Magnetization and Static Magnetic Susceptibility of Fine-Crystalline High-Temperature YBa2Cu3Oy Superconductors Synthesized by the Sol–Gel Method

A comparative study of the magnetization and static magnetic susceptibility of high-temperature superconductors (HTSC) YBa 2 Cu 3 O y synthesized by two variants of the sol–gel method with different average sizes of crystallites 〈 D 〉 ranging 0.4–2 μm has been performed in constant magnetic fields ( Н ≤ 6 kOe). It has been shown that the different annealing temperatures and times, at which their crystal structure is formed, change both the average sizes of crystallites 〈 D 〉 and the sizes of the structural homogeneity regions 〈 l 〉 and, at the same time, the magnetic field penetration depth (λ) and the coherence length (ξ). As a result, such parameters as 〈 D 〉 ~ λ and 〈 l 〉 ~ ξ become comparable, leading to a change in the physical characteristics of HTSCs. It has also been shown that the superconducting transition temperature T c determined from the measurements of magnetic characteristics in constant magnetic fields remains within values optimal for superconductivity ( T c ≈ 92 K) in the case of an optimal number ( y ) of oxygen atoms, which determine the levels of charge doping for a given compound.