Pressure induced phase transformations in diisopropylammonium bromide

Effect of high pressure on ferroelectric diisopropylammonium bromide (DIPAB) is investigated using Raman spectroscopy and angle-dispersive x-ray diffraction (XRD) measurements using a diamond anvil cell up to similar to 10 GPa. Raman spectroscopic studies indicate that the monoclinic (m-II) ferroelectric phase of DIPAB is unstable under slight compression, leading to changes in molecular conformation. We have observed new peaks appearing in the lattice mode region and CH3 stretching region giving indication of conformational change. XRD investigations reveal that the m-II phase (space group P2(1)) is partially transformed into a centrosymmetric, non-polar triclinic (P-1) structure at 0.7 GPa. Ferroelectricity is expected to weaken under compression above 0.7 GPa and ferroelectricity may disappear at a very high pressure when the m-II phase fully converted into triclinic P-1 phase. On releasing the pressure the ambient structure is fully recovered. The role of hydrogen bonds in the phase transformation is also discussed.