Ultra-low lattice thermal conductivity in tungsten-based scheelite ceramics

BaWO4, Ce2/3 ?1/3WO4 and La2/3 ?1/3WO4 polycrystalline ceramics were synthesized by conventional solidstate reaction route. The effect of cation-deficiency on the crystallographic structure, microstructure and thermal properties of these scheelite-type compounds were investigated. X-ray diffraction was used to identify the single-phase scheelite structure of the studied ceramics. Scanning Electron Microscopy technique has revealed a homogenous and dense microstructure with a few micro-cracks. The thermal conductivity of BaWO4 scheelite decreases from 1.3 +/- 0.2 to 1.0 +/- 0.1 W m-1 K-1 in the range 373-673 K. The cation-deficient scheelites Ce2/3 ?1/3WO4 and La2/3 ?1/3WO4 ceramics display an ultra-low thermal conductivity of 0.3 +/- 0.04 W m-1 K-1 and 0.2 +/- 0.03 W m-1 K-1 at 673 K, respectively. These materials exhibit among the lowest known values of thermal conductivity in crystalline oxides, in this temperature range. Therefore, they appear as very attractive for thermal barrier coating and thermoelectric applications.(c) 2023 Elsevier B.V. All rights reserved.