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At least 1,297 records · Page 72
All sourcesNASA NTRSDOE OSTI
DOE OSTI2014

Microstructure and electrical properties in W/Nb co-doped Aurivillius phase Bi{sub 4}Ti{sub 3}O{sub 12} piezoelectric ceramics

Highlights: • W/Nb codoped BIT ceramics were prepared by the mixed oxides route. • High nd{sup 0} electronic configuration of W/Nb reduces the lattice distortion and T{sub C}. • Oxygen vacancy is responsible for dielectric relaxation and DC conduction process. • W/Nb additives significantly enhanced the piezoelectric coefficient d{sub 33} value. • BWNb-10 ceramics possessed large remnant polarization and a wide sintering window. - Abstract: Aurivillius-type Bi{sub 4}Ti{sub 3-x}W{sub x/2}Nb{sub x/2}O{sub 12} ceramics were prepared by a conventional solid-state sintering method. The XRD patterns demonstrated that all compositions were a single three layered crystalline structure, involving a reduction of lattice distortion with an increase in W/Nb doping level. The electrical properties including dielectric, electrical conduction and piezoelectric properties were tailored by W/Nb additives. The Curie-temperature decreased, whereas the electrical resistivity drastically increased with introduction of W/Nb donor dopants. As a result, a high electric field can be applied during the poling process. The Bi{sub 4}Ti{sub 2.9}W{sub 0.05}Nb{sub 0.05}O{sub 12} ceramics exhibited optimum piezoelectric coefficient (d{sub 33} ∼22.8 pC/N), large remnant polarization (2P{sub r} ∼26.8 μC/cm{sup 2} @ 200 °C) together with a high Curie temperature (T{sub C} ∼635 °C). Furthermore, this composition possessed a wide sintering window with outstanding piezoelectric properties. These parameters indicate that Bi{sub 4}Ti{sub 2.9}W{sub 0.05}Nb{sub 0.05}O{sub 12}-based ceramic is a promising candidate for high temperature piezoelectric applications.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Crystallization, densification and dielectric properties of CaO–MgO–Al{sub 2}O{sub 3}–SiO{sub 2} glass with ZrO{sub 2} as nucleating agent

SEM micrographs for the pure CaO–MgO–Al{sub 2}O{sub 3}–SiO{sub 2} glass sintered at 850–1000 °C (a) 850 °C, (b) 900 °C, (c) 950 °C, (d) 1000 °C. - Highlights: • ZrO{sub 2} effects on the crystallization of LTCC glass system were investigated. • ZrO{sub 2} effects on the dielectric properties of LTCC glass system were investigated. • LTCC with a dielectric constant of 6.65 and a low dielectric loss can be obtained. - Abstract: The zirconium oxide effects on the crystallization and dielectric properties of CaO–MgO–Al{sub 2}O{sub 3}–SiO{sub 2} (CMAS) glass were investigated. The results showed that phyllosiloxide and anorthite crystallites were observed in sequence during sintering. For glass added with 8 wt% ZrO{sub 2}, homogeneously dispersed tetragonal ZrO{sub 2} crystallites were observed at 850 °C. The as-prepared CMAS glass–ceramics exhibited a dielectric constant of about 6–7 and a dielectric loss below 0.005 at 100 MHz. The dielectric properties of CMAS glass with 8 wt% ZrO{sub 2} sintered at 850 °C show a low dielectric constant of 6.65 and a dielectric loss tangent of about 2.5 × 10{sup −3}, which provides a promising candidate for LTCC applications.

36 MATERIALS SCIENCE↗
DOE OSTI2015

The formation and structure of mechano-synthesized nanocrystalline Sr{sub 3}Fe{sub 2}O{sub 6.4}: XRD Rietveld, Mössabuer and XPS analyses

Highlights: • The formation of mechano-synthesized nanocrystalline Sr{sub 3}Fe{sub 2}O{sub 7−δ} is investigated. • Pre-milling the reactants substantially lowers the formation temperature. • The core and surface structures were studied. • XRD and {sup 57}Fe Mössbauer spectroscopic analyses indicate the δ-value to be 0.60. • XPS shows a complex surface structure for the mechanosynthesized Sr{sub 3}Fe{sub 2}O{sub 7−δ} nanoparticles. - Abstract: The influence of ball milling and subsequent sintering of a 3:1 molar mixture of SrCO{sub 3} and α-Fe{sub 2}O{sub 3} on the formation of Sr{sub 3}Fe{sub 2}O{sub 7−δ} double perovskite is investigated with different analytical techniques. Milling the mixture for 110 h leads to the formation of SrCO{sub 3}-α-Fe{sub 2}O{sub 3} nanocomposites and the structural deformation of α-Fe{sub 2}O{sub 3} via the incorporation of Sr{sup 2+} ions. Subsequent sintering of the pre-milled reactants’ mixture has led to the partial formation of an SrFeO{sub 3} perovskite-related phase in the temperature range 400–600 °C. This was followed by the progressive development of an Sr{sub 3}Fe{sub 2}O{sub 7−δ} phase that continued to increase with increasing sintering temperature until a single-phased nanocrystalline Sr{sub 3}Fe{sub 2}O{sub 7−δ} phase was attained at 950 °C (12 h). This temperature is ∼350 °C lower than the temperature at which the material is prepared conventionally using the ceramic method. The evolution of different structural phases during the reaction process is discussed. Rietveld refinement of the X-ray diffraction data shows a value of 0.60 for the oxygen deficiency δ, in consistency with the Fe{sup 3+}/Fe{sup 4+} ratio derived from the {sup 57}Fe Mössbauer data recorded at both 300 K and 78 K. The Mössbauer data suggests that the Sr{sub 3}Fe{sub 2}O{sub 6.4} nanoparticles are superparamagnetic with blocking temperatures below 78 K. The surfaces of the Sr{sub 3}Fe{sub 2}O{sub 6.4} nanoparticles were shown to have a complex structure and composition relative to those of their cores with traces of SrCO{sub 3}, SrO and SrFeO{sub 3−δ} being detected.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

A mechanistic study on the synthesis of β-Sialon whiskers from coal fly ash

Graphical abstract: The appearance of bead-like whiskers indicated that the growth mechanism of the β-Sialon whiskers was different from the conventional one, in which a chain of droplets were formed and then consumed to participate in the formation of the whiskers. - Highlights: • β-Sialon whiskers were synthesized using waste fly ash by carbothemal reduction reaction under nitrogen atmosphere. • Rod-like β-Sialon whiskers with a diameter of 100–500 nm were formed. • Bead-like whiskers as intermediate morphology of the growing β-Sialon whiskers were found with increasing sintering time. • The growth mechanism of β-Sialon whiskers was different from the conventional VLS mechanism. • A chain of droplets were formed and participated in the formation of the whiskers. - Abstract: β-Sialon whiskers were produced at 1420 °C through carbothemal reduction reaction under nitrogen atmosphere using fly ash from coal-fired power plants. The effects of sintering time on the phase formation and morphology of the products were investigated by X-ray diffraction (XRD), scanning electron microscope (SEM) and energy dispersive spectrometer (EDS) techniques. Rod-like β-Sialon whiskers with the diameter of 100–500 nm were successfully formed. With increasing sintering time, bead-like morphology during the growth process of the whiskers was found, and growth mechanism of β-Sialon whiskers was also discussed in detail. The growth mechanism proposed in this study was different from the conventional vapor–liquid–solid (VLS) mechanism.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Composite electrolytes ceramic Li{sub 7}La{sub 3}Zr{sub 2}O{sub 12}/glassy Li{sub 2}O-Y{sub 2}O{sub 3}-SiO{sub 2}

Highlights: • We synthesized Li{sub 7}La{sub 3}Zr{sub 2}O{sub 12}-x wt% 40.2Li{sub 2}O·5.7Y{sub 2}O{sub 3}·54.1SiO{sub 2} (x = 1–10) composites. • Density of the composite samples is higher than one of the sintered Li{sub 7}La{sub 3}Zr{sub 2}O{sub 12}. • The composition with x = 5 has high total conductivity, 2.5 × 10{sup −5} S cm{sup −1} at 25 °C. - Abstract: We have investigated the effect of lithium yttrium-silicate glass 40.2Li{sub 2}O·5.7Y{sub 2}O{sub 3}·54.1SiO{sub 2} on the density and total conductivity of tetragonal Li{sub 7}La{sub 3}Zr{sub 2}O{sub 12}. An optimal sintering temperature (1200 °C) was selected on the basis of a composite with 1 wt% of the glass having the highest density and total conductivity after annealing at this temperature. A series of composites Li{sub 7}La{sub 3}Zr{sub 2}O{sub 12}-x wt% 40.2Li{sub 2}O·5.7Y{sub 2}O{sub 3}·54.1SiO{sub 2} (x = 1–10) was prepared. The samples were characterized by X-ray diffraction, scanning electron microscopy and differential scanning calorimetry. The data revealed that the sintering additive interacted with Li{sub 7}La{sub 3}Zr{sub 2}O{sub 12}, causing the glass to crystallize during annealing. The conductivity of the composites was studied using complex impedance spectroscopy over a temperature range of 20–250 °C. The composite with x = 5 exhibited the highest total conductivity at room temperature: 2.5 × 10{sup −5} S cm{sup −1}.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Control of donor-like effect in V2VI3 polycrystalline thermoelectric materials

Highlights: • Thermal control of donor-like effect for V{sub 2}VI{sub 3} polycrystalline materials is proposed. • Low-temperature sintering or hot deforming facilitates the donor-like effect. • Recovery role by high-temperature sintering/deforming enhances the Seebeck coefficient. • Temperature should be strictly selected for each V{sub 2}VI{sub 3} polycrystalline material. - Abstract: Intrinsic point defect plays a core role in improving thermoelectric performance of V{sub 2}VI{sub 3} polycrystalline materials. However, the control of intrinsic point defect is challenging during powder refinement due to the donor-like effect. This paper shows a systematic approach to thermal control the donor-like effect via engineering spark plasma sintering and hot deformation temperature. Bi{sub 2}Te{sub 2.85}Se{sub 0.15} polycrystalline alloy with high electron concentration was chosen as example to validate the method. The low Seebeck coefficient of n-type Bi{sub 2}Te{sub 2.85}Se{sub 0.15} polycrystalline, arising from strong donor-like effect after powder refinement, was enhanced by recovery role induced reduction in electron concentration through proper tuning sintering or deforming temperature. Repetitive hot deformation was applied to further improve the Seebeck coefficient via the recovery role and a maximum zT of 1.0 is obtained at 410 K. The present results give insights into developing higher performance V{sub 2}VI{sub 3} polycrystalline materials through thermal control the donor-like effect.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Synthesis of low core loss Finemet/Ni0.5Zn0.5Fe2O4 composites by co-precipitation method

Highlights: • Finemet/NiZn ferrite composites were synthesized by co-precipitation method. • Magnetic properties can be adjusted by controlling oxygen partial pressure. • It shows lower core loss about 30.5 mW/cm{sup 3} at 100 kHz and 100 mT. - Abstract: Finemet/Ni{sub 0.5}Zn{sub 0.5}Fe{sub 2}O{sub 4} core/shell structure composites have been prepared by a co-precipitation method followed by a high temperature sintering process. The formation mechanism of the core/shell structures and the effects of oxygen partial pressure during the sintering process on the phase structure, microstructure, and magnetic properties were discussed. Low and high oxygen partial pressures resulted in the formation of crystal defects and a reduction of the magnetic properties of the composites. The magnetic properties could be adjusted by controlling the oxygen partial pressure and the optimal magnetic properties of the composites were obtained by sintering under an oxygen partial pressure of 10%. The resulting composite exhibited a high permeability of 61, a high saturation magnetization of 135.5 emu/g and a low core loss of approximately 30.5 mW/cm{sup 3} at 100 kHz and 100 mT.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Fractal nature structure reconstruction method in designing microstructure properties

Highlights: • Structure and material’s properties, within the material’s consolidation triad: Synthesis – Structure – Properties. • The grain prediction methods is based on the measurements of the solid Euclidean geometric fractal characteristics. • The intergranular contacts inside the BaTiO3 -ceramic are responsible for intergranular capacities. • The inner complex geometry of intergrain contacts imposes fractal correction factor for permeability. - Abstract: In the process of predicting materials properties, it is necessary to predict microstructures. This is important for ceramic materials, for the purpose of miniaturization and for a higher level of integration. Although the method of material structure reconstruction is for the first time used on BaTiO{sub 3}-ceramics by these authors, it can also be used for silicate, refractory and other ceramics, and, for any powder-based material. The reconstruction is based on the grain perimeter fractal analysis and the Richardson method. The main contribution of this paper is establishing the relationship between the electronic properties of BaTiO{sub 3}-ceramics and its microstructural fractal nature. Similar relations can be used for any ceramics or even any materials. The samples consolidation includes both powder pressing (cold sintering phase) and sintering in a furnace (hot sintering phase). The fractal nature characterization has a very important role from the powder phase up to the final microstructure, through which structures it directly impacts electro-physical and other ceramics properties. Thereby, the new possibilities in the microstructure characterization applications are directly introduced to an engineering system, providing the new solutions related to computer aided support. This creates new industrial production and application possibilities, especially in the process of ceramics material consolidation, now based on microstructural properties, which is providing a basis for “fractal electronics’’ development.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Size-Dependent Adsorption and Adhesion Energetics of Ag Nanoparticles on Graphene Films on Ni(111) by Calorimetry

Interest in the use of carbon supports for late transition metal nanoparticle catalysts has expanded rapidly due to the increasing importance of electrocatalysts for clean energy and environmental technologies and the use and storage of renewable electricity. Compared to oxide supports, almost nothing is known about the effect of metal nanoparticle size on the energies of the metal atoms within carbon-supported nanoparticles, yet these energies are crucial for understanding their surface reactivity and sintering kinetics. Here, the growth morphology and adsorption energetics of vapor-deposited Ag onto clean graphene/Ni(111) surfaces have been studied using a combination of single-crystal adsorption calorimetry (SCAC) and He + low-energy ion scattering (LEIS). The differential heat of Ag adsorption is 207 kJ/mol for making ~30 atom Ag particles on graphene terraces at 100 K and 16 kJ/mol higher for making ~9 atom Ag clusters at defect sites at the same temperature. The heat of adsorption increases rapidly with Ag coverage as 3D Ag nanoparticles nucleate and grow in size, asymptotically reaching within 5 kJ/mol of the bulk Ag sublimation enthalpy (285 kJ/mol) by 2 ML. The heats of adsorption and Ag nanoparticle densities from LEIS (~10 16 /m 2 ) were combined to provide the Ag/graphene adhesion energy (E adh = 1.8 J/m 2 in the large-particle limit) and the Ag chemical potential (μ) versus effective particle diameter (D). The Ag chemical potential was well-fitted by μ(D) = (3γ v /M – E adh )(1 + (1.5 nm)/D)(2V m /D), where γ v /M is the surface energy of bulk Ag and V m is its molar volume. The same equation is known to fit similar data for late transition metals on clean surfaces of metal oxide single crystals. The adhesion energy of Ag measured here on graphene falls within the wide range measured for Ag on those oxide surfaces and is almost as large as on the oxide that binds Ag particles most strongly, namely CeO 2 (111), which is well-known to be very effective at resisting catalyst deactivation by metal sintering. Furthermore, these results imply that carbon supports will be effective at resisting sintering and that Ag particles smaller than 6 nm on graphene will bind small adsorbed reaction intermediates more weakly than supports with weaker adhesion to Ag, like MgO(100).

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2019

Catalysts in Coronas: A Surface Spatial Confinement Strategy for High-Performance Catalysts in Methane Dry Reforming

One of the grand challenges in industrial catalytic processes is the inevitable sintering and aggregation of conventional supported catalysts to large particles, leading to the decrease of activity and even deactivation with time. Herein, a surface spatial confinement strategy was employed to design high-performing catalysts for the dry reforming of methane (DRM). Specifically, active nickel (Ni) nanoparticles (NPs) were confined on the surface of a dendritic mesoporous silica (DMS) in the form of the “catalysts in coronas”. The Ni/DMS catalyst exhibited a high catalytic performance close to its equilibrium conversion (76% conversion for CH4 at 700 °C). More importantly, the prepared catalyst remained stable after 145 h time-on-stream at 700 °C without noticeable carbon deposition. This sintering and coking resistance was found to arise from the surface spatial confinement effect in which the three-dimensional dendritic layers in the corona posted a steric barrier against migration and aggregation of Ni NPs and size of Ni NPs was controlled below 5 nm, hence against sintering and coking. Meanwhile, the mesoporous feature of the layered wall facilitated mass transport of reactants to Ni species and further boosted catalysis. This strategy should be broadly applicable to a range of metal- and metal oxide-supported catalysts in high-temperature heterogeneous reactions, such as DRM, water gas shift reaction, and vehicle emission control related reactions.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2014

Microstructural and crystallographic imperfections of MgB{sub 2} superconducting wire and their correlation with the critical current density

A comprehensive study of the effects of structural imperfections in MgB{sub 2} superconducting wire has been conducted. As the sintering temperature becomes lower, the structural imperfections of the MgB{sub 2} material are increased, as reflected by detailed X-ray refinement and the normal state resistivity. The crystalline imperfections, caused by lattice disorder, directly affect the impurity scattering between the π and σ bands of MgB{sub 2}, resulting in a larger upper critical field. In addition, low sintering temperature keeps the grain size small, which leads to a strong enhancement of pinning, and thereby, enhanced critical current density. Owing to both the impurity scattering and the grain boundary pinning, the critical current density, irreversibility field, and upper critical field are enhanced. Residual voids or porosities obviously remain in the MgB{sub 2}, however, even at low sintering temperature, and thus block current transport paths.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Influence of La substitution on ferromagnetic properties of lead free Na{sub 0.5}Bi{sub 0.5}Ti{sub 0.988}Fe{sub 0.012}O{sub 3} multiferroic system

To study the effect of La doping and processing temperature, (Na{sub 0.5}Bi{sub 0.5}){sub 1−x}La{sub x}Ti{sub 0.988}Fe{sub 0.012}O{sub 3} (NBLTF) samples have been prepared by sol-gel method by employing two approaches namely with and without mol% excess of Na and Bi. X-ray diffraction analysis confirms the formation of rhombohedral perovskite structure in these samples with minor impurity phases. However, the impurity phases of stochiometric NBLTF samples disappear on increasing the sintering temperature from 650°C to 850°C. On other hand, NBLTF samples prepared with mol% excess of Na and Bi have shown pure perovskite structure only at lower sintering temperature 650°C and also at low concentration of La ∼ 1%. Transmission electron microscope investigation shows nano crystalline formation for all NBLTF samples sintered at 850°C. The enhancement in room temperature ferromagnetism is observed in La doped NBTF samples prepared at 850°C by taking stoichiometric amount of Na and Bi during synthesis.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2014

Milling time and temperature dependence on Fe{sub 2}TiO{sub 5} nanoparticles synthesized by mechanical alloying method

Fe{sub 2}TiO{sub 5} is one type of titanate oxides which has M{sub x}Ti{sub y}O{sub z} crystal structure. It has various kinds of applications due to its electric and magnetic properties such as spintronics, electromagnetic devices, and gas sensor. In this study, Fe{sub 2}TiO{sub 5} nanoparticles were synthesized by simple mechanical alloying using planetary ball milling machine with various milling times and sintering temperatures. TiO{sub 2} and Fe{sub 2}O{sub 3} powders obtained from coprecipitation process were used as starting materials. The resulted Fe{sub 2}TiO{sub 5} powders were characterized by X-Ray Diffraction (XRD), Scanning Electron Microscopy (SEM), and Vibration Sample Magnetometer (VSM) in order to observe crystal quality, particles morphology, and magnetic properties respectively. As the milling time increases and the sintering temperature decreases, the crystal size of Fe{sub 2}TiO{sub 5} phase decreases. The smallest crystal size of the synthesized Fe{sub 2}TiO{sub 5} nanoparticles was ∼ 51 nm obtained by the milling time of 25 hours and sintering at 1100°C. The distribution of the resulted Fe{sub 2}TiO{sub 5} nanoparticles was not so homogeneous due to the appearance of small amount impurities. The VSM measurements show that a paramagnetic property was observed which should be analyzed more details on the low external magnetic fields.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Influence of secondary phases on phase and microwave dielectric properties of new Ca{sub 2}Ce{sub 2}Ti{sub 5}O{sub 16} ceramics

Ca{sub 2}Ce{sub 2}Ti{sub 5}O{sub 16} ceramics processed via mix oxide route was investigated. Phase composition and microwave dielectric properties were measured using X-ray diffraction and a cavity method, respectively. CeO{sub 2} and another unidentified phase (that vanishes at ≥1400°C) existed as secondary phases along with the parent Ca{sub 2}Ce{sub 2}Ti{sub 5}O{sub 16} phase. The amount of the parent Ca{sub 2}Ce{sub 2}Ti{sub 5}O{sub 16} phase increased with increasing sintering temperature from 1350°C to 1450 °C accompanied by a decrease in the apparent density. The density decreased but ε{sub r} and Qufo increased with sintering temperature. An ε{sub r} ∼87.2, Qufo ∼5915 GHz and τ{sub f} ∼219 GHz was achieved for the sample sintered at 1450°C.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

The influence of temperature induced phase transition on the energy storage density of anti-ferroelectric ceramics

Anti-ferroelectric (AFE) composite ceramics of (Pb{sub 0.858}Ba{sub 0.1}La{sub 0.02}Y{sub 0.008})(Zr{sub 0.65}Sn{sub 0.3}Ti{sub 0.05})O{sub 3}-(Pb{sub 0.97}La{sub 0.02})(Zr{sub 0.9}Sn{sub 0.05} Ti{sub 0.05})O{sub 3} (PBLYZST-PLZST) were fabricated by the conventional solid-state sintering process (CS), the glass-aided sintering (GAS), and the spark plasma sintering (SPS), respectively. The influence of the temperature induced phase transition on the phase structure, hysteresis loops, and energy storage properties of the composite ceramics were investigated in detail. The measured results of X-ray diffraction demonstrate that the composite ceramics exhibit the perovskite phases and small amounts of non-functional pyrochlore phases. Compared with the CS process, the GAS and SPS processes are proven more helpful to suppress the diffusion behaviors between the PBLYZST and PLZST phases according to the field emission scanning electron microscopy, thereby being able to improve the contribution of PBLYZST phase to the temperature stability of the orthogonal AFE phase. When the ambient temperature rises from 25 °C to 125 °C, CS and GAS samples have undergone a phase transition from orthorhombic AFE phase to tetragonal AFE phase, which results in a sharp decline in the energy storage density. However, the phase transition temperature of SPS samples is higher than 125 °C, and the energy storage density only slightly decreases due to the disorder of material microstructure caused by the high temperature. As a result, the SPS composite ceramics obtain a recoverable high energy storage density of 6.46 J/cm{sup 3} and the excellent temperature stability of the energy storage density of 1.16 × 10{sup −2} J/°C·cm{sup 3}, which is 1.29 × 10{sup −2} J/°C·cm{sup 3} lower than that of CS samples and about 0.43 times as that of GAS samples.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Correlation of film morphology and defect content with the charge-carrier transport in thin-film transistors based on ZnO nanoparticles

The correlation of defect content and film morphology with the charge-carrier transport in field-effect devices based on zinc oxide nanoparticles was investigated. Changes in the defect content and the morphology were realized by annealing and sintering of the nanoparticle thin films. Temperature-dependent electrical measurements reveal that the carrier transport is thermally activated for both the unsintered and sintered thin films. Reduced energetic barrier heights between the particles have been determined after sintering. Additionally, the energetic barrier heights between the particles can be reduced by increasing the drain-to-source voltage and the gate-to-source voltage. The changes in the barrier height are discussed with respect to information obtained by scanning electron microscopy and photoluminescence measurements. It is found that a reduction of surface states and a lower roughness at the interface between the particle layer and the gate dielectric lead to lower barrier heights. Both surface termination and layer morphology at the interface affect the barrier height and thus are the main criteria for mobility improvement and device optimization.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2016

Effect of grain size on optical properties of iron oxide nanoparticles

In the present paper, iron oxide nanoparticles are successfully synthesized by the sol-gel method. The grain size is varied by sintering the nanoparticles at different temperature 400, 500, 600, 700 and 800 °C. Field emission scanning electron microscope (FESEM) image shows that the grains are uniformly distributed. The grain size increases from 15 nm to 35 nm with increasing the sintering temperature (400-800 °C). Energy dispersive X-ray spectroscopy (EDS) analysis shows that Fe is present in the stoichiometric ratio in all the synthesized samples. Fourier transform infrared spectroscopy (FTIR) spectra show that Fe-O stretching peaks appears at ∼495 cm{sup −1}. The value of energy band gap are found 2.75, 2.67, 2.62, 2.59, and 2.57 eV for the samples sintered at 400, 500, 600, 700 and 800 °C respectively. Therefore, the decrease in band gap with increasing the temperature has been observed. In this paper, the structural and optical properties have been explained on the basis of variation in the grain size with the temperature. The present studied samples more widely used in gas sensors and as catalysts.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2016

Structural properties and gas sensing behavior of sol-gel grown nanostructured zinc oxide

In this communication, we report the results of the studies on structural properties and gas sensing behavior of nanostructured ZnO grown using acetone precursor based modified sol-gel technique. Final product of ZnO was sintered at different temperatures to vary the crystallite size while their structural properties have been studied using X-ray diffraction (XRD) measurement performed at room temperature. XRD results suggest the single phasic nature of all the samples and crystallite size increases from 11.53 to 20.96 nm with increase in sintering temperature. Gas sensing behavior has been studied for acetone gas which indicates that lower sintered samples are more capable to sense the acetone gas and related mechanism has been discussed in the light of crystallite size, crystal boundary density, defect mechanism and possible chemical reaction between gas traces and various oxygen species.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗