engleski

Raman-scattering study of phase transitions in methylmercury(II) halides CH3HgX (X = Cl, Br, I)

The phase transition in methylmercury(II) halides CH3HgX, (X=Cl, Br, I) has been studied using Raman spectroscopy in the temperature range from 10 to 390 K. A soft mode was observed in all studied compounds. The low-frequency Raman spectra of all methylmercury(II) halides (MMH) show several common features. On these grounds and available structural data we conclude that all methylmercury(II) halides are isostructural, with a high-temperature tetragonal phase and a low-temperature orthorhombic one. The possible mechanism of the phase transition is described. The transition is ferroelastic, driven by the softening of a phonon at the Brillouin zone boundary. We assume that the transition is induced by the freezing of the eigenvector of a zone boundary transversal acoustic phonon, causing the cell doubling in the low-temperature phase.

Raman spectroscopy ; methylmercury(II) halides

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