X-ray study on the incommensurate phase of α-bis(N-methylsalicylaldiminato)copper(II) (α-CuNSal)

The temperature dependence of satellite reflections and diffuse scattering of α-CuNSal, Cu(C₈H₈NO)₂, was studied with X-ray film and counter techniques. At T_i = 305 (2)K a continuous and reversible phase transition from a commensurate to an incommensurate orthorhombic structure was observed. At T_C = 241 (2) K there occurs a first-order transition from the incommensurate to a commensurate monoclinic structure. In the incommensurate phase an intense diffuse scattering at the satellite reflections was observed, which is explained by phase fluctuations of the static displacement wave.