Thermal expansion measurements of nano-graphite using high-temperature X-ray diffraction

Graphite domain size dependences of the thermal expansion of nano-graphites were investigated using in-situ high-temperature X-ray diffraction over 25–500∘C. Carbon nanowalls (CNWs) composed of nano-graphite domains were employed as nano-graphite samples. CNWs with an appropriate domain size exhibited positive thermal expansion in both in-plane (a-axis) and out-of-plane (c-axis) directions, contrary to highly oriented pyrolytic graphite (HOPG), which showed negative thermal expansion along the in-plane direction.The results confirmed that reducing the size of the graphite domain lowers the temperature at which the thermal expansion along the in-plane direction changes from negative to positive. This switch to positive thermal expansion can be explained by the suppression of the out-of-plane vibration, which is related to the thermal contraction, and is caused by the smaller domain of CNWs compared to that of HOPG. [Display omitted]