High dielectric permittivity and hole-doping effect in La1-xSrxFeO3

We have measured the complex dielectric permittivity for ceramic samples of La1-xSrxFeO3 (0,2 less than or equal to x less than or equal to 0.8), which, unlike La1-xSrxMnO3 and La1-xSrxCoO3, do not exhibit a metal-insulator transition with a small amount of (x similar to 0.2) hole doping. This measurement is carried out as a function of Sr doping (0.2 less than or equal to x less than or equal to 0.8), frequency (20-10(6) Hz) and temperature (80-300 K). These results show strong temperature and frequency dependence and high real dielectric constant, >10(5), 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 similar to 10(7) 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 similar to 1) Sr doping and illustrate the doping effect on the dielectric polarization in La1-xSrxFeO3. [S0163-1829(98)02027-X].