Effect of nickel and calcium substitution on the superconducting properties of the Y1–x Ca x Ba2Cu3–y Ni y O7 – δ system with 0.1 ≤ x ≤ 0.3 and 0.0 ≤ y ≤ 0.2

Abstract

The effect of calcium (Ca) substitution in yttrium (Y) site and nickel (Ni) substitution in copper (Cu) site of Y1–x Ca x Ba2Cu3–y Ni y O7– δ (x = 0.1, 0.2, 0.3 and y = 0.0, 0.1, 0.2), materials prepared by solid state reaction method was investigated. Structural, average oxygen content and electrical resistivity measurements were studied using X-ray Diffraction (XRD), iodometric titration and four-probe method. From XRD analysis, all samples showed the orthorhombic symmetry of YBa2Cu3O7 – δ (YBCO). The average oxygen content δ increases with the substitution of Cu by Ni and Y by Ca. Such a phenomenon allows the appearance of oxygen vacancies in the samples. From the electrical resistivity results, critical temperature TC decreases with the content of substitution y of Ni in Y0.9 Ca0.1Ba2Cu3–y Ni y O7 – δ system. In Y0.9Ca0.1Ba2Cu2.9Ni0.1O7 – δ sample (y = 0.1), the variation ΔTC falls only of 7% approximately, whereas a reduction in ΔTC of 40% is observed in the YBa2Cu3–y Ni y O7 – δ system. The critical temperatures TC of the Y1–x Ca x Ba2Cu2.9Ni0.1O7 – δ system (x = 0.1, 0.2 and 0.3) decreases with the content of substitution x of Ca until reaching a minimum at 67 K when x = 0.2, then it increases again.