Elastic, optical, and dielectric properties and their pressure derivatives of rutile‐structure oxides in a modified rigid ion approximation

The elastic and static dielectric constants and their first pressure derivatives, and the optical mode frequencies and mode gammas at zero wave vector have been calculated for GeO2, TiO2, and SnO2 from a modified rigid ion model, in which first and second nearest neighbor central force repulsive interaction of Born‐Mayer type and oxygen–cation–oxygen angle bending forces are included. The nine free parameters of the model are determined from a least squares fit to the zero pressure values of the optical frequencies and elastic constants. The agreement with the experimental optical and elastic data at zero pressure is very good, and fair to moderate for the pressure derivatives.