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Significance Statement
This is the first report of reaching liquid thermal conductivity limit in solids through thermal evolution. The anomalous thermal evolution of β-Cu2Se structural and phonon transport are explained using computational and experimental analyses. Two distinct glass-like transitions are predicted from the first-principles calculations, and confirmed with in–situ electron energy loss spectroscopy. These structural heterogeneities (the large interstitial displacement of the Cu+ ions under a rigid Se framework at T ~ 800K and the thermal distortion of Se framework at T ~ 1000K) result in ultralow liquid-like phonon conductivity in solid. This first prototype for electron-crystal/phonon-liquid by experiment and theory is transformative with broad impact.
Figure Legend: Three-dimensional atomic trajectories of β-Cu2Se obtained from molecular dynamics simulation at T = 700 K for 5 ps. Blue lines and green spheres correspond to Cu and Se atoms.
Journal Reference
Acta Materialia 86 (2015) 247–253. Hyoungchul Kim1,2, Sedat Ballikaya3,4, Hang Chi3, Jae-Pyung Ahn5, Kiyong Ahn2, Ctirad Uher 3, Massoud Kaviany 1
[expand title=”Show Affiliations”]- Department of Mechanical Engineering, University of Michigan, Ann Arbor, MI 48109, USA.
- High-Temperature Energy Materials Research Center, Korea Institute of Science and Technology, Seoul 136-791, Republic of Korea.
- Department of Physics, University of Michigan, Ann Arbor, MI 48109, USA.
- Department of Physics, University of Istanbul, Vezneciler, Istanbul 34134, Turkey.
- Advanced Analysis Center, Korea Institute of Science and Technology, Seoul 136-791, Republic of Korea.
Abstract
We demonstrate a prototype thermal evolution path for liquid thermal conductivity in solids. Thermal evolution of b-Cu2Se shows large interstitial displacement of constituent atoms marked by glass-like transitions and an asymptotic liquid thermal transport. Using ab initio molecular dynamics (AIMD), we identify these transitions, and confirm them with in situ transmission electron microscopy and electron energy loss spectroscopy. The thermal disorder of the Cu+ ions forms homopolar Cu–Cu bonds under a rigid Se framework, and at yet higher temperatures the Se framework undergoes thermal distortion. The non-equilibrium AIMD prediction of lattice thermal conductivity shows significant suppression of the phonon transport, in agreement with experiments and molecular behavior. 2014 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
