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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 487 records · Page 27
All sourcesNASA NTRSDOE OSTI
DOE OSTI2014

Effect of samarium doping on the dielectric behavior of barium zircomium titanate ceramic

Samarium doped Barium Zirconium Titanate ceramic with general formula Ba{sub 1−x}Sm{sub 2x/3}Zr{sub 0.05}Ti{sub 0.95}O{sub 3} [x=0.0,0.01,0.02,0.03,0.04] has been prepared by high energy ball milling. The X-ray diffraction (XRD) patterns confirmed that these ceramics have a single phase with perovskite-type upto x≤0.03 and a small secondary phase exist at x=0.04. The temperature dependent dielectric study shows a ferroelectric phase transition and transition temperature decreases with an increase in the Samarium content.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Effect of Ti doping on high pressure behavior of BiMn{sub 2}O{sub 5}

Our high pressure x-ray diffraction studies on BiMn{sub 1.5}Ti{sub 0.5}O{sub 5} show iso-structural phase transition above 12 GPa similar to the one observed in undoped BiMn{sub 2}O{sub 5}; however anisotropic compressional behavior is found to be more enhanced in the doped case. Unlike undoped system, an anomalous lattice expansion along c axis has been observed in BiMn{sub 1.5}Ti{sub 0.5}O{sub 5} above 12 GPa; whereas the b lattice parameter has been found to be more compressible as compared to BiMn{sub 2}O{sub 5}. As doping with Ti reduces the magnetic interactions among Mn ions, the observed changes are suggestive of having adverse magnetic implications in the observed iso-structural phase transition.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Effect of Cu doping on the resistive switching of NiO thin films

Bipolar resistive switching is observed in the GaIn/Cu:NiO film/ITO device with active layer deposited by sol-gel spin-coating. The first-principles calculations indicate that Cu dopants with valence of +1 are located at the substitutional Ni sites rather than the interstitial ones. Cu doping introduces more oxygen vacancies in the film and increases the carrier mobility, however, excessive Cu dopants may assemble at the grain boundary resulting in larger set voltage. Current–voltage measurements indicate that the trap charge limited and space charge limited conduction dominate the high resistance state, while the low resistance state follows the Ohmic mechanism. The switching is attributed to the formation/rupture of oxygen vacancy filaments.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

Effect of Fe doping concentration on photocatalytic activity of ZnO nanosheets under natural sunlight

A facile room temperature, aqueous solution-based chemical method has been adopted for large-scale synthesis of Fe doped ZnO nanosheets. The XRD and SEM results reveal the as-synthesized products well crystalline and accumulated by large amount of interweave nanosheets, respectively. Energy dispersive spectroscopy data confirmed Fe doping of the ZnO nanosheets with a varying Fe concentration. The photoluminescence spectrum reveals a continuous suppression of defect related emissions intensity by increasing the concentration of the Fe ion. A photocatalytic activity using these samples under sunlight irradiation in the mineralization of methylene blue dye was investigated. The photocatalytic activity of Fe doped ZnO nanosheets depends upon the presence of surface oxygen vacancies.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2015

Effect of aluminium doping on structural and optical properties of ZnO thin films by sol-gel method

We systematically investigated the structural, morphological and optical properties of 0.05 mol % Al doped ZnO (Al:ZnO) thin films deposited on glass substrates by sol-gel spin coating method. The influences of Al doping in ZnO thin films are characterized by Powder X-ray diffraction study. ZnO and Al:ZnO thin films have showed hexagonal wurtzite structure without any secondary phase in c-axis (002) orientation. The SEM images also proved the hexagonal rod like morphologies for both films. All the films exhibited transmittance of 70-80% in the visible range up to 800 nm and cut-off wavelength observed at ∼390 nm corresponding to the fundamental absorption of ZnO. The band gap of the ZnO thin films slightly widened with the Al doping. The photoluminescence properties have been studied for Al: ZnO thin films and the results are presented in detail.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

Effect of Zn doping on structural and dielectric properties of tetragonal Ni{sub 1-x}Zn{sub x}Fe{sub 2}O{sub 4} (0.0 ≤ x ≤ 0.5)

A series of Ni-Zn ferrite with compositional formula Ni{sub 1-x}Zn{sub x}Fe{sub 2}O{sub 4} (0.0 ≤ x ≤ 0.5) were prepared by solid-state reaction route. The influence of the Zn content on the structural and dielectric properties of NiFe{sub 2}O{sub 4} was investigated using X-ray powder diffraction (XRD), Raman spectroscopy and dielectric measurements. XRD analysis reveals that the samples are polycrystalline single-phase cubic spinel in structure excluding the presence of any secondary phase corresponding to any structure. Slight variation in the lattice parameter of Zn doped NiFe{sub 2}O{sub 4} has been observed due to difference in ionic radii of cations. Raman analysis reveals the doublet like nature of A{sub 1g} mode for all synthesized samples. Small shift in Raman modes and increment in the line width has been observed with the doping ions. Furthermore, room temperature dielectric properties of all the prepared samples have been reported. It is observed that for each sample the dielectric constant decreases with an increase of frequency and becomes constant at higher frequencies.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

Effect of Ag doping and annealing on thermoelectric properties of PbTe

The present study reveals that annealing Ag doped PbTe thin films enhance thermoelectric properties. Phase formation was identified by using X-ray diffraction measurement. Annealing increases the crystallinity of both undoped and Ag doped PbTe. Electrical resistivity and thermoelectric power measurements are done using four probe and bridge method respectively. The increase in thermoelectric power of Ag doped PbTe is 29 % in comparison to undoped PbTe and it further increases to 34 % after annealing at 250{sup o} C for 1 hour whereas thermoelectric power increases by 14 % on annealing undoped PbTe thin films at same temperature.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

Effects of Er doping on Raman spectra and on the structural properties of YbMnO{sub 3}

Polycrystalline samples of Yb{sub 1-x}Er{sub x}MnO{sub 3} (x= 0, 0.1 and 0.2) were prepared by a solid state reaction procedure. Detailed crystal structure studies were performed using X-ray diffraction data obtained at room temperature. The application of the Rietveld method confirmed the reported hexagonal P6{sub 3}cm phase. Crystallographic parameters for the pure compounds are in agreement with those found in the literature. Changes in the lattice parameters, unit-cell volume, and polyhedral distortions observed in the compounds are explained as a function of x. Raman spectra show that the phonon peaks of Yb{sub 1-x}Er{sub x}MnO{sub 3} slightly shift to lower frequencies with doping.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

Effect of Co doping on structural, optical, magnetic and dielectric properties of Bi{sub 2}Fe{sub 4}O{sub 9}

Polycrystalline Bi{sub 2}Fe{sub 4}O{sub 9} and 2% Co doped Bi{sub 2}Fe{sub 4}O{sub 9} were prepared by solid state reaction route. X-ray diffraction (XRD) result reveals that there is no change in the crystal structure due to Co doping and the compound has orthorhombic structure. UV-visible spectroscopy confirms the decrease in band gap due Co doping. Zero field cooled magnetization measurement at 100 Oe magnetic field shows substantial decrease in the magnetic transition temperature. Room temperature frequency dependent dielectric permittivity at 1V DC bias shows ∼10% increase in Co doped sample with respect to pure Bi{sub 2}Fe{sub 4}O{sub 9}.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2016

Effect of HCl doping on optoelectrical and LPG sensing properties of nanostructured polyaniline thin films

Nanostructure Polyaniline thin films doped with 0.5 M, 0.7 M, and 1 M of HCL were synthesized by simple and inexpensive chemical oxidative polymerization technique at room temperature. All prepared thin films of Polyaniline were characterized by optical absorbance study by UV-visible spectroscopy. The absorbance spectrum of Polyaniline shows three fundamental peaks at 356, 419 and 820 nm with increase in absorption intensity. The electrical study shows magnitude of resistance of HCL doped Polyaniline is dependent on doping level. Furthermore, the thin film of Polyaniline was investigated by Scanning electron microscopy for surface morphology study. The SEM micrograph represents irregular granular morphology. In order to investigate LPG sensing properties, I-V characteristics of the Polyaniline films doped with 0.5 M, 0.7 M, and 1 M of HCL were recorded at room temperature in presence of air and 100 ppm of LPG. The observed values of sensitivity found to be 7.21%, 9.85% and 17.46 % for 0.5 M, 0.75 M, and 1.0 M of HCL doped Polyaniline thin films respectively.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2016

Effect of silver doping on ZnO nanocrystals

Ag doped ZnO nanocrystals were synthesized by co-precipitation method with the nominal compositions (x=0.00, 0.02, 0.04, 0.06). The as-synthesized Ag doped ZnO nanocrystals were characterized by X-ray diffraction (XRD), FTIR and UV-Vis. From XRD patterns samples shows hexagonal structure. The average crystallite size is in the range of 41-47 nm. All as synthesized Zn{sub 1−x}Ag{sub x}O nanocrystals are highly textured, with wurtzite structure along the (101) growth direction. The energy band gap of pure and Ag doped ZnO were calculated from UV-Vis spectra. FTIR spectra were confirmed that Ag substituted into ZnO. Chemical species of the samples were detected using FTIR spectra An increase in the hexagonal lattice parameters of ZnO is observed on increasing the Ag concentration. An optical absorption study shows an increment in the band gap with increasing Ag content. From optical study the samples determines blue shift. Atomic packing fraction (APF) and c/a ratio were calculated using XRD data. It confirms the formation of ZnO with the stretching vibrational mode around at 506 to 510 cm{sup −1}.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2016

Effect of cobalt doping on structural, optical and dielectric properties of TiO{sub 2}

A diluted magnetic semiconductor (DMS) Co-doped TiO{sub 2} is studied here for dielectric properties. Undoped and Co-doped TiO{sub 2} samples were prepared by sol-gel method. The formation of anatase phase has been investigated by X-ray diffraction (XRD). UV-Vis absorption spectra show that the incorporation of Co into the TiO{sub 2} lattice leads to redshift in the optical response, as well as lowering the band gap energy. The defect oriented emissions were seen from photoluminescence (PL) study. The dielectric properties of pure and Co-doped TiO{sub 2} samples were studied in the frequency range of 10 Hz to 10 MHz at different temperatures. Doped sample exhibit low dielectric constant when compared with host system. Both dielectric constant and ac conductivity increases with temperature.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2016

Effect of Cr doping on structural and magnetic properties of ZnS nanoparticles

The structural, optical and magnetic properties of pure and Cr doped ZnS nanoparticles were studied at room temperature. X-ray diffraction analysis confirmed the absence of any mixed phase and the cubic structure of ZnS in pure and Cr doped ZnS nanoparticles. Fourier transfer infrared spectra confirmed the Zn-S stretching bond at 664 cm{sup −1} of ZnS in all prepared nanoparticles. The UV-Visible absorption spectra showed blue shift which became even more pronounced in Cr doped ZnS nanoparticles. However, at relatively higher Cr concentrations a slower red shift was shown by the doped nanoparticles. This phenomenon is attributed to sp-d exchange interaction that becomes prevalent at higher doping concentrations. Further, magnetic hysteresis measurements showed that Cr doped ZnS nanoparticles exhibited ferromagnetic behavior at room temperature.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2016

Effect of cobalt doping on structural and optical properties of ZnO nanoparticles

Cobalt doped ZnO nanoparticles of uniform sizes were prepared by a chemical method using ZnCl{sub 2} and NaOH as the source materials. The formation of Co-doped ZnO nanoparticles was confirmed by transmission electron microscopy (TEM), high resolution TEM (HR-TEM) and selected area electron diffraction (SAED) studies. The optical properties of obtained products were examined using room temperature UV-visible and FTIR spectroscopy. SAED of cobalt doped ZnO nanoparticles shows homogeneous distribution of nanoparticles with hexagonal structure. The HRTEM image of the Co-doped ZnO nanoparticles reveals a clear lattice spacing of 0.52 nm corresponding to the interplanar spacing of wurtzite ZnO (002) plane. The absorption band at 857 cm{sup −1} in FTIR spectra confirmed the tetrahedral coordination of Zn and a shift of absorption peak to shorter wavelength region and decrease in absorbance with Co doping.is observed in UV-Visible spectra.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2016

Effect of Co doping on the structural and dielectric properties of ZnO nanoparticles

This paper reports on the synthesis of Co doped Zn{sub 1-x}Co{sub x}O (x= 0.0, 0.01, 0.02, 0.03 and 0.05) nanoparticles by solution combustion method using urea as a fuel. The Structural and dielectric properties of the samples were studied. Crystallite sizes were obtained from X-ray diffraction (XRD) patterns whose values decreased with increase in Co concentration. The XRD study reveals that Co{sup 2+} ions substitute the Zn{sup 2+} ion without changing the wurtzite structure of pristine ZnO up to Co concentrations of 5%. The dielectric constants, dielectric loss (tanδ) and ac conductivity (σ{sub ac}) were studied as the function of frequency and composition, which have been explained by Maxwell-Wagner type interfacial polarization and discussed Koops phenomenological theory.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2016

Effect of potassium doping on electronic structure and thermoelectric properties of topological crystalline insulator

Topological crystalline insulator (TCI), Pb{sub 0.6}Sn{sub 0.4}Te, exhibits metallic surface states protected by crystal mirror symmetry with negligibly small band gap. Enhancement of its thermoelectric performances needs tuning of its electronic structure particularly through engineering of its band gap. While physical perturbations tune the electronic structure of TCI by breaking of the crystal mirror symmetry, chemical means such as doping have been more attractive recently as they result in better thermoelectric performance in TCIs. Here, we demonstrate that K doping in TCI, Pb{sub 0.6}Sn{sub 0.4}Te, breaks the crystal mirror symmetry locally and widens electronic band gap, which is confirmed by direct electronic absorption spectroscopy and electronic structure calculations. K doping in Pb{sub 0.6}Sn{sub 0.4}Te increases p-type carrier concentration and suppresses the bipolar conduction via widening a band gap, which collectively boosts the thermoelectric figure of merit (ZT) to 1 at 708 K.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2016

Effects of electron doping level on minority carrier lifetimes in n -type mid-wave infrared InAs/InAs1−xSbx type-II superlattices

The minority carrier lifetime (τMC) and equilibrium electron concentration (i.e., the doping level, n0) are both important values that directly determine diffusion current in infrared photodetectors utilizing n-type absorbing regions. Here, time-resolved microwave reflectance measurements are used to non-destructively measure both of these values in mid-wave infrared InAs/InAs1−xSbx type-II superlattices with varying n-type doping levels between 2×1014 cm−3 and 2×1016 cm−3. The measured data are analyzed using carrier recombination theory to determine the doping level ranges where Shockley-Read-Hall (SRH), radiative, and Auger recombination limit τMC. The optimal doping level, which minimizes dark current, is experimentally determined and corresponds to the electron density at which τMC switches from SRH limited to Auger limited behavior. A comparison of two InAs/InAs1−xSbx photodetectors of different equilibrium electron densities demonstrates a decrease in dark current for a doping level near the optimal n0τMC product.

Kadlec, E. A.↗
DOE OSTI2023

Effect of Mg doping on carrier recombination in GaN

Time-resolved photoluminescence measurements have been performed on Mg-doped GaN for Mg concentrations in the low- to mid-10 19 cm -3 . As-grown and annealed (600–675 °C) samples were studied. In the as-grown samples, the nonradiative carrier lifetime was found to be about 200 ps and nearly independent of the Mg concentration. Upon annealing, the carrier lifetimes shorten to ~150 ps but, again, show little dependence on the annealing temperature. The analysis of possible Shockley–Read–Hall recombination centers and their behavior during doping and annealing suggests that the main nonradiative recombination center is the Mg–nitrogen vacancy complex. The weak dependence of the PL decay times on temperature indicates that carrier capture into this center has a very low potential barrier, and the nonradiative recombination dominates even at low temperatures.

36 MATERIALS SCIENCE↗