MODIFIED-MODEL IN POSITIVE TEMPERATURE-COEFFICIENT OF RESISTANCE BATIO3 CERAMICS

Current-voltage and resistivity-voltage measurements have been made on donor-doped BaTiO3 ceramics in order to investigate the nature of the current transport processes. It is found that the characteristics of the current-voltage do not follow the Heywang model [Solid-State Elect ron. 3, 51 (1961)]. Hence, the classical Heywang model is modified and the thermionic emission model with smoothly changed barrier resulted from image force is suggested. The modified theory coincides better wi th the experimental observation. The dependence between current densit y and voltage is J=J(0) exp[-(phi(0)-beta V-1/2)/kT]. The relationship between resistivity and voltage (voltage effect) is rho=(2kT/dJ(0) be ta)V-1/2 exp[(phi(0)-beta V-1/2)/kT]. From the modified model, the max imum barrier height of BaTiO3 ceramics can be deduced experimentally a s well. (C) 1996 American Institute of Physics.