Brent C. Melot

A 3.90 V iron-based fluorosulphate material for lithium-ion batteries crystallizing in the triplite structure

Li-ion batteries have empowered consumer electronics and are now seen as the best choice to propel forward the development of eco-friendly (hybrid) electric vehicles. To enhance the energy density, an intensive search has been made for new polyanionic compounds that have a higher potential for the Fe²⁺/Fe³⁺ redox couple. Herein we push this potential to 3.90 V in a new polyanionic material that crystallizes in the triplite structure by substituting as little as 5 atomic per cent of Mn for Fe in Li(Fe(1-δ)Mn(δ))SO₄F. Not only is this the highest voltage reported so far for the Fe²⁺/Fe³⁺ redox couple, exceeding that of LiFePO₄ by 450 mV, but this new triplite phase is capable of reversibly releasing and reinserting 0.7-0.8 Li ions with a volume change of 0.6% (compared with 7 and 10% for LiFePO₄ and LiFeSO₄F respectively), to give a capacity of ~125 mA h g⁻¹.

Dielectric anomalies and spiral magnetic order in CoCr2O4

We have investigated the structural, magnetic, thermodynamic, and dielectric properties of polycrystalline CoCr2O4, an insulating spinel exhibiting both ferrimagnetic and spiral magnetic structures. Below Tc=94 K the sample develops long-range ferrimagnetic order, and we attribute a sharp phase transition at TS27 K to the onset of long-range spiral magnetic order. Neutron measurements confirm that the structure remains cubic at 80 K and at 11 K; the magnetic ordering by 11 K is seen to be rather complex. Density functional theory supports the view of a ferrimagnetic semiconductor with magnetic interactions consistent with noncollinear ordering. Capacitance measurements on CoCr2O4 show a sharp decrease in the dielectric constant at TS, but also an anomaly showing thermal hysteresis falling between approximately T=50 and 57 K. We tentatively attribute the appearance of this higher-temperature dielectric anomaly to the development of short-range spiral magnetic order, and discuss these results in the context of utilizing dielectric spectroscopy to investigate noncollinear short-range magnetic structures.

Magnetodielectric coupling in Mn3O4

We have investigated the dielectric anomalies associated with spin-ordering transitions in the tetragonal spinel

Homoleptic uranium(IV) alkyl complexes: synthesis and characterization.

{\mathrm{Mn}}_{3}{\mathrm{O}}_{4}

Understanding and Promoting the Rapid Preparation of the Triplite-Phase of LiFeSO4F for Use as a Large-Potential Fe Cathode

using thermodynamic, magnetic, and dielectric measurements. We find that two of the three magnetic ordering transitions in

Synthesis, Structure and Magnetic Phase Transitions of the Manganese Succinate Hybrid Framework, Mn(C4H4O4)

{\mathrm{Mn}}_{3}{\mathrm{O}}_{4}

Dependence of the Li-Ion Conductivity and Activation Energies on the Crystal Structure and Ionic Radii in Li6MLa2Ta2O12

lead to decreases in the temperature-dependent dielectric constant at zero applied field. Applying a magnetic field to the polycrystalline sample leaves these two dielectric anomalies practically unchanged, but leads to an increase in the dielectric constant at the intermediate spin-ordering transition. We discuss possible origins for this magnetodielectric behavior in terms of spin-phonon coupling. Band structure calculations suggest that in its ferrimagnetic state,

Metallic Conductivity in a Two-Dimensional Cobalt Dithiolene Metal–Organic Framework

{\mathrm{Mn}}_{3}{\mathrm{O}}_{4}

Chemical and structural indicators for large redox potentials in fe-based positive electrode materials

corresponds to a semiconductor with no orbital degeneracy due to strong Jahn-Teller distortion.

Magnetic structures of LiMBO3 (M = Mn, Fe, Co) lithiated transition metal borates.

The addition of 4.5 equiv of LiCH(2)SiMe(3) to [Li(THF)](2)[U(O(t)Bu)(6)], in the presence of LiCl, results in the formation of the homoleptic uranium(IV) alkyl complex [Li(14)(O(t)Bu)(12)Cl][U(CH(2)SiMe(3))(5)] (1) in low yield. Complex 1 has been characterized by X-ray crystallography. As a solid, 1 is thermally stable for several days at room temperature. However, 1 rapidly decomposes in C(6)D(6), as indicated by (1)H and (7)Li{(1)H} NMR spectroscopy, owing to the lability of the [Li(14)(O(t)Bu)(12)Cl](+) cation. To avoid the formation of the [Li(14)(O(t)Bu)(12)Cl](+) counterion, alkylation of UCl(4) was investigated. Treatment of UCl(4) with 5 equiv of LiCH(2)SiMe(3) or LiCH(2)(t)Bu at -25 degrees C in THF/Et(2)O affords [Li(DME)(3)][U(CH(2)SiMe(3))(5)] (2) and [Li(THF)(4)][U(CH(2)(t)Bu)(5)] (3), respectively, in good yields. Similarly, treatment of UCl(4) with 6 equiv of MeLi or KCH(2)C(6)H(5) generates the U(IV) hexa(alkyl) complexes [Li(TMEDA)](2)[UMe(6)] (4) and {[K(THF)](3)[K(THF)(2)][U(CH(2)C(6)H(5))(6)](2)}(x) (5) in 38% and 70% yields, respectively. The structures of 3-5 have been confirmed by X-ray crystallography. Complexes 2, 3, and 5 are thermally stable solids which can be stored at room temperature for several days, whereas 4 decomposes upon warming above -25 degrees C. The electronic and magnetic properties of 2, 3, and 5 were also investigated by NIR spectroscopy and SQUID magnetometry.