A reconsideration of the relationship between the crystallite size La of carbons determined by X-ray diffraction and Raman spectroscopy

Non-graphitic carbon materials produced by pyrolyzing wood at temperatures from 400 to 2400 degrees C and various types of commercial carbon fibers were examined by X-ray diffraction and Raman spectroscopy. The specimens cover a wide range of crystallite sizes La, in particular also very small sizes below 2 nm. The X-ray data were evaluated using the Scherrer equation and by an advanced approach using full curve fitting. The ratio of the D/G band intensities was determined from the Raman data by different evaluation techniques. A critical assessment of the classical linear relationship between 1/L-a and the D/G ratio shows that the relationship breaks down for crystallite sizes below 2 nm in accordance with recent theoretical predictions. The results are compared with data from the literature, showing that there are additional discrepancies between the data from various carbon types at large L-a due to different methods of data evaluation. (c) 2006 Elsevier Ltd. All rights reserved.