Anion Rotational Disorder in Sodium Nitrate

抄録

The photographic study of X-ray diffuse scattering from a single crystal was made in order to determine the rotational disorder of NO₃ groups above the critical temperature 275°C. The rounded diffuse maxima which appear at the positions of super-lattice reflections of the ordered lattice are identified with those due to the disorder of NO₃ groups. It is concluded that the rotation of NO₃ group is hindered and the NO₃ group is almost bound in two positions which have the calcite-type of coordination with the surrounding Na atoms. There exists such a short-range order that the neighboring NO₃ groups have a tendency to take the ordered arrangement.