Post density functional theoretical studies of highly polar semiconductive Pb(Ti$_{1-x}$Ni$_{x}$)O$_{3-x}$ solid solutions: The effects of cation arrangement on band gap

TL;DR

This study employs advanced computational methods to analyze how cation arrangement influences the electronic properties and band gap of Ni-substituted PbTiO$_{3}$, revealing potential for solar energy applications.

Contribution

It demonstrates the importance of post-DFT methods for accurately predicting electronic structures in transition-metal oxides and explores the impact of cation ordering on band gap tuning.

Findings

LDA calculations are insufficient for Ni-PTO electronic structure prediction.

Cation arrangement significantly affects the band gap of Ni-PTO.

Ni-PTO exhibits a direct band gap suitable for solar energy devices.

Abstract

We use a combination of conventional density functional theory (DFT) and post-DFT methods, including the local density approximation plus Hubbard $U$ (LDA+$U$), PBE0, and self-consistent $GW$ to study the electronic properties of Ni-substituted PbTiO$_{3}$ (Ni-PTO) solid solutions. We find that LDA calculations yield unreasonable band structures, especially for Ni-PTO solid solutions that contain an uninterrupted NiO$_{2}$ layer. Accurate treatment of localized states in transition-metal oxides like Ni-PTO requires post-DFT methods. $B$-site Ni/Ti cation ordering is also investigated. The $B$-site cation arrangement alters the bonding between Ni and O, and therefore strongly affects the band gap ($E_{\rm g}$) of Ni-PTO. We predict that Ni-PTO solid solutions should have a direct band gap in the visible light energy range, with polarization similar to the parent PbTiO$_{3}$. This combination of properties make Ni-PTO solid solutions promising candidate materials for solar energy conversion devices.