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Intrinsic defects in and electronic properties of <i>θ</i> -Al <sub/>13</sub> Fe <sub/>4</sub> : an <i>ab initio</i> DFT study
摘要： θ-Al13Fe4 exhibits a rich variety of crystal physics. It contains twenty crystallographically different atomic species with a diversity of chemical coordination. An understanding of its structural and physical properties is a prerequisite for controlling its formation and its use. Here we investigate systematically the intrinsic defects in θ-Al13Fe4 using a ?rst-principles density-functional theory method. The calculations reveal that among the various intrinsic defects it is energetically favourable for Fe substitution of Al but on just three of the ?fteen Al sites. This results in a new structural model, Al68Fe24(Al, Fe)4(Al, Fe)2(Al, Fe)4 (the Roman numerals represent the Al sites) which updates the thermodynamic model, currently in use, which is associated with the formation of vacancies on some of the Al sites. The calculations demonstrate that the addition of Fe induces magnetism which gives rise to clustering. The calculations provide the dependence of the lattice parameters on Fe concentration and explain the experimental data in the literature. The information obtained here provides insight into the formation and properties of θ-Al13Fe4 and its role in the solidi?cation of Al alloys, in determination of the microstructure and related mechanical properties of the products, and in catalysis for organic reactions.
关键词： magnetic properties,density-functional theory calculations,intrinsic defects,θ-Al13Fe4,phase stability
更新于2025-09-19 17:15:36
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Interaction between Bi Dopants and Intrinsic Defects in LiNbO <sub/>3</sub> from Local and Hybrid Density Functional Theory Calculations
摘要： The interactions between Bi dopants including Bi-substituting Li (BiLi) and Bi-substituting Nb (BiNb) and the intrinsic antisite defects (NbLi) and Li vacancies (VLi) in LiNbO3 are investigated using local and hybrid density functional theories. Three charge-compensated defect clusters, BiLi4+ + NbLi4+ + 8VLi-, BiLi4+ + 4VLi-, and BiLi0 + 4VLi- + BiNb4+, are modeled in this work to investigate the effects of the Bi concentration. The most stable cluster configurations, the Bi-doping stability in the clusters, and the electronic state interaction between Bi and intrinsic defects have been studied in detail. It is found that BiLi4+ has a stronger electron-capturing ability than NbLi4+ in Bi-doped congruent LiNbO3. The BiLi-doping-induced local lattice distortion and the electron-trapping behavior remain unchanged with increasing Bi-doping concentration. However, the position of the Bi defect states in the band gap is found to be shifted in congruent LiNbO3. This is mainly attributed to the large lattice relaxation induced by the large number of Li vacancies instead of the ionic level redistribution caused by the direct interaction between Bi and intrinsic defects.
关键词： LiNbO3,Bi dopants,lattice distortion,defect clusters,intrinsic defects,density functional theory,electron trapping
更新于2025-09-19 17:15:36
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Reference Module in Chemistry, Molecular Sciences and Chemical Engineering || Interface Potentials, Intrinsic Defects, and Passivation Mechanisms in Al 2 O 3 , HfO 2 , and TiO 2 Ultrathin Films
摘要： For the tailoring of interface properties in terms of providing active centers for surface reactions, surface passivation, or the adjustment of surface potentials, ultrathin metal oxide surface coatings are of importance. In this contribution we report about the applicability of Al2O3, HfO2, and TiO2 ultrathin films prepared by atomic layer deposition (ALD) regarding the aforementioned items. We have selected these metal oxides because of their wide field of applications. HfO2 is the main competitor for the replacement of SiO2 in microelectronic devices.1,2 Al2O3 ALD films are applied for passivation schemes in silicon-based3 and more recently perovskite solar cells.4 TiO2 is, for example, attractive for resistive switching devices5 and as active or passive layer in energy conversion applications such as solar cells6 or water splitting devices,7,8 to name a few. Here, the use of the ALD technique brings advantages such as: (i) precise thickness control to optimize the trade-off between light absorption (in a range of depletion layer) and charge separation (thinner thickness),7 (ii) high conformity to coat complex structures accompanied by increased light absorption,7 and (iii) capability to control the band-gap narrowing by doping with W7 or N9,10 and hence allow visible light absorption.
关键词： Al2O3,HfO2,TiO2,ultrathin films,interface potentials,intrinsic defects,passivation mechanisms,atomic layer deposition
更新于2025-09-04 15:30:14