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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 1,369 records · Page 76
All sourcesNASA NTRSDOE OSTI
NASA NTRS1986

High-purity silicon crystal growth investigations

Information is given on evaporation and segregation contributions to impurity profiles of floating zone crystals (FZ); high-purity silicon float zoning (FZ); minority-carrier lifetime measurement of heavily doped silicon crystals; the effect of some crystal growth parameters on minority-carrier lifetime; and defect investigations by X-ray topography in graphical and tabular form. It was concluded that evaporation contributes substantially to impurity reduction when FZ or cold-crucible growth is conducted in a vacuum; boron and gallium may be more favorable dopants than indium or aluminum for obtaining high minority-carrier lifetimes; minority-carrier lifetimes greater than 100 microseconds are feasible at a 2 times 10 to the 17th power cm-3 doping level; minority-carrier lifetime decreases with increasing crystal cooling rate and also with the presence of dislocations; the method used to clean silicon feed rods affects lifetime; and microdefect densities in dislocation-free FZ crystals appear to be lower with Ga doping than with B doping.

Ciszek, T. F.↗
DOE OSTI2018

Determining the Concentration of Free Electrons in n-InSb from Far-Infrared Reflectance Spectra with Allowance for Plasmon–Phonon Coupling

Contactless nondestructive testing is a means for determining the concentration of free electrons N in indium antimonide (InSb) samples from far-infrared reflectance spectra recorded at room temperature. A computer program capable of determining the characteristic wave number from the Kramers–Kronig relation is developed. The calculated calibration dependence makes it possible to determine the electron concentration from the known characteristic wave number. It is shown that this dependence is described by a cubic polynomial. In the calculations, the energy dependence of the electron effective mass is taken into account. It is established that, in determining the electron concentration, account must be taken of plasmon–phonon coupling, specifically at N ≤ 5 × 10{sup 17} cm{sup –3}. The systematic error introduced into the determination of N by disregard of plasmon–phonon coupling is estimated. The software elaborated here makes it possible to calculate the electron concentration N from experimental reflectance spectra and to store and process the results. The software is tested by the example of the reflectance spectrum of heavily doped n-InSb.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2013

Frequency upconversion in Er{sup 3+} doped Y{sub 2}O{sub 3} nanophosphor:Yb{sup 3+} sensitization and tailoring effect of Li{sup +} ion

Graphical abstract: - Highlights: • Dual mode luminescence behavior of Er{sup 3+} in oxide phosphor. • Sensitization through Yb{sup 3+} codoping, and tailoring effect of lithium ion. • Phosphors for lighting and display applications. - Abstract: Er{sup 3+} doped Y{sub 2}O{sub 3} nanophosphor has been synthesized using solution combustion technique and further characterized for structure and optical properties. Optical properties of Er{sup 3+} ion have been studied both through frequency upconversion (UC) as well as through fluorescence (excitation, emission, and CIE co-ordinate analysis) processes. Further to enhance the UC emission of Er{sup 3+} ions, a two step process has been used. In the first step, Yb{sup 3+} ion has been co-doped, which acts as the sensitizer for Er{sup 3+} through energy transfer process. In the second step, different concentrations of Li{sup +} ions have been co-doped in the Er{sup 3+}/Yb{sup 3+}:Y{sub 2}O{sub 3} system. Fourier transform infrared analysis, and X-ray diffraction (XRD) followed by Le-Bail refinement of the XRD data reveal that the co-doping of Li{sup +} ion decreases unit cell parameter, increases the particle size, and removes the quenching centers (like OH, NO{sub x}, etc.), which all together causes a significant enhancement in UC emission. Optimum UC luminescence is attained for 5 mol% Li{sup +} doping concentration beyond which a quenching in UC emission is observed. This combined approach, i.e. Yb{sup 3+} sensitization and Li{sup +} ion tailoring simultaneously enhances the UC emission intensity of Er{sup 3+} several times in yttria matrix effectively. The strategy can be generalized in other hosts also which could help in the development of efficient photonic materials for lighting and display devices.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Nano-crystallization in ZnO-doped In{sub 2}O{sub 3} thin films via excimer laser annealing for thin-film transistors

In a previous work, we reported the high field effect mobility of ZnO-doped In{sub 2}O{sub 3} (IZO) thin film transistors (TFTs) irradiated by excimer laser annealing (ELA) [M. Fujii et al., Appl. Phys. Lett. 102, 122107 (2013)]. However, a deeper understanding of the effect of ELA on the IZO film characteristics based on crystallinity, carrier concentrations, and optical properties is needed to control localized carrier concentrations for fabricating self-aligned structures in the same oxide film and to adequately explain the physical characteristics. In the case of as-deposited IZO film used as the channel, a high carrier concentration due to a high density of oxygen vacancies was observed; such a film does not show the required TFT characteristics but can act as a conductive film. We achieved a decrease in the carrier concentration of IZO films by crystallization using ELA. This means that ELA can form localized conductive or semi-conductive areas on the IZO film. We confirmed that the reason for the carrier concentration decrease was the decrease of oxygen-deficient regions and film crystallization. The annealed IZO films showed nano-crystalline phase, and the temperature at the substrate was substantially less than the temperature limit for flexible films such as plastic, which is 50°C. This paves the way for the formation of self-aligned structures and separately formed conductive and semi-conductive regions in the same oxide film.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Non-linearity effects on the light-output calibration of light charged particles in CsI(Tl) scintillator crystals

The light output produced by light ions ( Z ≤ 4) in Csl(Tl) crystals is studied over a wide range of detected energies (E ≤ 300 MeV). Energy-light calibration data sets are obtained with the 10 cm crystals in the recently upgraded High-Resolution Array (HiRA10). We use proton recoil data from 40,48 Ca + CH 2 at 28 MeV/u, 56.6 MeV/u, 39 MeV/u and 139.8 MeV/u and data from a dedicated experiment with direct low-energy beams. We also use the punch through points of p, d, and t particles from 40,48 Ca + 56,64 Ni, 112,124 Sn collisions reactions at 139.8 MeV/u. Non-linearities, arising in particular from Tl doping and light collection effects in the CsI crystals, are found to significantly affect the light output and therefore the calibration of the detector response for light charged particles, especially the hydrogen isotopes. A new empirical parametrization of the hydrogen light output, $L(E,Z=1,A)$, is proposed to account for the observed effects. Results are found to be consistent for all 48 CsI(Tl) crystals in a cluster of 12 HiRA10 telescopes.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2014

Role of phonon scattering by elastic strain field in thermoelectric Sr{sub 1−x}Y{sub x}TiO{sub 3−δ}

Perovskite-type SrTiO{sub 3−δ} ceramics are multifunctional materials with significant potential as n-type thermoelectric (TE) materials. The electronic and thermal transport properties of spark plasma sintered polycrystalline Sr{sub 1−x}Y{sub x}TiO{sub 3−δ} (x = 0.05, 0.075, 0.1) ceramics are systematically investigated from (15–800) K. The Sr{sub 0.9}Y{sub 0.1}TiO{sub 3−δ} simultaneously exhibits a large Seebeck coefficient, α > −80 μV/K and moderately high electrical resistivity, ρ ∼ 0.8 mΩ-cm at a carrier concentration of ∼10{sup 21} cm{sup −3} at 300 K resulting in a high TE power factor defined herein as (α{sup 2}σT) ∼ 0.84 W/m-K at 760 K. Despite the similar atomic masses of Sr (87.6 g/mol) and Y (88.9 g/mol), the lattice thermal conductivity (κ{sub L}) of Sr{sub 1−x}Y{sub x}TiO{sub 3−δ} is significantly reduced with increased Y-doping, owing to the smaller ionic radii of Y{sup 3+} (∼1.23 Å, coordination number 12) compared to Sr{sup 2+} (∼1.44 Å, coordination number 12) ions. In order to understand the thermal conductivity reduction mechanism, the κ{sub L} in the Sr{sub 1−x}Y{sub x}TiO{sub 3−δ} series are phenomenologically modeled with a modified Callaway's equation from 30–600 K. Phonon scattering by elastic strain field due to ionic radii mismatch is found to be the prominent scattering mechanism in reducing κ{sub L} of these materials. In addition, the effect of Y-doping on the elastic moduli of Sr{sub 1−x}Y{sub x}TiO{sub 3−δ} (x = 0, 0.1) is investigated using resonant ultrasound spectroscopy, which exhibits an anomaly in x = 0.1 in the temperature range 300–600 K. As a result, the phonon mean free path is found to be further reduced in the Sr{sub 0.9}Y{sub 0.1}TiO{sub 3−δ} compared to that of SrTiO{sub 3−δ}, resulting in a considerably low thermal conductivity κ ∼ 2.7 W/m-K at 760 K. Finally, we report a thermoelectric figure of merit (ZT) ∼ 0.3 at 760 K in the Sr{sub 0.9}Y{sub 0.1}TiO{sub 3−δ}, the highest ZT value reported in the Y-doped SrTiO{sub 3} ceramics thus far.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2016

Synthesis and characterization of Sn-doped hematite as visible light photocatalyst

Highlights: • Sn-doped hematite nanoparticles are prepared by SCS in one step. • The Sn doping have the ability to inhibit particle growth of hematite. • Sn can enhance visible light harvesting and e{sup −}/h{sup +} separation. • Sn-doped hematite degrades MB under visible light effectively. • The products with 5 mol% Sn have the highest photocatalytic activity. - Abstract: Sn-doped hematite nanoparticles are prepared by solution combustion synthesis. The products are characterized with various analytical and spectroscopic techniques to determine their structural, morphological, light absorption and photocatalytic properties. The results reveal that all the samples consist of nanocrystalline hematite with mesoporous structures, and Sn has the ability to inhibit the growth of hematite particle. Compared to pure hematite, the doped hematite samples with appropriate amount of Sn show better activities for degradation of methylene blue under visible light irradiation. The highest activity is observed for 5% Sn doped hematite and this product has long-term stability and no selectivity for dye degradation. The enhanced performance of 5% Sn doped hematite is ascribed to the smaller particle size, increased ability to absorb in visible light, efficient charge separation as well as improved e{sup −} transfer associated with the effects of appropriate amount of Sn doped sample.

36 MATERIALS SCIENCE↗
DOE OSTI2013

High figure of merit and thermoelectric properties of Bi-doped Mg{sub 2}Si{sub 0.4}Sn{sub 0.6} solid solutions

The study of Mg{sub 2}Si{sub 1−x}Sn{sub x}-based thermoelectric materials has received widespread attention due to a potentially high thermoelectric performance, abundant raw materials, relatively low cost of modules, and non-toxic character of compounds. In this research, Mg{sub 2.16}(Si{sub 0.4}Sn{sub 0.6}){sub 1−y}Bi{sub y} solid solutions with the nominal Bi content of 0≤y≤0.03 are prepared using a two-step solid state reaction followed by spark plasma sintering consolidation. Within this range of Bi concentrations, no evidence of second phase segregation was found. Bi is confirmed to occupy the Si/Sn sites in the crystal lattice and behaves as an efficient n-type dopant in Mg{sub 2}Si{sub 0.4}Sn{sub 0.6}. Similar to the effect of Sb, Bi doping greatly increases the electron density and the power factor, and reduces the lattice thermal conductivity of Mg{sub 2.16}Si{sub 0.4}Sn{sub 0.6} solid solutions. Overall, the thermoelectric figure of merit of Bi-doped Mg{sub 2.16}Si{sub 0.4}Sn{sub 0.6} solid solutions is improved by about 10% in comparison to values obtained with Sb-doped materials of comparable dopant content. This improvement comes chiefly from a marginally higher Seebeck coefficient of Bi-doped solid solutions. The highest ZT∼1.4 is achieved for the y=0.03 composition at 800 K. - Graphical abstract: (a)The relationship between electrical conductivity and power factor for Sb/Bi-doped Mg{sub 2.16}(Si{sub 0.4}Sn{sub 0.6}){sub 1−y}(Sb/Bi){sub y} (0<y≤0.03) solid solutions. (b)The correlation between temperature and the combination of the lattice and the bipolar terms of thermal conductivity of Mg{sub 2.16}(Si{sub 0.4}Sn{sub 0.6}){sub 1−y}Bi{sub y} (0≤y≤0.03) solid solutions. (c)Temperature dependent dimensionless figure of merit ZT of Mg{sub 2.16}(Si{sub 0.4}Sn{sub 0.6}){sub 1−y}Bi{sub y} (0≤y≤0.03) solid solutions. - Highlights: • Bi doped Mg{sub 2.16}Si{sub 0.4}Sn{sub 0.6} showed 15% enhancement in the power factor as compared to Sb doped samples. • Bi doping reduced κ{sub ph} of Mg{sub 2.16}Si{sub 0.4}Sn{sub 0.6} due to stronger point defect scattering. • The highest ZT=1.4 at 800 K was achieved for Mg{sub 2.16}(Si{sub 0.4}Sn{sub 0.6}){sub 0.97}Bi{sub 0.03}.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2023

Improving Proton Conductivity by Navigating Proton Trapping in High Scandium-Doped Barium Zirconate Electrolytes

Proton-conducting oxides are used in intermediate-temperature (300 °C < T < 700 °C) applications of fuel cells, electrolyzers, membrane reactors, hydrogen pumps, and sensors. The proton conductivity of doped ABO 3 perovskites is partly dependent on the proton concentration and hence on the level of material hydration. However, how the material hydration ability is affected by differences in doping is not fully understood. Here, we show the prospect of proton trapping and detrapping that influences material hydration and dehydration. The proton-trapping influence is significant for Sc-doped BaZrO 3 compared to Y-doped BaZrO 3 . Here, our work offers a perspective to understand how defect interaction/associations influence the hydration ability of proton-conducting oxides. Furthermore, positron annihilation lifetime spectroscopy was revealed to be a valuable technique for studying the proton-trapping phenomena and the defect chemistry of dense proton conductors. Density functional theory calculations also showed that a high hydration level in Sc-doped BaZrO 3 boosts proton migration. In contrast, the effect of boosting the proton migration due to increased hydration is limited for Y-doped BaZrO 3 . This effect, in turn, might explain the trend of conductivity with dopant concentration in doped BaZrO 3 .

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

Low Regeneration Temperature Sorbents for Direct Air Capture of CO 2

Susteon Inc., in partnership with University of Wyoming and SoCalGas, successfully met all major technical objectives to (1) scale up the ionic liquid catalyst for amine-based sorbents for improved desorption and absorption kinetics, (2) evaluate the catalyzed amine-based sorbents for direct CO 2 capture process to determine CO 2 adsorption and desorption rates and energy requirements, and (3) based on the experimental results, develop a conceptual process design to perform a preliminary economic assessment to evaluate the potential for DAC process cost reduction using the catalyzed sorbents. Amine doped solid sorbents are effective for DAC applications and can be regenerated by heat or by a combination of heat, steam, and vacuum. The best sorbent composition identified was polyethyleneimine (PEI) on fumed silica with 200 ppm ionic liquid catalyst. This sorbent formulation was shown to have a CO 2 breakthrough capacity twice that of the non-catalyzed sorbent, in laboratory tests with air at 75% relative humidity (RH). The CO 2 adsorption rate was also 40% higher than that of the non-catalyzed sorbent. This type of sorbents has the attributes required for lowering the overall cost of DAC with high CO 2 capacity and high rate of adsorption. The combination of an industrially utilized amine-based sorbent with a highly active catalyst to form a new class of materials for DAC provides a technically viable pathway for reducing the cost of DAC to <$100/tonne of CO 2 . Laboratory measurements show that the silica/PEI (polyethyleneimine) sorbents with 100 ppm of ionic liquid catalyst have almost 100% higher CO 2 cyclic capacity and 40% higher adsorption rate. Generally, CO 2 desorption occurred at higher temperatures with a rate of desorption 10 times faster than adsorption (which occurred at ambient conditions). Therefore, adsorption rate is a much more important factor in the cost of DAC because it is directly linked to the CAPEX of the total system and the cycle time (i.e., sorbent productivity in ton/day of CO 2 captured per unit volume of the air contactor). An initial process design, coupled with techno-economic analysis, based on optimal experimental results and preliminary resulting from structured sorbent testing, showed a path to lower the DAC cost from the current cost of over $200/tonne CO 2 to less than $100/tonne with a scale-up, mature state of the technology, with projected material and process improvements. These results demonstrate the effectiveness of the catalyst in silica/PEI sorbents in enhancing sorbents’ CO 2 working capacity, in (a) increasing the rate of adsorption and desorption, and (b) in lowering the CAPEX and OPEX of the DAC system employing the ionic liquid catalyzed sorbents.

01 COAL, LIGNITE, AND PEAT↗
DOE OSTI2020

Effects of HFIR neutron irradiation on fracture toughness properties of standard and Ni-doped F82H

F82H is the Japanese reference reduced-activation ferritic-martensitic (RAFM) steel for fusion blanket applications. The harsh environment of a fusion reactor, such as neutron irradiation and He/H damage, can result in significant degradation of F82H fracture toughness. Therefore, understanding the fracture toughness behavior of F82H in the fusion environment is critical to ensure the long-term safe operation of the fusion reactor. Here, we summarize seven irradiation campaigns of the High Flux Isotope Reactor (HFIR) at Oak Ridge National Laboratory (ORNL) covering five variants of F82H steels, including F82H IEA, F82H Mod3, F82H doped with 1.4% natural Ni, F82H doped with 1.4% 58 Ni, and F82H doped with 1.4% 60 Ni. The irradiation temperatures covered the range from 220 °C to 530 °C and the neutron irradiation dose spanned 4 dpa to 70 dpa. The effects of neutron irradiation temperature, dose, materials composition, Ni doping, and He production on F82H fracture toughness are discussed. Our results showed that irradiation embrittlement monotonically decreased with increasing irradiation temperature until 400 °C for F82H IEA and F82H Mod3. F82H Mod3 showed better fracture toughness than F82H IEA both before and after neutron irradiation. We determined that 1.4% Ni alloying can be applied to F82H for simulating He effect in a fission reactor without jeopardizing the fracture toughness of the material. However, more studies are needed to understand the effect of high dose (>20 dpa) and He production on F82H fracture toughness.

36 MATERIALS SCIENCE↗
DOE OSTI2013

Conversion mechanism of conductivity of phosphorus-doped ZnO films induced by post-annealing

The effects of post-annealing on conductivity of phosphorus-doped ZnO (PZO) films grown at 500 Degree-Sign C by radio frequency magnetron sputtering are investigated in a temperature ranging from 600 Degree-Sign C to 900 Degree-Sign C. The as-grown PZO exhibits n-type conductivity with an electron concentration of 1.19 Multiplication-Sign 10{sup 20} cm{sup -3}, and keeps n-type conductivity as annealed at 600 Degree-Sign C-700 Degree-Sign C but electron concentration decreases with increasing temperature. However, it converts to p-type conductivity as annealed at 800 Degree-Sign C. Further increasing temperature, it still shows p-type conductivity but the hole concentration decreases. It is found that the P occupies mainly Zn site (P{sub Zn}) in the as-grown PZO, which accounts for good n-type conductivity of the as-grown PZO. The amount of the P{sub Zn} decreases with increasing temperature, while the amount of Zn vacancy (V{sub Zn}) increases from 600 Degree-Sign C to 800 Degree-Sign C but decreases greatly at 900 Degree-Sign C, resulting in that the amount of P{sub Zn}-2V{sub Zn} complex increases with increasing temperature up to 800 Degree-Sign C but decreases above 800 Degree-Sign C. It is suggested that the P{sub Zn}-2V{sub Zn} complex acceptor is responsible for p-type conductivity, and that the conversion of conductivity is due to the change of the amount of the P{sub Zn} and P{sub Zn}-2V{sub Zn} with annealing temperature.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Terbium induced glassy magnetism in La,Ca-based cobaltites

The La{sub 0.8–x}Tb{sub x}Ca{sub 0.2}CoO{sub 3} cobaltites of orthoperovskite Pbnm structure were investigated by the X-ray and neutron diffraction, specific heat, and magnetization measurements. The terbium doping has two important effects, it increases the size disorder on perovskite A-sites and influences the magnetic properties due to large Ising-type moments (∼8.9 Bohr magnetons per Tb). The compounds show a bulk magnetic moment below T{sub C} = 82 K, 53 K, and 30 K for x = 0.1, 0.2, and 0.3, respectively. The neutron diffraction evidences a long-range ferromagnetic arrangement of cobalt moments, combined below ∼20 K with ordering of terbium moments in a canted arrangement. A homogeneous magnetic phase is proved for the x = 0.1 sample, while x = 0.2 and 0.3 are in an intrinsically non-homogeneous magnetic state with long-range ordering only comprising 55% and 30% of the sample volumes. The ac susceptibility experiments prove a glassy character of the terbium doped samples and provide arguments for the short-range ordering above T{sub C} and wide distribution of relaxation times.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Successes and failures of Hubbard-corrected density functional theory: The case of Mg doped LiCoO{sub 2}

We have evaluated the successes and failures of the Hubbard-corrected density functional theory approach to study Mg doping of LiCoO{sub 2}. We computed the effect of the U parameter on the energetic, geometric, and electronic properties of two possible doping mechanisms: (1) substitution of Mg onto a Co (or Li) site with an associated impurity state and (2) formation of impurity-state-free complexes of substitutional Mg and point defects in LiCoO{sub 2}. We find that formation of impurity states results in changes on the valency of Co in LiCoO{sub 2}. Variation of the Co U shifts the energy of the impurity state, resulting in energetic, geometric, and electronic properties that depend significantly on the specific value of U. In contrast, the properties of the impurity-state-free complexes are insensitive to U. These results identify reasons for the strong dependence on the doping properties on the chosen value of U and for the overall difficulty of achieving agreement with the experimentally known energetic and electronic properties of doped transition metal oxides such as LiCoO{sub 2}.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS1986

Overcash, D. R.

The objectives of this investigation were to determine the characteristics of semiconductor devices at low temperatures. The output characteristics of several currently available semiconductor devices and devices fabricated at Marshall Space Flight Center were measured over a range of gate voltages. Large variations in low-temperature performance, not only from type to type, but from field effect transistor (FET) to FET of the same type were obtained. By increasing the carrier concentrations at low temperatures through extra heavy doping, metal oxide semiconductor field effect transistor (MOSFET) device was fabricated that operated at 4.2K. To verify the low-temperature operation of a heavily doped device, this procedure was repeated. Their noise spectrum was analyzed at 4.2K. Suggestions were made as to possible fabrication methods, techniques, and other semiconductor materials that might improve the device charactersitics at low temperatures. A procedure for using an electric field to drift dopants through the insulating oxide to produce a very thin, heavily doped region under the gate of a MOSFET was initiated. Capacitance s a function of voltage plots was suggested as a method for determining the level of dopant drift.

Source record↗
DOE OSTI2022

Activating dislocation mediated plasticity in boron carbide through Al-doping

Dislocation slip, deformation twinning, phase transformations, and fast fracture are energy dissipation mechanisms that accommodate mechanical loading in materials. The energetically unfavorable formation of dislocation attributes to the ease of cracking and the low damage tolerance observed in superhard ceramics, notably boron carbide. Here, this work demonstrates that room temperature dislocation slip can be enabled in boron carbide by altering its chemistry through Al doping. The activation of dislocation slip is mechanistically explained by quantum mechanics simulations and electron microscopy, which indicate that strain energy is released through basal icosahedral slip facilitated by icosahedral rotation and chain bond breaking and reconfiguring. The new insight gained through this work suggests that atomic doping could be an effective strategy to tune deformation mechanisms in boron carbide, which provides a significant potential for limiting amorphization and catastrophic failure, and opens a new strategy to enhance damage tolerance in brittle ceramics.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Annealing dynamics of WO{sub 3} by in situ XRD

Highlights: • Flame-made WO{sub 3} nanoparticles with closely controlled crystal and grain size. • Dynamic phase transition of annealing of pure and Si-doped WO{sub 3} by in situ XRD. • Irreversible evolution of WO{sub 3} crystallinity by heating/cooling during its annealing. • Si-doping alters the WO{sub 3} crystallinity dynamics and stabilizes nanosized WO{sub 3}. • Flame-made nano-WO{sub 3} can sense NO at the ppb level. - Abstract: Tungsten trioxide is a semiconductor with distinct applications in gas sensors, catalysis, batteries and pigments. As such the transition between its different crystal structures during its annealing are of interest, especially for sensor applications. Here, WO{sub 3} nanoparticles with closely controlled crystal and grain size (9–15 nm) and phase composition are made by flame spray pyrolysis and the formation of different WO{sub 3} phases during annealing is investigated. Most notably, the dynamic phase transition and crystal size evolution of WO{sub 3} during heating and cooling is monitored by in situ X-ray diffraction revealing how metastable WO{sub 3} phases can be captured stably. The effect of Si-doping is studied since it is used in practise to control crystal growth and phase transition during metal oxide synthesis and processing. Finally the influence of annealing on the WO{sub 3} sensing performance of NO, a lung inflammation tracer in the human breath, is explored at the ppb-level.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Fe-doping induced suppression of the second magnetic transition in Sr 4 Ru 3 O 10

Ruthenium oxide (Sr 4 Ru 3 O 10 ) exhibits a second magnetic transition at a temperature T M below its ferromagnetic (FM) transition (T C ~ 105 K), which has attracted considerable attention in the past two decades. Here, we successfully grew Sr 4 (Ru 1–x Fe x ) 3 O 10 (x = 0.01) crystal and systematically investigated the magnetotransport property of its nanosheets. We found a feature that there is an in-plane FM order aligned along < 110 > directions below T C without the occurrence of the second magnetic transition at T M , which is in contrast to that expected in pure Sr 4 Ru 3 O 10 nanosheets, where the in-plane FM order will rotate to the c direction below T M . Furthermore, a metamagnetic-like transition is also observed below ~50 K at about 2 T when the magnetic field is applied along the c axis. Finally, these results unambiguously demonstrate that the second magnetic transition at T M is actually a consequence of spin reorientation induced by the inherent coupling between the spin and lattice, which can be effectively tuned by element doping.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗