Combined experimental and DFT approach to BiNbO4 polymorphs

Md Zarif Hossain; Sadiq Shahriyar Nishat; Shahran Ahmed; Quazi Shafayat Hossain; M N I Khan; Tarique Hasan; Muhammad Shahriar Bashar; A K M Sarwar Hossain Faysal; Ishtiaque M Syed; Khandker Saadat Hossain; Sakhawat Hussain; Md Mosaddek Khan; Imtiaz Ahmed

doi:10.1039/d2ra07910k

Combined experimental and DFT approach to BiNbO₄ polymorphs

RSC Adv. 2023 Feb 14;13(8):5576-5589. doi: 10.1039/d2ra07910k. eCollection 2023 Feb 6.

Authors

Affiliations

¹ Materials Science Research Laboratory, Department of Electrical and Electronic Engineering, University of Dhaka Dhaka-1000 Bangladesh imtiaz@du.ac.bd.
² Department of Materials Science and Engineering, Rensselaer Polytechnic Institute Troy NY USA.
³ Materials Science Division, Atomic Energy Centre Dhaka-1000 Bangladesh.
⁴ Department of Physics, University of Jyväskylä Jyväskylä 40500 Finland.
⁵ Institute of Fuel Research and Development, Bangladesh Council of Scientific and Industrial Research Dhaka-1205 Bangladesh.
⁶ Department of Physics, University of Dhaka Dhaka-1000 Bangladesh.
⁷ Semiconductor Technology Research Centre, University of Dhaka Dhaka-1000 Bangladesh.
⁸ Centre for Advanced Research in Sciences, University of Dhaka Dhaka-1000 Bangladesh.
⁹ Nanophysics and Soft Matter Laboratory, Department of Physics, University of Dhaka Dhaka-1000 Bangladesh.
¹⁰ Department of Computer Science and Engineering, University of Dhaka Dhaka-1000 Bangladesh.

Abstract

Here we present a detailed ab initio study of two experimentally synthesized bismuth niobate BiNbO₄ (BNO) polymorphs within the framework of density functional theory (DFT). We synthesized orthorhombic α-BNO and triclinic β-BNO using a solid-state reaction technique. The underlying Pnna and P1̄ crystal symmetries along with their respective phase purity have been confirmed from Rietveld refinement of the powdered X-ray diffraction measurements in combination with generalized gradient approximation of Perdew-Burke-Ernzerhof (GGA-PBE) based DFT simulations. The scanning electron micrographs revealed average grain sizes to be 500 nm and 1 μm for α-BNO and β-BNO respectively. The energy-dispersive X-ray spectroscopy identified the Bi, Nb, and O with proper stoichiometry. The phase purity of the as-synthesized samples was further confirmed by comparing the local density approximation (LDA) norm-conserving pseudo-potential based DFT-simulated Raman peaks with that of experimentally measured ones. The relevant bond vibrations detected in Fourier transform infrared spectroscopy were matched with GGA-PBE derived phonon density of states simulation for both polymorphs. The structural stability and the charge dynamics of the polymorphs were verified from elastic stress and born charge tensor simulations respectively. The dynamical stability of the α-BNO was confirmed from phonon band structure simulation using density functional perturbation theory with Heyd-Scuseria-Ernzerhof (HSE06) hybrid functional. The electronic band gaps of 3.08 and 3.36 eV for α-BNO and β-BNO measured from UV-Vis diffuse reflectance measurements were matched with the sophisticated HSE06 band structure simulation by adjusting the Hartree-Fock exchange parameter. Both GGA-PBE and HSE06 functional were used to simulate complex dielectric function and its derivatives with the help of Fermi's golden rule to define the optical properties in the linear regime. All these may have provided a rigorous theoretical analysis for the experimentally synthesized α-BNO and β-BNO polymorphs.