SUPERCONDUCTIVITY in the high-transition-temperature (high-Tc) copper oxide superconductors seems to arise from layers of copper–oxygen squares, pyramids or octahedra. Recently the compound Sr2CuO2CO3 was found to contain layers of CuO6 octahedra1 (Fig. 1), suggesting that it might be made superconducting by appropriate doping. But the presence of carbonate as an impurity is known to degrade the superconducting properties of materials such as and (refs 2, 3), much effort having been made to minimize residual carbon in these compounds by optimizing processing methods4. It is thus of some interest to see whether Sr2CuO2CO3 can be made superconducting despite the carbonate ions incorporated in the structure. Here we report the synthesis, at 50 atm oxygen partial pressure, of superconducting (0.4≤x≤0.65, y≈O.1), with Tc (onset) up to ∼40 K and zero resistance at up to ∼26K. The crystal structure contains CuO2 sheets alternating with , slabs, which serve as charge reservoir layers: substitution of ∼10% copper for carbon in the slabs introduces holes into the CuO2 sheets, making the compound superconducting.

A new copper oxide superconductor containing carbon

The temperature and oxygen pressure conditions were determined by thermogravimetry for decomposition of phase-pure YBa 2 Cu 3 O 7− x and YBa 2 Cu 4 O 8 from 3 Pa to 0.1 MPA O 2 . All extant data were reviewed to determine the conditions for thermodynamic dynamic stability of phase-pure YBa 2 Cu 3 O 7− x and for compositions lying between YBa 2 Cu 3 O 7− x and CuO . Thermodynamic values for YBa 2 Cu 4 O 8 were derived, as was the 123-CuO section of the Y 2 O 3 -BaO-CuO phase diagram.

Decomposition of YBa2Cu3O7−x and YBa2Cu4O8 for po2≤0.1 MPa

The temperature ( T ) and oxygen pressure ( p O 2 ) conditions were determined from 6 Pa to 0.1 MPa O 2 for several equilibria in the YBa 2 Cu 3 O 7− x −BaCuO 2+ y −CuO−Ag system. These included the y − T − p O 2 interrelationships, the T - p O 2 conditions for decomposition of BaCuO 2+ y , and the effects of Ag on several eutectic and peritectic temperatures.

Study of phase behavior in the YBa2Cu3O7−x−BaCuO2+y−CuO−Ag system

In this paper we present a review of high-gas-pressure single crystal growth studies of YBa2Cu4O8 and Y2Ba4Cu7O15-x performed in oxygen pressure up to 3000 bar and Hg1-xMxBa2Can-1CunO2n+2+ (M = Pb, Re; n = 1-7) compounds in argon pressure up 11 000 bar at temperature up to 1200 °C. Chain compounds A1-xCuO2 (A = Sr, Ca, Ba) have been synthesized at high oxygen pressure up to 2000 bar. High-pressure phase diagram studies of the investigated systems are also discussed. Structure analyses of Y2Ba4CunO2n+x (n = 6-8), Hg1-xMxBa2Can-1CunO2n+2+ (M = Pb, Re; n = 1-8), Sr0.73CuO2 and (Sr,Ca)4Cu6O10 single crystals have been performed. The effects of substitutions and trends in bondlengths are discussed. The vortex state properties of HgBa2Ca2Cu3O8+ and YBa2Cu4O8 single crystals are compared. For Hg-based compounds, the influence of oxygen content, chemical substitutions and radiation defects on vortex pinning were determined. The quasi-one-dimensional cuprates Ca0.83CuO2 and Sr0.73CuO2 show an antiferromagnetically ordered state of long-range 3D character at T < 10 K. The spin dynamics of Sr0.73CuO2, measured by inelastic neutron scattering, indicate that this ordered state coexists with a dimerized singlet ground state.

https://iopscience.iop.org/article/10.1088/0953-2048/12/9/201/pdf

High-pressure synthesis, crystal growth, phase diagrams, structural and magnetic properties of Y2Ba4CunO2n+x, HgBa2Can-1CunO2n+2+ and quasi-one-dimensional cuprates

The effects of composition, processing time ( t ), temperature ( T ) and O 2 partial pressure ( p O 2 ) on the superconducting transition temperature, T c , were investigated for La 1+ z Ba 2- z Cu 3 O y . Tallon and Flower's prediction of T c ≈ 100 K [Physica C 204 (1993) 237] at z = 0 could not be attained. Instead, the T c maximum of 93–94K is similar to that of the yttria analog. As z was increased, the T c values increased gradually by a few kelvin until z = 0.2, which is at the orthorhombic to tetragonal transition, and then decreased more abruptly, with no superconductivity for z ≥0.5. Crucial steps in the process at all z values include the highest temperature anneal (1065°C) in 0.1 MPa O 2 , reduction of the oxygen content at 950°C and cooling to 300–400°C, both at 100–1000 Pa O 2 , and reoxygenation at 0.1 MPa O 2 during slow cooling (5–20°C/min) to T c decreased fairly monotonically with decreasing y at z = 0.08, and a La excess of 0.2 and Cu nonstoichiometry on both sides of Cu/(La+Ba) = 1 generally depressed T c .

Effects of composition and processing on the superconductivity of La1+zBa2-zCu3Oy☆

The YBa2Cu3O7−x and YBa2Cu4O8 phases were made from micron-size CuO, Y2O3, and BaCO3 by a process that included conversion at 50 to 1000 Pa O2 absolute. Thermogravimetric and X-ray analyses were used to characterize the conversion process. The process parameters included batch size, oxygen pressure, heating rate, final temperature, Y:Ba:Cu ratio, and CuO particle size. BaCuO2 was generally the only detectable intermediate phase. Friable powders with 150- to 600-ppm carbon were produced without the intermediate grinding and firing common to atmospheric processes.

Synthesis of Y-Ba-Cu-O superconductors in subatmospheric oxygen

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Decomposition of YBa2Cu3O7−x and YBa2Cu4O8 for po2≤0.1 MPa

Synthesis of Y-Ba-Cu-O superconductors in subatmospheric oxygen