Role of Ag₂S nanoparticles on the dynamics of silver ions in silver-ultraphosphate glass nanocomposites

Abstract

Glass nanocomposites in the system xAg₂S-(1-x)(40Ag₂O-60P₂O₅) have been prepared by mixing the reagent grade Ag₂S, AgNO₃, and NH₄H₂PO₄, preheating at 400°C for 1 h, melting at 900-960°C, and finally pressing the melts between aluminum plates to form transparent discs of 1 mm thickness. High resolution transmission electron micrographs (HR-TEM) help to find the constitution and composition of the glass nanocomposites. Ag₂S nanoparticles of typically 10 nm in diameter dispersed in the nanocomposite matrices have been identified. The dynamics of silver ions in these nanocomposites has been studied in a wide frequency range and in a wide temperature range. It has been observed that as x increases from 0.05 to 0.2, the electrical conductivity increases by 1 to 2 orders of magnitude. The activation energy for the electrical conductivity is 0.6-0.5 eV. There is evidence for the involvement of some silver ions in the building up of nanophases. Evaluation of the Ag⁺-ion concentration from the electrical conductivity using the Nernst-Einstein relation shows that typically 1021 cm^-3 ions participate in the conduction, which is 10-20% of the Ag⁺-ion concentration, as evaluated from the chemical composition of the material prepared. The ac electrical conductivity data suggest many interesting properties for the nanocomposites from the point of view of its applications. Ag₂S nanocrystals have also left a signature on the frequency exponent and the crossover frequency. Scaling of the conductivity spectra is observed to be independent of temperature but dependent on Ag₂S content at high frequencies.