Nuclear-Magnetic-Resonance Determination of Structural Domains in NaCN

Measurements of the first- and second-order quadrupole energy-level shifts are performed in a ${}_{}{}^{23}{}_{}{}^{}\mathrm{Na}$ NMR experiment in a single crystal of NaCN. Twelve orthorhombic domains are found below the phase transition at 15°C. They consist of six pairs of domains with each one oriented by an angle $2\beta$ relative to the other member of the pair. The angle is around the $c$ orthorhombic axis which coincides with the cubic [100] direction of the room-temperature pseudocubic phase. The angle $\beta$ is found to be ±(8.5°±1.5°) at 247°K.