摘要:

Multilayers of YBaCuO superconductors and Ni‐doped YBaCuO superconductors have been grown by the laser ablation technique to study the flux pinning properties of the nonmagnetic/magnetic superconducting heterostructures. Even though Ni doping depressed the superconducting properties of the single layer films, when sandwiched between high quality YBaCuO films, the composite showed high critical temperatures. Three‐layer and five‐layer structures of the YBaCuO/YBaCuNiO system become superconducting around 87 K when the doped layer thickness was below 100 A˚. Three‐layer structures grown on ZrO2(100) showed critical current densities of 3×106A/cm2at 77 K, which is about three times larger than the reported results in the literature. Epitaxial layer growth between the two superconductors was indicated by x‐ray diffraction measurements, which showed completec‐axis orientation with full width at half maximum of 0.45° in a (006) line scan. Behavior of the critical current up to 0.85 T and temperatures down to 66 K has been studied. Critical current densities close to 4.5×106A/cm2in 0.85 T fields perpendicular to the films have been obtained at 67 K.

ISSN:0003-6951    

DOI:10.1063/1.104155

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Superconducting Tl2Ba2CaCu2Oxfilms were fabricated using a three‐step process. Amorphous BaCaCuOF films were deposited on MgO(100) single‐crystal substrates by metalorganic chemical vapor deposition at 500 °C using fluorinated &bgr;‐diketonate complexes of Ba, Ca, and Cu. The fluorine was stripped in wet oxygen at 785 °C andc‐axis oriented Tl2Ba2CaCu2Oxfilms were then formed by annealing in dry at 870 °C in the presence of Tl2O3/Ba2Ca2CuN3Oxpellets. The best films showed onsets of superconductivity at 125 K and zero resistivity was achieved by 108 K. Critical current densities as high as 104A/cm2were obtained at 90 K.

ISSN:0003-6951    

DOI:10.1063/1.104156

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

We used synchrotron‐radiation photoemission to investigate the chemical reactions that occur during the silver cladding process of BiSrCaCuO−used to increase the critical current density by over a factor of 50. We find that the Cu‐O planes are not directly affected by the chemical reaction, and that such a reaction strongly affects the Bi and Sr atoms.

ISSN:0003-6951    

DOI:10.1063/1.103921

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Direct conversion of superconducting Y2Ba4Cu7O15−&dgr;(Y‐247) from YBa2Cu3O7−x(Y‐123) was achieved at atmospheric pressure. The Y‐247 samples were synthesized by the reactions of Y‐123 and Cu‐(NO3)2at 860 °C in an O2ambient. The results strongly suggest that Y‐247 is a thermodynamically more stable phase than Y‐123 at the atmospheric pressure. The conversion also provides a novel and simple route to synthesize the Y‐247 compound.

ISSN:0003-6951    

DOI:10.1063/1.104157

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

A pyrophoric technique using an explosive exothermic reaction has been developed to yield calcined and microscopically homogeneous (0.3 &mgr;m size) powders of multicomponent cuprate systems. The technique has been used to synthesize superconducting materials of variable composition of the typeM1M2⋅⋅⋅MnOx. The bulk materials prepared from these powders show sharp (1 K) superconducting transitions and nearly ideal Meissner effect.

ISSN:0003-6951    

DOI:10.1063/1.104158

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

In this letter we report on the application of highTcsuperconductors for fabrication of far‐infrared Fabry–Perot resonators. Thin films of YBa2Cu3O7−&dgr;deposited on MgO substrates by the laser ablation technique were used as reflectors. Two films on two different MgO plates were arranged parallel at a distance determining the lowest order resonance. We demonstrate operation of a resonator in a frequency range (up to about 300 cm−1) in which MgO is transparent at low temperature.

ISSN:0003-6951    

DOI:10.1063/1.103922

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Microstructure and magnetic hysteresis have been compared for two samples of the YBa2Cu3O7−&dgr;(&dgr;∼0) high‐temperature superconductor, one unirradiated, and one irradiated with fast neutrons (E≳0.1 MeV) to a fluence of 3×1018n/cm2. Notable changes in the microstructure include strain‐induced contrast from regions 2–7 nm in size. An intrinsic critical current density (Jc) of 4.6×106A/cm2in zero field at 4 K has been determined from magnetic hysteresis measurements for the irradiated sample while 1.2×106A/cm2is noted for the unirradiated sample. We propose that the observed defect structure in the irradiated material is responsible for increased pinning and consequently higherJc’s.

ISSN:0003-6951    

DOI:10.1063/1.104159

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

A scanning tunneling microscope has been used to directly deposit nanometer‐scale structures into the input coil of a planar dc superconducting quantum interference device microsusceptometer. Iron pentacarbonyl was used as the source gas for the deposits, yielding dots with diameters ranging from 10 to 30 nm and heights from 30 to 100 nm. Measurements on the particles at low temperatures show them to be magnetic and reveal macroscopic spin properties.

ISSN:0003-6951    

DOI:10.1063/1.103923

出版商:AIP    

年代:1990

数据来源: AIP