Superconducting YBa2Cu3O7-x Thin Films Research Articles

Micro-Raman studies of substrate temperature effects on pulsed laser deposition fabricated YBa2Cu3O7-x epitaxial thin films

Micro-Raman spectroscopy has been used to analyse the substrate temperature effects on high temperature superconducting YBa2Cu3O7-x thin films grown by the in situ pulsed laser deposition method. In particular, the dependence of the epitaxy quality on substrate temperature Ts is studied. Our results reveal that films with the highest epitaxy degree are grown with substrate temperature Ts between 680 and 720 °C, in good agreement with previous superconducting transition temperature measurements and x-ray diffraction analyses. In addition, the formation and distribution of impurities produced during growth are identified by Raman spectra and Raman imaging, and they are found to be more pronounced at higher substrate temperatures. Finally, localized Raman analysis has been performed to investigate the orientation of the single crystal grains in films grown at substrate temperature Ts>760 °C. It is confirmed that, within the experimental error of 3°, the crystal a/b-axes of these single crystal grains have a strong tendency to orient themselves along the crystal axis of the substrate, independent of their size, shape and orientation of the domain boundaries.

Effect of the laser sputtering parameters on the orientation of a cerium oxide buffer layer on sapphire and the properties of a YBa2Cu3Ox superconducting film

The effect of the laser sputtering parameters on the crystal properties of CeO2 buffer layers grown on a (\(1\underset{\raise0.3em\hbox{$\smash{\scriptscriptstyle-}$}}{1} 02\)) sapphire substrate and on the properties of superconducting YBa2Cu3Ox thin films are investigated. It is shown that (100) and (111) CeO2 growth is observed, depending on the sputtering conditions. A buffer layer with the desired unidirectional orientation can be obtained by varying the heater temperature, the pressure in the chamber, and the energy density of the laser beam at the target.

Plastic deformation and vortex dynamics instability of the flux-line lattice in high-temperature superconductors

Abstract The role of plastic deformations on the vortex dynamics instability of the fluxline lattice (FLL) in high-temperature superconductors is investigated. A model is proposed where elastic instability characterizes the FLL dynamics in a certain domain when the plastic energy of dislocation exceeds the pinning energy in that domain. Under these conditions, the velocity of the flux lines moving in this domain will change. Accordingly, the force—velocity relationship of the vortex lines or, equivalently, the I—V characteristics of the superconductor will experience the same change. A criterion for the appearance of the instability in the FLL is proposed by ΔE D/E pin ≥ 1, where ΔE D is the plastic energy of dislocation and E pin is the pinning energy of a rigid flux line. When this criterion is applied, the experimental measurements on superconducting YBa2Cu3O7-x thin films were reproduced. These results confirm the importance of plastic deformations in the behaviour of the FLL in superconductors.

Plastic deformation and vortex dynamics instability of the flux-line lattice in high-temperature superconductors

Abstract The role of plastic deformations on the vortex dynamics instability of the fluxline lattice (FLL) in high-temperature superconductors is investigated. A model is proposed where elastic instability characterizes the FLL dynamics in a certain domain when the plastic energy of dislocation exceeds the pinning energy in that domain. Under these conditions, the velocity of the flux lines moving in this domain will change. Accordingly, the force—velocity relationship of the vortex lines or, equivalently, the I—V characteristics of the superconductor will experience the same change. A criterion for the appearance of the instability in the FLL is proposed by ΔE D/E pin ≥ 1, where ΔE D is the plastic energy of dislocation and E pin is the pinning energy of a rigid flux line. When this criterion is applied, the experimental measurements on superconducting YBa2Cu3O7-x thin films were reproduced. These results confirm the importance of plastic deformations in the behaviour of the FLL in superconductors.

Comparison of high-pressure dc-sputtering and pulsed laser deposition of superconducting YBa2Cu3O x thin films

Superconducting YBa2Cu3Ox thin films were deposited on NdGaO3 (110) substrates using two different techniques: dc sputtering at high oxygen pressure and pulsed laser deposition. The structure, electrical properties, and surface morphology of the obtained films were compared. The superior crystal quality of dc-sputtered films fabricated at the same temperature and at oxygen pressure of the same range as for laser-deposited films can be explained by a lower deposition rate providing time for recrystallization processes. The re-evaporation becomes significant for dc sputtering at high deposition temperatures and results in Badeficient films. The high mobility of atoms on the surface of the growing film during laser deposition helps in the formation of smoothc-oriented areas of the film.

Growth instability in LnSrGaO4 (Ln: Pr,Nd) crystal pulling

K2NiF4-type LnSrGaO4 (Ln: Pr,Nd) are grown by the Czochralski-pulling method as a new substrate material for the growth of superconducting YBa2Cu3Ox thin films. The shape of the PrSrGaO4 crystals exhibits a strong “twisting” with a “foot”. This growth instability is investigated by evaluating melt flow and phase formation: melt surface-flow patterns are analyzed, and pseudo-binary phase formation is investigated. Anomalous melting and cooling are found to result in crystallization instability. Melt instability and crystallization instability must, therefore, closely relate to the growth instability.

Pulsed laser deposition of high-Tc superconducting YBa2Cu3Ox thin films in Ar/O2 atmosphere

Electrical and structural properties of superconducting YBa2Cu3Ox thin films, obtained with pulsed laser deposition in an Ar/O2 mixture at different oxygen partial pressures and constant total pressure, were studied. NdGaO3 (110) and LaAlO3 (001) substrates were used. The crystal quality of the films was found to correlate to the contents of inclusions with the axis oriented normal to the substrate plane. The increase of argon partial pressure resulted in decrease of particle density on the film surface to less than 106 cm−2, accompanied by an increase of a-oriented phase content and a rapid fall of the critical temperature from 91 K to 80 K

Preparation and properties of a capacitor structure formed by doubled-sided YBa2Cu3O7-x films on SrTiO3 substrate

The preparation of high-temperature superconducting YBa2Cu3O7-x thin films on both sides of the SrTiO3 substrate by DC magnetron sputtering is reported. The films on both sides of the substrate exhibited well-oriented crystalline structure with the c axis normal to the substrate surface, Tc=80-91 K and Rs less than 0.05 Omega at 77 K and 60 GHz. The properties of the resultant SrTiO3 capacitor with YBCO electrodes were examined at frequency of 1 GHz. The following parameters were obtained: relative dielectric permittivity of 4*103 at 77 K and dielectric loss tangents of 3*10-4 at 77 K. No hysteresis in the dependence of the capacitance on the DC bias voltage was observed.

硝酸塩水溶液のパルス噴霧熱分解法によるＹＢａ２Ｃｕ３Ｏ７−ｘ超伝導薄膜の作製

硝酸塩水溶液のパルス噴霧熱分解法によるＹＢａ２Ｃｕ３Ｏ７−ｘ超伝導薄膜の作製

Superconducting YBa2Cu3O7-x thin films prepared by DC plasma chemical vapour deposition

YBa2Cu3O7-x superconducting thin films were grown on polycrystalline yttria-stabilized zirconia (p-YSZ) and single-crystalline SrTiO3 substrates by DC plasma-assisted metallorganic chemical vapour deposition. A DC plasma was generated in the reaction chamber by applying a DC potential of 200 V at a plasma current of 2 mA. The as-deposited films on an SrTiO3 substrate at a temperature of 730 degrees C show a sharp resistive transition of Tc,zero=88 K. We show that DC plasma-assisted metallorganic chemical vapour deposition is useful to obtain YBa2Cu3O7-x thin films with the c axis normal to the p-YSZ and SrTiO3 substrates.

YBa2Cu3O7-x Superconducting Thin Films Grown on CaNdAlO4(100) Substrates

We report the fabrication of high temperature superconducting YBa2Cu3O7-x thin films on CaNdAlO4(100) substrate by pulsed laser deposition. Films have excellent features. X-ray diffraction patterns show that thin films are epitaxial with c-axis orientation normal to the surface of substrate. The four-terminal measurements indicate the zero resistance temperature of 92.1 K, and transition width of 0.7 K, the critical current density of 3 × 106 A/cm2 at 77 K and under zero magnetic field.

Persistent photoconductivity in insulating and superconducting YBa2Cu3Ox thin films: Temperature and spectral dependence.

Temperature and spectral dependencies of photoinduced changes of resistance in YBa[sub 2]Cu[sub 3]O[sub [ital x]] thin films with oxygen content ranging as 6.35[lt][ital x][lt]6.75 were measured on both sides of the metal-insulator transition (MIT). The absolute value of efficiency of initiation of photoinduced changes decreases with an increase of oxygen content, but the position of peaks in the spectral dependence does not change with a change of [ital x]. Temperature dependencies of efficiency have an anomaly at [ital T][similar to]220 K, which is present in all the samples studied and correlates with anomalies observed by other experimental techniques. Qualitatively similar temperature and spectral dependencies of efficiency for the samples in both the insulating and metallic phases may be considered as an indication that the persistent photoconductivity effect in Y-Ba-Cu-O on both sides of the MIT has a common origin.

YBa2SnO5.5: A New Phase in YBa2Cu3O7-SnO2 System

A new compound, YBa2SnO5.5 was found forming in YBa2Cu3O7-x-SnO2 system. Preparation of YBa2SnO5.5 as a single phase compound by solid state reaction method is reported for the first time. This new compound has a cubic structure with a lattice parameter a=8.42 Å. Kinetics of sintering and its dielectric properties are briefly discussed. No chemical reaction between YBa2Cu3O7-x and YBa2SnO5.5 was observed even at an elevated temperatue of 950°C. Sintered YBa2SnO5.5 is proposed as a new substrate material for the preparation of superconducting YBa2Cu3O7-x thin films.

I n s i t u growth of YBa2Cu3Ox thin films by reactive cosputtering

We have synthesized superconducting YBa2Cu3Ox thin films in situ using magnetron cosputtering with three metallic targets (Y, Ba, Cu). We present details of the sputtering chamber, as well as the growth conditions necessary to obtain superconducting films. We discuss the effects of oxygen and ozone partial pressure, differential pumping, O2–Ar plasma deposition and Ba–Cu alloy targets. We elaborate on our ozone condensing and delivery system. Finally, we describe the difficulties encountered with the deposition system and provide details of possible improvements.

High-Energy Ion Beam Analysis of YBa2Cu3Ox Thin Films

The composition and crystalline structure of high-Tc superconducting YBa2Cu3Ox thin films formed on MgO(100) and Si(100) substrates have been investigated by Rutherford backscattering and channeling techniques. Y, Ba, Cu contents have been analyzed by employing a high-energy (over 4.5 MeV) 4He ions and large scattering angle (near 170°) condition, where Y, Ba and Cu peaks are clearly separated from each other. Oxygen concentration has been obtained through the use of low primary energy (below 2.5 MeV) and small scattering angle (below 150°) conditions, where the O peak is separated from the background. The crystalline quality of the films has also been investigated by ion channeling techniques.