Abstract
Mixed metal oxides are increasingly investigated as functional pigments due to their structural versatility, stability, and tunable optical properties. In this work, LiMgVO4, a lithium-based ternary vanadate, was doped with Co2+ and Ni2+ to study phase evolution, local structure, and optical behaviour for near-infrared (NIR) reflective applications. Controlled substitution induced a transformation from an orthorhombic Na2CrO4-type (Cmcm) lattice to an inverse spinel (Fd3̅m), with a distinct miscibility gap between the phases. Solid-state 7Li and 51V MAS NMR confirmed dopant incorporation, showing paramagnetic relaxation enhancement at low levels and line broadening at higher concentrations. Diffuse reflectance spectroscopy revealed spin-allowed d–d transitions, correlating with systematic color evolution from dusty blue to black (Co) and pale yellow to brown (Ni). The doped LiMgVO4-0.02Co and LiMgVO4-0.02Ni compositions exhibited high NIR solar reflectance of ∼82% in the wavelength range 700–2500 nm, enabling effective solar heat management. These findings establish Co/Ni-doped LiMgVO4 as a promising mixed oxide pigment for sustainable cool coating applications.
