Identification of distinctive structural and optoelectronic properties of Bi2O3 polymorphs controlled by tantalum addition

Diverse crystal phases of bismuth (Bi) oxides induced by the addition of different amounts of tantalum (Ta) were synthesized. Their optoelectronic and redox properties were quantitatively investigated using combined experimental and computational approaches. Synthesis conditions that transform alpha-Bi2O3 into beta-Bi2O3 and delta-Bi2O3 in terms of the Ta quantity, as well as synthesis temperatures, are identified and demonstrated. The phase transition behavior and crystal structures were characterized by in situ high temperature X-ray diffraction (XRD), thermogravimetry-differential thermal analysis (TG/DTA), X-ray absorption near edge structures (XANES), and extended X-ray absorption fine structures (EXAFS). Density functional theory calculations employing the HSE exchange-correlation functional with spin-orbit coupling were used to quantitatively simulate the optoelectronic properties and band structures of beta-Bi2O3 and delta-Bi2O3. Along with the absorption coefficient and density of states, effective masses and dielectric constants were elucidated. The characterization study confirmed the distortion of Ta-O bonds in the Ta-supplemented beta-Bi2O3 and the substitutional positions of the Bi and Ta atoms in the delta-Bi2O3 and Bi3TaO7 compounds. The reducibility of these oxides was strongly influenced by the crystal phase confirmed by temperature-programmed reduction (TPR) analysis. These findings can be used as a bismuth oxides' benchmark for optoelectronic applications as well as thermal catalysis as the redox active center or the support.

Automated summary

This study synthesized diverse crystal phases of bismuth oxides induced by the addition of tantalum and investigated their optoelectronic and redox properties using experimental and computational methods. The synthesis conditions, phase transition behavior, and crystal structures were determined and characterized. The study also provided insights into the reducibility and substitutional positions of the atoms in the oxides. These findings are significant for the optoelectronic and thermal catalytic applications of bismuth oxides.