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Physical properties of neodymium tin oxide pyrochlore ceramics

Abstract

In this work, physical properties of neodymium tin oxide pyrochlore ceramics prepared by solid state reaction technique are investigated by means of X-ray diffraction, scanning electron microscopy, ultraviolet-visible light (UV-Vis) spectrophotometry and temperature dependent electrical resistivity measurements. The pyrochlore is observed to have a cubic FCC crystal lattice with lattice parameter of 10.578 Å. The planes of the cubic cell are best oriented in the [2 2 2] direction. From the X-ray, the UV-Vis spectrophotometry and the electrical resistivity data analysis, the grain size, strain, dislocation density, optical and thermal energy band gaps, localized energy band tail states and resistivity activation energies are determined and discussed. The pyrochlore is observed to have an optical energy band gap of ~3.40 eV. This value corresponds to 365 nm UV light spectra which nominates the neodymium tin oxide pyrochlore ceramics for the use as UV sensors.

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Dielectric properties of Bi-substituted LDHs synthesized by co-precipitation and sol-gel methods

Abstract

Magnesium-aluminum-bismuth layered double hydroxides (Mg3Al1−xBix; LDHs) were prepared using both coprecipitation and sol-gel methods. For the preparation of Mg/Al/Bi LDH by the co-precipitation method, the appropriate amounts of dissolved starting materials (Al(NO3)3 · 9H2O, Mg(NO3)2 · 6H2O and Bi(NO3)3 · 5H2O) were mixed with a solution of NaHCO3:NaOH. In the sol-gel processing, the precursor Mg–Al–Bi–O gels were synthesized using the same starting materials and ethylene glycol as complexing agent. The mixed-metal oxides obtained by subsequent heating of Mg–Al–Bi–O gels at 650 °C were reconstructed to Mg3Al1−xBix LDHs in water at 80 °C. All the synthesized products were characterized by X-ray diffraction (XRD) analysis, scanning electron microscopy (SEM) and dielectric measurements.

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Electrodeposition and magnetic properties of ternary Fe-Co-Ni alloy nanowire arrays with high squareness ratio

Abstract

Highly-ordered ternary Fe-Co-Ni alloy nanowire arrays with diameters of about 50 nm have been fabricated by alternating current (AC) electrodeposition into the nanochannels of porous anodic aluminum oxide templates. SEM and TEM results indicate that the alloy nanowires are highly ordered. XRD and HRTEM results show that the ternary FeCoNi alloy nanowires are polycrystalline, with HCP-FCC dual phase structure. Magnetic measurements demonstrate that the ternary alloy nanowire arrays have an obvious magnetic anisotropy with an easy magnetization direction being parallel to the nanowire arrays. Along the easy magnetization direction, the coercivity (Hc) and squareness ratio (S) increase as the annealing temperature increases, and reach a maximum level (Hc = 1337 Oe, S = 0.96) at 300 °C.

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Ferroelectric and dielectric properties of nanocrystalline BiFeO3 multiferroic ceramics synthesized by solution combustion method (SCM)

Abstract

Nanocrystalline multiferroic BiFeO3 ceramics was prepared by a novel solution combustion method (SCM). The X-ray diffraction (XRD) studies on structural properties of the synthesized ceramics reveal that the BiFeO3 ceramics has rhombhohedral perovskite structure with an average crystallite size of 15 nm. The ferroelectric P-E hysteresis loop measurement at room temperature shows unsaturated behavior with a partial reversal of polarization. Investigations on temperature dependence of dielectric constant in BiFeO3 demonstrate a clear dielectric anomaly at approximately around 380 °C, which corresponds to antiferromagnetic to paramagnetic phase transition (TN) and also evidences a possible coupling among the electric and magnetic dipoles of BiFeO3. A room temperature variation of dielectric constant “ɛ” and dielectric loss “tan δ” as a function of frequency in the range of 100 Hz — 1 MHz, confirms that both dielectric constant and loss are strong functions of frequency.

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Linear-nonlinear optical, dielectric and surface microscopic investigation of KH2PO4 crystal to uncover the decisive impact of dopant glycine

Abstract

Present investigation has been started to perform the comparative study of pure and glycine doped KH2PO4 (KDP) single crystals grown by most commercial slow solvent evaporation technique. The grown crystals were subjected to single crystal X-ray diffraction analysis to determine their structural parameters. The linear optical studies of pure and glycine doped KDP crystal have been undertaken within 200 nm to 1100 nm wavelength range by means of UV-Vis studies. The enhancement in second harmonic generation (SHG) efficiency of glycine doped KDP crystal has been determined using a standard Kurtz-Perry powder test. The dielectric measurements have been carried out to explore the impact of glycine dopant on dielectric constant and dielectric loss of KDP crystal. The surface growth habitat and etch pit density of glycine doped KDP crystal have been evaluated using the results of microscopic etching studies. In light of obtained results the suitability of glycine doped KDP crystal for device applications has been discussed.

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Investigation on room temperature photoluminescence of pure and aluminum doped zinc oxide nanoparticles

Abstract

Pure and aluminum doped zinc oxide nanoparticles were prepared by soft chemical method. The prepared nanoparticles were characterized by XRD, SEM-EDAX, UV-Vis, PL and FT-IR studies. XRD patterns revealed that the nanoparticles were crystallized in hexagonal wurtzite structure with an average particle size of 19 nm to 26 nm. The surface morphology was explored using SEM micrographs. The incorporation of aluminum was confirmed by EDAX and FT-IR studies. The band gaps of the particles were found from 3.48 eV to 3.53 eV through UV-Vis spectral studies. The defect related mechanism was investigated using PL measurements. The chemical functional groups in FT-IR spectra proved the formation of pure and aluminum doped zinc oxide nanoparticles.

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Size effect and dielectric properties of NH4H2PO4 — porous glass composites

Abstract

NH4H2PO4 nano-composite antiferroelectric materials in porous glass have been studied by means of dielectric and dilatometric investigations. Dielectric spectroscopy measurements in a wide frequency range are reported here for the first time, for both the antiferro- and paraelectric phases of ammonium dihydrogen phosphate (ADP) embedded in a porous matrix. Low frequency relaxation processes above the phase transition temperature were shown to occur. An investigation of the thermal expansion revealed a negative volume jump at the phase transition point. It was found that the phase transition temperature in ADP crystals embedded in porous glass decreased with the decrease of the mean pore size. The experimentally observed shift of the phase transition temperature is caused by a combination of size and pressure effects.

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Structural and optical properties of pure and Ag doped ZnO thin films obtained by sol gel spin coating technique

Abstract

We have investigated the influence of Ag doping on zinc oxide thin films. Pure and Ag doped, preferentially oriented transparent zinc oxide thin films were prepared by sol gel technique on a glass substrate using diethyl amine as a stabilizer. The X-ray diffraction analysis revealed that the films with hexagonal wurtzite type structure were polycrystalline in nature with a preferred grain orientation in the 101 direction. The crystallite sizes decreased from 34 nm to 27 nm after silver doping. Both photoluminescence and optical transmission measurements showed that the band gap increased after the Ag doping. The structure and optical characterization studies clearly indicated the incorporation of Ag in ZnO. Hence, the observed increase in the optical band gap and decrease in crystallite size can be directly attributed to the effect of Ag ion incorporation into the ZnO lattice.

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Influence of duration time of CVD process on emissive properties of carbon nanotubes films

Abstract

In this paper various types of films made of carbon nanotubes (CNTs) are presented. These films were prepared on different substrates (Al2O3, Si n-type) by the two-step method. The two-step method consists of physical vapor deposition step, followed by chemical vapor deposition step (PVD/CVD). Parameters of PVD process were the same for all initial films, while the duration times of the second step - the CVD process, were different (15, 30 min.). Prepared films were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and field emission (FE) measurements. The I-E and F-N characteristics of electron emission were discussed in terms of various forms of CNT films. The value of threshold electric field ranged from few V/μm (for CNT dispersed rarely on the surface of the film deposited on Si) up to ~20 V/μm (for Al2O3 substrate).

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Capacitive behavior of highly-oxidized graphite

Abstract

Capacitive behavior of a highly-oxidized graphite is presented in this paper. The graphite oxide was synthesized using an oxidizing mixture of potassium chlorate and concentrated fuming nitric acid. As-oxidized graphite was quantitatively and qualitatively analyzed with respect to the oxygen content and the species of oxygen-containing groups. Electrochemical measurements were performed in a two-electrode symmetric cell using KOH electrolyte.

It was shown that prolonged oxidation causes an increase in the oxygen content while the interlayer distance remains constant. Specific capacitance increased with oxygen content in the electrode as a result of pseudo-capacitive effects, from 0.47 to 0.54 F/g for a scan rate of 20 mV/s and 0.67 to 1.15 F/g for a scan rate of 5 mV/s. Better cyclability was observed for the electrode with a higher oxygen amount.

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