Unraveling the role of Cu2+ induced Jahn-Teller distortion and electron occupation alternation in modulating electronic and optical properties of CuxFe1-xFe2O4

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In recent years, attractive Fe3O4 and transition metal-doped Fe3O4 magnetic ferrites have received increasing attention due to their wide range of applications in catalyst carriers. The doping of Cu in Fe3O4 can tune optical and electrical properties. Due to the arrangement of the valence electrons of the Cu atoms, the distortion of Jahn-Teller (J-T) is very easy to occur. It needs to be studied that the physical mechanism of J-T distortion and energy band gap variation with Cu concentration. In this study, the electronic structure and optical properties of the CuxFe1-xFe2O4 (x = 0–1) defect system have been calculated based on the density-functional theory using the hybrid functional method. Two distinct types of J-T distortion, compression distortion and elongation distortion, have been present in our calculations. Furthermore, projected density of states (PDOS) has verified that the electron arrangement of compressed Cu2+ is (t2g)6 (dx2−y2)2 (dz2)1, then the electron arrangement of elongated Cu2+ is (t2g)6 (dz2)2 (dx2−y2)1. The doped Cu lowers the position of conduction band minimum (CBM), so the energy gap decreases with increasing of Cu concentration (0 < x < 1). When x = 1, the FeOct2+ is completely replaced by CuOct2+ and the valence band maximum (VBM) levels are provided by the doped Cu atom, then the energy gap is maximum. The elongated Cu2+ results in the CBM localized around the doped Cu, and increase the absorption intensity of visible light. It shows that the doped Cu atom system in the visible region of the absorption intensity increases and the absorption of light range is more extensive. Our findings demonstrate that distinct J-T distortions induced by Cu can efficiently modulate the electronic and optical properties of CuxFe1-xFe2O4. Cu doping changes the light absorption and extinction coefficients of Fe3O4. This provides a theoretical basis for the application of CuxFe1-xFe2O4 in wave absorption. At x = 0.5, the absorption coefficient of Cu-doped Fe3O4 is increased by 1.8 times. Because of its magnetic properties, it is easy to separate the catalyst. The application in catalyst support engineering has far-reaching research significance. This study is groundbreaking as it provides a detailed explanation at the electronic level for the physical mechanism of Jahn-Teller distortion in Cu2+. It is useful to investigate defect-induced light absorption and energy band engineering at the microscopic level.