Ionic conductivity and local structural features in Ce_1-xSm_xO_2-x/2.

Area of Science:

• Materials Science
• Electrochemistry
• Solid State Chemistry

Background:

• Samarium-doped ceria (SDC) is a leading electrolyte material for solid oxide fuel cells (SOFCs).
• SDC exhibits excellent ionic conductivity in the intermediate temperature range.
• Understanding the relationship between structure and conductivity is crucial for optimizing SDC performance.

Purpose of the Study:

• To investigate the transport properties and local structural features of Ce1-xSmxO2-x/2 with varying samarium content (0.1 ≤ x ≤ 0.7).
• To elucidate the role of defect clusters in influencing ionic conductivity in SDC.
• To correlate structural changes with conductivity variations at elevated temperatures.

Main Methods:

• Coupled impedance spectroscopy and micro-Raman spectroscopy were employed.
• Measurements were conducted up to 1073 K.
• Analysis focused on Ce1-xSmxO2-x/2 compositions.

Main Results:

• Nanosized carbon-based defect clusters were identified as the cause of decreased ionic conductivity, even at low samarium concentrations (x = 0.2).
• These clusters hinder conductivity before reaching the percolation threshold.
• Increasing samarium content leads to rearrangement and enlargement of defect clusters, and at higher concentrations, both size and number of clusters increase.

Conclusions:

• The presence and behavior of defect clusters significantly impact the ionic conductivity of Sm-doped ceria.
• Structural rearrangements of defect clusters, rather than just their number, dictate conductivity changes.
• Optimizing SDC for SOFCs requires careful consideration of defect cluster formation and evolution with dopant concentration.