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NiCo2S4@PPy core–shell nanotube arrays have been successfully prepared through three facile steps: solvothermal synthesis, solvothermal sulphurisation and subsequentin situelectropolymerisation of polypyrrole (PPy). Their structure and morphology were studied by XRD, FTIR, SEM and TEM. The results suggest that a thin layer of PPy with 8 nm in thickness is wrapped on the surface of NiCo2S4nanotubes. The coating PPy strong promotes pseudo-capacitance reaction of NiCo2S4nanotube arrays. NiCo2S4@PPy shows lower charge plateau and IR drop, higher discharge plateau and Coulombic efficiency. Rate performance is improved remarkably. Average specific capacitance at 24 mA cm−2is even two times that of the uncoated NiCo2S4. The galvanostatic cycling tests at 4 mA cm−2indicate NiCo2S4@PPy exhibit the highest specific capacitance of 1524 F g−1and improved capacitance retention to 78.5% after 3000 cycles. The corresponding values of the uncoated NiCo2S4nanotube arrays are only 1410 F g−1and 22%. The improved electrochemical performance is mainly attributed to unique core–shell nanotube array structure and the key assistant effect of the coating PPy which remarkably improves the conductive property of NiCo2S4long nanotubes and effectively enhances structure stability and cycling stability of NiCo2S4nanotubes. [ABSTRACT FROM PUBLISHER]

Molecular dynamics (MD) simulation is performed to study the interaction between deformation twin and annealing twin in iron crystal. Two samples are simulated in this paper. The annealing twin in each sample is considered pre-existing automatically and the deformation twin is formed in the process of mode-I type loading and emitted from the crack tip. The distances between the twin boundary of the annealing twin and the crack tip in two samples are different. The applied stress is imposed to the top and the bottom of each sample. When the stress intensity is KI = 0·94 MPa m1/2, the partial dislocation is emitted from the crack tip of each sample, but the sample with larger annealing twin grain size will move a greater distance. As KI is increased to 2 MPa m1/2, the larger the annealing twin grain size is, the faster it will grow and the smaller the size of the deformation twin from the crack tip. That is to say, the size of the annealing twin will hinder the formation of the deformation twin and then affect the mechanical property of the material. [ABSTRACT FROM AUTHOR]