Rare-earth cuprates for ceramic colouring application—An investigation

Abstract

The possible use of rare-earth cuprates R 2BaCuO 5 and R 2Cu 2O 5 (R = rare earth) type compounds for high temperature (above 1000 °C) ceramic pigment application is presented in this paper. The traditional ceramic powder mixing method was adopted for the manufacture of various samples (pigment powders) used in this study. Yellow-green coloured powders with a variation in the intensity were obtained with R 2BaCuO 5 (R = Sm) at different calcination temperatures (950–1050 °C) and soaking time up to 12 h. These powders were then optimized in terms of colour by altering the calcinations temperature. The products with the most attractive colour were obtained with the sample calcined at 1050 °C. The same yellow-green colour powders were observed when Sm was replaced by other rare earth oxides such as Ho, Yb, Er and calcined at the same temperature, except for Y. In the case of the Y addition, a dark green coloured powder was observed. The X-ray diffraction pattern of the samples indicated R 2BaCuO 5 (R = rare earth) to be the major phase present in each case, although traces of CuO and the respective rare earth oxides were still present. For R 2Cu 2O 5 (R = Dy), a bluish-green coloured pigment powders with a variation in their intensity were observed when calcined between (950 and 1050 °C) with a 2 h soaking time. The best result (as far as intense colour is concerned) was noticed with the sample calcined at 950 °C. The same bluish-green colour powders were observed when Dy was replaced by other rare earths such as Yb, Ho, Er and Y. SEM micrographs of both types of compounds (R 2BaCuO 5 and R 2Cu 2O 5) obtained at various calcination temperatures revealed the presence of agglomerates in the samples, with an average grain size in the range 1–3 μm. All the pigment powders of the type R 2BaCuO 5 with the exception of the Sm-doped materials were unstable at 1070 °C and produced a bubble rich surface (yttrium being the worst) when introduced into an unleaded commercial transparent glaze. In the case of Sm the yellow-green coloured powder turned to a light green. Similarly all the bluish-green coloured powders were unstable in the glaze except R = Dy and Y. In the case of Dy, a raindrop effect was observed on the surface of the ceramic tiles.