Blue pigments based on CoxZn1−xAl2O4 spinels synthesized by the polymeric precursor method

The CoxZn1−xAl2O4 system (x = 0; 0.1; 0.3; 0.5; 0.7; 0.9 and 1) was synthesized by the polymeric precursor method and characterized by the techniques XRD, TG-DTA, IR, UV–vis and colorimetry. The XRD patterns displayed the characteristic peaks of the spinel structure and a good crystallinity. The DTA curves showed an exothermic peak corresponding to the enthalpy of the transition taking place at about 700 °C. The infrared spectra displayed vibrations at about 650, 550, 540, 520, 500, 490 cm−1, which were ascribed to the spinel structure. The UV–vis spectra presented three bands at 550, 580 and 620 nm attributed to the Co2+ spin transitions in tetrahedral sites. The colorimetric data point out the formation of blue pigments, corresponding to highly negative values of b∗. The lightness, coordinate L∗, increases with the heat treatment temperature. These facts reveal that CoxZn1−xAl2O4 is a promising system that can be employed to obtain ceramic blue pigments.