Analytical electron microscopy study of high Tc superconductor YBa2Cu3O7

The high T_c superconducting material YBa₂Cu₃O₇ shows a complex relationship between microstructure and oxygen content, which are controlled by length of heat treatment, atmosphere, and quench rate. An AEM investigation studying changes in the oxygen near edge features was undertaken. Electron energy loss spectroscopy (EELS) measurements have the important advantage that they can be made on single crystal grains, allowing orentation-dependent studies. Both ion-milled and crushed samples with varying O₂ content were analyzed. The structure of YBaCu₃O₇ was determined by neutron diffraction to be orthorhombic with distinct Cu-O chains along the b-axis as well as Cu-O planes in the a—b plane. Therefore, by looking for a crystallographic dependence of the oxygen K-edge one might be able to distinguish inequivalent oxygen atoms by their core level binding energy and correlate site occupancy with varying O₂ content. The EELS results on the oxygen K-edge are strongly dependent on oxygen content, most noticeably when the c-axis is parallel to the electron beam.