Acceptor defects and impurities play a critical role in the performance of GaN‐based devices. Mg is the only acceptor impurity that gives rise to p‐type conductivity, while other acceptors (such as ...CN impurities and VGa defects) act as sources of compensation and trapping. From the point of view of theory, understanding the physics of acceptor species in GaN has long been a challenge. In the past, limitations of computational techniques made it difficult to quantitatively predict crucial quantities such as thermodynamic and optical transition levels. However, advances in first‐principles calculations, including the use of hybrid functionals in density functional theory, have led to a resurgence in efforts to understand properties of acceptors in nitrides. After briefly discussing advances in theoretical techniques, we review recent computational work on acceptor impurities in GaN and compare theoretical results with the available experimental data. We also present new hybrid density functional calculations on the transition levels of VGa and its complexes with O and H impurities. The results indicate that donor impurities significantly lower VGa transition levels, and that VGa3H and VGaON2H complexes give rise to yellow luminescence. We also discuss the properties of acceptor impurities in AlN and InN.
In this article recent advances in the understanding of acceptor species in the nitride semiconductors are reviewed. Achieving efficient p‐type doping in the nitrides is limited by the large ionization energies of these acceptors, and advanced theoretical calculations have shed light on the physical origin of this behavior. Also presented here are new results on gallium vacancies, which are thought to be the dominant acceptor point defects in GaN.
Enabling all‐solid‐state Li‐ion batteries requires solid electrolytes with high Li ionic conductivity and good electrochemical stability. Following recent experimental reports of Li3YCl6 and Li3YBr6 ...as promising new solid electrolytes, we used first principles computation to investigate the Li‐ion diffusion, electrochemical stability, and interface stability of chloride and bromide materials and elucidated the origin of their high ionic conductivities and good electrochemical stabilities. Chloride and bromide chemistries intrinsically exhibit low migration energy barriers, wide electrochemical windows, and are not constrained to previous design principles for sulfide and oxide Li‐ion conductors, allowing for much greater freedom in structure, chemistry, composition, and Li sublattice for developing fast Li‐ion conductors. Our study highlights chloride and bromide chemistries as a promising new research direction for solid electrolytes with high ionic conductivity and good stability.
Halide solid electrolytes: Lithium chloride and bromide materials exhibit low energy barriers for Li‐ion migration, wide electrochemical window, and good interface compatibility in all‐solid‐state Li‐ion battery, as illustrated by first principles computation study. These new classes of chemistries are suggested as promising new research direction of lithium solid electrolytes with both high ionic conductivity and good electrochemical stability for all‐solid‐state Li‐ion batteries.
The band structure, the density of states and optical absorption properties of Cu-doped ZnO were studied by the first-principles generalized gradient approximation plane-wave pseudopotential method ...based on density functional theory. For the Zn
Cu
O (
= 0,
= 0.0278,
= 0.0417) original structure, geometric optimization and energy calculations were performed and compared with experimental results. With increasing Cu concentration, the band gap of the Zn₁
Cu
O decreased due to the shift of the conduction band. Since the impurity level was introduced after Cu doping, the conduction band was moved downwards. Additionally, it was shown that the insertion of a Cu atom leads to a red shift of the optical absorption edge, which was consistent with the experimental results.
The United Nations Decade of Ecosystem Restoration is an opportunity for States to advance the development of substantive and qualitative international law obligations for conducting restoration ...activities. This will help countries move beyond the more quantitative target‐driven approach that currently focuses international commitments on the percentage of degraded areas that have to be restored. In this paper, we argue for two pathways for States to accelerate and pursue international obligations to undertake ecological restoration. Firstly, we advocate for the development of a new international legal principle on ecological restoration, adding to existing international environmental law principles such as the prevention principle, and aiming at achieving the highest level of recovery possible. Secondly, we advocate to utilize available mechanisms through the 1992 Convention on Biological Diversity and create a new protocol that will spell out a high ambition level for ecological restoration and a legal basis for adopting generally accepted rules and standards for restoration. The voluntary SER Principles and Standards can play an important role in the development of the legal principle on ecological restoration and standards of best practice.
Li2MnO3 is a critical component in the family of “Li‐excess” materials, which are attracting attention as advanced cathode materials for Li‐ion batteries. Here, first‐principle calculations are ...presented to investigate the electrochemical activity and structural stability of stoichiometric LixMnO3 (0 ≤ x ≤ 2) as a function of Li content. The Li2MnO3 structure is electrochemically activated above 4.5 V on delithiation and charge neutrality in the bulk of the material is mainly maintained by the oxidization of a portion of the oxygen ions from O2− to O1−. While oxygen vacancy formation is found to be thermodynamically favorable for x < 1, the activation barriers for O2− and O1− migration remain high throughout the Li composition range, impeding oxygen release from the bulk of the compound. Defect layered structures become thermodynamically favorable at lower Li content (x < 1), indicating a tendency towards the spinel‐like structure transformation. A critical phase transformation path for forming nuclei of spinel‐like domains within the matrix of the original layered structure is proposed. Formation of defect layered structures during the first charge is shown to manifest in a depression of the voltage profile on the first discharge, providing one possible explanation for the observed voltage fade of the Li‐excess materials.
The electrochemical activity, phase transformation, and oxygen stability of LixMnO3 (0 ≤ x ≤ 2) as a function of the Li content are investigated using ab initio calculations and statistical mechanics approaches. In particular, the mechanism of Mn migration from the Mn‐layer to the Li‐layer and the follow‐up process for the formation of spinel‐nucleus is intensively studied.
Qué resulta del encuentro entre la práctica del Estado de derecho y la práctica de los derechos humanos? Una noción lo expresa sintéticamente: la constitucionalización de la persona. Este artículo ...ahonda en su alcance, específicamente en la conformación de la totalidad de las actividades del Estado hacia el respeto y logro completo de los intereses fundamentales de todo ser humano. Lo hará mediante la inmersión en las características que definen a los derechos humanos: universalidad, indivisibilidad, interdependencia, inalienabilidad, progresividad, imprescriptibilidad, intangibilidad. Igualmente, en la identificación de las tendencias con las que actualmente se robustece la relación entre Estado de derecho y derechos humanos.
Extension principles for picture fuzzy sets Hasan, Mohammad Kamrul; Ali, Md. Yasin; Sultana, Abeda ...
Journal of intelligent & fuzzy systems,
01/2023, Volume:
44, Issue:
4
Journal Article
Peer reviewed
Picture fuzzy set (PFS), is a newly developed apparatus to treaty with uncertainties in problems where the opinions are yes, no, neutral, and refusal types. Extension principle is one of the key ...tools for describing uncertainties. It provides a general method for existing classical mathematical concepts to address fuzzy quantities. It has numerous applications in various arena of our real life. However, there are less works on extension principle for picture fuzzy sets. In this article, new extension principles namely minimal extension principle and average extension principle are proposed for picture fuzzy sets. Various properties of the minimal extension principle and the average extension principle for PFSs are also established. We also prove some properties of Zadeh’s extension principle for PFSs. Finally, arithmetic operations for PFSs based on the average extension principle are developed with numerical illustrations.
Selective nitrate‐to‐ammonia electrochemical conversion is an efficient pathway to solve the pollution of nitrate and an attractive strategy for low‐temperature ammonia synthesis. However, current ...studies for nitrate electroreduction (NO3RR) mainly focus on metal‐based catalysts, which remains challenging because of the poor understanding of the catalytic mechanism. Herein, taking single transition metal atom supported on graphitic carbon nitrides (g‐CN) as an example, the NO3RR feasibility of single‐atom catalysts (SACs) is first demonstrated by using density functional theory calculations. The results reveal that highly efficient NO3RR toward NH3 can be achieved on Ti/g‐CN and Zr/g‐CN with low limiting potentials of −0.39 and −0.41 V, respectively. Furthermore, the considerable energy barriers are observed during the formation of byproducts NO2, NO, N2O, and N2 on Ti/g‐CN and Zr/g‐CN, guaranteeing their high selectivity. This work provides a new route for the application of SACs and paves the way to the development of NO3RR.
Selective nitrate‐to‐ammonia electrochemical conversion is an advantageous strategy to solve the plight of both energy and environment. Taking single transition metal supported on graphitic carbon nitrides as an example, it is first demonstrated that the process of nitrate electroreduction can be efficiently achieved with low limiting potential on single‐atom catalysts by first‐principles calculations.
In this paper, we develop a direct method of moving planes for the fractional Laplacian. Instead of using the conventional extension method introduced by Caffarelli and Silvestre, we work directly on ...the non-local operator. Using the integral defining the fractional Laplacian, by an elementary approach, we first obtain the key ingredients needed in the method of moving planes either in a bounded domain or in the whole space, such as strong maximum principles for anti-symmetric functions, narrow region principles, and decay at infinity. Then, using simple examples, semi-linear equations involving the fractional Laplacian, we illustrate how this new method of moving planes can be employed to obtain symmetry and non-existence of positive solutions.
We firmly believe that the ideas and methods introduced here can be conveniently applied to study a variety of nonlocal problems with more general operators and more general nonlinearities.
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