Title: Phonon spectra of Cu₆PS₅Br superionic ferroelastic: experimental and theoretical studies
Author(s):

	I.P.Studenyak (Uzhgorod National University, Faculty of physics, 46Pidhirna Str., 88000 Uzhgorod, Ukraine) ,
	K.Z.Rushchanskii (Institute for Solid State Physics and Chemistry, Uzhgorod National University, 54 Voloshyn St., 88000 Uzhgorod, Ukraine) ,
	R.Yu.Buchuk (Uzhgorod National University, Faculty of physics, 46Pidhirna Str., 88000 Uzhgorod, Ukraine) ,
	V.O.Stephanovich (Institute for Solid State Physics and Chemistry, Uzhgorod National University, 54 Voloshyn St., 88000 Uzhgorod, Ukraine)

The anomalous temperature behavior of the Raman scattering bands at superionic phase transition of is revealed. Using density functional perturbation theory within local density approximation, ab initio long-wavelength phonons have been obtained for high-symmetry cubic structure. In the calculated phonon spectrum two unstable modes indicate the experimentally observed sequence of ferroelastic and superionic phase transitions.

Key words: superionic materials, lattice dynamics, phase transitions
PACS: 63.20.Dj, 64.60.Cn, 78.30.Hv