Wang Fang-Wei

High-capacity lithium-rich cathode oxides with multivalent cationic and anionic redox reactions for lithium ion batteries

Lithium-rich cathode oxides with capability to realize multivalent cationic and anionic redox reactions have attracted much attention as promising candidate electrode materials for high energy density lithium ion batteries because of their ultrahigh specific capacity. However, redox reaction mechanisms, especially for the anionic redox reaction of these materials, are still not very clear. Meanwhile, several pivotal challenges associated with the redox reactions mechanisms, such as structural instability and limited cycle life, hinder the practical applications of these high-capacity lithium-rich cathode oxides. Herein, we review the lithium-rich oxides with various crystal structures. The multivalent cationic/anionic redox reaction mechanisms of several representative high capacity lithium-rich cathode oxides are discussed, attempting to understand the origins of the high lithium storage capacities of these materials. In addition, we provide perspectives for the further development of these lithium-rich cathode oxides based on multivalent cationic and anionic redox reactions, focusing on addressing the fundamental problems and promoting their practical applications.

Crystallographic and magnetic structures of Pr6Fe13Ge studied by powder neutron diffraction

Crystallographic and magnetic structures of Pr6Fe13Ge have been investigated by high-resolution powder neutron diffraction in the temperature range of 10?300 K. The magnetic structure consists of ferromagnetic Pr6Fe13 slabs that alternate antiferromagnetically, along c, with the next Pr6Fe13 slab separated by a non-magnetic Ge layer. The magnetic moments lie within the ab-planes. The propagation vector of this structure is k=(001) with respect to the conventional reciprocal lattice of the I-centred structure. However, the temperature-dependence of neutron-scattering intensity of the (110) Bragg peak, very similar to the temperature-dependent magnetization measured by SQUID magnetometer, indicates that a small c-axis ferromagnetic component should be added to the above antiferromagnetic model.

Magnetic Properties and Spin State Transition of Gallium Doped Perovskite Cobaltite Oxide

A series of Ga doping perovskite cobaltite La2/3Sr1/3(Co1−yGay)O3 (y = 0, 0.1, 0.2, 0.3 and 0.4) are prepared by the standard solid-state reaction method. Their magnetic properties and Co ions spin state transitions are studied. Upon doping, no appreciable structure changes can be found. However, the corresponding Curie temperature sharply decreases and the magnetization is greatly reduced, indicating that Ga doping destroys the ferromagnetic interaction in the system. In addition, the high temperature magnetization data follow the Curie–Weiss law. At least one kind of Co ions (Co3+ or Co4+) favours the mixed spin state, and most Co ions are at the lower spin state (low and intermediate state). With increasing Ga content, more Co ions transit to the higher spin state.

The electrical transport behavior of Zn-treated Zn1-xMnxO bulks

Zn1ixMnxO bulks have been prepared by the solid state reaction method. Zn vapor treatment has been carried out to adjust the carrier concentration. For the Zn treated Zn1ixMnxO bulks, analysis of the temperature dependence of resistance and the fleld dependence of magnetoresistance demonstrates that the bound magnetic polarons (BMPs) play an important role in the electrical transport behavior. The hopping of BMPs dominates the electrical conduction behavior when temperature is below 170 K. At low temperature, paramagnetic Zn1ixMnxO bulks show a large magnetoresistance efiect, which indicates that the large magnetoresistance efiect in transition-metal doped ZnO dilute magnetic semiconductors is independent of their magnetic states.

Calculations of radioactivity and afterheat in the components of the CSNS target station

This paper shows the calculations of radioactivity and afterheat in the components of the China Spallation Neutron Source (CSNS) target station, with the Monte Carlo codes LAHET, MCNP4C and the multigroup code CINDER’90. These calculations provide essential data for the detailed design and maintenance of the CSNS target station.

The effect of doped ions on single-molecule magnets of the Mn12-Ac family

This paper investigates the single-molecule magnets of pure and Cr/Fe-doped Mn12-Ac. The components of the mixed crystals are identified by AC susceptibility technique. The ground-state spin and anisotropy parameters of doped Mn12-Ac are obtained: (i) Mn11Cr-Ac (S = 19/2, D = 0.62K, B = 0.0009 K, Δ = 63K), and (ii) Mn11Fe-Ac (S = 21/2, D = 0.39K, B = 0.001 K, Δ = 55K). The single-ion origin of the magnetic anisotropy is discussed.

Resonant tunnelling of the magnetization in molecular crystal of [(Mn1-xCrx)12O12 (CH3COO)16(H2O)4] ·2CH3COOH·4H2O (x=0,0.03,0.04,0.05)

The quantum tunnelling of magnetization (QTM) in single crystals of the single molecule magnet (Mn1-xCrx)12-Ac (x=0, 0.03, 0.04, 0.05) has been investigated. In comparison with its parent Mn12-Ac, a greater rate of magnetization relaxation and a lower effective potential-energy barrier have been observed in Cr-doping samples. This modulation of QTM due to the Cr-doping could be attributed to the small change of Sz due to the smaller spin of Cr itself and additional intrinsic but distributed transverse and longitudinal anisotropy raised by a subtle change of the local environment in the magnetic Mn12 core.

Structure and magnetic properties of a new single-molecule magnet [Mn11Fe1O12 (CH3COO)16(H2O)4] .2CH3COOH.4H2O

A new single-molecule magnet [Mn11Fe1O12(CH3COO)16(H2O)4].2CH3COOH.4H2O (Mn11Fe1) has been synthesized. The structure has been studied by the single crystal x-ray diffraction. The difference of Jahn–Teller distortion between Fe3+ and Mn3+ ion reveals that Fe3+ ion substitutes for Mn3+ ion on the Mn(3) sites in the Mn12 skeleton. The temperature dependence of the magnetization gives a blocking temperature TB=1.9K for Mn11Fe1. Based on the magnetization process analysis of the crystal at T=2K, we suggest that Mn11Fe1 has the ground state with a total spin S= 11/2.