Showing papers in "Physica B-condensed Matter in 2014"

Metamaterials-based enhanced energy harvesting: A review

Abstract: Advances in low power design open the possibility to harvest ambient energies to power directly the electronics or recharge a secondary battery. The key parameter of an energy harvesting (EH) device is its efficiency, which strongly depends on the conversion medium. To address this issue, metamaterials, artificial materials and structures with exotic properties, have been introduced for EH in recent years. They possess unique properties not easily achieved using naturally occurring materials, such as negative stiffness, mass, Poisson's ratio, and refractive index. The goal of this paper is to review the fundamentals, recent progresses and future directions in the field of metamaterials-based enhanced energy harvesting. An introduction on EH followed by the classification of potential metamaterials for EH is presented. A number of theoretical and experimental studies on metamaterials-based EH are outlined, including phononic crystals, acoustic metamaterials, and electromagnetic metamaterials. Finally, we give an outlook on future directions of metamaterials-based energy harvesting research including but not limited to active metamaterials-based EH, metamaterials-based thermal EH, and metamaterials-based multifunctional EH capabilities.

Bio-inspired green synthesis of Fe3O4 spherical magnetic nanoparticles using Syzygium cumini seed extract

Abstract: A novel and bio-inspired Fe 3 O 4 spherical magnetic nanoparticles (SMNPs) were synthesized using Syzygium cumini ( S. cumini ) seed extract, which is a non-toxic ecofriendly fruit waste material. S. cumini seed extract acts as a green solvent, reducing and capping agent in which sodium acetate acts as electrostatic stabilizing agent. The green synthesized nanoparticles were characterized with the help of various techniques such as X-ray diffraction (XRD), Raman spectroscopy, transmission electron microscopy (TEM), Energy-dispersive spectroscopy (EDS), Vibrating sample magnetometer (VSM), FTIR spectroscopy and nitrogen adsorption and desorption analysis techniques. The XRD study divulged that the synthesized SMNPs have inverse spinel cubic structure. The hysteresis loop of Fe 3 O 4 nanoparticles shows an excellent ferromagnetic behavior with saturation magnetization value of 13.6 emu/g.

Influence of lanthanum on the optomagnetic properties of zinc ferrite prepared by combustion method

Abstract: Pure and lanthanum doped zinc ferrite nanoparticles were synthesized by a combustion method using glycine as fuel. The mechanism of formation of these nanoferrites is discussed briefly. The prepared nanoparticles characterized using powder X-ray diffraction analysis (XRD) revealed the formation of cubic spinel phase with high crystallinity. Average crystallite size, X-ray density and bulk density were found to decrease with an increase in La3+ concentration. The chemical elements and states on the surface of these ferrites were determined using X-ray photoelectron spectroscopy (XPS). The detailed core level spectra of the photoelectron peaks of Zn 2p, Fe 2p, La 3d and O 1s were analyzed. The magnetic behavior of these nanoparticles was studied using a vibrating sample magnetometer (VSM) and corresponding changes in the saturation magnetization (Ms), coercivity (Hc) and remanent magnetization (Mr) were analyzed. The optical behavior of these ferrite nanoparticles was characterized by UV–Diffuse reflectance studies (UV–DRS). From the UV–DRS studies, the optical band gap was found to be in the range of 1.87–1.97 eV. The combustion method significantly produces large amount of products within a short time. Therefore, this method is potentially suitable for manufacturing industries for preparing the magnetic nanoparticles.

Modification and development of electrical and magnetic properties of PVA/PEO incorporated with MnCl2

Abstract: The electrical and magnetic properties PVA/PEO films incorporated with different weight percentage of MnCl 2 prepared by casting technique were studied. The Magnetic properties were investigated by electron spin resonance (ESR) and vibrating sample magnetometer (VSM). The electrical conductivity was enhanced depends on both frequencies and temperatures indicate the existence of charge carriers transported by hopping through defect sites attributed to increase in the number of mobile charge carriers of Mn +2 . The AC conduction mechanism and conduction parameters have been calculated according to the Correlated barrier hopping (CBH) model. ESR spectra reveals aggregated forms of Mn 2+ ions are formed at higher concentration and isolated forms at lower concentration. VSM shows paramagnetic nature for pure MnCl 2 and anti-ferromagnetic nature for doped samples due to overlapping of Mn d-states with valence band.

Physical and optical properties of dysprosium ion doped strontium borate glasses

Abstract: The effect of dysprosium ion (Dy3+) on the optical absorption and band gap energy of strontium borate glass systems prepared by melt quenching technique have been reported. The results show that the broad absorption edge of doped glasses shifts back and forth as a function of Dy2O3 concentrations. The intensities of five prominent and two weak optical transitions change accordingly with Dy2O3 concentrations. The defect centres are induced with the presence of Dy3+ ions in glass samples. This attributes to the intra-configurational (f–f) transitions of Dy3+ ions in glass network. In addition, the decreasing trend of optical band gap energy and Urbach energy can be related to defect centres created by Dy3+ ions. The FTIR study reveals the presence of BO3, BO4 vibration groups and the bending of B–O–B units. The asymmetric stretching of BO3 and BO4 was apparent at higher Dy2O3 concentrations. More tetrahedral BO4 units were formed by increasing Dy2O3 concentrations. The dependency of Dy2O3 concentrations on the optical properties is further discussed with other important physical properties.

Influence of formic acid on electrical, linear and nonlinear optical properties of potassium dihydrogen phosphate (KDP) crystals

Abstract: In present investigation 0.5 and 1 mol% formic acid (FA) added potassium dihydrogen phosphate (KDP) crystals have been grown by a slow evaporation technique. The cell parameters of the grown crystals were determined using single crystal X-ray diffraction analysis. The presence of different functional groups has been qualitatively analyzed by the FT-IR spectral analysis. The optical transparency and optical constants were assessed employing UV–visible studies in the range of 200–900 nm. The wide optical band gap of 1 mol% FA added KDP has been found to be 5 eV. The frequency dependent dielectric measurements were studied for pure and KDP added FA crystals. The enhanced second harmonic generation (SHG) efficiency of grown crystals was determined by a classical Kurtz–Perry powder technique. The encouraging third order nonlinear properties were examined employing a Z-scan technique using He–Ne laser, at 632.8 nm. The effective negative index of refraction and high figure of merit (FOM) essential for laser stabilization were determined for grown crystals.

Barkhausen noise as a microstructure characterization tool

Abstract: Magnetic Barkhausen noise (mBN) is known to be related to magnetization reversal mechanisms and the underlying microstructure in magnetic materials. However, the quantitative evaluation of the material properties is hindered by the stochastic nature of the method combined with the lack of standardization. In this paper, the results of interlaboratory tests on the same series of samples are presented. Electrical steel samples have been prepared with controlled grain size (11–148 μm) and strain (0–29%) and have been characterized using the mBN technique as developed in three different laboratories. In spite of the different methodologies used, mBN is found to increase with strain and decrease with decreasing grain size, in all cases. Of special interest is the variation of the double-peaked BN envelope with the grain size, with one peak occurring in positive and the other in negative fields. The significance of the methodology used in the correct interpretation of the results for a given material is discussed.

Structural and luminescence studies on Dy3+ doped lead boro–telluro-phosphate glasses

Abstract: This paper reports results obtained on the structural and luminescence properties of Dy3+doped lead boro−telluro-phosphate glasses prepared following the melt quenching technique. FTIR spectra exhibit the presence of B−O vibrations, P−O−P symmetric vibrations and Te−O stretching modes of TeO3 and TeO6 units. The metal–ligand bond was identified through UV−vis−NIR absorption spectra and to determine the band tailing parameter, direct and indirect band gap energy of the prepared glasses. The Judd−Ofelt (JO) intensity parameters (Ω2, Ω4 and Ω6), experimental and theoretical oscillator strengths were also determined and reported. Luminescence measurements were made to determine the transition probability (A), stimulated emission cross-section ( σ P E ) and branching ratio ( β R ) for the transitions that include 4F9/2→6H11/2, 6H13/2 and 6H15/2 bands. The effect of Dy3+ ion concentration on the intensity ratio of yellow to blue emission bands has also been studied and reported. The lifetime corresponding to the 4F9/2 level of the title glasses has been found to decrease with the increase in Dy3+ ion concentration. The chromaticity coordinates (x,y) have been estimated from the luminescence spectra and the suitability of title glasses for white light applications has been analyzed using CIE chromaticity diagram. The variation of optical properties with the concentration of dysprosium oxide content in the glasses have been studied and reported.

The alkali and alkaline earth metal doped ZnO nanotubes: DFT studies

Abstract: Doping of several alkali and alkaline earth metals into sidewall of an armchair ZnO nanotube has been investigated by employing the density functional theory in terms of energetic, geometric, and electronic properties. It has been found that doping processes of the alkali and alkaline metals are endothermic and exothermic, respectively. Based on the results, contrary to the alkaline metal doping, the electronic properties of the tube are much more sensitive to alkali metal doping so that it is transformed from intrinsic semiconductor with HOMO–LUMO energy gap of 3.77 eV to an extrinsic semiconductor with the energy gap of ~1.11–1.95 eV. The doping of alkali and alkaline metals increases and decreases the work function of the tube, respectively, which may influence the electron emission from the tube surface.

A computational study of adenine, uracil, and cytosine adsorption upon AlN and BN nano-cages

Abstract: Density-functional theory calculations are used to investigate the interaction of Al12N12 and B12N12 clusters with the adenine (A), uracil (U), and cytosine (C) molecules. The current calculations demonstrate that these hybrid adsorbent materials are able to adsorb the adenine, uracil, and cytosine molecules through exothermic processes. Our theoretical results reveal improvement in the adsorption of adenine, uracil, and cytosine on Al12N12 and B12N12. It is observed that B12N12 is highly sensitive to adenine, uracil, and cytosine compared with Al12N12 to serve as a biochemical sensor.

Structural and magnetic study of La0.7Sr0.3MnO3 nanoparticles and AC magnetic heating characteristics for hyperthermia applications

Abstract: We investigated structural and magnetic properties and alternating current magnetic heating characteristics of La 0.7 Sr 0.3 MnO 3 nanoparticles with respect to the possible application for magnetic hyperthermia treatments. Using Rietveld Profile refinement of powder X-ray diffraction data, the hexagonal structure has been observed. The particle sizes varied from 20 to 50 nm as the annealing temperature increases from 700 to 900 °C. The hysteresis loop is not observed and the good fit of Langevin function with magnetization data reveals the superparamagnetic nature at room temperature for all samples. Characteristic magnetic parameters of the particles including saturation magnetization in the temperature range 10–300 K, an effective anisotropy constant and a magnetocrystalline anisotropy constant have been determined. The Specific Absorption Rate for 15 mg/mL sample concentration was measured in alternating magnetic fields of 50–80 Oe at a fixed frequency of 236 kHz. In addition, the intrinsic loss power (ILP) has been calculated from SAR values. It is believed that La 0.7 Sr 0.3 MnO 3 nanoparticles with a high ILP will be useful for the in situ hyperthermia treatment of cancer.

Heterogeneous photocatalytic degradation of rose bengal: Effect of operational parameters

Abstract: The photocatalytic degradation of rose bengal dye has been investigated using ZnO nanoparticles as photocatalyst. ZnO nanoparticles were found to be efficient catalyst for the degradation of dye and 98% degradation was observed in 90 min. Effect of various operational parameters such as amount of catalyst (0.25–2.00 g/L), concentration of dye (0.01–0.05 mM) and pH (3–11) of dye solution on the rate of dye degradation was studied. The most favorable results for the degradation of rose bengal were observed at pH 5 at a catalyst loading of 1 g/L. Moreover, hydroxyl radicals have been detected in the photocatalytic reaction mixture by using terephthalic acid photoluminescence probing technique. The reusability of the catalyst has also been studied and catalyst was found to be active even after being used for 5 times.

Effect of photonic crystal and frequency selective surface implementation on gain enhancement in the microstrip patch antenna at terahertz frequency

Abstract: In this paper, microstrip patch antenna with frequency selective surface (FSS) and photonic band gap (PBG) structures in the frequency range of 0.5–0.7 THz is presented for wireless communications. Proposed patch antenna is designed on a substrate with uniform and non-uniform PBG structures. Here, the effects of substrate thickness, various radii and arrangement of holes on antenna resonance in both PBG forms are studied. Near zero characteristic on uniform and non-uniform PBG substrate is compared and the results show that along with increase in hole radius, antenna operating frequency and bandwidth are increased. Also, the FSS structure is designed as a perfect absorber. Finally, by using FSS and PBG structures simultaneously, gain enhancement, increase in directivity and pattern shaping are studied at THz field. The antenna gain in final structure is increased by 2 dBi (32%) in comparison to simple form and Half-Power beam width is reduced from 100°×80° in simple form to 72°×48° by using FSS and PBG. All simulations and designs are done by Ansoft HFSS and CST Microwave Studio simulation tools with different full wave methods.

A UV-prepared linear polymer electrolyte membrane for dye-sensitized solar cells

Abstract: The effects of LiClO4 and LiFS3SO3 on poly(glycidyl methacrylate)-based solid polymer electrolyte and its photoelectrochemical performance in a dye sensitized solar cell consisting of FTO/TiO2–dye/P(GMA)–LiClO4–EC/Pt were investigated. The electrochemical stability of films was studied by cyclic voltammetry (CV). The highest ionic conductivities obtained were 4.2×10−5 and 3.7×10−6 S cm−1 for the film containing 30 wt% LiClO4 and 25 wt% LiCF3SO3, respectively. The polymer electrolytes showed electrochemical stability windows up to 3 V and 2.8 V for LiClO4 and LiCF3SO3, respectively. The assembled dye-sensitized solar cell showed a sunlight conversion efficiency of 0.679% (Jsc=3 mA cm−2, Voc=0.48 V and FF=0.47), under light intensity of 100 mW cm−2.

Structural, optical and electrochromic properties of RF magnetron sputtered WO3 thin films

Abstract: Thin films of tungsten trioxide (WO 3 ) have been prepared by RF reactive magnetron sputtering of tungsten target at different substrate temperatures in the range 303–673 K and at fixed oxygen partial pressure of 6×10 −2 Pa and sputter pressure of 4 Pa. The effect of substrate temperature on the structural, morphological, optical and electrochromic properties of WO 3 films was systematically studied. The films formed at 303 K were of X-ray amorphous, while those deposited at substrate temperatures ≥473 K were crystallized into orthorhombic phase WO 3 . The crystallite size of the films increased from 17 to 24 nm with increase of substrate temperature from 473 to 673 K. Raman studies confirmed that the presence of O–W–O and W=O bonds in WO 3 films. The surface morphology of the films was significantly varied with substrate temperature. The optical transmittance data revealed that the optical band gap increased from 3.08 to 3.48 eV and refractive index increased from 2.18 to 2.26 with increase of substrate temperature from 303 to 673 K respectively. The WO 3 films formed at substrate temperature of 473 K exhibited better optical transmittance modulation of 40% between colored and bleached state with a color efficiency of 33.8 cm 2 /C and diffusion coefficient of 1.85×10 −11 cm 2 /s.

Spectroscopic properties and luminescence behaviour of europium doped lithium borate glasses

Abstract: Li2O–MO–B2O3 (MO=ZnO, CaO and CdO) glasses doped with europium are prepared by using the melt quenching technique to study their absorption and luminescence properties to understand their lasing potentialities. The XRD pattern of the glasses confirmed the amorphous nature and the IR spectra reveal the presence of BO3 and BO4 units in the glass network. Judd–Ofelt intensity parameters Ω λ (λ=2, 4, 6) are evaluated from the intensities of various absorption bands of optical absorption spectra. The J–O parameters have been used to calculate transition probabilities (A), lifetime ( τ R ), branching ratios ( β R ) and stimulated emission cross-section ( σ P ) for the 5D0→7FJ (J=1–4) transitions of the Eu3+ ions. The decay from the 5D0 level of Eu3+ ions in these glasses has been measured and analysed. Branching ratios and stimulated emission cross-sections measured for all these glasses show that the 5D0→7F1 transition under investigation has the potential for laser applications. The high stimulated emission cross-section and branching ratios from the present glasses suggests their potential for infra red lasers. The study of the thermoluminescence is also carried out and the data suggests that the CdBEu glass is suitable for thermoluminescence emission output among the three Eu3+ doped glasses.

Generation of white-light from Dy3+ doped Sr2SiO4 phosphor

Abstract: A single host lattice white light emitting Sr 2 SiO 4 :Dy 3+ powder phosphor was synthesized by solid state reaction process using a temperature of 1000 °C. The structure, particle morphology, chemical composition and oxidation states, photoluminescence (PL) and decay properties of the phosphor were analyzed using X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy and PL spectroscopy, respectively. The objective of this study was to prepare a phosphor that can be used in white light emitting diodes. The XRD patterns showed a monoclinic structure of Sr 2 SiO 4 with minor incidental secondary phases from unreacted precursors. An agglomeration of particles with irregular shapes was observed from the SEM micrographs. The PL emission spectra of the Sr 2 SiO 4 :Dy 3+ phosphor excited at 350 nm consist of blue, yellow and red line emissions at 486 nm, 575 nm and 668 nm corresponding respectively to the ( 4 F 9/2 → 6 H 15/2 ), ( 4 F 9/2 → 6 H 13/2 ) and ( 4 F 9/2 → 6 H 11/2 ) transitions of Dy 3+ . The combination of these emissions constituted white light as indicated on the Commission Internationale de L'Eclairage chromatic coordinate diagram. The decay characteristics show that the phosphor consists of a single exponential decay process.

Synthesis by molten salt method of the AFeO3 system (A=La, Gd) and its structural, vibrational and internal hyperfine magnetic field characterization

Abstract: Polycrystalline samples of LaFeO3 and GdFeO3 were synthesized by the molten salt method. Some properties and the quality of the resulting compounds were investigated. The crystal structure and purity of the samples were determined through X-ray diffraction and Rietveld analysis. The vibrational properties were characterized by Raman and IR spectroscopy. Mossbauer spectroscopy was used to determine the ionic state of the Fe ions and the internal hyperfine magnetic fields. Considerable reduction of the heat treatment (temperature and time) for the reaction to take place was achieved without detriment of the quality of the compounds.

Electrical properties, phase transitions and conduction mechanisms of the [(C2H5)NH3]2CdCl4 compound

Abstract: The [(C 2 H 5 )NH 3 ] 2 CdCl 4 hybrid material was prepared and its calorimetric study and electric properties were investigated at low temperature. The X-ray powder diffractogram has shown that the compound is crystallized in the orthorhombic system with Abma space group, and the refined unit cell parameters are a =7.546 A, b =7.443 A, and c =21.831 A. The calorimetric study has revealed two endothermic peaks at 216 K and 357 K, which are confirmed by the variation of f p and σ dc as a function of temperature. The equivalent circuit based on the Z-View-software was proposed and the conduction mechanisms were determined. The obtained results have been discussed in terms of the correlated barrier hopping model (CBH) in phase I (low temperature (OLT)), non-overlapping small polaron tunneling model (NSPT) in phase II (room temperature (ORT)) and the overlapping large polaron tunneling model in phase III (high temperature (OHT)). The density of localized states N F ( E ) at the Fermi level and the binding energy W m were calculated. The variation of the dielectric loss log( e ʺ) with log( ω ) was found to follow the empirical law, e ″= B ω m ( T ) .

Structural, dielectric and magnetic properties of cobalt ferrite prepared using auto combustion and ceramic route

Abstract: Cobalt ferrite is synthesized by using low temperature auto combustion and high temperature ceramic methods. The prepared samples have values of lattice constant equal to 8.40 A and 8.38 A for auto combustion and ceramic methods respectively. The FTIR spectrum of samples of the auto combustion method shows a high frequency vibrational band at 580 cm−1 assigned to tetrahedral site and a low frequency vibrational band at 409 cm−1 assigned to octahedral site which are shifted to 590 cm−1 and 412 cm−1 for the ceramic method sample. SEM micrographs of samples show a substantial difference in surface morphology and size of the grains between the two methods. The frequency dependent dielectric constant and ac conductivity of the samples measured from 1 Hz to 2 MHz at room temperature are reported. The room temperature magnetic hysteresis parameters of the samples are measured using VSM. The measured values of saturation magnetization, coercivity and remanent magnetization are 42 emu/g, 1553 Oe, 18.5 emu/g for the auto combustion method, 66.7 emu/g, 379.6 Oe, and 17.3 emu/g for the ceramic method, respectively. The difference in preparation methods and size of the grains causes interesting changes in electrical and magnetic properties.

Monte Carlo study of a mixed spin (1, 3/2) ferrimagnetic nanowire with core/shell morphology

Abstract: In this work, Monte Carlo simulation based on Metropolis algorithm was used to study the magnetic behavior of a ferrimagnetic nanowire on a hexagonal lattice with a spin-3/2 core surrounded by a spin-1 shell layer with antiferromagnetic interface coupling in the presence of the crystal field interactions. The influences of the crystal field interactions, the interfacial and core couplings on the critical and compensation behaviors of the nanowire, are investigated. The results present rich critical behavior, which includes the first-and second-order phase transitions, the tricritical and critical end points. In addition, the compensation points can appear for appropriate values of the system parameters.

Study of structural effect on Eu-substituted LSMO manganite for high temperature coefficient of resistance

Abstract: In this work, Eu substituted La0.7Sr0.3MnO3 (LSMO) is studied to achieve high temperature coefficient of resistance (TCR). The compounds La0.7−xEuxSr0.3MnO3 with x=0, 0.1 0.2 and 0.3 are prepared by solid state reaction route and their structural and transport properties are examined by different characterization techniques. The metal–semiconductor/insulator transition temperature (TMI) decreases from 390 K (for x=0) to 240 K (for x=0.3) with decrease in average ionic radius 〈 r A 〉 of A-site. The maximum TCR percentage of La0.7−xEuxSr0.3MnO3 compound is found to be increased for x=0.2 (1.9%) and for x=0.3 (3.36%) compared to its parent compound La0.7Sr0.3MnO3 (1.1%). The substitution of Eu increases the lattice distortion, which enhances the TCR value from 1.1% to 3.36%. The robustness of distortion increases with decreasing 〈 r A 〉 which is well correlated with the high magneto-resistance, and high TCR findings.

Effect of rare earth oxides and La3+ ion concentration on some properties of Ni–Zn ferrites

Abstract: The effect of both the rare earth ions and the La 3+ ion concentration on the dielectric properties of Ni 0.5 Zn 0.5 R y Fe 2− y O 4 ; 0.0≤ y ≤0.9, R=La, Yb, Dy and Ce is studied. All the samples are sintered at 1250 °C with heating rate of 4 °C/min and sintering time of 35 h. The ionic radii of the used rare earth (Yb 3+ , Dy 3+ , Ce 3+ and La 3+ ) are too large to occupy the octahedral site. They form a secondary phases on the grain boundaries. The X-ray data shows that the lattice parameter for the un- substituted ferrite sample is larger than the substituted one, which is the main feature for all rare earth elements. The dielectric properties show that the pure sample has a larger dielectric constant as well as a larger valence exchange with respect to substituted one. This means that introducing rare earth ions into the samples decreases e ′ owing to the decreasing Fe–Fe interaction. The lowest conduction for La substituted sample is attributed to the nature of La 3+ ions which is insoluble in the spinel lattice so it hindered Fe–R (3d–4f) coupling. This feature can help to obtain well applicable ferrites.

Ferromagnetism and ferroelectricity in Fe doped BaTiO3

Abstract: We report the investigation of crystal structure, magnetic and dielectric properties of BaTi 1− x Fe x O 3 samples for x =0.0–0.3. The parent compound is found to crystallize in tetragonal structure while Fe doped samples are found to crystallize in the mixture of tetragonal and hexagonal phases but they are free from any impurity phase. Room temperature ferromagnetism with the transition temperature ( T c ) of 462 K was observed for x =0.3 sample. Fe doped samples exhibit ferroelectric transition with transition temperature ( T cF ) in the range of 390 K for x =0.0–312 K for x =0.2. The dielectric constant, e′ is found to decrease with the increase in doping concentrations.

Application of Cu2O-doped phosphate glasses for bandpass filter

Abstract: Phosphate glasses doped with copper ions having general composition 42P 2 O 5 –39ZnO–(18− x ) Na 2 O–1CaO– x Cu 2 O [ x =2, 4, 6, 8, 10 mol%] were prepared using a conventional melt-quench technique. Physical and chemical properties of the glasses were investigated using X-ray diffraction technique and UV–visible optical absorption. The density was measured by Archimedes׳ method, and molar volume ( V M ) was calculated. It is found that density and molar volume show opposite trend by increasing Cu 2 O content. Absorbance and transmittance at the normal incidence are measured by a spectrophotometer in the spectral range of 190–1100 nm. Analyses of the obtained results were considered in the frame of current theories. Absorption data were used for absorption coefficient, the optical band gap ( E opt ), the cutoff in UV and IR bands to the bandpass filter, which confirmed the optical properties of this type of filter. E opt values for different glass samples are found to decrease with increasing Cu 2 O content.

Conductivity studies of LiCF3SO3 doped PVA: PVdF blend polymer electrolyte

Abstract: Different composition of lithium ion conducting PVA: PVdF: Lithium triflate (LiCF3SO3) polymer electrolytes have been prepared by solution casting technique. Dielectric and conductivity studies have been carried out for the prepared samples. The addition of salt into the polymer matrix increases the ionic conductivity of blend polymer electrolytes. The conductivity analysis reveals 80PVA: 20PVdF: 15LiCF3SO3 polymer electrolyte exhibits the maximum ionic conductivity of 2.7×10−3 S cm−1 at 303 K. The temperature dependence of ionic conductivity for all the composition of PVA: PVdF: LiCF3SO3 polymer films obey Arrhenius relation. Low activation energy has been obtained for highest conducting sample. The dielectric spectra show absolute β-relaxation peak.

Structural, optical and magnetic properties of Cr doped SnO2 nanoparticles stabilized with polyethylene glycol

Abstract: Pure and Cr (1, 3, 5 and 7 at%) doped SnO 2 nanoparticles were synthesized in aqueous solution by a simple chemical co-precipitation method using polyethylene glycol (PEG) as a stabilizing agent. The effect of Cr doping on the structural, optical and magnetic properties of SnO 2 nanoparticles was investigated. EDAX spectra confirmed the presence of Sn, O and Cr in near stoichiometry. XRD patterns revealed that particles of all samples were crystallized in single phase rutile type tetragonal crystal structure (P4 2 /mnm) of SnO 2 . The peak positions with Cr concentration shifted to higher 2 θ values. Lattice parameters were also decreased with increasing Cr concentration. TEM studies indicated that the particle size is in the range of 8–10 nm. The optical absorption studies indicated that the absorption edge shifted towards lower wavelengths with inclusion of Cr content. FTIR spectrum displays various bands that are due to fundamental overtones of PEG and O–Sn–O entities. Further it revealed that the undoped and as well as Cr doped SnO 2 nanoparticles were capped by PEG. Magnetization measurements at room temperature revealed that all the doped samples were ferromagnetic in nature. Well defined strong room temperature ferromagnetic hysteresis loop was observed for 1% Cr doped SnO 2 nanoparticles.

Luminescence of Ce doped MgAl2O4 prepared by the combustion method

Abstract: Magnesium aluminate (MgAl2O4) has received special attention as a technologically important material because of its attractive properties, such as mechanical strength, chemical inertness, a wideband gap, relatively low density, high melting point, high thermal shock resistance, low thermal expansion coefficient, resistance to neutron irradiation and low dielectric loss. It has also been used as a phosphor host activated by a variety of transition metal and lanthanide ions. A simple combustion method was employed for the preparation of Ce doped MgAl2O4 nanocrystals using metal nitrates as precursors and urea as a fuel in a preheated furnace at 520 °C. The as-prepared samples were annealed in a hydrogen atmosphere to improve their optical properties. The samples thus obtained were characterized by X-ray diffraction (XRD), UV–vis spectroscopy, X-ray photoelectron spectroscopy (XPS), scanning electron microscopy and photoluminescence spectroscopy (PL). The XRD data showed that all the samples had the spinel structure and the average particle size of the as-prepared samples was about 25 nm. PL spectra of Ce doped MgAl2O4 using an excitation wavelength of 350 nm produced broad green emission bands centred at 500 nm. Maximum green emission was obtained for the sample doped with 0.75 mol% Ce. UV–vis diffuse reflectance spectra and XPS were used to obtain more information on the conversion of Ce ions from the non-luminescent Ce4+ to the luminescent Ce3+ charge state.

First principle study of electronic and optical properties of the cubic perovskite BaSnO3

Abstract: Electronic, structural and optical properties of the cubic perovskite BaSnO3 have been calculated using the full potential linearized augmented plane wave (FP-LAPW) based on density functional theory (DFT). Exchange and correlation effects are taken into account by a generalized gradient approximation (GGA) and an orbital independent modified Becke–Johanson (MBJ) potential as coupled with GGA. The structural properties including the lattice constant, the bulk modulus and the pressure derivative of the bulk modulus are calculated. The results of our calculations are in good agreement with available theoretical and experimental data. We have also calculated the energy band gap using MBJGGA. The calculated indirect band gap ( R → Γ ) is 2.65 eV, while the smallest direct band gap ( Γ → Γ ) is 3.0 eV. The real and imaginary parts of dielectric function, refractive index, real part of optical conductivity, optical absorption coefficient and the energy loss function are also calculated. Furthermore, we have analyzed the interband contribution to the optical properties of the cubic BaSnO3 using the calculated band structure and the density of states. The spin–orbit coupling has been taken into account to calculate the frequency-dependent dielectric function and it is found to be quite small.

Enhanced magnetic and electrical properties of Y and Mn co-doped BiFeO3 nanoparticles

Abstract: Multiferroic (Y, Mn) substituted BiFeO3 had been synthesized by a facial sol–gel method. The single phase polycrystalline nature of samples was confirmed from X-ray diffraction pattern. The average particle size was estimated to be around 30–32 nm from transmission electron microscopy. The magnetic properties of codoped nanoparticles had been studied using Bloch equation and the estimated value of the Bloch constant was found to be much larger than usual ferromagnetic materials. Coercivity values for different temperature is used to calculate the blocking temperature and found to lie above room temperature. The dc electrical transport properties were studied in the temperature range 298– 523 K and explained using a Motts 3D variable range hopping model and the density of states was estimated near the Fermi level. The ac electrical data were found to follow the correlated barrier hopping model. Well-developed PE hysteresis loops were observed in codoped nanoparticles, which were attributed to a decrease in oxygen vacancies, bismuth volatisation due to doping and an increase of the effective potential barrier height for charge carriers.