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At least 1,027 records · Page 57
All sourcesNASA NTRSDOE OSTI
DOE OSTI2017

CaCoSO diluted magnetic antiferromagnet semiconductor as efficient thermoelectric materials

Highlights: • CaCoSO exhibit direct (Γ{sup v}- Γ{sup c}) gap of about 2.187 eV for spin-up (↑). • CaCoSO exhibit direct (K{sup v}-K{sup c}) gap of about 1.187 eV for spin-down(↓). • An indirect gap (Γ{sup v}-K{sup c}) of about 0.4 eV for the spin-polarized CaCoSO. • Small gap turn CaCoSO to be as promising candidate for thermoelectric materials. - Abstract: We have reported the thermoelectric properties of the recently synthesized CaCoSO single crystal by Salter et al. in 2016. It is quite interesting to mention that CaCoSO single crystals exhibit a direct energy gap (Γ{sup v}- Γ{sup c}) of about 2.187 eV for the spin-up (↑) channel, which turns out to be a (K{sup v}-K{sup c}) direct gap of about 1.187 eV for the spin-down (↓) channel, resulting in an indirect gap (Γ{sup v}-K{sup c}) of about 0.4 eV for the spin-polarized CaCoSO single crystal. Such a small gap makes CaCoSO a promising candidate for thermoelectric materials. Calculations reveal a remarkable finding that the CaCoSO single crystal exhibits high electrical conductivity, low thermal conductivity and a large Seebeck coefficient; therefore, based on these findings, the CaCoSO single crystal may be considered an efficient thermoelectric material. The electron clouds of CaO{sub 3}S{sub 4} and CoS{sub 3}O exhibit a planar shape with conjugated electron orbitals and exhibit a strong covalent Ca−O, Co−O bonding. This is another factor which makes CaCoSO a promising candidate for thermoelectric materials, since covalent bonding is more favorable for the transport of the carriers than ionic bonding. CaO{sub 3}S{sub 4} and CoS{sub 3}O are the main sources for the thermoelectric generator in CaCoSO. Therefore, based on the above findings, we can conclude that CaCoSO could be a promising thermoelectric material.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Scanning tunneling microscopy study of the antiferromagnetic topological insulator MnBi 2 Se 4

Topological insulators with intrinsic magnetic ordering such as MnBi 2 Se 4 have been predicted to host many exotic topological phenomena including dissipationless edge states and magnetoelectric effects. Here we use scanning tunneling microscopy to study the surface of MnBi 2 Se 4 epitaxial thin films. Large scale topographic images show steps between van der Waals layers and screw dislocations. While we find the Se-termination predominant on the surface, areas attributed to Bi-termination are found at the edges of small islands in as-grown films, or in larger areas upon removal of surface capping. Here, we compare these terminations through an analysis of step heights, atomic resolution images and tunneling spectroscopy. Tunneling spectra on the Se-termination reveals semiconducting behavior, with an apparent bandgap of >0.18eV that depends on the tip height. In contrast, tunneling spectra of the Bi-termination appears gapless, which could be an indication of dangling bond states on the surface. In both cases, a hexagonal 3.9Å lattice is observed that is consistent with the expected crystal structure.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗