Acta Materialia 51 (2003) 3511–3519 www.actamat-journals.com Impedance spectral studies of sol-gel alumina-silver nanocomposites Aji A. Anappara a , S.K. Ghosh a , P.R.S. Warrier b , K.G.K. Warrier a,∗ , W. Wunderlich c a Regional Research Laboratory, Council of Scientific & Industrial Research, Trivandrum 695019, India b Department of Physics, University College, Trivandrum 695001 India c Nagoya Institute of Technology, Ceramics Research, 466-8555 Nagoya, Japan Received 16 January 2003; received in revised form 2 March 2003; accepted 17 March 2003 Abstract The nanocomposite of alumina and silver in different weight percentages (0, 1, 5 and 20%) were prepared through solution sol-gel technique. The densities of the sintered pellets were determined employing Archimedes’ principle. The microstructural features of the nanocomposites were followed by scanning and transmission electron microscopic observations. The ac electrical response of the consolidated Al 2 O 3 -Ag nanocomposite samples was studied using imped- ance spectroscopy. The equivalent parameters were determined using computer simulation of the experimental data. The observed results were interpreted using the physical model and equivalent circuit. The impedance spectral analysis gives the information of the two distinct phases, including the adsorbed moisture content in the nanocomposite.  2003 Published by Elsevier Science Ltd on behalf of Acta Materialia Inc. Keywords: Sol-gel; Nanocomposite; Electrical properties; Impedance spectroscopy 1. Introduction The functional nanocomposites involving a cer- amic matrix and nanosized particles of transition metals, are known to exhibit multifunctional and attractive properties and are identified as potential candidates for structural [1,2], mechanical [3], catalytic [4,5], thermal [6,7], optical [8,9], mag- netic [10,11] electrical [12–15] applications. The ∗ Corresponding author. Tel.: +91-471-2490674, fax: +91- 471-2491712. E-mail address: warrierkgk@yahoo.com (K.G.K. Warrier). 1359-6454/03/$30.00  2003 Published by Elsevier Science Ltd on behalf of Acta Materialia Inc. doi:10.1016/S1359-6454(03)00170-8 mechanism behind such enhanced properties was found to be closely associated to the grain size, distribution, grain morphology, the nature of grain- boundaries and interfaces, the nature of intra-grain defects and interface purity [16]. Particularly, the electrical properties of such nanocomposites depend on its grain, grain-boundary contribution, degree of structural uniformity, variation in electri- cal conduction paths, stability and degradation- time dependent process [17]. Impedance spec- troscopy can be effectively used to differentiate these phenomena from one another by non-invas- ive and non-destructive means [18–20]. The nanoc- omposites of alumina with transition metals are