A study of the properties of the YBa₂Cu₃0_7-δ high temperature superconductorm

High temperature, T_c>90 K, superconductivity in YBa₂Cu₃O_7−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.