X-ray photoelectron spectroscopic studies of the valence state of Tl in single-Tl-O-layered TlBa1-xSrxLaCuO5 (0_etix_eti1)

The valence state of thallium in TlBa1-xSrxLaCuO5 (x=0.0, 0.4, 0.7, and 1.0) has been investigated by measuring Tl 4f core levels by x-ray photoelectron spectroscopy. It is shown that the valence state of Tl in TlBaLaCuO5 (nonsuperconducting) is 3+, whereas that in TlSrLaCuO5 (superconducting, Tc=32 K) is between 3+ and 1+. The origin of holes in the latter compound is discussed in terms of charge transfer between Tl ions and Cu-O layers as has been found in double-Tl-O-layered compounds. © 1992 The American Physical Society.