The thermoelectric power and dc conductivity of La2/3+xTiO3-δ (x = 0, 0.13) were investigated. The thermoelectric power was negative between 80K and 300K. The measured thermoelectric power of x = 0.13 increased linearly with increased temperatures and was represented by S0+BT. The x = 0 sample exhibited insulating behavior, while the x = 0.13 sample showed metallic behavior. The electric resistivity of x = 0.13 had a linear temperature dependence at high temperatures and a T3/2 dependence below about 100K. On the other hand, the electric resistivity of x = 0 has a linear relation between lnρ/T and 1/T in the range of 200 to 300K, and the activation energy for small polaron hopping was 0.23 eV. The temperature dependence of thermoelectric power and the resistivity of x = 0 suggests that the charge carriers responsible for conduction are strongly localized. This temperature dependence indicates that the charge carrier (x = 0) is an adiabatic small polaron. These experimental results are interpreted in terms of spin (x = 0.13) and small polaron (x = 0) hopping of almost localized Ti 3d electrons.

The dc resistivity and thermoelectric power of bilayered perovskite La1.4(Sr0.2Ca1.4)Mn2O7 weremeasured as a function of the temperature. In the ferromagnetic phase, ρ(T) was accurately predicted by a0+a2T2+a4.5T4.5 with and without an applied field. At high temperatures, a significant difference between theactivation energy deduced from the electrical resistivity and thermoelectric power, a characteristic of smallpolarons, was observed. All of the experimental data can be feasibly explained on the basis of the small polaron.