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

Negative thermal expansion (NTE) performance of Fe-2(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 degrees C. To stabilize the orthorhombic phase of Fe-2(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 Fe-2(MoO4)(3) is successfully reduced from 503.5 degrees C to 34.5 degrees 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 degrees 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 degrees C is broadened to 30-600 degrees C, and the corresponding coefficient of thermal expansion is -5.74 x 10(-6)degrees 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.