Structure and electronic properties of Grafoil heated with transition metals

Abstract We investigated the effects of iron, cobalt and nickel on the crystallinity and electronic properties of Grafoil (a polycrystalline graphite foil) by heating it with these metals at temperatures between 1000 and 2000°C and at 2800°C. Interlayer spacing d 0 0 2 decreased with increasing heat treatment temperature (HTT) irrespective of transition metals used, indicating the catalytic effect of these metals on improvement of graphite structure. Transverse magnetoresistance at 77 K increased with increasing HTT, passed through a maximum around 1500–1600°C, decreased at 2000°C, and then increased markedly at 2800°C for Grafoil heated with each metal. The effect of metal atoms as impurities introduced in Grafoil appears at 2000°C. Shifts of Hall coefficient toward the positive side were observed at 77 K for Grafoil heated with each metal, and the positive Hall coefficient was observed for each of the 2000 and 2800°C-treated ones. The results suggest that very small amounts of metal atoms were trapped in the crystal grains of Grafoil during the heat treatment and functioned as acceptors.