Localized electronic vacancy level and its effect on the properties of doped manganites

Abstract

Oxygen vacancies are common to most metal oxides and usually play a crucial role in determining the properties of the host material. In this work, we perform ab initio calculations to study the influence of vacancies in doped manganites $$\text {La}_{(1-\text {x})} \text {Sr}_{\text {x}} \text {MnO}_{3}$$ La ( 1 - x ) Sr x MnO 3 , varying both the vacancy concentration and the chemical composition within the ferromagnetic-metallic range ($$0.2\,<\,\text {x}\,<\,0.5$$ 0.2 < x < 0.5 ). We find that oxygen vacancies give rise to a localized electronic level and analyse the effects that the possible occupation of this defect state can have on the physical properties of the host. In particular, we observe a substantial reduction of the exchange energy that favors spin-flipped configurations (local antiferromagnetism), which correlate with the weakening of the double-exchange interaction, the deterioration of the metallicity, and the degradation of ferromagnetism in reduced samples. In agreement with previous studies, vacancies give rise to a lattice expansion when the defect level is unoccupied. However, our calculations suggest that under low Sr concentrations the defect level can be populated, which conversely results in a local reduction of the lattice parameter. Although the exact energy position of this defect level is sensitive to the details of the electronic interactions, we argue that it is not far from the Fermi energy for optimally doped manganites ($$\text {x}\,\sim \,1/3$$ x ∼ 1 / 3 ), and thus its occupation could be tuned by controlling the number of available electrons, either with chemical doping or gating. Our results could have important implications for engineering the electronic properties of thin films in oxide compounds.

Bandgap Engineering in Novel Fluorite‐Type Rare Earth High‐Entropy Oxides (RE‐HEOs) with Computational and Experimental Validation for Photocatalytic Water Splitting Applications

“…These vacancies are created due to charge distortion among multiple cations, which consequently alters the positions of conduction and valence bands. [ 67,68 ]…”

“…These vacancies are created due to charge distortion among multiple cations, which consequently alters the positions of conduction and valence bands. [67,68] Furthermore, after acquiring the bandgap data, another essential criterion required to establish a material suitable for an application is the position of valence and conduction band with respect to the redox potential of acceptor (lower in energy) or donor species (higher in energy) in order to determine the chemical potential of photogenerated holes or electrons, respectively. Electronic structure of a material ideal to be used as a photocatalyst for water splitting should allow both reduction of protons at E NHE (H + /H 2 ) = 0.0 eV (marked as the valence band minimum: VBM) and oxidation of water at E NHE (O 2 /H 2 O) = 1.23 eV (marked as conduction band minimum: CBM), where NHE stands for normal hydrogen electrode.…”

Vacancy Promotion in Layered Double Hydroxide Electrocatalysts for Improved Oxygen Evolution Reaction Performance

“…The 5% Ce-doped LDH achieved ∼100% FE toward OER, while Co–Ni LDH achieved ∼87% FE. The higher FE in the 5% Ce-doped LDH could be attributed to V O defects, which help to increase the electron transferability between the catalyst surface and adsorbates due to the presence of localized extra electrons in the defect sites . Based on the results of the DEMS measurements, the 5% Ce-doped LDH was used for electrolyzer measurements.…”

“…The higher FE in the 5% Ce-doped LDH could be attributed to V O defects, which help to increase the electron transferability between the catalyst surface and adsorbates due to the presence of localized extra electrons in the defect sites. 33 Based on the results of the DEMS measurements, the 5% Cedoped LDH was used for electrolyzer measurements. A comparison with an Ir-based catalyst 34 shown in Figure 1f showcases that the LDH system exhibits excellent electrochemical performance comparable to those of precious metal- Materials Characterization.…”

Harnessing Solar Energy Towards Synergistic Photothermal Catalytic Oxidation of Volatile Organic Compounds

“…This improves charge utilization and accelerates the rate of surface reactions. [92,97] These oxygen defects can be formed vialow metallic doping, [98] nonmetallic doping, [99] low concentration acid treatment, [88] and annealing under inert gases such as H 2 , Ar, and N 2 . [100] Electron techniques such as electron paramagnetic resonance (EPR) spectrometry are valuable quantitative characterization tools employed to further reveal the promotional role of oxygen vacancies during photothermal catalysis.…”