The ionic compressibilities and radii estimated for some transition metals in olivine structures

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The WMIN program of Busing (1970) in which the Born-type repulsive energy is assumed to calculate the ‘lattice energy’ of crystal, has been applied to estimate the repulsive parameters of four transition metals. The repulsive parameters, ionic radius A_i and ionic compressibility (softness parameter) B_i for Mn²⁺, Fe²⁺, Co²⁺ and Ni²⁺ are obtained from the structural data of Mn₂SiO₄, Fe₂SiO₄ Co₂SiO₄ and Ni₂SiO₄ (olivine structure) by the nonlinear least-squares refinements. The A_i and B_i parameters for Mg²⁺, Si⁴⁺ and O²⁻ ions determined previously for α-Mg₂SiO₄ (forsterite) were employed and fixed during the refinements. The ionic radii thus obtained have been compared with those of traditional ionic radius (Shannon and Prewitt, 1969) to explain their applications to the crystalchemical study of these minerals.