Roles of cations, electronegativity difference, and anionic interlayer interactions in the metallic versus nonmetallic character of Zintl phases related to arsenic

High Carrier Mobility in a Layered Antiferromagnet Integrated with Silicon

Coupling various functional properties in one material is always a challenge, more so if the material should be nanostructured for practical applications. Magnetism and high carrier mobility are key components for spintronic applications but rather difficult to bundle together. Here, we establish EuAl₂Si₂ as a layered antiferromagnet supporting high carrier mobility. Its topotactic synthesis via a sacrificial two-dimensional template results in epitaxial nanoscale films on silicon. Their outstanding structural quality and atomically sharp interfaces are demonstrated by diffraction and microscopy techniques. EuAl₂Si₂ films exhibit extreme magnetoresistance and a carrier mobility of above 10,000 cm² V^-1 s^-1. The marriage of these properties and magnetism makes EuAl₂Si₂ a promising spintronic material. Importantly, the seamless integration of EuAl₂Si₂ with silicon technology is particularly appealing for applications.

Chemical bonding origin of the unexpected isotropic physical properties in thermoelectric Mg3Sb2 and related materials

The Mg₃Sb₂ 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 [Mg₂Sb₂]²⁻ layers and ionic Mg²⁺ layers. Based on the quantitative chemical bonding analysis, we unravel instead that Mg₃Sb₂ 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 CaAl₂Si₂-type structure. Intriguingly, a parameter based on the electron density can be used as an indicator measuring the anisotropy of lattice thermal conductivity in Mg₃Sb₂-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.

The outstanding thermoelectric Mg₃Sb₂ is currently being intensely scrutinized. Here, the authors reveal a nearly isotropic three-dimensional chemical bonding network as the origin of isotropic physical properties in Mg₃Sb₂, indicating the breakdown of the simple layered Zintl phase view.

Crystal chemistry and thermoelectric transport of layered AM2X2compounds

This review highlights the chemical diversity and transport properties of AM₂X₂Zintl compounds and strategies to achieve a high thermoelectric figure of merit.