Sub-5 nm high-entropy nanoalloys beyond the hume-rothery limit

Lattice mismatch has long constrained alloy compositional design. Governed by the Hume-Rothery rules, severe atomic radius differences (δ) between the constituent elements of nano-alloys can lead to excessive lattice distortions or even phase separation. Therefore, synthesizing alloy nanoparticles with large δ-factors (>15%) is almost impossible, restricting structural and functional tunability. Here, we report a general plasma-assisted carbothermal flash sintering (PCFS) synthesis strategy to obtain sub-5 nm high-entropy alloys (HEAs) nanoparticles with δ-factors exceeding 15%. Plasma treatment helps compensate for the entropy reduction caused by high-δ, while non-equilibrium ultrafast synthesis prevents slow nucleation under thermodynamic steady-state conditions. Utilizing high-entropy to introduce medium-sized bridging elements, large atoms (lanthanides, >180 pm) and small atoms (Al) are successfully accommodated in a single-phase nanolattice with ordered lattice distortions. The resulting quasi-periodic lattice distortions (QPLD) formed via stress relief minimize structural defects and enable anomalous electronic and thermal transport properties. These nanoscale HEAs achieve an exceptional electromagnetic interference (EMI) shielding efficiency of ~99% at a thickness of only ~1.8 μm, which is two orders of magnitude thinner than conventional materials. This general strategy unlocks thousands of possible element combinations, providing a broad materials platform for advanced electronics, energy, and device applications.