Investigation of the Ag2SO4-BaSO4 Binary System from an SOx Sensor Point of View

The binary phase diagram of Ag2SO4 - BaSO4 system is proposed using X-ray powder diffraction, thermal analysis (DTA/DSC), manning electron microscopy, and electrical conductivity results. About 5 mol-% BaSO4 is soluble in beta-Ag2SO4. The two-phase (Ag2SO4+BaSO4) mixture exists for 10-90 mol-% of BaSO4 between room temperature and 578 degrees C An eutectic of 578 degrees C exists of the composition 70Ag(2)SO(4) + 30BaSO(4) The conductivity maximum within the solid solubility limits is due to the generation of extrinsic vacancies and lattice expansion as a result of partial substitution of the bigger aliovalent Ba2+ for the Ag+-ions. The eutectic composition shows the maximum conductivity in the entire binary system due to the minimum in grain size, thereby providing a maximum surface ion conducting path. About 1 min response time of the sensor based on using the eutectic composition, as solid electrolyte, is much shorter than that of the sensor with pure Ag2SO4.