The direct imaging of a linear defect using diffuse scattering in Zr-Nb b.c.c. solid solutions

Abstract

High-resolution dark-field electron microscopy, using diffuse scattering, has been employed in order to directly image a linear ω-like defect in Zr-Nb b.c.c. solid solutions. Phase-contrast calculations have been made of the defect image using the atomic structure of the defect which had previously been determined by a detailed analysis of the diffuse scattering distribution. Dark-field images formed using two diffuse ω reflections, show rows of white dots along the [111] direction, which are similar in appearance to the calculated images for the defect model. Quantitative measurements of the image intensity indicate that the observed images are from both single and superimposed linear defects. By a careful comparison of the fine structure of the calculated and observed images it is possible to confirm certain details of the atomic structure of the defect. The good agreement between the calculated and observed images from the standpoint of image size, [111] directionality, intensity and fine details is considered to constitute strong direct evidence for the existence of a linear defect in Zr-Nb b.c.c. solid solutions.