Electron Transport in Single-Domain, Ferroelectric Barium Titanate

Conductivity, Hall-effect, and Seebeck-coefficient measurements on single-domain crystals of $n$-type BaTi${\mathrm{O}}_3$ are described. In the cubic phase above 126°C, the electron mobility is 0.5 ${\mathrm{cm}}^2$/V sec. When the material becomes tetragonal, the mobility perpendicular to the $c$ axis increases rapidly to 0.54 ${\mathrm{cm}}^2$/V sec a few degrees below the transition temperature, then increases more slowly to 1.2 ${\mathrm{cm}}^2$/V sec as the temperature decreases to 26°C. The mobility parallel to the $c$ axis decreases rapidly to 0.35 ${\mathrm{cm}}^2$/V sec a few degrees below the transition, then decreases slowly to 0.13 ${\mathrm{cm}}^2$/V sec at 26°C. From the Seebeck-coefficient measurements, the density-of-states effective mass of cubic BaTi${\mathrm{O}}_3$ is $(6.5\mathrm{}\pm 2)m_0$. The experimental data in the tetragonal state are interpreted in terms of a relatively simple distortion of the band structure applicable to cubic perovskite-type semiconductors.