NMR Studies of a Nanocomposite Based on Molecular Ferroelectric Diisopropylammonium Bromide

The properties of the molecular ferroelectric diisopropylammonium bromide (C6H16BrN, DIPAB) particles embedded into a nanoporous opal matrix were studied by high-resolution nuclear magnetic resonance (NMR) in the temperature range from 295 to 450 K. The 13C NMR spectra were obtained using CP-MAS technique. The results showed that structural changes in nanostructured DIPAB particles are more complex than it was previously expected. The NMR spectra of DIPAB embedded into the opal matrix revealed the coexistence of two different crystalline structures within a wide temperature range. The monoclinic ferroelectric and orthorhombic non-polar phases were seen in nanoconfined DIPAB at room temperature, meanwhile the orthorhombic phase only was found in the bulk DIPAB crystalline powder. The NMR spectra showed that the transition from the orthorhombic to the ferroelectric phase upon heating is reconstructive. The total nanocomposite transforms into the ferroelectric structure at a temperature much higher than that for the relevant transition in bulk. The size effect also leads to the increase of the temperature of the phase transition from the ferroelectric P21 phase to the P21/m paraphrase.