Abstract
We have measured the complex dielectric permittivity for ceramic samples of which, unlike and do not exhibit a metal-insulator transition with a small amount of hole doping. This measurement is carried out as a function of Sr doping frequency and temperature (80–300 K). These results show strong temperature and frequency dependence and high real dielectric constant, 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 to 0.6 and it nearly vanishes at The static dielectric constant reaches 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 Sr doping and illustrate the doping effect on the dielectric polarization in
- Received 5 January 1998
DOI:https://doi.org/10.1103/PhysRevB.58.1252
©1998 American Physical Society