Raman spectra of NH4Br at high pressure and the location of the IV–V phase transition

The effect of pressure on the ν5(TO) lattice mode and on the internal modes ν1, ν3, and ν2+ν4 is reported for the phase IV of NH4Br at 100 K. The IV–V transition is located by changes in the Raman spectra in the temperature range between 100 and 300 K at a constant pressure of about 65 kbar. The II–IV phase transition shows a strong decrease of its pressure dependence pointing towards a triple point of the phases II–IV–V around 350 K and 65 kbar.