Formation and Structure of Spinel Solid Solution in Co₂GeO₄-Mg₂GeO₄-Zn₂GeO₄ and Ni₂GeO₄

Abstract

The structure of solid solutions formed in Co2GeO4-Mg2GeO4-Zn2GeO4 and Ni2GeO4-Mg2GeO4-Zn2GeO4 systems was studied by means of X-ray diffraction diagrams and visible reflectance spectra. The color of the solid solutions was examined.(1) Spinel [Sp I], olivine and phenacite solid solutions were formed around Co2GeO4 (Ni2GeO4), Mg2GeO4 and Zn2GeO4, respectively, in two ternary systems. Another spinel [Sp II] solid solutions were formed around Co1.2Zn0.8GeO4 and Ni0.8Zn1.2GeO4 in each system.(2) From the change of the value of lattice constant, the Sp I solid solution was found to be the normal-type spinel solid solution containing 4-coordinated Ge4+ ion. Reflectance spectra revealed the presence of 6-coordinated Co2+ and Ni2+ ions.(3) The results of the structure refinement by X-ray pattern fitting method and the change of the value of lattice constant suggested that the Sp II solid solution was the inverse-type spinel solid solution containing 6-coordinated Ge4+ ion.By annealing some specimens of the Sp II solid solution, the tetragonal spinel solid solution containing the 1:1 order of Ge4+ and divalent cation on octahedral sites was formed. These results supported that the Sp II solid solution was the inverse-type spinel solid solution.