VALENCE STATES OF BISMUTH AND THALLIUM IN SUPERCONDUCTING CUPRATES: A <font>Bi</font>–<font>L</font>₃ AND <font>Tl</font>–<font>L</font>₃ X-RAY ABSORPTION SPECTROSCOPIC STUDY

Based on a Bi – L 3 edge X-ray absorption spectroscopic study of superconducting bismuth cuprates and model Bi compounds, it is shown that Bi is essentially in the 3 + state in the cuprates. Tl – L 3 absorption edge studies a number of thallium cuprate superconductors along with those of model compounds show some evidence for the occupancy of the Tl -6s band, but Tl 3+ is the prepondarant species. Cu K-edge studies of the thallium cuprates show that Cu is essentially in the 2+ state.