AC transport measurements show that the vortex dynamics in a twinned superconducting Y-Ba-Cu-O single crystal are consistant with a second order vortex-solid melting transition. Indentification of the universal functions and consistent measurements of the critical exponents v = 0.7 and z= 3.0 found in magnetic fields from IkOe to 90kOe as well as DC transport measurements offer strong evidence for this transition.

YBa2Cu3O7−x thin films have been grown in-situ on Si (100) with a composite buffer layer of Pt/Ta/ONO (ONO stands for a S1O2 / Si3N4 /SiO2 trilayer) by plasma enhanced metal organic chemical vapor deposition (PE-MOCVD). X-ray diffraction measurements indicate that c-axis oriented YBa2Cu3O7−x films are formed in-situ at substrate temperatures as low as 650 °C on Pt/Ta/ONO/Si. The composite P/Ta/ONO provided an adherent metallic interlayer and effectively prevented the interaction between YBa2Cu3O7−x and Si. Four probe resistivity measurements indicate the onset of superconductivity at 92 K and achieved zero resistance at 65 K.

High Tc superconducting Gd-Ba-Cu-O materials were synthesized via the acetate precursor process. Aqueous solutions of < 0.6 M of metal cations were applied to substrates of yttria stabilized zirconia. Homogeneous films were applied to the substrates by use of the spin coating technique. The substrates were fired in air at 500°C in between each applied coat. After coating the substrates with 10–30 coats, they were crystallized by heating to 900°C in Ar or O2 with or without a 1 T magnetic field. The applied magnetic field was found to produce c-axis alignment for the thinner coats. Annealing in argon produced alignment but the effect was less pronounced than annealing in oxygen. Substrates with 30 coats were not aligned for either environment.

Thin films of YBa2Cu3O7/Ag multilayered structures have been grown by dc magnetron sputtering on MgO(lOO) substrates. The samples have been characterized by X-ray diffraction, scanning tunneling microscopy and resistivity measurements. Multilayers with YBCO layer thickness above 40nm show superconducting transitions and zero resistances higher than 70K. These layers show c-axis growth perpendicular to the substrate and the silver layers have preferential (111) orientation normal to the substrate too. Finally STM images reveal screw dislocation spirals at the YBCO layer surface even when the superconducting layer is grown on silver (111) underlayers.

The physical properties of the ceramic YBa2Cu(3-x)CoxOy have been investigated in order to evaluate its usefulness as a substrate material for YBCO superconductors. YBa2Cu(3-x)CoxOy has been found to be thermally and chemically compatible with 123 and displays adequate electrical properties for a substrate material. A material with the nominal composition of YBa2Cu2.2CO0.8O7 was investigated, extensively. The mechanical properties of this material were found to be poor, e.g., tensile strength was only 60 MPa. A semiconductor-like behavior was observed with a room-temperature resistivity of 70 mμ.cm and a resistivity equal to 4 × 106 mn.cm at 77K. [ Key words: YBa2Cu3Oy, cobalt substitution, substrate, electrical properties, thermal properties, processing]

-Heteroepitaxial superconducting Bi,Sr2CaCu2Ox (BSCCO 2212) thin films have been formed by solid phase epitaxy from amorphous films deposited on (100) LaA1O3 single crystal substrates by organometallic chemical vapor deposition. The epitaxial structure of the film is confirmed by x-ray diffraction including θ/2θ and Φ (in plane rotation) scans. Cross-sectional high resolution transmission electron microscopy indicates that the film-substrate interface is nearly atomically abrupt. Improvements in superconducting properties of the epitaxial thin films are noted in comparison to highly textured films deposited on MgO.

The multilayers based on Nb/NbO (S-I-S) were investigated in external magnetic fields at various temperatures. It was found that the shear deformation of the solid vortex lattice de-termenes critical current density in the case of large period structures and high parallel fields. The solid vortex lattice can be destroyed by decreasing of both the period and the upper critical field. The qualitative change of the magnetic field dependence of the volume pinning force was observed as temperature was increasing. It reveals structural transitioon from elasti-cally deformed flux line lattice to plastically deformed one. Thus the scaling low is destructed for these structures. We have determened the volume pinning force by direct summing of elementary pinning forces in oxide layers in this case.

Tl2Ba2Cuo6+δ(T1-2201) single crystals are prepared by a KCI flux method. In-plane and out-of plane resistivities (ρabρc as well as the in-plane Hall coefficient are measured for the single crystal samples with various 7c's. The ρc values are as large as ∼10−1 Ω cm, which is larger than that of YBa2Cu3O7, but smaller than that of Bi2Sr2CaCu2O8. Temperature dependences of ρc show metallic behaviors for both normal metallic and 75-K superconducting samples. Temperature dependence of in-plane resistivity par changes from ∼T2 to ∼T1 with increasing Tc In-plane Hall coefficient RH shows a characteristic maximum at about 100 K for all samples. Although both ρab and RH have rather a complicated temperature dependence, inverse Hall mobility μH(=ρab/RH always exhibits clear T2 dependence for all samples. These results suggest that the intrinsic scattering rate of this material varies as ∼T2, just like in an ordinary Fermi liquid, and that the carrier concentration actually changes with temperature like that observed in nH(=1/RHe).

Using in-situ reflection high-energy electron diffraction (RHEED), we studied the growth of Bi-Sr-Ca-Cu-O (BSCCO) thin films prepared by reactive evaporation using layer-by-layer deposition. Bi2Sr2CaCu2Ox(2212) tends to be grown three-dimensionally if it is grown directly on (100) SrTiO3, in contrast to Bi2Sr2CuOx(2201) which is easily grown two-dimensionally on SrTiO3. Two-dimensional 2212 growth can be realized, if a buffer layer of 2201 is deposited on (100) SrTiO3 and growth interruption is utilized after SrO layer deposition. A buffer layer of only two 2201 unit cells improved the surface crystallinity of the substrate for the epitaxial growth of 2212. Growth interruption for two minutes after the 2nd SrO layer in the half unit cell is necessary to keep two-dimensional layered growth. The resulting Tc (zero) is 76 K and Jc (at 4.2 K) is 1.5 × 106 (A/cm2) with these epitaxial films.

Preparation processing to obtain 124 single phase films has been studied by MOCVD. The YBCO thin films which were fabricated on MgO(100) and SrTiO3(100) substrates, respectively, were obtained under both conditions of Ts(temperature of susceptor)=800°C and Po2(oxygen partial pressure)=17.5torr. It was found that the oriented peaks of 124 c-axis and of 123 a-axis were more prominent than others at the composition ratio(Y/Ba/Cu=l.0/2.7/4.7), using the MgO(100) substrates. The 123 a-axis oriented grain was observed by using SEM and TEM. We have obtained thin films which were dominant in the 124 phase on the SrTiO3(100) substrates. The film surface morphology on the SrTiO3(100) substrate was smoother than that on the MgO(100) substrate. The origin of a-axis oriented grain growth was explained by the surface step(about 10 À) on MgO(100).

By means of a Langevin dynamic simulation we studied the current-voltage characteristics of a two-dimensional (2D) Josephson-coupled lattice as a model high-Tc superconducting film. The result illustrates qualitative features of non-Ohmic power-law scaling behaviors observed in transport measurements, including striking effects of applied magnetic fields. We thereby suggest that the Kosterlitz-Thouless transition associated with 2D vortex-antivortex pairs may dominate over the resistive transition in weak magnetic fields H/Hc2 ≪C 1. Through a simple theoretical estimate, we also show that the KT model illustrates the thickness-dependence of resistive transition temperature and electric field effect in ultra-thin YBa2Cu3O7−x films.

The interface between an a-axis oriented YBa2Cu3O7-x film and a NdGaO3(110) substrate has been investigated by cross-section transmission electron microscopy (TEM). The orientational relationship between the a-axis oriented film and substrate is YBa2Cu3O7-x[001] / NdGaO3[001]. This preferentially c-axis aligned direction of the YBa2Cu3O7-x film would be caused by a very small lattice mismatch (0.1%) between b(=a) lattice constant of YBa2Cu3O7-x and of the pseudo-cubic sub-lattices in NdGaO3 at a substrate temperature of 750°C. Two kinds of imperfections have been observed in the crystal lattice of YBa2Cu3O7-x near the interface; One is the deviation of YBa2Cu3O7-x [301] from NdGaO3 [111]. The other type is pair dislocations with a positive and negative Burgers vectors in the YBa2Cu3O7-x (103) planes. These two kinds of defects at the interface would be act to reduce the tensile stress within a distance of about l.lnm from the substrate interface.

High-resolution transmission electron microscopy (HREM) has been used to study the microstructures of Y-Ba-Cu-0 superconducting thin films in which the YBa2Cu4O8 phase was the main phase. From cross-sectional observations, the c-normal 123 phase predominated in the film near the substrate surface, while the c-normal 124 phase occupied the region near the film surface. Another remarkable microstructure was that a-normal 123 variants overcame the c-normal 123 region, but the c-normal 124 phase surpassed the a-normal 123 phase in the upper part of the film.

YBCO bulk ceramics pre-heated at low temperature before sintering were studied on the structure and superconducting properties mainly by varying the concentration of Ba/Y ratio.

At 15.8–16.2wt% of the oxygen content Oc calcurated from the compositions of yttrium, barium and copper on the assumption that the valence of copper is 2, (123) phase is main and critical temperature(Tc) and critical current density(Jc) reach to 88–90K and about 103A/cm2, respectively.

It is presumed that there is a possibility of the exixtence of oxygen deficient and disordered phase in addition to (123) and (211) phases and BaCuO2.

Sr1−xNdxCuOy thin films are grown on SrTiO3 substrates by rf-magnetron sputtering and pulsed-laser deposition. The sputter-deposited film with x=0 has an “infinite-layer” structure whose lattice constants are: α=0.390 nm and c=0.347 nm. When x is larger than 0.1, the films contain a phase of the Sr14CuO24O41 structure. The laser-deposited films of Sr1−xNdxCuOy with x≤.075 were single phase of the “infinite-layer” structure. The lattice parameter c decreased and the lattice parameter αincreased, as the Nd content, x, increased. The films with α=0.10 and 0.125 exhibited superconducting onset temperatures around 26 K. Weak Meissner signals were observed for these films at temperatures below 30 K.

Films of CeO2 have been grown on Si and glass substrates using the laser ablation deposition technique. X-ray diffraction measurements for the films deposited on glass indicated that they are the same as films grown on Si covered with the native oxide. This evidence supports a picture in which chemical rather than crystal-lographic effects constrain the film growth. The crystal quality for films grown on Si was shown to improve with increasing film thickness away from the amorphous layer. Low cooling rates as well as reduced film thickness were effective in avoiding the formation of micro-cracks. The surface morphology was shown to be dependent on the laser wave-length as well as the oxygen partial pressure. Thin films of YBa2Cu3O7δ could easily be grown on CeO2/Si showing c-axis orientation, whereas the growth of BiSrCaCuO (2212) on CeO2/Si resulted in the two films mixing with each other.

Films of Y1Ba2Cu3O7-y have been grown by off-axis DC sputtering onto substrates of (100) SrTiO3. LaAlO, LaGaO3, Yttria-stabilized Zirconia, and MgO. Our best films, grown on SrTiO3 substrates at a temperature of 650°C and a sputtering pressure of 100 mTorr (consisting of 80 mTorr Ar and 20 mTorr O2) have room temperature resistivities of 280 μΩ-cm, an inductive Tcof 88 K and an inductive Jc 'Sof∼ 2.6 × 106 A/cm2 at 77 K and 3.9 × 107 A/cm2at 4.2 K. Films grown on YSZ tend to have higher resistivities (∼ 600 μΩ-cm) but still have Tc's of 86 K and Jc's of - 106 A/cm2 at 77 K. Films down to 550 Å still have Tc's of 86 K and Jc's at 77 K > 106 A/cm2. Films grown at lower temperatures (600°C) on S1TiO3 begin to show a-axis growth, but the superconducting properties deteriorate.

The residual surface resistance of a number of films of YBa2Cu3O7−x, prepared by off-axis sputtering onto MgO substrates, has been measured using a parallel-plate resonator technique. Deposition conditions were kept constant, apart from the substrate temperature. There is no correlation between surface resistance and other important microscopic parameters, such as Tc and c-axis lattice parameter. There is, however, a trend to higher Rs with increasing volume fraction of in-plane misoriented material, although the correlation is not perfect. Furthermore, we have found that most of the misoriented material is localized at the film substrate interface and, therefore, is probably not responsible for most of the RF losses. The data suggest that at higher deposition temperatures, there is an increasing tendency for 45° misoriented material to appear in the films, and a significant fraction of this material may be present closer to the free film surface. Scanning Tunneling Microscopy (STM) qualitatively supports this conclusion.

Superconducting thin films of DyBa2Cu3O7-δ_ are deposited on MgO(100) substrates by an ozone-assisted coevaporation technique. At a relatively low substrate temperature (610°C) and with a fixed ozone flux we prepare highly c-axis oriented films with very good superconducting properties. The critical temperatures of the films are commonly above 85 K with critical currents above 10 5 A/cm2. We report on composition, microstructure, electrical resistivity and critical current of two good films.

We have grown thin film composites of and YBa2Cu3O7−x and LaAlO3 by co-sputtering. A film with composition of 10% LaAIO3 by volume had a transition temperature of 58K and critical current density of 1.2 × 106 A/cm2 at 4K. We measured the temperature dependence of the critical current and obtained a good fit with Ginzburg-Landau theory for thin films. A perpendicular magnetic field was applied, and the critical current and pinning force measured. At 70 kOe, the critical current was suppressed only a factor of 4 from its zero-field value. The measured pinning force was 2 × 109 dyn/cm3 at 70 kOe and is comparable to that of YBa2Cu3O7−x films.