Spark Plasma Sintering (SPS)-Assisted Synthesis and Thermoelectric Characterization of Magnéli Phase VO.

The Magnéli phase VO was synthesized in gram amounts from a powder mixture of VO/VO and vanadium metal, using the spark plasma sintering (SPS) technique. Its structure was determined with synchrotron X-ray powder diffraction data from a phase-pure sample synthesized by conventional solid-state synthesis. A special feature of Magnéli-type oxides is a combination of crystallographic shear and intrinsic disorder that leads to relatively low lattice thermal conductivities. SPS prepared VO has a relatively low thermal conductivity of κ = 2.72 ± 0.06 W (m K) while being a n-type conductor with an electrical conductivity of σ = 0.039 ± 0.005 (μΩ m), a Seebeck coefficient of α = -(35 ± 2) μV K, which leads to a power factor of PF = 4.9 ± 0.8 × 10W (m K) at ∼600 K. Advances in the application of Magnéli phases are mostly hindered by synthetic and processing challenges, especially when metastable and nanostructured materials such as VO are involved. This study gives insight into the complications of SPS-assisted synthesis of complex oxide materials, provides new information about the thermal and electrical properties of vanadium oxides at high temperatures, and supports the concept of reducing the thermal conductivity of materials with structural building blocks such as crystallographic shear (CS) planes.