CALCULATION OF DEFECT ENTROPIES IN IONIC CRYSTALS IN THE QUASIHARMONIC APPROXIMATION : APPLICATION TO FLUORITES P.W.M. Jacobs, M.A.H. Nerenberg, J. Govindarajan et T.M. Haridasan J. Phys. Colloques, 42 C6 (1981) C6-914-C6-916 DOI: 10.1051/jphyscol:19816272