An oriented (100) single crystal of rutile was equilibrated at an ambient oxygen partial pressure, PO2, of 1015 to 105Pa at 900 to 1400K. After a step change of PO2 to a new value, the equilibration kinetics was monitored by measuring electrical conductivity. Application of Fick's second law to the kinetic data gave the chemical (ambipolar) diffusion coefficient for both oxidation and reduction runs. The chemical diffusion coefficient Dchem was found to be invariant with respect to oxygen partial pressure.

Ambipolar Diffusion in TiO2. Radecka, M., Sobaś, P., Rekas, M.: Solid State Ionics, 1999, 119[1], 55-60