Thermal Expansion of Rutile from 100 to 700 °K

The thermal expansion of a single crystal of rutile (TiO₂) was determined in directions parallel to its crystallographic axes. A unique macroscopic technique was used wherein a cube-shaped specimen was cut from the anisotropic crystal, each of its six faces polished flat and nearly parallel to the face opposite it, and the expansion measured along each of its three body axes with an Abbe-Pulfrich interferometer. The relationship between the expansion along the body axes of the specimen and that in the crystallographic directions was determined from a Laue x-ray pattern. The unusual behavior of the thermal expansion that was observed can be explained by assuming an acoustical and optical contribution where the corresponding Grüneisen constants are 2.80 and 0.75 respectively.