SUPERCONDUCTIVITY AND VALENCE STATE OF TB IN LU1-XTBXBA2CU3O7-DELTA (0-LESS-THAN-OR-EQUAL-TO-X-LESS-THAN-OR-EQUAL-TO-0.7)

Abstract

Although both lutetium and terbium do not form superconducting REBa2Cu3O7-delta, we report here the formation of superconducting phase in thin films. Films are highly c-axis oriented with high current densities (3.0x10(6) A cm-2 at 77 K) observed in Lu0.5Tb0.5Ba2Cu3O7-delta. X-ray photoelectron spectroscopic analysis of Tb in the above film indicates that Tb is in a trivalent state. Further, as the redox potential of Tb (Tb4+ +e- --> Tb3+:E0 = 3.1 V) is close to that of Pr (Pr4+ +e- -->Pr3+:E0 = 3.2 V), we suggest that Pr also would be in a trivalent state and the mechanism by which the latter depresses T(c) must be of trivalent origin.