Splitting of libration mode frequencies in the vicinity of orientation phase transition in NH₄Br

Abstract

Vibrational spectra of NH₄Br at high pressures up to 4·5GPa have been studied by means of incoherent inelastic neutron scattering using sapphire anvil high pressure cell technique. Libration mode splitting was investigated in the vicinity of the orientation phase transition (P_tr = 2·7 GPa) and this effect disappears if pressure is less or higher than P_tr. This effect is explained in terms of two-well asymmetric potential.

Key Words:

• Ammonium bromide
• High pressure
• Neutron
• Libration mode