Oxygen-nonstoichiometry effect on the superconducting properties of the Sr-free Bi cuprates

F. Munakata; T. Kawano; H. Yamauchi; Y. Inoue

doi:10.1103/PhysRevB.42.8008

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Oxygen-nonstoichiometry effect on the superconducting properties of the Sr-free Bi cuprates

F. Munakata, T. Kawano, H. Yamauchi, Y. Inoue

DOI 10.1103/PhysRevB.42.8008 · Physical Review B

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Abstract

The effects of oxygen nonstoichiometry on normal-state electrical conduction in and the superconducting properties of Bi2Ca2.5Nd0.5Cu2Oy and Bi2Ca2.5La0.25Pr0.25Cu2Oy have been investigated. From the temperature dependence of the normal-state resistivity of Bi2Ca2.5Nd0.5Cu2Oy, it is speculated that oxygen nonstoichiometry controls the metal-to-semiconductor transition. From the dependence of the high-temperature resistivity on oxygen partial pressure and the thermogravimetric behavior of Bi2Ca2.5Nd0.5Cu2Oy and Bi2Ca2.5La0.25Pr0.25Cu2Oy, it is found that the charge carriers in these cuprates are holes. A long-period modulation is observed by electron diffraction. The modulation is near commensurate with a period equal to 9b. The superconducting properties of Bi2Ca2.5Nd0.5Cu2Oy and Bi2Ca2.5La0.25Pr0.25Cu2Oy are dependent on oxygen partial pressure during sintering, but the modulation period remains unchanged. Although the Cu oxidation states in both Bi2Ca2.5Nd0.5Cu2Oy and Bi2Ca2.5La0.25Pr0.25Cu2Oy, which are sintered at PO2=1 atm, are the same, being equal to 2.08, their superconducting properties are found to be different. This may suggest that the effective valences of Cu and O are different from the conventional integer values because of charge transfer between Cu and O.

Source-reported materials — not catalogue approval

Formula	Reported Tc (K)	Pressure (GPa)	Type
Bi2Ca2.5Nd0.5Cu2Oy Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula.	33	Pressure not reported	zero_resistance
Bi2Ca2.5Nd0.5Cu2Oy Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula.	54	Pressure not reported	onset
Bi2Ca2.5Nd0.5Cu2Oy Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula.	20	Pressure not reported	zero_resistance
Bi2Ca2.5Nd0.5Cu2Oy Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula.	47	Pressure not reported	onset
Bi2Ca2.5La0.25Pr0.25Cu2Oy Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula.	45	Pressure not reported	zero_resistance
Bi2Ca2.5La0.25Pr0.25Cu2Oy Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula.	63	Pressure not reported	onset
Bi2Ca2.5La0.25Pr0.25Cu2Oy Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula.	23	Pressure not reported	zero_resistance
Bi2Ca2.5La0.25Pr0.25Cu2Oy Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula.	52	Pressure not reported	onset