57Fe Mِssbauer and electronic spectroscopy study on a new synthetic hercynite-based pigment

A new blue hercynite-based pigment, stable at the processing temperatures for the ceramic application, has been synthesized. It is constituted by corundum and Ti-bearing hercynite. In order to clarify the complex Fe distribution evidenced by Baldi et al. [Proc. CIMTEC 2002(2003)], a 57Fe Mössbauer and diffuse reflectance spectroscopy study has been undertaken. Fe was found to be distributed between corundum, as trivalent, and hercynite, both as Fe(II) and Fe(III). Moreover, Fe(II) occupies both tetrahedral and octahedral sites in the latter mineral, according to a temperature dependent disorder. UV–VIS investigation revealed the presence of a broad band in the blue region, the shape and position of which was found to be due to an intervalence charge transfer mechanism between Fe(II) and Ti(IV) in two edge-sharing octahedra of hercynite.