摘要:

Dense oriented superconducting Bi‐Sr‐Ca‐Cu‐O films having zero resistance as high as 100 K have been made using a technique in which spray deposited and pyrolyzed films are densified by either melt quenching or flux sintering. The highestTcfilms were those prepared with PbO as a dopant/flux on MgO substrates. Films without lead doping prepared on both BeO and MgO substrates yielded resistive transitions of 81–83 K. For these latter films, it was demonstrated that a subsequent anneal in argon enhanced theTcto 87 K. The films were characterized by x‐ray diffraction, scanning electron microscopy, and four‐point probe resistance measurements. The critical current density of a film having aTcof 81 K was 4000 A/cm2at 78 K and 14 000 A/cm2at 55K.

ISSN:0003-6951    

DOI:10.1063/1.100778

出版商:AIP    

年代:1989

数据来源: AIP

摘要:

We show that thermally stimulated luminescence is an important method for detecting insulating impurity phases that commonly occur in highTcsuperconductors. The technique is sensitive to impurity phases at <1% level with a probe depth of ∼ 1 &mgr;m, which is the region of interest for many superconductor applications. Samples of Y2O3, Y2BaCuO5, YBa2Cu3O6.2, BaCO3, Ba3CuO4, BaCuO2, and YBa2Cu3Ox(x≊7) were investigated. All but the high quality sintered pellets of YBa2Cu3Oxexhibited relatively intense luminescence. The absence of luminescence, and thus of insulating phases, is correlated with low values of rf surface resistance.

ISSN:0003-6951    

DOI:10.1063/1.101419

出版商:AIP    

年代:1989

数据来源: AIP

摘要:

In this letter a new method for the observation of thermomagnetically written domains using Lorentz electron microscopy is discussed. Domains are written in a GdTbFe layer deposited on a specially prepared silicon wafer disk, provided with Si3N4windows. This allows direct observation by Lorentz microscopy of the magnetization patterns dynamically written under recording conditions. It is shown that by locally heating the GdTbFe layer with a continuous laser beam, combined with high‐frequency switching of the magnetic field, very high storage densities can be achieved. Domains with a length of 0.25 &mgr;m in the direction of disk rotation could be written.

ISSN:0003-6951    

DOI:10.1063/1.101420

出版商:AIP    

年代:1989

数据来源: AIP

摘要:

We have measured the frequency‐dependent complex dielectric permittivity of silicon oxynitride films in the frequency range 10−4–107Hz for temperatures of 290–365 K. The dielectric permittivity displays a conductivity relaxation at low frequencies and gradually goes over to an almost frequency‐independent complex permittivity at high frequencies. The experimental data can be accounted for by assuming that the conductivity relaxation is superimposed on the frequency‐independent contribution to the permittivity. On that premise, the conductivity relaxation and the onset of dc conductivity are in good agreement with calculations by the continuous time random walk model employing a distribution of transition rates pertinent to a fractal time process.

ISSN:0003-6951    

DOI:10.1063/1.100779

出版商:AIP    

年代:1989

数据来源: AIP

ISSN:0003-6951    

DOI:10.1063/1.101380

出版商:AIP    

年代:1989

数据来源: AIP