Effect of nickel and calcium substitution on the superconducting properties of the Y1-xCaxBa2Cu3-yNiyO7-δsystem with 0.1 ≤x≤ 0.3 and 0.0 ≤y≤ 0.2

The effect of calcium (Ca) substitution in yttrium (Y) site and nickel (Ni) substitution in copper (Cu) site of Y1-xCaxBa2Cu3-yNiyO7-delta(x = 0.1, 0.2, 0.3 andy = 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-delta(YBCO). The average oxygen content delta 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 temperatureT(C)decreases with the content of substitutionyof Ni in Y(0.9)Ca(0.1)Ba(2)Cu(3-y)Ni(y)O(7)(-)(delta)system. In Y(0.9)Ca(0.1)Ba(2)Cu(2.9)Ni(0.1)O(7)(-)(delta)sample (y = 0.1), the variation Delta T(C)falls only of 7% approximately, whereas a reduction in Delta T(C)of 40% is observed in the YBa(2)Cu(3-y)Ni(y)O(7)(-)(delta)system. The critical temperaturesT(C)of the Y(1-x)Ca(x)Ba(2)Cu(2.9)Ni(0.1)O(7)(-)(delta)system (x = 0.1, 0.2 and 0.3) decreases with the content of substitutionxof Ca until reaching a minimum at 67 K whenx = 0.2, then it increases again.