chemical diffusion

Diffusion under the influence of a gradient in chemical composition.
In concentrated solid solutions, e.g.
A_{1-x}B_{x}, or in diffusion couples,
the motion of one constituent causes a counterflow of the other
constituents(s) or vacancies. In this case one can define a diffusion
coefficient for the intermixing, which is called the chemical diffusion
coefficient or interdiffusion coefficient.

Source:

PAC, 1999, *71*, 1307*
(Definitions of Terms for Diffusion in the Solid State)
* on page 1310