Structural, morphological, spectroscopic, and electrochemical properties of Cr doped ZnAl₂O₄

The ZnAl_2-xCr_xO₄ (x = 0.0–0.1) ceramics were synthesized using microwave-hydrothermal method. The as synthesized powders were sintered at 1250 °C/4 h. All samples exhibit a cubic crystal structure and belong to Fd-3m space group. The lattice constant (a) increased from 8.085 Å (x = 0.0) to 8.128 Å (x = 0.04) and decreased for higher concentrations. The Fourier transform infrared spectra (FTIR) show tetrahedral and octahedral absorption bands in the region, 400 - 480 cm⁻¹ and 480 – 682 cm⁻¹, respectively. The X-ray photoelectron spectroscopy confirmed the valence states of Zn, Al, Cr, and O. The UV-vis spectra reveal a red shift with Cr³⁺ doping, reducing the bandgap energy (E_g) from 3.66 eV (x = 0.02) to 3.39 eV (x = 0.10). The electrochemical performance of the present samples was investigated using cyclic voltammetry (CV) and galvanostatic charge/discharge (GDC). The sample x = 0.10 exhibits high specific capacity of 143.671 F/g at a scan rate 5 mV/s. Therefore, the present samples may be useful for energy storage devices.