(Bi,R)2O3 (R: Nd, Sm and Dy) oxides as potential pigments

In this work we have tackled the feasibility of the colored oxides in the Bi2O3-R2O3 system as ecological inorganic pigments. We have prepared by solid state reaction the mixed oxides (Bi2O3)(1-x)(R2O3)(x), R: Nd, Sm and Dy, with nominal compositions: Nd, x=0.2 and 0.5; Sm, x=0.4; and Dy, x=0.35. The obtained orange (Bi2O3)(0.6)(Sm2O3)(0.4) and (Bi2O3)(0.65)(Dy2O3)(0.35) oxides present f.c.c. fluorite-type structure. (Bi2O3)(0.8)(Nd2O3)(0.2) oxide consists of a mixture of two phases which present f.c.c. delta -Bi2O3 and Bi-Sr-O-type structures in the 900-1200 degreesC temperature range. In the synthesis of the oxide with nominal composition (Bi2O3)(0.5)(Nd2O3)(0.5) we have obtained a greenish sample with higher neodymium content. This sample presents the Bi3R5O12-type structure. Diffuse reflectance data and color coordinates suggest that the (Bi2O3)(0.6)(Sm2O3)(0.4) and (Bi2O3)(0.65)(Dy2O3)(0.35) oxides are expected to be promising candidates as new ecological pigments. (C) 2001 Elsevier Science B.V. All rights reserved.