High resolution electron microscope observations of microstructures in A15 type Nb3X superconductors

Microstructures of superconducting Nb₃X(A15) compounds are studied by means of high resolution electron microscopy. Structure images are obtained with the 400kV high resolution electron microscope for both the annealed and ion-irradiated crystals. The images obtained from the annealed crystals show bright contrast patterns similar to the projections of Nb and X atoms comprising the A15 structure. Defects observed in the annealed crystal irradiated with 40 kV Nb⁺ ions show characteristic features in contrast. The dependence of image contrast on the element X and the atomic structures of the defects are discussed by comparison with the calculated images.