Intense Blue Colors in Wolframite-Type Co2+:MgWO4 Oxides Through Distortion in Co2+ Octahedra.

Abstract

New inorganic cobalt based blue pigments Mg1-xCoxWO4 (x =0.1, 0.2 and 0.3) have been prepared by the solid state reaction and flux added methods. The synthesized samples show intense blue color with very low doping concentration of cobalt. Raising cost and toxicity make a critical need to reduce the consumption of cobalt in the ceramic industry, at the same time trying to improve the efficiency and sustainability of pigments. The present investigation help us minimize the cobalt consumption and cost of production with respect to conventional blue ceramic colorants. Intense blue hue was obtained at relatively low doping concentration of Co2+(20 mol%) with b* value of 46.97, which is considerably bluer than cobalt aluminate spinel (b* = -32.70). UV-visible absorption properties are strongly related to the coordination environment of the Co2+ ions. Increasing the amount of cobalt induces a change in the local symmetry of MgO6 octahedra witnessed by the change of the metal-ligand bond distances.The changes are attributed to the larger ionic radius and electronegativity of Co2+ ions compared to the Mg2+ ions in the host lattice.These observations corroborate the important structural distorsions arising from the differences in ionic radii and electronegativity between the dopant and host cations.