Low-temperature and high-pressure Raman scattering study of the molecular crystal 2-amino-5-ethyl-1,3,4-thiadiazole

We investigated the temperature and pressure effects on the Raman spectra of the 2-amino-5-ethyl-1,3,4-thiadiazole (C4H7N3S). With the increase in temperature from 10 to 300 K, we observe the redshifts and changes in the linewidth and intensity, which is associated with the phonon anharmonicity. The C4H7N3S crystal is stable with an orthorhombic structure in the investigated temperature range. We founded that the behavior of the change in the Raman band with temperature varies for different phonon modes in the C4H7N3S. In particular, the behavior of the 65 and 95 cm(-1) bands as temperature increases are well explained by the phonon-phonon coupling, as proposed by the Balkanski, Wallis, and Haro model. As pressure increases, C4H7N3S undergoes a phase transition from the crystalline-to-crystalline phase at about 1.6 GPa indicated by the discontinuity in the slope d omega/dP, splitting of bands, and change in the number of the modes. The amorphization of the C4H7N3S occurs between 4.8 and 8.5 GPa identified by the disappearance of all external modes, while several internal modes are persistent. This phase transition became irreversible at about 10 GPa probably caused by the non-hydrostatic condition in liquid media.

Automated summary

The research found that different phonon modes in C4H7N3S exhibit varying Raman band behaviors with increasing temperature, while pressure causes different phase transitions in C4H7N3S at different pressure levels.