Abstract: Complex impedance spectra of BaTiO₃ with boron addition on the electrical characteristics of PTCR were studied. Cole-Cole plot shows a single semicircle
in room temperature (T<T_c) but shows a overlapping semicircle and skew circle above the Curie temperature (T_c<T<T_m), which may indicate
relaxational processes with multiple defects, such as V_Ba, V_o etc, from single defect such as V_Ba by thermal activation in the regions
of the grain boundary layer. The grain resistance, grain boundary resistance and relaxational time constant were calculated from the Cole-Cole plot and the barrier
height was calculated by the Heywang model. The results show that PTC effect originates from the grain boundary. The grain resistance exhibits NTC, but the grain boundary
resistance shows obviously PTC. Up to date, the Heywang model or Heywang-Jonker model is the most accepted model to explain the PTC mechanism by phenomenal explanation.

Key words: BaTiO₃ PTCR, Cole-Cole plot, complex-plane impedance spectra, heywang model