Wide band gap tunability in complex transition metal oxides by site-specific substitution

TL;DR

This study demonstrates that site-specific substitution in layered ferroelectric bismuth titanate with lanthanum cobaltite effectively narrows its band gap by up to one electron volt while maintaining ferroelectric properties, enabling tunable band gaps for oxide-based optoelectronic applications.

Contribution

It introduces a novel method of band gap tuning in complex transition metal oxides through site-specific substitution without losing ferroelectricity.

Findings

Band gap reduced by up to 1 eV.

Site-specific substitution creates a split-off state.

Ferroelectric properties are preserved.

Abstract

Fabricating complex transition metal oxides with a tuneable band gap without compromising their intriguing physical properties is a longstanding challenge. Here we examine the layered ferroelectric bismuth titanate and demonstrate that, by site-specific substitution with the Mott insulator lanthanum cobaltite, its band gap can be narrowed as much as one electron volt, while remaining strongly ferroelectric. We find that when a specific site in the host material is preferentially substituted, a split-off state responsible for the band gap reduction is created just below the conduction band of bismuth titanate. This provides a route for controlling the band gap in complex oxides for use in emerging oxide opto-electronic and energy applications.