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.
The spontaneous change might be kinetically slow. A crystal made a high temperatures can keep a higher number of defects even when it is cooled to room temperature.
ReplyDeleteIts the intrinsic equilibrium concerns, i.e., defect concentration, c = c(T).
DeleteIt really helps....
ReplyDeleted🔺G/dn=0 i need this calculation please help me
ReplyDeleteStarts with defect concentration, c = c(T), and energy, E = E(T), i.e., speed of molecules raises with T.
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