X-ray study on the evolution of thermal motion in the ferroelectric phase of NaNO2 - art. no. 014101

The cry stal structure of NaNO2 has been refined in the ferroelectric phase at 338, 378, and 418 K. The evolution of the thermal motion with increasin g temperature has been studied by comparing the anisotropic displacement pa rameters, including earlier values at low temperatures. The results support the rotation of NO2 around the c axis as the mechanism of polarization rev ersal. It is strongly suggested that the coupling between the translational amotion along the b axis and the rotational motion of the NO2 ion becomes stronger approaching to T-c, reducing the effective potential barrier for N O2 rotation. The location of the rotation center is estimated to be slightl y closer to the N atom. The electron density contribution from a small amou nt of disorder atoms has been found.