Abstract
Silver nanoparticles of diameters 3.4 to 13.2 nm grown at the interfaces between silicate glass and some oxide crystallites exhibited about six orders of magnitude reduction in resistivity for a relative humidity change from 25% to 80%. Sn-SnO2 nano core-shell structure prepared within a gel-derived silica glass film by electrodeposition technique followed by heat treatment showed large change in resistivity as a function of humidity. The resistivity also changed due to gas flow of CO2, C2H5OH and NO2, respectively. The latter arose because of reduction/oxidation of Sn4+/Sn2+ 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 SiO2 structure. A magnetodielectric (MD) parameter M.D. of 4.4% was obtained in this case. BaTiO3 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. parameter of 11% was found. Similarly mesoporous LiNbO3 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 ferrite (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 examples 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%.
Highlights
Sensing of humidity, gasses of different kinds, magnetic fields etc. have assumed significance in recent time because of the need to control these in the operation of various devices [1,2,3,4]
Silver particles of diameters in the range of 3.4 nm to 13.2 nm grown at the interfaces between silicate glass and Zn2SiO4, BaTiO3 and LiNbO3 respectively exhibited about four to six orders of magnitude reduction in resistivity for a relative humidity change from 25% to 90%
Sn-SnO2 nano core-shell structure prepared within a silica glass film showed three orders of magnitude resistivity decrease for a relative humidity change from 35% to 95%
Summary
Gasses of different kinds, magnetic fields etc. have assumed significance in recent time because of the need to control these in the operation of various devices [1,2,3,4]. Gasses of different kinds, magnetic fields etc. For humidity and gas sensing the surface area of the device becomes important because this controls the reaction with atomic/molecular species thereby changing some of its physical properties. Metal-metal oxide nano core-shell structure was grown within a suitable glass film for sensing humidity as well as some gasses. Multiferroic systems are ideal for sensing magnetic fields because these exhibit magnetoelectric coupling behavior [5,6]. Such materials are rare in nature and even those reported in the literature posse rather low value of magnetoelectric coupling coefficient [7].
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