Ion-size effect on superconducting transition temperature T-c in R1-x-yPrxCayBa2Cu3O7-z systems (R = Er, Dy, Gd, Eu, Sm, and Nd)

We observed a rare-earth ion-size effect on T-c in R1-x-yPrxCayBa2Cu3O7-z ( R = Er, Dy, Gd, Eu, Sm, and Nd) systems which is similar to that in R1-xPrx Ba2Cu3O7-z systems in our previous reports. For fixed Pr and Ca concentrati on (fixed x and y), T-c is linearly dependent on rare-earth ion radius r(R) (3+). For a fixed Pr concentration x, there exists a maximum of T-c (T-c,(m ax)) in T-c vs Ca concentration y curves. T-c,(max) shifts to = T-c,T-max - T-c,T-y=0; T-c,T-y=0 is the transition temperature T-c without Ca doping) increases with increasing R ion radius. We proposed an empirical formula fo r T-c (r(R)(3+), x,y) to fit our experimental data: T-c(x,y) = T-c0 - A bet a(2)(alpha/x + y/beta)(2) - Bx. All fitting parameters in this formula, T-c 0, B, beta, alpha/beta, and A beta(2), are rare-earth ion-size dependent.