Anti-phase boundaries and phase transitions in titanite; an X-ray diffraction study

X-ray diffraction rocking curves of titanite, CaTiSiO 5 , were measured using a novel high-resolution diffractometer. Three Bragg reflections were recorded as a function of temperature and their profiles analyzed in terms of a Gaussian Bragg peak and a diffuse scattering component with an overall Lorentzian shape. The temperature dependence of the Gaussian intensities of the rocking peaks of superstructure reflections, hkl with k+l odd, scale with the long-range order parameter as I infinity Q 2 infinity [T-T c ] (super 2beta ) , where beta = 0.14(1) is the effective order parameter exponent. The diffuse scattering intensity changes little with temperature at T<T c -20 K. Strong diffuse scattering is found at T>T c with centers of their Lorentzian diffraction profiles shifted by Delta omega nearly equal 0.5 degrees with respect to the position of the equivalent Bragg peak. A second phase transition at 825 K is confirmed and the possibility of a third transition at approximately 1150 K is discussed