof. Walter J. Pravica for useful discussions. We gratefully acknowledge support from the DOE Cooperative Agreement No. DE-FC08-01NV14049 with the University of Nevada, Las Vegas and from the Nevada/NASA Space Grant. The use of the Advanced Photon Source is supported by the DOE Office of Science, Office of Basic Energy Sciences, under contract no. DE-AC02-06CH11357. HP-CAT is supported by DOE-BES, DOE-NNSA, NSF and the W.M. Keck Foundation.