BiFeO3 (BFO) is a multiferroic material exhibiting both ferroelectric and antiferromagnetic ordering that has rendered it to a new dimension of multifunctionality. The remarkable property of multiferroic materials stems from the magnetoelectric effect i.e. the coupling between magnetic and electric ordering. Sol-gel technique has been adapted to get the nano BFO particles of ~30nm. BFO nanoparticles have been subjected to irradiation with 35MeV a-particles available at Variable Energy Cyclotron. Irradiation induced defects have been characterized by PAS. Magnetic & electrical polarization studies are going on.
Many materials when subjected to deformation exhibits unstable plastic flow beyond the elastic limit. In certain range of strain rates and temperatures many solid solutions, both substitutional and interstitial, exhibit serrated yielding which is also referred as the Portevin-Le Chatelier (PLC) effect in literature.
Molecular dynamics (MD) simulation has recently become a popular technique to study dislocation dynamics, which ultimately aims to predict the mechanical properties of crystalline materials. In VECC, simulation based works in dislocation dynamics have been initiated and the interesting results show a considerable promise for further contributory research in this important subject area. The primary areas of our interest are behavior of lattice resistance in nano-dimension, interaction between dislocation and defects, understanding the mechanism of dislocation climb at nanovoids etc. using MD simulation technique.
A medical cyclotron facility, is coming up in Kolkata by the Department of Atomic Energy, where we are involved in developing irradiation facilities to carry out accelerator based radiation damage studies on nuclear structural materials.
Microstructural characterization by X-ray diffraction technique are being carried out on nuclear structural materials such as Zirconium based alloys (Zircaloy-2, Zr-2.5%Nb and Zirlo), SS316L and D9 (Ti-modified austenitic stainless steel) in which defects have been introduced by either cold deformation (by hand-filing and cold-rolling) or by irradiation with charged particles (light ions and heavy ions from Variable Energy Cyclotron and ECR source).
Nanotubular structure of poly(3,4-ethylenedioxythiophene)–NiFe2O4 nanocomposites have been synthesized in reverse microemulsion polymerization technique with the nanotube size ~20nm as characterized by Transmission Electron Microscope. The surface capacitance of this nanotubular material has been quite high.
The arrays of cobalt nanowires with diameter 50, 150 and 275 nm were prepared by dc electrodeposition technique. Magnetization study showed the change in magnetic easy axis from axial to perpendicular direction as one increased the length of 50 and 150 nm wire.
Nickel nanowires in the pores of the alumina membranes have been developed by electro-deposition technique. The magnetic properties of the nanowires are changing sensitively with the length and the diameter of the nanowires. Competition between the shape anisotropy, magneto-crystalline anisotropy and strong magneto-static interaction between the nanowires has been observed.
Semiconducting oxides like ZnO display magnetism when doped (or, diluted) with magnetic transition elements. There is a phenomenon of polarization of charge carriers in the semiconductor by the spin of the magnetic elements doped. They are the candidates of the new generation Spintronics, i.e. spin coupled with electronics. ZnO doped with various atomic percentages of the transition metal Co (1-20 at.%) has been synthesized by wet chemical technique employing Zinc & Cobalt acetates. Particle sizes were in the range 60-100nm.
Magnetism can be induced in nontransitional metal oxides through the generation of defects introduced by ion irradiation. we undertook the studies on Argon ion irradiation on nontransitional semiconducting ZnO thin films.grown by RF sputtering at VECC. Thickness of the films were in the range 80-90nm.150 keV Ar (9+) ions were used with a range of 90nm. An onset of magnetism has been observed for the film irradiated at the fluence of 1x1016ions/cm2 evident from magnetization versus temperature plot.
Polyaniline (PANI) of high stability prepared in acidic aqueous solution using water soluble support polymer polyvinyl alcohol (PVA) was subjected to irradiation with 150keV Argon (Ar9+) ion. The dielectric constants are more for the Ar-implanted polymer than the unirradiated one. The dielectric loss is more for the implanted PANI rendering it useful for electromagnetic shielding.
Relaxor ferroelectric materials with a broad transition in dielectric constant have enormous applications in the field of actuators, transformers etc. Lead Zinc Niobate [Pb(Zn1/3Nb2/3)O3] (PZN) is a well known relaxor. But it is Pb-based and is likely to be toxic. To remove Pb, the complex perovskite lead barium zinc niobate, (Pb1-xBax)(Zn1/3Nb2/3)O3 ceramic at x = 0.25 [(Pb0.75Ba0.25)(Zn1/3Nb2/3)O3] was prepared by a columbite precursor method.