Stacking Disorder in KCuF₃

Abstract

By X-ray diffraction method a stacking disorder in pseudo-perovskite KCuF 3 is investigated. The stacking disorder seems to be connected with the existence of two kinds of polytype structures. Five specimens are examined; the diffraction patterns of them are typical to the five structural groups of KCuF 3 crystals. In the cases of three specimens, diffuse scattering along the c * axis is observed. By a preliminary study including a leastsquares refinement of the atomic coordinate in the crystals, a model of the disorder is established; the disorder is characterized by the displacement (1/2) a in a stacking of the layer parallel to the (001). The diffuse scattering due to the disorder is analyzed by using the intensity equation in a matrix form. In the cases of Reichweite S =1, 2 and 3, the existence and continuing probabilities of the layers are directly determined from Fourier transforms of the observed intensities.