THE POLARIZABILITIES AND DISPERSION COEFFICIENTS FOR IONS IN THE SOLID GROUP-IV OXIDES

The electric-dipole polarizabilities of all the ions in the solid group IV dioxides ZrO2, CeO2. ThO2 and UO2 are deduced from experimental high-frequency dielectric-constant data. The resulting polarizabilities of 2.76 +/- 0.15 au, 5.54 +/- 0.15 au and 8.82 +/- 0.15 au for Zr4+, Cd4+ and Th4+, being unaffected by the crystalline environment, pertain also to these free cations. The polarizabilities of the O2- ions are found to depend on their in-crystal environment, as parameterized by the closest cation-anion separation, in the same way as those of the anions in the M2O alkali oxides. The ionic polarizabilities are used to derive values with an estimated error of 5% for the coefficients governing the dipole-dipole dispersive attractions between all ion pairs in all four crystals. Taken in conjunction with ion wavefunctions calculated elsewhere, these coefficients are used to compute values, with estimated errors of about 20%, for the coefficients governing the dipole-quadrupole dispersive attractions between all the ions in ThO2 and UO2. Values are presented for the parameters governing the damping of these dispersive attractions when the overlap between the wavefunctions of the interacting ions is not negligible.