High Tc Magnetic Superconductors in Rare Earth (R) Barium Copper Oxide RBa2Cu3O7-δ

Superconductivity with critical transition temperature Tc near 90 K has been found in RBa2Cu3O7-δ compounds where R = Nd, Sm, Eu, Gd, Dy, Ho, Er, Tm, Yb, and Lu, and with Tc=56 K for R = La by electrical resistivity and low field magnetic susceptibility measurements. All compounds (except La) form in the orthorhombic, layered perovskite structure which is isomorphic to YBa2Cu3O7-δ. The lattice parameters of the compounds decrease in accordance with the metallic radii of the R trivalent ions. The electrical resistivity of the compounds studied (except for R = Nd) decreases with decreasing temperature and exhibit a sharp superconducting transition. Upper critical magnetic field Hc2 of the heavy R compounds (R from Dy to Yb) were measured and the highest initial slope |dHc2/dTc|Tc yet found for above 90 K superconductors was exhibited in TmBa2Cu3O7-δ with a value of 2.8 tesla/K.