Band gap narrowing in nitrogen-doped La2Ti2O7 predicted by density-functional theory calculations.

Area of Science:

• Materials Science
• Photocatalysis
• Computational Chemistry

Background:

• Lanthanum titanate (La2Ti2O7) exhibits photocatalytic properties.
• Enhancing photocatalytic activity, especially under visible light, is crucial for practical applications.
• Nitrogen doping is a common strategy to modify semiconductor band structures.

Purpose of the Study:

• To elucidate the origin of enhanced photocatalytic activity in N-doped La2Ti2O7.
• To understand the electronic structure modifications induced by nitrogen doping and oxygen vacancies.
• To correlate electronic structure changes with photocatalytic performance in both visible and UV light regions.

Main Methods:

• Spin-polarized conventional density functional theory (DFT) calculations.
• Heyd-Scuseria-Ernzerhof (HSE06) hybrid functional approach for electronic structure.
• Investigating the effects of nitrogen substitution for oxygen and interstitial Ti atoms.
• Analyzing the role of oxygen vacancies in conjunction with nitrogen doping.

Main Results:

• Nitrogen substitution for oxygen creates deep localized states within the band gap.
• Introducing interstitial Ti atoms also leads to localized energy states.
• A stable configuration of two nitrogen substitutions and one oxygen vacancy forms a continuum energy band above the valence band maximum.
• This continuum band extends light absorption into the visible light region.

Conclusions:

• The formation of a continuum energy band, rather than mid-gap states, is responsible for the enhanced visible light absorption.
• This electronic structure modification improves visible light photocatalysis without increasing charge recombination.
• The N-doped La2Ti2O7 maintains its ultraviolet light photocatalytic activity.
• The study provides a fundamental understanding of how doping strategies can optimize photocatalyst performance.