Effect of defects on Gibbs free energy

Below is the relationship of Gibbs free energy of a solid to its number of defects:

Adding a defect is normally endothermic so it makes the enthalpy less negative, but it also increases disorder and so increases in the entropy. Since initial defects increase entropy at a faster rate, then initial defects will increase TS more than they raise H. Therefore any crystal above T=0 will have its minimum Gibbs energy at a non-zero number of defects.

TS will also rise with temperature. You can tell from the above graph that this will shift the Gibbs free energy minimum to the right, thus increasing the number of defects, since any substance will spontaneously change towards the structure with the lowest Gibbs free energy.