DETERMINATION OF OXYGEN CONTENTS AND CATION VALENCES IN THE SUPERCONDUCTING BISMUTH AND THALLIUM CUPRATES

The oxygen contents and valences of cations in various superconducting cuprates such as Bi2Sr2(Ca, Y)Cu2Oy, Tl2Ba2Can-1CunOy, etc. which con tain two kinds of multi-valence metals have been determined by novel w et chemical methods. The wet chemical methods are based on the differe nces in oxidation power of each cation and at the last step an electro chemical method is employed for measuring the amount of reducing agent , i.e., CuCl. For superconducting Bi-based cuprates, a modified consta nt-current coulometry has been developed. For the superconducting Tl-b ased cuprates a constant-potential electrolysis method which makes it easy to control the electrolysis potential has been applied. The resul ts obtained for Bi2Sr2(Ca, Y)Cu2Oy have shown that both Bi- and Cu-val ences decrease with increasing Y, which is consistent with the results of earlier works. The results obtained for the double Tl-O layer supe rconductors show that the Tl valence is about +3 in all the thallium c uprates and different from the value obtained from XPS measurements of earlier works. The reason for this discrepancy is discussed.