M. Pal

Effect of Y-doping on optical properties of multiferroics BiFeO3 nanoparticles

We have synthesized yttrium-doped bismuth ferrite nanoparticles through a modified Pechini technique. X-ray diffractometer, transmission electron microscope (TEM) and ultraviolet–visible spectrophotometer (UV–Vis) probes have been utilized to characterize the nanoparticles. Average particle size estimated from TEM found to be 29xa0nm for Bi0.99Y0.01FeO3 samples. The band gap of the prepared BFO and BYFO nanoparticles varies from 1.97 to 2.29xa0eV, that is, within the visible range of the sunlight. This property of these nanoparticles can be utilized in photo catalytic decomposition of organic contaminants, such as Rhodamine-B (RhB) under visible light irradiation. We have explored and observed that RhB degrade up to 8xa0% while mixed with Bi0.90Y0.1FeO3 for 1xa0h under 40xa0W lamp due to photo catalysis together with sensitization.

Giant magnetodielectric and enhanced multiferroic properties of Sm doped bismuth ferrite nanoparticles

Improvements in magnetodielectric and multiferroic properties are essential for visualizing the real application of multiferroics, precisely, BiFeO3 (BFO). An enhancement of multiferroic and magnetodielectric properties has been achieved for chemically prepared nanocrystalline BFO by virtue of Sm doping. The X-ray diffraction study confirms the growth of single phase nanocrystalline BFO which corroborates TEM observation. The magnetic study delineates the ferromagnetic behavior of nanocrystalline Sm-doped BFO samples even at room temperature, which is absent in pristine samples. Surprisingly, a few orders of magnitude increase in resistivity is observed in Sm doped samples. Room temperature ferroelectric measurement showed that Sm doping improves the polarization significantly. In addition, we have achieved a giant change in the magnetodielectric properties of Sm doped samples which has not been reported so far. Large lattice strain arising due to the mismatch of ionic radii and the decrease of oxygen vacancies combined could play an important role in the enhancement of multiferroic properties of nanocrystalline Sm-doped BFO which is a promising multiferroic material.

Effect of Y-doping on the electrical transport properties of nanocrystalline BiFeO3

Effect of yttrium doping on the electrical transport properties of sol-gel prepare nanocrystalline BiFeO3 was investigated. A comprehensive state-of-the art sophisticated instruments like x-ray diffraction, differential thermal analyzer, field emission scanning electron microscope, and HRTEM were utilized to characterize the BiFeO3 nanoparticles. It was observed that the values of dc activation energy calculated from Arrhenius relation increase with increase of yttrium content. The variation of ac conductivity with frequency and temperature exhibits a correlated barrier hopping conduction mechanism. The dielectric permittivity of the sample reveals an increasing tendency with the concentration of yttrium and depends on both the grain and the interfacial grain boundary resistance. The activation energies for the dielectric relaxation estimated from the modulus spectra were found to be reasonably good agreement with those obtained from dc conductivity study.

Preparation of polystyrene–clay nanocomposite by solution intercalation technique

Polymer–clay nanocomposites of commercial polystyrene (PS) and clay laponite were prepared via solution intercalation technique. Laponite was modified suitably with the well known cationic surfactant cetyltrimethyl ammonium bromide by ion-exchange reaction to render laponite miscible with hydrophobic PS. X-ray diffraction analysis in combination with scanning electron microscopy gives an idea of structural and morphological information of PS–laponite nanocomposite for different varying organo-laponite contents. Intercalation of PS chain occurs into the interlayer spacings of laponite for low organo-laponite concentration in the PS–O-laponite mixture. However, aggregation and agglomeration occur at higher clay concentration. The molecular bond vibrational profile of laponite as well as PS–laponite nanocomposite have been explored by Fourier transform infrared spectroscopy. Thermogravimetric analysis along with differential scanning calorimetry results reveal the enhancement of both thermal stability and glass transition temperature of PS due to the incorporation of clay platelets.

AC Conducitivity in Bismuth-Substituted Barium Hexaferrites

Bismuth substituted barium hexaferrites in the composition series BaO·(6- x ) Fe 2 O 3 · x Bi 2 O 3 with 0< x <0.5 have been prepared and their electrical conductivity measured over the temperature range 325 to 510 K. The ac conductivity of the samples obeys a relation σ(ω)∼ω s with s having values in the range 0.5 to 0.8. The electrical conductivity is believed to arise due to the creation of Fe 2+ sites by the reducing action of Bi 3+ ions. The ac conductivity variation is explained on the basis of overlapping-large-polaron-tunnelling (OLPT) mechanism.

Gadolinium substitution induced defect restructuring in multiferroic BiFeO3: case study by positron annihilation spectroscopy

Positron annihilation spectroscopy (PAS) comprising of the measurements of positron lifetime and coincidence Doppler broadening spectra has been carried out to understand and monitor the evolution of the vacancy-type defects arising from the ionic deficiencies at lattice points of the multiferroic perovskite bismuth ferrite (BiFeO3) doped with 1, 5 and 10at% gadolinium (Gd 3+ ) ions. Negatively charged defects in the form of Bi 3+ monovacancies (V 3− Bi ) were present in the undoped nanocrystallites, which strongly trapped positrons. During the successive doping by Gd 3+ ions, the positron trapping efficiency decreased while the doped ions combined with the vacancies to form complexes, which became neutral. A fraction of the positrons got annihilated at the crystallite surfaces too, being evident from the very large positron lifetimes obtained and confirming the nano-size-specific characteristics of the samples. Further, the intercrystallite regions provided favourable sites for orthopositronium formation, although in minute concentrations. The dopant ion-complex formation was also depicted clearly by the defect characteristic S‐W plot. Also, the large change of electrical resistivity with Gd concentration has been explained nicely by invoking the defect information from the PAS study. The study has demonstrated the usefulness of an excellent method of defect identification in such a novel material system, which is vital information for exploiting them for further technological applications. (Some figures may appear in colour only in the online journal)

Adsorption of Cationic Laser Dye onto Polymer/Surfactant Complex Film

Fabrication of complex molecular films of organic materials is one of the most important issues in modern nanoscience and nanotechnology. Soft materials with flexible properties have been given much attention and can be obtained through bottom up processing from functional molecules, where self-assembly based on supramolecular chemistry and designed assembly have become crucial processes and technologies. In this work, we report the successful incorporation of cationic laser dye rhodamine 6G abbreviated as R6G into the pre-assembled polyelectrolyte/surfactant complex film onto quartz substrate by electrostatic adsorption technique. Poly(allylamine hydrochloride) (PAH) was used as polycation and sodium dodecyl sulphate (SDS) was used as anionic surfactant. UV-Vis absorption spectroscopic characterization reveals the formation of only H-type aggregates of R6G in their aqueous solution and both H- and J-type aggregates in PAH/SDS/R6G complex layer-by-layber films as well as the adsorption kinetics of R6G onto the complex films. The ratio of the absorbance intensity of two aggregated bands in PAH/SDS/R6G complex films is merely independent of the concentration range of the SDS solution used to fabricate PAH/SDS complex self-assembled films. Atomic force microscopy reveals the formation of R6G aggregates in PAH/SDS/R6G complex films.

AC Conductivity in Bismuth Oxide Doped Nickel-Zinc Ferrites

Substituted nickel zinc ferrites have been prepared in the composition series Ni 0.5 Zn 0.5 Bi x Fe 2.0- x O 4 with x having values in the range 0.05–0.2. The electrical conductivity of the samples has been measured over the temperature range 150 to 300 K at frequencies ranging from 1 kHz to 1 MHz. The ac conductivity shows a variation of ω s where ω is the angular frequency and s is an exponent having values in the range 0.6 to 0.8. Correlated barrier hopping model is found to be satisfactory in explaining the conductivity which arises due to the presence of Fe 2+ ions. The latter are created because a substantial amount of Bi 3+ gets oxidized to the Bi 5+ state.

UNUSUAL MAGNETIC PROPERTIES OF NANOCRYSTALLINE GdFeO3 PREPARED BY SOLID STATE REACTION ROUTE AT LOWER TEMPERATURE

Unusual magnetic properties of nanocrystalline orthoferrite, GdFeO3, synthesize by conventional solid state reaction (SSR) route based on stoichiometric mixing of Fe2O3 and Gd2O3 is reported here. The structural characterization of these nanoparticles was carried out by using X-ray diffraction (XRD) and high resolution transmission electron microscopy (HRTEM) techniques. We observe that the GdFeO3 phase start to precipitate at 1173 K which is rather lower for a SSR route. XRD and HRTEM studies confirm the growth of highly crystalline single phase GdFeO3 nanoparticles. Magnetic behavior shows the coexistence of weak ferromagnetism along with antiferromagnetic interaction. The field dependence magnetization delineates hysteresis loop at room temperature which is better at lower temperature.