Effect of high-pressure oxygen annealing in promoting superconductivity in YSr2Cu2.7Fe0.3Oy: Evidence for Fe coordination number change in the chains

F. Shi; W. J. Bresser; M. Zhang; Y. Wu; D. McDaniel; P. Boolchand

doi:10.1103/PhysRevB.54.6776

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Effect of high-pressure oxygen annealing in promoting superconductivity in YSr2Cu2.7Fe0.3Oy: Evidence for Fe coordination number change in the chains

F. Shi, W. J. Bresser, M. Zhang, Y. Wu, D. McDaniel, P. Boolchand

DOI 10.1103/PhysRevB.54.6776 · Physical Review B

T1

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Abstract

A superconducting transition temperature (Tc) of 60 K and a shielding fraction (Vsh) of nearly 100% is achieved in tetragonal YSr2Cu2.7Fe0.3Oy samples only after high pressure (27 MPa) oxygen annealing at 915 °C. On the other hand, samples synthesized at ambient pressure become barely superconducting (Tcmax≃30 K, Vsh≃4%) even after prolonged annealing in an oxygen ambient. Fe57 Mössbauer spectroscopy measurements suggest that in samples synthesized at ambient pressure, Fe cations localized in the chains are present in metastable corner-sharing tetrahedral units (site A). At high oxygen pressures these sites (A) trap oxygen locally to form distorted trigonal bipyramid units (site C) which promote superconductivity as revealed by magnetization measurements. Fe cations at site C act as effective flux-pinning sites, with such samples displaying not only a large intragrain critical current (Jcm) but also a secondary peak in Jcm at a finite external field characteristic of flux pinning in a quasi-two-dimensional material.

Source-reported materials — not catalogue approval

Formula	Reported Tc (K)	Pressure (GPa)	Type
YSr2Cu2.7Fe0.3Oy Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula.	60	Pressure not reported	onset
YSr2Cu2.7Fe0.3Oy Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula.	30	Pressure unresolved	unknown
YSr2Cu3O7 Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula.	60	Pressure not reported	unknown
YBa2Cu3O7 Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula.	90	Pressure unresolved	unknown