FREQUENCY AND FIELD-DEPENDENT CONDUCTIVITY IN PD-BASED METAL CLUSTER COMPOUNDS

Ligand stabilized metal cluster compounds and colloids consist of nano meter-size metal cores surrounded by ligand shells. We study the diele ctric properties of randomly packed aggregates of these compounds as a function of temperature T, electric field E and frequency omega. Core s were formed by Pd-atoms and stabilized by a selection of ligands. Th e core size varied between 2.4 and 3.6 nm (monodisperse) and 18 nm (5- 10% dispersion). The dielectric properties of all compounds show scali ng: the same functional dependence of the normalized conductivity on n ormalized frequency irrespective of temperature. The results imply tha t at room temperature at all frequencies below 1 THz exclusively hoppi ng between the particles is seen. More details of the hopping processe s are obtained by varying E. The observed dependences are consistent w ith stochastic models that use random packing of clusters inside the s ample.