Thermoelectric power, Hall effect, and mobility of n-type BaTiO3

The resistivity and the Hall and Seebeck effects of polycrystalline n-type Ba0.996Y0.004TiO3 and undoped, reduced single crystal BaTiO3 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 BaTiO3 single crystal decreased from 12 cm2 V-1 s-1 at 120 K to 2 cm2 V-1 s-1 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 1.2±0.3 cm2 V-1 s-1 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 BaTiO3 occurs via the conduction band rather than by a small polaron hopping.