Abstract
We report the results of dc resistivity, ac susceptibility, and thermopower study of partial substitution at Y (A site by Ca) and at Cu (B site by Ni) polycrystalline superconductors. The iodometric analysis reveals that the oxygen deficiency,δ,for YBa2Cu3O7-δ(S-I),Y0.9Ca0.1 Ba2Cu3O7-δ(S-II),Y0.8Ca0.2Ba2Cu3O7-δ(S-III) and Y0.9Ca0.1 Ba2(Cu0.99Ni0.01)3O7-δ(S-IV) samples are 0.16, 0.30, 0.39 and 0.29 respectively. The x-ray powder diffraction pattern indicates that all samples are in orthorhombic phase. The dc resistivity, ac susceptiblity and the thermopower measurements shows that the divalent Calcium doping at the trivalent Y site and transition metal Ni doping at Cu site causes a suppression of the superconducting transition temperature (Tc) from 89 to 81 K. The ac susceptibility confirms the ferromagnetic to antiferromagnetic phases at a defined Tc. The room temperature S value increases for Ca substituted YBa2Cu3O7-δwhile to that it decreases for Y0.9Ca0.1Ba2(Cu0.99Ni0.01)3O6.71. The above feature is an indicative of enhanced number of mobile holes for the Ca doped YBa2Cu3O7-δ, while to that the charge carrier density is reduced in simultaneous A (Ca) and B (Ni) site doped sample.
Highlights
IntroductionBoth alkaline earth and transition metal substitutions in cuprate superconductors are important for the phenomenon of superconductivity
We report the results of dc resistivity, ac susceptibility, and thermopower study of partial substitution at Y (A site by Ca) and at Cu (B site by Ni) polycrystalline superconductors
The dc resistivity, ac susceptiblity and the thermopower measurements shows that the divalent Calcium doping at the trivalent Y site and transition metal Ni doping at Cu site causes a suppression of the superconducting transition temperature (Tc) from 89 to 81 K
Summary
Both alkaline earth and transition metal substitutions in cuprate superconductors are important for the phenomenon of superconductivity. The transport measurements as dc electrical resistivity and thermopower are powerful probes to investigate the electronic states and phases of the host as well of the partially substituted YBCO either at A or at B site. It is inferred from the resistivity measurements that with the enhanced Ca doping at Y site, the resistivity of the samples decreases significantly [3,4]. We must mention that no result has been documented in the literature about thermopower for Ni doping at Cu site in YBa2Cu3O7- superconductors It is the purpose of the present paper to investigate the effect of transport properties on the simultaneous substitutional effects in YB2Cu3O7 superconductors. Y0.9Ca0.1Ba2 (Cu0.99Ni0.01)3O7- (S-IV) superconductors to delineate the substitutional effects both at A and B sites
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