DEFECT STRUCTURE, ELECTRICAL-PROPERTIES AND TRANSPORT IN BARIUM-TITANATE .5. WORK FUNCTION

Isothermal work function changes (DELTAPHI) of polycrystalline undoped BaTiO3 were measured in situ as a function of oxygen partial pressure in the range 1019-1153 K. Measurements were done by using a high temperature Kelvin probe equipped with an oxygen pump and oxygen gauge. The slope of the DELTAPHI versus log p(O2) dependence results in absolute values of the p(O2) exponent in the range 2.2 < n(PHI) < 2.8. Assuming that the surface is free of electrical charge, this range of values is lower than determined theoretically for the bulk phase of BaTiO3 (4.0 < n(PHI) < 4.8). The difference is interpreted in terms of the surface charge component, which results from oxygen chemisorption especially at higher p(O2).