Alkaline Earth (Ca) and Transition Metal (Ni) Doping on The Transport Properties Of Y_1-Xca_xba₂(Cu_1-Yniy)₃O_7-δ Superconductors

Abstract

We report the results of <i>dc</i> resistivity, <i>ac</i> 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 YBa₂Cu₃O_7-δ(S-I),Y_0.9Ca_0.1 Ba₂Cu₃O_7-δ(S-II),Y_0.8Ca_0.2Ba₂Cu₃O_7-δ(S-III) and Y_0.9Ca_0.1 Ba₂(Cu_0.99Ni_0.01)₃O_7-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 <i>dc</i> resistivity, <i>ac</i> 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 (T_c) from 89 to 81 K. The <i>ac</i> susceptibility confirms the ferromagnetic to antiferromagnetic phases at a defined T_c. The room temperature S value increases for Ca substituted YBa₂Cu₃O_7-δwhile to that it decreases for Y_0.9Ca_0.1Ba₂(Cu_0.99Ni_0.01)₃O_6.71. The above feature is an indicative of enhanced number of mobile holes for the Ca doped YBa₂Cu₃O_7-δ, while to that the charge carrier density is reduced in simultaneous A (Ca) and B (Ni) site doped sample.