Novel meta-phase arising from large atomic size mismatch

Discovery and regulation of new phases of matter drive science and technology forward. Here, we report unique meta-phase Cu-2(S,Te), Ag-2(S,Te), and Mg-2(Si,Sn) over a wide composition range. In the formation of meta-phase, the large diffusion coefficient mismatch counterbalances the large atomic size and electronegativity mismatches, thereby escaping phase separation and creating stable single-phased exquisite atomic structures beyond the classic Hume-Rothery (H-R) rule. Featured by the highly tunable contrasting degree of order/disorder of the sublattice, the meta-phase showcases electron localization/delocalization in Cu-2(S,Te), a rare co-existence of mechanical plasticity and amorphous characteristics in Ag-2(S,Te), along with inherently low lattice thermal conductivity and high thermoelectric performance in all three compounds. We envisage that the concept of meta-phase will usher in more innovations in materials research and technical applications.

Automated summary

This study reports the discovery of unique metal phases, Cu-2(S,Te), Ag-2(S,Te), and Mg-2(Si,Sn), with a wide composition range. The formation of these metal phases defies the classic Hume-Rothery rule due to mismatched diffusion coefficients, atomic sizes, and electronegativities. The metal phases exhibit highly tunable sublattice order/disorder and possess interesting electronic and thermal properties, suggesting potential applications in materials research and technology.