Small polarons in La2/3TiO3-δ

The thermoelectric power and dc conductivity of La2/3TiO3-delta (delta=0.057, 0.07, and 0.16) were investigated. The thermoelectric power is negative between 80 and 350 K. The measured thermoelectric power of La2/3TiO3-delta increases linearly with temperature, in agreement with the model proposed by C. Wood and D. Emin [Phys. Rev. B 29, 4582 (1984)], and represented by A+BT. This temperature dependence indicates that the charge carrier in this material is a small polaron. There exists a linear relation between log(sigma T) and 1/T in the range of 200-300 K, the activation energies for small polaron hopping were 0.15, 0.21, and 0.24 eV for delta=0.16, 0.07, and 0.057, respectively. These properties are discussed in terms of a hopping process involving small polarons. This conclusion is confirmed theoretically. Based upon polaron energies obtained experimentally, several parameters relevant to small polaron transport in this material are estimated. (C) 2000 American Institute of Physics. [S0021-8979(00)10117-3].