Rapid synthesis of W₁₈O₄₉via reactive spark plasma sintering with controlled anisotropic thermoelectric properties

Single phase W₁₈O₄₉sintered polycrystalline samples were successfully synthesized via one-step rapid reactive spark plasma sintering directly from commercially purchased WO₃and WO₂powders. Thermoelectric properties of the samples sintered at 15 and 30 MPa showed insignificant anisotropy, while a strong anisotropy was observed for the sample sintered at 50 MPa. The in-situ reaction under a high applied pressure allowed a preferential grain growth along the direction perpendicular to the pressure axis. The high anisotropy of the sample sintered at 50 MPa yielded the lowest thermal conductivity of 4 Wm^-1K^-1, resulting in a ZT value of 0.08 at 1073 K. This study offers the rapid and cost-effective preparation method for W₁₈O₄₉materials, which can also be applied for other tungsten suboxide phases, with partially controlled anisotropic properties by the influence of applied pressure for thermoelectric performance enhancement.