Stability of antiferroelectricity and molecular reorientation in the hexatic smectic IA* phase as studied by X-ray diffraction and NMR spectroscopy

Abstract

We have investigated molecular orientation in the hexatic antiferroelectric SI_A* phase by X-ray diffraction and nuclear magnetic resonance (NMR) spectroscopy. In the phase transition from SC_A* to SI_A*, the layer thickness increases and becomes larger than that in SA. The third-order diffraction peak intensity becomes stronger than the second-order one at this transition and increases with decreasing temperature in SI_A*. According to the magic angle spinning NMR measurements, on the other hand, the isotropic chemical shift scarcely moves at this transition. These results suggest that the layer structure is reconstructed by the molecular reorientation but not by a molecular conformation change. We have also discussed the stability of antiferroelectricity and the origin of its appearance in hexatic ordering.