Preparation and negative thermal expansion properties of Y2W3O12 thin films grown by pulsed laser deposition

Abstract

Y2W3O12 thin films have been grown on quartz substrates by pulsed laser deposition (PLD). The effects of oxygen pressure, substrate temperature and annealing temperature on the phase compositions and morphologies of the Y2W3O12 thin films were investigated using X-ray diffraction (XRD) and field emission scanning electron microscopy (FESEM). The negative thermal expansion coefficients of the Y2W3O12 ceramic target and thin film were investigated using high temperature X-ray diffraction (HTXRD) and thermal mechanical analyzer (TMA). The results indicate all the as-deposited Y2W3O12 thin films to show amorphous regardless of oxygen pressures from 5Pa to 20Pa and substrate temperatures from room temperature to 500°C. Y2W3O12 thin film grown at 500°C with an oxygen pressure of 10Pa displays the smoothest and most uniform surface morphology. Crystallized orthorhombic Y2W3O12 thin films were prepared by heating at 1000°C for 7min in air. The crystallized Y2W3O12 thin film is polycrystalline and shows a compact surface morphology. The mean grain size of Y2W3O12 thin film is about 0.2–1µm. Orthorhombic Y2W3O12 thin film exhibits an anisotropic negative thermal expansion. The thermal expansion coefficients of a-axis, b-axis c-axis and cell volumes are caculated to be −12.33×10−6K−1, −4.99×10−6K−1, −11.01×10−6K−1 and −28.22×10−6K−1 in the temperature range from 100 to 600°C, respectively. The average linear thermal expansion coefficient of the Y2W3O12 thin film is calculated to be −9.41×10−6K−1.