Thallium valency in superconducting oxides TlBa2Ca1-xYxCu2O7- delta(0<or=x<or=1)

Core-level electronic states for TlBa2Ca1-xYxCu2O7- delta (x=0, 0.1, 0.8 and 1.0) are investigated by X-ray photoelectron spectroscopy (XPS). As an effect of yttrium substitution, the Tl core-level shifts toward the higher binding energy side. This implies that electrons donated do not only fill the hole state in Cu-O, but also are partially transferred to the Tl site.