Surface Thermodynamic Functions for NaCl
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The surface entropy and surface specific heat at constant volume, and the vibrational contributions to the surface energy and surface Helmholtz free energy have been calculated as functions of temperature for the (100) surface of NaCl. To our knowledge, these are the first calculations of surface thermodynamic functions for an ionic crystal to be based on a realistic lattice-dynamical determination of the vibrational frequencies, rather than on the use of a continuum model, Einstein model, or unrealistically simple lattice model. The main approximations in the present treatment are the harmonic approximation and the neglect of the polarizabilities of the ions (i.e., the use of a rigid-ion model). Comparison is made between the present theoretical results and the experimental results for the excess heat capacity of finely divided NaCl. At low temperatures, the present results are in good agreement with the recent data of Barkman et al. The position of the peak in the surface specific heat is in good agreement with the data of Morrison and Patterson; a discrepancy of about 40% in the height of the peak may be due to experimental uncertainties in determining specific surface areas.
author list (cited authors)
Chen, T. S., Alldredge, G. P., de Wette, F. W., & Allen, R. E.