XBi 4 S 7 (X = Mn, Fe): New Cost‐Efficient Layered n ‐Type Thermoelectric Sulfides with Ultralow Thermal Conductivity
Résumé
A new class of cost‐efficient n‐type thermoelectric sulfides with a layered structure is reported, namely MnBi4S7 and FeBi4S7. Theoretical calculations combined with synchrotron X‐ray/neutron diffraction analyses reveal the origin of their electronic and thermal properties. The complex low‐symmetry monoclinic crystal structure generates an electronic band structure with a mixture of heavy and light bands near the conduction band edge, as well as vibrational properties favorable for high thermoelectric performance. The low thermal conductivity can be attributed to the complex layered crystal structure and to the existence of the lone pair of electrons in Bi3+. This feature combined with the relatively high power factor lead to a figure of merit as high as 0.21 (700 K) in undoped MnBi4S7, making this material a promising n‐type candidate for low‐ and intermediate‐temperature thermoelectric applications.
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