Structure and properties of nanoparticle glass composites

Ag nanoparticles of 1(.)5-7 nm mean size were prepared in soda-lime-silica glasses of varying iron oxide content. The presence of crystalline Ag particles was established and their shape and size characteristics were determined by electron microscopy. The lattice parameters of individual particles were determined using high-resolution electron microscopy at room temperature. These data revealed nearly no dependence on particle size or only a slight lattice dilatation for smaller particles in ion exchanged soda-lime-silica glass with high iron oxide (0(.)865% Fe2O3), but a distinct size dependent lattice contraction in glasses with low iron (0(.)13% Fe2O3). Temperature dependent EXAFS (extended x-ray absorption fine structure) spectra (-263 to 27 degrees C) at the Ag K-edge evaluated on the basis of an anharmonic Einstein model indicate an increasing thermal expansion coefficient for Ag nanoparticles with decreasing size. Dilatometer measurements to determine the thermal expansion coefficient and the glass transition temperature T-g of both, the base glass and the corresponding silver containing one, at temperatures ranging from about -170 to 600 degrees C show a considerable influence of silver incorporation into the glass matrix. By combination of dilatometric data of the matrix and EXAFS parameters of embedded nanoparticles their state of stress may be qualitatively explained.