Fluorinated graphene oxide for enhanced S and X-band microwave absorption

Here we report the microwave absorbing properties of three graphene derivatives, namely, graphene oxide (GO), fluorinated GO (FGO, containing 5.6 at. % Fluorine (F)), and highly FGO (HFGO, containing 23 at. % F). FGO is known to be exhibiting improved electrochemical and electronic properties when compared to GO. Fluorination modifies the dielectric properties of GO and hence thought of as a good microwave absorber. The dielectric permittivities of GO, FGO, and HFGO were estimated in the S (2 GHz to 4 GHz) and X (8 GHz to 12 GHz) bands by employing cavity perturbation technique. For this, suspensions containing GO/FGO/HFGO were made in N-Methyl Pyrrolidone (NMP) and were subjected to cavity perturbation. The reflection loss was then estimated and it was found that −37 dB (at 3.2 GHz with 6.5 mm thickness) and −31 dB (at 2.8 GHz with 6 mm thickness) in the S band and a reflection loss of −18 dB (at 8.4 GHz with 2.5 mm thickness) and −10 dB (at 11 GHz with 2 mm thickness) in the X band were achieved for 0.01 wt. % of FGO and HFGO in NMP, respectively, suggesting that these materials can serve as efficient microwave absorbers even at low concentrations

Magnetoelectric coupling in strained strontium titanate and Metglas based magnetoelectric trilayer

Direct magneto electric coupling is observed with a magnetoelectric coupling coefficient (MECC) of 806 mV cm−1 Oe−1 at 750 Hz in strontium titanate (STO) - Metglas - strontium titanate (STO-Metglas-STO) trilayer thin films with a total thickness of 600 nm. The piezoelectricity in the strained STO layer, which is otherwise a paraelectric material, enabled the sandwiched magneto electric structure to exhibit a fair sub resonant magneto electric coupling. Theoretical models proposed by Bichurin et al. and Hasanyan et al. are employed to calculate the values of MECC at sub resonant condition for the system, which is noted as 853 mV cm−1 Oe−1. The frequency dependence of MECC coefficient is also calculated and the resonance frequency is estimated as 706 Hz.publishe

Preferential exposure of certain crystallographic planes on the surface of spinel ferrites: a study by LEIS on polycrystalline spinel ferrite surfaces

Spinel ferrites are commercially important because of their excellent magnetic and catalytic properties. The study by Low Energy Ion Scattering (LEIS) can reveal atomic scale information on the surface. The surface of selected spinel ferrites was investigated by LEIS. It has been found that it is the octahedral sites which are preferentially exposed on the surface of the spinel ferrites. So the probable planes which are exposed on spinel ferrite surfaces are D(110) or B(111). This prediction using LEIS gives scope for tailor-making compounds with catalytically active ions on the surface for various catalytic reactions

A low-energy ion scattering (LEIS) study of the influence of the vanadium concentration on the activity of vanadium-niobium oxide catalysts for the oxidative dehydrogenation of propane

A series of vanadium-niobium oxide catalysts in which the vanadia content varies between 0.3 and 18 mol% was prepared by coprecipitation. These catalysts were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), low-energy ion scattering (LEIS), and by catalytic testing in the oxidative dehydrogenation reaction of propane. The results of the surface analysis by XPS and LEIS are compared, It is concluded that the active site on the catalyst surface contains 2.0 ± 0.3 vanadium atoms on average. This can be understood by assuming the existence of two or three different sites: isolated vanadium atoms, pairs of vanadium atoms, or ensembles of three vanadium atoms. At higher vanadium concentration more vanadium clusters with a higher activity are at the surface. LEIS revealed that as the vanadium concentration in the catalyst increases, vanadium replaces niobium at the surface. At vanadium concentrations above 8 mol%, new phases such as ß-(Nb, V)2O5 which are less active because vanadium is present in isolated sites are formed, while the vanadium surface concentration shows a slight decrease

On the magnetic properties of ultra-fine zinc ferrites

Zinc ferrite belongs to the class of normal spinels where it is assumed to have a cation distribution of Zn2+(Fe3+)2(O2−)4, and it is purported to be showing zero net magnetisation. However, there have been recent reports suggesting that zinc ferrite exhibits anomaly in its magnetisation. Zinc ferrite samples have been prepared by two different routes and have been analysed using low energy ion scattering, Mössbauer spectroscopy and magnetic measurements. The results indicate that zinc occupies octahedral sites, contrary to the earlier belief that zinc occupies only the tetrahedral sites in a normal spinel. The amount of zinc on the B site increases with decrease in particle size. The LEIS results together with the Mössbauer results and the magnetic measurements lead to the conclusion that zinc occupies the B site and the magnetisation exhibited by ultrafine particles of zinc is due to short range ordering.\ud \u