In which "Jx" stands for the flux ("flow") of vacancies in direction "x"; "D""x" is a constant for the material in that direction and formula_2 is the difference in concentration of vacancies in that direction. The law is valid for all principal directions in ("x", "y", "z")-space, so the "x" in the formula can be exchanged for "y" or "z". The result will be that they will become evenly distributed over the crystal, which will result in the highest mixing entropy.