Are there any solids that undergo diffusion? Are there any solids that undergo diffusion?


Introduction:

In school, my teacher is only talking about diffusion happening in liquids and I though that it may be able to happen to solids also.

Though I did think about how the concentration of the molecules in a solid was too concentrated for the molecules to pass through a cell membrane. What I am mainly wondering and would answer my question, is there a way that the molecules of a solid would break up into less concentration, in which they can undergo the process of diffusion.
Diffusion also occurs in solids. For example, (intentional or undesirable) movement of impurity atoms or other crystal defects can be very important for the fabrication of semiconductors.

The classical experiment to demonstrate diffusion (and to measure the diffusion coefficient) in solids is the diffusion of gold in lead. A thin layer of gold that is labelled with $\ce{^198Au}$ is applied to the surface of a lead sample using electrolysis. The sample is heated, and the penetration of gold atoms into the lead sample is observed using the β radiation from $\ce{^198Au}$.

You could use a similar experiment to measure self-diffusion (e.g. of gold atoms in gold).