NMR and NQR Study of Above-Room-Temperature Molecular Ferroelectrics Diisopropylammonium Chloride and Diisopropylammonium Perchlorate

Abstract

The phase transitions and molecular motions in organic ferroelectrics diisopropylammonium chloride and diisopropylammonium perchlorate have been studied by proton NMR and spin–lattice relaxation and by 14N NQR and spin–lattice relaxation. In diisopropylammonium chloride, proton T1 shows slowing of the reorientation of methyl groups and a discontinuous decrease at the ferroelectric to paraelectric phase transition. The 14N NQR frequencies are observed in the range characteristic for a C–NH2+–C ion. Diisopropylammonium perchlorate undergoes three phase transitions at varying temperatures. Proton and 14N T1 shows the presence of two slow motions: the reorientation of the methyl groups and a second slow motion in phases II and III which is most probably tumbling of diisopropylammonium ions. The discontinuous change of proton T1 and M2 at the ferroelectric to paraelectric phase transition is ascribed to exchange between two orientations of a diisopropylammonium ion in the paraelectric phase. The 14N quadrupole...