Enhanced stability and tunable bandgap of Zn- and Cu-doped cobalt aluminate

Abstract

Pristine and metal-doped cobalt aluminate samples were well synthesized using the sol–gel auto-combustion method. The physical properties of the synthesized samples were investigated employing X-ray diffraction and Raman spectroscopy. To validate structure stability, the influence of lattice strain was carried out by comparing Debye–Scherrer’s and Williamson-Hall plot method. Furthermore, Rietveld analysis was performed for precise structural parameters. Four Raman active modes (T2g(2) + T2g(3) + Eg + A1g) were examined within the range of 400 to 900 cm−1, confirming the formation of spinel structure. Here, an anomaly of the quadruple splitting of A1g mode in pristine and Zn2+-doped cobalt aluminate was observed. The FTIR spectroscopy shows metallic bonds confirming the absence of other functional groups. In UV–Vis spectroscopy, doping of Cu2+ (0.72 A) and Zn2+ (0.74 A) with nearly comparable ionic radii as Co2+ (0.72 A), optical bandgap increases ranging from 3.1 to 4.29 eV. Further, Urbach’s energy was plotted for all samples. Results show that doping of Cu2+ and Zn2+ supports reducing local lattice distortion. These features improved stability and wide optical bandgap ensure a vital role in state-of-the-art applications.