Phase Transition and Coefficients of Thermal Expansion in Al(2−x)In(x)W(3)O(12) (0.2 ≤ x ≤ 1)

Materials from theA(2)M(3)O(12) family are known for their extensive chemical versatility while preserving the polyhedral-corner-shared orthorhombic crystal system, as well as for their consequent unusual thermal expansion, varying from negative and near-zero to slightly positive. The rarest are near-zero thermal expansion materials, which are of paramount importance in thermal shock resistance applications. Ceramic materials with chemistry Al(2−x)In(x)W(3)O(12) (x = 0.2–1.0) were synthesized using a modified reverse-strike co-precipitation method and prepared into solid specimens using traditional ceramic sintering. The resulting materials were characterized by X-ray powder diffraction (ambient and in situ high temperatures), differential scanning calorimetry and dilatometry to delineate thermal expansion, phase transitions and crystal structures. It was found that the x = 0.2 composition had the lowest thermal expansion, 1.88 × 10(−6) K(−1), which was still higher than the end member Al(2)W(3)O(12) for the chemical series. Furthermore, the AlInW(3)O(12) was monoclinic phase at room temperature and transformed to the orthorhombic form at ca. 200 °C, in contrast with previous reports. Interestingly, the x = 0.2, x = 0.4 and x = 0.7 materials did not exhibit the expected orthorhombic-to-monoclinic phase transition as observed for the other compositions, and hence did not follow the expected Vegard-like relationship associated with the electronegativity rule. Overall, compositions within the Al(2−x)In(x)W(3)O(12) family should not be considered candidates for high thermal shock applications that would require near-zero thermal expansion properties.