Abstract
Rutile is the most common TiO2 mineral with extensive application in the field of optical materials, and trivalent cations can significantly substitute Ti4+ with charge balanced by protonation. Several M3+-doped (M = Al, Ni, Co, Cr, Ga, Fe, and Mn) rutile samples were synthesized at 3 GPa (gigapascal) and 1273 K. The MO6-octahedral distortion model provides a reasonable explanation for the order of the M3+ concentrations. The total Cr3+ concentration was measured to be as high as 6.8 at % (atomic percentage) since the Cr3+O6 distortion is very close to that of Ti4+O6. This high Cr content significantly affects the Ti–O bonds and the lattice vibrations, and a quarter of the doped Al3+ and Cr3+ populations are identified in the interstitial sites. The M3+ effect on OH-stretching vibration was investigated by Fourier transform infrared (FTIR) spectra, which is useful for studying hydration mechanism in natural rutile samples with complex cationic substitutions. Besides, the doped-M3+ effect on the optical properties, including absorption, loss function, reflectivity, and refractive index, was studied by theoretical calculation. Incorporation of transition metal cations, especially Mn3+, significantly improves its optical performance in the visible light region, which is also confirmed by micro ultraviolet–visible–near infrared (UV–vis–NIR) spectra.
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