Improving room temperature negative thermal expansion performance of Fe_2‐xSc_x(MoO₄)₃

Abstract

Negative 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.

Giant enhancement of anti-quenching upconversion luminescence in Sc2W3O12:Er3+/Yb3+ phosphors for temperature sensing

“…11,12 Isovalent (Al 3+ , Fe 3+ ) and heterovalent (Li + /Mg 2+ combination) ion doping methods have been used to optimize the NTE performance of A 2 M 3 O 12 materials and reduce hygroscopicity. 13–15 Moreover, the impurity doping is also extensively adopted to adjust the local symmetry and improve the photoluminescence performance of active ions. Tens of times upconversion luminescence enhancement was achieved by impurity doping.…”