Structure and properties of nanometer-sized materials

Nanometer-sized materials are solids which may be considered as a dense ensemble of atomic clusters with a diameter of a few nanometers. Depending on whether the individual clusters have a crystalline or a glassy structure, nanocrystalline materials or nanometer-sized glasses are formed. Nanocrystalline materials (NCM) are single or multiphase ploy-crystals, the crystal size of which is in the order of a few (typically 1 to 10) nanometers. These materials are of interest for the following three reasons: i. NCM seem to exhibit an atomic structure which differs from the crystalline state (with long range order) and the glassy state (with short range order). NCM seem to represent a new type of solid state structure.ii. The properties of NCM differ (in some cases by several orders of magnitude) from the properties of glasses and/or crystals with the same chemical composition.iii. NCM seem to permit the alloying of conventionally immiscible components such as metals and ceramics. The resulting alloys have been observed to exhibit new properties. If small (1 to 10 nm diameter) glass particles are consolidated, a new type of glasses, called nanometer-sized glasses, are obtained. These nanometer-sized glasses differ structurally from conventional glasses. Their short range order comprises nearest or next nearest neighbours only. The atomic arrangement beyond nearest neighbours seems random.