Microstructure and superconducting properties of Y-Ba-Cu-O films prepared by chemical spray pyrolysis

Y-Ba-Cu oxide superconducting films were prepared by spray pyrolysis on (100) MgO substrates and alumina coated with a silver buffer layer. Acetate, nitrate, and oxide precursors were used as starting materials. The optimum starting compounds have been assessed and the effectiveness of rapid thermal processing as a fabrication tool for annealing of highT _c superconducting films has been established. The superconducting behavior was found to be strongly dependent on the type of the precursor used, on the method of heat treatment, and on the substrate material. The films show preferred orientation and good adherence to the substrate. Transport measurements indicated that the films exhibited a superconducting transition with an onset temperature between 83–93 K and ending between 52–74 K. The critical current density was found to be strongly dependent on film processing.     

Synthesis of Y-Ba-Cu-O superconductors from Y2O3 BaO2, and Cu2O: The optional oxygen treatment

YBa₂Cu₃O_x superconductors were synthesized from mixed powders of Y₂O₃, BaO₂, and Cu₂O under oxygen, air, and argon atmospheres. All samples were superconductive at the boiling point of liquid nitrogen, indicating the oxygen treatment is optional for this powder synthesis method.     

Crystal structure analysis of Y2Cu2O5

Single crystals of Y₂Cu₂O₅ were obtained in the flux growth process by controlled heating of a mixture of Y₂O₃, BaO, and CuO in a molar ratio of 1∶8∶20. These crystals were analyzed by a single-crystal X-ray diffraction analysis. The crystal contains polymeric chains of Cu₂O₅ interspersed by yttrium ions surrounded by octahedral arrangements of oxygen atoms. Crystal data: space group=Pna2₁,a=10.799(2) Å,b=3.4990(5) Å,c=12.459(2) Å,Z=4, 380 reflections,R=0.026,R _w=0.030.     

Structure and morphology of titanium nitride films deposited by laser-induced chemical vapour deposition

Results on the deposition of titanium nitride on AISI M2 tool steel-type substrates by pyrolytic laser chemical vapour deposition are reported. Spots of TiN were deposited from a gas mixture of TiCl₄, nitrogen and hydrogen using a continuous wave quasi-TEM_oo CO₂ laser beam. The morphology and the structure of the deposited material were investigated by optical microscopy, scanning electron microscopy and X-ray diffraction. The chemical composition was studied with a scanning electron microscope with an energy dispersive spectrometer, and with an electron probe microanalyser. The topography of the coating was analysed with a stylus profilometer and different thickness profiles were measured depending on the laser-power densities and irradiation times. The morphology of the films showed a strong dependence on the laser-power density, interaction time and partial pressure of TiCl₄.     

Distributions of Y2Ba1Cu1O5 particles in fluorine-doped Y1Ba2Cu3O x superconductors

An experimental study has been carried out on the relationship between Y₂Ba₁Cu₁O₅ particles in Y₁Ba₂Cu₃O _x superconductors and electric furnace cooling rates. As the electric furnace cooling rates decrease, the Y₂Ba₁Cu₁O₅ particles become uniformly disperse in fluorine-doped Y₁Ba₂Cu₃O _x superconductors. However, the Y₂Ba₁Cu₁O₅ particles do not appear in the undoped Y₁Ba₂Cu₃O_x superconductors.     

Comparison of Y-Ba-Cu-O compounds prepared from BaCuO2 and Ba2Cu3O5+δ

Series of Y-Ba-Cu-O compositions were prepared from barium cuprates and Y₂O₃, using a two-step synthesis route. It has been shown that Ba₂Cu₃O_5+δ is essential in formation of the YBa₂Cu₃O_7?δ superconducting phase while BaCuO₂ is not an appropriate starting material. A wide composition range fromx=2 to 17 was prepared from Ba₂Cu₃O_5+δ in the YBa _x Cu_1.5x O _z series without disappearance of macroscopic superconductivity atT _c>77 K. Resistivity measurements hint at the existence of two superconducting phases. ESR investigations revealed a baseline hysteresis, depending on the actual value ofx.     

Standard Gibbs' energies of formation of BaCuO2, Y2Cu2O5 and Y2BaCuO5

The Gibbs' energies of formation of BaCuO₂, Y₂Cu₂O₅ and Y₂BaCuO₅ from component oxides have been measured using solid state galvanic cells incorporating CaF₂ as the solid electrolyte under pure oxygen at a pressure of 1.01×10⁵ Pa BaO + CuO BaCuO₂ G _f,ox ^o (± 0.3) (kJ mol^–1)=–63.4–0.0525T(K) Y₂O₃ + 2CuO Y₂Cu₂O₂ G _f,ox ^o (± 0.3) (kJ mol^–1)=18.47–0.0219T(K) Y₂O₃ + BaO + CuO Y₂BaCuO₅ G _f,ox ^o (± 0.7) (kJ mol^–1)=–72.5–0.0793T(K) Because the superconducting compound YBa₂Cu₃O_7– coexists with any two of the phases CuO, BaCuO₂ and Y₂BaCuO₅, the data on BaCuO₂ and Y₂BaCuO₅ obtained in this study provide the basis for the evaluation of the Gibbs' energy of formation of the 1-2-3 compound at high temperatures.     

Electrical properties of Ta2O5 films deposited on ZnO

High dielectric constant (high-k) Ta₂O₅films have been deposited on ZnO/p-Si substrate by microwave plasma at 150°C. Structure and composition of the ZnO/p-Si films have been investigated by X-ray diffraction (XRD), atomic force microscopy (AFM), scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS) for chemical composition. The electrical properties of the Ta₂O₅/ZnO/p-Si metal insulator semiconductor (MIS) structures were studied using high frequency capacitance-voltage (C-V), conductance-voltage (G-V) and current-voltage (I-V) characteristics. Charged trapping properties have been studied by measuring the gate voltage shift due to trapped charge generation under Fowler-Nordheim (F-N) constant current stressing.     

Current transport across grain boundaries in superconducting YBa2Cu3O7 films

Superconducting transport properties of YBa₂Cu₃O₇ grain boundaries have been investigated. The results of these experiments are summarized.     

Preparation and characterization of Y-system superconducting thin films by mist microwave-plasma chemical vapour deposition

Superconducting thin films of Y-Ba-Cu-O were prepared on single-crystal MgO (100) substrates by the mist microwave-plasma chemical vapour deposition (MPCVD) using an aqueous solution of metal nitrate. The growth rate was observed to be controlled by the concentration of metal nitrate in the solution. The X-ray diffraction patterns showed that the prepared films consisted of 123 phase with c-axis orientation perpendicular to the substrates. The dependence of T _c-zero (zero resistance) of films on the microwave power was investigated. In addition, the effect of the ozone on the preparation of films was investigated. The maximum T _c-zero (84 K) of as-deposited films was obtained at a metal concentration in the solution of 0.50 moll^–1, a microwave power of 300 W and an ozone concentration in oxygen gas of 3.0%.     

低氟化学溶液法制备REBa_2Cu_3O_(7-x)高温超导薄膜

提出了一种低氟溶液制备REBa2Cu3O7-x(REBCO)超导薄膜的方法。以醋酸盐为原料,二乙烯三胺、丙烯酸、三氟乙酸为反应物,甲醇为溶剂,制备了含有无氟RE盐(RE=Y、Yb、Nd),无氟Cu盐和含氟Ba盐的低氟REBCO前驱溶液。该溶液中氟含量只有传统的All-TFA溶液中氟含量的30%。利用该溶液制备REBCO薄膜,减少了热分解过程中HF气体的释放量,缩短了热分解周期。利用X射线小角掠射对薄膜热分解过程进行了分析,结果表明,低氟化学溶液法所得凝胶膜在热分解后,形成了RExBayFz化合物,避免了BaCO3相的形成,从而可获得高性能的REBCO薄膜。     

溶胶-凝胶法制备YBa2Cu3O7-x超导薄膜的研究

传统的TFA-MOD法制备YBa2Cu3O7-x薄膜,采用Y、Ba、Cu 3种金属的三氟醋酸盐(TFA)为先驱体,在热分解时,会产生大量的HF气体,即使通过将近20h的缓慢升温过程来对薄膜进行热分解,也难以获得较为光洁的表面,从而无法实现厚膜的制备.本文提出了一种新的含氟溶胶-凝胶工艺,通过减少溶胶中F的含量,并利用二乙醇胺做修饰剂,缩短了热分解时间,提高了薄膜的表面光洁度.利用该方法在(010)LaAlO3衬底上制备了具有良好c轴取向,临界转变温度为89K的YBCO超导薄膜.     

High-capacity superconducting current leads of Y1Ba2Cu3O7−x

We have fabricated and measured a high-capacity superconducting current lead composed of a Y₁Ba₂Cu₃O_7?x cylinder, 20 cm long and 0.9 cm² cross section. A steady-state, d.c., critical current of 225 A at a temperature of 77 K was measured in this sample, using a voltage criterion of 2×10^?7 V/cm (p = 8×10^?10 ohm-cm). This current was limited by the currentinduced, self magnetic field. To our knowledge this is the largest d.c. critical current so far reported in a Y₁Ba₂Cu₃O_7?x sample and demonstrates the possibility of using hightemperature superconducting HTS materials for current leads to low-temperature superconducting LTS magnets or in power distribution systems.     

The nature of stresses in hot-filament chemical vapour deposited diamond thin films on WC substrates

The nature of film stresses in hot-filament chemical vapour deposited (HFCVD) diamond thin films on tungsten carbide substrates, is reported. Commercial WC substrates were subjected to various surface treatments. Subsequently, they were coated with a diamond film and examined for stresses using X-ray diffraction. All but one of the stress measurements indicated various levels of compressive stresses in the film and at the film–substrate interface. These stresses are compared with those obtained by other researchers. Intrinsic film stresses were also computed for diamond films and found to be tensile. WC drills, of 0.125 in. diameter, were also diamond coated and the stress levels measured along drill flanks and flutes. Significant variations were found in these stresses, and the results were analysed from a film–substrate adhesion perspective.