Chromium-doped calcium zirconate – A potential red shade pigment: Preparation, characterization and testing

• Red hue pigments were obtained by doping CaZrO3 with chromium: CaZr1−xCrxO3.
• Increasing the chromium content leads to a decrease of CaZr1−xCrxO3 unit cell volume.
• The crystallite size of CaZr1−xCrxO3 decreases with increasing the chromium proportion.
• CaZr1−xCrxO3 solid solution is the only crystalline phase in the obtained pigments.
• CaZr1−xCrxO3 pigments are located in the red-yellow region of the CIEL*a*b* diagram.

Chromium doping of calcium zirconate, CaZr1−xCrxO3 (x = 0–0.07), leads to red shade pigments. XRD analysis confirmed that CaZr1−xCrxO3 solid solution is the only crystalline phase present in the samples annealed at 1400 °C. The substitution of Zr4+ by Cr4+ causes a progressive decrease of the unit cell volume, because Zr4+ has an ionic radius larger than Cr4+. The CaZr1−xCrxO3 crystallite size decreases as the substitution degree increases, from 64 nm (x = 0) to 46 nm (x = 0.07). The diffuse reflectance spectra of CaZr1−xCrxO3 pigments show a broad absorption band between 400 and 650 nm. CaZr1−xCrxO3 pigments are located in the red-yellow area of the CIEL*a*b* color space. The proportion of red ranges between 16.7 and 19.0, whilst the proportion of yellow varies between 6.4 and 8.2. The brightness of the pigments decreases as the chromium proportion increases. Testing the CaZr0.93Cr0.07O3 pigment in coloring a semi-transparent enamel showed that the pigment is dissolved by the molten glass. At the same time, Cr4+ is reduced to Cr3+, which is responsible for the green color of the enamel.