Influence of annealing in oxygen and argon on the superconducting properties of Li-doped YBCO single-grain bulks

Abstract YBa 2 (Cu 1- x Li x ) 3 O 7-δ single-grain bulk superconductors with different Li concentrations were grown using the top-seeded melt growth process. Structural analysis of the samples and magnetisation measurements showed that substitution of the Cu atoms by the Li atoms took place in the YBa 2 Cu 3 O 7-δ crystal lattice. This substitution was accompanied by the formation of effective pinning centres, which improved the pinning properties of the samples and increased the critical current density. Additional annealing and reannealing in oxygen and argon showed that the superconducting transition temperature displays substantially more suppression, when the Li-doped YBa 2 Cu 3 O 7-δ samples were annealed in argon, that was associated with different distribution of the Li atoms between the CuO chains and the CuO 2 planes in comparison to annealing in oxygen. Investigation of the critical current densities showed that the pinning properties of YBa 2 (Cu 1- x Li x ) 3 O 7-δ single-grain bulk superconductors did not depend on the arrangement of the Li atoms in the YBa 2 Cu 3 O 7-δ crystal lattice. It was also observed that the crystal lattice parameters and the mean diameter of the non-superconducting Y 2 BaCuO 5 particles systematically change with Li concentration.