Dependence of T_c on the RE-ion size in (RE,Ca)Ba₂Cu₃O₆

Polycrystalline samples of RE _0.6Ca_0.4Ba_1.6Sr_0.4Cu₃O₆ (RE = Nd, Gd, Dy, Y, Yb, Lu) without oxygen in the Cu(1)O chain have been prepared by the conventional solid-state reaction method. No superconductivity appears for larger RE = Nd, Gd, Dy, while superconductivity with T _c ∼50 K appears for smaller RE = Y, Yb, Lu. This is presumably because holes produced by the Ca-substitution for RE are more supplied to the conductive Cu(2)O₂ plane than to Cu(1) as the lattice becomes small. The maximum T _c = 53 K for RE = Lu is considerably lower than 90 K for REBa₂Cu₃O₇. This may be due to the low hole-concentration in the Cu(2)O₂ plane. (paper)