Synthesis and coloring performance of Ni-geikielite (Ni,Mg)TiO3 yellow pigments: Effect of temperature, Ni-doping and synthesis method

Solid solutions of Ni in MgTiO3 ilmenite (geikielite) were investigated as potential yellowish ceramic pigments or dyes. Ni-geikielite samples (Mg1−xNixTiO3, x = 0–0.4) were prepared by solid-state and citrate-gel routes and fired pigments were characterized by XRD, SEM/EDX, UV–vis–NIR and color measurement techniques. The increase of Ni-doping enhanced ilmenite stabilization in ceramic samples, obtaining almost single phase of Ni-geikielite for x = 0.4 at 1200 and 1400 °C. Fired pigments exhibited intense yellow colors at both temperatures, associated to Ni2+ ions in distorted octahedral A sites of ATiO3 ilmenite, and an increase of the orange hue with firing temperature arising from an enhanced (Mg,Ni)O6 polyhedral distortion. Noteworthy, citrate-gel samples exhibited a much higher reactivity, yielding well-crystallized Ni-geikielite at lower temperatures (800 °C/3 h), and leading to higher chroma yellow-orange colors even at lower Ni loadings. These pigments were partially stable in commercial low-temperature ceramic glazes, giving rise to weaker yellowish colors irrespective of the preparation route.