The influence of temperature on the color of TiO2:Cr pigments

TiO2:Cr brown pigments were prepared via a polymeric precursor derived from the Pechini method. The pigments were analyzed by infrared spectroscopy, X-ray diffraction, ultraviolet–vis spectroscopy, and colorimetry. The increase of the calcination temperature from 700 to 1000 °C led to a decrease in the L* values, corresponding to darkening of the pigments. The pigments obtained in this work are darker than those produced by a solid-state reaction method reported before. The change in the pigment color is due to the anatase–rutile phase transition, which leads to a shift in the charge transfer bond (Ti4+ ↔ O2−) due to a change in the crystal field around the chromophore ions. Moreover, the oxidation state of chromium was observed to change, and this also alters the color of the pigments.