Combined HRTEM, X-ray microchemical and EELS fine structure analysis of planar defects in YBa2Cu3O7-δ

High temperature superconductors in the systems YBa2Cu3O7-δ (123) and decomposed YBa2Cu4O7-δ (124) often contain planar faults with (001) as the nominal fault plane. Such planar defects have been analyzed using a unique combination of high resolution TEM (HRTEM) imaging and high resolution analytical electron microscopy (HRAEM). HRTEM confirmed that these planar faults are stacking faults with double or multiple insertion of crystal planes parallel to the c-plane of the crystal, most probably Cu-O planes. X-ray microanalysis clearly showed enrichment of copper associated with these defects. EELS fine structure of Cu-L23 edge from the fault regions resembled that of pure CuO. The combined results indicate that the planar defects are in fact insertions of extra Cu-O planes in an otherwise regular 123 crystal unit cell. (orig.)