Abstract
The resistivity-temperature (ρ-T) characteristics of the (Sr <sub>0.4</sub> Pb <sub>0.6</sub> )TiO <sub>3</sub> materials prepared by a microwave sintering process were examined. The resistivities were significantly lowered by increasing the rate of cooling and were substantially increased by a heat-treatment process. The Curie temperature was not altered by a fast cooling process but was shifted from T <sub>c</sub> = 302°C to 210°C when the as-sintered samples were post-heat-treated at 1200°C for 1 h. The high Curie temperature of the as-sintered samples was proposed to be due to the core-shell structure of the grains. The "shell", which contained Pb-rich perovskite of the composition (Sr <sub>0.29</sub> Pb <sub>0.71</sub> )TiO <sub>3</sub> , was homogenized with core material during heat treatment. The variation in resistivity was ascribed to the modification of the concentration of cationic vacancies. The donor level (E <sub>d</sub> ) and the deep trap level (E <sub>t</sub> ) of the materials were, respectively, evaluated from the Arrhenius plot of ρ-T characteristics at T < T <sub>c</sub> and T > T <sub>max</sub> regimes to be E <sub>a</sub> 0.078-0.193 eV and E <sub>t</sub> ≅ 1.66 eV + E <sub>f</sub> , where E <sub>f</sub> is the Fermi level.