Effect of compositional variation and annealing in oxygen on superconducting properties of Y1Ba2Cu3O8−y

Abstract

Changes in the ratios of cations by ∼10% off the ${\mathrm{Y}}_1$ ${\mathrm{Ba}}_2$ ${\mathrm{Cu}}_3$ ${\mathrm{O}}_{8\mathrm{-}\mathrm{y}}$ composition demonstrated that a range of solid solutions exists in this material. The critical temperature within this range is strongly composition dependent and falls off from above 90 K to ∼70 K. Annealing stoichiometric samples in 1 bar of oxygen at 700 °C for 36 and 108 h resulted in narrowing of the magnetic susceptibility transition and significant increases in the critical current density $J_c$, p-type effective carrier concentration $n^{\mathrm{*}}$, and upper critical field, $H_{c2}$. After annealing, $J_c$ between 5 and 60 kOe was (3–1.5)×${10}^4$ A/${\mathrm{cm}}^2$ at 4.2 K and (2–0.5)×${10}^2$ A/${\mathrm{cm}}^2$ at 77 K. The value of $n^{\mathrm{*}}$ after annealing was 4.2×${10}^{21}$ ${\mathrm{cm}}^{\mathrm{-}3}$. An extrapolated value of $H_{c2}$(T=0)=1.2 MOe was obtained from ‖${\mathrm{dH}}_{c2}$/dT‖=19 kOe/K. A set of microscopic superconducting parameters was derived from results of resistive measurements made on a single, annealed specimen.