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, UV–Vis 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 950–1200 °C. All the samples synthesized at 750–1200 °C located in the cyan color zone (h ∼ 195–235°). 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.