Y 1 Ba 2 Cu 3 O 7-x Films from Nitrate Solution using Rf Plasma Deposition
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YiBa2Cu307-x FILMS FROM NITRATE SOLUTION USING RF PLASMA DEPOSITION A. SHAH, T. HAUGAN, S. WITANACHCHI, S. PATEL, and D. T. SHAW, New York State Institute on Superconductivity, State University of New York at Buffalo, Bonner Hall, Buffalo, New York 14260 ABSTRACT A nitrate solution of Y, Ba and Cu was atomized and introduced into an inductively coupled argon - oxygen plasma operated at 4.4 kW and 13.56 MHz under atmospheric pressure. Asdeposited superconducting films were grown on (100) YSZ substrates heated to 650 0 C. Critical temperatures of 85 K and 2 critical current densities of 7.0 x 104 amp/cm at 77 K have been achieved. X-ray diffraction shows the films to be oriented with the c-axis perpendicular to the substrate surface. The effects of process parameters, solution composition, and aerosol concentration on the superconducting properties and microstructures will be discussed. INTRODUCTION Considerable progress has been made in the in-situ growth of superconducting YlBa2Cu3O7-x thin films. Different processing techniques have been developed, including e-beam evaporation, rf and dc sputtering, and laser ablation[i-3]. In this report we will describe a novel technique using a rf plasma torch and an atomized solution of Y, Ba and Cu nitrates as a precursor. Nitrate solution was used to synthesize Y1Ba2Cu307-x thin films by direct spraying on a heated surface(4]. Rf plasma deposition has been earlier used with 1A YlBa2Cu307-x powder as a precursor with good results[5]. Rf plasma has distinct advantages over many of the other film preparation methods. In this process, the composition of the compound is well controlled. This is helped by the electrodeless and hence uncontaminated high temperature plasma. Superconducting films are made in-situ by this process. This process is also facilitated by the atmospheric pressure argonoxygen plasma. Atmospheric processing is another distinct advantage over many of the other processes. High deposition rates and large surface area deposition are two other attractive features of this technique. EXPERIMENT The experimental system is illustrated in figure 1. It has two main subdivisions, the plasma torch and the atomizer. Power to the torch is supplied by a 10 kW rf generator operating at 13.56 MHz. Nitrates of Y, Ba and Cu are dissolved in water, in a non-stoichiometric ratio of 1:1.4:1.7, to form a 0.28M solution. The solution if; stored in the nebulizer. A Yttria stabilized Zirconia (YSZ) substrate is mounted on the substrate holder usually at a distance of 11 cm from the torch nozzle. The substrate is heated with a 250 W disk heater to a pre-deposition 0 temperature of 500 C. Plasma gases, argon, and oxygen are injected into the torch in a 1:1 ratio. The total plasma gas flow ranges Mat. Res. Soc. Symp. Proc. Vol. 169. ©1990 Materials Research Society
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from 10-12 1pm with aerosol carrier gas flow of 2-5 lpm. The droplet sizes are 1 to 4g in diameter. Plasma is ignited and operated at 4.4 kW. The solution is then atomized in the nebulizer and injected into the torch wit
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