Factors determining the band gap of a nanocrystalline multicomponent equimolar transition metal based high entropy oxide (Co,Cu,Mg,Ni,Zn)O

Abstract

A recently developed transition metal based high entropy oxide (Co,Cu,Mg,Ni,Zn)O (TM-HEO) with phase-pure rocksalt structure has been shown to have potential for a wide range of applications. In this investigation, the optical band gap of the TM-HEO was studied to understand the influence of each cation by synthesising lower combination compounds by systematically eliminating Co, Cu and Zn. Compared to the other cations, Cu played a more significant role in determining the band gap. The obtained band gaps lay in the range of 1.47 to 3.38 eV, making some of the systems relevant for visible light harvesting. Further, to study the variation of the band gap with defect states and crystallite size, the TM-HEO was synthesised using three bottom-up processes. These studies revealed that the band gaps of the TM-HEOs depended on the variation of the covalent nature and oxidation states of the cations.