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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 55 records · Page 3
All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

Charge doping effects on magnetic properties of single-crystal La 1-x Sr x (Cr 0.2 Mn 0.2 Fe 0.2 Co 0.2 Ni 0.2 )O 3 (0 ≤ x ≤ 0.5) high-entropy perovskite oxides

The observed influence of hole doping on magnetic properties is mapped for the compositionally complex high-entropy oxide ABO 3 perovskite La 1-x Sr x (Cr 0.2 Mn 0.2 Fe 0.2 Co 0.2 Ni 0.2 )O 3 (0 ≤ x ≤ 0.5). It is found that aliovalent A -site substitution is a viable means to manipulate the magnetically active B -site sublattice. A series of single-crystal films are synthesized and show a general trend toward stronger ferromagnetic response and a shift in magnetic anisotropy as the Sr concentration increases. Magnetometry demonstrates complex and nonuniform responses similar to rigid and uncoupled composites at intermediate dopings. This behavior points to the presence of locally inhomogeneous magnetic phase competition, where ferromagnetic and antiferromagnetic magnetic contributions create a frustrated matrix containing uncompensated spins at the boundaries between these regions. The observations are discussed in the context of known responses to hole doping in the less complex ternary LaT M O 3 (T M =Cr,Mn,Fe,Co,Ni) oxides, and they are found to be different from a simple sum of the doped parents. The results are summarized in a preliminary magnetic phase diagram.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Chromium doping effects on structural and dielectric properties of Mn-Zn cobaltites

The effect of transition metal Cr{sup 2+} ion as a dopant of Zn{sup 2+} in Mn{sub 0.5}Zn{sub 0.5}Co{sub 2}O{sub 4} is investigated. Co-doped Mn{sub 0.5}Zn{sub 0.5-x}Cr{sub x}Co{sub 2}O{sub 4} (x = 0, 0.3 and 0.5) cobaltites were prepared by solid-state reaction route. X-ray powder diffraction (XRD) analysis reveals that the samples prepared are polycrystalline single-phase cubic spinel in structure having a space group Fd3m. An increase in average particle size observed with Cr{sup 2+} doping. However other structural parameters such as X-ray density, micro strain and dislocation density shows almost a similar decreasing trend with increase in Cr{sup 2+}. High value of permittivity ∼10{sup 5} is observed for the parent Mn{sub 0.5}Zn{sub 0.5}Co{sub 2}O{sub 4} and shows a substantial decrease with increase in the Cr{sup 2+} doping. Higher doping of Cr{sup 2+} also increases the dielectric loss and hence limits its technological importance. At lower frequencies ac conductivity has been found to increase with increase in Cr{sup 2+} content.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

La{sub 2}Zr{sub 2}O{sub 7} Doping Effects on MOD-SmBCO-Coated Conductors

SmBa{sub 2}Cu{sub 3}O{sub 7-δ} (SmBCO)-coated conductors containing La{sub 2}Zr{sub 2}O{sub 7} (LZO) artificial pinning centers (APCs) were fabricated on buffered Hastelloy substrates by low fluorine metal organic deposition method (MOD). The properties of LZO-doped SmBCO film were systematically studied by x-ray diffraction (XRD), Raman spectra, and scanning electron microscope (SEM). Higher critical current density (J{sub c}) values not only in self field but also in applied magnetic field were obtained by moderate LZO doping.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2021

Gallium‐Doping Effects on Structure, Lithium‐Conduction, and Thermochemical Stability of Li 7‐3 x Ga x La 3 Zr 2 O 12 Garnet‐Type Electrolytes

Abstract One of the most promising electrolytes for all‐solid‐state lithium batteries is Li 7 La 3 Zr 2 O 12 . Previously, their thermodynamic stability, Li‐ion conductivity, and structural features induced by Ga‐doping have not been empirically determined or correlated. Here, their interplay was examined for Li 7−3 x Ga x La 3 Zr 2 O 12 with target x Ga=0, 0.25, 0.50, 0.75, and 1.00 atoms per formula unit (apfu). Formation enthalpies, obtained with calorimetry and found to be exothermic at all compositions, linearly decreased in stability with increased x Ga. At dilute x Ga substitution, the formation enthalpy curve shifted stepwise endothermically, and the conductivity increased to a maximum, coinciding with 0.529 Ga apfu. This correlated with percolation threshold analysis (0.558 Ga apfu). Further substitution (0.787 Ga apfu) produced a large decrease in the stability and conductivity due to a large increase in point defects and blocked Li‐migration pathways. At x Ga=1.140 apfu, a small exothermic shift was related to defect cluster organization extending the Li hopping distance and decreased Li‐ion conductivity.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2017

Ni-Doping Effects on Oxygen Removal from an Orthorhombic Mo 2 C (001) Surface: A Density Functional Theory Study

Density functional theory (DFT) calculations were used in this paper to investigate the effect of Ni dopants on the removal of chemisorbed oxygen (O*) from the Mo-terminated (T Mo ) and C-terminated (T C ) Mo 2 C(001) surfaces. The removal of adsorbed oxygen from the catalytic site is essential to maintain the long-term activity and selectivity of the carbide catalysts in the deoxygenation process related to bio-oil stabilization and upgrading. In this contribution, the computed reaction energetics and reaction barriers of O* removal were compared among undoped and Ni-doped Mo 2 C(001) surfaces. The DFT calculations indicate that selected Ni-doped surfaces such as Ni adsorbed on T Mo and T C Mo 2 C(001) surfaces enable weaker binding of important reactive intermediates (O*, OH*) compared to the undoped counterparts, which is beneficial for the O* removal from the catalyst surface. This study thus confirms the promoting effect of the Ni dopant on O* removal reaction on the T Mo Mo 2 C(001) and T C Mo 2 C(001) surfaces. Finally, this computational prediction has been confirmed by the temperature-programmed reduction profiles of Mo 2 C and Ni-doped Mo 2 C catalysts, which had been passivated and stored in an oxygen environment.

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

Size, Composition, and Support-Doping Effects on Oxygen Reduction Activity of Platinum-Alloy and on Non-platinum Metal-Decorated-Graphene Nanocatalysts

Recent investigations reported in the open literature concerning the functionalization of graphene as a support material for transition metal nanoparticle catalysts have examined isolated systems for their potential Oxygen Reduction Reaction (ORR) activity. In this work we present results which characterize the ability to use functionalized graphene (via dopants B, N) to upshift and downshift the adsorption energy of mono-atomic oxygen, O* (the ORR activity descriptor on ORR Volcano Plots), for various compositions of 4-atom, 7-atom, and 19-atom sub-nanometer binary alloy/intermetallic transition metal nanoparticle catalysts on graphene (TMNP-MDG). Our results show several important and interesting features: (1) that the combination of geometric and electronic effects makes development of simple linear mixing rules for size/composition difficult; (2) that the transition from 4- to 7- to 19-atom TMNP on MDG has pronounced effects on ORR activity for all compositions; (3) that the use of B and N as dopants to modulate the graphene-TMNP electronic structure interaction can cause shifts in the oxygen adsorption energy of 0.5 eV or more; (4) that it might be possible to make specific doped-graphene-Ni x Cu y TMNP systems which fall close to the Volcano Peak for ORR. Our results point to systems which should be investigated experimentally and may improve the viability of future fuel cell or other ORR applications, and provide new paths for future investigations of more detail for TMNP-MDG screening.

Chemistry↗
DOE OSTI2015

Sr doping effect on micro structural, transport and magnetic properties in Pr{sub 1-x}Sr{sub x}MnO{sub 3} (0.2 ≤ x ≤ 0.4) nanomanganite

In this article, microstructural, magnetic, magneto-transport, electronic transport properties of Pr{sub 1-x}Sr{sub x}MnO{sub 3} system have been systematically studied in nanometric dimension over the range 0.2 ≤ x ≤ 0.4 by preparing the compound through pyrophoric reaction route. XRD diffraction measurements indicate that all the samples are in orthorhombic Pbnm space group. Electronic and magneto-transport properties of these materials have been thoroughly investigated in nanometric grain size modulation. These Sr doped compounds at x=0.3 exhibit more ferromagnetic metallic behavior at zero field and negative magneto resistance in low temperature. The different magnetic phase was found using ac magnetic susceptibility measurement. Magneto –transport nature is explained using spin polarization tunneling model.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2016

Doping effect on the structural properties of Cu{sub 1−x}(Ni, Zn, Al and Fe){sub x}O samples (0<x<0.10): An experimental and computational study

In this work, the effect of insertion of transition metal, TM (=Ni, Zn, Al and Fe), ions in Cu{sub 1−x}TM{sub x}O samples (0<x<0.10) prepared via co-precipitation method is studied through experimental and computational methods. The analyses of X-ray diffraction (XRD) patterns using Rietveld refinement show that i) at x=0, all samples present a monoclinic crystal system with space group C2/c and ii) for increasing the TM-doping, Ni and Zn-doped samples show a small amount of spurious phases for concentrations above x=0.05. Based on these results, a defect disorder study for using atomistic computational simulations which is based on the lattice energy minimization technique is employed to predict the location of the dopant ions in the structure. In agreement with XRD data, our computational results indicate that the trivalent (Al and Fe ions) are more favorable to be incorporated into CuO matrix than the divalent (Ni and Zn ions). - Graphical Abstract: The effect of insertion of transition metal, TM (=Ni, Zn, Al and Fe), ions in Cu{sub 1−x}TM{sub x}O samples (0<x<0.10) prepared via co-precipitation method is studied through experimental and computational methods. Display Omitted.

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

Heavy doping effects in high efficiency silicon solar cells

The temperature dependence of the emitter saturation current for bipolar devices was studied by varying the surface recombination velocity at the emitter surface. From this dependence, the value was derived for bandgap narrowing that is in better agreement with other determinations that were obtained from the temperature dependence measure on devices with ohmic contacts. Results of the first direct measurement of the minority-carrier transit time in a transparent heavily doped emitter layer were reported. The value was obtained by a high-frequency conductance method recently developed and used for doped Si. Experimental evidence is presented for significantly greater charge storage in highly excited silicon near room temperature than conventional theory would predict. These data are compared with various data for delta E sub G in heavily doped silicon.

Lindholm, F. A.↗
DOE OSTI2022

Geometric and doping effects on radiative recombination in thin-film near-field energy converters

Modeling radiative recombination is crucial to the analysis of radiative energy converters. In this work, a local radiative recombination coefficient is defined and derived based on fluctuational electrodynamics that is applicable to thin-film cells in both the near field and far field. The predicted radiative recombination coefficient of an InAs cell deviates from the van Roosbroeck–Shockley relation when the thickness is less than 10 µm, and the difference exceeds fourfold with a 10 nm film. The local radiative recombination coefficient is orders of magnitude higher when an InAs cell is configured in the near field. The local radiative recombination coefficient reduces as the doping level approaches that of a degenerate semiconductor. The maximum output power and efficiency of a thermoradiative cell would be apparently overpredicted if the electroluminescence coefficient defined in this paper were taken as unity for heavily doped semiconductors.

Feng, Dudong↗
DOE OSTI2018

Controlling the Charge Density Wave Transition in Monolayer TiSe 2 : Substrate and Doping Effects

Abstract TiSe 2 is an exciting material because it can be tuned between superconducting and charge density wave (CDW) transitions. In the monolayer limit, TiSe 2 exhibits a sizable energy gap in the CDW phase that makes it a promising quantum material. It is shown that interfacing a single layer of TiSe 2 with dissimilar van der Waals materials enables control of its properties. Using angle‐resolved photoemission spectroscopy, the energy gap opening is analyzed as a function of temperature for TiSe 2 monolayers supported on different van der Waals substrates. A substantial increase in the CDW transition temperature of ≈45 K is observed on MoS 2 compared to graphite (highly oriented pyrolytic graphite) substrates. This control of the CDW in monolayer TiSe 2 is suggested to arise from varying charge screening of the unconventional CDW of TiSe 2 by the substrate. In addition, the suppression of CDW order and a complete closing of the energy gap by electron doping of monolayer TiSe 2 is demonstrated. Regulating the many‐body physics phenomena in monolayer TiSe 2 lays the foundation of modifying TiSe 2 in, for example, artificial van der Waals heterostructures and thus creates a new approach for utilizing the quantum states of TiSe 2 in device applications.

Kolekar, Sadhu↗
DOE OSTI2019

Doping Effect of Fe Ions on the Structural, Electrical, and Magnetic Properties of SrTiO{sub 3} Nanoceramic Matrix

In the present investigation, strontium titanate nanoceramic was synthesized by incorporating iron (Fe) ion with general formula SrTi{sub 1−x}Fe{sub x}O{sub 3} (x = 0.0, 0.1, 0.2, and 0.4) using sol-gel autocombustion method. The effect of Fe ions on the structural, morphological, electrical, dielectric, and magnetic properties of the prepared matrix has been investigated by various characterization techniques with the appropriate formulation. The structural properties such as phase space, crystallite size (D), and lattice parameter (a) of prepared matrix are calculated by X-ray diffraction (XRD) technique. The functional groups were analyzed by Fourier transform infrared spectroscopy (FT-IR). The surface morphology of the prepared nanoceramic matrix has been determined by using field emission scanning electron microscopy (FE-SEM) analysis. Calculation of average particle size and diffraction patterns was confirmed by using images from transmission electron microscopy (TEM) and selected area electron diffraction pattern (SAED), respectively. An energy dispersive spectrum analysis (EDS) confirmed the compositional stoichiometry in the investigated matrix. Electrical conductivity increased the prepared sample due to the increasing in the Fe concentration and temperature. The dielectric parameters in the frequency range of 30 Hz to 1 MHz were found higher at lower frequencies. The pure SrTiO{sub 3} matrix shows a paramagnetic nature at room temperature, but for a higher concentration of Fe doping was used to observe the weak ferromagnetic nature. Therefore, due to Fe ion concentration, the properties of the prepared matrix have been completely varied and enhancement in the magnetic properties was observed.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2015

Effective doping of low energy ions into superfluid helium droplets

We report a facile method of doping cations from an electrospray ionization (ESI) source into superfluid helium droplets. By decelerating and stopping the ion pulse of reserpine and substance P from an ESI source in the path of the droplet beam, about 10{sup 4} ion-doped droplets (one ion per droplet) can be recorded, corresponding to a pickup efficiency of nearly 1 out of 1000 ions. We attribute the success of this simple approach to the long residence time of the cations in the droplet beam. The resulting size of the doped droplets, on the order of 10{sup 5}/droplet, is measured using deflection and retardation methods. Our method does not require an ion trap in the doping region, which significantly simplifies the experimental setup and procedure for future spectroscopic and diffraction studies.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2015

Threshold switching behavior of Ag-Si based selector device and hydrogen doping effect on its characteristics

The effect of hydrogen treatment on the threshold switching property in a Ag/amorphous Si based programmable metallization cells was investigated for selector device applications. Using the Ag filament formed during motion of Ag ions, a steep-slope (5 mV/dec.) for threshold switching with higher selectivity (∼10{sup 5}) could be achieved. Because of the faster diffusivity of Ag atoms, which are inside solid-electrolytes, the resulting Ag filament could easily be dissolved under low current regime, where the Ag filament possesses weak stability. We found that the dissolution process could be further enhanced by hydrogen treatment that facilitated the movement of the Ag atoms.

36 MATERIALS SCIENCE↗