Synthesis and color development mechanism of Li2CoTi3O8 cyan pigments: Effect of synthetic temperature

Abstract

Li2CoTi3O8 has a spinel-type crystal structure, and it can be simply synthesized by a solid-state method using Li2CO3, CoO and TiO2. Li2CoTi3O8 is currently used as a cyan-colored pigment, and it is highly safe as is actually utilized for cosmetics. In this paper, we have studied the color development mechanism of Li2CoTi3O8 with changing the synthetic temperatures, using X-ray diffraction (XRD), CIE-L*a*b* color coordinates, hue angle h, UVVis spectroscopy, X-ray photoelectron spectroscopy (XPS) and electron spin resonance (ESR). Li2CoTi3O8 formation was partially confirmed even at 500 °C, and single-phase Li2CoTi3O8 was obtained at 9501200 °C. All the samples synthesized at 7501200 °C located in the cyan color zone (h 3 195235°). The color change with synthetic temperatures, from whitish to deep cyan, was well explained by the visible light absorptions of Co2+ ions with different coordinations.