The synthesis and thermal expansion property of Al_(2-x)Y_xW_3O_(12)

Near zero and negative thermal expansion materials have a number of important potential applications including circuit boards, optical substrates, dental restorations and so on. In this article, Al2-xYxW3O12 powder was synthesized by co -precipitate method. The X-ray diffraction (XRD) analysis indicates that the compounds are orthorhombic structure, and the lattice constant increase with the x value due to the different atom radius between Al3+ and Y3 +. The high temperature X - ray diffraction analysis exhibits that the intrinsic linear expansion coefficients of Al1.5Y0.5W3O12 and Al0.7 Y1.3W3O12 are +0. 85 × 10-6/℃ (20 -900℃) , -2. 6 × 10-6/℃ (20 -800℃), respectively. The compacts were sintered at temperature from 900 to 1100℃ for 10h. Their average thermal expansion coefficients from room temperature to 840℃ and their thermal expansion curves during heating (r. t. - 840 ℃) and cooling (840 - 400℃) were measured by thermal mechanic analysis (TMA) compressing method. The results indicate that the thermal expansion coefficient of Al2-x YxW3O12 can be adjusted to the desired values such as near zero and negative by changing the composition. The thermal expansion curves show hysteresis loops due to micro - cracks resulting from structure anisotropy.