Microtexture of highly crystallized graphite as studied by galvanomagnetic properties and electron channeling contrast effect

The relationship between microtexture and crystallinity of highly crystallized graphites with the residual resistivity ratio ρ_300K/ρ_4.2K of 3.45–5.50 was investigated. The graphite crystals studied were kish graphite (KG), highly oriented pyrolytic graphite (HOPG), and highly crystallized graphite films prepared from carbonized aromatic polyimide films. The study was made by the observations of an electron channeling pattern and electron channeling contrast image (ECI) under scanning electron microscope and the measurements of x-ray diffraction, magnetoresistance, and Hall coefficient. The values of the mean free path of the carriers λ, which approximates the mean crystal grain size, were estimated to be 2.6–6.1 μm from the magnetoresistance at 4.2 K for the highly crystallized graphites. The values of the average crystal grain diameter D in the basal plane evaluated from ECI were several hundred microns or more for KG, 60 μm for HOPG, and 6 and 12 μm for the graphite films. The difference between the values of λ and D for each crystallized graphite was discussed in relation to other results obtained.