Electrical properties of glass-metal nanocomposites synthesized by electrodeposition and ion exchange/reduction techniqu
- PDF / 2,658,448 Bytes
- 11 Pages / 576 x 792 pts Page_size
- 44 Downloads / 212 Views
Glass-metal nanocomposites involving silver have been grown within ion-exchanged lithia silicate glasses by an electrodeposition technique. The silver particle diameters range from 4.0 to 12.0 nm, depending on the alkali ion concentration in the precursor glass. Most of the samples exhibit metallic behavior. However, the effective Debye temperature characterizing the resistivity variation is found to decrease drastically as the particle size is reduced from 6.0 to 4.0 nm. This arises due to a larger fraction of atoms residing at the surface of the particles. Nanoparticles of silver, copper, and iron, respectively, with diameters ranging from 6.6 to 11.6 nm have also been grown within a glass-ceramic by an ion exchange and reduction technique. The electrical resistivity indicates a temperature dependent activation energy. The data cannot, however, be fitted to either a T~m or T~m law. The activation energy in the temperature range 200 to 300 K is controlled by an electron tunneling mechanism between the metal grains. In the lower temperature range a quantum size effect appears to be operative giving rise to a very low activation energy of the order of a few meV.
I. INTRODUCTION Physics of nanocrystalline materials has become a research area of intense activity lately.1 A number of techniques both physical and chemical have been developed to prepare nanoscale particles of both metals and inorganic compounds. A number of physical properties of these nanomaterials have been measured to explore novel effects in them. Both polycrystalline materials with nanosized grain dimensions2 and nanocomposites consisting of nanometer-sized particles dispersed in a matrix3 have been used for this purpose. Recently we have shown that metallic silver clusters with diameters of the order of a few nanometers can be formed within the surface of an oxide glass by an electrodeposition method.4 A silver-enriched oxide glass surface has been used as the electrolyte for this electrodeposition process. The clusters formed by the latter have a fractal structure. The fractal growth of this structure has been studied in detail for different glass compositions and reported earlier.5 We have now carried out electrical measurements on the glass-metal nanocomposites synthesized by the electrodeposition process referred to above. By changing the composition of the precursor glass, it has been possible to prepare composites with different metal particle diameters. We have also developed a technique involving an ion exchange reaction followed by reduction treatment to grow metallic particles of nanometer dimensions within a glass-ceramic.3'6 The nanoparticles are present J. Mater. Res., Vol. 9, No. 10, Oct 1994
in these materials within the surface to a depth of the order of a few tens of microns. The conductivity of these nanocomposites has been shown to be metallic in nature. The variation of resistivity as a function of temperature indicates that there is a phonon softening effect as the metal particle size is reduced. In some of the nanocomposites
Data Loading...
