A wet-chemistry method to determine the Bi and Cu valencies in Bi-Sr-Ca-Cu-O (2212) high-temperature superconductors

Abstract

A spectrometric method is presented to determine the average valency of Bi in Bi₂Sr₂CaCu₂O_8+δ high-temperature superconductors (HTSC's) to better than ±0.005. Isostatically pressed samples of varying oxygen content were prepared by sintering in Ar-O₂ atmospheres of oxygen partial pressures between 10^-5 and 1 bar and temperatures between 300 and 900°C. Bi and Cu valencies were determined by a combination of iodometric titration and the spectrometric method permanganometry. This method takes into account the decay with time of the permanganate concentration in acidic aqueous solution. The latter is determined by light-absorption measurement at λ=526 nm. In the selected sintering regime the Bi valency varies between 3.09 and 3.15, the Cu valency between 2.06 and 2.11. Both Bi and Cu valencies increase linearly with increasing oxygen content δ.