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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 an innately ultra‐low lattice thermal conductivity (κlat) of 0.47–0.27 Wm−1 K−1 and a high electrical conductivity (1238 – 800 S cm−1) in the temperature range 294–723 K. We investigated the origin of the low κlat by analysing the nature of the chemical bonding and its crystal structure. The interaction between Sn(5 s)/Ag(4d) and Te(5p) orbitals was found to generate antibonding states just below the Fermi level in the electronic band structure, resulting in a softening of the lattice in AgSnSbTe3. Furthermore, the compound exhibits metavalent bonding which provides highly polarizable bonds with a strong lattice anharmonicity while maintaining the superior electrical conductivity. The electronic band structure exhibits nearly degenerate valence‐band maxima that help to achieve a high Seebeck coefficient throughout the measured temperature range and, as a result, the maximum thermoelectric figure of merit reaches to ≈1.2 at 661 K in pristine single crystal of AgSnSbTe3. [ABSTRACT FROM AUTHOR]

Here, we present lattice dynamics associated with the local chemical bonding hierarchy in Zintl compound TlInTe2, which cause intriguing phonon excitations and strongly suppress the lattice thermal conductivity to an ultralow value (0.46–0.31 W m−1 K−1) in the 300–673 K. We established an intrinsic rattling nature in TlInTe2 by studying the local structure and phonon vibrations using synchrotron X‐ray pair distribution function (PDF) (100–503 K) and inelastic neutron scattering (INS) (5–450 K), respectively. We showed that while 1D chain of covalently bonded InTe2n-n transport heat with Debye type phonon excitation, ionically bonded Tl rattles with a frequency ca. 30 cm−1 inside distorted Thompson cage formed by InTe2n-n. This highly anharmonic Tl rattling causes strong phonon scattering and consequently phonon lifetime reduces to ultralow value of ca. 0.66(6) ps, resulting in ultralow thermal conductivity in TlInTe2. [ABSTRACT FROM AUTHOR]

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 an innately ultra‐low lattice thermal conductivity (κlat) of 0.47–0.27 Wm−1 K−1 and a high electrical conductivity (1238 – 800 S cm−1) in the temperature range 294–723 K. We investigated the origin of the low κlat by analysing the nature of the chemical bonding and its crystal structure. The interaction between Sn(5 s)/Ag(4d) and Te(5p) orbitals was found to generate antibonding states just below the Fermi level in the electronic band structure, resulting in a softening of the lattice in AgSnSbTe3. Furthermore, the compound exhibits metavalent bonding which provides highly polarizable bonds with a strong lattice anharmonicity while maintaining the superior electrical conductivity. The electronic band structure exhibits nearly degenerate valence‐band maxima that help to achieve a high Seebeck coefficient throughout the measured temperature range and, as a result, the maximum thermoelectric figure of merit reaches to ≈1.2 at 661 K in pristine single crystal of AgSnSbTe3. [ABSTRACT FROM AUTHOR]