SURFACE FOURIER TRANSFORM-INFRARED SPECTRAL STUDY OF THE EFFECT OF SILVER AND CARBON IN TL0.5PB0.5SR2CACU2O7-DELTA

The relation between the effect of silver on the amount of residual ca rbon and the rate of carbonate build-up on the surface of the particle s of Tl1212 and Bi2212 was studied by infrared spectroscopy using a di ffuse reflectance infrared-Fourier transform (DRIFT) cell. The result showed that appreciable amounts of carbonate still remained after calc ination at 940 degrees C when carbonates were used as starting materia ls. Samples prepared using oxides also showed the presence of carbonat e that originated from the CO2 adsorption at the surface during proces sing. The small amounts of surface carbonates were below the detection limit of X-ray diffraction. However, the DRIFT technique has been fou nd to be a convenient and effective method for qualitative and semi-qu antitative analysis of carbonate formation on the powder surface and a tmospheric degradation of thallium-and bismuth-compound superconductor s. The presence of silver decreased the rate of the carbonate formatio n on the Tl1212 and Bi2212 particle surface influencing the degradatio n process. Carbonate formation was more sensitive to the presence of s ilver in Tl1212 than in Bi2212. The presence of silver appeared to cha nge the hydroxylation kinetics of calcium and/or strontium, which was directly related to the carbonate forming process. (C) 1998 Chapman & Hall.