Electrical properties of sol-gel derived films containing composites of glass-ceramics and nanocrystalline silver
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Electrical properties of sol-gel derived films containing composites of glass-ceramics and nanocrystalline silver T. K. Kundu and D. Chakravorty Indian Association for the Cultivation of Science, Jadavpur, Calcutta 700 032, India (Received 25 September 1994; accepted 25 September 1995)
Sol-gel-derived films containing BaTiO 3 crystallites have been grown on suitable substrates using a precursor composition in the system Li2 O–BaO–TiO2 . Silver particles of diameters in the range 4.9 to 16.2 nm have been synthesized within these films by ion exchange and reduction technique. Electrical resistivities are found to vary from ,102 to 105 ohm-cm, depending on the silver particle diameter. A low activation energy, approximately a few millielectron volts, is found to characterize the electrical properties of most of the samples. A quantum size effect is invoked to explain the results.
I. INTRODUCTION
Synthesis of nanostructured materials has received major attention because their physical properties may be superior to those having coarser grain structures.1 Extensive research was carried out by Abeles et al.2,3 to elucidate the electrical properties of cermet films prepared by a radio frequency sputtering technique. The films had a microstructure consisting of nanosized metal particles dispersed in a ceramic matrix. One of the results reported was a low value of temperature coefficient of resistance (TCR) in the ceramic-metal nanocomposite systems at a metallic volume fraction ,0.5.4,5 Such a behavior was rationalized on the basis of the presence of both tunnelling and classical percolation contribution to electrical conduction. Recently it has been shown that nanocrystalline metallic particles can be conveniently grown at the glass-crystal interface of a glass-ceramic composite.6,7 We have now prepared by a sol-gel technique thick films of glass ceramics in the system Li2 O–BaO–TiO2 on a suitable substrate. After ion exchange and reduction treatments, nanocrystalline silver particles have been grown within them. The electrical properties of these films have been measured. Semiconducting behavior with a low activation energy is observed at low temperatures in these composites.
of lithium acetate in 10 ml of acetic acid. This solution is added to the solution (A) and the mixture is stirred for 1 h. A film from the above solution is deposited on a chemically cleaned microscope glass slide by a dip coating technique.8 The film is slowly heated, raising the temperature up to 803 K. The temperature is kept constant for 2.5 h, and subsequently the sample is slowly cooled to room temperature. The film thickness is measured from a micrograph taken with a scanning electron microscope (Hitachi Model No. S-415A). The details of this technique have been reported elsewhere.9 The film in the present experiment is found to have a thickness of ,10 mm and it is found to consist of a glass ceramic containing BaTiO3 crystallites of ,3 mm size. The film is subjected to a Li1 Ag1 ion exchange by
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