Scandium molybdate is the first obtained stable material with negative coefficient of thermal expansion (CTE). The structure of scandium molybdate may be represented as a three-dimensional carcass of joining ScO6 octahedra and MoO4 tetrahedra (Fig. 2.1). An anisotropic thermal expansion occurs as the result of a decrease in the sizes along two axes at the expense of rotation of polyhedral parts and an increase along the third axis. 1 Joining the polyhedral in the structure of orthorhombic scandium molybdate: (Left) The octahedra occupied with scandium are given. (Right) Tetrahedral occupied with molybdenum. https://s3-euw1-ap-pe-df-pch-content-public-u.s3.eu-west-1.amazonaws.com/9780429242878/d04804b0-234d-4a59-9414-5e56baafb6a5/content/fig2_1.tif"/>