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Issue 2, 2013
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Lone pair electrons minimize lattice thermal conductivity

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As over 93% of the world's energy comes from thermal processes, new materials that maximize heat transfer or minimize heat waste are crucial to improving efficiency. Here we focus on fully dense electrical insulators at the low end of the spectrum of lattice thermal conductivity κL. We present an experimentally validated predictive tool that shows how the high deformability of lone-pair electron charge density can limit κL in crystalline materials. Using first-principles density-functional theory (DFT) calculations, we predict that several ABX2 (groups I–V–VI2) compounds based on the rocksalt structure develop soft phonon modes due to the strong hybridization and repulsion between the lone-pair electrons of the group V cations and the valence p orbitals of group VI anions. In many cases, this creates lattice instabilities and the compounds either do not exist or crystallize in a different structure. Marginally stable ABX2 compounds have anharmonic bonds that result in strong phonon–phonon interactions. We show experimentally how these can reduce κL to the amorphous limit.

Graphical abstract: Lone pair electrons minimize lattice thermal conductivity

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The article was received on 06 Sep 2012, accepted on 22 Nov 2012 and first published on 22 Nov 2012

Article type: Paper
DOI: 10.1039/C2EE23391F
Citation: Energy Environ. Sci., 2013,6, 570-578
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    Lone pair electrons minimize lattice thermal conductivity

    M. D. Nielsen, V. Ozolins and J. P. Heremans, Energy Environ. Sci., 2013, 6, 570
    DOI: 10.1039/C2EE23391F

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