Thermal expansion and phase transition behavior of Al_2-xM _x(WO₄)₃ (M = Y, Ga and Se) ceramics

In order to obtain materials with a tailored thermal expansion, in particular zero-thermal-expansion between - 50-100°C, the possibility of preparation, thermal expansion behavior and phase transition of Al _2-xM_x (WO₄)₃ (M: Y, Ga and Sc) have been examined. Y was not substituted for the Al site in Al₂(WO ₄)₃. Al_2-xGa_x (WO₄) ₃ single phase could be prepared in x range as high as 0.4. The phase transition temperature involving abrupt expansion increased with an increase of Ga content, resulting in no phase transition for Al_1.6Ga _0.4 (WO₄)₃ between -50-100°C. However, zero-thermal expansion could not be obtained in Al_2-xGa _x(WO₄)₃ at the temperature range. Al _2-xSc_x(WO₄)₃ single phase was obtained for the whole x range. The temperature of the phase transition decreased with an increase of Sc content and the abrupt expansion due to the phase transition disappeared above - 50°C for the specimen with x larger than 0.3. The thermal expansion coefficient could be controlled with Sc content and zero-thermal-expansion was observed for the specimens with x around 0.1 and 1.5.