CORRELATION BETWEEN HOLE DEPLETION AND ATOMIC-STRUCTURE AT HIGH-ANGLE GRAIN-BOUNDARIES IN YBA2CU3O7-DELTA

Using a combination of high-resolution Z-contrast imaging and high-resolution electron energy loss spectroscopy (EELS) in the scanning transmission electron microscope (STEM), the local hole depletion and local atomic structure in the region of grain boundaries can be studied simultaneously. The atomic resolution Z-contrast image can be used to position the probe for energy loss spectroscopy, which by quantitative analysis of the pre-edge feature of the oxygen K-absorption edge can be used to measure the local hole depletion to an accuracy of approximately 5%. Additionally, as the Z-contrast technique is sensitive to the effects of damage from the specimen preparation, boundaries representative of the original material can be easily selected. Studies have been performed on both asymmetric and symmetric high-angle tilt boundaries in YBa2Cu3O7-delta films prepared by laser ablation on yttria-stabilised-zirconia (YSZ) substrates. The symmetric boundary shows no significant hole depletion in the boundary region whereas the asymmetric boundary has significant depletion in a zone extending over a far greater region than the disordered atomic structure indicated by the image.