We have demonstrated that using a transition metal ion to partially substitute Cu ion of the YSr2Cu3Oy can stabilize its crystal structure and retain superconductivity. The superconducting transition temperature in YSr2(Cu1-xMx)3Oy, where M is transition metal ion, ranges from 40K to 80K depending on the specific M ion. Lattice contraction due to Sr substitution makes the Ba/Sr ion to move closer to CuO plane, and consequently leads to a charge transfer between oxygen. Our study shows that the key factor controlling the structural stability in Y-Sr-Cu-O system is the effective ionic radius Sr in lattice. The introduction of transition metal doping is to increase the effective ionic radius of Sr through the increase of oxygen content.
Tamkang journal of science and engineering 3(3), pp.139-144