Shilpi Banerjee

Multiferroic behaviour of nanoporous BaTiO3

Nanoporous BaTiO3 particles with an average diameter of 27 nm have been synthesized using a soft template based on poloxamer. The pore width has been found to be ∼10 nm. The nanoporous particles have a surface area of 107 m2gm−1. This introduces a large surface area leading to the creation of a large number of oxygen vacancies. The latter contributes to the ferromagnetic behavior of the nanoparticles. A multiferroic property was exhibited by these particles. The oxygen vacancy concentration decreased as the BaTiO3 particle size increased. The magnetization decreased with an increase in the particle size. A magnetodielectric parameter of 11% has been observed in this system corresponding to an applied magnetic field of 10 kOe.

Alternating current conductivity and dielectric dispersion in copper-silica nanocomposites synthesized by electrodeposition

Composites of nanometer-sized copper metal with diameters varying from 3.2 to 11.4 nm dispersed in a silica gel medium were synthesized by an electrodeposition method. The ac conductivity and dielectric dispersion of these nanocomposites were measured over the frequency range 0.2 kHz–1.5 MHz at temperatures varying from 150 to 300 K. The ac conductivity showed a frequency dependence of ∝ωn where ω is the angular frequency and n∼0.62 the latter being temperature independent. The quantum mechanical tunneling model was used to explain this result. The dielectric modulus data were analyzed on the basis of a stretched exponential relaxation function. The values of the exponent β as extracted from such analysis were found to be in the range 0.31–0.42 and were temperature independent for different gel compositions. The activation energies were estimated from the temperature variation of frequency at which the imaginary part of the dielectric modulus was maximum. The activation energy value ∼0.24 eV could be expl...

Multifunctional behaviour of mesoporous LiNbO3

Mesoporous LiNbO3 nanoparticles with BET surface area 185 m2 g−1 were synthesized by using Pluronic P123 as soft template. The samples showed three functionalities, viz., photoluminescence, ferroelectricity, and ferromagnetism. Room temperature photoluminescence was observed at 390 nm wavelength due to oxygen vacancy. The mesoporous LiNbO3 showed ferromagnetic behavior at room temperature. Ferroelectric behavior of the samples was confirmed from the P-E hysteresis loop measurement. The samples showed a magneto-dielectric effect with the dielectric constant increasing by ∼4.5% for an applied magnetic field of 10 kOe due to magnetostriction of the material which changed the lattice parameter to bring about an increase in the dipole moment of the unit cell.

Magnetodielectric effect in Ni0∙5Zn0∙5Fe2O4–BaTiO3 nanocomposites

Composites comprising of nanoparticles of Ni0∙5Zn0∙5Fe2O4 (NZF) and BaTiO3 (BT), respectively were synthesized by a chemical method. The particles had diameters in the range of 15–31 nm. NZF was prepared by a coprecipitation technique. This was soaked in a sol containing BT. Compositions synthesized were xNZF-(1 – x) BT, where x = 0∙7, 0∙5 and 0∙3, respectively. The composites showed ferromagnetic hysteresis loops due to NZF phase. The analysis of coercivity variation as a function of temperature gave blocking temperatures in the range of 306–384 K depending on the diameter of the ferrite nanoparticles. This implied that superparamagnetic interactions are above these temperatures. The nanocomposites also exhibited ferroelectric behaviour arising due to the presence of BT. The remanent polarization of the samples was small. This was adduced to the nanosize of BT. The specimens showed magneto-dielectric (MD) effect in the magnetic field range 0–0∙7 Tesla. The MD parameter measured at the maximum magnetic field was around 2%. This was one order of magnitude higher than that reported so far in similar composite systems. This was explained on the basis of a two-phase inhomogeneous medium model with an interface between them, the phases possessing drastically different electrical conductivities.

Magnetodielectric effect of CuO grown within highly ordered two dimensional mesoporous silica template SBA 15

A two component, inhomogeneous medium can produce magnetodielectric (MD) effect without any magnetoelectric coupling. Here, we have prepared an inhomogeneous material by growing CuO within two dimensional mesostructures of silica template SBA-15 by a single step method. The (CuO)x-(SBA-15)1−x nanocomposites with different weight percentages (x = 0.2, 0.35, and 0.5) were characterized by small angle x-ray diffraction study and transmission electron microscopy. Both studies confirmed the highly ordered hexagonal mesostructure for CuO(20) where 20 is the weight percentage of CuO in nanocomposite (i.e., x = 0.2). The mesostructure was destroyed on increasing the percentage of CuO incorporated. The nanocomposites exhibited magnetodielectric effect with dielectric constant change of 4.4% and 3% for CuO(20) and CuO(35), respectively, at 1.8 T magnetic field. This effect was explained on the basis of a two dimensional inhomogeneous two component composite model. No such effect occurs in CuO(50) due to total disap...

High conductivity and nonlinear Seebeck coefficient of Ag2O containing (Bi–Pb–Sr–Ca–Cu–O) glassy precursors for high Tc superconductors

Electrical conductivities (σdc) of the as-quenched Bi3.5Pb0.5Sr3Ca3Cu4Ox+zAg2O (with z=1, 3, 5, and 10 wt %) glassy precursors for high Tc superconductors are found to be much higher (∼10−5−101 Ω−1cm−1) than those of the corresponding Ag2O free Bi3.5Pb0.5Sr3Ca3Cu4Ox (denoted by BPB) precursor glass (∼10−13−10−6 Ω−1cm−1). This unusually high conductivity is attributed to the increase of carrier concentrations caused by the addition of Ag2O (also observed from the Hall effect measurements). The experimentally observed high values of σdc do not follow Mott’s variable range hopping model which is in sharp contrast to the behavior of the corresponding pure BPB and many other conventional transition metal oxide glasses having high resistivities. Moreover, the Seebeck coefficients (S) of these glassy precursors show nonlinear variations (from negative at lower temperature to positive at higher temperature) which cannot be clearly explained by phonon drag or electron-phonon interaction. This behavior of S which i...

Synthesis and optical properties of nickel zinc ferrite nanoparticles grown within mesoporous silica template

Nanocomposite (NC) of nickel zinc ferrite (NZF) in mesoporous silica template (KIT-6) was synthesized and characterized in this work. Impregnation procedure was used to synthesize NZF nanoparticles within the pores of KIT-6. The samples were characterized by transmission electron microscopy (TEM), FTIR and UV–Vis absorption studies and room temperature (RT) photoluminescence (PL) measurement. The morphology from Transmission Electron Microscopy of the NC showed the ordered porous structure of KIT-6 remained undistorted even after the incorporation of NZF nanoparticles within its pores. From UV–Vis spectra of the NC, a blue shift in the absorption band due to quantum confinement effect was found. Due to some defects present a broad PL peak centred at 490 nm after excitation at 428 nm of the NC was observed.

Multifunctional Mesoporous Nanocomposites

Multifunctional behaviour viz., ferroelectric, ferromagnetic and magnetodielectric coupling has been reported in a number of nanocomposites. The latter were synthesized by growing nanoparticles of different kinds within a suitable matrix. Different morphologies of the particles were introduced. Both natural as well as synthetic mesoporous materials were used to prepare nanocomposite systems. Mesoporous structures with large surface areas and pore volumes were found to be effective in developing most efficient drug delivery systems. For identical reasons such structures were suitable as catalysts in various industrially important reaction processes, as humidity and gas sensors, as magnetic sensors. Mesoporous carbon based nanocomposites used as electrodes were found to improve the efficiency of lithium-ion batteries. Nanocomposites using mesoporous carbon and carbon nanotubes were shown to improve the performance of dye sensitized solar cells. In this article, the above mentioned developments are reviewed and discussed.