Nanocrystalline multicomponent entropy stabilised transition metal oxides

Multicomponent entropy stabilised oxides containing four and five metal elements in equiatomic amounts were successfully synthesised in nanocrystalline form by nebulised spray pyrolysis (NSP), flame spray pyrolysis (FSP) and reverse co-precipitation (RCP) techniques, demonstrating that entropy stabilisation of these recently discovered materials is independent of the synthesis method. Both 4- and 5-cationic systems, (Co,Mg,Ni,Zn)O and (Co,Cu,Mg,Ni,Zn)O, can be stabilised into a single rocksalt structure directly only using NSP, while in FSP and RCP, stabilisation can be achieved after thermal treatment. This result indicates, that in 5-cationic NSP system configurational entropy is high enough to directly stabilise single rocksalt phase at lower temperature, while higher synthesis temperature is required to compensate the lower configurational entropy in 4-cationic system. Retention of single-phase at room temperature indicates sluggish diffusion kinetics, making entropy stabilised phases quenchable.