Modulated Structural Characteristics and Microwave Properties of Spray Pyrolyzed Superconducting BCSCO Films

Abstract

Low-cost–based high-T _c superconducting thin film of Bismuth Strontium Calcium Cuprate on yittriya stabilized zirconia (YSZ) using spray pyrolysis deposition technique from nitrate precursors followed by rapid annealing at temperatures between 830 and 840°C in air and in O₂ is described. The films are highly oriented with the c-axis parallel to the plane of the substrate. Some satellite reflections that occur due to the modulation along the crystal lattice (parallel to c-axis) are observed. The prominent X-ray diffraction lines can be fitted to a tetragonal structure. A number of satellite X-ray reflections lines are observed which suggest the existence of modulation. These lines have been fitted in a superspace group $({\text{N}}\mathop {{\text{III}}}\limits^{{\text{Bb}}\underline {\text{m}} {\text{b}}} )$ with a = 3.832 Å and c = 48.826 Å indicating the existence of superposed modulated structure. Substrates (Al₂O₃, LiNbO₃, Si₃N₄, Si) other than YSZ could not produce superconducting films due to the diffusion of metal ions in the film causing poisoning effect in superconducting properties. Resistivity measurements indicate superconducting onset at 92 K and zero resistance at 77 K. Microwave induced dc voltage (μV) measurements as a function of microwave power (mW) were carried out at different temperatures down to 65 K for different annealing temperatures. It is noted that the slope of the line (μV vs. mW) are dependent on ramping of the processing temperatures. The decrease of slope suggested that weak-links between the superconducting grains are decreased as the ramping of the processing temperature is decreased keeping the ramping time constant. The interactions between film and the substrate are qualitatively discussed.