Abstract
The resistivity and the Hall and Seebeck effects of polycrystalline n-type and undoped, reduced single crystal were studied in the 100–300 K interval. Both Hall coefficient and resistivity showed similar temperature activated dependence for the single crystal in the rhombohedral phase and for the polycrystal in the rhombohedral and orthorhombic phases. Low-temperature Hall mobility in the single crystal decreased from at 120 K to at 220 K, implying a phonon scattering of charge carriers. The temperature dependence of the Hall mobility of the polycrystal showed a weak temperature dependence in the 100–220 K range with a maximum of at 170 K, probably indicating a transition from ionized impurity scattering at low temperature to a phonon scattering at higher temperatures. Temperature dependence of thermopower and Hall coefficient confirmed that the increase in conductivity of the single crystal below 200 K was caused by an increase in the concentration of the charge carriers. The results suggest that below 300 K, electron transport in occurs via the conduction band rather than by a small polaron hopping.
- Received 17 December 2002
DOI:https://doi.org/10.1103/PhysRevB.68.085205
©2003 American Physical Society