The crystal structure of rutile as a function of temperature up to 1600°C

The crystal structure of rutile (TiO₂) has been studied at high temperatures up to about 1600°C based on sets of single crystal X-ray diffraction intensities collected on a four-circle diffractometer. The thermal expansion coefficients for the a and c-axes in the measured temperature range were aa [formula omitted] and ac [formula omitted], respectively. The thermal response of the octahedra about Ti is such that the thermal coefficient for the four short equatorial Ti —O bonds was [formula omitted] and for the two long apical Ti —O bonds [formula omitted]. The rate of thermal expansion of the octahedral shared edge is relatively large under ~ 1200° C, while it becomes small above ~ 1200°C. An l to l₀ ratio, which we denote shrinkage index, however, decreases with the raise of temperature (l = the length of the shared edge at a temperature; l₀ = the edge length of a regular octahedron having the same volume as the Ti octahedron has at the same temperature).