A multicomponent equimolar proton-conducting quadruple hexagonal perovskite-related oxide system.

Since the high configurational entropy-driven structural stability of multicomponent oxide system was proposed Rost in 2015, many experiments and simulations have been done to develop new multicomponent oxides. Although many notable findings have shown unique physical and chemical properties, high configurational entropy oxide systems that have more than 3 distinct cation sites are yet to be developed. By utilizing atomic-scale direct imaging with scanning transmission electron microscopy and AC-impedance spectroscopy analysis, we demonstrated for the first time that a multicomponent equimolar proton-conducting quadruple hexagonal perovskite-related BaREAlZrO (RE = rare earth elements) oxide system can be synthesized even when adding eight different rare earth elements. In particular, as the number of added elements was increased, , as the configurational entropy was increased, we confirmed that the chemical stability toward CO was improved without a significant decrement of the proton conductivity. The findings in this work broaden the use of the crystal structure to which the multicomponent model can be applied, and a systematic study on the correlation between the configurational entropy and proton conductivity and/or chemical stability is noteworthy.