Electrical properties of Er-doped BaTiO/sub 3/ ceramics for PTCR applications

The electrical properties of Er-doped BaTiO/sub 3/ ceramics with different amounts of dopant in the range (0.25-8) at.% and with electron compensation were studied using D.C.-resistance and impedance spectroscopy (IS) measurements. The experimental results were compared with the Double Barrier Schottky theory for the description of the PTCR effect. D.C. resistance results and microstructure analyses were used to discuss the role of dopant concentration, mechanism of incorporation and cooling rate on the PTCR behaviour. Optimum processing parameters that ensure the best PTCR ratio were found. IS measurements were performed at various temperature over the whole transition range and grain boundary and bulk contributions were extracted by a non linear least squares fitting procedure. Dielectric constant and resistivity values were obtained and used to derive model parameters for different samples. Temperature dependence of total resistivity was calculated and compared to D.C. curves. The agreement is good in a large range of temperature, including the ferro-para phase transition.