Polar Transition-Metal Chalcogenide Structure and Properties of the New Pseudo-Hollandite Ba0.5Cr5Se8
Résumé
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.
Mots clés
Fused silica
Gamma rays
High resolution transmission electron microscopy
Semiconducting selenium compounds
Sintering
Solid state reactions
Spark plasma sintering
Thermal conductivity
Transition metals
Transmission electron microscopy
X ray diffraction
Antiferromagnetic state
Monoclinic symmetry
Powder X ray diffraction
Semiconducting behavior
Single-crystal X-ray diffraction studies
Structure and properties
Transition metal chalcogenides
Triclinic space group
Single crystals
Group theory
Chemical structure
Physical and chemical processes
Crystal structure