Sensing Behaviour of Some Nanocomposite Systems

Abstract

Silver nanoparticles of diameters 3.4 to 13.2 nm grown at the interfaces between silicate glass and some oxide crystal lites exhibited about six orders of magnitude reduction in resistivity for a relative humidity change from 25% to 80%. Sn-SnO 2 nano core-shell structure prepared within a gel-derived silica glass film by electrodeposition technique fol lowed by heat treatment showed large change in resistivity as a function of humidity. The resistivity also changed due to gas flow of CO 2 , C 2 H 5 OH and NO 2 , respectively. The latter arose because of reduction/oxidation of Sn 4+ /Sn 2+ species present at the shell layer of the nanostructures. Nickel nanosheets of thickness ~0.6 nm grown within the interlayer spaces of Na-4 mica crystallites showed a change of dielectric permittivity (5%) for an applied magnetic field of 1.2 Tesla. An inhomogeneous model was used to explain this behavior. Two dimensional CuO phase was grown within the channels of diameter ~5 nm of mesoporous SiO 2 structure. A magnetodielectric (MD) parameter M.D. of 4.4% was obtained in this case. BaTiO 3 nanoparticles of diameter ~25 nm having pores with diameter 10 nm showed multiferroic behavior which arose due to the presence of oxygen vacancies as a result of large surface area present. An M.D. pa rameter of 11% was found. Similarly mesoporous LiNbO 3 of 10 nm diameter showed an M.D. parameter of ~4.5% at a magnetic field 1 Tesla. A giant magnetocapacitance effect with a value of 44% at 1.5 T was observed in nickel zinc fer rite (NZF) impregnated mesoporous silica. A magnetocapacitance of 51% at magnetic field 1.7 T was found in the case of nanocomposites comprising of iron ion containing silica based nanoglass and mesoporous silica. In the last two ex amples the behavior was explained on the basis of Catalan model of space-charge polarization with extracted values of magnetoresistance of the NZF and nanoglass phases being 58%.