Bismuth Valence Studies of As-Grown Superconducting Bi-Sr-Ca-Cu-O Thin Films with T_c(zero) from 98 K to 66 K

Abstract

Bismuth valence of Bi-Sr-Ca-Cu-O superconducting film has been studied by X-ray photoemission spectroscopy. As-grown highly oriented Bi-Sr-Ca-Cu-O 2223 single-phase films with various critical temperatures from 98 K to 66 K were prepared by changing the Bi content. The Bi 4f core level electron spectra are decomposed into two components. These components are assigned to BiO and to Bi 2 O 3 which is located at an energy higher than the peak of BiO by about 1 eV. Then it was empirically determined that the critical temperature can be controlled by the Bi mean valence, and changes irrespective of the number of Cu-O planes. The critical temperature of the film increases with a decrease in the Bi mean valence which was calculated from the ratio of BiO/Bi 2 O 3 .