ANTIPHASE BOUNDARIES AND PHASE-TRANSITIONS IN TITANITE - AN X-RAY-DIFFRACTION STUDY

X-ray diffraction rocking curves of titanite, CaTiSiO5, 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 Ga ussian intensities of the rocking peaks of superstructure reflections, hkl with k + l odd, scale with the long-range order parameter as I al pha Q(2) alpha \T - T-c\(2 beta), where beta = 0.14(1) is the effectiv e order parameter exponent. The diffuse scattering intensity changes l ittle with temperature at T < T-c - 20 K. Strong diffuse scattering is found at T > T-c with centers of their Lorentzian diffraction profile s shifted by Delta omega approximate to 0.5 degrees with respect to th e position of the equivalent Bragg peak. A second phase transition at 825 K is confirmed and the possibility of a third transition at simila r to 1150 K is discussed.