A double depletion layer model for the PTCR effect in n-doped BaTiO3 ceramics described by the Landau-Devonshire theory

The interrelated semiconductor and ferroelectric properties of n-doped BaTiO3 ceramics were considered in order to describe their electrical properties in a large range of temperatures. The free electron system was described by a double barrier Schottky model and the lattice by the Landau-Devonshire theory of ferroelectricity. Resistivity-temperature R(T) curves for various model parameters were simulated and discussed. The model is able to explain the R(T) behaviour in a large range of temperatures including near the ferroelectric-to-paraelectric transition. One of the most interesting results of this theoretical approach is the limited range of the donor concentration and of surface state density for which semiconductor behaviour at room temperature can be obtained.