摘要:

Oriented superconducting YBa2Cu3O7thin films were deposited on yttria‐stabilized zirconia substrates by ion beam sputtering of a nonstoichiometric oxide target. The films exhibited zero‐resistance critical temperatures as high as 80.5 K without post‐deposition anneals. Both the deposition rate and theclattice parameter data displayed two distinct regimes of dependence on the beam power of the ion source. Low‐power sputtering yielded films with largecdimensions and lowTc’s. Higher power sputtering produced a continuous decrease in theclattice parameter and an increase in critical temperatures.

ISSN:0003-6951    

DOI:10.1063/1.103292

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Levitation and rotation of cylindrical rare‐earth magnets on yttrium‐barium‐copper‐oxide superconducting bearings has been sustained at speeds of up to 120 000 rpm with a surface speed of 40 m/s. The decay of the free rotation rate has been measured at both atmospheric pressure and a partial vacuum to 2.6 &mgr;m Hg. The decay measurements in vacuum indicate that the flux drag torques are constant and independent of speed. The magnetic shear stress on the rotor magnet is estimated to be 150 dyn/cm2. It is believed that drag torques on rotating magnets are related to asymmetry in the flux density pattern of the magnet.

ISSN:0003-6951    

DOI:10.1063/1.102795

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Superlattices of YBa2Cu3O7−x/YyPr1−yBa2Cu3O7−x(y=0.8 and 0.0) have been successfully growninsituon MgO and LaAlO3by using a multitarget pulsed laser deposition system. Satellite peaks have been observed in x‐ray diffraction for the superlattices with modulation wavelengths from about few tens of angstroms to few hundred angstroms. The x‐ray diffraction measurements also indicate that the multilayers havecaxis normal to the substrates. Good crystallinity has been observed in the superlattices with He ion backscattering minimum yields of about 10%, indicating highly oriented growth. The presence of a periodic layer structure was further confirmed by the observation of composition oscillations in these structures by secondary‐ion mass spectrometry.

ISSN:0003-6951    

DOI:10.1063/1.103293

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

We report on the temperature dependence of the critical current (Ic) nearTcfor two Y‐Ba‐Cu‐O thin films having zero‐dissipation temperature (Tc) of 81 K and a Y‐Ba‐Cu‐O thin film havingTcof 71 K. At temperatures higher than 0.9Tc, the critical current in a voltage criterion of 1 &mgr;V/cm appears proportional to (1−T/Tc)nwithn≊2, andn≊1.5 in a 10 &mgr;V/cm criterion, exhibiting the dependence ofnon the critical current criteria. This observation is in contrast with the report ofn=1.5 by Ogaleetal. [Phys. Rev. B36, 7210 (1987)], Yuanetal. [J. Appl. Phys.64, 4091 (1988)], and Horngetal. [Phys. Rev. B39, 9628 (1989)], implying thatn=2, the value for the superconductor‐normal metal‐superconductor tunneling junction of BCS superconductors nearTcmust be taken into consideration to understand the intergrain tunneling process in polycrystalline highTcthin films.

ISSN:0003-6951    

DOI:10.1063/1.103294

出版商:AIP    

年代:1990

数据来源: AIP