Stress-induced wurtzite to hexagonal phase transformation in zinc oxide nanowires.

The stress-induced wurtzite to hexagonal phase transformation in [0110] oriented zinc oxide nanowires were investigated using a molecular dynamics simulation and reactive force field potentials. The yield strength of the 2.13 x 1.93 nm wurtzite nanowires is 12 GPa at 50 K. The wurtzite to hexagonal phase transformation was successfully observed at stress plateaus (5-5.5 GPa at 50 K) located after the yield point of the wurtzite phase. The wurtzite to hexagonal phase transformation was a result of the propagation of {0111} twinning boundaries. During the phase transformation, the wurtzite and hexagonal phases were clearly separated by the {0111} twinning boundaries. To analyze the difference between ceramic and metallic systems, all the calculation data of wurtzite to hexagonal transformation were compared with stress-induced phase transformation in metallic nanowires such as CuZr and NiA1. As the result of the [0110] tensile loading of the ZnO nanowires, the hexagonal phase was obtained.

Dominant factors governing the rate capability of a TiO2 nanotube anode for high power lithium ion batteries.

Titanium dioxide (TiO(2)) is one of the most promising anode materials for lithium ion batteries due to low cost and structural stability during Li insertion/extraction. However, its poor rate capability limits its practical use. Although various approaches have been explored to overcome this problem, previous reports have mainly focused on the enhancement of both the electronic conductivity and the kinetic associated with lithium in the composite film of active material/conducting agent/binder. Here, we systematically explore the effect of the contact resistance between a current collector and a composite film of active material/conducting agent/binder on the rate capability of a TiO(2)-based electrode. The vertically aligned TiO(2) nanotubes arrays, directly grown on the current collector, with sealed cap and unsealed cap, and conventional randomly oriented TiO(2) nanotubes electrodes were prepared for this study. The vertically aligned TiO(2) nanotubes array electrode with unsealed cap showed superior performance with six times higher capacity at 10 C rate compared to conventional randomly oriented TiO(2) nanotubes electrode with 10 wt % conducting agent. On the basis of the detailed experimental results and associated theoretical analysis, we demonstrate that the reduction of the contact resistance between electrode and current collector plays an important role in improving the electronic conductivity of the overall electrode system.