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The critical current density and flux-creep activation energy of YBa 2 C 3 O 7 rings were determined from ac-susceptibility measurements. A novel approach was developed theoretically and experimentally to derive the flux-creep exponent from higher susceptibility harmonics. An alternative method using a scaling approach yielded similar sample-to-sample variations, but qualitatively different values for the flux-creep exponent. This is discussed considering the limits of validity of the logarithmic approximation to the flux-line activation energy.

With a multiterminal technique we have studied the behavior of the in-plane voltage in high-Tc superconducting YBa2Cu3O7 films as a function of temperature T, magnetic field B and distance from the input current electrodes. Regions with different superconducting transition temperatures were obtained by selective sputtering between gold electrodes. The non-local voltages, measured outside of the direct current path, show an excess signal near the critical temperature Tc(B) which resembles that measured in different superconductors and attributed partially to charge imbalance effects, the presence of phase-slip centers and vortex–antivortex-interactions. We have determined the decay length of the non-local voltages as a function of field and temperature. We compared and analyzed the excess voltage and decay length with a current distribution model and an equivalent circuit of resistances. This model accounts for all the measured behavior of the non-local voltages and of the decay length. We discuss also estimates of the decay length based on charge imbalance and vortex correlations models.

A scanning mapping technique of surface resistance (Rs) using the sapphire dielectric resonator was developed and demonstrated for a 3-inch-diameter YBa2Cu3Oy film. The area of the 3-inch film was divided by 5×5 mm grid for scan, resulting in 101 measurement points. Values of Rs in the film varied from 2.9 to 3.8 m Ω at 22 GHz and 77 K. The distribution of Rs corresponded to that of the critical current density. Sampling of quality factors at each point was performed using non-contact measurement between film and sapphire. Since the airtight chamber was filled with dry N2 gas to avoid film degradation by frost and water during the warming process, perfect non-destructive measurement is realized. Fluctuation of distance between the surface of film and dielectric rod was monitored by resonance frequency. Errors in Rs caused by the fluctuation were calculated within ±0.01 m Ω . Furthermore, the system could detect a small ( 0.3 mm ×0.5 mm ) scratch defect as well as the gradient of film thickness on Ag film. This technique is effective for inspection of large-area high temperature superconducting films for microwave applications.

We investigated the dielectric loss tangent (tanδ) of sapphire single crystals produced by edge-defined film-fed growth (EFG) method using a dielectric resonator with YBa2Cu3Oy (YBCO) films. Surface resistance (Rs) of the YBCO film was low enough to obtain high resolution of tanδ measurement. For comparison, tanδ of the sapphire prepared by the Czochralsky (Cz) method was also evaluated. Measurements of 14 sapphire rods showed that EFG sapphire tends to have lower tanδ than Cz sapphire, while defects in Cz crystal were 1/14–1/2 less than that in EFG crystal. It means that the number of defects does not influence tanδ, if the density of defects is within the order of 104/cm2. In most EFG sapphire the value of tanδ at 30 K was estimated to be

A method is proposed for the side-selective and non-destructive determination of the critical current density ( j c ) of high- T c superconducting (HTSC) thin films deposited on both sides of a thin wafer. The method makes use of the alteration of induced voltage in a coil by the superconducting transition in the HTSC thin film. This voltage alteration is measured in dependence on AC current in the coil. In order to obtain the value of the critical current density, the geometry of the induced current density distribution in the HTSC thin film, and from it the induced voltage in the coil, were calculated for T T c (full superconducting state of the film) as a function of the distance of film to coil. The finite element approach is used for the calculations. This procedure is applied to the semiautomatic routine characterization of j c of double-sided 3-inch diameter HTSC thin films, which are used for optimization of passive microwave devices.

the microstructure of epitaxial c oriented YBa 2 Cu 3 O 7−δ films deposited and patterned by different routine methods typical of device layouts is studied by TEM. Film systems up to three layers were either deposited or sputtered onto SrTiO 3 , LaAlO 3 , MgO, and R-cut sapphire buffered by CeO 2 or YSZ. Specific grain boundaries of accidental grains either a -axis up oriented or in-plane rotated are discussed in terms of their growth, flux pinnig, and weak-link behavior. These properties should be affected by adhering Y 2 O 3 inclusions which otherwise occur highly dispersed in the bulk, preferably of the sputtered films. Dislocations, probably attributed to twin boundaries and to faulty c -stacking, are considered in view of the film growth, mechanical relaxation, and flux pinning. Within a device pattern of YBCO/SrTiO 3 /YBCO, thoroughly good epitaxial orientation is also found on top of crossing layer edges in agreement with the measured high j c at the crossovers. Particular reference is given to the literature on the origin and the effects of microstructure defects.

A method is proposed for inductive measurement of the critical current density j c of HTSC thin films without lateral structuring on the base of a simple two-coil arrangement. The magnetic shielding of the HTSC thin film is measured in dependence on temperature and AC current in the primary coil. In order to obtain the value of the critical current density the geometry of the induced current-density distribution in the HTSC thin film was calculated for T T c (full shielding) by a finite element solution of the system of integral equations for the magnetic vector potential.

Temperature features forming the passband of microwave high-temperature superconducting band-pass filters during temperature change about 87–68.5 K have been investigated. We found that forming of different parts of the passband depends on temperature. Pictures of forming passband at difference temperature were obtained. The filter insertion loss during temperature change about 87–68.5 K was investigated. The insertion loss of a nine-pole YBCO band-pass filter at 83.5 K was about 0.5 dB, at 77 K––about 0.2–0.15 dB, and at 70 K––

Large-area pulsed laser deposition (PLD) has reached a state in terms of film quality and reproducibility which makes possible now real applications of PLD-YBa 2 Cu 3 O 7− δ (YBCO) thin films on both sides of R -plane sapphire substrates as HTSC devices in mobile communication systems. Bandpass filters optimized from PLD-YBCO thin films presently fulfill the requirements of the main national companies which are active in future communication techniques. A relatively simple PLD arrangement with fixed laser plume and rotating substrate, with an offset between the laser plume and the center of the substrate is employed to deposit laterally homogeneous 4 inch diameter Ag-doped YBCO thin films. With the experience of more than 1000 double-sided 3 inch diameter films a high degree of homogeneity and reproducibility of j c and R s is reached. The extension up to 8 inch substrate diameter will increase the productivity of the flexible PLD technique considerably.

Secondary neutrals mass spectrometry (SNMS) was used for the first time for detailed investigation of the elemental concentration depth profiles of Bi-Sr-Ca-Cu-O thin films on SrTiO 3 (110), MgO(100), YSZ(100) and Si(100) substrates with YSZ or SrTiO 3 buffer layers. All the high-temperatyre superconducting (HTSC) thin films and buffer layers have been prepared by in situ pulsed laser deposition (PLD). Strong indications were found for interdiffusion of Bi-Sr-Ca-Cu-O film, substrate (except SrTiO 3 single crystals) and buffer layer if substrate temperature during the HTSC film deposition of 20 min duration exceeded 750–800°C. Therefore, T c ( R = 0) of Bi 2 Sr 2 Ca 1 Cu 2 O 8+ y films on silicon substrates with buffer layer is not higher than 70 K at present. SNMS depth profiling gives a more detailed insight into interdiffusion phenomena of thin film systems than other analytical techniques.

High- T c superconducting Bi-Sr-Ca-Cu-O films have been prepared by in-situ excimer laser induced deposition on MgO (100), ZrO 2 (100) and textured yttrium stabilized zirconia (YSZ) buffer layers on silicon from Bi 2 Sr 2 Ca 2 Cu 3 O χ (2223) targets. Epitaxial YSZ films have been grown on Si (100) and Si (111) by in-situ deposition using a Nd-YAG laser. Under optimized deposition parameters we obtained nearly single Bi 2 Sr 2 Ca 1 Cu 2 O x (2212) phase high- T c superconducting films on ZrO 2 and on YSZ layers on Si substrates. On MgO single crystals we observed under the same experimental conditions a considerably higher amount of the 2201 phase. The T c (0) of more than 80 K of the films on ZrO 2 single cyrstals was reduced to T c (0)=70 K in the case of Si substrates with YSZ buffer layers due to interdiffusion at the necessary high substrate temperatures of about 825°C.

An arrangement for large area PLD on 3-inch wafers is proposed. For in-situ deposited YBCO thin films on r-plane sapphire with YSZ buffer layer we inductively measured within 3 inch diameter values of the critical temperature T c (90%) from 85.9 K to 86.7 K and values of the critical current density j c (77 K) from 1 × 10 6 to 2 × 10 6 A/cm 2 . Large area PLD seems to be a very promising technique for homogeneous coating of 3-inch wafers by epitaxial oxide thin films.