Spin state transition and giant dielectric constant in Pr0.987Na0.013CoO3

Pr0.987Na0.013CoO3 exhibits an anomaly in magnetic susceptibility and transport behavior around 200 K, which is associated with a thermally excited spin transition of Co3+. We show that introduction of Na+ in PrCoO3 induced a variable range hopping (VRH) conduction. At the transition temperature, the density of state near Fermi level increased, while the hopping distance and hopping energy decreased. Extrinsic electrode polarization was also observed at low frequency, leading to a giant dielectric constant. Both conductivity and dielectric relaxation frequency in bulk follow a simple temperature dependence, T-1/4, indicating a close relationship between VRH conduction and dielectric relaxation. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.3701613]