Two series of single phase triple-perovskite superconducting samples with nominal compositions of Gd(Ba2−xCax)Cu3Oy (Ca series, 0 ≤ x ≤ 0.30) and Gd(Ba2−xSrx)Cu3Oy (Sr series, 0 ≤ x′ ≤ 1.0) were prepared. Orthorhombicity decreases with increasing amount of Ca or Sr substitution. Part of Ca ions occupy R site and push the same amount of Gd3+ ion into Ba site, attracting negative oxygen ions to randomly occupy O(4) and O(5) sites on the basal plane which leads to a further reduction of orthorhombicity in Gd(Ba2−xCax)Cu3Oy series compared with the same amount of substitution in Sr series, in which, Sr only occupies the Ba site. Tc is dependent on the orthorhombicity of these samples, no matter wheater it is Ca or Sr substitution.
Physica C: Superconductivity and its Applications 341-348(PART 1), pp.623-624