POLARONIC CONDUCTION IN N-TYPE BATIO3 DOPED WITH LA2O3 OR GD2O3

The dielectric properties and conductivities (sigma) of BaTiO3 doped with 0.03 mol % of La2O3 or Gd2O3 were investigated in the temperature range of 10-300 K. A speculation over the experimental results, such as the temperature independence of conductivities below 30 K, linear Arrhenius relations between sigma-T3/2 and 1/T with an activation energy of 0.070 +/- 0.002 eV above 50 K, and relaxation absorptions in the loss tangents with an activation energy of 0.068 +/- 0.002 eV leads to the conclusion that the dominant conduction in n-type BaTiO3 is due to hopping motions of nonadiabatic small polarons. This conclusion is confirmed theoretically. Based upon polaron energies obtained experimentally, several parameters relevant to a nonadiabatic small polaron in this material are estimated.