Preparation And Properties Of Pr_1-xCa_xBa₂Cu₃O_7-δ And Tl₂Ba₂CaCu₂O₈ Superconductor Films Fabricated By Pulsed Laser Deposition

We have successfully prepared two kinds of high critical temperature superconductor epitaxial thin films, Pr_1-xCaxBa₂Cu₃O_7-δ and Tl₂Ba₂CaCu₂O₈, by using pulsed laser deposition (PLD), in order to make some explorations on basic physics research and application involved of superconductors.One of the works, which concentrated on physical problems, was employed on superconductivity and normal state transport properties of Pr_1-xCaxBa₂Cu₃O_7-δ thin films with Ca content 0.4≤x≤0.6. We have observed superconductivity in Pr_0.4Ca_0.6Ba₂Cu₃O_7-δ thin films deposited on STO substrates through optimizing deposition parameters and the best critical temperature we obtained in films of this composition was as high as 17 K. Besides investigation on the effect of growth temperatures, different substrates including LAO, MgO and YSZ, were also used to check their impacts on epitaxial orientation, surface morphology and critical temperature of as-grown films. For Pr_0.5Ca_0.5Ba₂Cu₃O_7-δ, samples of different oxygen contents were obtained via changing annealing partial pressure to investigate the evolution of Hall carrier concentration and Hall angle. Investigations were also made on different Ca content samples. From the double relaxation time modle proposed by Anderson, we plotted Hall angle vs. T2 and made linear fitting respectively for each Ca content sample. However, we found the fitting slopeαand intercept C decreased as Pr content increased, which was inconsistent with the interpretation that C is due to additional magnetic scattering.The other part of this dissertation aimed at the application field involved of superconductor thin films. Due to the relatively small surface resistance of superconductor thin films under the circumstance of liquid nitrogen, passive microwave apparatus fabricated by such films tend to possess the merits of relatively low energy loss and of relatively high quality factor. In addition, the penetration depth of HTS films is independence of applied microwave frequency. By means of this trait, one can design and fabricate non-dispersive transmission channels which are comparatively hard to be achieved if using traditional metal materials. We have successfully prepared large-area Tl-2212 thin films with 2 inch in diameter by ex situ method. In order to avoid contamination from toxic Tl element in vacuum chamber, Tl-free Ba₂CaCu₂O_x precursors were firstly deposited on LaAlO₃ substrates by PLD method and subsequently annealed in argon atmospheres at temperatures of 720-740℃. X-ray...