Microanalysis of a grain boundary's blocking effect in lanthanum silicate electrolyte for intermediate-temperature...

Area of Science:

• Solid-state chemistry
• Materials science
• Electrochemistry

Background:

• Lanthanum silicate electrolytes are crucial for solid oxide fuel cells.
• Understanding grain boundary effects is vital for optimizing ionic conductivity.
• Al-doping is employed to enhance the properties of lanthanum silicate.

Purpose of the Study:

• To investigate the blocking effect of grain boundaries in Al-doped lanthanum silicate.
• To elucidate the microstructural and chemical factors contributing to this blocking effect.
• To determine the dominant mechanism behind grain boundary impedance.

Main Methods:

• Synthesis of high-density Al-doped apatite-type lanthanum silicate.
• Characterization using impedance spectroscopy, scanning electron microscopy (SEM), X-ray diffraction (XRD), and transmission electron microscopy (TEM).
• Microstructural and chemical analysis of grain interiors (GI) and grain boundaries (GB).

Main Results:

• The grain boundary blocking effect was identified as an intrinsic property of the material.
• Microanalysis revealed chemical variations: grain boundary regions were La-rich and Si-poor compared to grain interiors.
• A strong space-charge effect at grain boundaries was observed, alongside degraded conductivity.

Conclusions:

• Chemical variations at grain boundaries significantly influence ionic conductivity.
• The space-charge effect at grain boundaries is the primary contributor to the observed blocking phenomenon.
• These findings are critical for designing improved lanthanum silicate electrolytes.