Improving room temperature negative thermal expansion performance of Fe 2‐x Sc x (MoO 4 ) 3

Abstract Negative thermal expansion (NTE) performance of Fe 2 (MoO 4 ) 3 is only found in a high‐temperature range due to its monoclinic‐to‐orthorhombic (M‐O) phase transformation temperature (PTT) at 503.5°C. To stabilize the orthorhombic phase of Fe 2 (MoO 4 ) 3 at room temperature, a series of Fe 2‐x Sc x (MoO 4 ) 3 (0≤x≤1.5) (abbreviated as F 2‐x S x M) were fabricated via solid‐state reaction. Results indicate that the M‐O PTT of Fe 2 (MoO 4 ) 3 is successfully reduced from 503.5°C to 34.5°C by A‐site cation substitution of Sc 3+ . The regulation mechanism is considered to be the decrease in electronegativity of (Fe 2‐x Sc x ) 6+ in F 2‐x S x M. Both variable temperature X‐ray diffraction (XRD) and thermal mechanical analysis (TMA) analysis results indicate that F 0.5 S 1.5 M exhibits anisotropic NTE in 100–700°C. The results indicate that it can effectively improve the densification of Sc‐substituted F 0.5 S 1.5 M ceramics by two‐step calcination process. Furthermore, higher second‐step calcination temperature is beneficial for the formation of single‐phased orthorhombic F 0.5 S 1.5 M. The NTE response temperature range of F 0.5 S 1.5 M ceramics second‐step sintered at 1000°C is broadened to 30–600°C, and the corresponding coefficient of thermal expansion is ‐5.74 × 10 −6 °C −1 . The ease in the proposed design and preparation method makes NTE F 0.5 S 1.5 M potential for a wide range of applications in precision mechanical, electronic, optical, and communication instruments.