Metavalent Bonding in GeSe Leads to High Thermoelectric Performance

Abstract

Orthorhombic GeSe is ap romising thermoelectric material. However,l arge band gap and strong covalent bonding result in al ow thermoelectric figure of merit, zT % 0.2. Here,w ed emonstrate am aximum zT % 1.35 at 627 K in p-type polycrystalline rhombohedral (GeSe) 0.9 (AgBiTe 2 ) 0.1 , which is the highest value reported among GeSe based materials.T he rhombohedral phase is stable in ambient conditions for x = 0.8-0.29 in (GeSe) 1Àx (AgBiTe 2 ) x .T he structural transformation accompanies change from covalent bonding in orthorhombic GeSe to metavalent bonding in rhombohedral (GeSe) 1Àx (AgBiTe 2 ) x .(GeSe) 0.9 (AgBiTe 2 ) 0.1 has closely lying primary and secondary valence bands (within 0.25-0.30 eV), which results in high power factor 12.8 mWcm À1 K À2 at 627 K. It also exhibits intrinsically low lattice thermal conductivity (0.38 Wm À1 K À1 at 578 K). Theoretical phonon dispersion calculations reveal vicinity of aferroelectric instability,with large anomalous Born effective charges and high optical dielectric constant, which, in concurrence with high effective coordination number,l ow band gap and moderate electrical conductivity,corroborate metavalent bonding in (GeSe) 0.9 (AgBiTe 2 ) 0.1 .W econfirmed the presence of low energy phonon modes and local ferroelectric domains using heat capacity measurement (3-30 K) and switching spectroscopyinpiezoresponse force microscopy, respectively.

Crystal Structure Classification of Copper‐Based Sulfides as a Tool for the Design of Inorganic Functional Materials

“…Reported lattice contribution to the thermal conductivity at room temperature for af ew representative materials of each group. [45,65,72,77,78,80,88,98,[104][105][106][107][108][109] Angewandte Chemie Table 2), has adramatic impact on the transport properties of the materials.T he presence of unconventional T-Cu bonds, which dramatically enhance the power factor of these sulfides, clearly confirms that the chemical bonding perspective developed by Wuttig and co-workers, [115,116] Kanadzidis and co-workers, [117] and Biswas and co-workers [118] is av ery promising approach for designing superior thermoelectrics. Thec omplexes affect the transport properties through their remote action on the symmetry of the surrounding tetrahedra that belong to the conductive network.…”

Crystal Structure Classification of Copper‐Based Sulfides as a Tool for the Design of Inorganic Functional Materials

“…Reported lattice contribution to the thermal conductivity at room temperature for af ew representative materials of each group. [45,65,72,77,78,80,88,98,[104][105][106][107][108][109] Table 2), has adramatic impact on the transport properties of the materials.T he presence of unconventional T-Cu bonds, which dramatically enhance the power factor of these sulfides, clearly confirms that the chemical bonding perspective developed by Wuttig and co-workers, [115,116] Kanadzidis and co-workers, [117] and Biswas and co-workers [118] is av ery promising approach for designing superior thermoelectrics. Thec omplexes affect the transport properties through their remote action on the symmetry of the surrounding tetrahedra that belong to the conductive network.…”

Revisiting the Chemical Stability of Germanium Selenide (GeSe) and the Origin of its Photocatalytic Efficiency

“…On the other hand, the presence of Se vacancies drastically improves thermoelectric figure of merit zT from 0.2 to 1.35 (at 627 K), owing to metavalent bonding being unfeasible in pristine GeSe. [19] We demonstrate that the surface transformation of GeSe in germanium-oxide species in ambient conditions is favored by vacancy defects. Precisely, we show that as-exfoliated stoichiometric GeSe single crystal assumes a germanium-oxide skin once it is exposed to air, with a thickness that increases up to 1.5 ± 0.2 nm after prolonged storage (40 days) in ambient atmosphere.…”