Thermal Expansion Anisotropy of Oxides and Oxide Solid Solutions

The thermal expansion properties of the oxides stishovite (the rutile form of SiO 2 ), tetragonal vanadium dioxide, and zincite (ZnO) were measured. Solid solutions of rutile‐, corundum‐, and zincite‐structure oxides were prepared, and the thermal expansion properties were measured in an effort to find compositions with more isotropic thermal expansion coefficients. The changes in the observed lattice constants and the changes expected on the basis of the cation radii were compared for both pure oxides and the oxide solid solutions. The difference in these changes indicates the variations to be expected in the thermal expansion anisotropy. A composition range containing the thermally isotropic composition in the system A1 2 O 2 ,‐Cr 2 O 3 was determined, and the isotropic composition was estimated to be 75% Al 2 O 3 ‐25% Cr 2 O 3 .