Analysis of ionic radii, electronic polarizabilities and refractive index of some solids with fluorite and rutile structures

An analysis of ionic radii and electronic polarizabilities of ions has been presented for twenty-eight solids with fluorite (CaF 2 ) and rutile (TiO 2 ) structures. It has been emphasized that the ionic radii and electronic polarizabilities obtained by Pauling, by taking into account the effective nuclear charges with screening parameters, correspond to interaction free state. The ionic radii in the crystalline state have been used those determined by Tosi based on the Born model of cohesion for ionic solids. The relationship between ionic radii and polarizabilities has been investigated and used to obtain crystalline state polarizabilities of ions in fluorite and rutile type compounds. The crystalline state radii and polarizabilities of cations increase and those of anions decrease as compared to free state values. This is consistent with the Fajans-Joos principle according to which the loosening of cations and tightening of anions take place in the crystalline bonded state relative to free state. The crystalline state polarizabilities have been used to determine the refractive indices of the materials using the Lorentz-Lorenz formula. Values of volume derivatives of refractive index related to the photoelastic behaviour have also been calculated.