Brown pigments based on perovskite structure of BiFeO3−δ

Light brown inorganic pigments based on BiFeO3 doped by Sr2+ cations were prepared by a conventional solid-state reaction at high temperature. This study is focused on the synthesis of Bi1−x Sr x FeO3−δ powders in a range of substitution (x = 0–0.35; with step size 0.05). The main role of strontium is to overcome the defects that come to exist during the evaporation of Bi over material preparation. The substitution of trivalent bismuth ions by divalent strontium ions results in oxygen deficiency in the lattice, which was proved by both thermogravimetric analysis and elemental analysis. The substitution has a positive effect on the thermal stability of samples. The thermal stability of BiFeO3 is 1046 K, whereas the substitution of 20 mol% of Bi3+ by Sr2+ ions shifted it to 1403 K and powder with composition Bi0.65Sr0.35FeO3−δ has a thermal stability that is higher than 1434 K. An increasing range of substitution is connected with the change in the pigment color from reddish-brown to orange-brown and back to reddish-brown. The Bi0.85Sr0.15FeO3−δ pigment prepared by calcination at 1273 K offers the most interesting color properties (L* = 45.57; a* = 20.38; b* = 26.23).