  The point defect thermodynamics in a general family of binary compounds,
including B2 compounds as a specific representative, are classified by way of
two non-trivial energy parameters. The scheme is applied to published ab initio
defect formation energies, and the variety of resulting phenomena is
demonstrated. Further, by introducing model assumptions the consequences for
the active diffusion mechanisms are deduced. It is shown that particularly for
the off-stoichiometric case, the assumed prevalence of either the six-jump
cycle or the triple-defect mechanism has to be reconsidered, as a number of
qualitatively different mechanisms emerge as likely candidates for the dominant
effect. Two of those, the 4+2-jump cycles and the waltzing-step mechanism, are
introduced here.
