Modification of transport properties in low-angle grain boundaries via calcium doping ofYBa2Cu3Oδthin films (original) (raw)
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Journal of Low Temperature Physics, 2008
The insulating and metallic behavior of the grain-boundary weak links has been studied in thallium rich and the samples with small amount of thallium in the charge reservoir layer of Cu 1−x Tl x Ba 2 Ca 3 Cu 4 O 12−δ superconductor thin films. The influence of the nature of grain boundaries on the inter-granular critical current density (J c) has also been investigated. From the power law dependence of H ac ∼ (1 − T p /T c) n , it was observed that n = 1 gives a best fit for the J c of thallium rich samples and n = 2 provides a best fit for the J c of the samples with small amount of thallium. The polycrystalline thin film samples showing the power law dependence of J c as n = 1 make superconductor-insulator-superconductor (SIS) type while the samples with n = 2 follow superconductor-normal metal-superconductor (SNS) types of Josephson junctions. The insulating grain boundaries decrease the inter-granular Josephson coupling and hence the transport properties are suppressed. Keywords Thin films • Cu 1−x Tl x Ba 2 Ca 3 Cu 4 O 12−δ superconductors • High J c • Grain boundaries
Applied Physics Letters, 2004
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Transport characterization of calcium-doped YBa2Cu3O7- delta thin films
Physical review. B, Condensed matter, 1995
We report systematic studies of the normal-state conductivity and thermopower of epitaxial Yi Ca Ba2Cu307 p thin films with 0 & x & 0.3 as a function of oxygen content. The superconducting transition temperature T is found to be parabolic in conductivity o. for each sample, with a universal scaling behavior for all 6lms with z & 0.2. The room-temperature thermopower, Sz» K, follows the universal correlation between T, and S$95 K reported by S. D. Obertelli et al. [Phys. Rev. B 46, 14 928 (1992)j for all films studied, despite the reduction in maximum T, with increasing calcium content. The thermopower is found to be superior to the conductivity as a measure of the hole concentration because of its reduced sensitivity to extrinsic contributions such as grain boundaries. By assuming that all the charge from oxygen deficiencies. and Ca substitution is transferred to the Cu-0 planes, and by using Obertelli s empirically-derived expression for hole concentration, we show that S295 K can be used to determine the oxygen content of the Alms. The equilibrium oxygen content is found to be reduced to compensate for the additional carriers introduced by Ca substitution in these films, just as has been previously observed in bulk Yi Ca Ba&Cu307-$.
Transport characterization of calcium-dopedYBa2Cu3O7−δthin films
Physical Review B, 1995
We report systematic studies of the normal-state conductivity and thermopower of epitaxial Yi Ca Ba2Cu307 p thin films with 0 & x & 0.3 as a function of oxygen content. The superconducting transition temperature T is found to be parabolic in conductivity o. for each sample, with a universal scaling behavior for all 6lms with z & 0.2. The room-temperature thermopower, Sz» K, follows the universal correlation between T, and S$95 K reported by S. D. Obertelli et al. [Phys. Rev. B 46, 14 928 (1992)j for all films studied, despite the reduction in maximum T, with increasing calcium content. The thermopower is found to be superior to the conductivity as a measure of the hole concentration because of its reduced sensitivity to extrinsic contributions such as grain boundaries. By assuming that all the charge from oxygen deficiencies. and Ca substitution is transferred to the Cu-0 planes, and by using Obertelli s empirically-derived expression for hole concentration, we show that S295 K can be used to determine the oxygen content of the Alms. The equilibrium oxygen content is found to be reduced to compensate for the additional carriers introduced by Ca substitution in these films, just as has been previously observed in bulk Yi Ca Ba&Cu307-$.
Physica C: Superconductivity, 2004
We report systematic studies of AC magnetic susceptibility and transport properties of Y 1-x Ca x Ba 2 Cu 3 O z bulk samples with 0≤x≤0.4. Single phase materials, reduction of carrier concentration and decrease of T c to 83K were obtained at doping levels up to 20%. For Y 0.7 Ca 0.3 Ba 2 Cu 3 O z sample the improvement of grains boundary transport and screening capabilities has been observed as a result of the optimal ratio between carrier concentration and impurity phase BaCuO 2 presence. The appearance of bulk pinning and nonlinear effects starting at the highest temperature were detected also.
Effect of Ca doping in YBCO superconducting thin films
Physica C: Superconductivity, 2004
We investigate the effect of partial substitution of Y by Ca in YBCO superconducting thin films. The films were grown on (1 0 0) SrTiO 3 single crystal substrates by pulsed laser deposition (PLD). The Ca doped film were ablated from Y 1Àx Ca x Ba 2 Cu 3 O 7Àd targets with x ¼ 0, 0.05, 0.07, and 0.10. The dc transport properties of the films in applied magnetic field are analyzed to study the role of Ca on the superconducting properties of YBCO films. The irreversibility line for the samples with x ¼ 0 and 5 at.% Ca was derived from the E-J curves using a scaling theory for the vortex-glass transition.