Materials Chemistry and Physics 111 (2008) 346–350 Contents lists available at ScienceDirect Materials Chemistry and Physics journal homepage: www.elsevier.com/locate/matchemphys X-ray diffraction line profile analysis of nanocrystalline graphite Adriyan Milev a,∗ , Michael Wilson b , G.S. Kamali Kannangara a , Nguyen Tran a a College of Health and Science, University of Western Sydney, Locked Bag 1797, Penrith South DC 1797, Australia b CSIRO, Petroleum, North Ryde NSW 2113, Australia article info Article history: Received 28 February 2007 Received in revised form 10 March 2008 Accepted 13 April 2008 Keywords: Graphite Milling N-Dodecane X-ray profile analysis Double-Voigt Fourier analysis Crystalline size distribution abstract The structure evolution to nanocrystalline graphite produced by ball milling in n-dodecane has been studied by Fourier analysis of broadened X-ray diffraction line profiles according to double-Voigt method. The Fourier analysis gave size and strain distributions of the coherently diffracting domains (X-ray crys- tallite size) and root-mean-square-strain (rmss) and their average values. The precursor graphite was defined by average crystal sizes of about hundreds of nanometers, measured along the in-plane and out- of-plane directions, and low rmss value of 0.38 × 10 -3 . During milling, the average crystallite sizes of graphite decreased to about 6 and 43nm along the out-of-plane and in-plane directions, respectively. Correspondingly, the rmss of milled graphite increased to 6.54 × 10 -3 . Analysis of the out-of-plane to in-plane crystallite size ratios showed that the crystallites became progressively thinner and flatter. A linear relationship between rmss and reciprocal crystallite size along the stacking axis revealed that size of disordered boundary regions gradually increased at the expense of ordered crystalline regions. A model describing crystalline–nanocrystalline transformation of graphite along different crystallographic axis was formulated and used to discuss the experimental data. It was concluded that a distortion- controlled process is responsible for the crystalline–nanocrystalline transformation of graphite milled in n-dodecane. © 2008 Elsevier B.V. All rights reserved. 1. Introduction Graphite consists of stacks of parallel two-dimensional graphene sheets with carbon atoms being arranged in hexagonal rings through localized in-plane 2s, 2p x and 2p y (sp 2 ) orbitals. The individual sheets are weakly bonded by delocalized out-of- plane 2p z orbitals, which overlap to give a delocalized ( electron system. The anisotropic graphite structure suggests different prop- erties along with different crystallographic axis: very high in-plane strength but very weak out-of-plane strength. In nanocrystalline graphitic materials (crystallite sizes less than 100 nm), a large pro- portion of the carbon atoms are situated within defects (vacancies, dislocations, grain boundaries and stacking faults) and strained lat- tice regions. Nanocrystalline graphitic materials are usually produced by ball milling [1–3]. The addition of liquid media can be benefi- cial, because it favours the cleavage of the particles, moderates the shocks and avoids loo large agglomeration of the particles. Milling in liquid media also prevents sample warming and excessive build ∗ Corresponding author at: College of Health and Science, School of Natural Sci- ences, University of Western Sydney, Locked Bag 1797, Penrith South DC 1797, Australia. Tel.: +61 2 9685 9945; fax: +61 2 9685 9915. E-mail address: a.milev@uws.edu.au (A. Milev). up of defects in the graphite structure [4,5]. The small crystallite sizes and the presence of defects open up opportunity for new applications such as anodes for lithium ion batteries [5,6], synthe- sis of carbon nanotubes [7,8] and recently as the reinforcing phase in nanocomposites [9]. Accurate characterization of structural parameters of nanocrys- talline graphite, such as crystallite size, size distribution and strain, is of critical importance for both fundamental and practical pur- poses. One of the most often used methods to study the structure at nano-size level is transmission electron microscopy (TEM). It provides the local details (grain size histograms, stacking-fault, dis- location densities, etc.) by direct imagining of a thin sample but it is difficult to obtain some statistically representative information over large volumes and/or in a great number of specimens. Thus, the reported research so far has been limited to characterization of average crystallite size and sometimes local microstrain [1,2,10–17]. Studies on the development of size and microstrain distributions en route to nanocrystalline graphite and the respective size–strain relationships have not been reported. Diffraction-line-profile analysis has the advantage of giving information about crystallite sizes over larger volumes and is sen- sitive to the strain fields of lattice defects, especially the different internal stresses related to dislocations. By extending the analysis to profiles at high order diffraction but from the same crystallo- graphic plane (i.e. 0 0 2, 0 0 4, etc.), it is possible to separate strain 0254-0584/$ – see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.matchemphys.2008.04.024