Formation and Color of Spinel Solid Solution in Li<sub>2</sub>O-MO-TiO<sub>2</sub> (M=Mg, Co, Ni) System

Abstract

This study was concerned with the formation of spinel solid solutions and color development in the system Li2O-MO-3TiO2 (M=Mg, Co, Ni). Specimens were prepared by calcining mixtures of oxides of cobalt and titanium, and carbonates of lithium, magnesium and nickel at 1000°C for 2h. The formation range of spinel solid solutions was examined by X-ray analysis, and the lattice parameter of each solid solution was calculated. The structures of Li2O-MgO-3TiO2 and Li2O-CoO-3TiO2 solid solutions were refined by the pattern fitting method for powder X-ray diffraction. The color was discussed by measuring the spectral reflectance. The results were summarized as follows;1) In the system Li2O-(1-x)MgO-xCoO-3TiO2, a spinel solid solution with super structure was observed in the range of 0<x<1.2) In Li2O-(1-x)MgO-xNiO-3TiO2 and Li2O-(1-x)CoO-xNiO-3TiO2 systems, a spinel solid solution with super structure was obtained in the range of 0<x<0.6. When x=0.8 and x=1.0, the formation of spinels was not observed.3) According to the results of structure refinement [cubic, S. G.=P4332, Z=4, a=8.377 (M=Mg), 8.373 (M=Co) A], the cation distribution of Li2O-MO-3TiO2 (M=Mg, Co) is nearly Li0.5M0.5 [Li0.5Ti1.5]O4 (M=Mg, Co). Li+ and Ti4+ in octahedral sites have the 1:3 order. Between the separations of Li+-O2- and Ti4+-O2- in octahedral sites, a fairly large difference was noted, As Ni2+ revealed strong octahedral site preference, an increase in Ni2+ caused the migration of Li+ from octahedral to tetrahedral sites in Li2O-(Mg, Co, Ni)O-3TiO2 system. Consequently, the intensity of superlattice lines of spinel decreased as the amount of Ni2+ increased.4) The color of spinels changed from white to turquoise in Li2O-(1-x)MgO-xCoO-3TiO2 system, from white through light yellow to yellow in Li2O-(1-x)MgO-xNiO-3TiO2 system, and from turquoise through green to yellow in Li2O-(1-x)CoO-xNiO-3TiO2 system.