No abstract

Comprehension of chemical bonding and its intertwined relation with charge carriers and heat propagation through a crystal lattice is imperative to design compounds for thermoelectric energy conversion. Here, we report the synthesis of large single crystal of new p‐type cubic AgSnSbTe3 which shows innately ultra‐low lattice thermal conductivity (κlat) of 0.47–0.27 Wm‐1K‐1 and high electrical conductivity (1238 ‐ 800 S cm‐1) in the temperature range 294–723 K.  We investigated the origin of such low κlat by analysing the nature of the chemical bonding and its crystal structure. The interaction between Sn (5s)/Ag (4d) and Te (5p) orbitals were found to generate antibonding states just below the Fermi level in electronic band structure resulting in softening of the lattice in AgSnSbTe3. Further, the compound exhibits metavalent bonding which provides highly polarizable bonds with strong lattice anharmonicity, while maintaining the superior electrical conductivity. The electronic band structure exhibits nearly degenerate valence band maxima that help to achieve high Seebeck coefficient throughout the measured temperature range and as a result maximum thermoelectric figure of merit reaches to ~1.2 at 661 K in pristine single crystal of AgSnSbTe3.

Comprehension of chemical bonding and its intertwined relation with charge carriers and heat propagation through a crystal lattice is imperative to design compounds for thermoelectric energy conversion. Here, we report the synthesis of large single crystal of new p‐type cubic AgSnSbTe3 which shows innately ultra‐low lattice thermal conductivity (κlat) of 0.47–0.27 Wm‐1K‐1 and high electrical conductivity (1238 ‐ 800 S cm‐1) in the temperature range 294–723 K.  We investigated the origin of such low κlat by analysing the nature of the chemical bonding and its crystal structure. The interaction between Sn (5s)/Ag (4d) and Te (5p) orbitals were found to generate antibonding states just below the Fermi level in electronic band structure resulting in softening of the lattice in AgSnSbTe3. Further, the compound exhibits metavalent bonding which provides highly polarizable bonds with strong lattice anharmonicity, while maintaining the superior electrical conductivity. The electronic band structure exhibits nearly degenerate valence band maxima that help to achieve high Seebeck coefficient throughout the measured temperature range and as a result maximum thermoelectric figure of merit reaches to ~1.2 at 661 K in pristine single crystal of AgSnSbTe3.