Synthesis and Optical-Electronic Characterization of Nickel Pyro-Vanadate A2NiV2O7 (A = Na, Ag) Semiconductors: Experimental, DFT, and Hybrid-DFT Approaches

Abstract

Semiconductors, with their exceptional properties, have diverse applications across fields such as photovoltaics, sensing, and catalysis. In the present study, nickel pyro-vanadate compounds of high purity and homogeneity, with the chemical formula A₂NiV₂O₇ (where A = Na, Ag), were synthesized under precisely controlled stoichiometric conditions. The primary focus is to investigate the optical and electronic properties of these compounds using a combination of experimental techniques and theoretical modeling. Initially, insights into the chemical structure and morphology of the synthesized semiconductor were obtained through powder x-ray diffraction (PXRD), Fourier-transform infrared spectroscopy (FTIR), and scanning electron microscopy (SEM). A₂NiV₂O₇ were found to be homogeneous, crystalline in nature, and isotypic with Κ₂CoV₂O₇, exhibiting alternating layers of NiV₂O₇ and Ag/Na. Moreover, absorption spectra obtained from UV–Vis diffuse reflectance spectroscopy (DRS) showed direct optical bandgaps of 1.83 eV for Na₂NiV₂O₇ and 1.92 eV for Ag₂NiV₂O₇, affirming their semiconductor properties. Further characterization was performed using density functional theory (DFT) and hybrid-DFT methods. These advanced techniques provide detailed understanding of the electronic structure and properties across different sodium–silver ratios. The computed electronic structures demonstrate the separation of the conduction band (CB) and valence band (VB) around the Fermi level, with bandgaps of 0.44 eV and 1.76 eV for Na₂NiV₂O₇, and 0.56 eV and 1.60 eV for Ag₂NiV₂O₇, as determined using the Perdew–Burke–Ernzerhof (PBE) and DFT+U methods, respectively. This comprehensive investigation offers valuable insights into the optical and electronic dynamics of nickel pyro-vanadate compounds, establishing a foundation for their potential applications in various fields, including optoelectronics, photocatalysis, and energy storage.

Graphical abstract