Evolution of atomic ordering in fine-grained YBa2Cu3O y high-temperature superconductors and its effect on superconducting transition temperature

Regularities of changes in unit cell parameters and superconducting properties of the optimally doped fine-grained YBa₂Cu₃O _y (y ≈ 6.92) high-temperature superconductors (HTSC) at the initial stage of the high-rate formation of orthorhombic crystal structure from the activated mixture of initial components are investigated. The orthorhombic distortion degree σ and the superconducting transition temperature T _c are characterized by uncommon correlation being different from that characteristic for coarse-grained samples. It is shown that there are much higher T _c values in fine-grained samples for a given parameter σ. It is concluded that all of the observed regularities are related to specific features of atomic disorder characteristic for fine-grained samples.