Surfaces of VO₂ -Polymorphs: Structure, Stability and the Effect of Doping

Area of Science:

• Materials Science
• Surface Science
• Computational Chemistry

Background:

• Vanadium dioxide (VO₂) exhibits a metal-insulator phase transition, making it a material of significant interest.
• Limited research exists on the catalytic activity and surface properties of various VO₂ polymorphs.
• Understanding surface behavior is crucial for VO₂ applications.

Purpose of the Study:

• To theoretically investigate the surface properties of stable VO₂ polymorphs.
• To explore the impact of molybdenum (Mo) doping on VO₂ surface stability and structure.
• To analyze the electronic and structural changes induced by doping.

Main Methods:

• Density-functional theory (DFT) calculations were employed.
• A self-consistent hybrid functional was utilized for high accuracy.
• Structural, electronic, and energetic properties of VO₂ surfaces were predicted.

Main Results:

• The rutile (R) phase surfaces of VO₂ were found to be unstable, undergoing spontaneous transition to the monoclinic M₁ phase.
• Molybdenum doping (even at 6.25%) significantly stabilizes the rutile VO₂ surfaces.
• Both M₁ and R surfaces exhibit substantial relaxation upon doping, with metal-metal distances changing up to 0.4 Å; Mo segregates to the topmost layer.

Conclusions:

• The inherent instability of rutile VO₂ surfaces can be overcome by Mo doping.
• Molybdenum doping offers a route to stabilize the rutile phase for potential applications.
• Surface relaxation and Mo segregation are key phenomena influenced by doping.