Electron microscope transmission images of coherent domain boundaries

The properties of the fringe patterns associated with coherent domain boundaries are discussed in detail on the basis of a model in which the crystal consists of two regions which have slightly different diffraction conditions, characterized by two different s-values. The fringe pattern is essentially the superposition of three independent fringe patterns. Two of these fringe patterns can be interpreted as the wedge fringes for the individual regions, the plane of separation being the boundary plane. The third fringe pattern, which is not present in a crystal of uniform thickness, consists of the thickness contours. The superposition of all three fringe Systems produces a kind of Moiré “pattern” of which the characteristics have been discussed. In a second paper these features will be compared with observations on nickel oxide and barium titanate.