Structural and superconducting properties of oxygen-deficient NdBa2Cu3O7- delta

Element specific imaging with high lateral resolution: an experimental study on layer structures

Planar defects and individual layers in ceramic material are chemically imaged by high resolution energy-filtering TEM using a post-column imaging electron energy filter. Objects are barium layers in the cuprate superconductor NdBa2Cu3O7-delta (isostructual to YBa2Cu3O7-delta) as well as planar defects and precipitates of beta-WB in tungsten- and chromium-doped TiB2. The barium layers with a spacing of 0.42 nm in the cuprate are resolved in jump-ratio images using the Ba_N edge. In the boride system the beta-WB precipitates with thickness of 0.8 nm can be chemically imaged in elemental maps of B_K, Ti_L,Cr_L and W_M. The B as well as the Ti map show a decrease in intensity at the precipitates, whereas in the W map an increase in intensity is observed. The boron-deficient layers with a spacing of 0.38 nm in the beta-WB precipitate can be resolved in boron jump-ratio images. Additionally, defects containing single boron-deficient layers are chemically imaged. Hence structures in the dimension of interatomic distances can be imaged with respect to their elemental constituents. Although high resolution electron spectroscopic images contain strong interference contrast from elastic scattering, after normalization or background subtraction the element specific images are dominated by chemical contrast.