Abstract:
A new class of compositionally complex oxides or polycation oxides called high entropy oxides (HEOs) or entropy stabilized oxides (ESOs) has generated considerable research interest over the past 5-6 years since the first report on transition metal based high entropy oxide (TM-HEO) appeared in 2015. In these systems, the high configurational entropy resulting from the presence of a multiple number of cations in equimolar proportions results in the stabilisation of a single phase despite the chemical complexity and has created new opportunities for novel materials design and discovery.

In this work, an attempt has been made to synthesize different compositions of nanocrystalline multicomponent spinel oxides (generally referred to as AxB3-xO4; A, B = Al, Fe, Mn, Cr, Mg, Zn, Co, Ni, etc.) containing at least 4 or more different elements in equiatomic amounts. These individual cations were selected on the basis of Pauling’s ionic radii rule for substitution in the tetrahedral and octahedral sites. Three bottom-up approaches, namely reverse co-precipitation, nebulised spray pyrolysis and flame spray pyrolysis were used to synthesise these oxides. The primary intention here was to identify the factors influencing structural stability as well as to investigate and characterise different functional properties, with emphasis on the potential of the phase-pure spinel oxides as electrode material for supercapacitor applications.