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

Abstract

Electrical conductivity and oxygen nonstoichiometry (delta) have been measured, respectively, by a dc 4-probe technique and coulometric titrometry on the system of polycrystalline Ti0.99Ga0.01O1.995-delta against oxygen activity in the range of -20 < log aO2 < or = 0 at different temperatures in the range of 1073 < or =T/K < or = 1373. It is found that isothermal conductivity varies as sigma alpha aO2m with m approximately -1/4, -1/5, -1/4, +1/4, in order of increasing aO2, 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.

Influence of Line Defects on the Electrical Properties of Single Crystal TiO2

“…[ 12 , 15 ] In other studies the same slip systems were found. [ 19 , 20 ] The electrical properties of TiO 2 were studied independently in the past [27][28][29] in slightly and strongly reducing atmosphere where nominally undoped TiO 2 is an n-type conductor, and in oxidizing atmosphere where rutile is p-type conducting. At intermediate temperatures, nominally undoped rutile single crystals are electronic conductors with very low ionic transference number.…”

“…[ 27 ] In case of signifi cantly doped rutile the ionic transference number depends on p O 2 ; the number is negligible at very low and high p O 2 and increases at intermediate p O 2 . [ 29 ] Based on simple mass action laws and electroneutrality conditions, the defect concentrations can be related to the oxygen partial pressure ( p O 2 ) when equilibrium with gas phase is established: [ 28 ] …”

Enhanced ionic conductivity in polycrystalline TiO2 by “one-dimensional doping”

“…In the case of homogenous doping, the solubility of the dopant depends on the ionic radius, and is only 0.1 mol% for Y 3+ (r = 0.9 Å) 12 and 1 mol% for Al 3+ (r = 0.54 Å) and Ga 3+ (r = 0.62 Å). 10,11 3.4. Discussion in terms of the space charge model…”

“…introducing aliovalent impurities (zerodimensional doping). Here, modification of the conductivity is limited by the solubility limit of the dopants in TiO 2 , 8 which is typically in the range of 10-15% for donor dopants like Nb, 9 and typically lower for acceptor dopants -up to 1% for Al and Ga 10,11 and only 0.1% for Y. 12 The low solubility of acceptors is due to their large ionic radii compared with the donors.…”

Oxidation kinetics of nitrogen doped TiO2−δ thin films

“…Generally, electrons, holes, anion vacancies, or titanium interstitials can be expected as point defects relevant for transport of matter and charge in TiO 2Àd . [33][34][35][36][37][38] Unfortunately, from the literature on the point defect structure of TiO 2Àd it is not immediately clear which electron-related defects are dominating in the oxygen deficient, N-doped a-TiO 2 thin films, i.e. V O ; V Â O ; Ti 0 Ti , and/or Ti I , at the relatively low temperatures of our experiments (500 1CÀ600 1C).…”