ENHANCEMENT OF TC IN YBA2CU3O7 BY CHEMICAL SUBSTITUTION IN BULK AND THIN-FILM MATERIALS - IMPLICATIONS FOR THE UPPER CRITICAL MAGNETIC-FIELD

Chemical substitution of La+3 for Ba+2 in compounds of composition YBa 2-xLaxCu3O7-delta is shown to increase the superconducting transition temperature T(c) by approximately 2 K and the electrical resistivity r ho(100 K) by 90% for x = 0.06. The increase of T(c) is argued to resul t from a reduction of the hole carrier density. These results lead to the speculation that the upper critical magnetic field H(c2) may be in creased by as much as 50% through this simple substitution. Thin films prepared by pulsed-laser deposition with x = 0.04 and 0.06 are shown to yield T(c) = 90.8 K.