STRUCTURAL INVESTIGATIONS ALONG THE JOIN CATIOSIO4-CASNOSIO4

High resolution synchrotron X-ray data were used to structurally chara cterize a series of compounds along the solid-solution titanite (HT-ph ase)-malayaite. The refinements reveal a high sensitivity of the cryst al symmetry on the amount of octahedral Sn present. This suggests a we ak interaction between dipoles formed through Ti out-of-centre distort ion. The structural evolution along the solid-solution also allows the identification of structural strain, which is caused by the geometric ally competing arrangement of corner sharing octahedral chains occupie d by Ti and Sn on one hand and edge sharing polyhedral chains occupied by Ca on the other hand. This strain is expressed in a systematic var iation of structural parameters, such as Ti-O-Ti angles, Ca displaceme nt parameters and Ca-O bond length distortion, as a function of octahe dral occupation.