Low-temperature fabrication of high-entropy rare earth hexaboride powders

Herein, we report a low-temperature method for synthesizing high-entropy rare earth hexaboride powders by reaction among rare earth oxides, B 4 C, and Al powders. Al was used as a reducing and decarburization agent in this process, which further reduced the Gibbs free energy change for the reaction of Re x O y with B 4 C to form REB 6 . By investigating the influence of reacting temperature and amount of Al added on preparation of LaB 6 , the optimum experimental conditions of this method were determined to be 1300 °C and 2 times the stoichiometric ratio of Al. Theoretical supports were proposed to verify the feasibility for formation of high-entropy borides. Then, multicomponent hexaborides La 0.5 Ce 0.5 B 6 , La 0.33 Ce 0.33 Nd 0.33 B 6 , and La 0.25 Ce 0.25 Nd 0.25 Sm 0.25 B 6 as well as high-entropy hexaboride La 0.2 Ce 0.2 Nd 0.2 Sm 0.2 Eu 0.2 B 6 powders were successfully prepared by doping with Ce, Nd, Sm, and Eu on LaB 6 . RE elements with different radius were uniformly distributed in the multicomponent boride powders without obvious segregation. More importantly, the lattice distortion and stress induced by the element substitution contribute to the reduction of the average powder particle size. Finally, the DTA-TG curves show that rare earth hexaborides have good oxidation resistances when the temperature is below about 1000 °C.