Ti–Ca–Al-doped YCrO3 pigments: XRD and UV–vis investigation

Compounds based on the YCrO3 perovskite structure, doped with Al, Ti and Ca, were studied by XRD and DRS, aiming at assessing their potential as green ceramic pigments. Nine samples were synthesized by the ceramic route according to the Y1-yCayCr1-x-yAlxTiyO3 stoichiometry, where 0 < x < 0.5 and 0 < y < 0.2. Doping affected the phase composition (minor amounts of Y2O3 and Y–Ti oxides were found) and induced a series of structural rearrangements in perovskite without symmetry changes, involving unit cell parameters, metal–oxygen distances and distortion of cation sites. Different trends were observed varying x and y. Optical properties were influenced by changes in perovskite crystal structure and stoichiometry. In particular, the oxidation of Cr3+ to Cr4+ had a deleterious effect on its green colour, turning to gray–brown. The occurrence of Cr4+ in the perovskite lattice was required to balance the replacement of Y3+ by Ca2+ ions not fully compensated by the designed coupled substitution of Ti4+ for Cr3+