Understanding Micro and Atomic Structures of Secondary Phases in Cu‐Doped SnTe. Issue 42 (18th September 2022)

• Record Type: Journal Article
• Authors: Kawami, Youichirou; Tran, Xuan Quy; Aso, Kohei; Yamamoto, Tomokazu; Wang, Yuan; Li, Meng; Yago, Anya; Matsumura, Syo; Nogita, Kazuhiro; Zou, Jin
• Is Part Of: Small. Volume 18:Issue 42(2022)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2022-09-18
• Subjects: Cs‐corrected scanning transmission electron microscopy -- lattice thermal conductivity -- secondary phase -- thermoelectricity; Nanotechnology -- Periodicals; Nanoparticles -- Periodicals; Microtechnology -- Periodicals; 620.5
• DOI: 10.1002/smll.202204225
• Languages: English
• ISSNs: 1613-6810

Abstract

Abstract: Highly efficient thermoelectric materials require, including point defects within the host matrix, secondary phases generating positive effects on lowering lattice thermal conductivity (κL ). Amongst effective dopants for a functional thermoelectric material, SnTe, Cu doping realizes the ultra‐low κL approaching the SnTe amorphous limit. Such effective κL reduction is first attributed to strong phonon scattering by substitutional Cu atoms at Sn sites and interstitial defects in the host SnTe. However, other crystallographic defects in secondary phases have been unfocused. Here, this work reports micro‐ to atomic‐scale characterization on secondary phases of Cu‐doped SnTe using advanced microscopes. It is found that Cu‐rich secondary phases begin precipitation ≈1.7 at% Cu ( x = 0.034 where Sn1− x Cu x Te). The Cu‐rich secondary phases encapsulate two distinct solids: Cu2 SnTe3 ( F 4 ¯ 3 m $F\bar{4}3m$ ) has semi‐coherent interfaces with SnTe ( F m 3 ¯ m $Fm\bar{3}{\rm{m}}$ ) such that they minimize lattice mismatch to favor the thermoelectric transport; the other resembles a stoichiometric Cu2 Te model, yet is so meta‐stable that it demonstrates not only various defects such as dislocation cores and ordered/disordered Cu vacancies, but also dynamic grain‐boundary migration with heating and a subsequent phase transition ≈350 °C. The atomic‐scale analysis on the Cu‐rich secondary phases offers viable strategies for reducing κL through Cu addition to SnTe. Abstract : Micro and atomic structures of Cu‐rich secondary phases in SnTe are investigated using advanced microscopes such as the Cs‐corrected scanning transmission electron microscope. This work provides direct evidence on semi‐coherent interfaces between SnTe ( F m 3 ¯ m $Fm\bar{3}{\rm{m}}$ ) and Cu2 SnTe3 ( F 4 ¯ 3 m $F\bar{4}3m$ ), and various structural defects in a layered Cu‐Te binary compound, which explains the ultralow lattice thermal conductivity of singly Cu‐doped SnTe.