M‐Doped Al ₂ TiO ₅ (M=Cr, Mn, Co) Solid Solutions and their Use as Ceramic Pigments

Abstract

New ceramic pigments based on the tialite (Al 2 TiO 5 ) structure, doped with Co (pink), Cr (green), or Mn (brown), were prepared through the pyrolysis of aerosols followed by calcination of the obtained powders at 1400°C. The expected decomposition of Al 2 TiO 5 into a mixture of Al 2 O 3 and TiO 2 on refiring was inhibited by Cr‐doping and also by co‐doping with Mg the Mn‐ or Co‐doped samples. Microstructure and phase evolution during pigment preparation were monitored by scanning electron microscopy and XRPD. Unit cell parameters of tialite were determined by Rietveld refinement of the X‐ray diffraction patterns, revealing in all cases the formation of solid solutions where the solubility of dopants in the Al 2 TiO 5 lattice followed the trend Co<Mn<Cr. The valence state and possible location of dopants in the tialite lattice were investigated by X‐ray photoelectron spectra and diffuse reflectance spectroscopies, which suggested the presence of Cr 3+ ions in a large interstitial site of the tialite lattice with a distorted octahedral geometry, and of Mn 3+ and Co 2+ ions in the Al 3+ octahedral sites of the tialite lattice in the former case, and in both Al 3+ and Ti 4+ octahedral sites in the latter. Testing the ceramic glazes assessed the technological behavior of pigments, which found that the color stability was reasonably good for the Mn‐doped tialite and the Cr‐doped pigment, although the latter suffered a small loss of green hue. The Co‐doped pigment was found to be not stable in glazes, undergoing a cobalt‐leaching effect.