Phase transformation and room temperature stabilization of various Bi2O3 nano-polymorphs
Ashish Gandhi1*, 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,
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