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The effect of Ca doping on the Li-ion conductivity and phase stability of the rock-salt-type LiBH phase emerging under high pressures in the range of gigapascals has been investigated. In situ electrochemical measurements under high pressure were performed using a cubic-anvil-type apparatus. Ca doping drastically enhanced the ionic conductivity of the rock-salt-type phase: the ionic conductivity of undoped and 5 mol %Ca-doped LiBH was 2.2 × 10 and 1.4 × 10 S·cm under 4.0 GPa at 220 °C, respectively. The activation volume of LiBH-5 mol %Ca(BH), at 3.2 cm·mol, was comparable to that of other fast ionic conductors, such as lithium titanate and NASICONs. Moreover, Ca-doped LiBH showed lithium plating-stripping behavior in a cyclic voltammogram. These results indicate that the conductivity enhancement by Ca doping can be attributed to the formation of a LiBH-Ca(BH) solid solution; however, the solid solution decomposed into the orthorhombic LiBH phase and the orthorhombic Ca(BH) phase after unloading the high pressure.

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A B S T R A C T This paper studies the fracture behaviour of cracked carbon nanotube (CNT)-based polymer composites by a combined numerical-experimental approach. Tensile tests were conducted on single-edge cracked plate specimens of CNT/polycarbonate composites at room temperature and liquid nitrogen temperature (77 K), and the critical loads for fracture instabilities were determined. Elastic-plastic finite element simulations of the tests were then performed to evaluate the J-integrals corresponding to the experimentally determined critical loads. Scanning electron microscopy examinations were also made on the specimen fracture surfaces, and the fracture mechanisms of the CNT-based composites were discussed.

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This paper investigates the fatigue failure and electrical resistance behaviors of carbon nanotube-based polymer composites at cryogenic temperatures. Tension-tension fatigue tests were performed on carbon nanotube /polycarbonate composites at room temperature and liquid nitrogen temperature (77 K), and the electrical resistance of the specimens was monitored during the tests. Based on the obtained results, the dependence of the mechanical and electrical responses of the nanocomposites on the temperature and the nanotube content was studied. Microscopic examinations were also carried out on the specimen fracture surfaces, and the failure mechanisms of the nanocomposites were discussed.