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Ultralow lattice thermal conductivity of Li2AgSb due to strong quartic anharmonicity
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DOI：10.1103/PhysRevB.111.094312.png)
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Abstract
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We calculate the thermoelectric transport properties of the inverse Heusler compound Li2AgSb by first principles calculation, combining self-consistent phonon theory, compression sensing technique, and Boltzmann transport theory. Due to the influence of atomic mass differences, bonding characteristics, and atomic vibrations, the frequency range of the phonon spectrum of the material is expanded, forming multiple band gaps. These band gaps limit some three-phonon (3ph) scattering channels and enhance the four-phonon (4ph) scattering process, thereby significantly improving the anharmonicity of Li2AgSb. In addition, multiple band gaps also lead to scattering partitioning, and phonon recombination processes occur in the ultrahigh-frequency region. In order to accurately reveal the impact of third-order anharmonicity on material properties, we introduced a bubble diagram to correct phonon self-energy and found that it has a significant impact on thermal conductivity. Furthermore, by combining multiple scattering mechanisms and spin-orbit coupling (SOC), we calculated the electrical transport properties of a direct semiconductor material with multiple band gaps that exhibits a unique band structure, including a highly dispersed multivalley conduction band minimum value and a flat, highly degenerate valence band maximum, resulting in ultrahigh power factors. The result shows that at 900 K and considering SOC, n-type Li2AgSb can reach a maximum ZT value of 5.86 under consideration of the bubble diagram, while p-type Li2AgSb can reach a maximum ZT value of 4.96 under consideration of the bubble diagram, so the thermoelectric properties of n-type Li2AgSb are much better.
Keywords:
AB-INITIO
PERFORMANCE
EFFICIENCY
SEMICONDUCTORS
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