Combined experimental and DFT approach to BiNbO₄ polymorphs.

Area of Science:

• Materials Science
• Solid-State Chemistry
• Computational Materials Science

Background:

• Bismuth niobate (BiNbO4) exists in multiple polymorphs with distinct properties.
• Understanding these polymorphs is crucial for their application in various fields.
• Experimental synthesis requires robust theoretical validation.

Purpose of the Study:

• To perform a detailed ab initio study of experimentally synthesized α-BiNbO4 and β-BiNbO4 polymorphs.
• To validate experimental findings using density functional theory (DFT).
• To investigate the structural, electronic, and optical properties of BiNbO4 polymorphs.

Main Methods:

• Experimental synthesis via solid-state reaction.
• Characterization using X-ray diffraction (XRD), Rietveld refinement, scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), Fourier transform infrared spectroscopy (FTIR), and UV-Vis diffuse reflectance spectroscopy.
• Theoretical calculations using DFT with GGA-PBE, LDA, and HSE06 functionals, including phonon band structure and dielectric function simulations.

Main Results:

• Successful synthesis and characterization of orthorhombic α-BNO (Pnna) and triclinic β-BNO (P1̄).
• Phase purity confirmed by XRD, Rietveld refinement, and DFT-simulated Raman spectra.
• Experimental band gaps (3.08 eV for α-BNO, 3.36 eV for β-BNO) closely matched HSE06 DFT simulations.
• Structural stability, charge dynamics, and optical properties were theoretically analyzed.

Conclusions:

• Comprehensive theoretical analysis supports the experimental synthesis and characterization of α-BNO and β-BNO polymorphs.
• DFT calculations provide valuable insights into the fundamental properties of these materials.
• The study establishes a strong theoretical foundation for future research and applications of bismuth niobate.