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Polar Transition-Metal Chalcogenide Structure and Properties of the New Pseudo-Hollandite Ba0.5Cr5Se8

Abstract : Single crystals of the new ternary selenide Ba0.5Cr5Se8 were synthesized using a self-flux method in fused silica tubes. This new phase was first considered to crystallize in the usual monoclinic symmetry for pseudo-hollandite compounds. However, single-crystal X-ray diffraction study showed unambiguously that Ba0.5Cr5Se8 crystallizes in the P1¯ triclinic space group with cell parameters a = 9.5084(4) Å, b = 7.1788(3) Å, and c = 8.9296(4) Å and α = 89.9979(16)°, β = 104.3958(22)°, γ = 100.8869(17)°, and Z = 2. Bulk samples were prepared by solid-state reaction and sintered using a spark-plasma sintering device. A combination of powder X-ray diffraction and transmission electron microscopy was used to perform structural analysis on spark plasma sintering prepared samples. Ba0.5Cr5Se8 orders antiferromagnetically with TN = 58 K and shows a semiconducting behavior with ρ300K = 0.35 Ω·cm and S300K = 230 μV·K-1. A maximum of the Seebeck coefficient of 315 μV·K-1 occurs at 635 K with ρ635K = 0.14 Ω·cm, while the thermal conductivity remains low and constant at about 0.8 W·m-1·K-1 from room temperature up to 873 K, leading to a maximum ZT of 0.12 around 800 K. A remarkably large increase of thermal conductivity is observed in the antiferromagnetic state. © 2015 American Chemical Society.
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R. Lefèvre, David Berthebaud, O. Perez, D. Pelloquin, S. Hébert, et al.. Polar Transition-Metal Chalcogenide Structure and Properties of the New Pseudo-Hollandite Ba0.5Cr5Se8. Chemistry of Materials, 2015, 27 (20), pp.7110-7118. ⟨10.1021/acs.chemmater.5b02933⟩. ⟨hal-02184167⟩



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