Non-Stoichiometry at Dislocation Cores in Perovskites and Related Materials

Abstract Z-contrast images and electron energy loss spectra (EELS) were obtained from low angle grain boundaries in SrTiO3 and YBa2Cu3O7-x (YBCO). Z-contrast images are easy to interpret and especially useful for positioning the beam to acquire EELS data from small sample areas [1], because both these techniques can be performed simultaneously. In high-temperature superconductors even a single grain boundary can reduce the critical current by up to four orders of magnitude. The band-bending model can quantitatively explain this phenomenon. YBCO is a hole-doped superconductor with about one hole per unit cell for optimum doping at x close to zero. It has a structure closely related to the perovskite structure, and Z-contrast images have shown that the dislocation cores are made up of similar structural units as in SrTiO3.[2,3] Our EELS measurements show clear evidence for band bending effects around isolated dislocation cores in an undoped 8° low angle grain boundary.