¹³C NMR of DIPAC and DIPAB organic ferroelectrics

Abstract

The diisopropylammonium chloride (C 6 H 16 ClN, DIPAC) and diisopropylammonium bromide (C 6 H 16 BrN, DIPAB) molecular crystals are recently discovered ferroelectrics with sufficiently high spontaneous polarization and Curie temperature. We performed first studies of these crystals by 13 C NMR. CP MAS spectra were collected within large temperature ranges covering the Curie points. The reconstructive phase transition from the initial orthorhombic P2 1 2 1 2 1 structure of DIPAB to the monoclinic ferroelectric P2 1 structure leads to an abrupt alteration in the 13 C spectrum. The 13 C spectra for DIPAC and DIPAB in the ferroelectric P2 1 phase are quite similar with four lines at lower frequencies, which correspond to the CH 3 groups, and two lines with close chemical shifts, which correspond to two CH groups. The transition into the paraphase leads to gradual reduction of the interline distances in the low-frequency quadruplet and in the doublet. The step-like changes in the interline frequency shifts at this transition indicating its first order. The analysis of the spectrum evolution in the paraphase shows that only a CH group lays in the reflection plane above the P2 1 → P2 1 /m transition, while the second CH group only moves closer to the reflection plane upon further heating.

Структурная Эволюция Молекулярного Сегнетоэлектрика Хлорида Диизопропиламмония (DIPAC)

“…2 (2). Он совпадает с рентгеновским спектром, полученным после синтеза DIPAC, и соответствует моноклинной структуре [3,11].…”

“…С момента открытия сегнетоэлектричества в DIPAC проводились различные исследования полярной фазы [7][8][9][10][11]. Однако эти исследования не затрагивали проблему стабильности сегнетоэлектрической модификации при комнатной температуре в течение длительного времени.…”