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 α-Cu2P2O7, β-Cu2P2O7 and β-Cu2V2O7 structures were obtained by incorporation of V(V) in the α-Cu2P2O7 and β-Cu2P2O7 structures and P(V) in the β-Cu2V2O7 structure. Solid solutions with the α-Cu2P2O7 structure are obtained at 500–600 °C when the vanadium:phosphorus ratio is lower than 2/3 (x ≤ 1.2). At 600 °C, these materials have a bright yellow colour. In these compositions, the transition to the β-Cu2P2O7 structure occurs at 800 °C. This transition modifies the colour but it keeps the yellow colouration for compositions. At 1000 °C, the Cu3P2O8 phase coexists with the β-Cu2P2O7 phase and the yellow colouration is lost. Solid solutions with the β-Cu2V2O7 structure are obtained at 600–800 °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   1.5 melted at 1000 °C.