Direct Synthesis and Structural Regulation of High-entropy Oxide Nanoparticles via Gas-phase Non-equilibrium Condensation

Abstract

High-entropy oxides possess unique structures and physicochemical properties, offering significant application potential across multiple fields. However, their synthesis remains challenging, with one key issue being how to integrate multiple oxide components with different crystal structures into single-phase high-entropy oxide nanoparticles (HEO-NPs). This study developed an oxygen gas-assisted gas-phase non-equilibrium condensation synthesis strategy, successfully preparing hexanary TiVCrFeTaW HEO-NPs comprising five oxide components with different crystal structures. The result shows that the addition of oxygen gas ensures sufficient oxidation of the nanoparticles, effectively inhibiting the formation of core-shell heterostructures caused by incomplete oxidation. Non-equilibrium gas-phase condensation process enables the uniform mixing and formation of a single crystalline phase from the various oxide components with different original structures. The synthesized HEO-NPs have an average particle size of 6-8 nm. Furthermore, by adjusting the sputtering power and gas flow parameters, the structural transition of the high-entropy oxide from amorphous to crystalline states was successfully controlled. This reveals the governing principles of gas flow rate and sputtering power on the crystallinity of the high-entropy oxide: HEO-NPs' crystallinity significantly increases when the gas flow rate is reduced and the sputtering power is increased. This study provides important guidance for the controllable synthesis of high-entropy oxide nanoparticles