Improving room temperature negative thermal expansion performance of Fe2‐xScx(MoO4)3

Abstract

AbstractNegative thermal expansion (NTE) performance of Fe2(MoO4)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 Fe2(MoO4)3 at room temperature, a series of Fe2‐xScx(MoO4)3 (0≤x≤1.5) (abbreviated as F2‐xSxM) were fabricated via solid‐state reaction. Results indicate that the M‐O PTT of Fe2(MoO4)3 is successfully reduced from 503.5°C to 34.5°C by A‐site cation substitution of Sc3+. The regulation mechanism is considered to be the decrease in electronegativity of (Fe2‐xScx)6+ in F2‐xSxM. Both variable temperature X‐ray diffraction (XRD) and thermal mechanical analysis (TMA) analysis results indicate that F0.5S1.5 M exhibits anisotropic NTE in 100–700°C. The results indicate that it can effectively improve the densification of Sc‐substituted F0.5S1.5 M ceramics by two‐step calcination process. Furthermore, higher second‐step calcination temperature is beneficial for the formation of single‐phased orthorhombic F0.5S1.5 M. The NTE response temperature range of F0.5S1.5 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 F0.5S1.5 M potential for a wide range of applications in precision mechanical, electronic, optical, and communication instruments.