Supercritical Synthesis of Phase-Pure GdxCe1-xO2-x/2 Nanoparticles (x ≤ 0.3) with a Random Defect Structure

Area of Science:

• Materials Science
• Nanotechnology
• Solid-State Chemistry

Background:

• Gadolinium-doped ceria (GDC) is crucial for catalysis and solid oxide fuel cells.
• Controlling nanoscale phase purity, dopant incorporation, and defect chemistry is critical for GDC performance.
• Existing synthesis methods require precise control over GDC properties.

Purpose of the Study:

• To identify synthesis conditions for producing GdxCe1-xO2-x/2 nanoparticles in a one-step process.
• To investigate the formation of homogeneous fluorite solid solutions under hydrothermal conditions.
• To understand the relationship between synthesis parameters, structure, and defect chemistry in GDC.

Main Methods:

• In situ and ex situ synchrotron powder X-ray diffraction (PXRD).
• Continuous-flow hydrothermal synthesis using cerium and gadolinium nitrates with urea.
• Rietveld refinement, pair distribution function analysis, and STEM-EDX mapping.

Main Results:

• Homogeneous GdxCe1-xO2-x/2 nanoparticles (0.0 ≤ x ≤ 0.3) synthesized via a one-step hydrothermal method.
• Supercritical conditions (400 °C) and basic pH are necessary for fluorite solid solution formation.
• Lattice expansion, increased microstrain, and reduced crystallite size observed with increasing Gd content.
• Statistically distributed Gd ions and oxygen vacancies, promoting oxygen mobility.

Conclusions:

• A continuous-flow hydrothermal method under supercritical conditions enables one-step synthesis of homogeneous GDC nanoparticles.
• Statistically distributed defects in GDC enhance oxygen mobility, contrasting with correlated defects in other oxygen conductors.
• The findings provide a pathway for optimizing GDC for energy applications like solid oxide fuel cells.