Environmentally benign inorganic red pigments based on tetragonal β-Bi2O3

This paper reports on the synthesis, characterization, and optical properties of a new class of environmentally friendly red pigments based on the tetragonal β-phase of Bi2O3. Stabilization of the metastable β-phase at room temperature has been successfully achieved through incorporation of various metal cations (M = Y3+, Zr4+, Eu3+, Nb5+). Doping with zirconia (Zr4+) yielded compounds showing the most promising red color coordinates (a* > 30) with the best value provided by the composition. Subsequently, this specific intermediate of the β-phase was further reacted with FeOOH to generate, under preservation of the β-Bi2O3-type structure, a red product with the formula (Bi1.95Zr0.05)0.8Fe0.4O3+δ. With color coordinates of L* = 49.9, a* = 31.1, and b* = 25.8, the newly developed pigment has been found to be superior compared to the conventional Fe2O3 pigment (Bayferrox 4130: L* = 37.4, a* = 28.9, and b* = 20.8).