Thermal expansion behaviors of yttrium tungstates in the WO3–Y2O3 system

Fully-dense, polycrystalline yttria (Y2O3) exhibits high infrared (IR) transmittance in the full mid range (3–5 µm) with low emittance, but lacks thermal-shock resistance for high-performance aerospace applications due to its low strength and high coefficient of thermal expansion (CTE). An attempt was made to develop a low CTE and high strength composite of Y2O3 by dispersing the phase, Y2W3O12, known to exhibit a high negative CTE. The sintered mixture of Y2O3 and Y2W3O12, however, does not form a stable, two-phase composite. The sintered mixture forms new Y2O3-rich phases, such as Y2WO6 and Y6WO12, depending on the relative amounts of Y2O3 and WO3. Investigation of the thermal-expansion behaviors of these yttrium tungstates revealed that they have high CTEs comparable to pure Y2O3. The goal of obtaining a near-zero CTE composite with Y2O3 as the matrix and a yttrium tungstate with a negative CTE as the dispersed phase cannot be realized in this system.