Optical Mode Gammas, Pressure Derivatives of Elastic and Dielectric Constants, and Stability of Rutile‐Structure Fluorides in the Rigid Ion Approximation

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AbstractThe microscopic Grueneisen parameters of all optical modes at zero wave vector, and the pressure derivatives of the elastic and dielectric constants of the difluorides XF, (X = Mg, Mn, Fe, Co, Ni, Zn) have been calculated from a rigid ion model with an effective ionic charge and with first and second nearest neighbor Born‐Mayer‐type central force short range interaction. The parameters of the model were previously determined from zero pressure values of the optical frequencies and elastic constants. The calculated values agree quite well with the few available experimental data. Several optical mode frequencies and elastic constant eigenvalues have negative pressure coefficients, which reflects and is related to the presence of several high pressure phases.