  We present a theoretical study of the impact of oxygen diffusion in oxide
crystals on metal dopants ionic state and the conduction type under dynamic
changes. The slow changes under thermal equilibrium are provided in a
companion, Part I paper. Oxygen vacancy formation acting as a shallow,
double-electronic donor, is assumed to result from the crystal exposure to a
low ambient oxygen pressure. Critical transitions from n- to a p-type at an
oxygen partial pressure Pi, and in ionization state of the metal dopant at an
oxygen partial pressure PM, are usually not simultaneous, and depend on the
different reaction constants. Invoking ambipolar diffusion for all
participating species, it is shown that oxygen vacancy diffusion exhibits well
defined characteristics in specific regions of the vacancy concentration
related to the said critical pressures. Particularly, the oxygen chemical
diffusivity is practically constant between Pi and PM, and increases sharply
for pressures P << Pi,PM and P >> P,PM. Prominent reaction fronts occur under
specific conditions in the two latter regions.
