The interaction of oxygen with manganese and its effect on surface state properties in PTCR BaTiO₃

Semiconducting BaTiO₃-based ceramics with varying manganese (Mn) acceptor concentrations (0.048–0.112 mol%) are systematically examined. By optimizing the Mn content, ceramics with electrical breakdown field strengths as high as 600 V/mm with simultaneous low decrease of resistance below phase transition (R_min/R₂₅ = 0.78) temperature are achieved. The observed differences in electrical properties are ascribed to modifications in grain boundary surface state properties. ¹⁸O tracer experiments at 800 °C reveal a clear enhancement of oxygen diffusivity with increasing Mn concentration. The comparison with resistance–temperature (R–T) characteristics indicates the simultaneous presence of various acceptors (e.g., adsorbed gases, Mn^4+/3+, Mn^3+/2+) with different energy levels and suggests a direct correlation between surface trap formation and oxygen diffusivity. We propose that the interaction of Mn with oxygen determines the number of surface states but also the depth of their energy level within bandgap, defining the resulting form of the R–T characteristic.