CoSb3-based mark mid-temperature skutterudites have been a benchthermoelectric material under intensive experimental and theoretical studies for decades. Doping and filling, to the first order, alter the crystal latti...CoSb3-based mark mid-temperature skutterudites have been a benchthermoelectric material under intensive experimental and theoretical studies for decades. Doping and filling, to the first order, alter the crystal lattice constant of CoSb3 in the context of ＂chemical pressure.＂ In this work, we employed ab initio density functional theory in conjunction with semiclassical Boltzmann transport theory to investigate the mechanical properties and especially how hydrostatic loadings, i.e., ＂physical pressure,＂ impact the electronic band structure, Seebeck coefficient, and power factor of pristine CoSb3. It is found that hydrostatic pressure enlarges the band gap, suppresses the density of states （DOS） near the valence band edge, and fosters the band convergence between the valley bands and the conduction band minimum （CBM）. By contrast, hydrostatic tensile reduces the band gap, increases the DOS near the valence band edge, and diminishes the valley bands near the CBM. Therefore, applying hydrostatic pressure provides an alternative avenue for achieving band convergence to improve thermoelectric properties of N-type CoSb3, which is further supported by our carrier concentration studies. These results provide valuable insight into the further improvement of thermoelectric performance of CoSb3-based skutterudites via a synergy of physical and chemical pressures.展开更多
We present a first-principles theoretical study of electric field- and straincontrolled intrinsic half-metallic properties of zigzagged aluminium nitride （A1N） nanoribbons. We show that the half-metallic property of...We present a first-principles theoretical study of electric field- and straincontrolled intrinsic half-metallic properties of zigzagged aluminium nitride （A1N） nanoribbons. We show that the half-metallic property of AIN ribbons can undergo a transition into fully-metallic or semiconducting behavior with application of an electric field or uniaxial strain. An external transverse electric field induces a full charge screening that renders the material semiconducting. In contrast, as uniaxial strain varies from compressive to tensile, a spin-resolved selective self-doping increases the half-metallic character of the ribbons. The relevant strain-induced changes in electronic properties arise from band structure modifications at the Fermi level as a consequence of a spin-polarized charge transfer between p-orbitals of the N and A1 edge atoms in a spin-resolved self-doping process. This band structure tunability indicates the possibility of designing magnetic nanoribbons with tunable electronic structure by deriving edge states from elements with sufficiently different localization properties. Finite temperature molecular dynamics reveal a thermally stable half-metallic nanoribbon up to room temperature.展开更多
基金supported by the Office of Science of the US Department of Energy (Nos. DEAC05-00OR22750 and DE-AC02-05-CH11231)the support of National Science Foundation (No. DMR-1307740)
文摘CoSb3-based mark mid-temperature skutterudites have been a benchthermoelectric material under intensive experimental and theoretical studies for decades. Doping and filling, to the first order, alter the crystal lattice constant of CoSb3 in the context of ＂chemical pressure.＂ In this work, we employed ab initio density functional theory in conjunction with semiclassical Boltzmann transport theory to investigate the mechanical properties and especially how hydrostatic loadings, i.e., ＂physical pressure,＂ impact the electronic band structure, Seebeck coefficient, and power factor of pristine CoSb3. It is found that hydrostatic pressure enlarges the band gap, suppresses the density of states （DOS） near the valence band edge, and fosters the band convergence between the valley bands and the conduction band minimum （CBM）. By contrast, hydrostatic tensile reduces the band gap, increases the DOS near the valence band edge, and diminishes the valley bands near the CBM. Therefore, applying hydrostatic pressure provides an alternative avenue for achieving band convergence to improve thermoelectric properties of N-type CoSb3, which is further supported by our carrier concentration studies. These results provide valuable insight into the further improvement of thermoelectric performance of CoSb3-based skutterudites via a synergy of physical and chemical pressures.
文摘We present a first-principles theoretical study of electric field- and straincontrolled intrinsic half-metallic properties of zigzagged aluminium nitride （A1N） nanoribbons. We show that the half-metallic property of AIN ribbons can undergo a transition into fully-metallic or semiconducting behavior with application of an electric field or uniaxial strain. An external transverse electric field induces a full charge screening that renders the material semiconducting. In contrast, as uniaxial strain varies from compressive to tensile, a spin-resolved selective self-doping increases the half-metallic character of the ribbons. The relevant strain-induced changes in electronic properties arise from band structure modifications at the Fermi level as a consequence of a spin-polarized charge transfer between p-orbitals of the N and A1 edge atoms in a spin-resolved self-doping process. This band structure tunability indicates the possibility of designing magnetic nanoribbons with tunable electronic structure by deriving edge states from elements with sufficiently different localization properties. Finite temperature molecular dynamics reveal a thermally stable half-metallic nanoribbon up to room temperature.
