Abstract
We have measured the complex dielectric permittivity for ceramic samples of La <sub>1-x</sub> Sr <sub>x</sub> FeO <sub>3</sub> (0.2≤x ≤0.8), which, unlike La <sub>1-x</sub> Sr <sub>x</sub> MnO <sub>3</sub> and La <sub>1-x</sub> Sr <sub>x</sub> CoO <sub>3</sub> , do not exhibit a metal-insulator transition with a small amount of (x∼0.2) hole doping. This measurement is carried out as a function of Sr doping (0.2≤x ≤0.8), frequency (20-10 <sup>6</sup> Hz) and temperature (80-300 K). These results show strong temperature and frequency dependence and high real dielectric constant, >10 <sup>5</sup> , on all compounds at room temperature. This high dielectric polarization is due to a thermally activated process. The associated dipolar thermal activation energy linearly decreases from 260 to 60 meV when Sr doping increases from x=0.2 to 0.6 and it nearly vanishes at x=0.8. The static dielectric constant reaches ∼10 <sup>7</sup> in high Sr-doping samples due to an extra low-frequency polarization enhancement where a relatively high ac conductivity is also observed. These results are consistent with the persistence of the insulating phase until high (x∼1) Sr doping and illustrate the doping effect on the dielectric polarization in La <sub>1-x</sub> Sr <sub>x</sub> FeO <sub>3</sub> .