Effects of (KMg)3+ co-doping and sintering temperature on the negative thermal expansion property of Sc2W3O12 ceramics

Abstract

(KMg)3+ co-doped Sc2W3O12 ceramics have been prepared via co-precipitation method. Effects of (KMg)3+ co-doping amount and sintering temperature on the phase constitution, microstructure, morphology, and negative thermal expansion (NTE) performance of KxMgxSc2-xW3O12 (0 ≤ x ≤ 1.25) ceramics were studied. Results indicate that: Sc3+ cations can be substituted by (KMg)3+ dual-cations and a composition-induced structural phase transition was observed in KxMgxSc2-xW3O12. For x ≤ 0.25, orthorhombic Sc2W3O12 gradually changed into hexagonal KxMgxSc2-xW3O12 and coexisted. Single phase KxMgxSc2-xW3O12 with hexagonal symmetry can be prepared for 0.25 < x ≤ 1. When x ≥ 1.25, (KMg)3+ substitution reaches its solid solution limit in Sc2W3O12, and impurity MgWO4 formed in the samples. As co-doping amount x increased, the NTE performance of the KxMgxSc2-xW3O12 (0 ≤ x ≤ 1) ceramics gradually enhanced. The coefficient of thermal expansion (CTE) of KxMgxSc2-xW3O12 (0 ≤ x ≤ 1) ceramics enhanced from −2.14 × 10−6 °C−1 to −19.68 × 10−6 °C−1 in 30–700 °C. With the increase of sintering temperature from 800 to 1100 °C, the grains grew up and the density of the K0.75Mg0.75Sc1.25W3O12 ceramics increased as well, and the NTE performance was also improved. The linear CTE of K0.75Mg0.75Sc1.25W3O12 ceramics enhances from −2.15 × 10−6 °C−1 to −14.70 × 10−6 °C−1 in 30–700 °C.