In situ high temperature X-ray diffraction study of anatase and rutile

In situ X-ray diffraction patterns of the powder titania polymorphs are recorded in a temperature range from room temperature (RT) to 1200 degrees C in static air and vacuum. The results show that the temperature converting anatase into futile is at 850 degrees C in static air and at 855 degrees C in vacuum. Lattice parameters for anatase (RT-850 degrees C) and rutile (RT, 900-1200 degrees C) in static air and those for anatase (27-850 degrees C) and rutile (950-1200 degrees C) in vacuum are refined. The variations of lattice parameters of anatase and futile with temperature (degrees C) are therefore well described. Linear (alpha) and volume (beta) thermal expansion coefficients of anatase (RT-850 degrees C) and rutile (RT, 900-1200 degrees C) are calculated. The change laws of alpha and beta with temperature for anatase and rutile in static air and vacuum are summarized. At RT, the thermal expansion coefficients for anatase are alpha(a) = 4.55063 x 10(-6)/degrees C, alpha(c) = 7.7543 x 10(-6)/degrees C, and beta = 16.85836 x 10(-6)/degrees C in static air and alpha(a) = 4.69429 x 10(-6)/degrees C, alpha(c) = 9.02850 x 10(-6)/degrees C, and beta = 18.69688 x 10(-6)/degrees C in vacuum while those for rutile are alpha(a) = 6.81243 x 10(-6)/degrees C, alpha(c) = 8.71644 x 10(-6)/degrees C, and beta = 22.22178 x 10(-6)/degrees C in static air and alpha(a) = 6.05834 x 10(-6)/degrees C, alpha(c) = 8.39280 x 10(-6)/degrees C, and beta = 20.52362 x 10(-6)/degrees C in vacuum, respectively.