Phonons and oxygen diffusion in Bi₂O₃and (Bi_0.7Y_0.3)₂O₃.

Area of Science:

• Materials Science
• Solid State Physics
• Computational Chemistry

Background:

• Bismuth oxide (Bi₂O₃) is a key material with potential applications in solid oxide fuel cells and sensors due to its ionic conductivity.
• Understanding the behavior of phonons and oxygen diffusion is crucial for optimizing its performance and exploring new applications.
• Yttrium doping is a common strategy to stabilize Bi₂O₃ phases and modify their properties.

Purpose of the Study:

• To investigate the phonon spectra and oxygen diffusion mechanisms in pure Bi₂O₃ and yttrium-doped (Bi_0.7Y_0.3)₂O₃.
• To elucidate the effect of temperature and yttrium doping on the vibrational properties and oxygen mobility.
• To identify the conditions and directions for efficient oxygen diffusion for technological applications.

Main Methods:

• Experimental measurement of phonon spectra in Bi₂O₃ up to 1083 K using inelastic neutron scattering.
• Ab initio calculations to determine atomic contributions to the phonon density of states in Bi₂O₃ and (Bi_0.7Y_0.3)₂O₃.
• Ab initio molecular dynamics simulations to analyze atomic correlations and predict oxygen diffusion behavior.

Main Results:

• Increasing temperature leads to a loss of sharp peak structure in the vibrational density of states for both materials.
• In δ-phase Bi₂O₃, Bi-Bi correlations remain ordered while O-O correlations exhibit liquid-like disorder at 1000 K.
• (Bi_0.7Y_0.3)₂O₃ shows broadened O-O correlations around 500 K, indicating possible oxygen conductivity at lower temperatures compared to undoped Bi₂O₃.

Conclusions:

• Yttrium doping significantly enhances oxygen diffusion kinetics in bismuth oxide at lower temperatures.
• Ab initio molecular dynamics predict macroscopic oxygen diffusion in (Bi_0.7Y_0.3)₂O₃ at temperatures suitable for technological applications.
• The study clarifies the preferred diffusion pathways in both δ-Bi₂O₃ and (Bi_0.7Y_0.3)₂O₃.