ATOM-PROBE FIELD-ION MICROSCOPY OF HIGH-TEMPERATURE SUPERCONDUCTING MATERIALS

Overview & Synopsis

The high-temperature superconducting oxides YBa2Cu3O7 and YBa2(Cu1-xFex)3O7 (x=.01) have been studied using the field-ion microscope and the atom probe. Specimen preparation techniques for materials of different densities are discussed. Micrographs of YBa2Cu3O7 taken in argon at approximately the transition temperature Tc yield little crystallographic information, but often show "bright spots" that seem to be associated with the oxide nature of the superconductor. Mass spectra taken from superconducting YBa2Cu3O7 have a nominal Y:Ba:Cu composition of nearly 1:2:3, though microfluctuations within this phase have been observed. In particular, composition fluctuations at approximately twice the lattice parameter along the c-axis are described. In addition, changes in the field-evaporation of atoms from the surface at different temperatures, imaging gas conditions, and pulse fractions were examined.