A WET-CHEMISTRY METHOD TO DETERMINE THE BI AND CU VALENCIES IN BI-SR-CA-CU-O (2212) HIGH-TEMPERATURE SUPERCONDUCTORS

A spectrometric method is presented to determine the average valency o f Bi in Bi2Sr2CaCu2O8+delta high-temperature superconductors (HTSC's) to better than +/- 0.005. Isostatically pressed samples of varying oxy gen content were prepared by sintering in Ar-O2 atmospheres of oxygen partial pressures between 10(-5) and 1 bar and temperatures between 30 0 and 900-degrees-C. Bi and Cu valencies were determined by a combinat ion of iodometric titration and the spectrometric method permanganomet ry. This method takes into account the decay with time of the permanga nate concentration in acidic aqueous solution. The latter is determine d by light-absorption measurement at lambda = 526 nm. In the selected sintering regime the Bi valency varies between 3.09 and 3.15, the Cu v alency between 2.06 and 2.11. Both Bi and Cu valencies increase linear ly with increasing oxygen content delta.