An experimental study on thermal diffusivity of nanocrystalline Ag

Thermal diffusivity (TD) and its relation to the microstructure of nanocrystalline Ag (n-Ag), synthesized by inert-gas condensation and in-situ compaction, was investigated by photoacoustic technique. The results indicated that a dramatic decrease of TD in n-Ag (which is about 27% that of p-Ag for the n-Ag with grain size 20 nm) is related to its small grain size and large volume fraction of interfacial component, and originates mainly from reduction of its thermal conductivity. Annealing experiments showed that TD is not only affected by its grain size, but also strongly dependent on the microstructure of the interfaces. The increase of TD with increasing grain size can be explained by attributing it mainly to the rise of effective electron density; while increasing TD by annealing where no substantial grain growth occurred, reflects an increase of electron transmission coefficient during annealing, which could also lead to a rise in effective electron density. In addition, the prompt decrease of TD with decreasing specimen density as it is lower than 93% could be reasonably attributed to the increasing number of extended boundaries in n-Ag.