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At least 1,369 records · Page 76
All sourcesNASA NTRSDOE OSTI
DOE OSTI2016

Frequency and field dependent dynamic properties of CoFe{sub 2−x}Al{sub x}O{sub 4} ferrite nanoparticles

Highlights: “CoFe{sub 2−x} Al{sub x}O{sub 4} ferrite nanoparticles: Static and dynamic properties” • Grain size reduction with Al{sup 3+} content. • Reduction in Ms, Hc, with increasing Al{sup 3+} content. • Increase in resonance frequency with applied field. • Decrease in resonance field with increase in Al{sup 3+} content. • Decrease in Gilbert parameter with increase in Al{sup 3+} content. - Abstract: Aluminum doped CoFe{sub 2−x}Al{sub x}O{sub 4} (0 ≤ x ≤ 0.9) nanoparticles were synthesized via auto-combustion. Formation of single phase cubic spinel structure was confirmed by X-ray diffraction (XRD) analysis. XRD analysis suggests a linear decrease in lattice cell parameters and grain size (90–55 nm) with the increase in Al{sup 3+} content. The saturation magnetization of samples decrease with increasing Al{sup 3+} content due to magnetic dilution effect. A concomitant linear reduction in coercivity was also observed mainly due to decrease in magnetic anisotropy. Frequency and field dependent dynamic properties of nanoparticles were studied by ferromagnetic resonance (FMR) technique. The resonance frequency increases linearly with magnetic field for all nanoparticles. Magnetic field dependent experimental absorption data (S{sub 21} vs. frequency) were compared with effective medium theory considering an effective demagnetization field and was observed to be in good agreement with each other. High Al{sup 3+} content reduces the Gilbert damping parameter thus making CoFe{sub 2−x}Al{sub x}O{sub 4} as an attractive material for high frequency applications.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Correlation among far-infrared reflection modes, crystal structures and dielectric properties of Ba(Zn{sub 1/3}Nb{sub 2/3})O{sub 3}–CaTiO{sub 3} ceramics

Highlights: • Crystal symmetry decreases with CT concentration from cubic to hexagonal structure. • Lattice constants as well as the ordered degree change with CT concentration. • Ordered structures turn from 1:1 to 1:2 ordering with change of crystal structures. • There is a correlation between FIR phonon modes and dielectric properties. • There is a correlation between FIR phonon modes and crystal structures. - Abstract: Ba(Zn{sub 1/3}Nb{sub 2/3})O{sub 3} (BZN)–CaTiO{sub 3} (CT) microwave dielectric ceramics were synthesized at 1395 °C for 4 h using conventional solid-state sintering technique with different CT contents. The ceramics were characterized by X-ray diffraction (XRD) and far-infrared reflection (FIR) spectroscopy to evaluate correlations among crystal structures, dielectric properties, and infrared modes. XRD results showed that crystal symmetry decreased with increased CT concentration from cubic to hexagonal structure, and lattice constants and ordered degree changed accordingly. Ordered phases transformed from 1:1 to 1:2 ordered structure with crystal-structure change. FIR results demonstrated that two new IR active modes appeared at 300 cm{sup −1}, and another new mode appeared at 600 cm{sup −1} for the x ≥ 0.60 sample, which agreed with the change in crystal structures as confirmed by XRD results. Correlations between FIR modes and dielectric properties were established.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Microstructural, optical and ethanol sensing properties of sprayed Li-doped Mn{sub 3}O{sub 4} thin films

Highlights: • Li doped Mn{sub 3}O{sub 4} was grown on glass substrate via the low cost effective spray pyrolysis technique. • Li doping notably tuned the optical band gap of Mn{sub 3}O{sub 4} thin film. • The incorporation of Li ions was found to provide an enhancement of ethanol sensitivity. - Abstract: Lithium-doped manganese oxide thin films have been deposited onto glass substrate by the spray pyrolysis technique. The effect on structural, morphological, optical and ethanol sensitivity properties of the films with different Li concentrations was investigated. The X-ray diffraction (XRD) studies of Li doped Mn{sub 3}O{sub 4} thin films revealed polycrystalline tetragonal structure with lattice parameters: a = 5.73 Å and c = 9.46 Å. The most intense band at 653.26 cm{sup −1} observed in room temperature Raman spectrum of all films corresponds to the tetragonal crystal structure of Mn{sub 3}O{sub 4}. Optical band gap energy was found to vary in the range of 2.23–2.82 eV by an increase in Li-doping concentration up to 15%. The resistance based gas sensing measurements showed a clear response already at a low ethanol concentration of 0.1%. The films showed promising ethanol sensing behavior; especially the sample doped with 3% of lithium exhibits the most excellent sensing performance.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Investigations of spherical Cu NPs in sodium lauryl sulphate with Tb{sup 3+} ions dispersed in PVA films

Highlights: • Cu NPs were prepared in SDS using 1064 nm laser radiation at fluence 37, 64 and 88 J/cm{sup 2}. • Spherical Cu NPs with average diameter varying between 10 and 50 nm atdifferent fluence. • PL of Tb3+ ions in PVA polymer film is maximum with Cu NPS at fluence 37 J/cm{sup 2}. • PVA films of Cu NPs displayed a highly temperature-dependent electrical conductivity. • These copper NPs embedded PVA films can be used as novel, low-cost sensor materials. - Abstract: Cu nanoparticles (NPs) have been prepared in SDS solution using 1064 nm laser radiation at different fluence 37 J/cm{sup 2}, 64 J/cm{sup 2} and 88 J/cm{sup 2} and structurally characterized. The TEM measurements reveal the presence of nanoparticles of spherical shape with different size. The size of the nanoparticles and their concentration increases with the increase of fluence.The effect of these Cu nanoparticles on the emissive properties of Tb{sup 3+} ion in polymer films has been studied. It is found that emission intensity of Tb{sup 3+} first increases and then deceases both with concentration of Cu NPs as well as with sizes. The PL intensity of Tb{sup 3+} ions is minimum for Cu NPs prepared with highest fluence. It has been explained in term of local field effect. This was also verified by life time measurements. These thin PVA films of copper nanoparticles displayed a highly temperature-dependent electrical conductivity with sensitivity at least comparable to commercial materials which suggest the use of these copper NPs embedded PVA films as novel, low-cost sensor materials.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Preparation and improved photocatalytic activity of mesoporous WS{sub 2} using combined hydrothermal-evaporation induced self-assembly method

Highlights: • One-step method for synthesis of mesoporous WS{sub 2} was proposed. • Role of CTAB surfactant on formation of mesoporous WS{sub 2} was elucidated. • Possible growth mechanism of the mesoporous structure is also reported. • 0.1 wt% mesoporous WS{sub 2} catalyst exhibited high photocatalytic activity under UV light. - Abstract: In this paper, we report mesoporous WS{sub 2} nanosheets with a crystalline network that were synthesized using CTAB as a structure-directing agent via self-assembly induced by hydrothermal and thermal evaporation. Powder X-ray diffraction, Raman spectra, and high-resolution X-ray photoelectron spectroscopy results confirmed the formation of WS{sub 2} structures. Scanning electron microscopy and transmission electron microscopy were used to observe the as-prepared mesoporous frameworks. The mesoporous WS{sub 2} nanosheets have a surface area of 197 m{sup 2} g{sup −1}. A possible growth mechanism is reported for these mesoporous WS{sub 2} nanosheets. The mesoporous WS{sub 2} nanosheets demonstrate high photocatalytic activity. Among different concentrations, 0.1 wt% mesoporous WS{sub 2} shows superior catalytic activity compared to pristine WS{sub 2} nanosheets.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Energy transfer and 2.0 μm emission in Tm{sup 3+}/Ho{sup 3+} co-doped α-NaYF{sub 4} single crystals

Highlights: • Cubic NaYF{sub 4} single crystals co-doped with ∼1.90 mol% Tm{sup 3+} and various Ho{sup 3+} concentrations were grown by Bridgman method. • The maximum fluorescence lifetime was 23.23 ms for Tm{sup 3+} (1.90 mol%)/Ho{sup 3+} (3.89 mol%) co-doped α-NaYF{sub 4}. • The obtained energy transfer rate (W{sub ET}) and energy transfer efficiency (η) of Tm{sup 3+}:{sup 3}F{sub 4} are 1077 s{sup −1} and 95.0%, respectively. • The maximum emission cross section reached 1.06 × 10{sup −20} cm{sup 2}. - Abstract: Cubic NaYF{sub 4} single crystals co-doped with ∼1.90 mol% Tm{sup 3+} and various Ho{sup 3+} concentrations were grown by Bridgman method. The energy transfer from Tm{sup 3+} to Ho{sup 3+} and the optimum fluorescence emission around 2.04 μm of Ho{sup 3+} ion were investigated based on the measured absorption spectra, emission spectra, emission cross section and decay curves under excitation of 800 nm LD. The emission intensity at 2.04 μm increased with the increase of Ho{sup 3+} concentration from 0.96 mol% to 3.89 mol% when the concentration of Tm{sup 3+} was held constantly at ∼1.90 mol%. Moreover, the maximum emission cross section reached 1.06 × 10{sup −20} cm{sup 2} and the maximum fluorescence lifetime was 23.23 ms for Tm{sup 3+}(1.90 mol%)/Ho{sup 3+}(3.89 mol%) co-doped one. According to the measured lifetime of Tm{sup 3+} single-doped and Tm{sup 3+}/Ho{sup 3+} co-doped samples, the maximum energy transfer efficiency of Tm{sup 3+}:{sup 3}F{sub 4} level was 95.0%. Analysis on the fluorescence dynamics indicated that electric dipole–dipole is dominant for the energy transfer from Tm{sup 3+} to Ho{sup 3+}.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Enhanced 2.7- and 2.9-μm emissions in Er{sup 3+}/Ho{sup 3+} doped fluoride glasses sensitized by Pr{sup 3+} ions

Highlights: • Enhanced 2.7 and 2.9 μm emissions were observed in fluoride glass. • Energy transfer mechanism among Er{sup 3+}, Ho{sup 3+} and Pr{sup 3+} was investigated. • High emission cross sections at 2.7- and 2.9-μm were obtained. - Abstract: In this report, Er{sup 3+}/Ho{sup 3+}/Pr{sup 3+} tri-doped fluoride glass was prepared. The enhancement of 2.7 and 2.9 μm emissions from Er{sup 3+}/Ho{sup 3+}doped system were achieved successfully after the addition of Pr{sup 3+}. The combination of low OH{sup −} concentration, low maximum phonon energy and high mid-infrared transmittance is beneficial to the realization of mid-infrared emissions. The energy transfer mechanism among Er{sup 3+}, Ho{sup 3+} and Pr{sup 3+} was investigated. The decay profiles of several levels were measured to further examine the enhanced mid-infrared emissions. Moreover, high stimulated emission cross sections at 2.7- and 2.9 μm (1.08 × 10{sup −20} cm{sup 2} and 2.0 × 10{sup −20} cm{sup 2}, respectively) were determined. Er{sup 3+}/Ho{sup 3+}/Pr{sup 3+} tri-doped fluoride glass might provide a new choice for mid-infrared laser.

36 MATERIALS SCIENCE↗
DOE OSTI2016

A novel blue-greenish emitting phosphor Ba{sub 3}LaK(PO{sub 4}){sub 3}F:Tb{sup 3+} with high thermal stability

Highlights: • The Ba{sub 3}LaK(PO{sub 4}){sub 3}F:Tb{sup 3+} phosphors exhibit a broad excitation band. • The Ba{sub 3}LaK(PO{sub 4}){sub 3}F:Tb{sup 3+} emission color adjust from blue to green. • The Ba{sub 3}LaK(PO{sub 4}){sub 3}F:Tb{sup 3+} show superior thermal stability. - Abstract: Ba{sub 3}La{sub 1−m}K(PO{sub 4}){sub 3}F:mTb{sup 3+}(m = 0.01–0.50) phosphors have been prepared by a traditional high temperature solid-state reaction. XRD analysis verified the apatite-type phase structure of the as-prepared samples, and the morphology has been checked by the Scanning electron microscope (SEM). The emission spectrum of Ba{sub 3}LaK(PO{sub 4}){sub 3}F:Tb{sup 3+} phosphor consists of two regions, blue emission band from 380 to 470 nm and green emission band from 470 to 650 nm. With increasing Tb{sup 3+} ions doped concentration (m), the color hue of Ba{sub 3}La{sub 1−m}K(PO{sub 4}){sub 3}F:mTb{sup 3+}adjusts from blue to green. On the basis of concentration quenching method, the critical distance between Tb{sup 3+} ions is calculated to be 7.98 Å, suggesting that multipolar interaction predominate in quenching process. In addition, the temperature-dependence PL spectra of Ba{sub 3}LaK(PO{sub 4}){sub 3}F:0.01Tb{sup 3+} and Ba{sub 3}LaK(PO{sub 4}){sub 3}F:0.40Tb{sup 3+} phosphor are given,which exhibit superior thermal stability.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Effect of doping ions on the structural defect and the electrical behavior of CaCu{sub 3}Ti{sub 4}O{sub 12} ceramics

Graphical abstract: The dielectric constant decreases with Ta doping, increases with Y doping and keeps almost constant with Zr doping compared with that of pure CCTO. - Highlights: • Y and Ta doping cause different defect types and concentration. • Defect influences the grain boundary mobility and results in different grain size. • Y doping increases the dielectric constant and decreases the nonlinear property. • Ta doping decreases the dielectric constant and enhances the nonlinear property. • Zr doped sample has nearly the defect type and dielectric properties as CaCu{sub 3}Ti{sub 4}O{sub 12}. - Abstract: The microstructure, dielectric and electrical properties of CaCu{sub 3}Ti{sub 4−x}R{sub x}O{sub 12} (R = Y, Zr, Ta; x = 0 and 0.005) ceramics were investigated by XRD, Raman spectra, SEM and dielectric spectrum measurements. Positron annihilation measurements have been performed to investigate the influence of doping on the defects. The results show that all samples form a single crystalline phase. Y and Ta doping cause different defect types and increase the defect size and concentration, which influence the mobility of grain boundary and result in the different grain size. Y doping increases the dielectric constant and decreases the nonlinear property while Ta doping lead to an inverse result. Zr-doped sample has nearly the defect type, grain morphology and dielectric properties as pure CaCu{sub 3}Ti{sub 4}O{sub 12}. The effects of microstructure including the grain morphology and the vacancy defects on the mechanism of the dielectric and electric properties by doping are discussed.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Preparation of gold nanoparticles and determination of their particles size via different methods

Graphical abstract: Preparation of gold nanoparticles via NaBH{sub 4} reduction method, and determination of their particle size, size distribution and morphology by using different techniques. - Highlights: • Gold nanoparticles were synthesized by NaBH{sub 4} reduction method. • Excess of reducing agent leads to tendency of aggregation. • The particle size, size distribution and morphology were investigated. • Particle size was determined both experimentally as well as theoretically. - Abstract: Gold nanoparticles have been used in various applications covering both electronics, biosensors, in vivo biomedical imaging and in vitro biomedical diagnosis. As a general requirement, gold nanoparticles should be prepared in large scale, easy to be functionalized by chemical compound of by specific ligands or biomolecules. In this study, gold nanoparticles were prepared by using different concentrations of reducing agent (NaBH{sub 4}) in various formulations and their effect on the particle size, size distribution and morphology was investigated. Moreover, special attention has been dedicated to comparison of particles size measured by various techniques, such as, light scattering, transmission electron microscopy, UV spectrum using standard curve and particles size calculated by using Mie theory and UV spectrum of gold nanoparticles dispersion. Particle size determined by various techniques can be correlated for monodispersed particles and excess of reducing agent leads to increase in the particle size.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Quadratic general rotary unitized design for doping concentrations and up-conversion luminescence properties of Er{sup 3+}/Yb{sup 3+} co-doped NaLa(MoO{sub 4}){sub 2} phosphors

Highlights: • NaLa(MoO4)2: Er3+/Yb3+ phosphor is synthesized by solid state method. • QGRUD is first applied to the codoping concentration option. • Optimized phosphor presents more stable UC emissions than the commercial phosphor. - Abstract: It is still a great challenge that designing proper codoping concentrations of rare earth ions for achieving intensest expected emission from the studied phosphor. In this work, the quadratic general rotary unitized design (QGRUD) was introduced into the codoping concentration option of NaLa(MoO{sub 4}){sub 2}: Er{sup 3+}/Yb{sup 3+} phosphor for upconversion (UC) applications, and the optimum doping concentrations of Er{sup 3+} and Yb{sup 3+} for achieving maximum UC luminescence intensity, which is close to commercial NaYF{sub 4}:Er{sup 3+}/Yb{sup 3+} phosphor, were obtained. The two-photon process was assigned to the green UC emissions in the optimized NaLa(MoO{sub 4}){sub 2}: Er{sup 3+}/Yb{sup 3+} phosphor. It was also demonstrated that the optimized phosphor presented more stable upconversion emissions than the commercial NaYF{sub 4}:Er{sup 3+}/Yb{sup 3+} phosphor.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Electrochemical properties of Sn-based nanopowders synthesized by a pulsed wire evaporation method and effect of binder coating

Highlights: • Sn-based nanoparticles are fabricated by using the pulsed wire evaporation method. • The electrodes are prepared by mixing the graphene and coating the surface. • Coating the surface of electrode is used with brushing of simple and facile method. • The electrochemical measurements are performed with galvanostatic experiments. • The coating electrode maintains capacity nearly of 501 mAh g{sup −1} up to 100 cycles. - Abstract: Sn-based nanoparticles are prepared with the O{sub 2} concentrations in chamber of Ar atmosphere (by v/v) by using the pulsed wire evaporation (PWE) method. The prepared electrodes are only Sn-based powder electrode, its binder coating electrode and Sn-based powder/graphene nanocomposite electrode. Morphology and structure of the synthesized powders and electrodes are investigated with a field emission scanning electron microscope (FE-SEM) and an X-ray diffraction (XRD) analysis. The electrochemical measurements were performed with galvanostatic cycling experiments using a coin type cell of CR2032 (Ø20, T3.2 mm). The binder coating electrode is superior to others and maintains delithiation capacity nearly of 501 mAh g{sup −1} as 58.3% of first delithiation capacity at 0.2 C-rate up to 100 cycles.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Intense 2.7 μm mid-infrared emission of Er{sup 3+} in oxyfluoride glass ceramic containing NaYF{sub 4} nanocrystals

Highlights: • Transparent oxyfluoride glass-ceramics containing NaYF{sub 4}:Er{sup 3+} nanocrystals have been prepared. • Intense 2.7 μm emission of the glass-ceramics has been demonstrated. • Prolonged decay lifetimes of Er{sup 3+}:{sup 4}I{sub 11/2} and {sup 4}I{sub 13/2} levels have been achieved. - Abstract: Transparent oxyfluoride glass ceramics containing NaYF{sub 4}:Er{sup 3+} nanocrystals have been prepared by melt quenching and subsequent thermal treatment. X-ray diffraction and high-resolution transmission electron microscopy analysis confirmed the precipitation of NaYF{sub 4} nanocrystals in glass. Energy dispersive spectrometer results evidenced the preferential concentration of Er{sup 3+} ions in nanocrystals. Mid-infrared, upconversion, and near-infrared emissions were measured upon excitation with 980 nm laser diode and the luminescence mechanisms were discussed. Intense 2.7 μm emission originating from the Er{sup 3+}:{sup 4}I{sub 11/2} → {sup 4}I{sub 13/2} transition was achieved due to the incorporation of Er{sup 3+} ions into the precipitated low phonon energy fluoride nanocrystals. The results indicate that oxyfluoride glass ceramic containing NaYF{sub 4}:Er{sup 3+} nanocrystals is a promising candidate material for 2.7 μm laser.

36 MATERIALS SCIENCE↗
DOE OSTI2016

An efficient visible-light photocatalyst prepared by modifying AgBr particles with a small amount of activated carbon

Highlights: • An efficient visible-light photocatalyst was prepared by modifying AgBr particles. • A small amount of activated carbon was used to modify AgBr particles. • The modified AgBr exhibited improved visible-light photocatalytic performances. - Abstract: An efficient visible-light photocatalyst was successfully prepared by modifying AgBr particles with a small amount of activated carbon (AC) via a simple chemical precipitation approach. The AC/AgBr composite was characterized by X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy, UV–vis diffuse reflection spectroscopy, photoluminescence spectroscopy, electrochemical impedance spectroscopy. The photocatalytic performances of the AC/AgBr composite were investigated by evaluating photodegradation of methyl orange (MO) and phenol under visible light irradiation, and the effects of the AC content in the composite, concentrations of AC/AgBr composite and MO, carrier scavengers on MO photodegradation rate were systematically investigated. The results indicated that the modification of AC can hardly change the crystalline and crystal size of AgBr particles, while significantly improve their specific surface areas, visible-light absorption and separation efficiency of photogenerated electron–hole pairs. Compared with pure AgBr, the AC/AgBr composite exhibited drastically enhanced visible-light photocatalytic activity and stability. The photogenerated electrons and holes, hydroxyl radicals are responsible to the photodegradation of organic pollutants, and the photogenerated holes are the main active species. On the basis of the results and the properties of AC and AgBr, the visible-light photocatalytic mechanism of the AC/AgBr composite was discussed.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Synthesis of Cu{sub 2}ZnSnS{sub 4} nanoparticles and controlling the morphology with polyethylene glycol

Highlights: • Cu{sub 2}ZnSnS{sub 4} nanoparticles were synthesized by wet chemical technique. • First report on the effect of using polyethylene glycol as a structure directing agent on Cu{sub 2}ZnSnS{sub 4} nanoparticles. • The morphology of Cu{sub 2}ZnSnS{sub 4} nanoparticles changes into nanoflakes and nanorods structures with polyethylene glycol concentration. • Polyethylene glycol assisted Cu{sub 2}ZnSnS{sub 4} nanoparticle film exhibits optical bandgap of 1.5 eV which is suitable for the application in solar cells. - Abstract: Cu{sub 2}ZnSnS{sub 4} nanoparticles were synthesized by wet chemical technique using metal thiourea precursor at 250 °C. The structural and morphological properties of as grown nanoparticles have been characterized by X-ray diffraction, Raman spectroscopy, scanning electron microscopy and transmission electron microscopy. The influence of different concentration of polyethylene glycol as structure directing agent on the morphologies of Cu{sub 2}ZnSnS{sub 4} nanoparticles are investigated on thin films deposited by spin coating technique. The mean crystallite size of the Cu{sub 2}ZnSnS{sub 4} nanoparticles was found to improve with polyethylene glycol concentration. Scanning electron microscopy images of Cu{sub 2}ZnSnS{sub 4} revealed aggregated spherical shaped nanoparticles whereas the polyethylene glycol assisted Cu{sub 2}ZnSnS{sub 4} nanoparticle films show nanoflakes and nanorods structures with increasing concentration of polyethylene glycol. Transmission electron microscopy analysis has also been performed to determine the size and structure of nanorods. UV–vis absorption spectroscopy shows the broad band absorption with optical bandgap of 1.50 eV for polyethylene glycol assisted Cu{sub 2}ZnSnS{sub 4} films.

36 MATERIALS SCIENCE↗
DOE OSTI2016

A simple method to fabricate an NIR detector by PbTe nanowires in a large scale

Highlights: • PbTe nanowires were grown by tellurization of the Pb sheets for the first time. • It was observed a band gap value for the PbTe nanostructures in the NIR region. • NIR detector was fabricated in a large scale using a simple method. • Effect of Te concentration on morphology of PbTe nanostructures was investigated. - Abstract: A simple method was used to fabricate a near-infrared (NIR) detector using PbTe nanostructures. Samples were synthesized by tellurization of lead sheets in a tube furnace. PbTe nanostructures with wires and flakes shapes were grown on the lead sheets that were placed at 300 and 330 °C, respectively, while, PbTe nanoporous were grown at 360 and 390 °C. X-ray diffraction patterns and X-ray photoelectron spectra results indicated that, the PbTe phase was formed in all samples. UV–vis diffuse reflectance spectra measurements showed a band gap for the PbTe nanostructures in the near-infrared region of the electromagnetic spectrum. Actually, the results indicated that, the band gap values of the PbTe nanowires and nanoporous were 1.54 eV and 1.61 eV, respectively. Finally, the PbTe nanostructures were used as a simple photoresponse device under a red light source. The photoresponse results revealed, PbTe nanowires are promising for photoelectrical applications in the NIR region.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Improving of the electrical and magnetic properties of BiFeO{sub 3} by doping with yttrium

Bismuth ferrite is one of the most promising multiferroic materials, and the main barriers for exploiting all of its specific properties are difficulties in obtaining pure, high resistive material with nanosized grains. Doping of BiFeO{sub 3} with different transition metals and rare earth elements is often used way for overcoming these obstacles. Yttrium doped bismuth ferrite, Bi{sub 1−x}Y{sub x}FeO{sub 3} (x = 0; 0.01; 0.03; 0.05; 0.1), was prepared by auto-combustion method. X-ray diffraction patterns and Raman results showed that partial phase transition from rhombohedral to orthorhombic structure took place at around 10 mol% of Y. Effect of Y doping on microstructure was studied from SEM micrographies, showing the reduction of grain size in doped samples. Electrical measurements showed continuous improvement of resistivity with Y doping, whereas the values of saturation and remnant polarizations exhibit maximums at around 5 mol% of Y. Yttrium doping also enhanced magnetic properties, leading to weak ferromagnetism.

36 MATERIALS SCIENCE↗
DOE OSTI2016

New methods for the preparation and dielectric properties of La{sub 2−x}Sr{sub x}NiO{sub 4} (x = 1/8) ceramic

Highlights: • A new fuel in solution combustion synthesis of fine powder La{sub 15/8}Sr{sub 1/8}NiO{sub 4}. • Changes in the morphology of the ceramic La{sub 15/8}Sr{sub 1/8}NiO{sub 4} after thermobaric treatment. • Changes in structural parameters of the La{sub 15/8}Sr{sub 1/8}NiO{sub 4} after thermobaric treatment. • Increase of the dielectric constant of the thermobaric treated ceramic La{sub 15/8}Sr{sub 1/8}NiO{sub 4}. • Using of dielectric modulus and impedance formalisms, of equivalent circuits method. - Abstract: The perovskite-type oxide La{sub 2−x}Sr{sub x}NiO{sub 4} (x = 1/8) was prepared by a new precursor route. The reaction proceeds in the self-ignition mode. Single-phase powder and gas-tight ceramic samples can be produced by single annealing of decomposition products. It was shown that as a result of thermobaric treatment of La{sub 2−x}Sr{sub x}NiO{sub 4} (x = 1/8) the solid solution La{sub 2−x}Sr{sub x}NiO{sub 4} with a higher concentration of strontium and the second phase La{sub 3}Ni{sub 2}O{sub 7} are formed. Short-term (5 min) thermobaric treatment (P = 2.5 GPa) at t° = 900 °C changes the unit cell parameters, but is not accompanied by structural transitions. At the same time, morphological restructuring of the sample occurs—the agglomerates delaminate into thin plates crystals. It was established that the permittivity of the material exposed to thermobaric treatment is much higher compared to that of the sample annealed at atmospheric pressure and virtually does not depend on frequency in a wide temperature range.

36 MATERIALS SCIENCE↗