Determination of Average Valences of Copper and Thallium Separately in the Superconducting Thallium Cuprates

Abstract

A novel wet chemical route based on potentiostatic electrolysis and different reactivities with water is proposed to distinguish the average valences of copper and thallium in thallium cuprates. In the first experiment the sum of the extra oxidation states above +2 for copper and +I for thallium is obtained by reducing both Cu³⁺ and Tl³⁺ with CuCl. As a result, we can estimate the oxygen content of the sample, In the second experiment Cu³⁺ is allowed to react completely with water before CuCl is added to determine the remaining oxidation power of the solution and thereby the valence of thallium. In both experiments, the excess of Cu¹⁺ is electrolyzed as a final analysis step. The validity of the method is demonstrated with experimental results on YBa₂Cu₃O_z, Tl₂O and Tl₂O₃, which are the reference materials for Cu²⁺, Tl¹⁺ and Tl³⁺, respectively. The average valence of Cu and T1 in the properties of superconducting thallium cuprates with double Tl-O layers, i.e. Tl₂Ba₂Ca_n−1Cu_nO_z(n=1–4), are successfully determined using this new technique.