First-principles study of band gap engineering via oxygen vacancy doping in perovskiteABB′O3solid solutions

Abstract

Oxygen vacancies in perovskite oxide solid solutions are fundamentally interesting and technologically important. However, experimental characterization of the vacancy locations and their impact on electronic structure is challenging. We have carried out first-principles calculations on two Zr-modified solid solutions, Pb(Zn 1/3 Nb 2/3 )O3 and Pb(Mg 1/3 Nb 2/3 )O3, in which vacancies are present. We find that the vacancies are more likely to reside between low-valent cation-cation pairs than high-valent cation-cation pairs. Based on the analysis of our results, we formulate guidelines that can be used to predict the location of oxygen vacancies in perovskite solid solutions. Our results show that vacancies can have a significant impact on both the conduction and valence band energies, in some cases lowering the band gap by ≈0.5 eV. The effects of vacancies on the electronic band structure can be understood within the framework of crystal field theory.

Effects of sintering process on the structural, dielectric, and optical absorption properties of KNbO3‐based ceramics

“…However, no appropriated assignment was addressed. Here, a possible explanation for understanding the KBNNO spectra is O 2– vacancies on the octahedron NiO 6 . Not less important is with respect to the static distortion of the Ni host site, which appears to be larger in NiNb 2 O 6 than in KBNNO samples.…”

“…As observed, the ceramic color showed to be strongly dependent on the sintering temperature and dwell time. This suggests that both factors have a direct influence on the Ni–O bond lengths, O–Ni–O angles, site charge distribution, or even possible displacements of oxygen vacancies and/or atoms from NiO 6 octahedra . The remarkable change in the color is not only a result of small change in the energy‐level spacing, since the absorbance peaks practically do not vary in energy positions with the different process steps.…”

Integration of first-principles methods and crystallographic database searches for new ferroelectrics: Strategies and explorations

“…Examples of the former include Pb(Ti 1−x Ni x )O 3−x [15,16], Ba(Ti 1−x−y Ce x Pd y )O 3−y [17] and PZN-type relaxors [18]. Recently it has been shown [19] that values of epitaxial strain that make SrTiO 3 ferroelectric also significantly reduce its band gap from the bulk value of 3.2 eV, greatly increasing its value as a photocatalyst.…”

Infrared‐to‐ultraviolet light‐absorbing BaTiO3‐based ferroelectric photovoltaic materials

“…The majority of traditional ferroelectric oxide systems have band gaps >3 eV and only a small fraction of the solar spectrum contributes to photovoltaic energy conversion; BiFeO 3 is one notable exception with a band gap (2.7 eV) that lies within the visible spectrum . There have been several theoretical predictions of band gap reductions in oxide ferroelectrics through chemical substitution; experimental examples include LaCoO 3 ‐doped Bi 4 Ti 3 O 12 , cation‐ordered Bi(Fe,Co)O 3 , KBiFe 2 O 5 , PbTiO 3 ‐Bi(Ni 2/3+x Nb 1/3−x )O 3− δ , and Ba(Ni 0.5 Nb 0.5 )O 3− δ ‐doped KNbO 3 (KBNNO) . For the latter two systems, the reduction in the band gap was achieved by introducing lower valent Ni 2+ acceptors and associated oxygen vacancies, , that were predicted to create an additional electronic band within the band gap region …”