Superconductivity at 67 K in (Pb,Cu)Sr2(Ca,Y)Cu2O7 by precise adjustment of oxygen

X. X. Tang; D. E. Morris; A. P. B. Sinha

doi:10.1103/PhysRevB.43.7936

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Superconductivity at 67 K in (Pb,Cu)Sr2(Ca,Y)Cu2O7 by precise adjustment of oxygen

X. X. Tang, D. E. Morris, A. P. B. Sinha

DOI 10.1103/PhysRevB.43.7936 · Physical Review B

T1

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Abstract

We demonstrate that high-temperature superconductivity (HTSC) with Tc=67 K can be induced in (Pb,Cu)Sr2(Y,Ca)Cu2O7−δ by precise oxygen adjustment, which is accomplished by heat treatment in high P(O2), followed by quenching. Superconductivity with Tc≊17 K was previously reported in this compound obtained by quenching from high temperature in 1 atm of oxygen. Since quenching leaves less oxygen than in annealed samples, it appears paradoxical that HTSC can be induced in this compound by high-pressure oxygen treatment. We find that, while oxidation in high P(O2) produces HTSC, excess oxygen taken up during subsequent annealing at lower temperature destroys the superconductivity; so quenching is required for high Tc. Thermogravimetric analysis shows that weakly bound oxygen is taken up into several distinct sites, one of which is required for the appearance of HTSC. However, occupation of the most weakly bound sites is detrimental to HTSC, at least in (Pb,Cu)Sr2(Y,Ca)Cu2O7. The appearance and then destruction of high-temperature superconductivity by adding successive amounts of oxygen in different sites may be a powerful tool to explore the mechanism of high-temperature superconductivity.

Source-reported materials — not catalogue approval

Formula	Reported Tc (K)	Pressure (GPa)	Type
(Pb,Cu)Sr2(Ca,Y)Cu2O7 Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula.	67	Pressure not reported	onset
(Pb0.5Cu0.5)Sr2(Y0.6Ca0.4)Cu2O6.99 Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula.	67	Pressure not reported	onset
(Pb,Cu)Sr2(Y,Ca)Cu2O7 Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula.	17	Pressure not reported	unknown
La2-xSrxCaCu2O6 Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula.	—	Pressure not reported	unknown