Possible mechanisms for interconversion of polar forms for the ferroelectric diisopropylammonim halides Diisopropylammonium chloride (DIPAC) and diisopropylammonium bromide (DIPAB) crystalize in the P21 phase, and have recently been shown to undergo a ferroelectric transition along the b crystallographic axis. These crystals revert to centrosymmetric disordered phase, P21/m above their Curie temperatures, 440, and 426 K, respectively. The mechanism for the interconversion of the two forms polar forms during the ferroelectric transition has not yet been reported. This work explores three possible models for the polar reversal for the DIPAC system, (1) an internal double-hydride migration requiring minimal rotation of isopropyl groups, (2) 180o rotation of one isopropyl group, and (3) halide-assisted double hydrogen migration. Plane wave density functional method calculations were used to model transition structures, energies, and piezoelectric force constants for the three models. Molecular dynamics was used to look for modes of relaxation from the proposed transition state models. Overall, the 180o rotation model is predicted to have a significantly lower energy barrier than the double hydrogen transfer, while the halogen-assisted mechanism provided a valid alternative to rotation.

Possible mechanisms for interconversion of polar forms for the ferroelectric diisopropylammonim halides

249th National Meeting (2015)

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