Configurational and residual entropies of nonergodic crystals and the entropy’s behavior on glass formation
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We use thermodynamics of lattice vacancies to test the merits of the view that (i) statistical entropy, k(B) ln Omega, vanishes on vitrification of a liquid and hence there is no residual entropy and (ii) k(B) ln Omega of a nonergodic state would increase with time t as its structure relaxes. We argue that this view conflicts with the precepts of the configurational entropy of a crystal, -R[x ln x+(1-x)ln(1-x)], where x is the fractional population of vacancies, and with the observed decrease in x with t on structural relaxation. The issue of whether the entropy of a kinetically arrested crystal state is equal to k(B) ln Omega or equal to -R[x ln x+(1-x)ln(1-x)] can be resolved by measuring the vapor pressure, the emf of an electrolytic cell, and by scanning calorimetry. We also consider how the energy landscapes of a crystal and liquid differ, and point out that since crystals are in a nonequilibrium state, their thermodynamic data are inappropriate for testing the validity of the third law.