Defect structure in δ-Bi₅PbY₂O_11.5

Area of Science:

• Solid-state chemistry
• Materials science
• Crystallography

Background:

• The δ-Bi2O3 type phases are known for their high oxide-ion conductivity.
• Understanding defect structures is crucial for optimizing ionic conductivity in solid electrolytes.
• δ-Bi5PbY2O11.5 serves as a model system with a higher vacancy concentration than unsubstituted δ-Bi2O3.

Purpose of the Study:

• To characterize the average and local defect structure of δ-Bi5PbY2O11.5.
• To investigate oxide-ion vacancy ordering and cation-cation interactions.
• To elucidate the relationship between defect structure and ionic transport.

Main Methods:

• Conventional Rietveld analysis of neutron diffraction data.
• Reverse Monte Carlo (RMC) analysis of total neutron scattering data.
• Ab initio molecular dynamics (MD) simulations.

Main Results:

• Oxide-ion vacancies exhibit a preference for association with Pb2+ cations.
• Evidence of Pb2+ cation clustering was observed.
• A non-random distribution of vacancy pair alignments with a preference for 〈100〉 ordering was identified.
• Thermal variation in vacancy ordering and a predominance of oxide-ion jumps in the 〈100〉 direction were indicated by MD simulations.

Conclusions:

• The defect structure of δ-Bi5PbY2O11.5 is characterized by preferential association of oxide-ion vacancies with Pb2+ cations and 〈100〉 ordering.
• These findings provide insights into the mechanisms governing ionic conductivity in substituted δ-Bi2O3 phases.
• The developed methodology allows for the study of vacancy ordering and cation interactions in complex oxide systems.