Effect of compositional variation and annealing in oxygen on superconducting properties ofY1Ba2Cu3O8−y

Abstract

Changes in the ratios of cations by \ensuremath{\sim}10% off the ${\mathrm{Y}}_{1}$${\mathrm{Ba}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{8\mathrm{\ensuremath{-}}\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 \ensuremath{\sim}70 K. Annealing stoichiometric samples in 1 bar of oxygen at 700 \ifmmode^\circ\else\textdegree\fi{}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)\ifmmode\times\else\texttimes\fi{}${10}^{4}$ A/${\mathrm{cm}}^{2}$ at 4.2 K and (2--0.5)\ifmmode\times\else\texttimes\fi{}${10}^{2}$ A/${\mathrm{cm}}^{2}$ at 77 K. The value of ${n}^{\mathrm{*}}$ after annealing was 4.2\ifmmode\times\else\texttimes\fi{}${10}^{21}$ ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}3}$. An extrapolated value of ${H}_{c2}$(T=0)=1.2 MOe was obtained from \ensuremath{\Vert}${\mathrm{dH}}_{c2}$/dT\ensuremath{\Vert}=19 kOe/K. A set of microscopic superconducting parameters was derived from results of resistive measurements made on a single, annealed specimen.

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