Effect of calcination temperature on the structure of Cu x Co 1-x Al 2 O 4 blue ceramic nano-pigment

The effect of copper doping on the cobalt ferrite was investigated. Ceramic, pigment, nanoparticles of composition, Cu_xCo_1-xAl₂O₄ (x = 0.0–1), were prepared using a chemical co-precipitation method. The effect of calcination temperature on the structure of the materials was investigated at 200, 500, 900 and 1200°C. The ceramic pigments were characterized by XRD, FTIR, TEM, UV-vis and colorimetric methods. The XRD patterns displayed the characteristic peaks of the spinel structure and cubic unit cell. The XRD results at 200, 500, 900 and 1200°C showed that the cobalt spinel phase formed at 500°C. The FTIR spectra displayed vibrations which were ascribed to the spinel structure. Particle sizes were determined by TEM to be 140 nm and 70 nm for CoAl₂O₄ and Cu_0.5Co_0.5Al₂O₄, respectively. The UV-vis spectra had three bands attributed to the Co²⁺ spin transitions in tetrahedral sites. The calorimetric data confirm the formation of sky blue pigments with highly negative b^* values.