Journal of the European Ceramic Society 25 (2005) 2081–2084 Microstructural characterization of mechanically activated ZnO–Cr 2 O 3 system Z.V. Marinkovi´ c a,∗ , L. Manˇ ci´ c b , P. Vuli´ c c , O. Miloˇ sevi´ c b a Center for Multidisciplinary Studies, University of Belgrade, Kneza Viˇ seslava 1a, 11000 Belgrade, Serbia and Montenegro b Institute of Technical Sciences of Serbian Academy of Sciences and Arts, Knez-Mihailova 35/IV, 11000 Belgrade, Serbia and Montenegro c Department of Crystallography, Faculty of Mining and Geology, Ðuˇ sina 7, 11000 Belgrade, Serbia and Montenegro Available online 26 March 2005 Abstract An equimolar mixtures of starting ZnO and Cr 2 O 3 powders were mechanically activated by grinding using a planetary ball mill for various periods of time (40–320 min). Formation of nanocrystalline ZnCr 2 O 4 as normal spinel structure at room temperature is detected in all samples—after ball-milling. A detailed XRD structural analysis (the relative phase abundances of different phases, lattice parameter changes, site occupancy, the average primary crystallite sizes, crystal lattice microstrains) is realized by the pattern decomposition technique, performed in accordance with the procedure based on Rietveld software KOALARIET-XFIT. Due to the importance of cation distribution on the chemical and physical properties of spinels, a study of site occupation factors of ZnCr 2 O 4 spinels has been undertaken. The calculation based on the atomistic methods for the description of the perfect and defect spinel ZnCr 2 O 4 crystal lattice is applied and the presence of the individual structural defects is determined. © 2005 Elsevier Ltd. All rights reserved. Keywords: Milling; Defects; X-ray methods; Spinels 1. Introduction Oxide with the spinel structure are some of the most stud- ied compounds in solid state sciences due to their wide range of applications as a humidity sensors, 1 semiconductors, 2 magnetic materials, 3 catalysts, 4 among others. The general formula of oxide spinels is AB 2 O 4 , and the distribution configuration is represented as IV (A 1-x B x ) VI (B 2-x A x )O 4 . Normal spinels have x = 0, whereas inverse spinels have x = 1; any distribution is possible between the extremes. The unit cell contains eight unit formulas and the symmetry is cubic, space group Fd ¯ 3m, with a cell edge close to 8 ˚ A. 5–7 The anionic array is described by the monovari- ant equivalent position 32e u , point symmetry ¯ 3m. The actual value of the free parameter u (commonly known as the oxy- gen positional parameter) shows a slight deviation from 1/4 if the unit cell origin is taken at a centre of symmetry ¯ 3m, ∗ Corresponding author. Tel.: +381 11 555 258; fax: +381 11 3055 289. E-mail address: mzorica@mi.sanu.ac.yu (Z.V. Marinkovi´ c). equiposition 16c. This deviation usually increase the volume ratio between the occupied A and B sites, respectively, 8a (1/8, 1/8, 1/8), ¯ 43m, and 16d (1/2, 1/2, 1/2), ¯ 3m. 5–7 Determination of the cation distribution is of considerable relevance because the theoretical interpretation of the chem- ical and physical properties of these compounds depends on this distribution. 2–4,8 Some of these materials are interest- ing also because they may become non-stochiometric, thus giving defective spinels. Mechanochemistry is one of the most promising low tem- perature methods of synthesis. Nucleation process is initiated at room temperature, exhibiting more homogeneous distribu- tion, larger specific surface area and smaller particle size of products as compared with those, prepared by conventional solid state method 3,8 . To our knowledge, the phase transformation kinetics of ball-milled chromates has not yet been studied in detail by X-ray powder structure refinement method. Subject of this work is a detailed investigation of the structural features of ZnCr 2 O 4 spinel phase synthesized from mixtures of starting 0955-2219/$ – see front matter © 2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.jeurceramsoc.2005.03.085