Abstract
Measurements of the low-frequency permittivity at and dc resistivity are reported for . Static dielectric constants are determined from the low- limiting behavior of the permittivity. The estimated polarizability for bound holes implies a radius comparable to the interatomic spacing, consistent with the small polaron picture established from prior transport studies near room temperature and above on nearby compositions. Relaxation peaks in the dielectric loss associated with charge-carrier hopping yield activation energies in good agreement with low- hopping energies determined from variable-range hopping fits of the dc resistivity. The doping dependence of these energies suggests that the orthorhombic, canted antiferromagnetic ground state tends toward an insulator-metal transition that is not realized due to the formation of the ferromagnetic insulating state near concentration .
- Received 6 April 2006
DOI:https://doi.org/10.1103/PhysRevB.74.144428
©2006 American Physical Society