Antoine Villesuzanne

LiMSO4F (M = Fe, Co and Ni): promising new positive electrode materials through the DFT microscope

A theoretical study of the lithium intercalated LiMSO(4)F and deintercalated MSO(4)F systems, where M = Fe, Co and Ni has been performed within the framework of density functional theory. Beyond predictions of structural evolution and average voltages versus a lithium electrode, we have applied partial density of states and Baders topological analysis of the electron density to the study of lithium deintercalation. Upon lithium extraction, charge rearrangement occurs for nickel between different d-orbitals, but with little net positive charge gain, while cobalt and iron atoms end up with a clear oxidized state. The participation of oxygen ions in accepting the electron of the lithium is thus enhanced for LiNiSO(4)F. However, this effect does not affect the long-range electrostatic interactions a lot in the lithiated phase, since the valence of all transition metals is very close due to initial lower oxidized state for the Ni atom in the host. It is found that this is not essentially a long-range electrostatic interaction within the lithiated phase but within the host which explains, at least partly, the increase in voltage by passing from Fe to Ni. Our results also shed light upon the possibility of getting an approximate evaluation of the local strain associated with delithiation from the atomic volume evolutions, which are also likely to affect the electrochemical potential.

Rapid Hydrothermal Synthesis of VO2 (B) and Its Conversion to Thermochromic VO2 (M1)

The present study provides a rapid way to obtain VO2 (B) under economical and environmentally friendly conditions. VO2 (B) is one of the well-known polymorphs of vanadium dioxide and is a promising cathode material for aqueous lithium ion batteries. VO2 (B) was successfully synthesized by rapid single-step hydrothermal process using V2O5 and citric acid as precursors. The present study shows that phase-pure VO2 (B) polytype can be easily obtained at 180 °C for 2 h and 220 °C for 1 h, that is, the lowest combination of temperature and duration reported so far. The obtained VO2 (B) is characterized by X-ray powder diffraction, high-resolution scanning electron microscopy, and Fourier transform infrared spectroscopy. In addition, we present an indirect way to obtain VO2 (M1) by annealing VO2 (B) under vacuum for 1 h.

Transport and magnetic properties of La2NiO4+δ (0 ≤ δ ≤ 0.25)

Materials with La{sub 2}NiO{sub 4+{delta}} composition, {delta} ranging between 0 and 0.25, have been prepared either by solid state reaction or electrochemical oxidation; their electrical conductivity, thermoelectric power, and magnetic susceptibility behaviors are reported. The compounds remain semiconducting in the whole range of composition and, at low temperature, the resistivity increases with {delta}. The sign of the Seebeck coefficient changes for {delta} {approx} 0.2 and the thermal variation shows complex behavior. La{sub 2}NiO{sub 4.03} exhibits a thermally activated hopping and an antiferromagnetic ordering. When {delta} increases, variable range hopping or nearest neighbor hopping, involving at least two types of carriers, can account for the transport properties. The magnetic behavior of materials with {delta} {le} 0.18 reveals either 3D or 2D magnetic correlations whereas the susceptibility of La{sub 2}NiO{sub 4.25} (La{sub 8}Ni{sub 4}O{sub 17}) follows a Curie-Weiss law below 170 K; a change in the electronic configuration of the nickel ions arises beyond this temperature.

Study of disorder in a tetragonal tungsten bronze ferroelectric relaxor: a structural approach

Electron diffraction analysis, nuclear magnetic resonance measurements, structure determinations and refinements were performed on two ferroelectric lead-containing ceramics (classical and relaxor), with tetragonal tungsten bronze structure, in order to investigate the origin of the relaxor behaviour in such compounds. In both compounds the lead atoms are found to be off-centred in the CN (coordination number) 15 (A2) site. The main difference between the two compositions is the proportion of lead in this site: in the relaxor composition, the A2 site is at least half occupied by lead atoms. Disorder in the repartition of lead and potassium atoms in the A1 (CN 12) and A2 sites was also studied via combinatorial calculations to correlate the evolution of the relaxor behaviour in the Pb5Ta10O30–Li10Ta10O30–K10Ta10O30 ternary system with composition. The combinatorial study demonstrated that the relaxor behaviour is enhanced by the disorder in cationic repartition.

Electrochemical properties of crystallized dilithium squarate: insight from dispersion-corrected density functional theory

The stacking parameters, lattice constants, and bond lengths of solvent-free dilithium squarate (Li(2)C(4)O(4)) crystals were investigated using density functional theory with and without dispersion corrections. The shortcoming of the GGA (PBE) calculation with respect to the dispersive forces appears in the form of an overestimation of the unit cell volume up to 5.8%. The original Grimme method for dispersion corrections has been tested together with modified versions of this scheme by changing the damping function. One of the modified dispersion-corrected DFT schemes, related to a rescaling of van der Waals radii, provides significant improvements for the description of intermolecular interactions in Li(2)C(4)O(4) crystals: the predicted unit cell volume lies then within 0.9% from experimental data. We applied this optimised approach to the screening of hypothetical framework structures for the delithiated (LiC(4)O(4)) and lithiated (Li(3)C(4)O(4)) phases, i.e. oxidized and reduced squarate forms. Their relative energies have been analysed in terms of dispersion and electrostatic contributions. The most stable phases among the hypothetical models for a given lithiation rate were selected in order to calculate the corresponding average voltages (either upon lithiation or delithiation of Li(2)C(4)O(4)). A first step towards energy partitioning in view of interpretating crystal phases relative stability in link with (de)-intercalation processes has been performed through the explicit evaluation of electrostatic components of lattice energy from atomic charges gained with the Atoms in Molecules (AIM) method.

Ferroelectric and crystallographic properties of the Sr2−xK1+xNb5O15−xFx solid solution

Abstract The Sr2−xK1+xNb5O15−xFx (0⩽x⩽1) solid solution of tetragonal tungsten bronze (TTB)-type was characterized by both crystallographic and dielectric properties. For small values of x (0⩽x

First principles investigation of the electronic structure of La2MnNiO6: An insulating ferromagnet

Abstract Using first principles density functional theory (DFT) calculations based on the full-potential linearized augmented plane wave method (LAPW), we investigated the electronic and magnetic structures for the ferromagnetic and antiferromagnetic states of La2MnNiO6 and analyzed the site-projected density of states and electronic dispersion curves. Our calculations show that the ground state of La2MnNiO6 is ferromagnetic insulating with the magnetization in agreement with Hunds first rule and experimental findings.

Short-range magnetic order and temperature-dependent properties of cupric oxide

The temperature dependence of the optical and magnetic properties of CuO were examined by means of hybrid density functional theory calculations. Our work shows that the spin exchange interactions in CuO are neither fully one-dimensional nor fully three-dimensional. The temperature dependence of the optical band gap and the (63)Cu nuclear quadrupole resonance frequency of CuO originate from the combined effect of a strong coupling between the spin order and the electronic structure and the progressive appearance of short-range order with temperature.

Density functional theory analysis of the interplay between Jahn-Teller instability, uniaxial magnetism, spin arrangement, metal-metal interaction and spin-orbit coupling in Ca3CoMO6 (M = Co, Rh, Ir)

In the isostructural oxides Ca(3)CoMO(6) (M = Co, Rh, Ir), the CoMO(6) chains made up of face-sharing CoO(6) trigonal prisms and MO(6) octahedra are separated by Ca atoms. We analyzed the magnetic and electronic properties of these oxides on the basis of density functional theory calculations including on-site repulsion and spin-orbit coupling, and examined the essential one-electron pictures hidden behind results of these calculations. Our analysis reveals an intimate interplay between Jahn-Teller instability, uniaxial magnetism, spin arrangement, metal-metal interaction, and spin-orbit coupling in governing the magnetic and electronic properties of these oxides. These oxides undergo a Jahn-Teller distortion, but their distortions are weak, so that their trigonal-prism Co(n+) (n = 2, 3) ions still give rise to strong easy-axis anisotropy along the chain direction. As for the d-state split pattern of these ions, the electronic and magnetic properties of Ca(3)CoMO(6) (M = Co, Rh, Ir) are consistent with d(0) < (d(2), d(-2)) < (d(1), d(-1)) but not with (d(2), d(-2)) < d(0) < (d(1), d(-1)). The trigonal-prism Co(3+) ion in Ca(3)Co(2)O(6) has the L = 2 configuration (d(0))(1)(d(2), d(-2))(3)(d(1), d(-1))(2) because of the metal-metal interaction between adjacent Co(3+) ions in each Co(2)O(6) chain, which is mediated by their z(2) orbitals, and the spin-orbit coupling of the trigonal-prism Co(3+) ion. The spins in each CoMO(6) chain of Ca(3)CoMO(6) prefer the ferromagnetic arrangement for M = Co and Rh but the antiferromagnetic arrangement for M = Ir. The octahedral M(4+) ion of Ca(3)CoMO(6) has the (1a)(1)(1e)(4) configuration for M = Rh but the (1a)(2)(1e)(3) configuration for M = Ir, which arises from the difference in the spin-orbit coupling of the M(4+) ions and the Co···M metal-metal interactions.

First-principles study of the electronic and magnetic structures of the tetragonal and orthorhombic phases of Ca 3 Mn 2 O 7

On the basis of density functional theory electronic band structure calculations using the augmented spherical wave method, the electronic and magnetic properties of the orthorhombic and tetragonal phases of