Models of the current–voltage dependence of BaTiO3 with positive temperature coefficient of resistivity

Current–voltage j(V) characteristics of barium titanate based positive temperature coefficient of resistivity thermistors were analyzed in terms of space charge limited current, trap-filled limited current, Frenkel–Poole, double-Schottky barrier, and small radii polaron models. It is shown that for the double-Schottky barrier model, the j(V) dependence does not obey the relation j∝exp (eV/2kT) at temperatures near or above the resistivity maximum. Instead, the j(V) characteristics show significant dependence on the interface charge. With increasing temperature, the region of nonlinear j(V) dependence is expected to shift towards higher voltages due to an increase in the equilibrium concentration of unoccupied interface states.