Temperature dependence of thermal expansion coefficient of silver nanoparticles and of bulk material determined by EXAFS.

The thermal expansion behaviour of silver fcc has been described by an anharmonic Einstein model using EXAFS data in the temperature range between 10 and 300 K. The linear expansion coefficient of a bulk silver foil agrees well with X-ray diffraction data. In the case of silver particles embedded in a silicate glass matrix, this parameter shows an increase for particles of 3.2 nm in size by 70% whereas samples with an average size of particles of 5.1 nm show no changes compared with bulk fcc. The increase for small particles reflects the size effect as well as the influence of the surrounding matrix of glass. The results reveal a substantial influence of the distribution of particle sizes on the expansion coefficient.