  We present a theoretical study of the impact of oxygen diffusion in oxide
crystals on metal dopants ionic state and the conduction type under thermal
equilibrium. Oxygen vacancy formation acting as a shallow, double-electronic
donor is assumed to result from the crystal exposure to a low ambient oxygen
pressure. It is shown, that 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. Experimental study of the different species
concentrations at thermodynamic equilibrium as functions of pressure and
temperature should allow assessment of various reversible reaction constants
controlling the process. In the Part II companion paper, the kinetic
(diffusion) characteristics are considered in detail.
