Characterization of yellow and red inorganic pigments from Mg0.5Cu1.5VxP2-xO7 (0 ≤ x ≤ 2) solid solutions

The structural characterization of Mg0.5Cu1.5VxP2-xO7 (0.0 <= x <= 2.0) compositions was performed and the colour parameters of these materials measured. Solid solutions in the alpha-Cu2P2O7, beta-Cu2P2O7 and beta-Cu2V2O7 structures were obtained by incorporation of V(V) in the alpha-Cu2P2O7 and beta-Cu2P2O7 structures and P(V) in the beta-Cu2V2O7 structure. Solid solutions with the alpha-Cu2P2O7 structure are obtained at 500-600 degrees C when the vanadium:phosphorus ratio is lower than 2/3 (x <= 1.2). At 600 degrees C, these materials have a bright yellow colour. In these compositions, the transition to the beta-Cu2P2O7 structure occurs at 800 degrees C. This transition modifies the colour but it keeps the yellow colouration for compositions. At 1000 degrees C, the -Cu3P2O8 phase coexists with the beta-Cu2P2O7 phase and the yellow colouration is lost. Solid solutions with the beta-Cu2V2O7 structure are obtained at 600-800 degrees C when the amount of vanadium is high (x >= 1.5). The increase in the amount of vanadium in Mg0.5Cu1.5VxP2-xO7 (0.0 <= x <= 2.0) compositions changes the colour of the materials from yellow to red at 600 degrees C (the Mg0.5Cu1.5P2O7 composition, x = 0.0, is pale green). The colour of the materials darkens with increasing temperature and compositions with x > 1.5 melted at 1000 degrees C.