Program: K6 Nanoscale Systems K6 Nanoscale Systems K6.1. F. Berry (Milton Keynes): Nanocrystalline Oxides and Sulphides Prepared by Hydrothermal Processing and Mechanical Milling - The Use of Mössbauer Spectroscopy in Characterisation K6.2. G. Le Caër (Rennes): Synthesis of Nanocrystalline Materials by Mechanical Activation and by High-Energy Ball-Milling K6.3. E. Tronc (Paris): Studies of Nanoparticles by Mössbauer Spectroscopy and Magnetic Measurement: Surface and Interaction Effects K6.4. Q. Pankhurst (London): Nanoscale Granular Alloys K6.5. O. Schneeweiss (Brno): Properties of Mg-TM (TM = Fe, Ni, Co) Nanocomposites O6.1. R. Zbořil: Mössbauer Study of Nanocrystalline Fe2O3 Phases from thermal Processes - Identification, characterization a Formation Mechanism O6.2. B. David (Brno): Magnetic Behaviour of the Fe-C Oxidized Nanopowder Prepared by Laser Pyrolysis K6.1 Nanocrystalline Oxides and Sulphides Prepared by Hydrothermal Processing and Mechanical Milling - The Use of Mössbauer Spectroscopy in Characterisation F.J. Berry Department of Chemistry, The Open University, Milton Keynes, United Kingdom The properties of materials can be dramatically changed when one or more dimensions are in the 1-100 nm regime. The resulting changes in chemical and physical behaviour have been of intense and growing interest over the past decade and a new research area, that of nanostructured materials, has emerged. Mössbauer spectroscopy is an important technique for the characterisation of these interesting materials. In this lecture the synthesis of nanocrystalline tin-doped a-FeOOH (goethite) by hydrothermal processing will be described. The influence of pH on the morphology of the particles, particularly the formation of acicular crystals and their structural characterisation by X-ray powder diffraction and EXAFS will be described. The use of 57Fe- and 119Sn-Mössbauer spectroscopy to characterise the magnetic properties of both the acicular crystals and those with more regular morphology will be discussed. The formation of nanocrystalline iron sulphides by mechanical milling will also be described. The use of 57Fe Mössbauer spectroscopy to follow the evolution of the iron sulphide phases will be discussed. K6.2 Synthesis of Nanocrystalline Materials by Mechanical Activation and by High-Energy Ball-Milling G. Le Caër1, P. Delcroix2 and S. Bégin-Colin2 1) Groupe Matiere Condensée et Matériaux, C.N.R.S. U.M.R. 6626, Université de Rennes-I, Rennes, France 2) Laboratoire de Science et Génie des Materiaux et de Métallurgie, C.N.R.S. U.M.R., Nancy, France High-energy ball-milling is a possible route for synthesizing new materials and notably nanostructured materials: Mechanical alloying of mixtures of powders is a method of synthesis of all sorts of materials which include crystalline materials with nanometer-sized grains with a typical average size of ~ 10 nm. Most often, for instance in metallic materials, the average particle size is however not in the nm-range but typically micronic or submicronic. Every powder particle is thus a polycrystal with a high density of grain boundaries. Their high density of defects may strongly influence their properties, for instance mechanical, or the kinetics of processes, which occur during annealing. High-energy ball-milling is moreover a way of changing the conditions in which chemical reactions usually occur either by inducing chemical reactions during milling (mechanochemistry) or by modifying the reactivity of as-milled solids (mechanical activation). The mechanically activated synthesis of nanocrystalline compounds with various morphologies will be described. Grinding of materials whose chemical composition remains the same during milling is a way of inducing phase transformations in solids : amorphization or polymorphous transformations of compounds, disordering of ordered alloys. The fundamental role of competing interactions in the establishment of dynamical stationary states during milling has been stressed recently. It will be exemplified with binary alloys showing either a trend to ordering or a trend to unmixing. Contributions of Mössbauer spectrometry to the characterization of ground materials will be described. K6.3 Studies of Nanoparticles by Mössbauer Spectroscopy and Magnetic Measurement: Surface and Interaction Effects E. Tronc Laboratoire de Chimie de la Matiere Condensee, UMR 7574 CNRS, Universite Pierre et Marie Curie, Paris, France Abstract not delivered. K6.4 Nanoscale Granular Alloys Q.A. Pankhurst Department of Physics and Astronomy, University College London, London, United Kingdom The structural and magnetic properties of the Fe-Cu-Ag class of technologically relevant ternary metallic alloys will be discussed. These alloys are members of a family of nanoscale granular alloys that are of current interest in both giant magnetoresistive alloys and nanocrystalline soft magnets. Sample preparation, by mechanical alloying, and structural characterisation by Rietveld analysis of x-ray diffraction data, and by differential scanning calorimetry, will be described. Magnetic characterisation by DC magnetometry and frequency-dependent AC susceptibility will be compared to the nanosecond-timescale information accessible via zero field and applied field Mössbauer spectroscopy. A new application of zero field muon spin relaxation methods to the problem will be considered. It will be shown that in almost all cases the superparamagnetic blocking transitions are clearly affected by the existence of intergranular interactions, which shift them to higher temperatures than would be expected from non-interacting grains. K6.5 Properties of Mg-TM (TM = Fe, Ni, Co) Nanocomposites O. Schneeweiss, Y. Jirásková and T. Žák Institute of Physics of Materials, Academy of Sciences of the Czech Republic, Brno, Czech Republic Nanocomposites MgO-TM (TM=Fe,Ni,Co) were prepared by controlled heat treatments of compacted spark synthesised nanopowders. The heat treatment was carried out according phase transitions observed on thermomagnetic curves and DTA/TG measurements. Phase analysis was derived from Mössbauer spectroscopy, x-ray diffraction and magnetization measurement. In the as-prepared powder, materials of electrodes, amorphous Mg-TM phases and TM in MgO phases were determined. The TG/DTA curves documented high adsorption capacity of moisture and air gases at the nanocrystals surfaces and interfaces. During annealing, MgO is formed by reaction of Mg nanocrystals with adsorbed oxygen and water. TM atoms form ferromagnetic clusters and particles of metals and/or alloys. Low temperature dependence of magnetization shows spin-glass like (mictomagnetic) behaviour. The magnetoresistance agrees with those observed on similar systems with tunnelling magnetoresistance. O6.1 Mössbauer Study of Nanocrystalline Fe2O3 Phases from thermal Processes - Identification, characterization a Formation Mechanism R. Zbořil and M. Mashlan Faculty of Sciences, Palacky University, Olomouc, Czech Republic The primary stages of the thermally induced conversions and oxidations of iron-containing materials are related with the formation of nanonocrystalline Fe2O3 phases. Taking into account the number of industrial applications of Fe2O3 nanoparticles, the combination of the solid-state reaction with the post processing (chemical, magnetic) separation can be used as the potential method for their preparation. On the other hand, the presence of Fe2O3 nanophases often complicates some industrial technologies as the calcination method of the red ferric pigment manufacture or the steel manufacture. The poor crystallinity or the low content of Fe2O3 in the sample can result in the troublesome identification of the particular polymorphs using common methods (XRD, IR). However, the unambiguous finding of the crystal structure of the nanocrystalline phase is very important both for the optimization of the mentioned industrial processes and for the general study of the Fe2O3 polymorphism including the mutual polymorphic transformations. 57Fe Mössbauer spectroscopy is a unique method that allows one to distinguish and identify individual polymorphs forming the nanocrystalline sample and to analyze their formation mechanism during thermally induced solid-state reactions. Just Mössbauer spectroscopy supported by atomic force microscopy and XRD was used for the identification and characterization of Fe2O3 nanoparticles formed during thermal oxidations of FeCO3 and FeC2O4, and thermal conversion of Fe2(SO4)3. a-Fe2O3 nanoparticles with the hexagonal corundum structure were identified as the primary phase from iron(II) carbonate, g-Fe2O3 nanoparticles with the cubic spinel structure were formed from iron(II) oxalate, while b-Fe2O3 particles (15-30 nm) with the rare cubic bixbyite structure together with orthorhombic e-Fe2O3 particles (40-60 nm) were produced by thermal treatment of iron(III) sulfate. The relation between the structural properties of the initial ferrogenous precursor and the polymorphic type of the formed iron(III) oxide is discussed. O6.2 Magnetic Behaviour of the Fe-C Oxidized Nanopowder Prepared by Laser Pyrolysis B. David1, R. Alexandrescu2, M. Vondráček1 and O. Schneeweiss1 1) Institute of Physics of Materials, Academy of Sciences of the Czech Republic, Brno, Czech Republic 2) National Institute for Lasers, Plasma and Radiation Physics, Bucharest, Romania Nanopowder of the Fe-C based material was prepared by laser irradiation of the Fe(CO)5 vapours mixed with C2H4 as a carrier gas. The as prepared powder was characterized by TEM, XRD and IR. Magnetic behaviour was investigated using Mössbauer spectroscopy and magnetic measurements. In the sample of the as prepared state there were identified bcc a-Fe, Fe3C and iron oxide phases in agreement of all methods applied. Comparison of Mössbauer spectra taken at 300K and at 20K shows that prevailing amount of oxide particles exhibits superparamagnetic behaviour. The hysteresis loop corresponds well to an assembly of nanoparticles. In the thermomagnetic curve (measured in vacuum at increasing temperature up to 800°C) critical temperatures of the phases a-Fe, Fe3C and g-Fe2O3 can be identified. The part of the curve corresponding to decreasing temperature and subsequent measurement of the Mössbauer spectra witnesses that changes in the phase composition of the sample occurred. During the heating at measurement of the thermomagnetic curve the Fe3C decomposed and important amount of wustite (FeO) was formed. The hysteresis loop indicates particle (grain) coarsening.