The conductivity of oxide cathodes. Part 14: Migration and desorption of negative ions of oxygen in the hollow-pore system

The field-directed movements of a negative ion of oxygen in the hollow-pore system of an oxide matrix are examined experimentally. It is shown that two basic mechanisms are possible. The first mode has a low activation energy of 0.6 eV and limits the ion movement to a migratory slide along the surface of the solid particle. This migration is a start-stop process with the ion spending much of its time in residence at localized adsorption centres on the surface of the particle. The second mode has a high activation energy of 2.4 eV and is therefore a relatively rare event. It involves the desorption of an ion from an adsorption centre, its ejection into space and its subsequent free flight across the hollow pore. It follows that almost all of the negative-ion movement in an oxide matrix is by surface migration along the contiguous chains of solid particles.