Diffuse Rods Research Articles

Diffuse X-ray scattering and change of the lattice parameters of NaOH at the transition from the orthorhombic to the monoclinic phase

NaOH crystals consist of layers. At 240°C the layers glide upon each other and cause a transition from an orthorhombic to a monoclinic phase. Measurements of the monoclinic angle β show that this transition proceeds continuously. Near the transition temperature there is a strong disorder scattering, which corresponds to diffuse rods in the reciprocal lattice. The intensity distribution along the rods was measured as well as the temperature dependence of the profile of the rods. The observed diffuse scattering is explained by a dynamic disorder model.