Question

Explain why all crystals contain defects at temperatures above 0 K. Draw a diagram which

shows how the free energy, enthalpy and entropy of a crystal change on the introduction

of defects into the structure.

Answer 1

The creation of single, unassociated point defects in an elemental, crystalline solid increases the internal energy of the system and the enthalpy of the defect formation is positive. But the configurational entropy of the system also increases, and the equilibrium concentration of the defects will be reached when the Gibbse energyof the system is at minimum. Thermodynamically, point defects will thus always be present in a crystal above 0 K.