Electron diffraction study of lizardite 1T with stacking faults

Abstract

The stacking faults observed in the structure of the mineral lizardite 1T belonging to the polytype group A are investigated using the digital oblique-texture electron diffraction patterns, difference Fourier-potential maps, and model diffraction patterns obtained for this compound. Numerical simulation of the diffraction profiles along the first (the 02l and 11l reflections) and second (the 20l and 13l reflections) ellipses in the oblique-texture electron diffraction patterns is performed for finite sequences of ten layers with the use of the Markovian statistical model in the quasi-homogeneous approximation. The specific features of the intensity distributions along the first and second ellipses are associated with the manifestation of translational (displacements of the layers by ±b/3) and orientational (rotations of the layers through an angle of 180°) defects of the layer stacking, respectively. For both ellipses, the experimentally observed intensity distributions are in the best agreement with the diffraction profiles calculated for stacking faults at a content of approximately 25%, the short-range order parameter S = 1, and the maximum degree of ordering in the layer alternation. It is demonstrated that the irregularities revealed in the layer alternation in the structure of lizardite 1T (which is characterized by an identical orientation of the adjacent layers) arise from layer displacements by ±b/3 and, to a considerable extent, from the formation of sequences with opposite orientations of the adjacent layers. As a result, the structure of lizardite 1T nanocrystals involves a combination of layer sequences that are typical of structures belonging to the polytype groups A and D.