Chemical bonding origin of the unexpected isotropic physical properties in thermoelectric Mg<sub>3</sub>Sb<sub>2</sub> and related materials.
basic_science · Level V
Where this comes from
- Record sourced from PubMed, PMID 30413702.
- Also identified by DOI 10.1038/s41467-018-06980-x and PMC identifier 6226478.
- Licence recorded as CC BY.
- The licence permits redistribution, so the abstract is shown in full and the full text is available from the publisher.
Abstract
The Mg<sub>3</sub>Sb<sub>2</sub> structure is currently being intensely scrutinized due to its outstanding thermoelectric properties. Usually, it is described as a layered Zintl phase with a clear distinction between covalent [Mg<sub>2</sub>Sb<sub>2</sub>]<sup>2-</sup> layers and ionic Mg<sup>2+</sup> layers. Based on the quantitative chemical bonding analysis, we unravel instead that Mg<sub>3</sub>Sb<sub>2</sub> exhibits a nearly isotropic three-dimensional bonding network with the interlayer and intralayer bonds being mostly ionic and surprisingly similar, which results in the nearly isotropic structural and thermal properties. The isotropic three-dimensional bonding network is found to be broadly applicable to many Mg-containing compounds with the CaAl<sub>2</sub>Si<sub>2</sub>-type structure. Intriguingly, a parameter based on the electron density can be used as an indicator measuring the anisotropy of lattice thermal conductivity in Mg<sub>3</sub>Sb<sub>2</sub>-related structures. This work extends our understanding of structure and properties based on chemical bonding analysis, and it will guide the search for and design of materials with tailored anisotropic properties.