Synthesis and negative thermal expansion performance of (NaMg)3+ codoped Sc2W3O12 ceramics

Abstract

A series of Na_xMg_xSc_2 − xW₃O₁₂ (0 ≤ x ≤ 0.75) ceramics has been prepared by the coprecipitation process. The phase composition, crystal structure, morphology, and thermal expansion behavior of Na_xMg_xSc_2 − xW₃O₁₂ samples were investigated. The results show that (NaMg)³⁺ substitution causes a phase transition in Na_xMg_xSc_2 − xW₃O₁₂. For 0 < x ≤ 0.25, both orthorhombic Sc₂W₃O₁₂ and hexagonal Na_xMg_xSc_2 − xW₃O₁₂ coexist in the sample. For 0.25 < x ≤ 0.75, (NaMg)³⁺ double cations successfully replace Sc³⁺, and single-phase hexagonal Na_xMg_xSc_2 − xW₃O₁₂ ceramics were prepared. For x = 1, the impurity MgWO₄ was detected. As the (NaMg)³⁺ codoping amount increases, the grain size grew up and the density of the Na_xMg_xSc_2 − xW₃O₁₂ ceramics increased. The coefficients of thermal expansion (CTE) of negative thermal expansion (NTE) Na_xMg_xSc_2 − xW₃O₁₂ (0 ≤ x ≤ 0.75) ceramics were improved from −6.02 × 10⁻⁶°C⁻¹ to −15.19 × 10⁻⁶°C⁻¹ in 30–700°C. Moreover, as the sintering temperature increased, the CTEs of Na_0.75Mg_0.75Sc_1.25W₃O₁₂ ceramics were improved from −10.36 × 10⁻⁶°C⁻¹ to −13.64 × 10⁻⁶°C⁻¹.