Dielectric relaxation in interfacial amorphous phase of copper core-copper oxide shell nanocomposites in gel-derived silica glasses

Abstract

Composites of copper core-copper oxide shell nanoparticles in a gel-derived silica glass were prepared by a chemical method. The core-shell structure formed a percolative system within the glass. The copper core had diameters in the range 3.5-4.8 nm with the shell thickness varying from 1.0 to 1.6 nm. The dielectric modulus for these nanocomposites was measured over the frequency range 100 Hz-6 MHz at temperatures varying from 330 to 535 K. The modulus spectra were analyzed by a Kohlrausch-Williams-Watts stretched exponential relaxation function. The exponent β for the nanocomposites was found to have values ~0.47 whereas the value obtained in the case of the precursor glass was 0.67. This clearly brought out the difference between the glass medium and the interfacial amorphous phase generated in the nanocomposites. The activation energies for the dielectric relaxation were found to be in reasonable agreement with those obtained earlier for dc conductivity.