Chromium incorporation into TiO2 at high pressure

Chromium incorporation into TiO2 up to 3 GPa at 1300 °C and 900 °C has been studied by XRD as well as TEM. A CaCl2 type TiO2 polymorph has been observed in the quenched samples from high pressure. Two different mechanisms of solubility occur in the recovered samples. Chromium replaces titanium on normal octahedral sites but it also occupies interstitial octahedral sites, especially in the samples recovered from higher pressures. Interstitial chromium is responsible for an orthorhombic distortion of the TiO2 rutile structure in the quenched samples and gives rise to a (1 1 0) twinned CaCl2-structured polymorph. This phase is very likely the result of temperature quench at high pressure. The formation of this phase is directly related to the chromium content of the TiO2 grains. Chromium solubility in TiO2 increases with increasing the synthesis pressure. TiO2 is able to accommodate up to 15.3 wt% Cr2O3 at 3 GPa and 1300 °C, compared to 5.7 wt% at atmospheric pressure at the same temperature.