Doping of ceria surfaces with lanthanum: a DFT + U study

Area of Science:

• Materials Science
• Surface Science
• Computational Chemistry

Background:

• Ceria (cerium oxide) is a crucial material in catalysis and solid oxide fuel cells.
• Understanding defect formation in doped ceria is essential for optimizing its properties.
• Lanthanum doping is a common strategy to modify ceria's oxygen storage capacity.

Purpose of the Study:

• To investigate defect formation in La-doped ceria (111) and (110) surfaces.
• To elucidate the role of DFT+U calculations in describing these defects.
• To understand the unusual compensation mechanisms in La-doped ceria.

Main Methods:

• Density Functional Theory (DFT) calculations.
• DFT corrected for on-site Coulomb interactions (DFT+U) with specific U values for Ce 4f and O 2p states.
• Surface defect energy calculations for (111) and (110) ceria surfaces.

Main Results:

• DFT+U accurately describes the formation of an oxygen hole defect (La'(Ce) + O.(o)) when La substitutes a Ce(3+) site.
• The formation energy of oxygen vacancies is reduced by La doping but remains positive.
• Oxygen vacancy formation leads to Ce(3+) and a compensated oxygen hole, an unusual mechanism for this class of materials.

Conclusions:

• The DFT+U method is critical for understanding defect states in La-doped ceria.
• Cerium's facile reduction plays a key role in the observed unusual defect formation.
• Experimental validation of these computational findings is recommended.