Author
D. G. Wickham
Bio: D. G. Wickham is an academic researcher from Massachusetts Institute of Technology. The author has contributed to research in topics: Tetragonal crystal system & Ferrimagnetism. The author has an hindex of 4, co-authored 4 publications receiving 563 citations.
Papers
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TL;DR: In this article, a number of spinels containing manganese and crystallizing with the spinel structure have been shown to have a tetragonal distortion from cubic symmetry, which is attributed to the properties of Mn 3+ ions occupying the octahedral positions in the lattice.
238 citations
TL;DR: In this article, the properties of the system Li+xNi++1−2xNi+++xO for the entire range 0.3 < x < 0.5 are reported.
225 citations
TL;DR: The indirect exchange mechanism which produces spontaneous magnetization in metal oxides is an optimum if two interacting cations are located on opposite sides of an anion as mentioned in this paper, however, the coupling rules which have been developed for this case are not applicable to spinels in which the cation-anion-cation angles differ appreciably from 180\ifmmode^\circ\else\textdegree\fi{}.
Abstract: The indirect-exchange mechanisms which produce spontaneous magnetization in metal oxides are an optimum if two interacting cations are located on opposite sides of an anion. The coupling rules which have been developed for this case are not applicable to spinels in which the cation-anion-cation angles differ appreciably from 180\ifmmode^\circ\else\textdegree\fi{}. An examination of the $d$-orbital symmetry of various cations in respect to the crystal lattice leads to several suggestions concerning the magnetic interactions in spinels. Of particular interest are those spinels containing cations with three or fewer $d$ electrons in the octahedral sites, or four if the symmetry is tetragonal. The properties of several spinels of this kind are considered in the light of the suggestions offered. Direct interactions between octahedral-site cations appear to be possible.
67 citations
TL;DR: In this article, a partial ordering of Li and Ni ions into alternate sets of (111) planes which couple antiparallel to one another, the moments within any set being either ferromagnetic or paramagnetic, depending upon the number of nonmagnetic near neighbors in the neighboring planes.
Abstract: Crystallographic and magnetic measurements of the system Li+xNi++1−2xNi+++xO for the entire range 0≤x<0.5 are reported. For values of x≤0.3, the lattice appears to be antiferromagnetic and is cubic above the Curie temperature. For the range of compositions 0.3
64 citations
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TL;DR: New strategies are needed for batteries that go beyond powering hand-held devices, such as using electrode hosts with two-electron redox centers; replacing the cathode hosts by materials that undergo displacement reactions; and developing a Li(+) solid electrolyte separator membrane that allows an organic and aqueous liquid electrolyte on the anode and cathode sides, respectively.
Abstract: Each cell of a battery stores electrical energy as chemical energy in two electrodes, a reductant (anode) and an oxidant (cathode), separated by an electrolyte that transfers the ionic component of the chemical reaction inside the cell and forces the electronic component outside the battery. The output on discharge is an external electronic current I at a voltage V for a time Δt. The chemical reaction of a rechargeable battery must be reversible on the application of a charging I and V. Critical parameters of a rechargeable battery are safety, density of energy that can be stored at a specific power input and retrieved at a specific power output, cycle and shelf life, storage efficiency, and cost of fabrication. Conventional ambient-temperature rechargeable batteries have solid electrodes and a liquid electrolyte. The positive electrode (cathode) consists of a host framework into which the mobile (working) cation is inserted reversibly over a finite solid–solution range. The solid–solution range, which is...
6,950 citations
TL;DR: In this paper, a generalization of the Local Density Approximation (LDA) method for the systems with strong Coulomb correlations is presented which gives a correct description of the Mott insulators.
Abstract: The generalization of the Local Density Approximation (LDA) method for the systems with strong Coulomb correlations is presented which gives a correct description of the Mott insulators. The LDA+U method is based on the model hamiltonian approach and allows to take into account the non-sphericity of the Coulomb and exchange interactions. parameters. Orbital-dependent LDA+U potential gives correct orbital polarization and corresponding Jahn-Teller distortion. To calculate the spectra of the strongly correlated systems the impurity Anderson model should be solved with a many-electron trial wave function. All parameters of the many-electron hamiltonian are taken from LDA+U calculations. The method was applied to NiO and has shown good agreement with experimental photoemission spectra and with the oxygen Kα X-ray emission spectrum.
3,331 citations
TL;DR: In this paper, a new system LixCoO2 (0 Li x CoO 2 Li ) is proposed, which shows low overvoltages and good reversibility for current densities up to 4 mA cm−2 over a large range of x.
2,960 citations
TL;DR: In this article, a review is concerned with the neglected class of inorganic compounds, which contain ions of the same element in two different formal states of oxidation, and a number of references cite that many individual examples of this class have been studied, yet they have very rarely been treated as a class, and there has never before, to our knowledge, been a systematic attempt to classify their properties in terms of their electronic and molecular structures.
Abstract: Publisher Summary This review is concerned with the neglected class of inorganic compounds, which contain ions of the same element in two different formal states of oxidation. Although the number of references cited in our review show that many individual examples of this class have been studied, yet they have very rarely been treated as a class, and there has never before, to our knowledge, been a systematic attempt to classify their properties in terms of their electronic and molecular structures. In the past, systems containing an element in two different states of oxidation have gone by various names, the terms “mixed valence,” nonintegral valence,” “mixed oxidation,” “oscillating valency,” and “controlled valency” being used interchangeably. Actually, none of these is completely accurate or all-embracing, but in our hope to avoid the introduction of yet another definition, we have somewhat arbitrarily adopted the phrase “mixed valence” for the description of these systems. The concept of resonance among various valence bond structures is one of the cornerstones of modern organic chemistry.
2,208 citations
TL;DR: In this article, Li has been inserted chemically and electrochemically into Mn3O4 and Li[Mn2]O4 at room temperature from X-ray diffraction.
1,555 citations