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

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 x 10(-6)degrees C-1 to -15.19 x 10(-6)degrees C-1 in 30-700 degrees C. Moreover, as the sintering temperature increased, the CTEs of Na0.75Mg0.75Sc1.25W3O12 ceramics were improved from -10.36 x 10(-6)degrees C-1 to -13.64 x 10(-6)degrees C-1.