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 temp erature Kelvin probe equipped with an oxygen pump and oxygen gauge. Th e slope of the DELTAPHI versus log p(O2) dependence results in absolut e values of the p(O2) exponent in the range 2.2 < n(PHI) < 2.8. Assumi ng 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 sur face charge component, which results from oxygen chemisorption especia lly at higher p(O2).