Abstract
Abstract Colored hibonite-type oxides with a general formula CaAl12-xMxO19 were prepared by solid state reactions through M-site substitution of aluminum with various di-, tri- and tetravalent cations (M = Fe, Mn, Cr, Cu, Ga, In, Ti, Ge, Sn or any combination thereof), where Fe, Mn, Cr and Cu are chromophore ions. Neutron Rietveld refinements of CaAl9.5Fe2.5O19, CaAl11.5Mn0.5O19 and CaAl10SnMnO19 compounds show that Fe3+ and Mn2+ ions prefer to occupy the tetrahedral site, while Mn3+ has an evident preference for both tetrahedral and octahedral sites and Sn4+ for octahedral site in the hibonite structure. No oxygen vacancies are found by structural analyses. Magnetic measurement confirms divalent Mn for CaAl11Sn0.5Mn0.5O19 and trivalent Mn for CaAl11.5Mn0.5O19. Diffuse reflectance spectra reveal that the d-d transitions occurring in transition metal chromophores are mainly responsible for the observed colors. The colored powders exhibit fairly high reflectance in the near-infrared region (750–2500 nm) which makes them potential candidates for cool pigment applications. Synthesis and characterization methods are briefly reviewed for hibonite type of oxides, especially those containing Fe, Mn, Cr and Cu.
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