Enhanced negative thermal expansion property in (KMg)xSc2-x(WO4)3 ceramics synthesized by solid–state reaction

Abstract

Negative thermally expanded (NTE) (KMg)xSc2-x (WO4)3 (0 = x ≤ 1.5) ceramics have been prepared via solid-state reaction. X-ray diffraction (XRD) analysis reveals that (KMg)xSc2-x (WO4)3 undergoes a composition-induced phase transition as the (KMg)3+-substitution content increases. For x = 0.25, both hexagonal (KMg)xSc2-x (WO4)3 and orthorhombic Sc2(WO4)3 coexisted in the sample. For 0.25 < x ≤ 1, a single-phase, hexagonal (KMg)xSc2-x (WO4)3, was obtained. When x is further increased to 1.25, monoclinic MgWO4 impurity was detected in the sample. Meanwhile, as x increases, the grain size of (KMg)xSc2-x (WO4)3 ceramics grows up. Hexagonal (KMg)xSc2-x (WO4)3 ceramics show high densification and strong NTE property. Thermomechanical analysis indicates that the linear coefficients of thermal expansion (CTEs) of hexagonal (KMg)xSc2-x (WO4)3 ceramics decrease from −7.48 × 10−6 °C −1 to −14.06 × 10−6 °C −1 with the increase of x. High-temperature XRD analysis reveals that hexagonal (KMg)0.5Sc1.5(WO4)3 show an anisotropic NTE. The intrinsic linear CTEs are αa = αb = −6.74 × 10−6 °C −1, αc = 11.03 × 10−6 °C −1 and the volumetric CTE is αv = −2.52 × 10−6 °C −1.