Abstract
Materials from theA2M3O12 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 Al2−xInxW3O12 (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 Al2W3O12 for the chemical series. Furthermore, the AlInW3O12 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 Al2−xInxW3O12 family should not be considered candidates for high thermal shock applications that would require near-zero thermal expansion properties.
Highlights
The ceramic phases of the general formula A2 M3 O12 and the related families, such as ABM3 O12, ABM2 XO12 and A2 MX2 O12, have potential for thermal shock resistance applications, since they can present near-zero thermal expansion over wide and technologically relevant temperature intervals, including room temperature (RT) [1]
It was very similar to what would be expected for the orthorhombic Pbcn space group, but presented additional features, namely two extra diffraction lines situated at 23.8◦ and 25.9◦ (2θ), while the most intense peak, close to 22.4◦ (2θ), was not divided into two separate diffraction lines as it was for orthorhombic system (Figure 1a–c)
The X-ray powder diffraction (XRPD) patterns at RT (Figure 1) suggested that AlInW3 O12 is monoclinic at RT and not orthorhombic, as previously proposed [13,14]
Summary
The ceramic phases of the general formula A2 M3 O12 and the related families, such as ABM3 O12 , ABM2 XO12 and A2 MX2 O12 , have potential for thermal shock resistance applications, since they can present near-zero thermal expansion over wide and technologically relevant temperature intervals, including room temperature (RT) [1]. Evans et al presented a brief report [11] of dilatometry measurements, showing near-zero to low-positive CTEs for this system in the range of 0.2 ≤ x ≤ 0.5, while Mary and Sleight [12], using the same technique, reported zero thermal expansion for the AlInW3 O12 phase within the temperature range between RT and 727 ◦ C. There are no comparative studies of intrinsic (XRPD) and extrinsic (dilatometry) CTE for the Al2−x Inx W3 O12 system, so it is not clear whether this system could be used to achieve near-zero CTE phases; the evaluation the of suitability of the Al2−x Inx W3 O12 (x = 0.2–1.0) system for near-zero thermal expansion materials was the main knowledge gap to be filled by the present study. XRPD, dilatometry, differential scanning calorimetry and thermogravimetric analysis over the composition range of 0.2 ≤ x ≤ 1, and with wide temperature intervals, ranging from cryogenic to high temperatures
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
