Crystal Structure, Thermal Expansivity and High-Temperature Vibrational Spectra on Natural Hydrous Rutile

A natural rutle sample was measured byin situhigh-temperature X-ray diffraction (XRD) patterns, as well as Raman and Fourier transform infrared (FTIR). Crystal structure is refined on the sample with 1.4 mol.% Fe and 510 +/- 120 ppmw. H2O. The unit-cell and TiO(6)octahedral volumes are expanded by 0.7%-0.8 degrees/o for Fe(3+)incorporation, as compared with the reported Ti-pure samples. The volumetric thermal expansion coefficient (alpha, K-1) could be approximated as a linear function ofT(K): 4.95(3)x10(-9)xT+21.54(5)x10(-6), with the averaged value alpha(0)=30.48(5)x10(-6)K(-1), in the temperature range of 300-1 500 K. The internal Ti-O stretching (A(1g)andB(2g)) and O-Ti-O bending (E-g) modes show 'red shift', whereas the multi-phonon process exhibits 'blue shift' at elevated temperature. The rotational mode (B-1g) for TiO(6)octahedra is nearly insensitive to temperature variations. The OH-stretching bands at 3 279 and 3 297 cm(-1)are measured by high-temperature spectroscopy experiments. Both the IR-active and Raman-active OH-stretching modes shift to lower frequencies at higher temperature, with the signal intensities decreasing. And after quenching, we expect about 43% dehydration around 873 K, and 85% dehydration at 1 273 K for this hydrous sample.