Proton Beam Texturing of Superconducting YBaCuO Ceramics
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Proton Beam Texturing of Superconducting YBaCuO Ceramics Makhmud Kalanov and Elvira M. Ibragimova, Inst of Nuclear Physics, Ulugbek, 702132, Tashkent, UZBEKISTAN. E-mail: [email protected]
Abstract Resistive superconducting (SC) transition, current-voltage characteristics, and X-ray diffraction (XRD) of YBaCuO ceramics have been studied after exposure to 18 MeV proton beam at 300 K. In the interval of 1013 -5×1014 cm-2 the irradiation induced oxygenation of weak intergrain contacts and grain alignment, anisotropy and broadening of SC-transition measured along and across the proton beam, and residual magnetization were found. The proton induced anisotropic texture is responsible for the critical current increase at 77 K and the resistivity decrease at 90-200 K. In a higher dose interval of 1013 - 1015 cm-2 the SC-transition parameters degrade and the resistivity increases, depending on a texture degree, weak intergrain links become deoxygenated and no texture occurs. The magnetization (pinning) and the anisotropy of SC-transition can be due to localization of charges at the proton induced defects (mostly in oxygen sublattices).
Introduction Due to promise of bulk high Tc superconductors for power and magnet application two important problems must be solved: i) how to avoid weak links between grains for increasing the overall transport critical current Ic and ii) how to create stable strong flux pinning centres for enhancing the magnetisation critical current density jc.. It is possible to diminish an amount of the high angular intergrain contacts (weak links) by means of the melt texturing growth technique [1] or the thermal and γ-radiation treatment [2] causing increase in Ic and jc.. A proper irradiation with fast neutrons was found to produce the defects distributed homogeneously in bulk HTSC materials, which were responsible for a significant enhancement of jc especially at high magnetic fields and temperatures, but it was accompanied by a decrease in Tc and conductivity, also undesirable neutron induced radioactivity [3]. Charged particles having limitation in the penetration depth can produce some improving effects on transport and magnetic properties. The 200-300 keV protons decrease a normal state resistivity ρ and increase Tc. of YBCO films [4]. And 500 keV proton irradiation of tetraphase YBCO followed by annealing in oxygen at 300-800 C cause tetra-ortho-phase transition [5]. At energies of 3-5 MeV (ranges are about 50-80µm) strong pinning centres are formed, but Tc decreases by a few K [6]. Ex-situ 13 15 -2 2 MeV proton irradiation of YBCO films at 300 K to fluences 10 -10 cm causes linear decrease in Tc and Ic and broadening the transition due to destroying weak links by atom disorder, however no effect on surface resistance and impedance occurred [7]. A large growth in jc was induced by 800 MeV protons without noticeable change in Tc [8]. The dimensional defect structures of YBa2Cu3O7 single crystals, resulting from fast neutron and proton bombardment and responsible for strong flux pinning,
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