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CONTENTS
Volume 2, Number 2, June 2013
 

Abstract
High quality nanoparticles of neodymium barium niobium (NdBa2NbO6) perovskites have been synthesized using an auto ignition combustion technique for the first time. The nanoparticles thus obtained have been characterized by powder X-ray diffraction, thermo gravimetric analysis, differential thermal analysis, Fourier transform infrared spectroscopy, Raman spectroscopy and transmission electron microscopy. UV- Visible absorption and photoluminescence spectra of the samples are also recorded. The structural analysis shows that the nano powder is phase pure with the average particle size of 35 nm. The band gap determined for NdBa2NbO6 is 3.9 eV which corresponds to UV-radiation for optical inter band transition with a wavelength of 370nm. The nanopowder could be sintered to 96% of the theoretical density at 1325oC for 2h. The ultrafine cuboidal nature of nanopowders with fewer degree of agglomeration improved the sinterability for compactness at relatively lower temperature and time. During the sintering process the wide band gap semiconducting behavior diminishes and the material turns to a high permittivity dielectric. The microstructure of the sintered surface was examined using scanning electron microscopy. The striking value of dielectric constant er = 43, loss factor tan s = 1.97 X 10–4 and the observed band gap value make it suitable for many dielectric devices.

Key Words
nanoparticles; combustion synthesis; perovskites; neodymium; barium niobate; sintering

Address
Kumpamthanath Chacko Mathai : Department of Physics, St. Aloysius\'College, Edathua-689573, Kerala, India
Sukumariamma Vidya : Electronic Materials Research Laboratory, Department of Physics, Mar Ivanios College,
Thiruvananthapuram- 695 015, Kerala, India
Sam Solomon : Department of Physics, St. John\'s College, Anchal, Kollam District 691306, Kerala, India
Jijimon Kumpukattu Thomas : Electronic Materials Research Laboratory, Department of Physics, Mar Ivanios College,
Thiruvananthapuram- 695 015, Kerala, India

Abstract
Objective of this study is to calculate gamma buildup factors for pointed and isotropic gamma sources in depleted uranium, uranium dioxide, natural uranium, tin, water and concrete using MCNP4C code. The thickness of the media ranges from 0.5 to 10 mean-free-path (mfp) and gamma energy ranges from 0.5 to 10 MeV. Owing to the outstanding accuracy of MCNP in calculation involving gamma interaction, results fairly match those reported previously. The maximum relative error is 2%.

Key Words
MCNP code; radiation shielding; buildup factors; mean free path; gamma

Address
Abouzar Kiyani :Payam Noor University, Nahavand, Iran
Abbas Ali Karami: Bu-Ali Sina University, Department of Physics, Hamedan, Iran
Marziye Bahiraee: Payam Noor University, Nahavand, Iran
Hossein Moghadamian: Applied Sciences University, Islamshahr Branch, Iran

Abstract
In the present investigation, nanocomposite films with poly(methyl methacrylate) (PMMA) as a polymer matrix and barium titanate as a filler were prepared by solution casting method. Barium titanate nano particles were prepared using Ti(IV) triethanolaminato isopropoxide and hydrated barium hydroxide as precursors and tetra methyl ammonium hydroxide (TMAH) as a base. The nanocomposite films were characterized using XRD, FTIR, SEM and dielectric spectroscopy techniques. Dielectric measurements were performed in the frequency range 100 Hz-10 MHz. Dielectric constant of nanocomposites were found to depend on the frequency, the temperature and the filler fraction. Dissipation factors were also influenced by the frequency and the temperature but not much influenced by the filler fractions. The 10 wt% of BT-PMMA nanocomposite had the lowest dielectric constant of 3.58 and dielectric loss tangent of 0.024 at 1MHz and 25oC. The dielectric mixing model of Modified Lichtenecker showed the close fit to the experimental data.

Key Words
BT-PMMA nanocomposite; XRD; SEM; FTIR; dielectric constant

Address
Ravindra H. Upadhyay and Rajendra R. Deshmukh : Department of Physics, Institute of Chemical Technology, Matunga, Mumbai-400019, India

Abstract
The changes of plastic plateau in the stress-strain curves of annealed polypropylene (PP) films during stretching under room temperature were followed and the corresponding melting properties and microstructure were characterized by differential scanning calorimetry (DSC) and scanning electron microscopy (SEM). It was found that during stretching the plastic plateau disappeared progressively with the increase of drawing ratio. At the same time, the endotherm plateau in DSC curves also disappeared progressively. The presence of the plastic plateau was attributed to the stretching of unstable crystalline part which was formed by tie chains around initial row-nucleated lamellae structure during annealing. During stretching, the unstable part was stretched and converted to bridges connecting separated lamellae. There was direct relationship between the disappearance of plastic plateau and pore formation.

Key Words
polypropylene; row-nucleated lamellae structure; melt-stretching mechanism; micropores;hard elastomer

Address
Caihong Lei, Shuqiu Wu, Ruijie Xu, Yunqi Xu and Xinlong Peng : School of Materials and Energy, Guangdong University of Technology, Guangzhou 510006, China

Abstract
Impedance and electrical conduction studies of Ba(Nd1/2Nb1/2)O3 ceramic prepared using conventional high temperature solid-state reaction technique are presented. The crystal symmetry, space group and unit cell dimensions were estimated using Rietveld analysis. X-ray diffraction analysis indicated the formation of a single-phase cubic structure with space group p Pm3m. Energy dispersive X-ray analysis and scanning electron microscopy studies were carried to study the quality and purity of compound. The circuit model fittings were carried out using the impedance data to find the correlation between the response of real system and idealized model electrical circuit. Complex impedance analyses suggested the dielectric relaxation to be of non-Debye type and negative temperature coefficient of resistance character. The correlated barrier hopping model was employed to successfully explain the mechanism of charge transport in Ba(Nd1/2Nb1/2)O3. The ac conductivity data were used to evaluate the density of states at Fermi level, minimum hopping length and apparent activation energy.

Key Words
ceramics; perovskite; lead-free; permittivity; impedance analysis; electrical conductivity

Address
K. Amar Nath : University Department of Physics, T.M. Bhagalpur University, Bhagalpur 812007, India
K. Prasad, : University Department of Physics, T.M. Bhagalpur University, Bhagalpur 812007, India.
K.P. Chandra : Department of Physics, S.M. College, Bhagalpur 812001, India
A.R. Kulkarni: Department of Metallurgical Engineering and Materials Science, Indian Institute of Technology, Mumbai 400076, India


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