Revealing significant changes in electronic energy configurations via cation atom positions in Co(Gaₓ,Al_1-x)₂O₄ spinel oxides

This study aims to elucidate the correlation between the partial spinel oxide phase ratio and the electronic energy configuration of Co(Gaₓ,Al_1-x)₂O₄ (x = 0.00, 0.25, 0.50, 0.75, and 1.00) spinel oxides. Nanoparticles of Co(Ga,Al)₂O₄ were synthesized through a chemical route, and the crystal structure parameters and electronic energy configurations were investigated concerning the positions of Al and Ga in the spinel oxide lattice. Rietveld refinements were conducted based on three different phase formations, including a normal spinel lattice and two separate partial inverse spinel phase formations. The lattice parameters for Co(Ga₀.₅,Al₀.₅)₂O₄ particles, assuming three crystal phases in Rietveld refinement, were calculated as 8.2181 ± 0.0001 Å (in normal spinel oxide phase), 8.22551 ± 0.0001 Å (in partial spinel oxide phase), and 8.1485 ± 0.0001 Å (in partial spinel oxide phase). The parameters were associated with the lattice micro strain of samples. Additionally, a significant change in electronic energy configurations was demonstrated by the trend in band gap values associated with Al replacement in the lattice and cation atom positions. The highest band gap, 3.48 ± 0.01 eV, was calculated for Co(Ga₀.₅,Al₀.₅)₂O₄ particles.