A review of the electrochemical performance of alloy anodes for lithium-ion batteries

http://nanomechanics.mit.edu/sites/default/files/documents/Kumar_03.pdf

Mechanical behavior of nanocrystalline metals and alloys

Principle of equal-channel angular pressing for the processing of ultra-fine grained materials

Understanding the correlation between magnetic properties and nanostructure involves collaborative efforts between chemists, physicists, and materials scientists to study both fundamental properties and potential applications. This article introduces a classification of nanostructure morphology according to the mechanism responsible for the magnetic properties. The fundamental magnetic properties of interest and the theoretical frameworks developed to model these properties are summarized. Common chemical and physical techniques for the fabrication of magnetic nanostructures are surveyed, followed by some examples of recent investigations of magnetic systems with structure on the nanometer scale. The article concludes with a brief discussion of some promising experimental techniques in synthesis and measurements.

Magnetic Properties of Nanostructured Materials

Amorphous ribbons of composition Fe/sub 73.5/Cu/sub 1/Nb/sub 3/Si/sub 13.5/B/sub 9/ have been annealed above their crystallization temperature, which produces a homogeneous, ultrafine grain structure of alpha FeSi with typical grain diameters of 10-20 nm. The temperature dependence of saturation magnetization reveals two different magnetic phases which correspond to the alpha -FeSi grains and the grain boundary phase, respectively. The nanocrystalline material exhibits excellent soft magnetic properties which are discussed within the framework of the random anisotropy model. >

Grain structure and magnetism of nanocrystalline ferromagnets

Nanocrystalline materials an approach to a novel solid structure with gas-like disorder?

Recently, nanometer-sized crystalline materials have been proposed to represent a new solid-state structure which exhibits neither long-range order (like crystals) nor short-range order (like glasses). It was the purpose of this study to test this idea by x-ray diffraction experiments. Nanometer-sized crystalline materials are polycrystals in which the size of the crystallites is a few (1--10) nanometers. Structurally, these materials consist of the following two components, the volume fraction of which is about 50% each: a crystalline component, formed by all atoms located in the lattice of the crystallites, and an interfacial component comprising the atoms situated in the interfaces. It is this interfacial component which was proposed to exhibit an atomic arrangement without short- or long-range order. In order to test this idea, the interference function of nanometer-sized crystalline iron (6-nm crystal size) was measured by x-ray diffraction. The measured interference function was compared with the interference function computed by assuming the interfacial component to be short-range ordered or to consist of randomly displaced atoms (no short- or long-range order). It was found that the experimental interference function can only be matched by the computed one if the interfacial component is assumed to have no short- or long-range order.

X-ray diffraction studies of the structure of nanometer-sized crystalline materials

Nanocrystalline materials, which have been proposed to represent a new solid state structure, are investigated by Mossbauer spectroscopy. Nanocrystalline materials are polycrystals with a crystal size of typically 1–10 nm. These materials consist of two components of comparable volume fractions: a crystalline component and an interfacial component, formed by the atoms located either in the crystals or in the interfacial regions between them. As the atomic configurations of both components are different, two kinds of Mossbauer spectra are expected. Iron nanocrystalline material is found to exhibit a two‐component Mossbauer spectrum, consisting of a crystalline component and a second one with different Mossbauer parameters. The Mossbauer parameters of the second subspectrum are consistent with the model of the interfacial component of a nanocrystalline material.

Investigation of nanocrystalline iron materials by Mössbauer spectroscopy

Nanometer-sized polycrystalline materials are polycrystals prepared by compacting very small crystallites (5--10 nm in diameter) under high pressures. The initial studies of Gleiter and co-workers indicate a wide distribution of interatomic distances within the disordered intercrystalline phase, which can be investigated accurately due to its high relative volume fraction in these materials. In the present paper the investigation of nanometer-sized Fe polycrystals by positron lifetime spectroscopy is reported. The influence of the compacting pressure and thermal annealing was studied. The positron lifetimes ${\ensuremath{\tau}}_{1}$=180\ifmmode\pm\else\textpm\fi{}15 ps, ${\ensuremath{\tau}}_{2}$=360\ifmmode\pm\else\textpm\fi{}30 ps, and long-lived components between 1 and 5 ns, have been observed with saturation trapping of positrons. These values are different from the positron lifetimes in well-annealed bulk iron, in amorphous iron alloys, or in the uncompacted fine nanometer-sized iron crystals (\ensuremath{\tau}=443 ps). Based on the present results the lifetime ${\ensuremath{\tau}}_{1}$ in nanometer-sized Fe polycrystals is attributed to positron trapping in vacancy-size free volumes in the crystallite interfaces. This is in agreement with the hypothesis of an interfacial structure with a wide distribution of interatomic distances. The lifetime ${\ensuremath{\tau}}_{2}$ is ascribed to positron annihilation in microvoids at the intersections of interfaces. Hence, positron lifetime spectroscopy on nanometer-sized polycrystalline materials appears to supply a specific tool for studying the interfacial structure of solids. The long-lived components indicate ortho-positronium (o-Ps) formation in larger voids.

R. Birringer

Papers

Nanocrystalline materials an approach to a novel solid structure with gas-like disorder?

X-ray diffraction studies of the structure of nanometer-sized crystalline materials

Investigation of nanocrystalline iron materials by Mössbauer spectroscopy

Structure of nanometer-sized polycrystalline iron investigated by positron lifetime spectroscopy.

Hydrogen in amorphous and nanocrystalline metals