G.D. Liu

Synthesis of porous peanut-like LiNi0.5Mn1.5O4 cathode materials through an ethylene glycol-assisted hydrothermal method using urea as a precipitant

The high voltage spinel LiNi0.5Mn1.5O4 with a peanut-like morphology and porous structure was synthesized by an ethylene glycol-assisted hydrothermal method using urea as a precipitant followed by high-temperature calcination. For comparison, the LiNi0.5Mn1.5O4 sample was also synthesized in the aqueous solution in the absence of ethylene glycol (EG). The as-prepared materials were characterized by XRD, SEM, TEM, FT-IR, CV, EIS and galvanostatic charge/discharge tests. The presence of EG in the hydrothermal process improves the dispersity and decreases the particle size of the final LiNi0.5Mn1.5O4 product, thus leading to its better rate capability, whose discharge capacity at a 10C rate could reach as high as 121.4 mA h g−1. On the other hand, the presence of EG in the hydrothermal process could make the reagents mix more homogeneously, thus leading to higher crystallinity, lower impurity and Mn3+ contents, which are advantageous to the cycling performance. Furthermore, the porous structure of the LiNi0.5Mn1.5O4 material could effectively mitigate the volume change caused by the repeated Li+ insertion/extraction process, which is also conducive to the cycling stability. The LiNi0.5Mn1.5O4 cathode material synthesized by the EG-assisted hydrothermal process shows a capacity retention rate of 96.4% after 100 cycles at a 1C rate. Additionally, a possible formation mechanism for the Ni0.25Mn0.75CO3 precursor with a peanut-like morphology was also proposed.

Towards fully compensated ferrimagnetic spin gapless semiconductors for spintronic applications

Extensive first-principles calculations suggest that inverse Heusler compounds , , , and are the candidates to achieve fully compensated ferrimagnetic spin gapless semiconductors. It is shown that only the holes can be 100% spin polarized in , while both the excited electrons and the holes around the Fermi level 100% spin polarized in the others. A simple rule for searching potential fully compensated ferrimagnetic spin gapless semiconductors in Heusler compounds is proposed. Due to the spin gapless semiconducting and the fully compensated ferrimagnetic properties, these compounds offer distinct advantage towards the development of the practical spintronic devices.

Improved structural and electrochemical performances of LiNi0.5Mn1.5O4 cathode materials by Cr3+ and/or Ti4+ doping

High voltage LiNi0.45M0.05Mn1.5O4 (M = Ni, Cr, Ti, Cr0.5Ti0.5) cathode materials were synthesized by solid-state method, and the effects of Cr/Ti doping alone and co-doping on the crystalline structure, Mn3+ content, particle morphology and electrochemical performance of LiNi0.5Mn1.5O4 cathode materials were systematically investigated. The as-prepared samples were characterized by XRD, FT-IR, SEM, CV, EIS and galvanostatic charge/discharge cycling tests. XRD results show that both pristine and doped materials have cubic spinel structure with Fd3m space group, and the Cr and/or Ti doping can effectively prevent the formation of LiyNi1−yO impurity phase. FT-IR spectra indicate that the Cr and/or Ti doping increases the disordering degree of Ni/Mn ions in 16d octahedral sites. SEM observation discloses that the Cr and/or Ti doping increases the particle size distribution homogeneity and decreases the average primary particle size. EIS analysis illustrates that the Cr and/or Ti doping decreases the charge transfer resistance and increases the Li+ ion diffusion coefficient. All of the above-mentioned factors are believed to be advantageous to the cycling stability and rate capability. Among which, the Cr and Ti co-doped sample LiNi0.45Cr0.025Ti0.025Mn1.5O4 exhibits optimal cycling performance with a capacity retention rate of 102.1% after 100 cycles at 1C rate, and optimal rate capability with a discharge capacity of 118.7 mA h g−1 at 10C rate, which is 96.1% of its capacity at 0.2C rate. The excellent electrochemical performance of LiNi0.45Cr0.025Ti0.025Mn1.5O4 cathode material may be mainly attributed to the presence of appropriate Mn3+ content and higher Li+ ion diffusion coefficient.

The effect of internal and external stress on two-way shape-memory behaviour in Co49Ni21.6Ga29.4 single crystals

The effect of the internal stress on the two-way shape memory in Co49Ni21.6Ga29.4 single crystals has been investigated. We found that the internal stress generated natively by the solidifying process works as a tensile force along the growth direction. Applying different compressive pre-stresses along the [0 0 1] direction, the shape-memory strain can be continuously changed from +1.0% to −2.3%. In the [1 1 0] direction, the strain monotonically increases from −2.0% to −4.0% due to a strong detwinning produced by the consistent effect of the external and internal stresses.

Antisite-induced half-metallicity and fully-compensated ferrimagnetism in Co–Mn–V–Al alloy

We predicted that Co–Mn–V–Al alloy is a fully-compensated half-metallic ferrimagnet in CoVMnAl-type atomic arrangement with 25% ~ 50% Co–Mn antisites using band structure calculations. The CoVMnAl-type atomic arrangement with about 30% Co–Mn antisites was successfully synthesized. The measurements of magnetic properties and electronic transport properties confirmed the half-metallicity and fully-compensated ferrimagnetism. We argued that the half-metallicity and ferrimagnetism in Co–Mn–V–Al compounds originate from the antisite between the Co and Mn atoms, which implies a new way to search for half-metallic material in Heusler alloys.

The investigation of magnetostriction of different phases in Fe-Co alloys

Magnetostrictive material is an important magnetic functional material and can be applied in many fields such as micro-sensors and micro-actuators [1-3]. Among magnetostrictive materials, non-rare-earth Fe-based alloys have gained great interest due to their high mechanical strength, good ductility, large magnetostriction at low saturation fields, high imposed-stress levels, and relatively low cost [4]. However, there were few reports about relation of magnetostriction and phase structure. In this paper, a series of Fe100-xCox alloys was synthesized in different phase components. The largest magnetostriction was achieved in Fe25Co75 which was the composition near the morphotropic-phase boundaries (MPB). In addition, Fe20Co80 alloys with the b.c.c and f.c.c pure phase were separately synthesized by different preparation methods. It was found that its b.c.c phase showed a negative magnetostriction, while f.c.c phase had a positive magnetostriction. The magnetostriction behaviors were explained for the Fe-Co alloys with different phases.