Anionic Redox Activity in a Newly Zn-Doped Sodium Layered Oxide P2-Na2/3 Mn1− y Zn y O2 (0 < y < 0.23)

The revival of the Na‐ion battery concept has prompted intense research activities toward new sustainable Na‐based insertion compounds and their implementation in full Na‐ion cells. Efforts are parted between Na‐based polyanionic and layered compounds. For the latter, there has been a specific focus on Na‐deficient layered phases that show cationic and anionic redox activity similar to a Na0.67Mn0.72Mg0.28O2 phase. Herein, a new alkali‐deficient P2‐Na2/3Mn7/9Zn2/9O2 phase using a more electronegative element (Zn) than Mg is reported. Like its Mg counterpart, this phase shows anionic redox activity and no O2 release despite evidence of cationic migration. Density functional theory (DFT) calculations show that it is the presence of an oxygen nonbonding state that triggers the anionic redox activity in this material. The phase delivers a reversible capacity of 200 mAh g−1 in Na‐half cells with such a value be reduced to 140 mAh g−1 in full Na‐ion cells which additionally shows capacity decay upon cycling. These findings establish Na‐deficient layered oxides as a promising platform to further explore the underlying science behind O2 release in insertion compounds based on anionic redox activity

Some open questions in TDDFT: Clues from Lattice Models and Kadanoff-Baym Dynamics

Two aspects of TDDFT, the linear response approach and the adiabatic local density approximation, are examined from the perspective of lattice models. To this end, we review the DFT formulations on the lattice and give a concise presentation of the time-dependent Kadanoff-Baym equations, used to asses the limitations of the adiabatic approximation in TDDFT. We present results for the density response function of the 3D homogeneous Hubbard model, and point out a drawback of the linear response scheme based on the linearized Sham-Schl\"uter equation. We then suggest a prescription on how to amend it. Finally, we analyze the time evolution of the density in a small cubic cluster, and compare exact, adiabatic-TDDFT and Kadanoff-Baym-Equations densities. Our results show that non-perturbative (in the interaction) adiabatic potentials can perform quite well for slow perturbations but that, for faster external fields, memory effects, as already present in simple many-body approximations, are clearly required.Comment: 15 pages, submitted to Chemical Physic

Oxygen redox chemistry without excess alkali-metal ions in Na2/3_{2/3}[Mg0.28_{0.28}Mn0.72_{0.72}]O2_2

The search for improved energy-storage materials has revealed Li- and Na-rich intercalation compounds as promising high-capacity cathodes. They exhibit capacities in excess of what would be expected from alkali-ion removal/reinsertion and charge compensation by transition-metal (TM) ions. The additional capacity is provided through charge compensation by oxygen redox chemistry and some oxygen loss. It has been reported previously that oxygen redox occurs in O 2$p$ orbitals that interact with alkali ions in the TM and alkali-ion layers (that is, oxygen redox occurs in compounds containing Li$^+$–O(2$p$)–Li$^+$ interactions). Na$_{2/3}$[Mg$_{0.28}$Mn$_{0.72}$]O$_2$ exhibits an excess capacity and here we show that this is caused by oxygen redox, even though Mg$^{2+}$ resides in the TM layers rather than alkali-metal (AM) ions, which demonstrates that excess AM ions are not required to activate oxygen redox. We also show that, unlike the alkali-rich compounds, Na$_{2/3}$[Mg$_{0.28}$Mn$_{0.72}$]O$_2$ does not lose oxygen. The extraction of alkali ions from the alkali and TM layers in the alkali-rich compounds results in severely underbonded oxygen, which promotes oxygen loss, whereas Mg$^{2+}$ remains in Na$_{2/3}$[Mg$_{0.28}$Mn$_{0.72}$]O$_2$, which stabilizes oxygen

Lattice density-functional theory of the attractive Hubbard model

International audienceThe attractive Hubbard model is investigated in the framework of lattice density-functional theory (LDFT).The ground-state energy E = T + W is regarded as a functional of the single-particle density matrix γij withrespect to the lattice sites, where T [γ ] represents the kinetic and crystal-field energies and W[γ ] the interactionenergy. Aside from the exactly known functional T [γ ], we propose a simple scaling approximation to W[γ ],which is based on exact analytic results for the attractive Hubbard dimer and on a scaling hypothesis withinthe domain of representability of γ . As applications, we consider one-, two-, and three-dimensional finite andextended bipartite lattices having homogeneous or alternating onsite energy levels. In addition, the Bethe lattice isinvestigated as a function of coordination number. Results are given for the kinetic, Coulomb, and total energies,as well as for the density distribution γii , nearest-neighbor bond order γij , and pairing energy �Ep, as a functionof the interaction strength |U|/t, onsite potential ε/t , and band filling n = Ne/Na . Remarkable even-odd andsuper-even oscillations of �Ep are observed in finite rings as a function of band filling. Comparison with exactLanczos diagonalizations and density-matrix renormalization-group calculations shows that LDFT yields a verygood quantitative description of the properties of the model in the complete parameter range, thus providing asignificant improvement over the mean-field approaches. Goals and limitations of the method are discussed

Influence of local structural distortion on the magnetism of Na 2 IrO 3 compounds

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Site-occupation Green's function embedding theory: A density functional approach to dynamical impurity solvers

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Structure, Magnetism, and First-Principles Modeling of the Na 0.5 La 0.5 RuO 3 Perovskite

International audienceHigh-purity polycrystalline Na0.5La0.5RuO3 was synthesized by a solid-state method, and its properties were studied by magnetic susceptibility, heat capacity, and resistivity measurements. We find it to be an orthorhombic perovskite, in contrast to an earlier report, with random La/Na mixing. With a Curie–Weiss temperature of −231 K and an effective moment of 2.74 μB/mol Ru, there is no magnetic ordering down to 1.8 K. A broad hump at 1.4 K in the heat capacity, however, indicates the presence of a glassy magnetic transition, which we attribute to the influence of the random distribution of Na and La on the perovskite A-sites. Comparison to CaRuO3, a structurally ordered ruthenate perovskite with a similar A-site ionic radius and magnetic properties, is presented. First-principles calculations indicate that the Na–La distribution determines the local magnetic exchange interactions between Ru ions, favoring either antiferromagnetic or ferromagnetic coupling when the local environment is Na- or La-rich. Thus, our data and analysis suggest that mixing cations with different charges and sizes on the A-site in this perovskite results in magnetic frustration through a balance of local magnetic exchange interactions

Modelling CO 2 transfer in foil ripened semi-hard Swiss-type cheese

International audienceDespite CO2 production and diffusion during ripening of semi-hard Swiss-type cheese are considered as important quality parameters, the research concerning key gas production and transfer in cheese remains widely overlooked. In this study, experimentally assessed CO2 production was coupled with transfer coefficients in a mathematical model in order to predict CO2 gradients formed inside the cheese during ripening. The permeability coefficient of CO2 through the multilayer barrier packaging which wraps the cheese during ripening was also included in the model. The presented model was validated by assessing the CO2 concentration in the cheese and its partial pressure in the packaging headspace. CO2 production rate was found to be the most important input parameter affecting CO2 gradients formed in cheese during ripening whereas the other input parameters (solubility, diffusivity, permeability) had little effect on the total CO2 gradient

An appraisal of the impact of compositional and ripening parameters on CO2 diffusivity in semi-hard cheese

International audienceThis study focuses on CO2 diffusivity, which is one of the most important factors impacting eye growth in semi-hard cheese, but yet has scarcely been investigated in literature. The effect of compositional and ripening parameters on experimental CO2 diffusivity in semi-hard cheese was studied. CO2 diffusivity in semi-hard cheese showed a complex relationship with temperature in the range 4 to 25 °C, represented by a quadratic curve with the highest diffusivity at 13 °C. Salt was found to impact CO2 diffusivity, with a decrease of about 60% for 0 to 2.7% w/w salt addition, which may be ascribed to viscosity increase of the cheese matrix and “salting in” effect of protein. CO2 diffusivity was found to increase with moisture content from 39 to 42% w/w, then it decreased from 42 to 48% w/w. Inevitable changes in protein content of the three cheese variants may be responsible for the complex behaviour observed

The intriguing question of anionic redox in high-energy density cathodes for Li-ion batteries

International audienceThe energy density delivered by a Li-ion battery is a key parameter that needs to be significantlyincreased to address the global question of energy storage for the next 40 years. This quantity is directlyproportional to the battery voltage (V) and the battery capacity (C) which are difficult to improvesimultaneously when materials exhibit classical cationic redox activity. Recently, a cumulative cationic4+ 5+ 2À nÀ(M /M ) and anionic (2O /(O2) ) redox activity has been demonstrated in the Li-rich Li2 MO3 familyof compounds, therefore enabling doubling of the energy density with respect to high-potentialcathodes such as transition metal phosphates and sulfates. This paper aims to clarify the origin of thisextra capacity by addressing some fundamental questions regarding reversible anionic redox inhigh-potential electrodes for Li-ion batteries. First, the ability of the system to stabilize the oxygen holes2À nÀgenerated by Li-removal and to achieve a reversible oxo- to peroxo-like (2O /(O2) ) transformation iselucidated by means of a metal-driven reductive coupling mechanism. The penchant of the system forundergoing this reversible anionic redox or releasing O2 gas is then discussed with regards toexperimental results for 3d- and 4d-based Li2MO3 phases. Finally, robust indicators are built as tools topredict which materials in the Li-rich TM-oxide family will undergo efficient and reversible anionicredox. The present finding provides insights into new directions to be explored for the development ofhigh-energy density materials for Li-ion batteries