Atomic-Scale Visualization and Quantification of Configurational Entropy in Relation to Thermal Conductivity: A...

It remains a daunting task to quantify the configurational entropy of a material from atom-revolved electron microscopy images and correlate the results with the material's lattice thermal conductivity, which strides across statics, dynamics, and thermal transport of crystal lattice over orders of magnitudes in length and time. Here, a proof-of-principle study of atomic-scale visualization and quantification of configurational entropy in relation to thermal conductivity in single crystalline trigonal GeSb₂Te₄ (aka t-GeSb₂Te₄) with native atomic site disorder is reported. A concerted effort of large t-GeSb₂Te₄ single crystal growth, in-lab developed analysis procedure of atomic column intensity, the visualization and quantification of configurational entropy including corresponding modulation, and thermal transport measurements enable an entropic "bottom-up" perspective to the lattice thermal conductivity of t-GeSb₂Te₄. It is uncovered that the configurational entropy increases phonon scattering and reduces phonon mean free path as well as promotes anharmonicity, thereby giving rise to low lattice thermal conductivity and promising thermoelectric performance. The current study sheds lights on an atomic scale bottom-up configurational entropy design in diverse regimes of structural and functional materials research and applications.