Research Papers in Physics and Astronomy

 

Date of this Version

5-15-1969

Comments

Published in Physical Review Volume 181, Number 3, 15 May 1969. Copyright 1969. Used by permission.

Abstract

The results of an extended calculation of the normal modes of the NaF lattice are presented. Three models have been considered : a "rigid-ion" (RI) model, a "deformation-dipole" model with central F--F- short- range interactions (DDNNN), and a “deformation-dipole" model including both central F--F- interactions and a noncentral component in the first-neighbor, short-range interactions [DDNNN(NC)]. For each of these models we have derived frequency spectra for both 300 and 0°K input parameters, the associated dispersion curves for symmetry directions, Debye characteristic temperatures ΘD, moment functions ωD(n), and the Na+ and F- Debye-Waller parameters B1 and B2 and their ratio BI/Bz.O f the three models, the two DD variations give good agreement with the observed dispersion curves, the DDNNN models being slightly better and giving somewhat closer agreement with the observed Bvalues.

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