Abstract
Chemical substitution of La+3 for Ba+2 in compounds of nominal composition YBa2−xLaxCu3O7−δ is shown to increase the superconducting transition temperature Tc by ∼2 K and the electrical resistivity ρ(100 K) by 90% for x=0.06. The increase of Tc is argued to result from a reduction of the hole carrier density. These results lead to the speculation that the upper critical magnetic field Hc2 may be increased by as much as 50% through this simple substitution.