Effect of hole-trapping on mass/charge transport properties in acceptor-doped BaTiO3

The equilibrium conductivity and chemical diffusivity of Al-doped, single-crystalline BaTiO3 [C. R. Song and H. I. Yoo, J. Am. Ceram. Soc., 2000, 83, 773] have been re-analyzed by taking account of possible hole-trapping by acceptor-dopants (Al) with reference to the data on undoped BaTiO3 [C. R. Song and H. I. Yoo, Phys. Rev. B, 2000, 61, 3975]. The trapping effect is accounted for by the effective mobility of free holes involving the weighted mobility of trapped holes and by the modified thermodynamic factor due to the shift of the stoichiometric composition of the acceptor-doped system. The equilibrium constant of the trapping reaction Al(Ti)x = Al(Ti)' + h* is evaluated as Ka = 1.9 x 10(23) exp(-1.04 eV/kT) cm(-3) and the mobility of trapped holes (Al(Ti)x) as u(x) approximately = 720 exp(-1.04 eV/kT) cm2 V(-1) s(-1) as the upper bound while those of free electrons and holes as un = 0.044 + 0.010 cm2 V(-1) s(-1) and up approximately = 0.024 +/- 0.007 cm2 V(-1) s(-1), respectively, in the temperature range of 800 degrees C to 1100 degres C. The effect of hole-trapping on DC conductivity, chemical diffusivity and oxygen nonstoichiometry is exhaustively analyzed and further experiments are proposed that allow one to determine the trapping energy of acceptor impurities.