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Employing Interfaces with Metavalently Bonded Materials for Phonon Scattering and Control of the Thermal Conductivity in TAGS‐ x Thermoelectric Materials
Author(s) -
Rodenkirchen Cynthia,
Cagi Matteo,
Jakobs Stefan,
Cheng Yudong,
Keutgen Jens,
Yu Yuan,
Wuttig Matthias,
CojocaruMirédin Oana
Publication year - 2020
Publication title -
advanced functional materials
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 6.069
H-Index - 322
eISSN - 1616-3028
pISSN - 1616-301X
DOI - 10.1002/adfm.201910039
Subject(s) - thermoelectric effect , materials science , covalent bond , thermoelectric materials , thermal conductivity , seebeck coefficient , stoichiometry , phonon , matrix (chemical analysis) , scattering , chemical bond , chemical physics , crystallography , nanotechnology , condensed matter physics , thermodynamics , composite material , chemistry , optics , organic chemistry , physics
Abstract The thermoelectric compound (GeTe) x (AgSbTe 2 ) 1− x , in short (TAGS‐ x ), is investigated with a focus on two stoichiometries, i.e., TAGS‐50 and TAGS‐85. TAGS‐85 is currently one of the most studied thermoelectric materials with great potential for thermoelectric applications. Yet, surprisingly, the lowest thermal conductivity is measured for TAGS‐50, instead of TAGS‐85. To explain this unexpected observation, atom probe tomography (APT) measurements are conducted on both samples, revealing clusters of various compositions and sizes. The most important role is attributed to Ag 2 Te nanoprecipitates (NPs) found in TAGS‐50. In contrast to the Ag 2 Te NPs, the matrix reveals an unconventional bond breaking mechanism. More specifically, a high probability of multiple events (PME) of ≈60% is observed for the matrix by APT. Surprisingly, the PME value decreases abruptly to ≈20–30% for the Ag 2 Te NPs. These differences can be attributed to differences in chemical bonding. The precipitates' PME value is indicative of normal bonding, i.e., covalent bonding with normal optical modes, while materials with this unconventional bond breaking found in the matrix are characterized by metavalent bonding. This implies that the interface between the metavalently bonded matrix and covalently bonded Ag 2 Te NP is partly responsible for the reduced thermal conductivity in TAGS‐50.