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

Abstract

A series of NaxMgxSc2 − xW3O12 (0 ≤ x ≤ 0.75) ceramics has been prepared by the coprecipitation process. The phase composition, crystal structure, morphology, and thermal expansion behavior of NaxMgxSc2 − xW3O12 samples were investigated. The results show that (NaMg)3+ substitution causes a phase transition in NaxMgxSc2 − xW3O12. For 0 < x ≤ 0.25, both orthorhombic Sc2W3O12 and hexagonal NaxMgxSc2 − xW3O12 coexist in the sample. For 0.25 < x ≤ 0.75, (NaMg)3+ double cations successfully replace Sc3+, and single‐phase hexagonal NaxMgxSc2 − 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 NaxMgxSc2 − xW3O12 ceramics increased. The coefficients of thermal expansion (CTE) of negative thermal expansion (NTE) NaxMgxSc2 − 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 Na0.75Mg0.75Sc1.25W3O12 ceramics were improved from −10.36 × 10−6°C−1 to −13.64 × 10−6°C−1.