Highly Oriented Superconducting Bi - Sr - Ca - Cu - Oxide Thin Films by the Solution Sol - Gel Process
- PDF / 610,064 Bytes
- 4 Pages / 420.48 x 639 pts Page_size
- 8 Downloads / 186 Views
HIGHLY ORIENTED SUPERCONDUCTING Bi - Sr - Ca - Cu - OXIDE THIN FILMS
BY THE SOLUTION SOL - GEL PROCESS P. RAVINDRANATHAN, S. KOMARNENI, A. S. BHALLA, AND R. ROY, MATERIALS RESEARCH LABOROTORY, THE PENNSYLVANIA STATE UNIVERSITY, UNIVERSITY PARK, PA 16802 ABSTRACT Highly oriented Bi2Sr 2 CaCu 2 O8 + films were prepared on MgO and SrTiO 3 substrates by the solution sol - gel (SMG) method. The tetra phasic sol containing bismuth, strontium, calcium and copper oxides was coated on the substrate by spin casting and calcined at 870°C for 10 minutes. X- ray diffraction patterns of the films showed the formation of the superconducting phase with preferential orientation along the C- axis. The microwave absorbtion data as a funtion of temperature revealed the onset temperature to be 90°K for the film coated on MgO substrate. INTRODUCTION The recent discovery of superconductivity above 80'K in the Bi - Sr - Ca - Cu - 0 (BSCC) system [1-41 has stimulated great interest in the preparation of high quality high Tc BSCC films. Several methods have been reported for the preparation of this high Tc material in thin film form , including multitarget magnetron sputtering [5,6],and coevaporation[7]. In this paper, we report an alternative method of thin film preparation for Bi2 Sr 2 CaCu 2 08+x compound via the SSG tecnique. The advantages of this method are compositional homogeneity, lower processing temperature and enhanced densification [8]. Higly oriented films of Bi2Sr 2 CaCu 2 08+x on MgO and SrTiO 3 substrates were prepared and characterized.
EXPERIMENTAL PROCEDURE Copper oxide sol was prepared by dissolving anhydrous copper acetate, Cu(CH3COO)2 (0.03 mole) in methoxy ethanol at 70°C and refluxing the solution at 135°C for 15-20 hours. Bismuth nitrate, Bi(N0 3 ) 3 .5H 2 0, (0.03 mole) was disolved in methoxy ethanol at 70°C and mixed with copper oxide sol. Strontium (0.03 mole) and calcium (0.015 mole) metals were dissolved in isopropanol separately at 70°C and they were added to the mixture of bismuth and copper oxide sols. This mixture was refluxed at 135'C for 10-12 hours. All these reactions were carried out in argon atmosphere. A slight excess of deionized water mixed with methoxy ethanol in 1:4 ratio was added for hydrolysis and the mixture was refluxed for 6-10 hours. The metal oxide sols were precipitated quantitatively from the reaction mixture by simultaneous hydrolytic decomposition of the alkoxides. The intimately mixed sols were used to make films both on hot pressed SrTiO 3 and single crystal MgO substrates. Small amount of cladan binder was added to adjust the viscosity of these sols and the films were coated using a spin coater. The sol was spin casted on the substrate at a speed of 2000 rpm for 45 seconds. After each coating, the film was dried at 100°C and coated again. About ten layers were coated and calcined first at 800°C for 6 hours and then at 870°C for 10 minutes in air. Phase formation of the superconducting oxide, was confirmed by powder X-ray diffraction and surface morphology characterization was d
Data Loading...
