X-Ray Studies on the Sub-Grain Boundaries of LiF Single Crystals by the Limited Projection Topography

Limited projection topography is applied to three-dimensional observations of the sub-grain boundaries in LiF single crystals. (1) When the density ρ of dislocation constituting a sub-grain boundary is low or tilt-angle θ is small (ρ<5×105/cm2, θ<4''), individual dislocations forming an array in sub-grain boundary can be observed. (2) When ρ is comparatively high (ρ>2×106/cm2, θ>9''), only interference fringes are observed, which are confirmed to be Pendellösung ones associated with the wedge formed by sub-grain boundary and the surface of specimen. (3) When ρ is in the intermediate range (∼1×106/cm2, θ∼6''), both the dislocation arrays and interference fringes are observed overlapping each other. The conditions for appearance of the dislocation images and the interference fringes are explained by taking into account the elastic distortion around the dislocations.