1,720,984 research outputs found
Combined Role of Biaxial Strain and Nonstoichiometry for the Electronic, Magnetic, and Redox Properties of Lithiated Metal-Oxide Films: The LiMn2O4 Case
No full textUnderstanding
the interplay between strain and nonstoichiometry
for the electronic, magnetic, and redox properties of LiMn2O4 films is essential for their development as Li-ion
battery (LIB) cathodes, photoelectrodes, and systems for sustainable
spintronics applications as well as for emerging applications that
combine these technologies. Here, density functional theory (DFT)
simulations suggest that compressive strain increases the reduction
drive of (111) LiMn2O4 films by inducing >1
eV upshift of the valence band edge. The DFT results indicate that,
regardless of the crystallographic orientation for the LiMn2O4 film, biaxial expansion increases the magnetic moments
of the Mn atoms. Conversely, biaxial compression reduces them. For
ferromagnetic films, these changes can be substantial and as large
as over 4 Bohr magnetons per unit cell over the simulated range of
strain (from −6 to +3%). The DFT simulations also uncover a
compensation mechanism whereby strain induces opposite changes in
the magnetic moment of the Mn and O atoms, leading to an overall constant
magnetic moment for the ferromagnetic films. The calculated strain-induced
changes in atomic magnetic moments reflect modifications in the local
electronic hybridization of both the Mn and O atoms, which in turn
suggests strain-tunable, local chemical, and electrochemical reactivity.
Several energy-favored (110) and (111) ferromagnetic surfaces turn
out to be half-metallic with minority-spin band gaps as large as 3.2
eV and compatible with spin-dependent electron-transport and possible
spin-dependent electrochemical and electrocatalytic properties. The
resilience of the ferromagnetic, half-metallic states to surface nonstoichiometry
and compositional changes invites exploration of the potential of
LiMn2O4 thin films for sustainable spintronic
applications beyond state-of-the-art, rare-earth metal-based, ferromagnetic
half-metallic oxides
(Sub)surface-Promoted Disproportionation and Absolute Band Alignment in High-Power LiMn2O4 Cathodes
Full text linkWe present an isotropic (Ueff) and anisotropic (U-J) Hubbard and van der Waals (vdW)-corrected density functional theory study of bulk and low-index surfaces of lithium manganese oxide LiMn2O4 (LMO), a promising cathode material for high-power Li-ion batteries. Use of anisotropic (U-J) corrections in the simulation of bulk LMO leads to improved agreement with available experimental data, whereas vdW corrections do not affect the results. Carefully converged relaxation of slab geometries indicates that when vdW corrections are included the spinel-reconstructed Li-terminated (111) surface is always energetically favored for both Ueff and (U-J) methods regardless of the LMO phase. In contrast, neglect of vdW corrections leads to the (001) surface in orthorhombic phase being favored when applying (U-J) corrections. Independent of the simulation protocol and crystalline phase, (111) truncation, reconstructed or not, promotes LMO disproportionation and appearance of Mn2+ cations without the need of any chemical or electrochemical surface treatment. Absolute band alignment of the considered surfaces reveals increased reductive propensity for the (111) terminations. Finally, our computational findings are discussed with respect to available data on the observed surface dependence of Mn disproportionation and electrochemical passivation of LMO substrates
The Role of Thermal Fluctuations and Vibrational Entropy: A Theoretical Insight into the δ‑to‑α Transition of FAPbI<sub>3</sub>
No full textFormamidinium
lead iodide as a typical organometal perovskite has
attracted considerable interest due to its suitable electronic structure.
However, the intrinsic mechanisms of its unwanted δ-to-α
phase transition remain elusive. By combined first-principles calculations,
lattice dynamics analysis, and molecular dynamics simulations, we
assign the α phase to the highly dynamic tetragonal phase, with
the high-symmetry cubic structure emerging as a dynamically unstable
maximum in the system’s potential energy landscape. Finite-temperature
Gibbs free energy calculations confirm that the δ-to-α
transition should be considered as a hexagonal-to-tetragonal transition
in contrast to the previous hexagonal-to-cubic assignment. More importantly,
phonon thermal property calculations indicate that the driving force
of the process is the vibrational entropy difference. These results
point out the dynamical nature of the α phase and the key role
of the vibrational entropy in perovskite-related phase transitions,
the harnessing of which is critical for the successful uptake of organometal
perovskites in commercial applications
Understanding the Cosolvation Effect of Dendrimers
No full textMolecules that are virtually insoluble in certain solvents may be uploaded to “hostile”
phases by dendrimers. Prime examples of this phenomenon are Eosin Y, EY, and Rose Bengal,
RB, that are not soluble in CH2Cl2 where they can, however, be solvated through the interaction
with a fourth generation dendrimer of polypropylene amine, POPAM-4D. The two dyes share
the same carbon framework and differ for the pattern of halogenation, and yet their cosolvation
varies over a factor of 4: six Eosin Y and ∼25 Rose Bengals are solvated by the macromolecule.
Leveraging on a previous report where molecular dynamics simulations of 12 EY@POPAM-4D
in CH2Cl2 showed a reduction to the experimental limit of 6, we now perform similar calculations
with an excess, i.e., 40, of RB@POPAM-4D. The simulations quantitatively reproduce the
cosolvation effect. They also provide a microscopic understanding of its origin and of motions-interactions of the macromolecule and both of its guests
Understanding the Cosolvation Effect of Dendrimers
No full textMolecules that are virtually insoluble in certain solvents may be uploaded to “hostile”
phases by dendrimers. Prime examples of this phenomenon are Eosin Y, EY, and Rose Bengal,
RB, that are not soluble in CH2Cl2 where they can, however, be solvated through the interaction
with a fourth generation dendrimer of polypropylene amine, POPAM-4D. The two dyes share
the same carbon framework and differ for the pattern of halogenation, and yet their cosolvation
varies over a factor of 4: six Eosin Y and ∼25 Rose Bengals are solvated by the macromolecule.
Leveraging on a previous report where molecular dynamics simulations of 12 EY@POPAM-4D
in CH2Cl2 showed a reduction to the experimental limit of 6, we now perform similar calculations
with an excess, i.e., 40, of RB@POPAM-4D. The simulations quantitatively reproduce the
cosolvation effect. They also provide a microscopic understanding of its origin and of motions-interactions of the macromolecule and both of its guests
Understanding the Cosolvation Effect of Dendrimers
No full textMolecules that are virtually insoluble in certain solvents may be uploaded to “hostile”
phases by dendrimers. Prime examples of this phenomenon are Eosin Y, EY, and Rose Bengal,
RB, that are not soluble in CH2Cl2 where they can, however, be solvated through the interaction
with a fourth generation dendrimer of polypropylene amine, POPAM-4D. The two dyes share
the same carbon framework and differ for the pattern of halogenation, and yet their cosolvation
varies over a factor of 4: six Eosin Y and ∼25 Rose Bengals are solvated by the macromolecule.
Leveraging on a previous report where molecular dynamics simulations of 12 EY@POPAM-4D
in CH2Cl2 showed a reduction to the experimental limit of 6, we now perform similar calculations
with an excess, i.e., 40, of RB@POPAM-4D. The simulations quantitatively reproduce the
cosolvation effect. They also provide a microscopic understanding of its origin and of motions-interactions of the macromolecule and both of its guests
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
The Role of Thermal Fluctuations and Vibrational Entropy: A Theoretical Insight into the to Transition of FAPbI3
No full textFormamidinium
lead iodide as a typical organometal perovskite has
attracted considerable interest due to its suitable electronic structure.
However, the intrinsic mechanisms of its unwanted δ-to-α
phase transition remain elusive. By combined first-principles calculations,
lattice dynamics analysis, and molecular dynamics simulations, we
assign the α phase to the highly dynamic tetragonal phase, with
the high-symmetry cubic structure emerging as a dynamically unstable
maximum in the system’s potential energy landscape. Finite-temperature
Gibbs free energy calculations confirm that the δ-to-α
transition should be considered as a hexagonal-to-tetragonal transition
in contrast to the previous hexagonal-to-cubic assignment. More importantly,
phonon thermal property calculations indicate that the driving force
of the process is the vibrational entropy difference. These results
point out the dynamical nature of the α phase and the key role
of the vibrational entropy in perovskite-related phase transitions,
the harnessing of which is critical for the successful uptake of organometal
perovskites in commercial applications
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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