A ZnFe 2 O 4 /γ-Fe 2 O 3 nanocomposite (theoretical specific capacity: 1002 mA h g −1 ) was successfully synthesized by laser pyrolysis, a very attractive nanosynthesis technique characterized by ...high versatility and flexibility. The obtained nanopowder was thoroughly characterized by XRD, XPS, Mössbauer spectroscopy and HRTEM, which confirmed the presence of two phases. A bimodal size distribution with small particles (tens of nanometers) and large ones (above 500 nm) was revealed by SEM and TEM. The ZnFe 2 O 4 /Fe 2 O 3 nanocomposite was tested as a negative electrode material for lithium-ion batteries, showing significantly improved lithium storage properties with a high reversible capacity and rate capability compared to a pure ZnFe 2 O 4 electrode. A capacity exceeding 1200 mA h g −1 is sustained after 100 cycles at 100 mA g −1 , with a gradual increase of the capacity during cycling. At 500 mA g −1 current rate, a reversible and stable capacity of 360 mA h g −1 is observed after 300 cycles. Electrochemical measurements with several electrolytes and electrode formulations were also conducted in order to explore the origin of the extra capacity and its increase with cycling.
The main goal of this paper is to investigate the interaction of atomic oxygen with graphite surfaces, using first principles total energy calculations. Oxygen coverage, position and crystallographic ...orientation of the surfaces are the main parameters of this study. At the basal surface, the binding energy is given by the contribution of the in-network interaction between oxygen atoms and between oxygen and graphite. Relaxation effects are non-negligible at low and medium coverages. Zig-zag surfaces are the most reactive ones, followed by armchair and basal ones. For both surfaces, the oxidative etching process that forms the CO and CO
2 gases is also discussed on the basis of our calculations.
A new crystalline ground state was discovered in the Au–Si system through first-principles electronic structure calculations. The new structure was found using the experimentally and theoretically ...determined local atomic structure in the liquid as a guide for the solid state. Local atomic structure in the liquid was matched with that for all known crystal structures as compiled in the Pauling File structural database. The best matching crystalline structures were then explicitly calculated using first-principles methods. Most candidate crystal structures were found to be close, but above the enthalpy of a composition weighted average of the face-centered cubic Au and diamond structure Si terminal phases, but one crystal structure was more stable than the terminal phases by about 10
meV
atom
–1 at
T
=
0
K. As first-principles simulations of local structure are feasible for most liquid alloys, the present methodology is applicable to other alloys lying near a eutectic composition.
We present a series of ab initio molecular dynamics simulations (MD) for liquid Ni, Zr and Ta to investigate the local structure and its evolution upon undercooling, and we analyze our results with ...respect to recent neutron scattering experiments. By means of the common-neighbor analysis, which gives a three-dimensional image of the inherent structures, we have found an evolution upon undercooling that depends on the system under consideration. The short-range order (SRO) of Ni is characterized by icosahedral and distorted icosahedral structures, and undercooling is accompanied by the occurrence of a complex polytetrahedral SRO that consists of more numerous Frank and Kasper polyhedra larger than the simple icosahedron. The same holds for Zr but we show that a strong competition exists with the bcc-like SRO which increases with the degree of undercooling. The SRO of Ta shows a complex polytetrahedral type order, very close to that of the A15 phase upon undercooling. The time evolution of the configurations is also examined in terms of the mean-square displacement.
Hollow nanoparticles made of a noble metal and a non-noble metal can be synthesized by a combination of galvanic replacement and the nanoscale Kirkendall effect. In these nanostructures, a metallic ...shell composed of individual nanocrystallites interconnected via grain boundaries surrounds a central cavity that is accessible to molecules through nanometre-sized pores. Moreover, because atomic vacancies enter the metal lattice during their formation, the surface of hollow metal nanoparticles is jagged both at the atomic and the nanometre scale. That gives them specific electrocatalytic properties, which are illustrated with reactions of increasing complexity (COads monolayer electrooxidation, oxygen reduction reaction, methanol and ethanol electrooxidation) and rationalized with Density Functional Theory calculations.
Following our previous studies on Pu
1
−x
M
x
(M
=
Al, Ga and In) compounds G. Robert, A. Pasturel, B. Siberchicot, Phys. Rev. B 68 (2003) 75109 we present
ab initio calculations on Pu
1
−x
M
x
(M
=
...Ge, Zn). The formation energies of the systems are calculated in the framework of GGA-ferromagnetic approximation. The densities of states are analyzed and a correlation between the five systems is considered in relationship with the stability of the δ phase solid solution.
We present a brief overview of recent
ab initio based developments to designing bulk thermodynamic properties and phase equilibria for alloys. We also discuss the potential links that exist between
...ab initio methodologies and the Calphad phenomenological approach, in order to build an efficient and predictive tool for the calculation of phase equilibria of complex, multi-component often found in industrial alloys.
Nous présentons une réflexion sur l'état de l'art des calculs des propriétés thermodynamiques des alliages et de leurs équilibres de phases à partir de méthodes issues de la mécanique quantique. Nous discutons aussi l'intégration de ces méthodes dans l'approche phénoménologique de type Calphad permettant ainsi d'aborder de manière prédictive l'étude de la stabilité de phases de systèmes multi-composants à applications industrielles.
PDF
