Original paper
Microstructure of Superconducting Ceramics of YBa2Cu3O7-x
Müller, Wolfgang Friedrich; Wolf, Thomas; Flükiger, René
Neues Jahrbuch für Mineralogie - Abhandlungen Band 161 Heft 1 (1989), p. 41 - 67
24 references
published: Jul 27, 1989
ArtNo. ESP154016101003, Price: 29.00 €
Abstract
Transmission electron microscopic methods including electron diffraction and energy dispersive X-ray microanalysis were used in order to study the microstructure of two different superconducting YBa2Cu3O7-x ceramic samples. The samples consist of YBa2Cu3O7-x crystals (with a grain size of about 1 to 10 µm) and additional phases which may have a concentration of the order of 0.1 percent. The dominant crystal defects of YBa2Cu3O7-x are twin lamellae on {110}. The twinning is due to the phase transition P 4/mm to Pmmm during cooling which is connected with loss of point group symmetry. Both twin laws (110) and (110) were frequently observed in suitably oriented crystals. When twin lamellae intersect, a kind of chess board pattern is formed, which gives rise to complicated electron diffraction patterns. Occasionally, free dislocations were seen. They had the Burgers vector [100] or [010]. Defects parallel (001) in YBa2Cu3O7-x are an alteration effect caused by attack of the atmosphere. The additional phases found are Y2BaCuO5, Y2Cu2O5, CuO, BaCuO2 and amorphous YBa2Cu3O7-x· Y2BaCuO5, and Y2Cu2O5 occur as intracrystalline inclusions of YBa2Cu3O7-x, CuO and BaCuO2 as the fillings of triple point junctions of YBa2Cu3O7-x grains. The few grain boundary phases observed were mostly amorphous layers 5 to 15 nm in width.
Keywords
YBa2Cu3O7-x • Y2BaCuO5 • Y2Cu2O5 • CuO • BaCuO2 • superconductor • microstructure • transmission electron microscopy • phase transition • twinning • dislocations • grain boundary phases