Neutron Diffraction Studies on Chemical and Magnetic Structure of Multiferroic PbFe0.67W0.33O3

We report on the single phase synthesis and room temperature structural characterization of PbFe0.67W0.33O3 (PFW) multiferroic. The PFW was synthesized by low temperature sintering, Columbite method. Analysis of powder XRD pattern exhibits single phase formation of PFW with no traces of pyrochlore phase. Detailed analysis of room temperature neutron diffraction (ND) reveals cubic phase at room temperature, space group Pm-3m. The ND pattern clearly reveals magnetic Bragg peak at 2theeta = 18.51 (Q = 1.36{\AA}-1). The refinement of magnetic structure reveals G-type antiferromagnetic structure in PFW at room temperature. The dielectric constant and loss tangent decreases with increasing frequency. The room temperature P-E measurements shows a non-linear slim hysteresis, typical nature of relaxor multiferroics, with saturation and remnant polarizations of Ps = 1.50 microC/cm2 and Pr = 0.40 microC/cm2, respectively.Comment: 3 pages, 5 figures, conferenc

Improvement in flowability of thermo-chemical storage material by using nanostructured additives

Thermal energy storage is an advancing technology for storing energy that encourages clean energy systems without adversely affecting the environment. This technology allows us to use energy at different times by storing it temporarily. For example in a non-conventional energy source like solar thermal power plant, all its energy is produced during broad day light. The excess energy produced during a sunny day is usually stored in the thermal storage materials, which can later be used in the night to generate electricity. One such advantageous way of storing energy is through thermo-chemical storage. In a space craving society, high storage capability makes it an efficient way to store energy. However at present thermo-chemical storage is in its elementary stage, where in its limited to only one pilot scale system. Considering the thermodynamics and kinetics it has been shown that CaO/Ca(OH)2 reaction system is a potential gas/solid thermochemical heat storage system. However the behavior in a lab sized non-moving bed reactor was mainly dominated by heat and mass transfer limitations arising due to small particle size and changes in bulk properties. This was overcome to a certain level using a moving bed reactor but due to the change in the reactor type the flowability factor dominated adversely. Nevertheless during the recent studies at DLR it was found out that small amount of industrial grade SiO2 (Aerosil®) nanoparticles would enhance the flowability of Ca(OH)2 in a considerable way. But in contrast it effects the heat development leading to low thermal efficiency due to the formation of inert side products. In this study it is found out that small amount of nanostructured Al2O3 (Aeroxide®) not only plays a significant role in stabilizing cyclability and bulk properties but also contributes to the overall heat development

Kharif Sorghum in Karnataka: An Economic Analysis

Sorghum, which once occupied more than 18 M ha of area in the country, has been on a continuous decline during the past two decades and has fallen down to 10.39 M ha. Most of the decline in area has occurred in kharif sorghum. This warrants critical examination of the changing scenario of kharif sorghum and identification of the reasons thereof. For the macro analysis, secondary data on various aspects of kharif sorghum have been used, whereas the farm survey data have been used to draw the inferences at the micro level with respect to changing scenario of kharif sorghum. The growth rates in area, production and productivity of kharif sorghum have been computed. The Herfindahl index has been computed to find out crop diversification in the sample districts of Dharwad and Belgaun. The deceleration in the kharif sorghum area in the overall period 1970-71 to 1997-98 and different sub-periods has been found due to the diversion of kharif sorghum area to more remunerative crops like oil seeds (groundnut and sunflower), and pulses. Belgaum district displayed a moderate degree of crop diversification compared to that of Dharwad district. Unfavourable prices, declining yields, inadequate credit and adverse climatic conditions have been identified as the major reasons for the replacement of kharif sorghum crop in the two sample districts. The net returns and benefit-cost ratio have been found low in the cultivation of kharif sorghum compared to those of its competing crops, viz. cotton, green gram and groundnut.Agricultural and Food Policy,

Composition Dependent Room Temperature Structure, Electric and Magnetic Properties in Magnetoelectric Pb (Fe1/2Nb1/2) O3Pb (Fe2/3W1/3) O3 Solid-Solutions

We report on the studies of room temperature (RT) crystal structure, electric and magnetic properties of (1−x) Pb(Fe1/2Nb1/2)O3 – x Pb(Fe2/3W1/3)O3 (PFN1−x – PFWx) (x = 0.0, 0.2, 0.4, 0.6, 0.8 and 1.0) solid solutions through the measurements of X-ray diffraction, FTIR, scanning electron microscopy (SEM), Neutron diffraction, Raman, Magnetic, Mössbauer and ferroelectric measurements. FTIR spectra showed two main perovskite related transmission bands. The SEM analysis shows an average grain size of 2 μm for all the solid solutions. Rietveld refinement was performed on RT X-ray diffraction (XRD) and neutron diffraction (ND), which reveals, the monoclinic phase for x = 0.0 with space group Cm and Cubic phase for x = 1.0 with space group Pm-3m. In other words, increasing x, the samples exhibit a gradual phase transition from monoclinic to cubic. In addition, the Raman spectroscopy corroborates the change in structural symmetry from monoclinic (Cm) to cubic (Pm-3m) on varying x. The coexistence of both monoclinic and cubic symmetries was observed between x = 0.2–0.8. Magnetic measurements shows that, the magnetic phase transition from paramagnetic to antiferromagnetic (AFM) was observed at or above RT for x = 0.6 and above. The magnetic structure was refined using the propagation vector k = (½, ½, ½) and structure was found to be G-type antiferromagnetic. Magnetic properties (M-H loops) shows, a weak ferromagnetic behaviour with antiferromagnetic ordering at RT. At RT, x = 0.0–0.6 the samples exhibits disordered paramagnetic property but weakly coupled with antiferromagnetic domains. But, x = 0.8 and 1.0 samples show antiferromagnetic and they are weakly coupled with paramagnetic domains. The temperature dependent magnetization (M(T)) confirms, the augmentation of Néel temperature (TN) from 155 K to 350 K on increasing x. Mössbauer spectroscopy confirms superparamagnetic nature with the presence of Fe in 3+ state and on increasing x, the spectra changes from doublet to sextet. The ferroelectric (P-E) study confirms the existence of ferroelectric ordering with leaky behaviour. The reasonable ferroelectric loops with antiferromagnetic properties indicate samples with x = 0.2–0.6 show good magnetoelectric characteristics and may find applications in multiferroics

Multiwalled carbon nanotube-based patch antenna for bandwidth enhancement

A novel carbon nanotube (CNT)-based rectangular microstrip antenna for wide impedance bandwidth applications has been designed and developed. The copper patch commonly placed on the substrate in a conventional rectangular microstrip antenna is replaced with a CNT patch prepared using spin coating. The MWCNT patch antenna was fabricated by spin coating method and it exhibits an increased impedance bandwidth of 20. The enhancement of the impedance bandwidth does not affect the broadside radiation characteristics. The carbon nanotubes are highly conductive nanomaterial. Due to this unique property, each nanotube present on the surface resonates electromagnetic waves individually and influences the enhancement in the bandwidth. The simple design and fabrication of the proposed antenna can be employed for synthetic aperture radar applications. © 2017 Elsevier B.V

Structural and magnetic properties of nanocrystalline BaFe12O19 synthesized by microwave-hydrothermal method

Nanocrystalline BaFe12O19 powders were prepared by microwave-hydrothermal method at 200 °C/45 min. The as-synthesized powders were characterized by using X-ray diffraction (XRD), thermogravimetry (TG) and differential thermal analysis (DTA). The present powders were densified at different temperatures, i.e., 750, 850, 900 and 950 °C for 1 h using microwave sintering method. The phase formation and morphology studies were carried out using XRD and field emission scanning electron microscopy (FE-SEM). The average grain sizes of the sintered samples were found to be in the range of 185–490 nm. The magnetic properties such as saturation magnetization and coercive field of sintered samples were calculated based on magnetization curves. A possible relation between the magnetic hysteresis curves and the microstructure of the sintered samples was investigated

Electric field-induced tuning of magnetism in PbFe0.5Nb0.5O3 at room temperature

We study the influence of electrical poling, carried out at room temperature, on the structure and magnetism of Pb(Fe0.5Nb0.5)O-3 by analyzing the differences observed in structural and magnetic properties before and after the electrical poling. The changes observed in magnetization of Pb(Fe0.5Nb0.5)O-3 before and after electrical poling exhibit considerably strong converse magnetoelectric effect at room temperature. In addition, the strengthening of Fe/Nb-O bond due to electrical poling is discussed on the basis of Raman spectral studies and analysis of neutron diffraction patterns. The potential tunability of magnetization with electrical poling can be an ideal tool for realization of application potential of this multiferroic material. (C) 2015 AIP Publishing LLC

Low-temperature neutron diffraction and magnetic studies on the magnetoelectric multiferroic Pb(Fe0.534Nb0.4W0.066)O3

We report detailed low-temperature magnetic and neutron diffraction studies on 0.8 Pb(Fe0.5Nb0.5)O3�0.2 Pb(Fe0.67W0.33)O3 which is written as Pb(Fe0.534Nb0.4W0.066)O3 (PFWN) in the general form. Magnetic susceptibility measurement data show that PFN exhibits antiferromagnetic to paramagnetic transition (TN) around 155 K (Matteppanavar et al. in J Mater Sci 50:4980�4993. doi:10.1007/s10853-015-9046-5, 2015). In the present solid solution, the magnetic susceptibility (�) shows Néel temperature enhanced up to around 187 K. Temperature-dependent neutron diffraction studies well support the tuning up of TN from 155 to 187 K. On decreasing the temperature, for T < TN (TN = 187 K), an extra peak grows at scattering vector Q = 1.35 à �1, which indicates the onset of antiferromagnetic ordering. The observed magnetic structure is G-type antiferromagnetic with the propagation vector, k = 0.25, 0.5, 0.5. The refined monoclinic lattice parameters (a, b and c), angle (β), unit cell volume, derivative of unit cell volume, magnetic moments and integrated intensity of magnetic peak (111) show anomaly around the TN, which is a manifestation of spin�lattice coupling. Also, the lattice parameters (a, b and c) and unit cell volume exhibit negative thermal expansion below TN and a large thermal expansion above TN. © 2017, Springer Science+Business Media New York

Evidence for Room-Temperature Weak Ferromagnetic and Ferroelectric Ordering in Magnetoelectric Pb(Fe0.634W0.266Nb0.1)O3 Ceramic

We report the evidence of weak ferromagnetic and ferroelectric ordering in polycrystalline Pb(Fe0.634 W0.266Nb0.1)O3 (0.8(PbFe2/3W1/3)O3�0.2Pb(Fe1/2Nb1/2) O3) (PFWN) ceramic at room temperature. The Pb(Fe0.634 W0.266Nb0.1)O3solid solution synthesized through the columbite method. The obtained single-phase Pb(Fe0.634 W0.266Nb0.1)O3ceramic was subjected to X-ray diffraction, neutron diffraction, magnetization, Mössbauer spectroscopy, and ferroelectric measurements. The X-ray diffraction and neutron diffraction pattern confirms the formation of single phase without any traces of pyrochlore phases, having cubic structure with Pm-3m space group. The Rietveld refinements were carried out on both patterns, and ND data confirms the G-type antiferromagnetic structure with propagation vector (k = 1/2, 1/2, and 1/2). However, along with the antiferromagnetic ordering of the Fe spins, we also observed the existence of weak ferromagnetism. This result was confirmed through (i) a clear opening of hysteresis (M � H) loop, (ii) bifurcation of the field-cooled (FC) and zero-field-cooled (ZFC) susceptibilities, (iii) spin-glass behavior, and (iv) Mössbauer spectroscopy. © 2016, Springer Science+Business Media New York