Structure of an LiKSO4 single crystal studied by 7Li and 39K NMR at low temperature

The 7 Li and 39 K nuclear magnetic resonances in an LiKSO 4 single crystal grown by the slow evaporation method have been investigated using a Bruker FT nuclear magnetic resonance (NMR) spectrometer. From the experimental data, the quadrapole coupling constant and asymmetry parameter were determined at room temperature and low temperature, respectively. Unlike the case at 300 K, the 7 Li NMR line consists of three sets at 180 K, while 39 K nucleus exhibits six sets for the rotation around the three crystallographic axes. The three resonance lines of 7 Li and 39 K at low temperature can be explained by the existence of three kinds of twin domain, rotated with respect to each other by 120° around the c -axis. The three resonance lines are also related to the crystallographic mirror plane. Structure of ferroelastic LiKSO 4 crystals at 180 K can be directly inferred from the domain pattern obtained by 7 Li and 39 K NMR. The above results show that the equations of the twin boundaries belong to the mm 2 F 6 mm ferroelastic species. Therefore, the symmetry of phases III and II is given by orthorhombic structure with Cmc 2 1 ( mm 2) and hexagonal structural with P 6 3 mc (6 mm ), respectively.