Electrical conductivity and oxygen nonstoichiometry of acceptor (Ga)-doped titania

Electrical conductivity and oxygen nonstoichiometry (delta) have been measured, respectively, by a dc 4-probe technique and coulometric titrometry on the system of polycrystalline Ti(0.99)Ga(0.01)O(1.995)-delta against oxygen activity in the range of -20 < log aO(2) <= 0 at different temperatures in the range of 1073 <= T/K <= 1373. It is found that isothermal conductivity varies as sigma proportional to a(O2)(m) with m approximate to -1/4, -1/5, -1/4, +1/4, in order of increasing aO(2), finally exhibiting an n-type (m = -1/4) to p-type (m = +1/4) transition crossing the stoichiometric composition (delta = 0), in perfect agreement with the oxygen nonstoichiometry variation. The electrical conductivity and oxygen nonstoichiometry isotherms are combined to evaluate the ionic partial conductivity and transference number, the intrinsic electronic excitation equilibrium constant, and eventually both mobilities of electrons and holes without employing any assumption at all. The partial molar enthalpy and entropy of the component oxygen are also evaluated as functions of nonstoichiometry.