Tailored phase transition temperature and negative thermal expansion of Sc-substituted Al2Mo3O12 synthesized by a co-precipitation method

Scandium-substituted Al2Mo3O12 ceramics corresponding to the general formula Al2-xScxMo3O12 (0 <= x <= 0.5) were fabricated by the co-precipitation reaction. Sc3+ is proved to successfully replace Al3+ and reduces the average grain size of the Al2-xScxMo3O12 ceramics from 6 mu m to 1 mu m. Sc3+ substitution induces a crystal structure change from monoclinic to orthorhombic symmetry. When the Sc3+ substitution content (x) is <0.4, Al2-xScxMo3O12 ceramics crystalize in a monoclinic structure and exhibit positive thermal expansion, while when x >= 0.4, the Al2-xScxMo3O12 ceramics crystalize in an orthorhombic structure and display negative thermal expansion (NTE), indicating that the phase transition temperature of Sc3+-substituted Al2Mo3O12 ceramics can be successfully reduced from 204.8 degrees C to room temperature with increasing substituted Sc3+ content. Orthorhombic Al1.6Sc0.4Mo3O12 shows stable NTE above room temperature. Its coefficient of thermal expansion is -2.02 x 10(-6) degrees C-1 from 25 degrees C to 500 degrees C. The theoretical calculation result also accords well with the above experimental data.