Synthesis and negative thermal expansion performance of (NaMg) ³⁺ codoped Sc ₂ W ₃ O ₁₂ ceramics

Abstract A series of Na x Mg x Sc 2 − x W 3 O 12 (0 ≤ x ≤ 0.75) ceramics has been prepared by the coprecipitation process. The phase composition, crystal structure, morphology, and thermal expansion behavior of Na x Mg x Sc 2 − x W 3 O 12 samples were investigated. The results show that (NaMg) 3+ substitution causes a phase transition in Na x Mg x Sc 2 − x W 3 O 12 . For 0 < x ≤ 0.25, both orthorhombic Sc 2 W 3 O 12 and hexagonal Na x Mg x Sc 2 − x W 3 O 12 coexist in the sample. For 0.25 < x ≤ 0.75, (NaMg) 3+ double cations successfully replace Sc 3+ , and single‐phase hexagonal Na x Mg x Sc 2 − x W 3 O 12 ceramics were prepared. For x = 1, the impurity MgWO 4 was detected. As the (NaMg) 3+ codoping amount increases, the grain size grew up and the density of the Na x Mg x Sc 2 − x W 3 O 12 ceramics increased. The coefficients of thermal expansion (CTE) of negative thermal expansion (NTE) Na x Mg x Sc 2 − x W 3 O 12 (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 0.75 Mg 0.75 Sc 1.25 W 3 O 12 ceramics were improved from −10.36 × 10 −6 °C −1 to −13.64 × 10 −6 °C −1 .