Phase transformation and room temperature stabilization of various Bi₂O₃ nano-polymorphs

Ashish Gandhi^1*, Chi-Yuan Lai¹, Kuan-Ting Wu¹, P. V. R. K. Ramacharyulu¹, Valmiki B. Koli¹, Chia-Liang Cheng¹, Shyue-Chu Ke¹, Sheng Yun Wu¹

¹Department of Physics, National Dong Hwa University, Hualien, Taiwan

* Presenter:Ashish Gandhi, email:acg.gandhi@gmail.com

We report the structural evolution sequence from β-Bi₂O₃→γ-Bi₂O₃→α-Bi₂O₃ at the expense of metallic Bi nanoparticles (NPs) simply by annealing in the air. The RT stabilization of β-Bi₂O₃ NPs was attributed to the effect of reduced surface energy due to adsorbed carbon species. Whereas, oxygen vacancy defects may have played a significant role in the RT stabilization of γ-Bi₂O₃ NPs. All the annealed samples with different crystalline phases exhibited strong red-band emission peaking around 700 nm and covering around 60-85 % integrated intensity of photoluminescence spectra. Based on our experimental findings, the air annealing induced oxidation of Bi NPs and transformation mechanism within various Bi₂O₃ nano-polymorphs is presented. The outcome of this study suggests that oxygen vacancy defects at nanoscale play a significant role in both structural stabilization and phase transformation within various Bi₂O₃ nano-polymorphs, which is significant from theoretical consideration.

Keywords: β-Bi₂O₃, γ-Bi₂O₃, nano-polymorphs, carbon species, oxygen vacancies