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

Abstract

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 = Al^′_Ti + h˙ is evaluated as K_a = 1.9 × 10²³exp(−1.04 eV/kT) cm⁻³ and the mobility of trapped holes (Al^×_Ti) as u_× ≈ 720 exp(−1.04 eV/kT) cm² V⁻¹ s⁻¹ as the upper bound while those of free electrons and holes as u_n = 0.044 ± 0.010 cm² V⁻¹ s⁻¹ and u_p ≈ 0.024 ± 0.007 cm² V⁻¹ s⁻¹, respectively, in the temperature range of 800 °C to 1100 °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.