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Abstract:
The Magneli phase V6O11 was synthesized in gram amounts from a powder mixture of V6O11/V7O13 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 Magneli-type oxides is a combination of crystallographic shear and intrinsic disorder that leads to relatively low lattice thermal conductivities. SPS prepared V6O11 has a relatively low thermal conductivity of kappa = 2.72 +/- 0.06 W (m K)(-1) while being a n-type conductor with an electrical conductivity of sigma = 0.039 +/- 0.005 (mu V m)(-1), a Seebeck coefficient of alpha = -(35 +/- 2) mu V K-1, which leads to a power factor of PF = 4.9 +/- 0.8 X 10(-5)W (m K-2)(-1) at similar to 600 K. Advances in the application of Magneli phases are mostly hindered by synthetic and processing challenges, especially when metastable and nanostructured materials such as V6O11 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.
