Role of interface on electrical conductivity of carbon nanotube/alumina nanocomposite

Interface of multiwalled carbon nanotube (MWCNT)/alumina (Al₂O₃) nanocomposites have been studied using TEM. At low sintering temperature (T_sin=1500 °C), a 3–5 nm thick amorphous interface region was noticed. Nanocomposite sintered at 1700 °C possessed a well-defined graphene layer coating on matrix grains as the interface between CNT and Al₂O₃. A mechanism of such layered interface formation has been proposed. No traceable chemical reaction product was observed at the interface even after sintering at 1700 °C. It was noticed that while DC electrical conductivity (σ_DC) of 1500 °C sintered 2.4 vol% MWCNT/Al₂O₃ nanocomposite was only~0.02 S/m, it raised to ~21 S/m when sintering was done at 1700 °C. Such 10³ times increase in σ_DC of present nanocomposite at a constant CNT loading was not only resulted from the exceptionally high electron mobility of CNT but the well-crystallized graphene interface on insulating type Al₂O₃ grains also significantly contributed in the overall increase of electrical performance of the nanocomposite, especially, when sintering was done at 1700 °C.