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An Instant Change of Elastic Lattice Strain during Cu 2 Se Phase Transition: Origin of Abnormal Thermoelectric Properties
Author(s) -
Bai Hui,
Su Xianli,
Yang Dongwang,
Zhang Qingjie,
Tan Gangjian,
Uher Ctirad,
Tang Xinfeng,
Wu Jinsong
Publication year - 2021
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.202100431
Subject(s) - materials science , thermoelectric effect , condensed matter physics , thermoelectric materials , phase transition , seebeck coefficient , anisotropy , electrical resistivity and conductivity , thermal conductivity , conductor , phase (matter) , chemical physics , thermodynamics , composite material , chemistry , physics , engineering , organic chemistry , quantum mechanics , electrical engineering
The superionic conductor Cu 2 Se is a promising thermoelectric material due to its low thermal conductivity. An abnormal but clear change in the thermoelectric parameters has been observed during the phase transformation from the ordered and non‐cubic α‐Cu 2 Se to the disordered and cubic β‐Cu 2 Se. However, the microstructural origin of the abnormal change and its implications for thermoelectric applications remain largely unknown. Herein, by mimicking the real working conditions of thermoelectrics, the phase transition from α‐ to β‐Cu 2 Se induced by the rising temperature has been carefully investigated by in situ transmission electron microscopy. It is observed that an abrupt and anisotropic volume‐change in the Se‐sublattice occurs when the temperature is raised to the phase transition point. The abnormal change in the crystalline volume versus temperature, which is caused by the local migration of Cu‐ions, induces an instant and uncommon strain‐field, which reduces the carrier's mobility and increases the electrical resistance. Local migration of Cu‐ions is responsible for a quite low thermal conductivity. Such effects exist only at the instance of the phase transition. Observing the thermoelectric response of the structure during the phase transition may provide insights into the development of high performance thermoelectric materials, which fall beyond the traditional approaches.