A high temperature diffraction study of synthetic titanite CaTiOSiO4

作者：Malcherek T^*; Domeneghetti CM; Tazzoli V; Salje EKH; Bismayer U

来源：Phase Transitions, 1999, 69(1): 119-131.

DOI：10.1080/01411599908208013

• titanite
• CaTiSiO5
• malayaite
• site disorder
• X-ray diffraction

The results of a high temperature single crystal X-ray diffraction study of synthetic titanite within the stability field of the A2/a (C2/c) paraphase (T > 500 K) are reported. The structure has been refined using a conventional model and one in which the Ca atom is disordered over two positions. A break in thermal expansion near T-c = 825 K correlates with an effective volume contraction of the Ti octahedron. When refined with split Ca position a reorientation of the Ca displacement vector at T-c is found, resulting in a more symmetrical structural arrangement of the disordered Ca cations with respect to the surrounding Ti cations. In the conventional model this reorientation is seen as a break in the thermal elongation of the shortest Ti-Ca distance. The observed temperature of the isosymmetrical structural instability is in agreement with previous observations based on Hard Mode IR and Raman spectroscopic measurements. A possible mechanism causing the observed structural changes and similarities to the thermal behaviour of the isostructural malayaite, CaSnSiO5, are discussed.

• 出版日期1999