YBa2Cu3O7 High-temperature Superconductors Research Articles

Growth of Bicrystal Films of YBa2Cu3O7 High-Temperature Superconductor, with CuO Planes Tilted by up to 90°, on SrTiO3 Crystals

Bicrystal substrates, in which (100) planes in both single-crystal parts are rotated with respect to the surface by different angles around the [100] and [110] directions (parallel simultaneously to both the surface and bicrystal boundary), have been fabricated by solid-phase intergrowth on SrTiO3 crystals. Epitaxial bicrystal YBa2Cu3O7 films with different tilt angles of CuO planes to the surface have been grown on these bicrystals by pulsed laser deposition. The structure of these films has been investigated by X-ray diffraction. The films are shown to remain epitaxial when the film lattice is rotated from the position in which its (001) plane is oriented parallel to the surface by angles of up to 41° and 49° around the [100] and [110] axes, respectively. The possibility of growing bicrystal films of YBa2Cu3O7 high-temperature superconductor (HTSC), in which the CuO planes at different sides of the bicrystal boundary make different angles (up to 90°, which is the maximum possible angle from the symmetry point of view), has been demonstrated based on these data.

Growth of Complex Epitaxial Multi-Component Oxide Thin Films and Heterostructures with Strong Anisotropy

ABSTRACTWe briefly review our data on MOCVD growth problems of sandwich stacked heterostructures based on Bi-Sr-Ca-Cu-O and YBa2Cu3O7 high temperature superconductors. Non-superconducting layers were (Ca, Sr)CuO2, (Ca, Ba)CuO2 and Bi4Ti3O12. Structures were with c-axis normal or inclined with about 45° vs. the surface of the substrate. Film-substrate lattice relationship, growth mechanism and the resulting morphology controlling roughness and uniformity, stability domain of the phases and inter diffusion are all important aspects toward significant progress in the field. Our analysis indicates that requirements are more severe for non-c-axis heterostructures, and suggest some ideas for further improvements.

Bi 3 + cluster primary ions in SIMS depth profiling of YBaCuO high-temperature superconductor films

SIMS depth profiling of YBa2Cu3O7 high-temperature superconductor films was performed using a TOF.SIMS-5 instrument. A new approach was proposed to obtain additional information on the phase composition of YBa2Cu3O7 films based on detection of cluster secondary ions.

Current instability mechanisms in liquid-coolant-cooled high-temperature superconductors

The stable current distribution in Bi2Sr2CaCu2O8, Bi2Sr2Ca2Cu3O8, and YBa2Cu3O7 high-temperature superconductors depending on conditions of cooling thereof by liquid cryocoolants—helium, hydrogen, and nitrogen, respectively—is studied. It is shown that the current instability mechanism may change in going from one coolant to another. Consequently, stable states may be disturbed, first, when the conditions of cooling the superconductor surface change from nucleate boiling to film boiling. Such a thermal mechanism of stable current state disturbance is observed largely when a superconductor is cooled by liquid helium. Second, even for the nucleate boiling of a liquid coolant, current instability may result from the stable formation of the voltage-current characteristic of the superconductor. This type of injected current stability disturbance is most likely when a superconductor is cooled by liquid nitrogen. Criteria for determining a current instability mechanism in relation to the properties of the superconductor and coolant are given.

Structure formation in yttrium-barium cuprate superconductor films obtained from solutions of methacrylates on lanthanum aluminate substrates

Nanoscale structuring of YBa2Cu3O7 high-temperature superconductor films on a lanthanum aluminate LaAlO3 substrate was studied after annealing at 200–850°C. For this purpose, a 0.5% aerosol of Y, Ba, and Cu methacrylates was deposited on the substrate. A general scheme of the mechanism of complex oxide film formation from chemical solutions is suggested. The formation of complex oxide film structures from solutions was found to be a three-stage process irrespective of the deposition procedure. It included the liquid-phase, pyrolytic, and high crystallization stages.

Numerical modelling of the processes of exposure and development in electron beam lithography on high temperature superconductor thin films

In the present work a numerical modelling of the processes of exposure and development of the resist during electron beam lithography (EBL) on structures incorporating YBa2Cu3O7 high temperature superconductor (HTS) thin films is performed. Monte Carlo method is used to simulate the penetration of accelerated electrons in the target and to obtain radial distributions of absorbed electron energy density in the resist, during the irradiation of structures: 125nm polymethylmethacrylate (PMMA) resist layer (PMMA is the most widely used electron resist)/YBa2Cu3O7 film of thickness d=0, 100 or 300nm (YBa2Cu3O7 is the most promising HTS material for deposition of thin films)/SrTiO3 or MgO substrate (these are the most often used substrates for YBa2Cu3O7 thin films growth) at beam energies E0=25, 50 or 75keV. These distributions are approximated by a proper analytical function (combination of double Gaussian and exponential functions), called “proximity function”, the parameters of which are calculated using an original Monte Carlo technique and are used as input data in the modelling of the process of development of the electron resist.

A.C. Susceptibility and Specific Heat in Low B.C. Fields of La2-xSrxCuO4 and YBa2Cu3O7 High Temperature Superconductors

We report the giant effect of small d.c. fields on a.c. diamagnetic transitions in La2-xSrxCuO4, and YBa2Cu3O7. An unexpected frequency effect is observed. In order to elucidate the apparent conflict Between the high critical field slope as measured by magnetoresistance experiments and the large depression of a.c. diamagnetic transitions, we locate the bulk transition by high resolution specific heat measurements in small fields. The results, together with d.c. magnetization measurements near Tc and SEM micrographs, suggest a model where superconducting regions with a high critical field are separated by weak links.