Journal of Solid State Chemistry 170 (2003) 30–38 Control of grain size and morphologies of nanograined ferrites by adaptation of the synthesis route: mechanosynthesis and soft chemistry N. Guigue-Millot, a, * S. B ! egin-Colin, b Y. Champion, c M.J. H . ytch, c G. Le Ca . er, d and P. Perriat e a Laboratoire de Recherches sur la R ! eactivit ! e des Solides, UMR 5613 CNRS/Universit ! e de Bourgogne, BP 47 870, 21078 Dijon Cedex, France b Laboratoire de Science et G ! enie des Mat ! eriaux M! etalliques, UMR 7584, 54042 Nancy Cedex, France c Centre d’Etudes de Chimie M! etallurgique, CNRS, 15 rue G. Urbain, 94407 Vitry Cedex, France d Groupe Mati " ere Condens ! ee et Mat ! eriaux, UMR 6626, Universit ! e de Rennes-I, Avenue du G ! en ! eral Leclerc, 35042 Rennes Cedex, France e Groupe d’Etudes de M! etallurgie Physique et de Physique des Mat ! eriaux, INSA de Lyon, 69621 Villeurbanne Cedex, France Received 1 March 2002; received in revised form 27 June 2002; accepted 5 August 2002 Abstract Nanocrystalline Fe-based spinels with composition Fe 2.5 Ti 0.5 O 4 can be synthesized using two different routes: soft chemistry and high-energy ball milling. This paper is focussed on the fact that each type of synthesis process can lead to powders with a crystallite size of about 15 nm but with significant differences in the grain size distribution and the agglomeration state. Whereas in the case of mechanosynthesis, the ball-milled powders consist of aggregates, those obtained by soft chemistry are very well dispersed. Moreover the chosen investigated nanopowders present a blocked/superparamagnetic transition depending on the grain size. The grain size morphologies obtained by the two techniques of synthesis can then be fully characterized by complementary experiments: in addition to high-resolution image processing, specific measurements adapted to the study of magnetic relaxation can be used for weighting differently their small and large size tails: namely, magnetization measurements and M . ossbauer spectrometry. r 2002 Elsevier Science (USA). All rights reserved. Keywords: Mechanosynthesis; Soft chemistry; Nanoparticles; Spinels; High-resolution transmission electron microscopy; M. ossbauer spectrometry 1. Introduction Nanostructured materials are known to exhibit properties different from those of conventional materi- als with coarser microstructure. The so-called ‘‘nano- metric effect’’ is a major issue of discussion both experimentally and theoretically [1]. However, the influence of synthesis methods on materials properties is rarely considered in the literature. We have previously demonstrated that nanometer-sized titanoferrites synthesized either by mechanical alloying or by soft chemistry display different characteristics [2], namely in: deviations from oxygen stoichiometry, defects, cation distributions, etc. In this paper we investigate differences in the morphology properties, mainly the state of aggregation and the particle size distribution, originat- ing from the two synthesis techniques. Such differences may strongly influence properties of these nanomater- ials. Moreover the nanometer-sized studied titanofer- rites present a magnetic relaxation depending on the grain size. This property is, in fact, used here to compare the relevant differences in the morphological character- istics of the powders synthesized by the two techniques. Indeed, in addition to classical grain size characteriza- tions, specific magnetic measurements appropriate for the determination of grain size distributions in aggre- gated nanometric titanoferrites are used. Ferrites with spinel structure Fe 3x M x O 4 (M is a cation, M = Mn, Zn, Mo, V, etc and 0p x p1) have been thoroughly studied over many decades [3]. In these spinel phases, a change of the cation-to-anion ratio leads possibly to a deviation d from oxygen stoichiometry: (Fe 3x M x ) 1d O 4 [4]. In the spinel structure, two types of *Corresponding author. E-mail address: nmillot@u-bourgogne.fr (N. Guigue-Millot). 0022-4596/03/$ - see front matter r 2002 Elsevier Science (USA). All rights reserved. PII:S0022-4596(02)00012-9