(Ni, Mg)₂SiO₄及び(Co, Mg)₂SiO₄合成かんらん石の光学吸収スペクトル

抄録

Optical absorption spectra of synthetic (Ni, Mg)₂SiO₄ and (Co, Mg)₂SiO₄ olivines have been reexamined at room temperature in the near ultraviolet, visible and near infrared ranges, by the method of diffuse reflection attenuance. The samples were synthesized by sintering the pellets of NiO, MgO and SiO₂ mixture and CoO, MgO and SiO₂ mixture. Both of the spectra of the two kinds of olivines consist of three bands, which are consistent with the crystal field theory, and two kinds of bands which were assigned to transition metal in the distinct octahedra, are superposed on each three bands. The spectra of (Co, Mg)₂SiO₄ olivine series are more complicated, because two bands of high energy side are superposed on each others. High and low spin configurations of Ni²⁺ ion (3d⁸) have theoretically no difference. But it was revealed that the Co²⁺ ion in olivine has high spin state. After the assignments of these spectra, the value of Dq and Racah value B were determined as(Ni, Mg)₂SiO₄ Dq (cm^-1) B (cm^-1)M(1) 856 980M(2) 762 902(Co, Mg)₂SiO₄M(1) 940 920M(2) 720 820The excess CFSE is a few kcal/mole in M (1) site of both olivines.