Unveiling the Electronic Structure of Grain Boundaries in Anatase with Electron Microscopy and First-Principles Modeling.

James A. Quirk,Hiromichi Ohta,Gowoon Kim,Keith P. McKenna,Bin Miao,Bin Feng,Yuichi Ikuhara

doi:10.1021/acs.nanolett.1c03099

Abstract

Polycrystalline anatase titanium dioxide has drawn great interest, because of its potential applications in high-efficiency photovoltaics and photocatalysts. There has been speculation on the electronic properties of grain boundaries but little direct evidence, because grain boundaries in anatase are challenging to probe experimentally and to model. We present a combined experimental and theoretical study of anatase grain boundaries that have been fabricated by epitaxial growth on a bicrystalline substrate, allowing accurate atomic-scale models to be determined. The electronic structure in the vicinity of stoichiometric grain boundaries is relatively benign to device performance but segregation of oxygen vacancies introduces barriers to electron transport, because of the development of a space charge region. An intrinsically oxygen-deficient boundary exhibits charge trapping consistent with electron energy loss spectroscopy measurements. We discuss strategies for the synthesis of polycrystalline anatase in order to minimize the formation of such deleterious grain boundaries.

Highlights

Polycrystalline anatase titanium dioxide has drawn great interest, because of its potential applications in highefficiency photovoltaics and photocatalysts
While surfaces play a significant part in technological applications, polycrystalline materials unavoidably contain large numbers of grain boundaries (GBs), which are expected to play a decisive role in determining their electronic properties
Given the challenges associated with performing experiments to directly address GB properties in anatase, one can turn to computational modeling to provide insight and predictions at the atomic scale

Summary

Introduction

Polycrystalline anatase titanium dioxide has drawn great interest, because of its potential applications in highefficiency photovoltaics and photocatalysts. We observe Σ5[331̅]{103} GBs, which we propose are present due to the intersection of Σ3{112} twin boundaries, which form in the anatase grains (see Figure S1 in the Supporting Information).

Results

Conclusion