High temperature,T c>90 K, superconductivity in YBa2Cu3O7−δ samples was observed from resistivity and magnetic susceptibility measurements. The zero-field-cooled susceptibility of the material was 60 to 100% of the ideal diamagnetic value depending on sample preparation. Structure identification by X-ray diffraction at both 293 and 89 K exhibited the same orthorhombic structure. Scanning tunnelling microscope investigations of the sample surface revealed steep step structure with 10×10 nm2 size crystallites and 5 to 100 nm high terraces. Temperature cycling between 77 and 293 K sometimes led to the appearance of white barium lumps on the surface and in the bulk of the sample causing the transition to the low resistance state at 90 K to disappear.
Naukkarinen, K., Arlauskas, K., Grönberg, L., Laiho, R., & Vanhatalo, J. (1989). A study of the properties of the YBa Cu 0 high temperature superconductorm. Journal of Materials Science, 24(4), 1203-1206. https://doi.org/10.1007/BF02397048