Synthesis, negative thermal expansion and optical performances of In0.5Sc1.5Mo3O12 thin films via sol-gel spin coating

Abstract

Orthorhombic In0.5Sc1.5Mo3O12 thin films have been synthesized using the sol-gel spin coating. Influences of post-annealing temperatures on crystal structure, morphology, negative thermal expansion (NTE) and optical performances of the thin films were studied using XRD, SEM, XPS, high-temperature XRD and UV–Vis–NIR spectrophotometer. XRD and SEM results show that as-prepared thin film is in an amorphous state with a smooth and dense surface. Orthorhombic In0.5Sc1.5Mo3O12 thin films were obtained after post-annealing in 550–750 °C. The higher the annealing temperature in 550–750 °C, the better the crystallinity of orthorhombic In0.5Sc1.5Mo3O12 thin films. In addition, the grain size of the In0.5Sc1.5Mo3O12 thin film also grows as the annealing temperature increases. The resulting orthorhombic In0.5Sc1.5Mo3O12 thin films exhibit anisotropic NTE. Its volumetric coefficient of thermal expansion (CTE) is −3.44 × 10−6 °C−1, while the CTEs in a-, b- and c-axis directions are −4.70 × 10−6 °C−1, 5.37 × 10−6 °C−1, and -4.10 × 10−6 °C−1 in 25–700 °C, respectively. In addition, the transmittance of orthorhombic In0.5Sc1.5Mo3O12 thin films post-annealed at 750 °C is around 87.75 %–95.03 %.