Electronic and Optical Characteristics of alfa and delta Bi₂O₃: A DFT Study

The objective of this study is to investigate the structural, electronic, and optical properties of alfa - Bi<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf>O<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf> and delta - Bi<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf>O<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf> for optical sensing applications. The computations used density functional theory through CASTEP, which utilized the GGA correlational function and ultrasoft pseudo potential PBE. The resulting structural parameters align with the available theoretical and experimental evidence. The band structure of the two polymorphs was determined, alfa - Bi<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf>O<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf> exhibiting an indirect band gap of 2.47 eV and delta - Bi<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf>O<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf> exhibiting a direct band gap of 1.91 eV, respectively, in agreement with experimental data and theoretical findings. The hybridization of O-2p and Bi-6s orbitals was shown by the TDOS calculations and the PDOS of the Bi and O atoms. Both undergo optical absorption in the ultraviolet and a short range of visible light regions. The refractive index of both materials is comparable; this significant result arouses interest in studying the effects on oxygen absorption caused by the crystalline structure of the delta phase. The results of the optical conductivity reflect its semiconductor character, thereby validating the calculations obtained.