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Sample records for o3 nitrogen-saturated site

  1. California black oak response to nitrogen amendment at a high O3, nitrogen-saturated site.

    PubMed

    Grulke, N E; Dobrowolski, W; Mingus, P; Fenn, M E

    2005-10-01

    In a nitrogen (N) saturated forest downwind from Los Angeles, California, the cumulative response to long-term background-N and N-amendment on black oak (Quercus kelloggii) was described in a below-average and average precipitation year. Monthly measurements of leaf and branch growth, gas exchange, and canopy health attributes were conducted. The effects of both pollutant exposure and drought stress were complex due to whole tree and leaf level responses, and shade versus full sun leaf responses. N-amended trees had lower late summer carbon (C) gain and greater foliar chlorosis in the drought year. Leaf water use efficiency was lower in N-amended trees in midsummer of the average precipitation year, and there was evidence of poor stomatal control in full sun. In shade, N-amendment enhanced stomatal control. Small differences in instantaneous C uptake in full sun, lower foliar respiration, and greater C gain in low light contributed to the greater aboveground growth observed.

  2. IMPLICATION OF LAKE WATER RESIDENCE TIME ON THE CLASSIFICATION OF NORWEGIAN SURFACE WATER SITES INTO PROGRESSIVE STAGES OF NITROGEN SATURATION

    EPA Science Inventory

    Seasonal behaviour of NO3- in surface water is often used as an indicator on a catchment's ability to retain N from atmospheric deposition. In this paper, we classify 12 pristine sites (five streams and seven lakes) in southernmost Norway according to the N saturation stage conce...

  3. Emission of Nitrous Oxide in Temperate Forests with Different Stages of Nitrogen Saturation in Central Japan

    NASA Astrophysics Data System (ADS)

    Shaoyan, F.

    2015-12-01

    Long-term nitrogen deposition has caused a problem called nitrogen saturation in forest ecosystems globally. Aber et al. (1989) suggested that nitrogen saturation activate soil nitrification in forest systems, which is the main process of N2O production in aerobic condition. Thus, nitrogen saturation may affect significantly the N2O emission from forests, while the impact on flux has not been quantitatively evaluated yet. In the present study, 3-year monitoring of N2O emission was performed in an N-saturated forests (Tama Hill, Tokyo): the emission rate of N2O was measured monthly by a closed chamber method at 12 plots along a slope, and the net nitrification rate of surface soil (0-10 cm) was measured 4 times in situ. In addition, a comparative research was conducted in summer in eight temperate forests with different stages of nitrogen saturation in central Japan; the N2O flux, soil moisture, nitrogen availability and stream water NO3- concentration were measured at each site. In an N-saturated forests, the annual N2O emission was estimated to be 0.88 kg N ha-1year-1 , showing a typical seasonal variation . The seasonal patterns of N2O emission were significantly related to soil moisture and ambient temperature. We also found high spatial variation of N2O flux among 12 plots along the slope, which was generally higher at the bottom. Moreover, a positive correlation was found between the rate of N2O emission and the net nitrification rate with WFPS<60%, while it was unclear in some humid spots with WFPS>60% , probably due to the effect of denitrification. In comparison sites, the N2O emission rate ranged nearly 16-fold from 0.13-2.11 g N ha-1day-1 was linearly related to the stream water NO3- concentration ranged 10-fold from 0.14 to 1.4 mg N/L. Our results revealed N enrichment in forest obviously stimulate soil N2O emission. Keywords: Nitrous oxide, nitrogen saturation, nitrification, temperate forest

  4. A-site layer terminated perovskite substrate: NdGaO3

    NASA Astrophysics Data System (ADS)

    Ohnishi, Tsuyoshi; Takahashi, Kazuhiro; Nakamura, Masashi; Kawasaki, Masashi; Yoshimoto, Mamoru; Koinuma, Hideomi

    1999-04-01

    A perovskite single-crystal substrate, NdGaO3 (001), was thermally annealed in air to give an atomically defined surface structure. From analysis with coaxial impact-collision ion scattering spectroscopy, the terminating atomic layer was identified to be NdO1+δ , i.e., the A-site oxide monolayer in perovskite ABO3. This result is contrary to the B-site oxide (BO2-δ) termination observed in other perovskite surfaces, such as wet etched SrTiO3 and LaAlO3 or annealed (LaAlO3)0.3-(Sr2AlTaO6)0.7 (LSAT).

  5. Physiological and developmental effects of O3 on cottonwood growth in urban and rural sites.

    PubMed

    Gregg, Jillian W; Jones, Clive G; Dawson, Todd E

    2006-12-01

    Previously we found that cloned cottonwood saplings (Populus deltoides) grew twice as large in New York, New York, USA, compared to surrounding rural environments and that soils, temperature, CO2, nutrient deposition, and microclimatic variables could not account for the greater urban plant biomass. Correlations between final season biomass and cumulative O3 exposures, combined with twofold growth reductions in an open-top chamber experiment provided strong evidence that higher cumulative O3 exposures in rural sites reduced growth in the country. Here, we assess the field gas exchange, growth and development, and allocation responses underlying the observed growth differences and compare them with isolated O3 responses documented in the open-top chamber experiment. Cottonwoods showed no visible foliar injury, reduced photosynthesis of recently expanded foliage, early leaf senescence, protective reduction in stomatal conductance, or compensatory allocation to shoot relative to root biomass for either the chamber or field experiment. Instead, O3-impacted chamber plants had significantly higher conductance and reduced photosynthesis of older foliage that led to reduced leaf area production and a twofold biomass reduction in the absence of visible injury. Rural-grown field plants showed the same pattern of significantly higher conductance in the absence of concomitant increases in photosynthesis that was indicative of a loss of stomatal control. Incremental changes in foliar production were also significantly inversely related to fluctuations in ambient O3 exposures. The similarity in biomass, gas exchange, phenological, and allocation responses between chamber and field experiments indicate that mechanisms accounting for reduced growth at rural sites were consistent with those in the open-top chamber O3 experiment. This study shows the limitation of visible symptoms as a sole diagnostic factor for documenting detrimental O3 impacts and points toward a new approach to

  6. Site dilution in SrRuO3: effects on structural and magnetic properties

    NASA Astrophysics Data System (ADS)

    Gupta, Renu; Pramanik, A. K.

    2017-03-01

    We have investigated the effect of site dilution with substitution of nonmagnetic element in SrRu1‑x Ti x O3 (x  ⩽  0.7). The nature of ferromagnetic state in SrRuO3 is believed to be of itinerant type with transition temperature {{T}\\text{c}}∼ 162 K. Crystallographically, SrRuO3 has a distorted orthorhombic structure. Substitution of \\text{T}{{\\text{i}}+4} (3d 0) for Ru+4 (4d 4), however, does not introduce significant structural modification due to their matching ionic radii. This substitution, on the other hand, is expected to tune the electronic correlation effect and the d electron density in the system. With Ti substitution, we find that magnetic moment and Curie temperature decreases but T c remains unchanged which has been attributed to opposite tuning of electron correlation effect and density of states within the framework of itinerant ferromagnetism. The estimated critical exponent (β) related to magnetization implies a mean-field type of magnetic nature in SrRuO3. The value of β further increases with x which is understood from the dilution effect of magnetic lattice. The system evolves to exhibit Griffiths phase like behavior above T c which is usually realized in diluted ferromagnet following local moment model of magnetism. Our detail analysis of magnetization data indicates that magnetic state in SrRuO3 has contribution from both itinerant and local moment model of magnetism.

  7. Iron spin state and site distribution in FeAlO3-bearing bridgmanite

    NASA Astrophysics Data System (ADS)

    Mohn, Chris E.; Trønnes, Reidar G.

    2016-04-01

    DFT at the GGA, GGA + U and hybrid functional levels were used to investigate thousands of different Al and Fe3+ configurations of MgSiO3-FeAlO3 (MS-FA) and MgSiO3-FeAlO3-Al2O3 bridgmanite at deep mantle conditions. Comparison of the different functionals and atomic charge analysis suggests that GGA, frequently used to explain high to low spin transitions observed in several Mössbauer and X-ray emission spectroscopy experiments, is hampered by spurious self-interaction errors in the exchange-correlation energy. Configurational Boltzmann averaging shows that the B site is thermally inaccessible to Fe3+ at the GGA + U and hybrid levels, and we find no evidence for a spin-pairing transition in fully (thermodynamically) equilibrated samples of bridgmanite, even at the lowermost mantle conditions. The comparison of the cation radii of Fe3+ and Mg supports a spin transition accompanied by a site exchange, but the flexibility of Fesbnd O bonds to locally adapt promotes the incorporation of iron in the irregularly coordinated A-site. The concept of ionic radii is therefore unsuitable for analysis of spin state and site exchange in bridgmanite at these conditions. Consistent with previous computational work and experimental studies with glass and gel as starting material, we find that ferric iron kinetically trapped at the B site undergoes a spin transition under lowermost mantle conditions. In bridgmanite with mole fraction of Fe3+ >Al a charge-balancing amount of low spin Fe3+ will be thermodynamically stable at the B site, but because bridgmanite in peridotitic and basaltic lithologies mostly has Al/Fetotal above unity, FA with high spin Fe3+ in the A-site will be the dominant iron component. The lack of a Fe3+ spin transition in the FA-component has important implications for bridgmanite-ferropericlase partitioning of iron and magnesium and the mineral physics of the lowermost mantle.

  8. Site Determination of Mn Doping in Protein Encapsulated γ-Fe2O3 Nanoparticles

    NASA Astrophysics Data System (ADS)

    Pool, V.; Klem, M.; Jolley, C.; Douglas, T.; Young, M.; Arenholz, E.; Idzerda, Y. U.

    2010-03-01

    In this study, Mn has been doped (0-33%) into 6 nm, γ-Fe2O3 nanoparticles grown inside the horse-spleen ferritin (HSF) protein and compared to similarly protein encapsulated pure γ-Fe2O3 and Mn-oxide nanoparticles to determine the Mn doping site. By using soft-X-ray absorption spectroscopy (XAS), soft-X-ray magnetic circular dichroism (XMCD), and frequency dependent Alternating Current Magnetic Susceptibility (ACMS), we have ascertained that the Mn dopant is substituting preferentially as Mn^+2 and prefers the octahedral site in the γ-phase Fe2O3 spinel structure. The measured Mn L23 XAS spectra are compared to measured reference powders and molecular-orbital calculations supporting this conclusion of the Mn dopant substitution site. We find that the Mn L23 XAS multiplet structure for the nanoparticles is simpler than for our bulk standards, complicating this identification but suggesting that the nanoparticle lattices are relaxed from the distortions present in the bulk.

  9. Photophysical and photocatalytic properties of SrTiO3 doped with Cr cations on different sites.

    PubMed

    Wang, Defa; Ye, Jinhua; Kako, Tetsuya; Kimura, Takashi

    2006-08-17

    Usually, SrTiO3 monodoped with Cr cations at the Ti4+ site hardly shows visible light photocatalytic activity. Revealing the origin of this issue is important for us to find an alternative approach to make SrTiO3 active under visible light irradiation. In this paper, two Cr-doped SrTiO3-(Sr0.95Cr0.05)TiO3 and Sr(Ti0.95Cr0.05)O3-were synthesized by a conventional solid-state reaction method, and their photophysical and photocatalytic properties were studied comparatively. It was found that both (Sr0.95Cr0.05)TiO3 and Sr(Ti0.95Cr0.05)O3 showed considerable absorption to visible light. However, their photocatalytic activities for H2 evolution from aqueous methanol solution under visible light irradiation were significantly different: the H2 evolution rate over (Sr0.95Cr0.05)TiO3 (approximately 21 micromol/h) was more than 100 times that over Sr(Ti0.95Cr0.05)O3 (approximately 0.2 micromol/h). X-ray photoelectron spectroscopy analysis results revealed that the Cr cations doped at the Sr2+ site were all trivalent state (Cr3+), while those doped at the Ti4+ site were mixed valent states (Cr3+ and Cr6+). The different photocatalytic activities of H2 evolution are supposed to closely relate to the different valent states of Cr doped at different sites (Sr2+ or Ti4+) in SrTiO3. Possible electronic structures of (Sr0.95Cr0.05)TiO3 and Sr(Ti0.95Cr0.05)O3 were proposed in relation to their photophysical and photocatalytic properties.

  10. Magnetic transition in Y-site doped multiferroic YMnO3

    NASA Astrophysics Data System (ADS)

    Thakur, Rajesh K.; Thakur, Rasna; Gaur, N. K.

    2016-05-01

    We have synthesized polycrystalline hexagonal Y1-xSrxMnO3 (x=0.02, 0.1) compounds by using conventional solid state reaction method. The detailed structural investigations are carried out by using XRD studies which reveals the single phase formation of the reported compounds with hexagonal structure and space group P63cm (JCPDS: 25-1079). Further the XRD data of reported compounds were analyzed by RIETVELD (FULLPROFF) method which shows the decrease in the lattice parameter with increasing concentration of divalent strontium to Y-site. The observed pointed kinks in the specific heat study are indicative of the probable coupling in between the electric and magnetic orders in this class of materials. The reported systematic specific heat studies shows that the antiferromagnetic (AFM) transition temperature (TN) shifts to higher value with increasing concentration of Sr2+ ion in the YMnO3 compound which is attributed to the enhanced lattice contribution to the specific heat in the this compound. The present compound shows the independence of specific heat and magnetic transition temperature with applied magnetic field of 8T and 12T.

  11. Lower tropospheric distributions of O3 and aerosol over Raoyang, a rural site in the North China Plain

    NASA Astrophysics Data System (ADS)

    Wang, Rui; Xu, Xiaobin; Jia, Shihui; Ma, Ruisheng; Ran, Liang; Deng, Zhaoze; Lin, Weili; Wang, Ying; Ma, Zhiqiang

    2017-03-01

    The North China Plain (NCP) has become one of the most polluted regions in China, with the rapidly increasing economic growth in the past decades. High concentrations of ambient O3 and aerosol have been observed at urban as well as rural sites in the NCP. Most of the in situ observations of air pollutants have been conducted near the ground so that current knowledge about the vertical distributions of tropospheric O3 and aerosol over the NCP region is still limited. In this study, vertical profiles of O3 and size-resolved aerosol concentrations below 2.5 km were measured in summer 2014 over a rural site in the NCP, using an unmanned aerial vehicle (UAV) equipped with miniature analyzers. In addition, vertical profiles of aerosol scattering property in the lower troposphere and vertical profiles of O3 below 1 km were also observed at the site using a lidar and tethered balloon, respectively. The depths of the mixed layer and residual layer were determined according to the vertical gradients of lidar particle extinction and aerosol number concentration. Average O3 and size-resolved aerosol number concentration in both the mixed and residual layer were obtained from the data observed in seven UAV flights. The results show that during most of the flights the O3 levels above the top of mixed layer were higher than those below. Such a positive gradient in the vertical distribution of O3 makes the residual layer an important source of O3 in the mixed layer, particularly during the morning when the top of mixed layer is rapidly elevated. In contrast to O3, aerosol number concentration was normally higher in the mixed layer than in the residual layer, particularly in the early morning. Aerosol particles were overwhelmingly distributed in the size range < 1 µm, showing slight differences between the mixed and residual layers. Our measurements confirm that the lower troposphere over the rural area of the NCP is largely impacted by anthropogenic pollutants locally emitted or

  12. Spatial distribution of active sites on a ferroelectric PbTiO3 photocatalyst for photocatalytic hydrogen production.

    PubMed

    Li, Rengui; Zhao, Yue; Li, Can

    2017-03-07

    The separation of photogenerated charge carries is a challenging issue in artificial photocatalyst systems for solar energy conversion. It has been reported that spatial charge separation can take place between different facets of semiconductor-based crystals with regular morphology and facets, which could be used to rationally deposit cocatalysts on the right facets. However, the spatial separation of photogenerated electrons and holes is still a big challenge for a particulate photocatalyst without regular morphology and specific facets. In this work, we demonstrated that photogenerated electrons and holes can be regularly separated on ferroelectric PbTiO3 photocatalyst even without regular morphology and facets. The reduction cocatalyst and oxidation cocatalyst could be selectively formed on different sites via an in situ photochemical deposition method. It is found that the photoactivity and hydrogen production for PbTiO3 with spatially separated dual-cocatalysts is remarkably enhanced to more than 100 times greater compared to native PbTiO3, which is much higher than that the case of dual-cocatalysts with a random distribution. The intrinsic electric fields and spontaneous electric polarization in the bulk of PbTiO3 are proposed to play important roles in the spatial distribution of active sites on irregular PbTiO3 particles. Our work emphasizes the essential roles of two important factors, efficient charge separation strategy and the location of dual-cocatalysts on the right sites, to construct integrated artificial photocatalyst systems for solar energy conversion.

  13. Highly Dispersed SiO(x)/Al2O3 Catalysts Illuminate the Reactivity of Isolated Silanol Sites.

    PubMed

    Mouat, Aidan R; George, Cassandra; Kobayashi, Takeshi; Pruski, Marek; van Duyne, Richard P; Marks, Tobin J; Stair, Peter C

    2015-11-02

    The reaction of γ-alumina with tetraethylorthosilicate (TEOS) vapor at low temperatures selectively yields monomeric SiO(x) species on the alumina surface. These isolated (-AlO)3Si(OH) sites are characterized by PXRD, XPS, DRIFTS of adsorbed NH3, CO, and pyridine, and (29)Si and (27)Al DNP-enhanced solid-state NMR spectroscopy. The formation of isolated sites suggests that TEOS reacts preferentially at strong Lewis acid sites on the γ-Al2O3 surface, functionalizing the surface with "mild" Brønsted acid sites. For liquid-phase catalytic cyclohexanol dehydration, these SiO(x) sites exhibit up to 3.5-fold higher specific activity than the parent alumina with identical selectivity.

  14. Highly dispersed SiOx/Al2O3 catalysts illuminate the reactivity of isolated silanol sites

    DOE PAGES

    Mouat, Aidan R.; George, Cassandra; Kobayashi, Takeshi; ...

    2015-09-23

    The reaction of γ-alumina with tetraethylorthosilicate (TEOS) vapor at low temperatures selectively yields monomeric SiOx species on the alumina surface. These isolated (-AlO)3Si(OH) sites are characterized by PXRD, XPS, DRIFTS of adsorbed NH3, CO, and pyridine, and 29Si and 27Al DNP-enhanced solid-state NMR spectroscopy. The formation of isolated sites suggests that TEOS reacts preferentially at strong Lewis acid sites on the γ-Al2O3 surface, functionalizing the surface with “mild” Brønsted acid sites. As a result, for liquid-phase catalytic cyclohexanol dehydration, these SiOx sites exhibit up to 3.5-fold higher specific activity than the parent alumina with identical selectivity.

  15. Ab initio investigations of A-site doping on the structure and electric polarization of HoMnO3

    NASA Astrophysics Data System (ADS)

    S, Sathya Sheela; C, Kanagaraj; Natesan, Baskaran

    2015-06-01

    We have investigated the effect of A-site doping on the structure and electric polarization of orthorhombic HoMnO3 using ab initio density functional theory calculations. We find that the substitution of rare earth ions, such as Lu, Y and La in place of Ho in orthorhombic HoMnO3 modifies the local structure around Mn ions drastically, and leads to the formation of two distinct Mn sites Mn(0) and Mn(1). As a result, large variance between Mn(0)O6 and Mn(1)O6 octahedral distortions arises. This variance in the octahedral distortions drives the disparate hopping of electrons between the eg orbitals enhancing the electronic polarization with increasing rare earth ion radius. The largest polarization of 7 µC/cm2 is obtained for La doped HoMnO3. This increase in polarization has been explained on the basis of radius mismatch induced local structural effects.

  16. Temporal Trends in Stream Nitrate Sources Across a Nitrogen Saturation Gradient

    NASA Astrophysics Data System (ADS)

    Rose, L.; Elliott, E.

    2013-12-01

    Elevated stream nitrate export can serve as an indicator of forest nitrogen saturation. From January through December 2010, we measured δ15N, δ18O, Δ17O, and concentrations of nitrate in weekly stream samples collected from three hardwood-dominated catchments at Fernow Experimental Forest (Parsons, WV). Based on long-term (>30 years) records of stream nitrate concentration, each catchment represents a unique N saturation stage, ranging from Stage 1 (N-limited) to Stage 3 (N-exporting). The catchments differed in mean stream nitrate export, dominant overstory species composition, and land use history, but patterns of δ15N, δ18O, and Δ17O were remarkably similar. δ15N values ranged from +1 to +6‰ across all catchments, with the highest values occurring in the summer. Trends in δ18O values were also similar among catchments, but the seasonal pattern was the opposite of that observed for δ15N, with the highest values during the dormant season and lowest values during the summer (range = -9 to +13‰ across all catchments). From January through June 2010, Δ17O values were low in the Stage 2 and 3 catchments (range = -1 to +3‰), indicating small contributions of atmospheric nitrate to streams. However, Δ17O values were always lower in the Stage 3 nitrogen saturated catchment (and nearly always zero), suggesting greater microbial turnover of atmospherically deposited nitrate despite the advanced nitrogen saturation stage. We explore potential explanations for the observed seasonal trends in δ15N, δ18O, and Δ17O of nitrate and discuss the utility of Δ17O in assessing catchment N saturation status.

  17. Local structure investigation of Eu doped SrSnO3 samples surrounding Sr site

    NASA Astrophysics Data System (ADS)

    Basu, S.; Patel, D. K.; Sudarsan, V.; Kulshreshtha, S. K.; Jha, S. N.; Bhattacharyya, D.

    2013-02-01

    In the present study, Eu doped SrSnO3 samples have been prepared and the local structure surrounding Sr atom has been studied by Synchrotron based EXAFS measurements at Sr K-edge (16105 eV). EXAFS analysis show that the average Sr-O bond distances show a marginal increase compared to the undoped sample. There is a general decreasing trend in the coordination number values for all samples upto 3% Eu doped SrSnO3. The introduction of Eu3+ replacing Sr2+ creates anionic vacancies to preserve the electronegativity in the system. The 4% Eu doped SrSnO3 sample shows unusually high coordination values in both Sr-O and Sr-Sn shell thus confirming increased perturbation in the lattice.

  18. Structure and magnetism in S r1 -xAxTc O3 perovskites: Importance of the A -site cation

    NASA Astrophysics Data System (ADS)

    Reynolds, Emily; Avdeev, Maxim; Thorogood, Gordon J.; Poineau, Frederic; Czerwinski, Kenneth R.; Kimpton, Justin A.; Yu, Michelle; Kayser, Paula; Kennedy, Brendan J.

    2017-02-01

    The S r1 -xB axTc O3 (x =0 , 0.1, 0.2) oxides were prepared and their solid-state and magnetic structure studied as a function of temperature by x-ray and neutron powder diffraction. The refined Tc moments at room temperature and Néel temperatures for B a0.1S r0.9Tc O3 and B a0.2S r0.8Tc O3 were 2.32 (14 ) μβ and 2.11 (13 ) μβ and 714 ∘C and 702 ∘C , respectively. In contrast to expectations, the Néel temperature in the series S r1 -xAxTc O3 decreases with increasing Ba content. This observation is consistent with previous experimental measurements for the two series A M O3 (M =Ru , Mn; A =Ca , Sr, Ba) where the maximum magnetic ordering temperature was observed for A =Sr . Taken with these previous results the current work demonstrates the critical role of the A -site cation in the broadening of the π* bandwidth and ultimately the magnetic ordering temperature.

  19. Quantitative study of band structure in BaTiO3 particles with vacant ionic sites

    NASA Astrophysics Data System (ADS)

    Oshime, Norihiro; Kano, Jun; Ikeda, Naoshi; Teranishi, Takashi; Fujii, Tatsuo; Ueda, Takeji; Ohkubo, Tomoko

    2016-10-01

    Levels of the conduction band minimum and the valence band maximum in ion-deficient BaTiO3 particles were investigated with optical band gap and ionization energy measurements. Though it is known that the quantification of the band structure in an insulator is difficult, due to the poor electrical conductivity of BaTiO3, systematic variation in the band energy levels was found that correlated with the introduction of vacancies. Photoelectron yield spectroscopy provided direct observation of the occupancy level of electrons, which is altered by the presence of oxygen and barium vacancies. In addition, the conduction band deviation from the vacuum level was determined by optical reflectance spectroscopy. Our results show that: (1) Introduction of oxygen vacancies forms a donor level below the conduction band. (2) The conduction band is shifted to a lower level by a larger number of oxygen vacancies, while the valence band also shifts to a lower level, due to the reduction in the density of O 2p orbitals. (3) Introduction of barium vacancies widens the band gap. Since barium vacancies can induce a small number of oxygen vacancies with accompanying charge compensation, this behavior suppresses any large formation of donor levels in the gap states, indicating that cation vacancies can control the number of both donor and acceptor levels.

  20. High stability of electro-transport and magnetism against the A-site cation disorder in SrRuO3.

    PubMed

    Wang, Y L; Liu, M F; Liu, R; Xie, Y L; Li, X; Yan, Z B; Liu, J-M

    2016-06-14

    It is known that the electro-transport and magnetism of perovskite alkaline-earth ruthenate oxides are sensitive to the lattice distortion associated with the A-site cation size. Orthorhombic CaRuO3 and cubic BaRuO3 exhibit distinctly different electro-transport and magnetic properties from orthorhombic SrRuO3. It has been suggested that SrRuO3 can be robust against some intrinsic/external perturbations but fragile against some others in terms of electro-transport and magnetism, and it is our motivation to explore such stability against the local site cation disorder. In this work, we prepare a set of SrRuO3-based samples with identical averaged A-site size but different A-site cation disorder (size mismatch) by Ca and Ba co-substitution of Sr. It is revealed that the electro-transport and magnetism of SrRuO3 demonstrate relatively high stability against this A-site cation disorder, characterized by the relatively invariable electrical and magnetic properties in comparison with those of SrRuO3 itself. A simple electro-transport network model is proposed to explain quantitatively the measured behaviors. The present work suggests that SrRuO3 as an itinerant electron ferromagnetic metal possesses relatively high robustness against local lattice distortion and cation occupation disorder.

  1. High stability of electro-transport and magnetism against the A-site cation disorder in SrRuO3

    NASA Astrophysics Data System (ADS)

    Wang, Y. L.; Liu, M. F.; Liu, R.; Xie, Y. L.; Li, X.; Yan, Z. B.; Liu, J.-M.

    2016-06-01

    It is known that the electro-transport and magnetism of perovskite alkaline-earth ruthenate oxides are sensitive to the lattice distortion associated with the A-site cation size. Orthorhombic CaRuO3 and cubic BaRuO3 exhibit distinctly different electro-transport and magnetic properties from orthorhombic SrRuO3. It has been suggested that SrRuO3 can be robust against some intrinsic/external perturbations but fragile against some others in terms of electro-transport and magnetism, and it is our motivation to explore such stability against the local site cation disorder. In this work, we prepare a set of SrRuO3-based samples with identical averaged A-site size but different A-site cation disorder (size mismatch) by Ca and Ba co-substitution of Sr. It is revealed that the electro-transport and magnetism of SrRuO3 demonstrate relatively high stability against this A-site cation disorder, characterized by the relatively invariable electrical and magnetic properties in comparison with those of SrRuO3 itself. A simple electro-transport network model is proposed to explain quantitatively the measured behaviors. The present work suggests that SrRuO3 as an itinerant electron ferromagnetic metal possesses relatively high robustness against local lattice distortion and cation occupation disorder.

  2. High stability of electro-transport and magnetism against the A-site cation disorder in SrRuO3

    PubMed Central

    Wang, Y. L.; Liu, M. F.; Liu, R.; Xie, Y. L.; Li, X.; Yan, Z. B.; Liu, J.-M.

    2016-01-01

    It is known that the electro-transport and magnetism of perovskite alkaline-earth ruthenate oxides are sensitive to the lattice distortion associated with the A-site cation size. Orthorhombic CaRuO3 and cubic BaRuO3 exhibit distinctly different electro-transport and magnetic properties from orthorhombic SrRuO3. It has been suggested that SrRuO3 can be robust against some intrinsic/external perturbations but fragile against some others in terms of electro-transport and magnetism, and it is our motivation to explore such stability against the local site cation disorder. In this work, we prepare a set of SrRuO3-based samples with identical averaged A-site size but different A-site cation disorder (size mismatch) by Ca and Ba co-substitution of Sr. It is revealed that the electro-transport and magnetism of SrRuO3 demonstrate relatively high stability against this A-site cation disorder, characterized by the relatively invariable electrical and magnetic properties in comparison with those of SrRuO3 itself. A simple electro-transport network model is proposed to explain quantitatively the measured behaviors. The present work suggests that SrRuO3 as an itinerant electron ferromagnetic metal possesses relatively high robustness against local lattice distortion and cation occupation disorder. PMID:27297396

  3. Nd substitution in y/ba sites in melt processed YBa2Cu3O7- δ through Nd2O3 additions

    NASA Astrophysics Data System (ADS)

    Varanasi, Chakrapani; Mc Ginn, Paul J.; Blackstead, Howard A.; Pulling, David B.

    1995-12-01

    YBa2Cu3O7- δ (Y123) samples with excess Nd2O3 and Y2O3 additions in the same molar ratios were melt textured in air. In the Nd-doped samples, in addition to Y ion site substitution, partial substitution into the Ba2+ sites is anticipated because of the similar ionic sizes of Nd3+ and Ba2+. The microstructure, Tc, and magnetic properties of Nd-doped samples were analyzed and compared with undoped Y123 and samples with excess Y2O3. The Nd2O3 additions lead to significant magnetization improvements, likely due to both rare earth- and Ba-site substitution by the doped Nd3+ ions, and to increases in Tc. Y2O3 additions resulted in no marked property enhancement.

  4. Structural and thermoelectric properties of A-site substituted (Sr1-x-yCaxNdy)TiO3 perovskites

    NASA Astrophysics Data System (ADS)

    Somaily, Hamoud H.

    Detailed structural results and models are reported for a special class of A-site substituted perovskites, (Sr1-x-yCaxNd y)TiO3, obtained with high resolution NPD data as a function of temperature and Nd composition. Two series with various A-site concentrations were synthesized and investigated. Each series was designed to have a nominally constant tolerance factor. At room temperature (RT), I determine the space groups of the Sr-rich and Sr poor series as being tetragonal I4/mcm and orthorhombic Pbnm, respectively. The RT structures remain unchanged upon increasing the Nd3+ content. However, three different orthorhombic phases, Pbnm, Ibmm, Pbcm, are determined for the Sr-rich series as a function of decreasing temperature; whereas, for the Sr-poor series the orthorhombic Pbnm structure is found to persist throughout the full range of measured temperatures. A phase diagram is constructed and proposed in the temperature range 0-1000 K. Thermoelectric properties of (Sr 1-x-yCaxNdy)TiO3 were also investigated and the best figure of merit ZT=0.07 was obtained with the Sr-rich series.

  5. Analysis of nitrogen saturation potential in Rocky Mountain tundra and forest: implications for aquatic systems

    USGS Publications Warehouse

    Baron, Jill S.; Ojima, Dennis S.; Holland, Elisabeth A.; Parton, William J.

    1994-01-01

    We employed grass and forest versions of the CENTURY model under a range of N deposition values (0.02–1.60 g N m−2 y−1) to explore the possibility that high observed lake and stream N was due to terrestrial N saturation of alpine tundra and subalpine forest in Loch Vale Watershed, Rocky Mountain National Park, Colorado. Model results suggest that N is limiting to subalpine forest productivity, but that excess leachate from alpine tundra is sufficient to account for the current observed stream N. Tundra leachate, combined with N leached from exposed rock surfaces, produce high N loads in aquatic ecosystems above treeline in the Colorado Front Range. A combination of terrestrial leaching, large N inputs from snowmelt, high watershed gradients, rapid hydrologic flushing and lake turnover times, and possibly other nutrient limitations of aquatic organisms constrain high elevation lakes and streams from assimilating even small increases in atmospheric N. CENTURY model simulations further suggest that, while increased N deposition will worsen the situation, nitrogen saturation is an ongoing phenomenon.

  6. Local fields at nonmagnetic impurity sites in a perovskite La 0 . 7 Ca 0 . 3 MnO 3

    NASA Astrophysics Data System (ADS)

    Sato, W.; Komatsuda, S.; Osa, A.; Sato, T. K.; Ohkubo, Y.

    2016-12-01

    The magnetic hyperfine field and electric field gradient at the 111Cd(leftarrow ^{111m}Cd) and 111Cd(leftarrow ^{111}In) probe nuclei introduced in a perovskite manganese oxide La0.7Ca0.3MnO3 ( T C ˜ 250 K) were measured for the study of the local magnetism and structure by means of time-differential perturbed angular correlation spectroscopy. In the ferromagnetic phase at 77 K, a very slight supertransferred magnetic hyperfine field (SMHF) (< 0.014 T) combined with a well-defined electric field gradient was observed at the nonmagnetic 111Cd nucleus on the La/Ca A site. This observation suggests that the large magnetic hyperfine field ( B h f = 6.9 T) measured, in our previous work, at the 140Ce probe nucleus on the A site originates from the contribution of a 4 f spin oriented by the SMHF from adjacent Mn ions.

  7. MDA8 O3 Values at Rural Surface Sites in Nevada, USA: Results from Two Years of the Nevada Rural Ozone Initiative (NVROI)

    NASA Astrophysics Data System (ADS)

    Gustin, M. S.; Fine, R.; Miller, M. B.; Burley, J. D.; Jaffe, D. A.; Pierce, R. B.; Lin, M.

    2014-12-01

    Local anthropogenic emissions are limited in Nevada (USA); however, data collected at Great Basin National Park (GBNP), which is located in rural eastern Nevada, indicate that ozone (O3) routinely exceeds the threshold proposed for a more stringent National Ambient Air Quality Standard (NAAQS). Here, we focused on data collected between July 2011 and June 2013. For this period, the maximum daily 8-h average (MDA8) O3 at GBNP exceeded the current NAAQS threshold (75 ppb) 7 times. Our analyses indicate that a combination of sources including emissions from regional wildfires and urban areas of southern California as well as stratospheric intrusions and long-range transport of Asian pollution contributed to elevated O3 observed at GBNP. Although MDA8 O3 measured at GBNP was well correlated with that measured at 5 other rural Nevada sites during this period, MDA8 O3 was 3.1 to 12.6 ppb greater at GBNP than at these other rural sites which emphasizes the need for spatially detailed measurements particularly in areas of complex terrain. The maximum MDA8 O3 at these 6 rural NV sites ranged from 68 to 80 ppb. GBNP was the only rural site to exceed the current NAAQS threshold during the period considered; however, when lower thresholds were considered the spatial and temporal extent of exceedances in rural Nevada increased indicating that interstate and international cooperation will be necessary to reduce ambient O3 concentrations in rural Nevada. MDA8 O3 at rural Nevada sites were significantly correlated with measurements at urban Nevada (r = 0.64 to 0.82; p < 0.05) and rural California (r = 0.61 to 0.83; p = 0.00) sites suggesting that common mechanisms influence O3 observed throughout the region.

  8. Site-selected doping of upconversion luminescent Er3+ into SrTiO3 for visible-light-driven photocatalytic H2 or O2 evolution.

    PubMed

    Shi, Jinwen; Ye, Jinhua; Ma, Lijing; Ouyang, Shuxin; Jing, Dengwei; Guo, Liejin

    2012-06-11

    A series of upconversion luminescent erbium-doped SrTiO(3) (ABO(3)-type) photocatalysts with different initial molar ratios of Sr/Ti have been prepared by a facile polymerized complex method. Er(3+) ions, which were gradually transferred from the A to the B site with increasing Sr/Ti, enabled the absorption of visible light and the generation of high-energy excited states populated by upconversion processes. The local internal fields arising from the dipole moments of the distorted BO(6) octahedra promoted energy transfer from the high-energy excited states of Er(3+) with B-site occupancy to the host SrTiO(3) and thus enhanced the band-to-band transition of the host SrTiO(3). Consequently, the erbium-doped SrTiO(3) species with B-site occupancy showed higher photocatalytic activity than those with A-site occupancy for visible-light-driven H(2) or O(2) evolution in the presence of the corresponding sacrificial reagents. The results generally suggest that the introduction of upconversion luminescent agents into host semiconductors is a promising approach to simultaneously harnessing low-energy photons and maintaining redox ability for photocatalytic H(2) and O(2) evolution and that the site occupancy of doped elements in ABO(3)-type perovskite oxides greatly determines the photocatalytic activity.

  9. Electronic and magnetic properties of GaFeO3: Ab initio calculations for varying Fe/Ga ratio, inner cationic site disorder, and epitaxial strain

    NASA Astrophysics Data System (ADS)

    Atanelov, J.; Mohn, P.

    2015-09-01

    In this study we present ab initio density-functional theory calculations on stoichiometric, cation-doped, and strained GaFeO 3 . We start with a detailed discussion of the origin of the antiferromagnetic (AFM) superexchange in stoichiometric GaFeO 3 and give a molecular orbital description of the exchange mechanism derived from our calculations. In addition, we study the properties of the Fe-O-Fe bonds for different geometries to underline the angle and distance dependence of the AFM coupling as formulated in the Goodenough-Kanamori rules. We describe the AFM ground state of GaFeO 3 as a result of two intrinsic Fe-O-Fe chains that meander through the crystal along the c direction. The magnetocrystalline anisotropy energies are calculated for the stoichiometric phase with and without inner cationic site disorder, and the presence of a sublattice-dependent anisotropy is examined. Furthermore, we perform our studies of Ga2 -xFe xO3 for varying Fe concentrations x (0.0 ≤x ≤2.0 ) where at a value of x =0.0 and x =2.0 it transforms into the isomorphic ɛ -Ga 2O3 and ɛ -Fe 2O3 phases, respectively. The effect of strain was also studied. Incorporating dopants and applying strain to the simulation cell changes the intrinsic geometry and thus the magnetic properties of gallium ferrite.

  10. Atomic arrangements around the O3 site in Al- and Cr-rich oxy-tourmalines: a combined EMP, SREF, FTIR and Raman study

    NASA Astrophysics Data System (ADS)

    Bosi, Ferdinando; Skogby, Henrik; Lazor, Peter; Reznitskii, Leonid

    2015-06-01

    A study of natural oxy-tourmalines belonging to the system oxy-dravite-chromo-alumino-povondraite-oxy-chromium-dravite from the Sludyanka crystalline complex (Southern Baikal region, Russia) was carried out to explore the characteristic vibrational bands in the principal (OH)-stretching frequency and their relations to the O3 anion site of the tourmaline structure. Relevant information was obtained using electron microprobe analysis (EMPA), structural refinement (SREF), infrared (IR) and Raman single-crystal spectroscopy. The studied oxy-tourmalines are characterized by the substitution Al ↔ Cr, which is accompanied by redistribution of Mg over the Y and Z sites. The occurrence of strong correlations between relative peak area intensities for two IR bands at 3,565 and 3,519 cm-1 and cation site populations derived from SREF and EMP data allowed assignment of the band at 3,565 cm-1 to the cluster [ Y Mg Z Al Z (Al,Mg)]-O3 and the band at 3,519 cm-1 to the cluster [ Y Cr Z (Cr,Al) Z (Cr,Al,Mg))]-O3. It appears that the combination of polarized IR and Raman spectra collected with the electric vector E⊥ c and E// c may provide a useful characterization of the local (OH) environments around the O3 site of the tourmaline structure.

  11. Charge distribution and hyperfine interactions in the vicinity of impurity sites in In2O3 doped with Fe, Co, and Ni

    NASA Astrophysics Data System (ADS)

    Sena, C.; Costa, M. S.; Muñoz, E. L.; Cabrera-Pasca, G. A.; Pereira, L. F. D.; Mestnik-Filho, J.; Carbonari, A. W.; Coaquira, J. A. H.

    2015-08-01

    In this paper, first-principles calculations based on density functional theory (DFT) were used to determine TM (TM=Fe, Ni, Co) and Cd impurity locations in the In2O3 host structure, their charge states, the electronic and structural relaxations induced in the host lattice as well as to interpret previous and supplementary experimental results of hyperfine interactions. Different techniques were carried out to characterize TM-doped In2O3 bulk samples prepared by the sol-gel method starting from very pure metals. Perturbed angular correlation (PAC) spectroscopy, a sensitive nuclear technique capable of measuring interactions from electronic charge and spins within an atomic distance, was used to experimentally determine hyperfine interactions at cation sites of In2O3 doped with Co and Ni using 111In →111Cd as probe nuclei. Room temperature results of magnetization measurements in In2O3 doped with Fe, Co and Ni show ferromagnetic ordering coexisting with a paramagnetic behavior for all samples. Results of PAC spectroscopy and DFT calculations show that TM atoms locate as second nearest neighbors of Cd probes preferentially occupy symmetric sites of the doped In2O3 crystal structure with lattice parameters slightly different from that of pure In2O3. Moreover, while a major population of 111Cd probes observes almost the same hyperfine interactions measured for pure In2O3, a small population detects magnetic dipole interactions with magnetic hyperfine field at Cd probes of 2.6 T, 3.1 T, and 4.6 T, respectively for Ni, Co, and Fe doping presenting an almost linear dependence on the number of unpaired 3d electrons of the transition metal impurity.

  12. Site Determination of Doped Ga Ions in SrTiO3:Pr3+ Phosphor for Field Emission Displays by XAFS

    SciTech Connect

    Honma, Tetsuo; Yamamoto, Hajime

    2007-02-02

    The enormous enhancement of the emission intensity from SrTiO3:Pr3+ by addition of Al or Ga ions was found. In case of Al, it was reported that the emission enhancement is caused by charge compensation and reduction of planar faults in the host lattices. In order to clarify the mechanism of the enhancement of the emission from SrTiO3:Pr3+ by addition of Ga ions, we investigated the local structure of doped Ga ions in SrTiO3:Pr3+ (a red phosphor for Field Emission Display) by XAFS analysis. The XAFS analysis indicates that doped Ga ions substitute for Ti site in the crystal.

  13. Infrared Spectroscopic Study of the Adsorption of HCN by gamma-Al2O3: Competition with Triethylenediamine for Adsorption Sites

    SciTech Connect

    Kim, S.; Sorescu, D.C.; Yates, J.T., Jr.

    2007-04-12

    The adsorption and vibrational properties of chemisorbed HCN on Lewis acid sites, Lewis base sites, and Brønsted Al-OH acid sites on a partially hydroxylated [gamma]-Al2O3 surface have been obtained by a combination of FTIR and density functional theory studies. The vibrational modes from the molecular and dissociative adsorption of HCN were assigned by using deuterium and 13C-labeled D13CN molecules at 170 K. In addition, [eta]2(C, N)-HCN bonding is also found from the [nu](CdN) vibrational spectra. Good correlation of the calculated vibrational frequencies for the adsorbed species with experimental data is found. The effect of triethylenediamine (TEDA) (also called 1, 4-diazabicyclo [2.2.2]octane, DABCO) on the adsorption of hydrogen cyanide (HCN) on the high area [gamma]-Al2O3 surface has been investigated using transmission FTIR spectroscopy. During HCN adsorption on TEDA-functionalized surfaces, there is no spectral change or emerging feature in either the TEDA or HCN spectral regions, indicating that no direct interaction occurs between these two molecules. Instead, we found that TEDA competes with HCN for the active sites on [gamma]-Al2O3. The observed [nu](C [identical with] N) mode on a TEDA-precovered surface is due to the HCN adsorption on Lewis base sites (Al-O-Al) which are less affected by TEDA preadsorption.

  14. Enhanced Removal of Arsenic and Antimony in the Mining Site by Calcined γ-Fe2O3/Layered Double Hydroxide Nanocomposite

    NASA Astrophysics Data System (ADS)

    Lee, Sang-Ho; Choi, Heechul; Kim, Kyoung-Woong

    2016-04-01

    chemical complexation between γ-Fe2O3 and LDH in the nanocomposite. The saturation magnetization of raw γ-Fe2O3 and calcined γ-Fe2O3/LDH nanocomposite were 63.2 and 14.3 emu/g, respectively. Although there was distinct decrease of saturation magnetization of calcined γ-Fe2O3/LDH nanocomposite, the particles were rapidly separated by external magnetic field. The kinetic study revealed that the removal of arsenic and antimony reached equilibrium quickly at about 120 min for initial concentration of 50 mg/L. The regeneration rate of arsenic may retain 70% for five regeneration cycles by 0.5M NaOH with 5M NaCl solution, whereas antimony showed lower regenerability than arsenic due to the higher irreversible fraction in calcined γ-Fe2O3/LDH nanocomposite. Consequently, the effective removal efficiency for arsenic and antimony with its easy magnetic separation makes γ-Fe2O3/LDH nanocomposite be a potential for the field application in the contaminated sites including several mining sites in Korea.

  15. Ti3+ on Nb site: A paramagnetic Jahn-Teller center in vacuum-reduced LiNbO3:Mg:Ti single crystals

    NASA Astrophysics Data System (ADS)

    Corradi, G.; Zaritskii, I. M.; Hofstaetter, A.; Polgár, K.; Rakitina, L. G.

    1998-10-01

    An axial EPR signal observed in vacuum annealed LiNbO3 single crystals doped with 8 mol % Mg and 0.05 mol % Ti has been attributed to Ti3+ on Nb site. The g tensor components (g||=1.760+/-0.005 and g⊥=1.786+/-0.005 for T=5 K and g||=g⊥=1.893+/-0.005 for T=74 K), resulting in outstandingly low values of the orbital reduction factor (from k=0.16 to 0.13), can be explained by a dynamic pseudo-Jahn-Teller effect. The vibronic coupling of the center is much stronger than that reported for other nd1 centers with similar trigonally distorted octahedral coordination in LiNbO3 like the Ti3+ on Li site and trapped Nb4+ polarons on both cation sites. Stronger coupling for ions on or near the Nb site is understood as a result of smaller trigonal splitting of the ground state due to the more central position of the Nb site in the oxygen octahedron. Electron transfer from the observed Ti3+ center to lattice niobiums, resulting in Nb4+ trapped polarons, has been stimulated by illumination in the near UV region. The average energy difference of the involved Ti4+/3+ and Nb5+/4+ donor levels has been estimated to be 70+/-23 meV depending also on the distance of compensating Mg2+ ions on nearby Li sites.

  16. (La1-xSrx)0.98MnO3 perovskite with A-site deficiencies toward oxygen reduction reaction in aluminum-air batteries

    NASA Astrophysics Data System (ADS)

    Xue, Yejian; Miao, He; Sun, Shanshan; Wang, Qin; Li, Shihua; Liu, Zhaoping

    2017-02-01

    The strontium doped Mn-based perovskites have been proposed as one of the best oxygen reduction reaction catalysts (ORRCs) to substitute the noble metal. However, few studies have investigated the catalytic activities of LSM with the A-site deficiencies. Here, the (La1-xSrx)0.98MnO3 (LSM) perovskites with A-site deficiencies are prepared by a modified solid-liquid method. The structure, morphology, valence state and oxygen adsorption behaviors of these LSM samples are characterized, and their catalytic activities toward ORR are studied by the rotating ring-disk electrode (RRDE) and aluminum-air battery technologies. The results show that the appropriate doping with Sr and introducing A-site stoichiometry can effectively tailor the Mn valence and increase the oxygen adsorption capacity of LSM. Among all the LSM samples in this work, the (La0.7Sr0.3)0.98MnO3 perovskite composited with 50% carbon (50%LSM30) exhibits the best ORR catalytic activity due to the excellent oxygen adsorption capacity. Also, this catalyst has much higher durability than that of commercial 20%Pt/C. Moreover, the maximum power density of the aluminum-air battery using 50%LSM30 as the ORRC can reach 191.3 mW cm-2. Our work indicates that the LSM/C composite catalysts with A-site deficiencies can be used as a promising ORRC in the metal-air batteries.

  17. NH3 adsorption on the Lewis and Bronsted acid sites of MoO3 (0 1 0) surface: A cluster DFT study

    NASA Astrophysics Data System (ADS)

    Yan, Zhifeng; Fan, Junyan; Zuo, Zhijun; Li, Zhe; Zhang, Jinshan

    2014-01-01

    The adsorption of NH3 on the Lewis and Bronsted acid sites of MoO3 (0 1 0) surface has been investigated based on the density functional theory (DFT) method using the clusters models. The calculated results indicate that NH3 could strongly adsorb on both the Lewis and Bronsted acid sites in the form of NH3 species and NH4+ respectively, whereas the adsorption on the Lewis acid site is found to be more favorable energetically than that on the Bronsted acid site. For the Lewis acid site Mulliken population analysis shows a donation of lone pairs from NH3 to the surface and activation of N-H bond. The overlaps of N-s, N-p and Mo-d orbitals suggest the strong interaction between N and Mo atoms. For the Bronsted acid site N-H bond is also activated by the formation of NH4+ species. The hybridizations between H and O atoms as well as N and H atoms are the major reasons for strong chemical adsorption of NH3 and the existence of NH4+ species, which partly attributed to the presence of N-H… O hydrogen bonds. Furthermore, the formation of a second Lewis acid site at adjacent or diagonal site results in slight changes of adsorption stability, structural changes and charge redistributions, suggesting its small influence on NH3 adsorption.

  18. Valence states and metamagnetic phase transition in partially B -site-disordered perovskite EuMn0.5Co0.5O3

    NASA Astrophysics Data System (ADS)

    Vasiliev, A. N.; Volkova, O. S.; Lobanovskii, L. S.; Troyanchuk, I. O.; Hu, Z.; Tjeng, L. H.; Khomskii, D. I.; Lin, H.-J.; Chen, C. T.; Tristan, N.; Kretzschmar, F.; Klingeler, R.; Büchner, B.

    2008-03-01

    The valence states of transition metals were studied by measuring the x-ray absorption spectra at both MnL2,3 and CoL2,3 edges of partially B -site-disordered perovskite EuMn0.5Co0.5O3 . By comparison with analogous spectra in various Co- and Mn-based compounds, the divalent state of the Co ions and the tetravalent state of the Mn ions were established analogous to Mn4+/Co2+ charge ordering found by Dass and Goodenough [Phys. Rev. B 67, 014401 (2003)] in LaMn0.5Co0.5O3 . The specific heat and magnetic susceptibility data indicate the formation of the magnetically ordered state at TC˜120K . The first-order metamagnetic transitions seen in EuMn0.5Co0.5O3 at T

  19. Co-doping of (Bi(0.5)Na(0.5))TiO(3): secondary phase formation and lattice site preference of Co.

    PubMed

    Schmitt, V; Staab, T E M

    2012-11-14

    Bismuth sodium titanate (Bi(0.5)Na(0.5))TiO(3) (BNT) is considered to be one of the most promising lead-free alternatives to piezoelectric lead zirconate titanate (PZT). However, the effect of dopants on the material has so far received little attention from an atomic point of view. In this study we investigated the effects of cobalt-doping on the formation of additional phases and determined the preferred lattice site of cobalt in BNT. The latter was achieved by comparing the measured x-ray absorption near-edge structure (XANES) spectra to numerically calculated spectra of cobalt on various lattice sites in BNT. (Bi(0.5)Na(0.5))TiO(3) + x mol% Co (x = 0.0, 0.5, 1.0, 2.6) was synthesized via solid state reaction. As revealed by SEM backscattering images, a secondary phase formed in all doped specimens. Using both XRD and SEM-EDX, it was identified as Co(2)TiO(4) for dopant levels >0.5 mol%. In addition, a certain amount of cobalt was incorporated into BNT, as shown by electron probe microanalysis. This amount increased with increasing dopant levels, suggesting that an equilibrium forms together with the secondary phase. The XANES experiments revealed that cobalt occupies the octahedral B-site in the BNT perovskite lattice, substituting Ti and promoting the formation of oxygen vacancies in the material.

  20. Effects of cation disorder and size on metamagnetism in A-site substituted Pr0.5Ca0.5MnO3 system

    NASA Astrophysics Data System (ADS)

    Mavani, K. R.; Paulose, P. L.

    2005-04-01

    The effects of A-site cation disorder and size on metamagnetism of ABO3 type charge and orbital ordered Pr0.5Ca0.5MnO3 system have been studied by substituting Ba+2 for Ca+2 or La+3 for Pr+3. Substitution of 5% Ba+2 or 5% La+3 drastically reduces the critical magnetic field (Hc) for metamagnetism and induces successive steplike metamagnetic transitions at low temperatures. Interestingly, with further increase in substitution, Hc rises. We find that there is a sharp decrease in electrical resistivity corresponding to the metamagnetic transitions, which is indicative of strongly correlated magnetic and electronic transitions in these manganites.

  1. Effect of Surface Site Interactions on Potentiometric Titration of Hematite (α-Fe2O3) Crystal Faces

    SciTech Connect

    Chatman, Shawn ME; Zarzycki, Piotr P.; Preocanin, Tajana; Rosso, Kevin M.

    2013-02-01

    Time dependent potentiometric pH titrations were used to study the effect of atomic scale surface structure on the protonation behavior of the structurally well defined hematite/aqueous electrolyte interfaces. Our recently proposed thermodynamic model [1,23] was applied to measured acidimetric and alkalimetric titration hysteresis loops, collected from highly organized (001), (012), and (113) crystal face terminations using pH equilibration times ranging from 15 to 30 mins. Hysteresis loop areas indicate that (001) faces equilibrate faster than the (012) and (113) faces, consistent with the different expected ensembles of singly, doubly, and triply coordinated surface sites on each face. Strongly non-linear hysteretic pH-potential relationships were found, with slopes exceeding Nernstian, collectively indicating that protonation and deprotonation is much more complex than embodied in present day surface complexation models. The asymmetrical shape of the acidimetric and alkalimetric titration branches were used to illustrate a proposed steric "leaky screen" repulsion/trapping interaction mechanism that stems from high affinity singly-coordinated sites electrostatically and sterically screening lower affinity doubly and triply coordinated sites. Our data indicate that site interaction is the dominant phenomenon defining surface potential accumulation behavior on single crystal faces of metal oxide minerals.

  2. Strong magnetic frustration and anti-site disorder causing spin-glass behavior in honeycomb Li2RhO3

    PubMed Central

    Katukuri, Vamshi M.; Nishimoto, Satoshi; Rousochatzakis, Ioannis; Stoll, Hermann; van den Brink, Jeroen; Hozoi, Liviu

    2015-01-01

    With large spin-orbit coupling, the electron configuration in d-metal oxides is prone to highly anisotropic exchange interactions and exotic magnetic properties. In 5d5 iridates, given the existing variety of crystal structures, the magnetic anisotropy can be tuned from antisymmetric to symmetric Kitaev-type, with interaction strengths that outsize the isotropic terms. By many-body electronic-structure calculations we here address the nature of the magnetic exchange and the intriguing spin-glass behavior of Li2RhO3, a 4d5 honeycomb oxide. For pristine crystals without Rh-Li site inversion, we predict a dimerized ground state as in the isostructural 5d5 iridate Li2IrO3, with triplet spin dimers effectively placed on a frustrated triangular lattice. With Rh-Li anti-site disorder, we explain the observed spin-glass phase as a superposition of different, nearly degenerate symmetry-broken configurations. PMID:26434954

  3. Methanol Synthesis over Cu/ZnO/Al2O3: The Active Site in Industrial Catalysis

    SciTech Connect

    Behrens, Malte

    2012-03-28

    Unlike homogeneous catalysts, heterogeneous catalysts that have been optimized through decades are typically so complex and hard to characterize that the nature of the catalytically active site is not known. This is one of the main stumbling blocks in developing rational catalyst design strategies in heterogeneous catalysis. We show here how to identify the crucial atomic structure motif for the industrial Cu/ZnO/Al{sub 2}O{sub 3} methanol synthesis catalyst. Using a combination of experimental evidence from bulk-, surface-sensitive and imaging methods collected on real high-performance catalytic systems in combination with DFT calculations. We show that the active site consists of Cu steps peppered with Zn atoms, all stabilized by a series of well defined bulk defects and surface species that need jointly to be present for the system to work.

  4. Site Distribution - Studies of Rh Supported on Al2O3 - An Infrared Study of Chemisorbed CO.

    DTIC Science & Technology

    1980-05-01

    by block ntin.efr) Chemisorption; CO; dispersion; extinction coefficient; infrared spectroscopy;J rhodium ABSRAC (Conuinue en reverse aid* It n.e..mvty...chemisorption sites (8). Previous work on Al203-supported rhodium has demonstrated dispersion- dependent catalytic activity (9). In this note we report the...variation in spectral features observed for chemisorbed CO on Al203-supported rhodium samples as the metal loading is varied from 0.2% to 10.0% by

  5. Active Oxygen Vacancy Site for Methanol Synthesis from CO2 Hydrogenation on In2O3(110): A DFT Study

    SciTech Connect

    Ye, Jingyun; Liu, Changjun; Mei, Donghai; Ge, Qingfeng

    2013-06-03

    Methanol synthesis from CO2 hydrogenation on the defective In2O3(110) surface with surface oxygen vacancies has been investigated using periodic density functional theory calculations. The relative stabilities of six possible surface oxygen vacancies numbered from Ov1 to Ov6 on the perfect In2O3(110) surface were examined. The calculated oxygen vacancy formation energies show that the D1 surface with the Ov1 defective site is the most thermodynamically favorable while the D4 surface with the Ov4 defective site is the least stable. Two different methanol synthesis routes from CO2 hydrogenation over both D1 and D4 surfaces were studied and the D4 surface was found to be more favorable for CO2 activation and hydrogenation. On the D4 surface, one of the O atoms of the CO2 molecule fills in the Ov4 site upon adsorption. Hydrogenation of CO2 to HCOO on the D4 surface is both thermodynamically and kinetically favorable. Further hydrogenation of HCOO involves both forming the C-H bond and breaking the C-O bond, resulting in H2CO and hydroxyl. The HCOO hydrogenation is slightly endothermic with an activation barrier of 0.57 eV. A high barrier of 1.14 eV for the hydrogenation of H2CO to H3CO indicates that this step is the rate-limiting step in the methanol synthesis on the defective In2O3(110) surface. We gratefully acknowledge the supports from the National Natural Science Foundation of China (#20990223) and from US Department of Energy, Basic Energy Science program (DE-FG02-05ER46231). D. Mei was supported by the US Department of Energy, Office of Basic Energy Sciences, Division of Chemical Sciences, Geosciences & Biosciences. The computations were performed in part using the Molecular Science Computing Facility in the William R. Wiley Environmental Molecular Sciences Laboratory (EMSL), which is a U.S. Department of Energy national scientific user facility located at Pacific Northwest National Laboratory in Richland, Washington. PNNL is a multiprogram national laboratory

  6. Role of [FeOx(OH)y] surface sites on the adsorption of β-lactamic antibiotics on Al2O3 supported Fe oxide.

    PubMed

    Pinto, Paula S; Medeiros, Tayline P V; Ardisson, José D; Lago, Rochel M

    2016-11-05

    In this work, [FeOx(OH)y]/Al2O3 composites with different Fe oxyhydroxy contents, i.e. 10, 20 and 50wt% treated at 150, 200, 300 and 450°C were investigated as adsorbents of β-lactamic antibiotics, i.e. cephalexin, ceftriaxone and especially amoxicillin, from aqueous solutions. The obtained results showed that the nature of the surface Fe(3+) species play a fundamental role on the adsorption process. The most efficient adsorption was obtained for the sample 150Fe50A (50% [FeOx(OH)y] supported in Al2O3 treated at 150°C) whereas the thermal treatment at higher temperatures caused a strong decrease on the adsorption capacity. Mössbauer, XRD, FTIR, Raman, TG-MS, SEM, CHN and BET of the composite 150Fe50A suggested an approximate composition of FeO0.65(OH)1.7 whereas at 450°C strong dehydroxylation process takes place to form FeO1.4(OH)0.21. These results combined with competitive adsorption using amoxicillin mixed with phosphate or H2O2 suggest that the antibiotic molecules adsorb by complexation on surface sites likely based on FeOx(OH)y by the replacement of the labile OH ligands.

  7. Effect of A-site cations on the broadband-sensitive upconversion of AZrO3:Er3+,Ni2+ (A = Ca, Sr, Ba) phosphors

    NASA Astrophysics Data System (ADS)

    Luitel, Hom Nath; Mizuno, Shintaro; Tani, Toshihiko; Takeda, Yasuhiko

    2017-02-01

    We investigated broadband-sensitive upconversion processes in a series of AZrO3 type perovskites codoped with Ni2+ and Er3+, especially giving focus on the effect of the A-site host cations viz. Ca, Sr, Ba. Absorption and Stokes emission of the Ni2+ changed remarkably according to the A-site cations making difference in the Ni2+ to Er3+ energy transfer efficiency. The energy transfer extent from the Ni2+ sensitizers to the Er3+ emitters and the back transfer from the Er3+ to the Ni2+ were studied to clarify the guide for efficient broadband-sensitive upconversion. The Ni2+ to Er3+ energy transfer efficiency and hence the Er3+ upconversion emission intensity was dependent on the extent of overlap between the Er3+ absorption and the Ni2+ emission bands. Larger the overlap, faster was the energy transfer from the Ni2+ to the Er3+, leading to more intense Er3+ upconversion emission. However, back energy transfer from the Er3+ to the Ni2+ due to significant overlap of the Er3+ emission band with the Ni2+ absorption band reduced the upconversion emission intensity. Another important factor is the upconversion efficiency of the Er3+ emitters themselves after the energy transfer from the Ni2+ sensitizers, which was significantly improved when the symmetry around the Er3+ was lowered. As a result of these combined effects, the CaZrO3 host exhibited the most intense Ni2+-sensitized upconversion emission compared to the Sr and Ba analogues. Thus, for the efficient broadband-sensitive upconversion to be realized, a low symmetry host to manifest efficient upconversion of the Er3+ emitters and controlled Ni2+ absorption and emission bands to suppress the back energy transfer while maintaining efficient energy transfer in the forward direction are essential.

  8. Characterization of Ordering in A-Site Deficient Perovskite Ca1-xLa2x/3TiO3 Using STEM/EELS.

    PubMed

    Danaie, Mohsen; Kepaptsoglou, Demie; Ramasse, Quentin M; Ophus, Colin; Whittle, Karl R; Lawson, Sebastian M; Pedrazzini, Stella; Young, Neil P; Bagot, Paul A J; Edmondson, Philip D

    2016-10-03

    The vacancy ordering behavior of an A-site deficient perovskite system, Ca1-xLa2x/3TiO3, was studied using atomic resolution scanning transmission electron microscopy (STEM) in conjunction with electron energy-loss spectroscopy (EELS), with the aim of determining the role of A-site composition changes. At low La content (x = 0.2), adopting Pbnm symmetry, there was no indication of long-range ordering. Domains, with clear boundaries, were observed in bright-field (BF) imaging, but were not immediately visible in the corresponding high-angle annular dark-field (HAADF) image. These boundaries, with the aid of displacement maps from A-site cations in the HAADF signal, are shown to be tilt boundaries. At the La-rich end of the composition (x = 0.9), adopting Cmmm symmetry, long-range ordering of vacancies and La(3+) ions was observed, with alternating La-rich and La-poor layers on (001)p planes, creating a double perovskite lattice along the c axis. These highly ordered domains can be found isolated within a random distribution of vacancies/La(3+), or within a large population, encompassing a large volume. In regions with a high number density of double perovskite domains, these highly ordered domains were separated by twin boundaries, with 90° or 180° lattice rotations across boundaries. The occurrence and characteristics of these ordered structures are discussed and compared with similar perovskite systems.

  9. Variations of surface O3 in August at a rural site near Shanghai: influences from the West Pacific subtropical high and anthropogenic emissions.

    PubMed

    He, Jingwei; Wang, Yuxuan; Hao, Jiming; Shen, Lulu; Wang, Long

    2012-11-01

    Large day-to-day variability in O(3) and CO was observed at Chongming, a remote rural site east of Shanghai, in August 2010. High ozone periods (HOPs) that typically lasted for 3-5 days with daily maximum ozone exceeding 102 ppb were intermittent with low ozone periods (LOPs) with daily maximum ozone less than 20 ppb. The correlation analysis of ozone with meteorological factors suggests that the large variations of surface ozone are driven by meteorological conditions correlated with the changes in the location and intensity of the west Pacific subtropical high (WPSH) associated with the East Asian summer monsoon (EASM). When the center of WPSH with weaker intensity is to the southeast of Chongming site, the mixing ratios and variability of surface ozone are higher. When the center of WPSH with stronger intensity is to the northeast of Chongming site, the mixing ratios and variability of surface ozone are lower. Sensitivity simulations using the GEOS-Chem chemical transport model indicate that meteorological condition associated with WPSH is the primary factor controlling surface ozone at Chongming in August, while local anthropogenic emissions make significant contributions to surface ozone concentrations only during HOP.

  10. A-site deficient Ba 1- xCo 0.7Fe 0.2Ni 0.1O 3- δ cathode for intermediate temperature SOFC

    NASA Astrophysics Data System (ADS)

    Liu, Ze; Cheng, Ling-zhi; Han, Min-Fang

    A-site cation-deficient Ba 1- xCo 0.7Fe 0.2Nb 0.1O 3- δ (B 1- xCFN, x = 0.00-0.15) oxides are synthesized and evaluated as cathode materials for intermediate temperature solid oxide fuel cells (IT-SOFCs). The reactivity between B 1- xCFN and gadolinia doped ceria (GDC) is observed at different temperature, and no second phase is detected under 1050 °C. The increasing in A-site cation deficiency results in a steady decrease in cathode polarization resistance. Among the various B 1- xCFN oxides test, GDC based anode supported cells with B 0.9CFN cathode possess the smallest interfacial polarization resistance (R p). The R p is as low as 0.283 and 0.046 Ω cm 2 at 500 and 600 °C, respectively. The anode supported cell with B 0.9CFN provides maximum power densities of 1062 and 1139 mW cm -2 at 600 and 650 °C, respectively. The results suggest that B 0.9CFN is a great potential cathode material for IT-SOFCs.

  11. High affinity P2x-purinoceptor binding sites for [35S]-adenosine 5'-O-[3-thiotriphosphate] in rat vas deferens membranes.

    PubMed Central

    Michel, A. D.; Humphrey, P. P.

    1996-01-01

    1. The binding sites labelled by [35S]-adenosine 5'-O-[3-thiotriphosphate]([35S]-ATP gamma S) at 4 degrees C in rat vas deferens membranes were studied and compared to the sites labelled by [3H]-alpha,beta-methylene ATP ([3H]-alpha beta meATP) to ascertain whether [35S]-ATP gamma S can be used to label the P2x purinoceptor. 2. In the presence of 4 mM CaCl2, the binding of 0.2 nM [35S]-ATP gamma S to vas deferens membranes was increased 3.4 fold, when compared to studies performed in the absence of calcium. However, binding did not appear to be solely to P2x purinoceptors since [35S]-ATP gamma S labelled a heterogeneous population of sites and about 72% of the sites possessed high affinity (pIC50 = 7.5) for guanosine 5'-O-[3-thiotriphosphate] (GTP gamma S). Even in the presence of 1 microM GTP gamma S, to occlude the sites with high affinity for GTP gamma S, the binding of [35S]-ATP gamma S was heterogeneous and since there was also evidence of extensive metabolism of ATP in the presence of calcium, the binding of [35S]-ATP gamma S under these conditions was not studied further. 3. In the absence of calcium ions, [35S]-ATP gamma S bound to a single population of sites (pKD = 9.23; Bmax = 4270 fmol mg-1 protein). Binding reached steady state within 3 h (t1/2 = 38 min), was stable for a further 4 h and was readily reversible upon addition of 10 microM unlabelled ATP gamma S (t1/2 = 45 min). In competition studies the binding of 0.2 nM [35S]-ATP gamma S was inhibited by a number of P2x purinoceptor agonists and antagonists, but not by adenosine receptor agonists, staurosporine (1 microM) or several ATPase inhibitors. The rank order of agonist affinity estimates (pIC50 values) in competing for the [35S]-ATP gamma S binding sites was: ATP (9.01), 2-methylthio- ATP (8.79), ATP gamma S (8.73), alpha beta meATP (7.57), ADP (7.24), beta, gamma-methylene ATP (7.18), L-beta, gamma-methylene ATP (5.83), alpha, beta-methylene ADP (4.36). 4. Affinity estimates (pIC50 values) for

  12. Tuning optical absorption and photoexcited recombination dynamics in La1-xSrxFeO3-δ through A-site substitution and oxygen vacancies

    NASA Astrophysics Data System (ADS)

    Smolin, Sergey; Scafetta, Mark; Choquette, Amber; Sfeir, Matthew; Baxter, Jason; May, Steven

    We study optical absorption and recombination dynamics in La1-xSrxFeO3-δ thin films, uncovering the effects of tuning nominal Fe valence via A-site substitution and oxygen stoichiometry. Variable angle spectroscopic ellipsometry was used to measure static optical properties, revealing a linear increase in absorption coefficient at 1.25 eV and a red-shifting of the optical absorption edge with increasing Sr fraction. The absorption spectra can be similarly tuned through the introduction of oxygen vacancies, indicating the critical role that nominal Fe valence plays in optical absorption. Dynamic optoelectronic properties were studied with ultrafast transient reflectance spectroscopy, revealing similar nanosecond photoexcited carrier lifetimes for oxygen deficient and stoichiometric films with the same nominal Fe valence. These results demonstrate that while the static optical absorption is strongly dependent on Fe valence tuned through cation or anion stoichiometry, oxygen vacancies do not appear to play a significantly detrimental role in the recombination kinetics. Nsf: ECCS-1201957, MRI DMR-0922929, MRI DMR-1040166. This research used resources of the Center for Functional Nanomaterials, which is a U.S. DOE Office of Science Facility, at Brookhaven National Laboratory under Contract No. DE-SC0012704.

  13. Static and dynamic optical properties of La1-xSrxFeO3-δ: The effects of A-site and oxygen stoichiometry

    DOE PAGES

    Sergey Y. Smolin; Sfeir, Matthew Y.; Scafetta, Mark D.; ...

    2015-12-09

    Perovskite oxides are a promising material class for photovoltaic and photocatalytic applications due to their visible band gaps, nanosecond recombination lifetimes, and great chemical diversity. However, there is limited understanding of the link between composition and static and dynamic optical properties, despite the critical role these properties play in the design of light-harvesting devices. To clarify these relationships, we systemically studied the optoelectronic properties in La1-xSrxFeO3-δ epitaxial films, uncovering the effects of A-site cation substitution and oxygen stoichiometry. Variable-angle spectroscopic ellipsometry was used to measure static optical properties, revealing a linear increase in absorption coefficient at 1.25 eV and amore » red-shifting of the optical absorption edge with increasing Sr fraction. The absorption spectra can be similarly tuned through the introduction of oxygen vacancies, indicating the critical role that nominal Fe valence plays in optical absorption. Dynamic optoelectronic properties were studied with ultrafast transient reflectance spectroscopy, revealing similar nanosecond photoexcited carrier lifetimes for oxygen deficient and stoichiometric films with the same nominal Fe valence. Furthermore, these results demonstrate that while the static optical absorption is strongly dependent on nominal Fe valence tuned through cation or anion stoichiometry, oxygen vacancies do not appear to play a significantly detrimental role in the recombination kinetics.« less

  14. Oxygen trapping and cation site-splitting in Y(2-x)PrxO3+δ (0.0≤x<2.0 and δ≤1.0)

    NASA Astrophysics Data System (ADS)

    Lussier, Joey A.; Devitt, Graham; Szkop, Kevin M.; Bieringer, Mario

    2016-10-01

    The reduction and oxidation of the solid solution Y2-xPrxO3+δ (0.0≤x<2.0 and δ≤1.0) is investigated with emphasis on potential solid state electrolyte applications in solid oxide fuel cells. The fully reduced solid solution Y2-xPrxO3 (0.0≤x<2.0) crystallizes in the bixbyite structure (Ia 3 bar) . The oxidized solid solution Y2-xPrxO3+δ (0.0≤x<1.4) forms bixbyite phases (Ia 3 bar) whereas Y2-xPrxO3+δ (1.4≤x<2) compositions form fully disordered defect fluorite structures (Fm 3 bar m) with variable oxide defect concentrations. The two cation positions are investigated in detail using synchrotron powder X-ray and time of flight neutron diffraction data. In the bixbyite structures the 8c cation site splits into the 16c cation site and the 24d cation position migrates toward the ideal fluorite coordination upon oxidation. Reductive in-situ diffraction experiments reveal the co-existence of the fluorite and bixbyite structure only in a narrow temperature range. During oxidation of the bixbyite phase a new 16c oxide anion site is populated. The impact of the 16c oxide site population on the cation sublattice is being discussed.

  15. Dependence of the Jahn-Teller distortion in LaMn 1-x ScxO3 on the isovalent Mn-site substitution

    NASA Astrophysics Data System (ADS)

    Subías, G.; Cuartero, V.; Blasco, J.; García, J.; Meneghini, C.; Aquilanti, G.

    2016-05-01

    We investigated the relative importance of removing the Mn3+ Jahn-Teller distortion in driving ferromagnetism in LaMn1-xScxO3 combining x-ray powder diffraction and x-ray absorption spectroscopy at the Mn and Sc K-edges. By increasing the Sc content, the orthorhombic distortion of the Pbnm cell in LaMnO3 decreases but the unit-cell remains slightly distorted in LaScO3. Besides, the nearly tetragonal-distorted MO6 in LaMnO3 continuously evolves into a nearly regular one in LaScO3. On the other hand, x-ray absorption spectra show that the MnO6 octahedron remains Jahn-Teller distorted and the ScO6 octahedron is nearly regular along the whole series. Moreover, the ordering of the Mn3+ Jahn-Teller distortion is not disrupted in the ab plane for any Sc concentration. This contrasts with the Ga- substituted compounds, where a regular MnO6 is found for x>0.5. However, both LaMn0.5Sc0.5O3 and LaMn0.5Ga0.5O3 show ferromagnetic behavior independently of the presence (or not) of Jahn-Teller distorted Mn3+. Thus, our results point to the Mn-sublattice dilution as the main effect in driving ferromagnetism in these manganites over local structure effects previously proposed by the spin flipping or the vibronic superexchange models.

  16. Impact of tropical convection and ENSO variability in vertical distributions of CO and O3 over an urban site of India

    NASA Astrophysics Data System (ADS)

    Sahu, L. K.; Sheel, Varun; Kajino, M.; Deushi, M.; Gunthe, Sachin S.; Sinha, P. R.; Yadav, Ravi; Pal, Devendra; Nedelec, P.; Thouret, Valérie; Smit, Herman G.

    2016-09-01

    This study is based on the analysis of the measurement of ozone and water vapor by airbus in-service aircraft (MOZAIC) data of vertical ozone (O3) and carbon monoxide (CO) over Hyderabad during November 2005-March 2009. Measurements in the upper troposphere show highest values of O3 (53-75 ppbv) and CO (80-110 ppbv) during the pre-monsoon and post-monsoon seasons, respectively. The episodes of strong wind shears (>20 ms-1) were frequent during the monsoon/post-monsoon months, while weak shear conditions (<10 ms-1) were prevalent during the winter season. The profiles of both O3 and CO measured under southerly winds showed lower values than under northerly winds in each season. The strong and weak wind shears over the study region were associated with the El Niño and La Niña conditions, respectively. The outgoing long-wave radiation (OLR) and wind shear data indicate enhancement in the convective activity from monsoon to post-monsoon period. Higher levels of O3 were measured under the strong shear conditions, while CO and H2O show enhancements under weak shear conditions. The near surface observation and simulations show increase of O3 with increasing OLR, while insignificant relation in the upper region. In case of CO, the MOZAIC and CCM2 show weaker dependence while MOZART-4 shows rapid increase with OLR indicating large overestimation of convective transport. A modified Tiedtke convective scheme provides better representation compared to the Hack/Zhang-McFarlane schemes for both O3 and CO during the monsoon season. The difference between observation and simulations were particularly large during transition from El Niño to La Niña phases. The different convection scheme and horizontal resolution in the MOZART-4 and CCM2 seem to be the major causes of disagreement between these models. Vertical profiles of both O3 and CO during extreme events such a tropical cyclones (TCs) show strong influence of the convective-dynamics over Bay of Bengal (BOB).

  17. Does nitrogen saturation theory apply to unpolluted temperate forests? A test along a forest soil nitrogen gradient in Oregon

    NASA Astrophysics Data System (ADS)

    Perakis, S. S.; Sinkhorn, E. R.

    2011-12-01

    Natural gradients of soil nitrogen (N) can be used to evaluate the consequences of long-term ecosystem N enrichment, and to test the applicability of N saturation theory as a general framework for understanding ecosystem N dynamics. Temperate forest soils of the Oregon Coast Range experience low rates of atmospheric N deposition, yet display among the highest soil N accumulations ever reported worldwide. We measured plant and soil (0-1m) N stocks and natural abundance delta15N, plant production, N uptake and return in litterfall, soil gross and net N mineralization rates, and hydrologic N losses of nine Douglas-fir forests growing across an exceptionally wide soil N gradient in the Oregon Coast Range. Ecosystem N content ranged from 8,788 to 22,667 kg N/ha across sites, with highest N accumulations near the coast, and 96-98% of total ecosystem N residing in mineral soil. Ecosystem delta15N displayed a curvilinear relationship with ecosystem N content that reflected competing influences of N input from biological fixation at low-N sites and fractionating N losses at high-N sites. Simulation modeling of ecosystem N and delta15N mass balance suggest that cycles of wildfire can promote unusually high natural N accumulation by fostering early successional biological nitrogen fixation. Surface mineral soil (0 - 10 cm) N concentrations were tightly correlated to total soil N stocks to 1 m depth, and in contrast to predictions of N saturation theory, were linearly related to 10-fold variation in net N mineralization from 8 - 82 kg N/ha-yr. Net N mineralization was unrelated to soil C:N, soil texture, precipitation and temperature differences among sites. Net nitrification accounted for < 20% of net N mineralization at low N sites, increasing to 85 - 100% of net N mineralization at intermediate and high N sites, and was associated with soil pH decline from 5.8 to 4.1 across sites. The ratio of net:gross N mineralization and nitrification increased along the gradient

  18. Effect of isovalent non-magnetic Fe-site doping on the electronic structure and spontaneous polarization of BiFeO3

    NASA Astrophysics Data System (ADS)

    Singh, Poorva; Roy, Amritendu; Garg, Ashish; Prasad, R.

    2015-05-01

    We report the results of our first-principles calculations on the effect of isovalent, non-magnetic, Al3+ ion doping on the electronic structure and spontaneous polarization of multiferroic BiFeO3. Our calculations reveal that Al3+ doping in BiFeO3 results in the reduction of Fe-O-Fe bond angle, leading to the weakening of antiferromagnetic superexchange interaction, further substantiated by the reduction of exchange interaction constant with increasing doping level. Lowering of well-depth is suggestive of reduced switching potential and improved P-E loop with lowered coercivity. Chemical bonding analysis by electron localization function shows that cation-oxygen bonding is of mixed ionic-covalent character, with marginal increase in the covalent character with increasing doping concentration. Large spontaneous polarization of undoped BiFeO3 is retained with lower doping level (6.25%), while for higher doping content (31.25%), the spontaneous polarization is reduced, primarily due to larger c/a ratio at higher doping level.

  19. A-site deficient La0.2Sr0.7TiO3-δ anode material for proton conducting ethane fuel cell to cogenerate ethylene and electricity

    NASA Astrophysics Data System (ADS)

    Liu, Subiao; Behnamian, Yashar; Chuang, Karl T.; Liu, Qingxia; Luo, Jing-Li

    2015-12-01

    A site deficient La0.2Sr0.7TiO3-δ (LSTA) and a highly proton conductive electrolyte BaCe0.7Zr0.1Y0.2O3-δ (BCZY) are synthesized by using solid state reaction method. The performance of the electrolyte-supported single cell, comprised of LSTA + Cr2O3 + Cu//BCZY//(La0.60Sr0.40)0.95Co0.20Fe0.80O3-δ (LSCF)+BCZY, is fabricated and investigated. LSTA shows remarkably high electrical performance, with a conductivity as high as 27.78 Scm-1 at 1150 °C in a 10% H2/N2 reducing atmosphere. As a main anode component, it shows good catalytic activity towards the oxidation of ethane, causing the power density to considerably increase from 158.4 mW cm-2 to 320.9 mW cm-2 and the ethane conversion to significantly rise from 12.6% to 30.9%, when the temperature increases from 650 °C to 750 °C. These changes agree well with the polarization resistance which dramatically decreases from 0.346 Ωcm2 to 0.112 Ωcm2. EDX measurement shows that no element diffusion exists (chemical compatibility) between anode (LSTA + Cr2O3+Cu) and electrolyte (BCZY). With these properties, the pure phase LSTA is evaluated as a high electro-catalytic activity anode material for ethane proton conducting solid oxide fuel cell (PC-SOFC).

  20. Role of lightning phenomenon over surface O3 and NOx at a semi-arid tropical site Hyderabad, India: inter-comparison with satellite retrievals

    NASA Astrophysics Data System (ADS)

    Venkanna, R.; Nikhil, G. N.; Sinha, P. R.; Siva Rao, T.; Swamy, Y. V.

    2016-08-01

    The influence of lightning over surface-level trace gases was examined for pre-monsoon and monsoon seasons in the year 2012. Lightning events were measured using ground-based electric field monitor (EFM) and space-based lightning imaging sensor (LIS). The results showed that lightning frequency was higher during pre-monsoon period compared to monsoon, which is in good agreement with the satellite retrievals. The increase in concentration of NOx on lightning event led to a subsequent decrease in surface O3 due to the titration reaction. Source apportionment study of SO2/NOx (S/N) and CO/NOx (C/N) ratios and poor correlation of NOx vs CO and NOx vs SO2 on the lightning day confirmed the emission of NOx from dissimilar sources.

  1. Site correlation effects in the dynamics of iron impurities Fe2+ / Fe3+ and antisite defects Nb4+ Li / Nb5+ Li after a short-pulse excitation in LiNb O3

    NASA Astrophysics Data System (ADS)

    Carnicero, J.; Carrascosa, M.; García, G.; Agulló-López, F.

    2005-12-01

    The correlation effects between excitation and trapping sites after light excitation in a Li-deficient Fe-doped LiNbO3 crystal have been quantitatively analyzed. They appear as a direct consequence of the thermally activated random transport (hopping) of electrons (free polarons) by using a Monte Carlo approach. The physical consequences of those effects, not present in usual coherent band-transport analyses, are explored and discussed in the light of available experiment. In particular, nonexponential decay kinetics for the evolution of electrons trapped at antisites (small polarons) are predicted.

  2. Dynamical mechanism of phase transitions in A-site ferroelectric relaxor (Na1/2Bi1/2)TiO3

    NASA Astrophysics Data System (ADS)

    Deng, Guochu; Danilkin, Sergey; Zhang, Haiwu; Imperia, Paolo; Li, Xiaobing; Zhao, Xiangyong; Luo, Haosu

    2014-10-01

    The dynamical phase transition mechanism of (Na1/2Bi1/2)TiO3 (NBT) was studied using inelastic neutron scattering. Softening was observed of multiple phonon modes in the phase transition sequence of NBT. As usual, the softening of the zone center transverse optical modes Δ5 and Σ3 was observed in the (200) and (220) zones, showing the Ti vibration instabilities in TiO6 octahedra for both cubic-tetragonal (C-T) and tetragonal-rhombohedral (T-R) phase transitions. In these two phase transitions, however, Ti4+ has different preferential displacement directions. Surprisingly, the longitudinal optic mode also softens significantly toward the zone center in the range of the transition temperature, indicating the Na+/Bi3+ vibration instability against TiO6 octahedra during the T-R phase transition. Strong inelastic diffuse scattering shows up near M(1.5, 0.5, 0) and R(1.5, 1.5, 0.5) in the tetragonal and rhombohedral phases, respectively, indicating the condensations of the M3 and R25 optic modes for the corresponding transitions. This reveals the different rotation instabilities of TiO6 in the corresponding transition temperature range. Bottleneck or waterfall features were observed in the dispersion curves at certain temperatures but did not show close correlations to the formation of polar nanoregions. Additional instabilities could be the origin of the complexity of phase transitions and crystallographic structures in NBT.

  3. Site engineering in chemical solution deposited Na1/2Bi1/2TiO3 thin films using Mn acceptor

    NASA Astrophysics Data System (ADS)

    Feng, Chao; Yang, Changhong; Geng, Fangjuan; Lv, Panpan; Yao, Qian

    2016-02-01

    A series of Mn doped Na1/2Bi1/2TiO3 (NBT) thin films with dopant concentrations from 0 to 4 at% (NBTMn x , x = 0, 0.01, 0.02, 0.04) were fabricated on the indium tin oxide/glass substrates by chemical solution deposition. The effects of Mn doping content on crystalline, ferroelectric and dielectric properties were investigated. All thin films exhibit phase-pure polycrystalline perovskite structures. For the insulating measurement, at low electric field, space charge limited conduction or a grain boundary limited behavior is responsible for the leakage behavior of NBTMn x thin films, whereas at the high electric field, the dominant mechanism is changed to the interface-limited Fowler-Nordheim tunneling except NBTMn0.04. The leakage current density is reduced by more than three orders of magnitude in NBTMn0.02 compared with that of NBT thin film. Also, the enhanced ferroelectric properties of NBTMn0.02 thin film can be observed in polarization-electric filed hysteresis loop with P r of 38 μC cm-2, which is consistent with the result of the normalized capacitance-voltage curve. The dielectric constant and dissipation factor of NBTMn0.02 thin film are 501 and 0.04, respectively at 100 kHz. These electrical property improvements are attributed to the decrease of oxygen vacancy-induced leakage current.

  4. Trends in aluminium export from a mountainous area to surface waters, from deglaciation to the recent: effects of vegetation and soil development, atmospheric acidification, and nitrogen-saturation.

    PubMed

    Kopácek, Jirí; Hejzlar, Josef; Kana, Jirí; Norton, Stephen A; Porcal, Petr; Turek, Jan

    2009-11-01

    We reconstructed the history of terrestrial export of aluminium (Al) to Plesné Lake (Czech Republic) since the lake origin approximately 12,600 year BC, and predicted Al export for 2010-2050 on the basis of previously published and new data on mass budget studies, palaeolimnological data, and MAGIC modelling. We focused on three major Al forms; ionic Al (Al(i)), organically-bound Al (Al(o)), and particulate Al hydroxide [Al(OH)(3)]. In early post-glacial time, Plesné Lake received high terrestrial export of Al, but with a minor proportion of Al(OH)(3) (4-25 microM), and concentrations of Al(i) and Al(o) were negligible. Since the forest and soil development ( approximately 9900-9000 year BC), erosion has declined and soil organic acids increased export of Al(o) from soils. The terrestrial Al(o) leaching ( approximately 7.5 microM) persisted throughout the Holocene until the industrial period. Then, Al(i) concentrations continuously increased (up to 28 microM in the mid-1980s) due to atmospheric acidification; the Al(i) leaching was mostly associated with sulphate. The proportion of Al(i) associated with nitrate has been increasing since the beginning of lake recovery from acidification after approximately 1990 due to reduction in sulphur deposition and nitrogen-saturation of the catchment, leading to persistent nitrate leaching. Currently, nitrate has become the dominant strong acid anion and the major Al(i) carrier. Al(o) (5.5 microM) is predicted to dominate Al concentrations around 2050, but the predicted Al(i) concentrations ( approximately 4 microM) are uncertain because of uncertainty associated with the future nitrate leaching and its effect on soils.

  5. Investigation of chemical compatibility between B-site doped La substituted SrTiO3 anode and stabilized zirconia electrolyte

    NASA Astrophysics Data System (ADS)

    Chen, Gang; Qian, Yu Min; Liu, Man; Ma, Wan Qing; Geng, Shu Jiang; Meng, Xiang Ying; Yu, Kai; Liu, Guo Qiang

    2016-10-01

    High temperature annealing test results indicate that B site dopant of LST and corresponding doping concentration have strong impact on the inter-diffusion behaviors at A-site deficient LST and ScSZ interface, which provides solid evidence for the improvement of the long term stability of LST anode. First principle calculation results indicate that B site doping of Al, Ga and Sc can enhance the neighboring Tisbnd O bonding which increases the VFE of Ti in LST that stabilizes the material and blocks the ion diffusion path at the same time. To minimize B site cation vacancy concentration, a threshold doping concentration exists at which the resulting VFE of Ti can overwhelm that of Sc which effectively suppresses the Sc/Ti ion exchange at the LST/ScSZ interface. But introduction of the B-site dopant may deteriorate the stability due to the lower VFE of dopant itself which becomes new source of instability at high doping concentration. Appropriate doping to balance the improvement and drawback of the dopant is the key for the overall stability of the material.

  6. Nb K-edge x-ray absorption investigation of the pressure induced amorphization in A-site deficient double perovskite La1/3NbO3.

    PubMed

    Marini, C; Noked, O; Kantor, I; Joseph, B; Mathon, O; Shuker, R; Kennedy, B J; Pascarelli, S; Sterer, E

    2016-02-03

    Nb K-edge x-ray absorption spectroscopy is utilized to investigate the changes in the local structure of the A-site deficient double perovskite La1/3NbO3 which undergoes a pressure induced irreversible amorphization. EXAFS results show that with increasing pressure up to 7.5 GPa, the average Nb-O bond distance decreases in agreement with the expected compression and tilting of the NbO6 octahedra. On the contrary, above 7.5 GPa, the average Nb-O bond distance show a tendency to increase. Significant changes in the Nb K-edge XANES spectrum with evident low energy shift of the pre-peak and the absorption edge is found to happen in La1/3NbO3 above 6.3 GPa. These changes evidence a gradual reduction of the Nb cations from Nb(5+) towards Nb(4+) above 6.3 GPa. Such a valence change accompanied by the elongation of the average Nb-O bond distances in the octahedra, introduces repulsion forces between non-bonding adjacent oxygen anions in the unoccupied A-sites. Above a critical pressure, the Nb reduction mechanism can no longer be sustained by the changing local structure and amorphization occurs, apparently due to the build-up of local strain. EXAFS and XANES results indicate two distinct pressure regimes having different local and electronic response in the La1/3NbO3 system before the occurence of the pressure induced amorphization at  ∼14.5 GPa.

  7. Nb K-edge x-ray absorption investigation of the pressure induced amorphization in A-site deficient double perovskite La1/3NbO3

    NASA Astrophysics Data System (ADS)

    Marini, C.; Noked, O.; Kantor, I.; Joseph, B.; Mathon, O.; Shuker, R.; Kennedy, B. J.; Pascarelli, S.; Sterer, E.

    2016-02-01

    Nb K-edge x-ray absorption spectroscopy is utilized to investigate the changes in the local structure of the A-site deficient double perovskite La1/3NbO3 which undergoes a pressure induced irreversible amorphization. EXAFS results show that with increasing pressure up to 7.5 GPa, the average Nb-O bond distance decreases in agreement with the expected compression and tilting of the NbO6 octahedra. On the contrary, above 7.5 GPa, the average Nb-O bond distance show a tendency to increase. Significant changes in the Nb K-edge XANES spectrum with evident low energy shift of the pre-peak and the absorption edge is found to happen in La1/3NbO3 above 6.3 GPa. These changes evidence a gradual reduction of the Nb cations from Nb5+ towards Nb4+ above 6.3 GPa. Such a valence change accompanied by the elongation of the average Nb-O bond distances in the octahedra, introduces repulsion forces between non-bonding adjacent oxygen anions in the unoccupied A-sites. Above a critical pressure, the Nb reduction mechanism can no longer be sustained by the changing local structure and amorphization occurs, apparently due to the build-up of local strain. EXAFS and XANES results indicate two distinct pressure regimes having different local and electronic response in the La1/3NbO3 system before the occurence of the pressure induced amorphization at  ˜14.5 GPa.

  8. Peptidyl-CCA deacylation on the ribosome promoted by induced fit and the O3'-hydroxyl group of A76 of the unacylated A-site tRNA.

    PubMed

    Simonović, Miljan; Steitz, Thomas A

    2008-11-01

    The last step in ribosome-catalyzed protein synthesis is the hydrolytic release of the newly formed polypeptide from the P-site bound tRNA. Hydrolysis of the ester link of the peptidyl-tRNA is stimulated normally by the binding of release factors (RFs). However, an unacylated tRNA or just CCA binding to the ribosomal A site can also stimulate deacylation under some nonphysiological conditions. Although the sequence of events is well described by biochemical studies, the structural basis of the mechanism underlying this process is not well understood. Two new structures of the large ribosomal subunit of Haloarcula marismortui complexed with a peptidyl-tRNA analog in the P site and two oligonucleotide mimics of unacylated tRNA, CCA and CA, in the A site show that the binding of either CA or CCA induces a very similar conformational change in the peptidyl-transferase center as induced by aminoacyl-CCA. However, only CCA positions a water molecule appropriately to attack the carbonyl carbon of the peptidyl-tRNA and stabilizes the proper orientation of the ester link for hydrolysis. We, thus, conclude that both the ability of the O3'-hydroxyl group of the A-site A76 to position the water and the A-site CCA induced conformational change of the PTC are critical for the catalysis of the deacylation of the peptidyl-tRNA by CCA, and perhaps, an analogous mechanism is used by RFs.

  9. Peptidyl-CCA deacylation on the ribosome promoted by induced fit and the O3′-hydroxyl group of A76 of the unacylated A-site tRNA

    SciTech Connect

    Simonović, Miljan; Steitz, Thomas A.

    2008-11-24

    The last step in ribosome-catalyzed protein synthesis is the hydrolytic release of the newly formed polypeptide from the P-site bound tRNA. Hydrolysis of the ester link of the peptidyl-tRNA is stimulated normally by the binding of release factors (RFs). However, an unacylated tRNA or just CCA binding to the ribosomal A site can also stimulate deacylation under some nonphysiological conditions. Although the sequence of events is well described by biochemical studies, the structural basis of the mechanism underlying this process is not well understood. Two new structures of the large ribosomal subunit of Haloarcula marismortui complexed with a peptidyl-tRNA analog in the P site and two oligonucleotide mimics of unacylated tRNA, CCA and CA, in the A site show that the binding of either CA or CCA induces a very similar conformational change in the peptidyl-transferase center as induced by aminoacyl-CCA. However, only CCA positions a water molecule appropriately to attack the carbonyl carbon of the peptidyl-tRNA and stabilizes the proper orientation of the ester link for hydrolysis. We, thus, conclude that both the ability of the O3'-hydroxyl group of the A-site A76 to position the water and the A-site CCA induced conformational change of the PTC are critical for the catalysis of the deacylation of the peptidyl-tRNA by CCA, and perhaps, an analogous mechanism is used by RFs.

  10. Postperovskite phase equilibria in the MgSiO3-Al2O3 system.

    PubMed

    Tsuchiya, Jun; Tsuchiya, Taku

    2008-12-09

    We investigate high-P,T phase equilibria of the MgSiO(3)-Al(2)O(3) system by means of the density functional ab initio computation methods with multiconfiguration sampling. Being different from earlier studies based on the static substitution properties with no consideration of Rh(2)O(3)(II) phase, present calculations demonstrate that (i) dissolving Al(2)O(3) tends to decrease the postperovskite transition pressure of MgSiO(3) but the effect is not significant ( approximately -0.2 GPa/mol% Al(2)O(3)); (ii) Al(2)O(3) produces the narrow perovskite+postperovskite coexisting P,T area (approximately 1 GPa) for the pyrolitic concentration (x(Al2O3) approximately 6 mol%), which is sufficiently responsible to the deep-mantle D'' seismic discontinuity; (iii) the transition would be smeared (approximately 4 GPa) for the basaltic Al-rich composition (x(Al2O3) approximately 20 mol%), which is still seismically visible unless iron has significant effects; and last (iv) the perovskite structure spontaneously changes to the Rh(2)O(3)(II) with increasing the Al concentration involving small displacements of the Mg-site cations.

  11. Remarkable Strontium B-Site Occupancy in FerroelectricPb(Zr1-xTix)O3 Solid Solutions Doped with Cryolite-Type StrontiumNiobate

    SciTech Connect

    Feltz, A.; Schmidt-Winkel, P.; Schossman, M.; Booth, C.H.; Albering, J.

    2007-04-26

    New high-performance ferroelectric materials based on Pb(Zr{sub 1-x}Ti{sub x})O{sub 3} (PZT) that are doped with cryolite-type strontium niobate (SNO, Sr{sub 4}(Sr{sub 2-2y/3}Nb{sub 2+2y/3})O{sub 11+y}V{sub 0,1-y} with 0 {le} y {le} 1), hence denoted PZT:SNO, and their microscopic structure are described. The combination of exceptional piezoelectric properties, i.e. a piezoelectric strain constant of d{sub 33} {approx} 760 pm/V, with excellent stability and degradation resistance makes ferroelectric PZT:SNO solid solutions very attractive for use in novel and innovative piezoelectric actuator and transducer applications. Extended X-ray absorption fine-structure (EXAFS) analyses of PZT:SNO samples revealed that {approx}10 % of the Sr cations occupy the nominal B-sites of the perovskite-type PZT host lattice. This result was supported by EXAFS analyses of both a canonical SrTiO{sub 3} perovskite and two SNO model and reference compounds. Fit models that do not account for Sr cations on B-sites were ruled out. A clear Sr-Pb peak in Fourier transformed EXAFS data visually confirmed this structural model. The generation of temporary oxygen vacancies and the intricate defect chemistry induced by SNO-doping of PZT are crucial for the exceptional materials properties exhibited by PZT:SNO materials.

  12. Structure and magnetism of the A site scandium perovskite (Sc0.94Mn0.06)Mn0.65Ni0.35O3 synthesized at high pressure.

    PubMed

    Thomas, Chris I; Suchomel, Matthew R; Duong, Giap V; Fogg, Andrew M; Claridge, John B; Rosseinsky, Matthew J

    2014-04-13

    Scandium perovskite (Sc0.94Mn0.06)Mn0.65Ni0.35O3, synthesized at high pressure and high temperature, has a triclinic structure (space group ) at room temperature and ambient pressure with a √2ap×√2ap×2ap structure with α≈90(°),β≈89(°),γ≈90(°). Magnetic measurements show that the material displays Curie-Weiss behaviour above 50 K with C=2.11 emu K mol(-1) (μeff=4.11 μB per formula unit) and θ=-95.27 K. Bond valence sum analysis of the crystal structure shows that manganese is present in three different oxidation states (+2, +3, +4), with the +2 oxidation state on the A site resulting in a highly tilted perovskite structure (average tilt 21.2(°) compared with 15.7(°) calculated for LaCaMnNbO6), giving the formula (Sc3+(0.94)Mn2+(0.06))(Mn4+(0.41)Mn3+(0.09))(Mn3+(0.15)Ni2+(0.35))O3.

  13. Unraveling the effect of La A-site substitution on oxygen ion diffusion and oxygen catalysis in perovskite BaFeO3 by data-mining molecular dynamics and density functional theory.

    PubMed

    Chen, Chi; Baiyee, Zarah Medina; Ciucci, Francesco

    2015-10-07

    BaFeO3 (BFO) is a promising parent material for high-temperature oxygen catalysis. The effects of La substitution on the oxygen ion diffusion and oxygen catalysis in A-site La-substituted BFO are studied by combining data-driven molecular dynamics (MD) simulations and density functional theory (DFT) calculations. The data-driven MD simulations are capable of providing atomic level information regarding oxygen jumps at different sites, bridging the resolution gap of analysis between MD and DFT. The simulations identify several effects due to the introduction of La. First, according to simple electroneutrality considerations and DFT calculations, La tends to decrease the concentration of oxygen vacancies in BFO. Second, La substitution lowers the activation energy of local oxygen migration, providing faster paths for oxygen diffusion. The MD analysis predicts a higher hopping rate through La-containing bottlenecks as well as easier oxygen jumps from the La-rich cages and lower dwell times of oxygen in those cages. DFT calculations confirm a lower migration energy through La-containing bottlenecks. Third, the electrocatalytic activity of the material decreases with La, as indicated by a lower O p-band center and higher oxygen vacancy formation energies.

  14. Relaxor or classical ferroelectric behavior in A-site substituted perovskite type Ba 1- x(Sm 0.5Na 0.5) xTiO 3

    NASA Astrophysics Data System (ADS)

    Abdelmoula, N.; Chaabane, H.; Khemakhem, H.; Von der Mühll, R.; Simon, A.

    2006-08-01

    New ferroelectric ceramics of ABO 3 perovskite type were synthetized in the Ba 1- x(Sm 0.5Na 0.5) xTiO 3 system by solid state reaction technique. The effect of the replacement of barium by samarium and sodium in the A cationic site on structural and physical properties was investigated. These compounds crystallize with tetragonal or cubic symmetry. The material is classical ferroelectric for 0⩽x⩽0.1 and x⩾0.5, and present a relaxor behavior for 0.2⩽x<0.4. The dielectric behavior depends upon the cationic disorder in the A-site and the cell size. Small rate substitution allows a ferroelectric-paraelectric transition. For higher rate of substitution the possible random position of the Sm-Na cations brings to a relaxor state and when the substitution rate x becomes higher than 0.5, the material comes back to a ferroelectric state due to the reduced cell size. Some of these new compositions are of interest for applications due to their physical properties and environmentally friendly character.

  15. A-site- and/or B-site-modified PbZrTiO3 materials and (Pb, Sr, Ca, Ba, Mg) (Zr, Ti, Nb, Ta)O3 films having utility in ferroelectric random access memories and high performance thin film microactuators

    NASA Technical Reports Server (NTRS)

    Roeder, Jeffrey F. (Inventor); Chen, Ing-Shin (Inventor); Bilodeau, Steven (Inventor); Baum, Thomas H. (Inventor)

    2001-01-01

    A modified PbZrTiO.sub.3 perovskite crystal material thin film, wherein the PbZrTiO.sub.3 perovskite crystal material includes crystal lattice A-sites and B-sites at least one of which is modified by the presence of a substituent selected from the group consisting of (i) A-site substituents consisting of Sr, Ca, Ba and Mg, and (ii) B-site substituents selected from the group consisting of Nb and Ta. The perovskite crystal thin film material may be formed by liquid delivery MOCVD from metalorganic precursors of the metal components of the thin film, to form PZT and PSZT, and other piezoelectric and ferroelectric thin film materials. The thin films of the invention have utility in non-volatile ferroelectric memory devices (NV-FeRAMs), and in microelectromechanical systems (MEMS) as sensor and/or actuator elements, e.g., high speed digital system actuators requiring low input power levels.

  16. A-SITE-AND/OR B-SITE-MODIFIED PBZRTIO3 MATERIALS AND (PB, SR, CA, BA, MG) (ZR, TI,NB, TA)O3 FILMS HAVING UTILITY IN FERROELECTRIC RANDOM ACCESS MEMORIES AND HIGH PERFORMANCE THIN FILM MICROACTUATORS

    NASA Technical Reports Server (NTRS)

    Roeder, Jeffrey F. (Inventor); Chen, Ing-Shin (Inventor); Bilodeau, Steven (Inventor); Baum, Thomas H. (Inventor)

    2004-01-01

    A modified PbZrTiO.sub.3 perovskite crystal material thin film, wherein the PbZrTiO.sub.3 perovskite crystal material includes crystal lattice A-sites and B-sites at least one of which is modified by the presence of a substituent selected from the group consisting of (i) A-site substituents consisting of Sr, Ca, Ba and Mg, and (ii) B-site substituents selected from the group consisting of Nb and Ta. The perovskite crystal thin film material may be formed by liquid delivery MOCVD from metalorganic precursors of the metal components of the thin film, to form PZT and PSZT, and other piezoelectric and ferroelectric thin film materials. The thin films of the invention have utility in non-volatile ferroelectric memory devices (NV-FeRAMs), and in microelectromechanical systems (MEMS) as sensor and/or actuator elements, e.g., high speed digital system actuators requiring low input power levels.

  17. Reactivity of Hydrogen and Methanol on (001) Surfaces of WO3, ReO3, WO3/ReO3 and ReO3/WO3

    SciTech Connect

    Ling, Sanliang; Mei, Donghai; Gutowski, Maciej S.

    2011-05-16

    Bulk tungsten trioxide (WO3) and rhenium trioxide (ReO3) share very similar structures but display different electronic properties. WO3 is a wide bandgap semiconductor while ReO3 is an electronic conductor. With the advanced molecular beam epitaxy techniques, it is possible to make heterostructures comprised of layers of WO3 and ReO3. These heterostructures might display reactivity different than pure WO3 and ReO3. The interactions of two probe molecules (hydrogen and methanol) with the (001) surfaces of WO3, ReO3, and two heterostructures ReO3/WO3 and WO3/ReO3 were investigated at the density functional theory level. Atomic hydrogen prefers to adsorb at the terminal O1C sites forming a surface hydroxyl on four surfaces. Dissociative adsorption of a hydrogen molecule at the O1C site leads to formation of a water molecule adsorbed at the surface M5C site. This is thermodynamically the most stable state. A thermodynamically less stable dissociative state involves two surface hydroxyl groups O1CH and O2CH. The interaction of molecular hydrogen and methanol with pure ReO3 is stronger than with pure WO3 and the strength of the interaction substantially changes on the WO3/ReO3 and ReO3/WO3 heterostructures. The reaction barriers for decomposition and recombination reactions are sensitive to the nature of heterostructure. The calculated adsorption energy of methanol on WO3(001) of -65.6 kJ/mol is consistent with the previous experimental estimation of -67 kJ/mol. This material is based upon work supported as part of the Center for Molecular Electrocatalysis, an Energy Frontier Research Center funded by the US Department of Energy, Office of Science, Office of Basic Energy Sciences.

  18. Postperovskite phase equilibria in the MgSiO3–Al2O3 system

    PubMed Central

    Tsuchiya, Jun; Tsuchiya, Taku

    2008-01-01

    We investigate high-P,T phase equilibria of the MgSiO3–Al2O3 system by means of the density functional ab initio computation methods with multiconfiguration sampling. Being different from earlier studies based on the static substitution properties with no consideration of Rh2O3(II) phase, present calculations demonstrate that (i) dissolving Al2O3 tends to decrease the postperovskite transition pressure of MgSiO3 but the effect is not significant (≈-0.2 GPa/mol% Al2O3); (ii) Al2O3 produces the narrow perovskite+postperovskite coexisting P,T area (≈1 GPa) for the pyrolitic concentration (xAl2O3 ≈6 mol%), which is sufficiently responsible to the deep-mantle D″ seismic discontinuity; (iii) the transition would be smeared (≈4 GPa) for the basaltic Al-rich composition (xAl2O3 ≈20 mol%), which is still seismically visible unless iron has significant effects; and last (iv) the perovskite structure spontaneously changes to the Rh2O3(II) with increasing the Al concentration involving small displacements of the Mg-site cations. PMID:19036928

  19. Orbital configuration in CaTiO3 films on NdGaO3

    DOE PAGES

    Cao, Yanwei; Park, Se Young; Liu, Xiaoran; ...

    2016-10-13

    Despite its use as a constituent layer for realization of a polar metal and interfacial conductivity, the microscopic study of electronic structure of CaTiO3 is still very limited. Here, we epitaxially stabilized CaTiO3 films on NdGaO3 (110) substrates in a layer-by-layer way by pulsed laser deposition. The structural and electronic properties of the films were characterized by reflection-high-energy-electron-diffraction, X-ray diffraction, and element-specific resonant X-ray absorption spectroscopy. To reveal the orbital polarization and the crystal field splitting of the titanium 3d state, X-ray linear dichroism was carried out on CaTiO3 films, demonstrating the orbital configuration of dxz/dyz < dxy < d3z2-r2more » < dx2-y2. To further explore the origin of this configuration, we performed the first-principles density function theory calculations, which linked the orbital occupation to the on-site energy of Ti 3d orbitals. Finally, these findings can be important for understanding and designing exotic quantum states in heterostructures based on CaTiO3.« less

  20. Properties of epitaxial LaMnO3/SrTiO3 interfaces.

    NASA Astrophysics Data System (ADS)

    Christen, Hans M.; Kim, Dae Ho; Lee, Ho Nyung; Varela, Maria; Petit, Leon; Schulthess, Thomas

    2007-03-01

    Electronic effects at interfaces between dissimilar oxides are known to have fundamental consequences on their transport and magnetic properties. Interfaces between the band insulator SrTiO3 and the antiferromagnetic charge-transfer insulator LaMnO3 provide a particularly interesting platform to test such effects. Both perovskites are grown epitaxially by pulsed-laser deposition, and electron energy loss spectra (EELS) collected in a scanning transmission electron microscope (STEM) show interfacial valence changes on the Mn-sites, while Ti remains in a 4+ state even in direct contact with the LaO layer of the LaMnO3. This observation is fully consistent with computational results obtained for such structures using the self-interaction corrected (SIC) local spin density (LSD) method. In this presentation, we discuss the physical origin and consequences of these valence changes in single interfaces as well as LaMnO3/SrTiO3 superlattices. This research was sponsored by the Office of Basic Energy Sciences, Division of Materials Sciences and Engineering, U.S. Department of Energy, under contract DE-AC05-00OR22725 with Oak Ridge National Laboratory (ORNL), managed and operated by UT-Battelle, LLC, and ORNL's Laboratory Directed Research and Development Program.

  1. An assessment of the relationship between potential chemical indices of nitrogen saturation and nitrogen deposition in hardwood forests in southern Ontario.

    PubMed

    Watmough, Shaun A

    2010-05-01

    Southern Ontario receives the highest levels of atmospheric nitrogen (N) deposition in Canada and there are concerns that forests in the region may be approaching a state of 'N saturation'. In order to evaluate whether potential chemical indices provide evidence of N saturation, 23 hardwood plots were sampled along a modeled N-deposition gradient ranging from 9.3 to 12.8 kg/ha/year. All plots were dominated by sugar maple (Acer saccharum Marsh.) and foliar N and foliar delta(15)N were positively correlated with modeled N deposition. However, forest floor N content and the C:N ratio were unrelated to N deposition, but were instead related to soil pH and annual temperature; lower C:N ratios and higher N content in the forest floor were found at the most acidic sites in the cooler, northern part of the study region despite lower N deposition. Likewise, delta(15)N values in surface mineral soil and the (15)N enrichment factor of foliage (delta(15)N foliage - delta(15)N soil) are correlated to soil pH and temperature and not N deposition. Further, potential N mineralization, ammonification, and nitrification in Ontario maple stands were highest in the northern part of the region with the lowest modeled N deposition. Nitrogen cycling in soil appears to be primarily influenced by the N status of the forest floor and other soil properties rather than N deposition, indicating that chemical indices in soil in these hardwood plots may not provide an early indicator of N saturation.

  2. C/G to A/T transversions represent the main type of mutation induced by gamma-irradiation in double-stranded M13mp10 DNA in a nitrogen-saturated solution.

    PubMed

    Braun, J E; Wanamarta, A H; van den Akker, E; Lafleur, M V; Retèl, J

    1993-10-01

    To get more insight into the possible mutagenic consequences of DNA damage induced by radiation-generated H radicals (.H), a nitrogen-saturated solution of double-stranded (ds) M13mp10 DNA in phosphate buffer was irradiated with gamma-rays. Under these conditions 55% of the DNA-damaging species consists of H radicals and 45% of OH radicals (.OH). The mutations were investigated in a 144-bp mutational target sequence inserted into the lacZ alpha gene. A very specific mutation spectrum was obtained with respect to the type of mutations. Twenty out of the 28 radiation-induced mutations were C/G to A/T transversions; the remaining 8 mutations were 4 C/G to G/C transversions, 2 C/G to T/A transitions, one T/A to A/T transversion and only one -1 bp deletion. The mutations were rather randomly distributed along the 144-bp mutation target sequence with no clear mutational hot spots. When these results are compared with those we have obtained previously after irradiation of ds M13mp10 DNA under O2 (100% .OH) or N2O (90% .OH; 10% .H) (Hoebee et al., 1988, 1989), the data strongly suggest that H radicals may be responsible for the observed C/G to A/T transversions but not for -1 bp deletions.

  3. Interaction of Nd dopants with broadband emission centers in Bi2O3-B2O3 glass: local energy balance and its influence on optical properties

    NASA Astrophysics Data System (ADS)

    Ishii, Masashi; Fuchi, Shingo; Takeda, Yoshikazu

    2015-10-01

    Chemical and energetic interactions between broadband infrared intrinsic emission centers (IECs) of bismuthates and extrinsic emission centers (EECs) of Nd2O3 dopants were optically and electronically investigated. Although no visible absorption from the IEC was found in untreated Bi2O3-B2O3 glass, it was clearly observed after a moderate thermal treatment of  <200 °C, indicating chemical activity of O-deficient sites as the origin of IECs. On the other hand, Nd2O3 doping chemically stabilized the Bi2O3-B2O3 glass and suppressed IEC formation. By using a microwave measurement sensitive to electric dipoles, we found a ‘switching’ in local energy balance resulting from the Nd2O3 doping. This was explained by metallization of the O-deficient sites in the Bi2O3-B2O3 glass and multi-phonon excitation of IEC and EEC complexes in the Nd2O3-Bi2O3-B2O3 glass phosphor. Although the electric dipole observed by the microwave measurement was not necessarily caused by IEC, emission properties of the IEC and EEC complexes were consistent with energy balance switching; emissions from IECs after thermal treatment were quenched by EECs with multi-phonon excitation.

  4. Interaction of Nd dopants with broadband emission centers in Bi2O3-B2O3 glass: local energy balance and its influence on optical properties.

    PubMed

    Ishii, Masashi; Fuchi, Shingo; Takeda, Yoshikazu

    2015-10-07

    Chemical and energetic interactions between broadband infrared intrinsic emission centers (IECs) of bismuthates and extrinsic emission centers (EECs) of Nd2O3 dopants were optically and electronically investigated. Although no visible absorption from the IEC was found in untreated Bi2O3-B2O3 glass, it was clearly observed after a moderate thermal treatment of  <200 °C, indicating chemical activity of O-deficient sites as the origin of IECs. On the other hand, Nd2O3 doping chemically stabilized the Bi2O3-B2O3 glass and suppressed IEC formation. By using a microwave measurement sensitive to electric dipoles, we found a 'switching' in local energy balance resulting from the Nd2O3 doping. This was explained by metallization of the O-deficient sites in the Bi2O3-B2O3 glass and multi-phonon excitation of IEC and EEC complexes in the Nd2O3-Bi2O3-B2O3 glass phosphor. Although the electric dipole observed by the microwave measurement was not necessarily caused by IEC, emission properties of the IEC and EEC complexes were consistent with energy balance switching; emissions from IECs after thermal treatment were quenched by EECs with multi-phonon excitation.

  5. Dielectric Properties of BaTiO3 Codoped with Er2O3 and MgO

    NASA Astrophysics Data System (ADS)

    Hwang, Jin Hyun; Choi, Sang Keun; Han, Young Ho

    2001-08-01

    The effect of Er2O3 and MgO addition on the dielectric properties of BaTiO3 ceramics was studied in a reduced atmosphere. MgO effectively prevented the material from being reduced and suppressed grain growth. An X7R material with moderate temperature dependence was developed by the addition of MgO with higher than 2.0 mol% Er2O3 to BaTiO3, which is ascribed to the decrease in grain size and the grain core-grain shell structure. In the presence of equimolar amount of B-site metal ions, there was no evidence to support the incorporation of Er ions into the octahedral and dodecahedral cation sites.

  6. Manifestation of screening effects and A-O covalency in the core level spectra of A site elements in the ABO3 structure of Ca1-xSrxRuO3

    NASA Astrophysics Data System (ADS)

    Singh, Ravi Shankar; Maiti, Kalobaran

    2007-08-01

    We investigate the evolution of Ca2p and Sr3d core level spectra in Ca1-xSrxRuO3 using photoemission spectroscopy. Core level spectra in this system exhibit multiple features and unusual evolution with the composition and temperatures. Analysis of the core level spectra in conjunction with the band structure results indicates final state effects due to different core hole screening channels. Such screening in the photoemission final states can be attributed to the large A-O covalency in these systems. Changes in the core level spectra with temperature and composition suggest significant modification in A-O (A=Ca/Sr) covalency in Ca-dominated samples, which gradually reduces with the increase in Sr content and becomes insignificant in SrRuO3 . This study thus provides a direct evidence of cation-oxygen covalency and its evolution with temperature, which may be useful in understanding the unusual ground state properties of these materials.

  7. Nitrogen Saturation in Highly Retentive Watersheds?

    NASA Astrophysics Data System (ADS)

    Daley, M. L.; McDowell, W. H.

    2009-12-01

    Watershed managers are often concerned with minimizing the amount of N delivered to N-limited estuaries and coastal zones. A major concern is that watersheds might reach N saturation, in which N delivered to coastal zones increases due to declines in the efficiency of N retention despite constant or even reduced N inputs. We have quantified long-term changes in N inputs (atmospheric deposition, imported food and agricultural fertilizers), outputs (N concentration and export) and retention in the urbanizing Lamprey River watershed in coastal NH. Overall, the Lamprey watershed is 70% forested, receives about 13.5 kg N/ha/yr and has a high rate of annual N retention (85%). Atmospheric deposition (8.7 kg/ha/yr) is the largest N input to the watershed. Of the 2.2 kg N/ha/yr exported in the Lamprey River, dissolved organic N (DON) is the dominant form (50% of total) and it varies spatially throughout the watershed with wetland cover. Nitrate accounts for 30% of the N exported, shows a statistically significant increase from 1999 to 2009, and its spatial variability in both concentration and export is related to human population density. In sub-basins throughout the Lamprey, inorganic N retention is high (85-99%), but the efficiency of N retention declines sharply with increased human population density and associated anthropogenic N inputs. N assimilation in the vegetation, denitrification to the atmosphere and storage in the groundwater pool could all be important contributors to the current high rates of N retention. The temporal and spatial patterns that we have observed in nitrate concentration and export are driven by increases in N inputs and impervious surfaces over time, but the declining efficiency of N retention suggests that the watershed may also be reaching N saturation. The downstream receiving estuary, Great Bay, already suffers from low dissolved oxygen levels and eelgrass loss in part due to N loading from the Lamprey watershed. Targeting and reducing anthropogenic sources of N that are not retained in the watershed and maintaining high rates of N retention will be of utmost concern for coastal managers.

  8. NMR and Mössbauer Study of Al2O3-Eu2O3

    NASA Astrophysics Data System (ADS)

    Nava, N.; Salas, P.; Llanos, M. E.; Pérez-Pastenes, H.; Viveros, T.

    2005-02-01

    Alumina-europia mixed oxides with 5 and 10 wt.% Eu2O3 were studied by Mössbauer spectroscopy, 27Al MAS-NMR and X-ray diffraction (XRD). The samples were prepared by the sol-gel technique. The XRD patterns for the calcined samples show a broad peak around 2 θ = 30° which is assigned to the Eu2O3; after treatment with hydrogen at 1073 K no reduction to Eu+2 or Eu0 was observed. The NMR spectra show three peaks, which are assigned to the octahedral, pentahedral and tetrahedral aluminum sites; the intensity of each peak depends on the concentration of europium ions. The Mössbauer spectra of the calcined samples show a single peak near zero velocity which is attributed to the Eu+3; after H2 treatment at 1073 K similar spectra were obtained, suggesting Eu+3 is not reducibly at this temperature.

  9. Photo-resistive properties of LaAl0.6Cr0.4O3/SrTiO3 heterostructures: a comparative study with LaAlO3/SrTiO3.

    PubMed

    V, Aswin; Kumar, Pramod; Pal, Prabir; Dogra, Anjana

    2016-03-15

    We report photoconductivity measurements on LaAl(1-x)Cr(x)O3/SrTiO3 (x=0, 0.4) heterostructures. A polar layer modification of metallic LaAlO3/SrTiO3 heterostructure with Cr in the Al sites resulted in an increased photo-response (PR) and relaxation time, in addition to a distinct shift in the spectral weight toward the red end of the spectrum. The visible light photoconductivity is explained by d-d photoconductivity of Cr3+ valence states of the x=0.4 sample. Besides the established UV sensitivity, we observe a weak peak in PR around 690 nm possibly emanating from the mid-gap states arising from oxygen vacancies.

  10. Origin of interface magnetism in BiMnO3/SrTiO3 and LaAlO3/SrTiO3 heterostructures.

    PubMed

    Salluzzo, M; Gariglio, S; Stornaiuolo, D; Sessi, V; Rusponi, S; Piamonteze, C; De Luca, G M; Minola, M; Marré, D; Gadaleta, A; Brune, H; Nolting, F; Brookes, N B; Ghiringhelli, G

    2013-08-23

    Possible ferromagnetism induced in otherwise nonmagnetic materials has been motivating intense research in complex oxide heterostructures. Here we show that a confined magnetism is realized at the interface between SrTiO3 and two insulating polar oxides, BiMnO3 and LaAlO3. By using polarization dependent x-ray absorption spectroscopy, we find that in both cases the magnetism can be stabilized by a negative exchange interaction between the electrons transferred to the interface and local magnetic moments. These local magnetic moments are associated with magnetic Ti3+ ions at the interface itself for LaAlO3/SrTiO3 and to Mn3+ ions in the overlayer for BiMnO3/SrTiO3. In LaAlO3/SrTiO3 the induced magnetism is quenched by annealing in oxygen, suggesting a decisive role of oxygen vacancies in this phenomenon.

  11. Trapped charge densities in Al2O3-based silicon surface passivation layers

    NASA Astrophysics Data System (ADS)

    Jordan, Paul M.; Simon, Daniel K.; Mikolajick, Thomas; Dirnstorfer, Ingo

    2016-06-01

    In Al2O3-based passivation layers, the formation of fixed charges and trap sites can be strongly influenced by small modifications in the stack layout. Fixed and trapped charge densities are characterized with capacitance voltage profiling and trap spectroscopy by charge injection and sensing, respectively. Al2O3 layers are grown by atomic layer deposition with very thin (˜1 nm) SiO2 or HfO2 interlayers or interface layers. In SiO2/Al2O3 and HfO2/Al2O3 stacks, both fixed charges and trap sites are reduced by at least a factor of 5 compared with the value measured in pure Al2O3. In Al2O3/SiO2/Al2O3 or Al2O3/HfO2/Al2O3 stacks, very high total charge densities of up to 9 × 1012 cm-2 are achieved. These charge densities are described as functions of electrical stress voltage, time, and the Al2O3 layer thickness between silicon and the HfO2 or the SiO2 interlayer. Despite the strong variation of trap sites, all stacks reach very good effective carrier lifetimes of up to 8 and 20 ms on p- and n-type silicon substrates, respectively. Controlling the trap sites in Al2O3 layers opens the possibility to engineer the field-effect passivation in the solar cells.

  12. Pressure-induced ferroelectric to paraelectric transition in LiTaO3 and (Li,Mg)TaO3

    DOE PAGES

    Yamanaka, Takamitsu; Nakamoto, Yuki; Takei, Fumihiko; ...

    2016-02-16

    X-ray powder diffraction and Raman scattering of LiTaO3 (LT) and (Li,Mg)TaO3 (LMT) have been measured under pressure up to 46 GPa. Above 30 GPa, the ferroelectric rhombohedral phase (R3c, Z – 6) of LiTaO3 transforms to a paraelectric orthorhombic phase (Pnma with Z – 4) with a large hysteresis. Rietveld profile fitting analysis shows that the Li-O bond is compressed and approaches that of Ta-O with pressure. The cation distribution analysis of the orthorhombic perovskite structure shows that Li and Ta are located in the octahedral 8-fold coordination sites. Difference Fourier |Fobs(hkl)| - |Fcal(hkl)| maps of LiTaO3 and (Li,Mg)TaO3 indicatemore » polarization in the c axis direction and a more distinct electron density distribution around the Ta position for (Li,Mg)TaO3 compared to LiTaO3. The observed effective charges indicate that for (Li,Mg)TaO3 without vacancies Ta5+ becomes less ionized as a function of Mg substitution. Considering both site occupancy and effective charge analysis, Ta5+ is reduced to Ta4.13+. Mg2+ and O2- change to Mg1.643+ and O1.732 -, respectively. The space- and time-averaged structures of the dynamical vibration of atoms can be elucidated from the electron density analysis by difference Fourier and temperature factors T(hkl) in the structure refinement. The refinement of the temperature factor is consistent with the cation distribution assuming full stoichiometry. The residual electron density induced from the excess electron in (Li,Mg)TaO3 indicates more electrons around the Ta site, as confirmed by the effective charge analysis. Raman spectra of LiTaO3 and (Li,Mg)TaO3 show notable changes over the measured pressure range. Raman peaks centered at 250 cm–1 and 350 cm–1 at ambient pressure merge above 8 GPa, which we associate with the diminishing of difference in distances between Li-O and Ta-O bonds with pressure in both materials. Finally, Raman spectra show significant changes at 28 GPa and 33 GPa for LT and LMT

  13. CH3-ReO3 on gamma-Al2O3: understanding its structure, initiation,and reactivity in olefin metathesis

    SciTech Connect

    Salameh, Alain; Joubert, Jerome; Baudouin, Anne; Lukens, Wayne; Delbecq, Francoise; Sautet, Philippe; Basset, Jean Marie; Coperet,Christophe

    2007-01-20

    Me-ReO3 on gamma-alumina: understanding the structure, theinitiation and thereactivity of a highly active olefin metathesiscatalyst Heterolytic splitting of the C-H bond of the methyl group ofCH3ReO3 on AlsO reactive sites of alumina as a way to generate the activesite of CH3ReO3 supported on gamma-Al203.

  14. Effect of A-site ionic size variation on TCR and electrical transport properties of (Nd0.7-xLax)0.7Sr0.3MnO3 with x = 0, 0.1 and 0.2

    NASA Astrophysics Data System (ADS)

    Vadnala, Sudarshan; Asthana, Saket; Pal, Prem; Srinath, S.

    2015-02-01

    In this work, the structural and transport properties of (Nd0.7-xLax)0.7Sr0.3MnO3 manganites with x = 0, 0.1 and 0.2 prepared by solid state reaction route are studied. These compounds are found to be crystallized in orthorhombic structural form. Experimental results showing a shift in the metal to semiconductor/insulator transition temperature (TMI) towards room temperature (289 K) with the substitution of Nd by La, as the value of x is varied in the sequence (0,0.1,0.2), have been provided. The shift in the TMI, from 239 K (for x=0) to near the room temperature 289 K (for x=0.2), is attributed to the fact that the average radius of site-A increases with the percentage of La. The maximum temperature coefficients of resistance (TCR) of (Nd0.7-xLax)0.7Sr0.3MnO3 (x= 0.1 and 0.2) are found to be higher compared to its parent compound Nd0.7Sr0.3MnO3. The electrical transport mechanisms for (Nd0.7-xLax)0.7Sr0.3MnO3 (x= 0 to 0.2) are explored by using different theoretical models, for temperatures below and above TMI. An appropriate enlightenment for the observed behavior is discussed in detail.

  15. Influence of fires on O3 concentrations in the western U.S.

    PubMed

    Jaffe, Dan; Chand, Duli; Hafner, Will; Westerling, Anthony; Spracklen, Dominick

    2008-08-15

    Because forest fires emit substantial NOx and hydrocarbons--known contributors to O3 production--we hypothesize that interannual variation in western U.S. O3 is related to the burned area. To evaluate this hypothesis we used a gridded database of western U.S. summer burned area (BA) and biomass consumed (BC) by fires between 101-125 degrees W. The fire data were compared with daytime summer O3 mixing ratios from nine rural Clean Air Status and Trends Network (CASTNET) and National Park Service (NPS) sites. Large fire years exhibited widespread enhanced O3. The summer BA was significantly correlated with O3 at all sites. For each 1 million acres burned in the western U.S. during summer, we estimate that the daytime mean O3 was enhanced across the region by 2.0 ppbv. For mean and maximum fire years, O3 was enhanced by an average of 3.5 and 8.8 ppbv, respectively. At most sites O3 was significantly correlated with fires in the surrounding 5 x 5 degrees and 10 x 10 degrees regions, but not with fires in the nearest 1 x 1 degree region, reflecting the balance between O3 production and destruction in a high NOx environment. BC was a slightly better predictor of O3, compared with BA. The relationship between O3 and temperature was examined at two sites (Yellowstone and Rocky Mountain National Parks). At these two sites, high fire years were significantly warmer than lowfire years; however, daytime seasonal meantemperature and O3 were not significantly correlated. This indicates that the presence of fire is a more important predictor for O3 than is temperature.

  16. Ground-level O3 pollution and its impacts on food crops in China: a review.

    PubMed

    Feng, Zhaozhong; Hu, Enzhu; Wang, Xiaoke; Jiang, Lijun; Liu, Xuejun

    2015-04-01

    Ground-level ozone (O3) pollution has become one of the top environmental issues in China, especially in those economically vibrant and densely populated regions. In this paper, we reviewed studies on the O3 concentration observation and O3 effects on food crops throughout China. Data from 118 O3 monitoring sites reported in the literature show that the variability of O3 concentration is a function of geographic location. The impacts of O3 on food crops (wheat and rice) were studied at five sites, equipped with Open Top Chamber or O3-FACE (free-air O3 concentration enrichment) system. Based on exposure concentration and stomatal O3 flux-response relationships obtained from the O3-FACE experimental results in China, we found that throughout China current and future O3 levels induce wheat yield loss by 6.4-14.9% and 14.8-23.0% respectively. Some policies to reduce ozone pollution and impacts are suggested.

  17. Variation of properties of glasses along the 3Bi2O3 X 5B2O3-4PbO X B2O3 and PbO X 2B2O3-2PbO X Bi2O3 sections of the PbO-Bi2O3-B2O3 ternary system

    SciTech Connect

    Zargarova, M.I.; Shuster, N.S.

    1985-07-01

    Already published data on the phase diagrams of Pb-B2O3, Bi2O3-B2O3, and PbO-Bi2O3 systems serve as the basis of this investigation, together with original experiments on the PbO-Bi2O3-B2O3 ternary system. The authors establish the quasi binary nature of the 3Bi2O3 X 5B2O3 - 4PbO X B2O3 section with the formation of the congruently melting ternary compound 3Bi2O3 X 8PbO X 7B2O3, and they demonstrate the role of the ternary compound 3Bi2O3 X 8PbO X 7B2O3 as a glass former in the PbO-Bi2O3 - B2O3 system.

  18. High-pressure synthesis of BiFeO3-BiAlO3 and BiFeO3-MnTiO3 solid solution

    NASA Astrophysics Data System (ADS)

    Shimura, Gen; Kusaba, Keiji; Miyawaki, Tetsuya; Niwa, Ken; Asano, Hidefumi; Hasegawa, Masashi

    2013-06-01

    There have been so many investigations for high-pressure synthesis of perovskite-type oxides in the material science field. Multiferroic material is particularly attracted in the field of electronic device materials. BiFeO3 (ferroelectric antiferromagnet) is known as the only Bi-contained perovskite which can be synthesized at ambient pressure. We investigated solid solution systems of BiFeO3-BiAlO3 and BiFeO3-MnTiO3 under high pressure and high temperature to synthesize a new multiferroic compound in the present study. Chemical reagents of simple oxides were mixed with a mortar as a starting material. The mixture was rapped with a gold foil, and it encased in a cubic pressure-medium with a graphite furnace. High pressure experiments were carried out using two DIA-type high pressure apparatuses installed in Nagoya University. X-ray powder diffraction patterns of all recovered specimens were collected using Cu-K α radiation and magnetic susceptibilities for some of the recovered specimens were measured using a vibrating sample magnetometer. In the system of BiFeO3-BiAlO3, the BiFeO3-type solid solution was only obtained in the both Fe- and Al-rich composition. While in the system of BiFeO3-MnTiO3, no solid solutions were observed.

  19. Effects of Dopant on Depoling Temperature in Modified BiScO3 - PbTiO3

    NASA Technical Reports Server (NTRS)

    Kowalski, Benjamin; Sehirlioglu, Alp

    2014-01-01

    In recent years there has been a renewed interest for high temperature piezoelectrics for both terrestrial and aerospace applications. These applications are limited in part by the operating temperature, which is usually taken as one half of the Curie temperature (Tc), and is 200C for one of the most widely used commercial piezoelectrics, Pb(Zr,Ti)O3 (PZT). In an effort to increase Tc, subsequent research into high temperature Bi(BB)O3 PbTiO3 piezoelectrics led to the discovery of the morphotropic phase boundary (MPB) in the high-Tc BiScO3 PbTiO3 (BS-PT) system with a Tc of 460C and a d33 of 460 pmV. The Tc marks the ferroelectric to paraelectric phase transformation and while, in general, a phase transformation leads to thermal depoling in piezoelectrics with low or moderate Tcs, for high Tc piezoelectrics thermally assisted dipole rotation can lead to randomization of domains at temperatures below Tc. It becomes necessary to determine the depoling temperature (Td) which dictates the actual working temperature range. By doping for Sc and Ti the Td can be shifted while maintaining similar electromechanical properties as a function of temperature. The effect of this B-site doping on depoling temperature has been explored through the characterization of microstructure and weakhigh field measurements.

  20. Current understanding of structure-processing-property relationships in BaTiO3-Bi(M)O3 dielectrics

    DOE PAGES

    Beuerlein, Michaela A.; Kumar, Nitish; Usher, Tedi -Marie; ...

    2016-09-01

    Here, as part of a continued push for high permittivity dielectrics suitable for use at elevated operating temperatures and/or large electric fields, modifications of BaTiO3 with Bi(M)O3, where M represents a net-trivalent B-site occupied by one or more species, have received a great deal of recent attention. Materials in this composition family exhibit weakly coupled relaxor behavior that is not only remarkably stable at high temperatures and under large electric fields, but is also quite similar across various identities of M. Moderate levels of Bi content (as much as 50 mol%) appear to be crucial to the stability of themore » dielectric response. In addition, the presence of significant Bi reduces the processing temperatures required for densification and increases the required oxygen content in processing atmospheres relative to traditional X7R-type BaTiO3-based dielectrics. Although detailed understanding of the structure–processing–property relationships in this class of materials is still in its infancy, this article reviews the current state of understanding of the mechanisms underlying the high and stable values of both relative permittivity and resistivity that are characteristic of BaTiO3-Bi(M)O3 dielectrics as well as the processing challenges and opportunities associated with these materials.« less

  1. Stabilisation of Fe2O3-rich Perovskite Nanophase in Epitaxial Rare-earth Doped BiFeO3 Films

    PubMed Central

    Zhang, Huairuo; Reaney, Ian M.; Marincel, Daniel M.; Trolier-McKinstry, Susan; Ramasse, Quentin M.; MacLaren, Ian; Findlay, Scott D.; Fraleigh, Robert D.; Ross, Ian M.; Hu, Shunbo; Ren, Wei; Mark Rainforth, W.

    2015-01-01

    Researchers have demonstrated that BiFeO3 exhibits ferroelectric hysteresis but none have shown a strong ferromagnetic response in either bulk or thin film without significant structural or compositional modification. When remanent magnetisations are observed in BiFeO3 based thin films, iron oxide second phases are often detected. Using aberration-corrected scanning transmission electron microscopy, atomic resolution electron energy loss spectrum-mapping and quantitative energy dispersive X-ray spectroscopy analysis, we reveal the existence of a new Fe2O3-rich perovskite nanophase, with an approximate formula (Fe0.6Bi0.25Nd0.15)3+ Fe3+O3, formed within epitaxial Ti and Nd doped BiFeO3 perovskite films grown by pulsed laser deposition. The incorporation of Nd and Bi ions on the A-site and coherent growth with the matrix stabilise the Fe2O3-rich perovskite phase and preliminary density functional theory calculations suggest that it should have a ferrimagnetic response. Perovskite-structured Fe2O3 has been reported previously but never conclusively proven when fabricated at high-pressure high-temperature. This work suggests the incorporation of large A-site species may help stabilise perovskite-structured Fe2O3. This finding is therefore significant not only to the thin film but also to the high-pressure community. PMID:26272264

  2. First principles study of Ca in BaTiO3 and Bi0.5Na0.5TiO3

    NASA Astrophysics Data System (ADS)

    Fongkaew, Ittipon; T-Thienprasert, Jiraroj; Limpijumnong, Sukit

    2015-11-01

    BaTiO3-Bi0.5Na0.5TiO3 is one of the promising candidates as a high-temperature relaxor with a high Curie temperature and several preferred dielectric characteristics. It has been found experimentally for a long time that adding calcium to BaTiO3-Bi0.5Na0.5TiO3 improves its temperature characteristic of the capacitance [J. Electron. Mater. 39, 2471]. In this study, Calcium (Ca) defects in perovskite BaTiO3 and Bi0.5Na0.5TiO3 have been studied based on first-principles calculations. In both BaTiO3 and Bi0.5Na0.5TiO3, our calculations showed that Ca atom energetically prefers to substitute for the cations, that is Ba, Bi, Na and Ti, depending on the growth conditions. In most cases, Ca predominantly substitutes on the A-site without providing additional electrical carriers (serve as either neutral defects or self-compensating defects). The growth conditions where Ca can be forced to substitute for B-site (with limited amount) and the conditions where Ca can be forced to serve as an acceptor are identified. Details of the local structures, formation energies and electronic properties of these Ca defects are reported.

  3. Control of orbital reconstruction in (LaAlO3)M/(SrTiO3)N(001) quantum wells by strain and confinement

    NASA Astrophysics Data System (ADS)

    Doennig, David; Pentcheva, Rossitza

    2015-01-01

    The diverse functionality emerging at oxide interfaces calls for a fundamental understanding of the mechanisms and control parameters of electronic reconstructions. Here, we explore the evolution of electronic phases in (LaAlO3)M/(SrTiO3)N (001) superlattices as a function of strain and confinement of the SrTiO3 quantum well. Density functional theory calculations including a Hubbard U term reveal a charge ordered Ti3+ and Ti4+ state for N = 2 with an unanticipated orbital reconstruction, displaying alternating dxz and dyz character at the Ti3+ sites, unlike the previously reported dxy state, obtained only for reduced c-parameter at aSTO. At aLAO c-compression leads to a Dimer-Mott insulator with alternating dxz, dyz sites and an almost zero band gap. Beyond a critical thickness of N = 3 (aSTO) and N = 4 (aLAO) an insulator-to-metal transition takes place, where the extra e/2 electron at the interface is redistributed throughout the STO slab with a dxy interface orbital occupation and a mixed dxz + dyz occupation in the inner layers. Chemical variation of the SrTiO3 counterpart (LaAlO3 vs. NdGaO3) proves that the significant octahedral tilts and distortions in the SrTiO3 quantum well are induced primarily by the electrostatic doping at the polar interface and not by variation of the SrTiO3 counterpart.

  4. Stabilisation of Fe2O3-rich Perovskite Nanophase in Epitaxial Rare-earth Doped BiFeO3 Films.

    PubMed

    Zhang, Huairuo; Reaney, Ian M; Marincel, Daniel M; Trolier-McKinstry, Susan; Ramasse, Quentin M; MacLaren, Ian; Findlay, Scott D; Fraleigh, Robert D; Ross, Ian M; Hu, Shunbo; Ren, Wei; Rainforth, W Mark

    2015-08-14

    Researchers have demonstrated that BiFeO3 exhibits ferroelectric hysteresis but none have shown a strong ferromagnetic response in either bulk or thin film without significant structural or compositional modification. When remanent magnetisations are observed in BiFeO3 based thin films, iron oxide second phases are often detected. Using aberration-corrected scanning transmission electron microscopy, atomic resolution electron energy loss spectrum-mapping and quantitative energy dispersive X-ray spectroscopy analysis, we reveal the existence of a new Fe2O3-rich perovskite nanophase, with an approximate formula (Fe0.6Bi0.25Nd0.15)(3+) Fe(3+)O3, formed within epitaxial Ti and Nd doped BiFeO3 perovskite films grown by pulsed laser deposition. The incorporation of Nd and Bi ions on the A-site and coherent growth with the matrix stabilise the Fe2O3-rich perovskite phase and preliminary density functional theory calculations suggest that it should have a ferrimagnetic response. Perovskite-structured Fe2O3 has been reported previously but never conclusively proven when fabricated at high-pressure high-temperature. This work suggests the incorporation of large A-site species may help stabilise perovskite-structured Fe2O3. This finding is therefore significant not only to the thin film but also to the high-pressure community.

  5. O3 flux-related responsiveness of photosynthesis, respiration, and stomatal conductance of adult Fagus sylvatica to experimentally enhanced free-air O3 exposure.

    PubMed

    Löw, M; Häberle, K-H; Warren, C R; Matyssek, R

    2007-03-01

    Knowledge of responses of photosynthesis, respiration, and stomatal conductance to cumulative ozone uptake (COU) is still scarce, and this is particularly the case for adult trees. The effect of ozone (O(3)) exposure on trees was examined with 60-year-old beech trees (FAGUS SYLVATICA) at a forest site of southern Germany. Trees were exposed to the ambient O(3) regime (1 x O(3)) or an experimentally elevated twice-ambient O(3) regime (2 x O(3)). The elevated 2 x O (3) regime was provided by means of a free-air O(3) canopy exposure system. The hypotheses were tested that (1) gas exchange is negatively affected by O(3) and (2) the effects of O(3) are dose-dependent and thus the sizes of differences between treatments are positively related to COU. Gas exchange (light-saturated CO(2) uptake rate A(max), stomatal conductance g (s), maximum rate of carboxylation Vc (max), ribulose-1,5-bisphosphate turnover limited rate of photosynthesis J (max), CO(2) compensation point CP, apparent quantum yield of net CO(2) uptake AQ, carboxylation efficiency CE, day- and nighttime respiration) and chlorophyll fluorescence (electron transfer rate, ETR) were measured IN SITU on attached sun and shade leaves. Measurements were made periodically throughout the growing seasons of 2003 (an exceptionally dry year) and 2004 (a year with average rainfall). In 2004 Vc(max), J(max), and CE were lower in trees receiving 2 x O(3) compared with the ambient O(3) regime (1 x O(3)). Treatment differences in Vc (max), J (max), CE were rather small in 2004 (i.e., parameter levels were lower by 10 - 30 % in 2 x O(3) than 1 x O(3)) and not significant in 2003. In 2004 COU was positively correlated with the difference between treatments in A (max), g (s), and ETR (i.e., consistent with the dose-dependence of O(3)'s deleterious effects). However, in 2003, differences in A(max), g (s), and ETR between the two O(3) regimes were smaller at the end of the dry summer 2003 (i.e., when COU was greatest). The

  6. Lattice dynamics of cubic PbTiO3

    NASA Astrophysics Data System (ADS)

    Tomeno, Izumi; Fernandez-Baca, Jaime A.; Marty, Karol J.; Tsunoda, Yorihiko; Oka, Kunihiko

    2012-02-01

    The lattice dynamics of cubic PbTiO3 has been investigated using inelastic neutron scattering. We found four kinds of soft modes in cubic PbTiO3: (1) the TO modes toward the γ point, (2) the TA λ3 mode toward the R point, (3) the TA λ3 mode around the midpoint (1/4,1/4,1/4), and (4) the TA branches in the entire range. Moreover, the TO σ4 branch becomes flat away from the zone center. The steep dispersion of the TO modes toward γ is isotropic and confined to the region ξ<0.2. The temperature dependence of the γ15 mode up to 1173 K is explained by a combination of the Lydanne-Sachs-Taller relation and the Curie-Weiss law. In contrast, the TA λ3 modes at the midpoint and R point are weakly temperature dependent. The coexistence of the soft γ15 and R25 modes is in agreement with the predicted phonon instability. The midpoint softening suggests the tendency toward forming a fourfold periodicity along the [1,1,1] direction. The energy of the TO δ5 branch for cubic PbTiO3 is considerably higher than that for Pb(Zn1/3Nb2/3)O3. This indicates that the TO modes are dominated by the B-site atom motion.

  7. Plasma etching behavior of Y2O3 ceramics: Comparative study with Al2O3

    NASA Astrophysics Data System (ADS)

    Cao, Yu-Chao; Zhao, Lei; Luo, Jin; Wang, Ke; Zhang, Bo-Ping; Yokota, Hiroki; Ito, Yoshiyasu; Li, Jing-Feng

    2016-03-01

    The plasma etching behavior of Y2O3 coating was investigated and compared with that of Al2O3 coating under various conditions, including chemical etching, mixing etching and physical etching. The etching rate of Al2O3 coating declined with decreasing CF4 content under mixing etching, while that of Y2O3 coating first increased and then decreased. In addition, the Y2O3 coating demonstrated higher erosion-resistance than Al2O3 coating after exposing to fluorocarbon plasma. X-ray photoelectron spectroscopy (XPS) analysis confirmed the formations of YF3 and AlF3 on the Y2O3 and Al2O3 coatings, respectively, which acted as the protective layer to prevent the surface from further erosion with fluorocarbon plasma. It was revealed that the etching behavior of Y2O3 depended not only on the surface fluorination but also on the removal of fluoride layer. To analyze the effect of porosity, Y2O3 bulk samples with high density were prepared by spark plasma sintering, and they demonstrated higher erosion-resistances compared with Y2O3 coating.

  8. Comparison of the structural and magnetic properties of ground-state SrTcO 3 and CaTcO 3 from first principles

    NASA Astrophysics Data System (ADS)

    Ma, Chun-Lan; Zhou, Tong

    2012-01-01

    The generalized gradient approximation (GGA) plus on-site Coulomb interaction corrections (GGA+ U) method is employed for the total energies and electronic structure calculations of SrTcO 3 and CaTcO 3. G-type antiferromagnetic (G-AFM) is found to be ground state for both compounds, in consistence with the previous experimental results. The mechanism of Neel temperature of SrTcO 3 being higher than that of CaTcO 3 is explored. The insulating band gaps of SrTcO 3 and CaTcO 3 are found to be 1.71 eV and 1.74 eV, respectively. The magnetic moment of Tc1 is found to be 2.237μB in SrTcO 3 unit cell and 2.266μB in CaTcO 3 unit cell. Structural parameters and electronic structure of the two compounds are examined to explore the origin of their different electrical and magnetic characters.

  9. Thermodynamics of mixing in MgSiO 3-Al 2O 3 perovskite and ilmenite from ab initio calculations

    NASA Astrophysics Data System (ADS)

    Jung, D. Y.; Vinograd, V. L.; Fabrichnaya, O. B.; Oganov, A. R.; Schmidt, M. W.; Winkler, B.

    2010-07-01

    The thermodynamic mixing functions of MgSiO 3-Al 2O 3 solid solutions in perovskite and ilmenite structures were modeled based on the results of ab initio calculations applied to a set of supercell structures containing 64 and 48 exchangeable sites, respectively. The sampled structures were constructed from the supercells of the end-members MgSiO 3 perovskite and Al 2O 3 corundum by inserting double AlAl and MgSi defects, respectively, at all possible distances. From these calculations the pairwise effective interactions were derived and used to calculate enthalpy differences between successive configurations produced in Monte Carlo simulation runs. The temperature dependent enthalpies of mixing of the solid solutions were evaluated as averages over the Monte Carlo runs while the free energies of mixing were calculated with the method of thermodynamic integration. The phase equilibria of perovskite, ilmenite and garnet in the Mg-Si-Al-O system were calculated using the computed models of mixing and the standard thermodynamic properties of the end-members from the data base of Fabrichnaya (1999). The obtained activity-composition models are in good agreement with available experimental constraints, thereby showing that the thermodynamic effects of mixing in silicate solid solutions with coupled substitutions can be reliably predicted based on ab initio calculated total energies of a small set of supercell structures.

  10. Formation enthalpies of LaLn'O3 (Ln'=Ho, Er, Tm and Yb) interlanthanide perovskites

    NASA Astrophysics Data System (ADS)

    Qi, Jianqi; Guo, Xiaofeng; Mielewczyk-Gryn, Aleksandra; Navrotsky, Alexandra

    2015-07-01

    High-temperature oxide melt solution calorimetry using 3Na2O·MoO3 at 802 °C was performed for interlanthanide perovskites LaLn'O3 (Ln'=Ho, Er, Tm and Yb) and lanthanide oxides (La2O3, Ho2O3, Er2O3, Tm2O3 and Yb2O3). The enthalpies of formation of these interlanthanide perovskites from binary lanthanide oxides at room temperature (25 °C) were determined to be -8.3±3.4 kJ/mol for LaHoO3, -9.9±3.0 kJ/mol for LaErO3, -10.8±2.7 kJ/mol for LaTmO3 and -12.3±2.9 kJ/mol for LaYbO3. There is a roughly linear relationships between these enthalpy values and the tolerance factor for these and for other LaM3+O3 (M=In, Sc, Ga, Al, Fe and Cr) perovskites, confirming that the distortion of the perovskites as results from ionic radius difference of A-site and B-site cations, is the main factor determining the stability of these compounds.

  11. Structural Changes of Y2O3 and La2O3 Films by Heat Treatment

    NASA Astrophysics Data System (ADS)

    Yamamoto, Takashi; Izumi, Yukiko; Hashimoto, Hideki; Oosawa, Masanori; Sugita, Yoshihiro

    2006-08-01

    Structural changes of Y2O3 films and La2O3 films deposited on some oxidized silicon substrates were studied using X-ray photoelectron spectroscopy (XPS), Secondary ion mass spectrometry (SIMS), and Fourier transform infrared spectroscopy attenuated total reflection method (FT-IR ATR). Y2O3 and La2O3 films on chemical oxide and NH3 annealed oxy-nitride were prepared by the Low-pressure chemical vapor deposition (LPCVD) method using an lanthanide-dipivaloyl-methanate (Ln-DPM) complex. The Y2O3 film and the La2O3 film on the both kinds of substrate already contained a partly silicate structure at the interface side as a result of an interface reaction during the deposition process. During post deposition annealing, the whole film structure of the Y2O3 and the La2O3 on the chemical oxide changed to a silicate structure due to silicon diffusion with interface reaction. In the case of the Y2O3 film, this interface reaction can be suppressed using thermal oxy-nitride as the interfacial layer. In the case of the La2O3 film, the suppression effect using oxy-nitride was smaller than the case with the Y2O3 film. Also, it was found that there was a strong correlation between the structural change of the films and the change of flat-band-voltage of both Y2O3 and La2O3 MIS diodes during post-deposition-annealing.

  12. Photoresponse dynamics in amorphous-LaAlO3/SrTiO3 interfaces

    PubMed Central

    Di Gennaro, Emiliano; Coscia, Ubaldo; Ambrosone, Giuseppina; Khare, Amit; Granozio, Fabio Miletto; di Uccio, Umberto Scotti

    2015-01-01

    The time-resolved photoconductance of amorphous and crystalline LaAlO3/SrTiO3 interfaces, both hosting an interfacial 2-dimensional electron gas, is investigated under irradiation by variable-wavelengths, visible or ultraviolet photons. Unlike bare SrTiO3 single crystals, showing relatively small photoconductance effects, both kinds of interfaces exhibit an intense and highly persistent photoconductance with extraordinarily long characteristic times. The temporal behaviour of the extra photoinduced conductance persisting after light irradiation shows a complex dependence on interface type (whether amorphous or crystalline), sample history and irradiation wavelength. The experimental results indicate that different mechanisms of photoexcitation are responsible for the photoconductance of crystalline and amorphous LaAlO3/SrTiO3 interfaces under visible light. We propose that the response of crystalline samples is mainly due to the promotion of electrons from the valence bands of both SrTiO3 and LaAlO3. This second channel is less relevant in amorphous LaAlO3/SrTiO3, where the higher density of point defects plays instead a major role. PMID:25670163

  13. Transparent Conducting Properties of SrSnO3 and ZnSnO3

    DOE PAGES

    Ong, Khuong P.; Fan, Xiaofeng; Subedi, Alaska; ...

    2015-04-29

    We report optical properties of doped n-type SrSnO3 and ZnSnO3 in relation to potential application as transparent conductors. We find that the orthorhombic distortion of the perovskite structure in SrSnO3 leads to absorption in the visible as the doping level is increased. This arises from interband transitions. We find that strain tuning could modify this absorption, but does not eliminate it. On the other hand, we find that ZnSnO3 although also having a non-cubic structure, can retain excellent transparency when doped, making it a good candidate transparent conductor.

  14. LiNbO3 Cylinder Fiber

    NASA Technical Reports Server (NTRS)

    Kornreich, Philip

    2004-01-01

    We have successfully fabricate optical fiber with a thin layer of LiNbO3 at the boundary of the glass core and clear glass cladding. The construction of this fiber is based on our successful Semiconductor Cylinder Fibers (SCF). A schematic representation of a LiN bo, Cylinder Fiber. These fibers can be used as light modulators, sonar detectors and in other applications. The core diameter of the fiber is sufficiently small compared to the light wavelength and the indices of refraction of the core and cladding glasses are sufficiently close in value so that there is sufficient light at the core cladding boundary to interact with the LiNbO3 layer. This fiber functions best when just a single light mode propagates through the fiber. The idea for a LiNbO3 Cylinder Fiber came from Dr. Tracee Jamison of NASA. The optical properties of LiNbO3 can be changed with strain or the application of an electric field. Thus these fibers can be used as acoustic sensors as for example in a sonar. They can also be used as electric field operated light modulators. However, for this application the fibers would be made with a cross section in the form of a "D". The core with its surrounding LiNbO, layer would be close to the flat portion of the "D" shaped fiber. Two metal contacts would be deposited on the flat portion of the fiber on either side of the core. A voltage applied across these contacts will result in an electric field in the core region that can be used for modulating the optical properties of the LiNbO3 layer. To our knowledge this is the first ever LiNbO3 Cylinder Fiber made.

  15. Vought O3U-1 Corsair

    NASA Technical Reports Server (NTRS)

    1931-01-01

    Vought O3U-1 Corsair: This aircraft, the Vought O3U-1 Corsair, was the first aircraft tested in the Full Scale Tunnel. It is shown here during preliminary tests in the FST before the balance was enclosed. NACA engineers checked the lift and drag characteristics of several aircraft with the results of earlier flight tests. Smith DeFrance concluded NACA TR No. 459, 'The agreement that has been obtained between the flight and full-scale tunnel results, together with the consistent manner in which measurements can be repeated when check tests are made, has demonstrated the accuracy and value of the equipment for aeronautical research.' (p. 298)

  16. Synthesis of Paramelaconite: Cu 4O 3

    NASA Astrophysics Data System (ADS)

    Morgan, P. E. D.; Partin, D. E.; Chamberland, B. L.; O'Keeffe, M.

    1996-01-01

    Evidence for the natural occurrence and synthetic preparation of copper oxides other than CuO and Cu2O is reviewed. The unequivocal synthesis of Cu4O3(paramelaconite) is reported for the first time. It is achieved by extraction of copper or its oxides with concentrated aqueous ammonia in a Soxhlet apparatus. Quantitative X-ray diffraction analysis of one preparation showed that it consisted of 35% Cu4O3, 27% Cu2O, and 38% CuO for a gross composition CuO0.77.

  17. Frustration of Negative Capacitance in Al2O3/BaTiO3 Bilayer Structure

    NASA Astrophysics Data System (ADS)

    Kim, Yu Jin; Park, Min Hyuk; Lee, Young Hwan; Kim, Han Joon; Jeon, Woojin; Moon, Taehwan; Do Kim, Keum; Jeong, Doo Seok; Yamada, Hiroyuki; Hwang, Cheol Seong

    2016-01-01

    Enhancement of capacitance by negative capacitance (NC) effect in a dielectric/ferroelectric (DE/FE) stacked film is gaining a greater interest. While the previous theory on NC effect was based on the Landau-Ginzburg-Devonshire theory, this work adopted a modified formalism to incorporate the depolarization effect to describe the energy of the general DE/FE system. The model predicted that the SrTiO3/BaTiO3 system will show a capacitance boost effect. It was also predicted that the 5 nm-thick Al2O3/150 nm-thick BaTiO3 system shows the capacitance boost effect with no FE-like hysteresis behavior, which was inconsistent with the experimental results; the amorphous-Al2O3/epitaxial-BaTiO3 system showed a typical FE-like hysteresis loop in the polarization – voltage test. This was due to the involvement of the trapped charges at the DE/FE interface, originating from the very high field across the thin Al2O3 layer when the BaTiO3 layer played a role as the NC layer. Therefore, the NC effect in the Al2O3/BaTiO3 system was frustrated by the involvement of reversible interface charge; the highly stored charge by the NC effect of the BaTiO3 during the charging period could not be retrieved during the discharging process because integral part of the polarization charge was retained within the system as a remanent polarization.

  18. Frustration of Negative Capacitance in Al2O3/BaTiO3 Bilayer Structure.

    PubMed

    Kim, Yu Jin; Park, Min Hyuk; Lee, Young Hwan; Kim, Han Joon; Jeon, Woojin; Moon, Taehwan; Kim, Keum Do; Jeong, Doo Seok; Yamada, Hiroyuki; Hwang, Cheol Seong

    2016-01-08

    Enhancement of capacitance by negative capacitance (NC) effect in a dielectric/ferroelectric (DE/FE) stacked film is gaining a greater interest. While the previous theory on NC effect was based on the Landau-Ginzburg-Devonshire theory, this work adopted a modified formalism to incorporate the depolarization effect to describe the energy of the general DE/FE system. The model predicted that the SrTiO3/BaTiO3 system will show a capacitance boost effect. It was also predicted that the 5 nm-thick Al2O3/150 nm-thick BaTiO3 system shows the capacitance boost effect with no FE-like hysteresis behavior, which was inconsistent with the experimental results; the amorphous-Al2O3/epitaxial-BaTiO3 system showed a typical FE-like hysteresis loop in the polarization - voltage test. This was due to the involvement of the trapped charges at the DE/FE interface, originating from the very high field across the thin Al2O3 layer when the BaTiO3 layer played a role as the NC layer. Therefore, the NC effect in the Al2O3/BaTiO3 system was frustrated by the involvement of reversible interface charge; the highly stored charge by the NC effect of the BaTiO3 during the charging period could not be retrieved during the discharging process because integral part of the polarization charge was retained within the system as a remanent polarization.

  19. Understanding the Interactions of CO2 with Doped and Undoped SrTiO3.

    PubMed

    Wu, Qiyuan; Cen, Jiajie; Goodman, Kenneth R; White, Michael G; Ramakrishnan, Girish; Orlov, Alexander

    2016-07-21

    SrTiO3 and doped SrTiO3 have a wide range of applications in different fields. For example, Rh-doped SrTiO3 has been shown to have photocatalytic activity for both hydrogen production and CO2 conversion. In this study, both undoped and Rh-doped SrTiO3 were synthesized by hydrothermal and polymerizable complex methods. Different characterizations techniques including X-ray photoelectron spectroscopy (XPS), XRD, Raman, and UV/Vis spectroscopy were utilized to establish correlations between the preparation methods and the electronic/structural properties of Rh-doped SrTiO3 . The presence of dopants and oxygen vacancies substantially influenced the CO2 interactions with the surface, as revealed by the in situ infrared spectroscopic study. The presence of distinctly different adsorption sites was correlated to oxygen vacancies and oxidation states of Ti and Rh.

  20. (Pb,Cd)-O covalency in PbTiO3-CdTiO3 with enhanced negative thermal expansion.

    PubMed

    Wang, Fangfang; Xie, Ying; Chen, Jun; Fu, Honggang; Xing, Xianran

    2014-03-21

    Recently experiments have found that negative thermal expansion is a common phenomenon in PbTiO3-based materials, and their negative thermal expansion is affected by various substitutions. Interestingly, Cd substitution in PbTiO3 has a unique effect in enhancing negative thermal expansion compared with any other A-site substitutions. Therefore, studying Cd substitution in PbTiO3, the role of which still remains unclear, would bring us deeper understanding on the nature of the negative thermal expansion of PbTiO3-based materials. Structure calculations, density of states, Bader analysis and the minimum electron density of Pb1-xCdxTiO3 supercells have been reported on the chemical bond through first-principles calculations here. We found that the hybridization between (Pb,Cd)-O orbitals exists in tetragonal phase. Furthermore, the hybridization between Cd-O orbitals is stronger than that between Pb-O orbitals, and Cd-O covalency promotes the average A-site hybridization. Simultaneously, the average bulk coefficient of thermal expansion is negative and inversely proportional to the Cd substitution amount. So, (Pb,Cd)-O covalency in the tetragonal Pb1-xCdxTiO3 is responsible for the nature of enhanced negative thermal expansion in accordance with our previous experimental investigations.

  1. Electrical characteristics of SrTiO3/Al2O3 laminated film capacitors

    NASA Astrophysics Data System (ADS)

    Peng, Yong; Yao, Manwen; Chen, Jianwen; Xu, Kaien; Yao, Xi

    2016-07-01

    The electrical characteristics of SrTiO3/Al2O3 (160 nm up/90 nm down) laminated film capacitors using the sol-gel process have been investigated. SrTiO3 is a promising and extensively studied high-K dielectric material, but its leakage current property is poor. SrTiO3/Al2O3 laminated films can effectively suppress the demerits of pure SrTiO3 films under low electric field, but the leakage current value reaches to 0.1 A/cm2 at higher electric field (>160 MV/m). In this study, a new approach was applied to reduce the leakage current and improve the dielectric strength of SrTiO3/Al2O3 laminated films. Compared to laminated films with Au top electrodes, dielectric strength of laminated films with Al top electrodes improves from 205 MV/m to 322 MV/m, simultaneously the leakage current maintains the same order of magnitude (10-4 A/cm2) until the breakdown occurs. The above electrical characteristics are attributed to the anodic oxidation reaction in origin, which can repair the defects of laminated films at higher electric field. The anodic oxidation reactions have been confirmed by the corresponding XPS measurement and the cross sectional HRTEM analysis. This work provides a new approach to fabricate dielectrics with high dielectric strength and low leakage current.

  2. Ferromagnetism in chemically reduced LiNbO3 and LiTaO3 crystals

    NASA Astrophysics Data System (ADS)

    Yan, Tao; Ye, Ning; Xu, Liuwei; Sang, Yuanhua; Chen, Yanxue; Song, Wei; Long, Xifa; Wang, Jiyang; Liu, Hong

    2016-05-01

    The ferromagnetism of bulk LiNbO3 and LiTaO3 at room temperature was investigated for the first time in the present work. The stoichiometric LiNbO3 is non-magnetic, while congruent LiNbO3 and LiTaO3 show very weak ferromagnetism. After chemical reduction in a mixture of zinc and lithium carbonate powders under flowing nitrogen, the ferromagnetic behavior of each sample became clear, with an increased value of magnetization. The saturation magnetization, the magnetic remanence and the coercive field of reduced congruent LiNbO3 are 7.0  ×  10-3 emu g-1, 0.65  ×  10-3 emu g-1 and 0.050 kOe, respectively. The ferromagnetism of chemically reduced LiNbO3 and LiTaO3 can be explained by considering the intrinsic Li vacancies, the appearance of Nb4+ (or Ta4+) on the surface with non-zero net spin and the oxygen vacancies at the surface.

  3. Phase transition and chemical order in the ferroelectric perovskite (1-x)Bi(Mg3/4W1/4)O3-xPbTiO3 solid solution system

    NASA Astrophysics Data System (ADS)

    Stringer, C. J.; Eitel, R. E.; Shrout, T. R.; Randall, C. A.; Reaney, I. M.

    2005-01-01

    Building on the ferroelectric family based on the Bi(Me+3)O3-PbTiO3 solid solutions, the complex solid solution (1-x )Bi(Mg3/4W1/4)O3-xPbTiO3 [(1-x)BMW-xPT] was investigated. This system was found to exhibit a broad morphotropic phase boundary at x ˜0.48mol% PbTiO3 with a corresponding Curie temperature of 205°C separating pseudocubic and tetragonal ferroelectric phases. Based on dielectric, x-ray diffraction (XRD), and calorimetric data, a simple dielectric phase field diagram was established. On further structural analysis with diffraction contrast transmission electron microscopy along with XRD, evidence of B-site chemical ordering was found for the (1-x )Bi(Me'Me″)O3-xPbTiO3 perovskite family.

  4. Thermodynamic Assessment of the Y2o3-yb2o3-zro2 System

    NASA Technical Reports Server (NTRS)

    Jacobson, Nathan S.; Liu, Zi-Kui; Kaufman, Larry; Zhang, Fan

    2002-01-01

    Yttria-zirconia (Y2O3-ZrO2) is the most widely used of the rare earth oxide-zirconia systems. There are numerous experimental studies of the phase boundaries in this system. In this paper, we assess these data and derive parameters for the solution models in this system. There is current interest in other rare earth oxide-zirconia systems as well as systems with several rare earth oxides and zirconia, which may offer improved properties over the Y2O3-ZrO2 system. For this reason, we also assess the ytterbia-zirconia (Yb2O3-ZrO2) and Y2O3-Yb2O3-ZrO2 system.

  5. Control of orbital reconstruction in (LaAlO3)M/(SrTiO3)N(001) quantum wells by strain and confinement

    PubMed Central

    Doennig, David; Pentcheva, Rossitza

    2015-01-01

    The diverse functionality emerging at oxide interfaces calls for a fundamental understanding of the mechanisms and control parameters of electronic reconstructions. Here, we explore the evolution of electronic phases in (LaAlO3)M/(SrTiO3)N (001) superlattices as a function of strain and confinement of the SrTiO3 quantum well. Density functional theory calculations including a Hubbard U term reveal a charge ordered Ti3+ and Ti4+ state for N = 2 with an unanticipated orbital reconstruction, displaying alternating dxz and dyz character at the Ti3+ sites, unlike the previously reported dxy state, obtained only for reduced c-parameter at aSTO. At aLAO c-compression leads to a Dimer-Mott insulator with alternating dxz, dyz sites and an almost zero band gap. Beyond a critical thickness of N = 3 (aSTO) and N = 4 (aLAO) an insulator-to-metal transition takes place, where the extra e/2 electron at the interface is redistributed throughout the STO slab with a dxy interface orbital occupation and a mixed dxz + dyz occupation in the inner layers. Chemical variation of the SrTiO3 counterpart (LaAlO3 vs. NdGaO3) proves that the significant octahedral tilts and distortions in the SrTiO3 quantum well are induced primarily by the electrostatic doping at the polar interface and not by variation of the SrTiO3 counterpart. PMID:25601648

  6. Fe2O3/Co3O4 composite nanoparticle ethanol sensor

    NASA Astrophysics Data System (ADS)

    Mirzaei, Ali; Park, Sunghoon; Sun, Gun-Joo; Kheel, Hyejoon; Lee, Chongmu; Lee, Sangmin

    2016-08-01

    In this study Fe2O3/Co3O4 nanocomposites were synthesized by using a simple hydrothermal route. The X-ray diffraction analysis results showed that the synthesized powders were pure and nanocrystalline in nature. Moreover, scanning electron microscopy revealed that Fe2O3 nanoparticles had spherical shapes while Co3O4 particles had a rod-like morphology. The ethanol sensing properties of Fe2O3/Co3O4 nanocomposites were examined and compared with those of pristine Fe2O3 nanoparticles. The gas sensing properties of Fe2O3/Co3O4 nanocomposites were shown to be superior to those of pristine Fe2O3 nanoparticles and for all concentrations of ethanol, the response of the nanocomposite sensor was shown to be higher than that of the pristine Fe2O3 nanoparticle sensor. In detail, the response of the Fe2O3/Co3O4 nanocomposite sensor to 200 ppm of ethanol at 300 °C was about 3 times higher than that of pristine sensor. Also, in general, the response and recovery times of the Fe2O3/Co3O4 nanocomposite sensor were shorter than those of the pristine one. The improved sensing characteristics of the Fe2O3/Co3O4 sensor were attributed to a combination of several effects: the formation of a potential barrier at the Fe2O3-Co3O4 interface, the enhanced modulation of the conduction channel width accompanying the adsorption and desorption of ethanol gas, the catalytic activity of Co3O4 for the oxidation of ethanol, the stronger oxygen adsorption of p-type Co3O4, and the formation of preferential adsorption sites.

  7. Coupled skyrmion sublattices in Cu2OSeO3

    SciTech Connect

    Langner, M.C.; Roy,, S.; Mishra, S. K.; Lee, J. C. T.; Shi,, X. W.; Hossain, M. A.; Chuang, Y.-D.; Seki, S.; Tokura, Y.; Kevan, S. D.; Schoenlein, R. W.

    2014-04-18

    We report the observation of a skyrmion lattice in the chiral multiferroic insulator Cu2OSeO3 using Cu L3-edge resonant soft x-ray diffraction. We observe the unexpected existence of two distinct skyrmion sub-lattices that arise from inequivalent Cu sites with chemically identical coordination numbers but different magnetically active orbitals . The skyrmion sublattices are rotated with respect to each other implying a long wavelength modulation of the lattice. The modulation vector is controlled with an applied magnetic field, associating this Moir'e-like phase with a continuous phase transition. Our findings will open a new class of science involving manipulation of quantum topological states.

  8. LiNbO3 Cylinder Fiber

    NASA Technical Reports Server (NTRS)

    2004-01-01

    We have successfully fabricate optical fiber with a thin layer of LiNbO3 at the boundary of the glass core and dear glass cladding. The construction of this fiber is based on our successful Semiconductor Cylinder Fibers (SCF). A schematic representation of a LiNbO3 Cylinder Fiber is shown. These fibers can be used as light modulators, sonar detectors and in other applications. The core diameter of the fiber is sufficiently small compared to the light wavelength and the indices of refraction of the core and cladding glasses are sufficiently close in value so that there is sufficient light at the core cladding boundary to interact with the LiNbO3 layer. This fiber functions best when just a single light mode propagates through the fiber. The idea for a LiNbO3 Cylinder Fiber came from Dr. Tracee Jamison of NASA. The optical properties of LiNbO3 can be changed with strain or the application of an electric field. Thus these fibers can be used as acoustic sensors as for example in a sonar. They can also be used as electric field operated light modulators. However, for this application the fibers would be made with a cross section in the form of a 'D'. The core with its surrounding LiNbO, layer would be close to the flat portion of the 'D' shaped fiber. Two metal contacts would be deposited on the flat portion of the fiber on either side of the core. A voltage applied across these contacts will result in an electric field in the core region that can be used for modulating the optical properties of the LiNbO, layer. To our knowledge this is the first ever LiNbO, Cylinder Fiber made.

  9. Preparation and Investigation of Electrodeposited Ni-NANO-Cr2O3 Composite Coatings

    NASA Astrophysics Data System (ADS)

    Jiang, Jibo; Feng, Chenqi; Qian, Wei; Yu, Libin; Ye, Fengying; Zhong, Qingdong; Han, Sheng

    2016-12-01

    The electrodeposition of Ni-nano-Cr2O3 composite coatings was studied in electrolyte containing different contents of Cr2O3 nanoparticles (Cr2O3 NPs) on mild steel surfaces. Some techniques such as X-ray diffraction (XRD), scanning electron microscopy (SEM), microhardness, the potentiodynamic polarization curves (Tafel) and electrochemical impedance spectroscopy (EIS) were used to compare pure Ni coatings and Ni-nano-Cr2O3 composite coatings. The results show that the incorporation of Cr2O3 NPs resulted in an increase of hardness and corrosion resistance, and the maximum microhardness of Ni-nano-Cr2O3 composite coatings reaches about 495 HV. The coatings exhibit an active-passive transition and relatively large impedance values. Moreover, the effect of Cr2O3 NPs on Ni electrocrystallization is also investigated by cyclic voltammetry (CV) and EIS spectroscopy, which demonstrates that the nature of Ni-based composite coatings changes attributes to Cr2O3 NPs by offering more nucleation sites and less charge transfer resistance.

  10. Use of passive ambient ozone (O3) samplers in vegetation effects assessment

    USGS Publications Warehouse

    Krupa, S.; Nosal, M.; Peterson, D.L.

    2001-01-01

    A stochastistic, Weibull probability model was developed and verified to simulate the underlying frequency distributions of hourly ozone (O3) concentrations (exposure dynamics) using the single, weekly mean values obtained from a passive (sodium nitrite absorbent) sampler. The simulation was based on the data derived from a co-located continuous monitor. Although at the moment the model output may be considered as being specific to the elevation and location of the study site, the results were extremely good. This effort for the approximation of the O3 exposure dynamics can be extended to other sites with similar data sets and in developing a generalized understanding of the stochastic O3 exposure-plant response relationships, conferring measurable benefits to the future use of passive O3 samplers, in the absence of continuous monitoring. Copyright ?? 2000 Elsevier Science Ltd.

  11. Two-dimensional electron gas in GaAs/SrHfO3 heterostructure

    NASA Astrophysics Data System (ADS)

    Wang, Jianli; Yuan, Mengqi; Tang, Gang; Li, Huichao; Zhang, Junting; Guo, Sandong

    2016-06-01

    The III-V/perovskite-oxide system can potentially create new material properties and new device applications by combining the rich properties of perovskite-oxides together with the superior optical and electronic properties of III-Vs. The structural and electronic properties of the surface and interface are studied using first-principles calculations for the GaAs/SrHfO3 heterostructure. We investigate the specific adsorption sites and the atomic structure at the initial growth stage of GaAs on the SrHfO3 (001) substrate. Ga and As adsorption atoms preferentially adsorb at the top sites of oxygen atoms under different coverage. The energetically favorable interfaces are presented among the atomic arrangements of the GaAs/SrHfO3 interfaces. Our calculations predict the existing of the two-dimensional electron gas in the GaAs/SrHfO3 heterostructure.

  12. Engineered Mott ground state in a LaTiO3+δ/LaNiO3 heterostructure

    PubMed Central

    Cao, Yanwei; Liu, Xiaoran; Kareev, M.; Choudhury, D.; Middey, S.; Meyers, D.; Kim, J.-W.; Ryan, P. J.; Freeland, J.W.; Chakhalian, J.

    2016-01-01

    In pursuit of creating cuprate-like electronic and orbital structures, artificial heterostructures based on LaNiO3 have inspired a wealth of exciting experimental and theoretical results. However, to date there is a very limited experimental understanding of the electronic and orbital states emerging from interfacial charge transfer and their connections to the modified band structure at the interface. Towards this goal, we have synthesized a prototypical superlattice composed of a correlated metal LaNiO3 and a doped Mott insulator LaTiO3+δ, and investigated its electronic structure by resonant X-ray absorption spectroscopy combined with X-ray photoemission spectroscopy, electrical transport and theory calculations. The heterostructure exhibits interfacial charge transfer from Ti to Ni sites, giving rise to an insulating ground state with orbital polarization and eg orbital band splitting. Our findings demonstrate how the control over charge at the interface can be effectively used to create exotic electronic, orbital and spin states. PMID:26791402

  13. Engineered Mott ground state in a LaTiO3+δ/LaNiO3 heterostructure

    DOE PAGES

    Cao, Yanwei; Liu, Xiaoran; Kareev, M.; ...

    2016-01-21

    In pursuit of creating cuprate-like electronic and orbital structures, artificial heterostructures based on LaNiO3 have inspired a wealth of exciting experimental and theoretical results. However, to date there is a very limited experimental understanding of the electronic and orbital states emerging from interfacial charge transfer and their connections to the modified band structure at the interface. Towards this goal, we have synthesized a prototypical superlattice composed of a correlated metal LaNiO3 and a doped Mott insulator LaTiO3+δ, and investigated its electronic structure by resonant X-ray absorption spectroscopy combined with X-ray photoemission spectroscopy, electrical transport and theory calculations. The heterostructure exhibitsmore » interfacial charge transfer from Ti to Ni sites, giving rise to an insulating ground state with orbital polarization and eg orbital band splitting. Here, our findings demonstrate how the control over charge at the interface can be effectively used to create exotic electronic, orbital and spin states.« less

  14. Enhanced oxide ion conductivity in stabilized delta-Bi2O3.

    PubMed

    Punn, Rita; Feteira, Antonio M; Sinclair, Derek C; Greaves, Colin

    2006-12-06

    The substitution of Re into Bi2O3 allows stabilization of the delta-Bi2O3 structure by additional substitution of any lanthanide ion to give, for example, phases of composition Bi12.5La1.5ReO24.5. Some of these phases have been found to show exceptionally high oxide ion conductivity at low temperatures, ca 10-3 S cm-1 at 300 degrees C. The phases show a significant structural difference from other delta-Bi2O3 phases previously reported, with interstitial anion sites displaced further from the ideal fluorite position, (1/4,1/4,1/4).

  15. Visible photocatalytic and photoelectrochemical activities of TiO2 nanobelts modified by In2O3 nanoparticles.

    PubMed

    Yang, Hongru; Tian, Jian; Bo, Yanyan; Zhou, Yanli; Wang, Xinzhen; Cui, Hongzhi

    2017-02-01

    Novel In2O3 nanoparticle/TiO2 nanobelt heterostructures with enhanced visible-light photocatalytic and photoelectrochemical (PEC) performance were successfully prepared via a facile hydrothermal method. Well-dispersed In2O3 nanoparticles with small sizes are uniformly attached on the surface of TiO2 nanobelts to form In2O3 nanoparticle/TiO2 nanobelt heterostructures. The TiO2 nanobelts as backbones restrict the aggregation of In2O3 nanoparticles, resulting in the formation of smaller In2O3 nanoparticles with more interaction sites for pollutants. The visible photocatalytic activity of as-prepared heterostructures for degradation of methyl blue (MB) is higher than those of TiO2 nanobelts and In2O3 nanoparticles alone. Moreover, the In2O3 nanoparticle/TiO2 nanobelt heterostructure shows an enhanced PEC performance under irradiation of visible light. The enhanced photocatalytic and PEC activities are mainly ascribed to the synergic effect of efficient charge separation of heterostructure, visible-light harvesting ability of In2O3, and the formation of preferential adsorption sites by the small size of In2O3 nanoparticles. Finally, based on the experimental results of Mott-Schottky, UV-vis DRS, photocurrent and open-circuit voltage response, a possible photocatalytic mechanism over the In2O3 nanoparticle/TiO2 nanobelt heterostructure is proposed.

  16. Renewable H2 from glycerol steam reforming: effect of La2O3 and CeO2 addition to Pt/Al2O3 catalysts.

    PubMed

    Montini, Tiziano; Singh, Rakesh; Das, Piyali; Lorenzut, Barbara; Bertero, Nicolás; Riello, Pietro; Benedetti, Alvise; Giambastiani, Giuliano; Bianchini, Claudio; Zinoviev, Sergey; Miertus, Stanislav; Fornasiero, Paolo

    2010-05-25

    Glycerol is the main byproduct of biodiesel production and its increased production volume derives from the increasing demand for biofuels. The conversion of glycerol to hydrogen-rich mixtures presents an attractive route towards sustainable biodiesel production. Here we explored the use of Pt/Al(2)O(3)-based catalysts for the catalytic steam reforming of glycerol, evidencing the influence of La(2)O(3) and CeO(2) doping on the catalyst activity and selectivity. The addition of the latter metal oxides to a Pt/Al(2)O(3) catalyst is found to significantly improve the glycerol steam reforming, with high H(2) and CO(2) selectivities. A good catalytic stability is achieved for the Pt/La(2)O(3)/Al(2)O(3) system working at 350 degrees C, while the Pt/CeO(2)/Al(2)O(3) catalyst sharply deactivates after 20 h under similar conditions. Studies carried out on fresh and exhausted catalysts reveal that both systems maintain high surface areas and high Pt dispersions. Therefore, the observed catalyst deactivation can be attributed to coke deposition on the active sites throughout the catalytic process and only marginally to Pt nanoparticle sintering. This work suggests that an appropriate support composition is mandatory for preparing high-performance Pt-based catalysts for the sustainable conversion of glycerol into syngas.

  17. Epitaxial growth and magnetic properties of ultraviolet transparent Ga2O3/(Ga1−xFex)2O3 multilayer thin films

    PubMed Central

    Guo, Daoyou; An, Yuehua; Cui, Wei; Zhi, Yusong; Zhao, Xiaolong; Lei, Ming; Li, Linghong; Li, Peigang; Wu, Zhenping; Tang, Weihua

    2016-01-01

    Multilayer thin films based on the ferromagnetic and ultraviolet transparent semiconductors may be interesting because their magnetic/electronic/photonic properties can be manipulated by the high energy photons. Herein, the Ga2O3/(Ga1−xFex)2O3 multilayer epitaxial thin films were obtained by alternating depositing of wide band gap Ga2O3 layer and Fe ultrathin layer due to inter diffusion between two layers at high temperature using the laser molecular beam epitaxy technique. The multilayer films exhibits a preferred growth orientation of crystal plane, and the crystal lattice expands as Fe replaces Ga site. Fe ions with a mixed valence of Fe2+ and Fe3+ are stratified distributed in the film and exhibit obvious agglomerated areas. The multilayer films only show a sharp absorption edge at about 250 nm, indicating a high transparency for ultraviolet light. What’s more, the Ga2O3/(Ga1−xFex)2O3 multilayer epitaxial thin films also exhibits room temperature ferromagnetism deriving from the Fe doping Ga2O3. PMID:27121446

  18. Epitaxial growth and magnetic properties of ultraviolet transparent Ga2O3/(Ga1-xFex)2O3 multilayer thin films

    NASA Astrophysics Data System (ADS)

    Guo, Daoyou; An, Yuehua; Cui, Wei; Zhi, Yusong; Zhao, Xiaolong; Lei, Ming; Li, Linghong; Li, Peigang; Wu, Zhenping; Tang, Weihua

    2016-04-01

    Multilayer thin films based on the ferromagnetic and ultraviolet transparent semiconductors may be interesting because their magnetic/electronic/photonic properties can be manipulated by the high energy photons. Herein, the Ga2O3/(Ga1-xFex)2O3 multilayer epitaxial thin films were obtained by alternating depositing of wide band gap Ga2O3 layer and Fe ultrathin layer due to inter diffusion between two layers at high temperature using the laser molecular beam epitaxy technique. The multilayer films exhibits a preferred growth orientation of crystal plane, and the crystal lattice expands as Fe replaces Ga site. Fe ions with a mixed valence of Fe2+ and Fe3+ are stratified distributed in the film and exhibit obvious agglomerated areas. The multilayer films only show a sharp absorption edge at about 250 nm, indicating a high transparency for ultraviolet light. What’s more, the Ga2O3/(Ga1-xFex)2O3 multilayer epitaxial thin films also exhibits room temperature ferromagnetism deriving from the Fe doping Ga2O3.

  19. Effect of O3 and O3/H2O2 on algae harvesting using chitosan.

    PubMed

    Pranowo, R; Lee, D J; Liu, J C; Chang, J S

    2013-01-01

    We examined the effects of pre-oxidation using ozone (O3) and a combination of O3 and hydrogen peroxide (O3/H2O2) on algae suspensions and their harvesting. Inactivation of algae cells, release of intracellular organic matter (IOM), mineralization of extracellular organic matter (EOM), and changes in molecular weight distribution of EOM were found after pre-oxidation. Enhanced separation efficiency of turbidity, dissolved organic carbon (DOC), protein, and polysaccharide using chitosan and polyaluminum chloride (PACl) was found after pre-oxidation, especially when algae cells were subject to O3/H2O2. Chitosan showed higher efficiency than PACl. Judging from the remarkable increase in floc size, it was proposed that released IOM formed complexes with cationic chitosan and resulted in enhanced dual flocculation and facilitated algae separation.

  20. Raman scattering efficiency in LiTaO3 and LiNbO3 crystals

    NASA Astrophysics Data System (ADS)

    Sanna, S.; Neufeld, S.; Rüsing, M.; Berth, G.; Zrenner, A.; Schmidt, W. G.

    2015-06-01

    LiTaO3 and LiNbO3 crystals are investigated here in a combined experimental and theoretical study that uses Raman spectroscopy in a complete set of scattering geometries and corresponding density-functional theory calculations to provide microscopic information on their vibrational properties. The Raman scattering efficiency is computed from first principles in order to univocally assign the measured Raman peaks to the calculated eigenvectors. Measured and calculated Raman spectra are shown to be in qualitative agreement and confirm the mode assignment by Margueron et al. [J. Appl. Phys. 111, 104105 (2012), 10.1063/1.4716001], thus finally settling a long debate. While the two crystals show rather similar vibrational properties overall, the E-TO9 mode is markedly different in the two oxides. The deviations are explained by a different anion-cation bond type in LiTaO3 and LiNbO3 crystals.

  1. TES/Aura L2 Ozone (O3) Lite Nadir (TL2O3LN)

    Atmospheric Science Data Center

    2015-08-26

    TES/Aura L2 Ozone (O3) Lite Nadir (TL2O3LN) News:  TES News ... Level:  L2 Instrument:  TES/Aura L2 Ozone Spatial Coverage:  5.3 km nadir Spatial ... OPeNDAP Access:  OPeNDAP Parameters:  Ozone Order Data:  Search and Order:   Earthdata Search ...

  2. Upper limit to magnetism in LaAlO3/SrTiO3 heterostructures

    NASA Astrophysics Data System (ADS)

    Fitzsimmons, Michael

    2012-02-01

    In 2004 Ohtomo and Hwang reported unusually high conductivity in LaAlO3 and SrTiO3 bilayer samples. Since then, metallic conduction, superconductivity, magnetism, and coexistence of superconductivity and ferromagnetism have been attributed to LaAlO3/SrTiO3 interfaces. Very recently, two studies have reported large magnetic moments attributed to interfaces from measurement techniques that are unable to distinguish between interfacial and bulk magnetism. Consequently, it is imperative to perform magnetic measurements that by being intrinsically sensitive to interface magnetism are impervious to experimental artifacts suffered by bulk measurements. Using polarized neutron reflectometry, we measured the neutron spin dependent reflectivity from four LaAlO3/SrTiO3 superlattices. Our results indicate the upper limit for the magnetization averaged over the lateral dimensions of the sample induced by an 11 T magnetic field at 1.7 K is less than 2 G. SQUID magnetometry of the neutron superlattice samples sporadically finds an enhanced moment (consistent with past reports), possibly due to experimental artifacts. These observations set important restrictions on theories which imply a strongly enhanced magnetism at the interface between LaAlO3 and SrTiO3. Work performed in collaboration with N.W. Hengartner, S. Singh, M. Zhernenkov (LANL), F.Y. Bruno, J. Santamaria (Universidad Complutense de Madrid), A. Brinkman, M.J.A. Huijben, H. Molegraaf (MESA+ Institute for Nanotechnology), J. de la Venta and Ivan K. Schuller (UCSD). [4pt] Work supported by the Office of Basic Energy Science, U.S. Department of Energy, BES-DMS and DMR under grant DE FG03-87ER-45332. Work at UCM is supported by Consolider Ingenio CSD2009-00013 (IMAGINE), CAM S2009-MAT 1756 (PHAMA) and work at Twente is supported by the Foundation for Fundamental Research on Matter (FOM).

  3. Interfacial-layers-free Ga2O3(Gd2O3)/Ge MOS Diodes

    NASA Astrophysics Data System (ADS)

    Lee, C. H.; Lin, T. D.; Lee, K. Y.; Huang, M. L.; Tung, L. T.; Hong, M.; Kwo, J.

    2008-03-01

    High κ dielectric Ga2O3(Gd2O3) films were deposited directly on Ge by Molecular-Beam-Epitaxy without the employment of GeON interfacial layer. Excellent electrical properties, such as a high κ value of 14.5, a low leakage current density of only 3x10-9 A/cm^2 at Vfb+1V, and well-behaved CV characteristics, were demonstrated, even being subjected to a 500^oC annealing in N2 ambient for 5 min. An abrupt Ga2O3(Gd2O3)/Ge interface without any interfacial layer was revealed by high-resolution transmission electron microscopy as well as in-situ x-ray photoelectron spectroscopy (XPS). Detailed XPS studies indicate that the oxide/Ge interface consists of mainly Ge-O-Gd bonding, distinctly different from that of native oxide. Furthermore, the 500^oC annealing did not change the chemical bonding, implying a great thermodynamic stability of the hetero-structure. The outstanding electrical and thermodynamic properties qualified Ga2O3(Gd2O3) as a promising dielectric for Ge and proved the GeON interfacial layer to be unnecessary.

  4. Nature of weak magnetism in SrTiO3/LaAlO3 multilayers.

    PubMed

    Salman, Z; Ofer, O; Radovic, M; Hao, H; Ben Shalom, M; Chow, K H; Dagan, Y; Hossain, M D; Levy, C D P; Macfarlane, W A; Morris, G M; Patthey, L; Pearson, M R; Saadaoui, H; Schmitt, T; Wang, D; Kiefl, R F

    2012-12-21

    We report the observation of weak magnetism in superlattices of LaAlO(3)/SrTiO(3) using β-detected nuclear magnetic resonance. The spin lattice relaxation rate of ^{8}Li in superlattices with a spacer layers of 8 and 6 unit cells of LaAlO(3) exhibits a strong peak near ~35 K, whereas no such peak is observed in a superlattice with spacer layer thickness of 3 unit cells. We attribute the observed temperature dependence to slowing down of weakly coupled electronic moments at the LaAlO(3)/SrTiO(3) interface. These results show that the magnetism at the interface depends strongly on the thickness of the spacer layer, and that a minimal thickness of ~4-6 unit cells is required for the appearance of magnetism. A simple model is used to determine that the observed relaxation is due to small fluctuating moments (~0.002μ(B)) in the two samples with a larger LaAlO(3) spacer thickness.

  5. Piezoelectric and Dielectric Properties of Multilayered BaTiO3/(Ba,Ca)TiO3/CaTiO3 Thin Films.

    PubMed

    Zhu, Xiao Na; Gao, Ting Ting; Xu, Xing; Liang, Wei Zheng; Lin, Yuan; Chen, Chonglin; Chen, Xiang Ming

    2016-08-31

    Highly oriented multilayered BaTiO3-(Ba,Ca)TiO3-CaTiO3 thin films were fabricated on Nb-doped (001) SrTiO3 (Nb:STO) substrates by pulsed laser deposition. The configurations of multilayered BaTiO3-(Ba,Ca)TiO3-CaTiO3 thin films are designed with the thickness ratio of 1:1:1 and 2:1:1 and total thickness ∼300 nm. Microstructural characterization by X-ray diffraction indicates that the as-deposited thin films are highly c-axis oriented and large in-plane strain is determined in BaTiO3 and CaTiO3 layers. Piezoresponse force microscopy (PFM) studies reveal an intense in-plane polarization component, whereas the out-of-plane shows inferior phase contrast. The optimized combination is found to be the BaTiO3-(Ba0.85Ca0.15)TiO3-CaTiO3 structure with combination ratio 2:1:1, which displays the largest domain switching amplitude under DC electric field, the largest room-temperature dielectric constant ∼646, a small dielectric loss of 0.03, and the largest dielectric tunability of ∼50% at 400 kV/cm. These results suggest that the enhanced dielectric and tunability performance are greatly associated with the large in-plane polarization component and domain switching.

  6. Canopy-level stomatal narrowing in adult Fagus sylvatica under O3 stress - means of preventing enhanced O3 uptake under high O3 exposure?

    PubMed

    Matyssek, R; Baumgarten, M; Hummel, U; Häberle, K-H; Kitao, M; Wieser, G

    2015-01-01

    Spatio-temporally consistent O(3) doses are demonstrated in adult Fagus sylvatica from the Kranzberg Forest free-air fumigation experiment, covering cross-canopy and whole-seasonal scopes through sap flow measurement. Given O(3)-driven closure of stomata, we hypothesized enhanced whole-tree level O(3) influx to be prevented under enhanced O(3) exposure. Although foliage transpiration rate was lowered under twice-ambient O(3) around noon by 30% along with canopy conductance, the hypothesis was falsified, as O(3) influx was raised by 25%. Nevertheless, the twice-ambient/ambient ratio of O(3) uptake was smaller by about 20% than that of O(3) exposure, suggesting stomatal limitation of uptake. The O(3) response was traceable from leaves across branches to the canopy, where peak transpiration rates resembled those of shade rather than sun branches. Rainy/overcast-day and nightly O(3) uptake is quantified and discussed. Whole-seasonal canopy-level validation of modelled with sap flow-derived O(3) flux becomes available in assessing O(3) risk for forest trees.

  7. ITO-free flexible organic photovoltaics with multilayer MoO3/LiF/MoO3/Ag/MoO3 as the transparent electrode

    NASA Astrophysics Data System (ADS)

    Chen, Shilin; Dai, Yunjie; Zhao, Dewei; Zhang, Hongmei

    2016-05-01

    We present efficient flexible organic photovoltaics (OPVs) with multiple layers of molybdenum oxide (MoO3)/LiF/MoO3/Ag/MoO3 as the transparent electrode, where the thin Ag layer yields high conductivity and the dielectric layer MoO3/LiF/MoO3 has high transparency due to optical interference, leading to improved power conversion efficiency compared with indium tin oxide (ITO) based devices. The MoO3 contacting organic active layer is used as a buffer layer for good hole extraction. Thus, the multilayer MoO3/LiF/MoO3/Ag/MoO3 can improve light transmittance and also facilitate charge carrier extraction. Such an electrode shows excellent mechanical bendability with a 9% reduction of efficiency after 1000 cycles of bending due to the ductile nature of the thin metal layer and dielectric layer used. Our results suggest that the MoO3/LiF/MoO3/Ag/MoO3 multilayer electrode is a promising alternative to ITO as an electrode in OPVs.

  8. Photoinduced charge transfer properties and photocatalytic activity in Bi2O3/BaTiO3 composite photocatalyst.

    PubMed

    Fan, Haimei; Li, Haiyan; Liu, Bingkun; Lu, Yongchun; Xie, Tengfeng; Wang, Dejun

    2012-09-26

    A series of Bi(2)O(3)/BaTiO(3) composite photocatalysts with different mass ratios of Bi(2)O(3) vs BaTiO(3) were prepared by an impregnating-annealing method. X-ray diffraction (XRD), high-resolution transmission electron microscopic (HRTEM), and UV-vis diffuse reflection spectroscopy (DRS) confirmed that Bi(2)O(3) and BaTiO(3) coexisted in the composites. The results of surface photovoltage (SPV) experiments showed enhancements of photovoltaic response in composites, which indicated a higher separation efficiency of photoinduced charges due to the establishment of an efficient interfacial electric field between Bi(2)O(3) and BaTiO(3) in the composites. The consistency of phtocatalytic activity and photovoltaic response intensity of photocatalysts showed that the efficiency interfacial electric field between Bi(2)O(3) and BaTiO(3) played an important role in improving the degradation efficiency of Rhodamine B (RhB). The 60%-Bi(2)O(3)/BaTiO(3) sample with the best activity was found by optimizing the mass ratios of Bi(2)O(3) vs. BaTiO(3). On the basis of the work function (WF) measurements, a reasonable energy band diagram was proposed for BaTiO(3)/Bi(2)O(3) composite. It would be helpful in designing and constructing high efficiency heterogeneous semiconductor photocatalyst.

  9. Photocatalytic activity of Zr:SrTiO 3 under UV illumination

    NASA Astrophysics Data System (ADS)

    Chen, Liang; Zhang, Shouchen; Wang, Liqiu; Xue, Dongfeng; Yin, Shu

    2009-01-01

    SrTiO 3 is a well-known efficient photocatalyst and has various industrial applications such as water or air purification antibacterial agents and self-cleaning surfaces. In this work, pure SrTiO 3 and Zr:SrTiO 3 photocatalysts were prepared by the sol-gel method and then tested by scanning electron microscopy (SEM) and X-ray diffraction, respectively. The crystal phase of Zr:SrTiO 3 shows a typical perovskite structure, in which Ti sites are substituted by Zr atoms. The as-prepared yellow Zr:SrTiO 3 powders were then used as UV photocatalysts. Photocatalytic degradation activity of methylene blue over zirconium-doped SrTiO 3 catalysts was tested under UV illumination. The high activity of Zr:SrTiO 3 was due to the defects of its crystal lattice, thus the energy needed by the semiconductor photoproduction electron transition to the conduction band was smaller than the intrinsic absorption band. The optimal conditions of our experiments are as follows: under 8% doping density of Zr, 10 mg/l initial concentration of methylene blue, 0.15 g photocatalyst dosage, 6.5 of pH value and 4 h of UV illumination time, the degradation rate of methylene blue can reach 93.6%.

  10. First principles investigations of structural, elastic, dielectric and piezoelectric properties of { Ba,Sr,Pb } TiO3, { Ba,Sr,Pb } ZrO3 and { Ba,Sr,Pb } { Zr,Ti } O3 ceramics

    NASA Astrophysics Data System (ADS)

    Akgenc, Berna; Tasseven, Cetin; Cagin, Tahir

    2015-03-01

    We use first-principle density-functional study of structural, anisotropic mechanical, dielectric and piezoelectric properties of {Ba,Sr,Pb}TiO3, {Ba,Sr,Pb}ZrO3 and {Ba,Sr,Pb}{Zr,Ti}O3 alloys in cubic perovskite structures at zero temperature. Because there is significant interest in finding new piezoelectrics that do not contain toxic elements such as lead. In this study, we compare piezoelectric response of those alloys to synthesize outstanding piezoelectric materials. In perovskite structures, the spontaneous polarization is due to enormous values of Born effective charges computed by linear response within density functional perturbation theory, which are much larger than predicted nominal charge. We deeply investigated the effects of composition, order and site defects structure on piezoelectric constants.

  11. Development of a statistical model to identify spatial and meteorological drivers of elevated O3 in Nevada and its application to other rural mountainous regions.

    PubMed

    Fine, Rebekka; Miller, Matthieu B; Gustin, Mae Sexauer

    2015-10-15

    Measurements of O3 at relatively remote monitoring sites are useful for quantifying baseline O3, and subsequently the magnitude of O3 not controllable by local regulations. As the National Ambient Air Quality Standard (NAAQS) for O3 becomes more stringent, there is an increased need to quantify baseline O3 particularly in the Western US, where regional and global sources can significantly enhance O3 measured at surface sites, yielding baseline mixing ratios approaching or exceeding the NAAQS threshold. Past work has indicated that meteorological conditions as well as site specific spatial characteristics (e.g. elevation, basin size, gradient) are significantly correlated with O3 intercepted at rural monitoring sites. Here, we use 3 years of measurements from sites throughout rural Nevada to develop a categorical tree model to identify spatial and meteorological characteristics that are associated with elevated baseline O3. Data from other sites in the Intermountain Western US are used to test the applicability of the model for sites throughout the region. Our analyses indicate that increased elevation and basin size were associated with increased frequency of elevated O3. On a daily time scale, relative humidity had the strongest association with observed MDA8 O3. Seventy-four percent of MDA8 O3 observations>60 ppbv occurred when daily minimum relative humidity was <15%. Further, we found that including ancillary pollutant data did not improve the predictive accuracy for measurements >60 ppbv whereas including upper air meteorological measurements improved the accuracy of predicting periods when O3 was >60 ppbv. These findings indicate that transport, rather than local production, influences O3 measurements in Nevada, and that high elevation sites in rural Nevada, are representative of baseline conditions in the Intermountain Western US.

  12. Multiferroic RMnO3 thin films

    NASA Astrophysics Data System (ADS)

    Fontcuberta, Josep

    2015-03-01

    Multiferroic materials have received an astonishing attention in the last decades due to expectations that potential coupling between distinct ferroic orders could inspire new applications and new device concepts. As a result, a new knowledge on coupling mechanisms and materials science has dramatically emerged. Multiferroic RMnO3 perovskites are central to this progress, providing a suitable platform to tailor spin-spin and spin-lattice interactions. With views towards applications, the development of thin films of multiferroic materials have also progressed enormously and nowadays thin-film manganites are available, with properties mimicking those of bulk compounds. Here we review achievements on the growth of hexagonal and orthorhombic RMnO3 epitaxial thin films and the characterization of their magnetic and ferroelectric properties, we discuss some challenging issues, and we suggest some guidelines for future research and developments. En ce qui concerne les applications, le développement de films minces de matériaux multiferroïques a aussi énormément progressé, et de nos jours des films minces de manganites avec des propriétés similaires à celles des matériaux massifs existent. Nous passons en revue ici les résultats obtenus dans le domaine de la croissance de couches minces épitaxiés de RMnO3 hexagonal et orthorhombique et de la caractérisation de leurs propriétés magnétiques et ferroélectriques. Nous discutons certains enjeux et proposons quelques idées pour des recherches et développements futurs.

  13. Correlation driven charge order at LaAlO3/SrTiO3 and LaTiO3/SrTiO3 Interfaces

    NASA Astrophysics Data System (ADS)

    Pentcheva, Rossitza

    2007-03-01

    Correlated behavior at complex oxide interfaces offers additional degrees of freedom to compensate charge imbalance not available e.g. in polar semiconductor heterostructures. This can result in electronic, charge and magnetic phases that do not exist in the bulk and offers new possibilities for device applications. For instance, the interfaces of LaTiO3 and SrTiO3 [1] as well as LaAlO3 and SrTiO3 [2] show metallic conductivity, although the respective bulk materials are Mott (LTO) and band insulating (STO, LAO). Here we present the results of material-specific correlated band theory (LDA+U) employing the FP-LAPW code in the WIEN2k implementation for a variety of (n,m) multilayers containing n LTO (or LAO) and m STO-layers. To explore the relaxation length towards bulk behavior n and m is varied between 1 and 9. We find that charge mismatch at the LTO/STO IF is accommodated by the formation of a charge and orbitally ordered (CO/OO) layer with a checkerboard arrangement of Ti^3+ and Ti^4+ and an antiferromagnetic coupling of the Ti^3+-spins [3]. Lattice relaxations lead to the observed conducting behavior. An analogous diluted layer of Ti^3+ spins is obtained for the n-type LAO/STO interface, although the corresponding bulk materials are nonmagnetic. For a structurally ideal p-type LAO/STO IF the measured insulating behavior can only be understood by a charge disproportionation on the oxygen sublattice and the formation of a CO/OO magnetic OPπ hole. Alternatively, charge compensation by oxygen vacancies and the formation of a charge conjugate F-center is considered. [1] A. Ohtomo, and H.Y. Hwang, Nature 423, 378 (2002). [2] A. Ohtomo, D.A. Muller, J.L. Grazul, and H.Y. Hwang, Nature 419, 378 (2002). [3] R. Pentcheva and W.E. Pickett, cond-mat/0608212. [4] R. Pentcheva and W.E. Pickett, Phys. Rev. B 74, 035112 (2006).

  14. Consequences of Ca multisite occupation for the conducting properties of BaTiO3

    NASA Astrophysics Data System (ADS)

    Zulueta, Y. A.; Dawson, J. A.; Leyet, Y.; Anglada-Rivera, J.; Guerrero, F.; Silva, R. S.; Nguyen, Minh Tho

    2016-11-01

    In combination with the dielectric modulus formalism and theoretical calculations, a newly developed defect incorporation mode, which is a combination of the standard A- and B-site doping mechanisms, is used to explain the conducting properties in 5 mol% Ca-doped BaTiO3. Simulation results for Ca solution energies in the BaTiO3 lattice show that the new oxygen vacancy inducing mixed mode exhibits low defect energies. A reduction in dc conductivity compared with undoped BaTiO3 is witnessed for the incorporation of Ca. The conducting properties of 5 mol% Ca-doped BaTiO3 are analyzed using molecular dynamics and impedance spectroscopy. The ionic conductivity activation energies for each incorporation mode are calculated and good agreement with experimental data for oxygen migration is observed. The likely existence of the proposed defect configuration is also analyzed on the basis of these methods.

  15. First-principles calculations on the four phases of BaTiO3.

    PubMed

    Evarestov, Robert A; Bandura, Andrei V

    2012-04-30

    The calculations based on linear combination of atomic orbitals basis functions as implemented in CRYSTAL09 computer code have been performed for cubic, tetragonal, orthorhombic, and rhombohedral modifications of BaTiO(3) crystal. Structural and electronic properties as well as phonon frequencies were obtained using local density approximation, generalized gradient approximation, and hybrid exchange-correlation density functional theory (DFT) functionals for four stable phases of BaTiO(3). A comparison was made between the results of different DFT techniques. It is concluded that the hybrid PBE0 [J. P. Perdew, K. Burke, M. Ernzerhof, J. Chem. Phys. 1996, 105, 9982.] functional is able to predict correctly the structural stability and phonon properties both for cubic and ferroelectric phases of BaTiO(3). The comparative phonon symmetry analysis in BaTiO(3) four phases has been made basing on the site symmetry and irreducible representation indexes for the first time.

  16. Electronic properties of ultrathin GdTiO3 thin films and GdTiO3/SrTiO3 interfaces

    NASA Astrophysics Data System (ADS)

    Moetakef, Pouya; Jalan, Bharat; Zhang, Jack; Allen, S. James; Stemmer, Susanne

    2011-03-01

    Interfaces between Mott insulators, such as the rare earth titanates, and band insulators, such as SrTiO3, have recently attracted much attention. We report on the transport properties of epitaxial rare earth titanate thin films, GdTiO3, grown by molecular beam epitaxy (MBE) and those of heterostructures with SrTiO3 and GdTiO3. Growth of GdTiO3 was performed by shuttered growth of alternating titanium tetra isopropoxide (TTIP) and Gd fluxes, in the absence of any additional oxygen. We show that to stabilize the GdTiO3 perovskite phase, SrTiO3 buffer layers are needed for growth on perovskite substrates, such as LSAT ((LaAlO3)0.3(Sr2AlTaO6)0.7). The contribution of n-type SrTiO3 buffer layers and that of the SrTiO3/GdTiO3 interfaces to the transport properties are determined by measurements of the electrical resistance and Hall coefficient as a function of temperature and magnetic field.

  17. Synthesis, Structure, and Ethanol Gas Sensing Properties of In2O3 Nanorods Decorated with Bi2O3 Nanoparticles.

    PubMed

    Park, Sunghoon; Kim, Soohyun; Sun, Gun-Joo; Lee, Chongmu

    2015-04-22

    Bi2O3-decorated In2O3 nanorods were synthesized using a one-step process, and their structure, as well as the effects of decoration of In2O3 nanorods with Bi2O3 on the ethanol gas-sensing properties were examined. The multiple networked Bi2O3-decorated In2O3 nanorod sensor showed responses of 171-1774% at ethanol concentrations of 10-200 ppm at 200 °C. The responses of the Bi2O3-decorated In2O3 nanorod sensor were stronger than those of the pristine-In2O3 nanorod sensors by 1.5-4.9 times at the corresponding concentrations. The two sensors exhibited short response times and long recovery times. The optimal Bi concentration in the Bi2O3-decorated In2O3 nanorod sensor and the optimal operation temperature of the sensor were 20% and 200 °C, respectively. The Bi2O3-decorated In2O3 nanorod sensor showed selectivity for ethanol gas over other gases. The origin of the enhanced response, sensing speed, and selectivity for ethanol gas of the Bi2O3-decorated In2O3 nanorod sensor to ethanol gas is discussed.

  18. Comparative ab initio calculations of SrTiO3/BaTiO3 and SrZrO3/PbZrO3 (0 0 1) heterostructures

    NASA Astrophysics Data System (ADS)

    Piskunov, Sergei; Eglitis, Roberts I.

    2016-05-01

    Using a B3PW hybrid exchange-correlation functional within the density functional theory (DFT) we calculated from the first principles the electronic structure of BaTiO3/SrTiO3 and PbZrO3/SrZrO3 (0 0 1) interfaces. The optical band gap of both BaTiO3/SrTiO3 and PbZrO3/SrZrO3 (0 0 1) interfaces depends mostly from BaO or TiO2 and SrO or ZrO2 termination of the upper layer, respectively. Based on the results of our calculations we predict increase of the Ti-O and Zr-O chemical bond covalency near the SrTiO3/BaTiO3 and SrZrO3/PbZrO3 (0 0 1) interfaces as compared to the BaTiO3 and PbZrO3 bulk.

  19. Segregation of Mn2+ Dopants as Interstitials in SrTiO3 Grain Boundaries

    SciTech Connect

    Yang, Hao; Kotula, Paul G.; Sato, Yukio; Chi, Miaofang; Ikuhara, Yuichi; Browning, Nigel D.

    2013-10-03

    Mn doped SrTiO3 shows promising magnetic and electrical properties, but the doping mechanism remains unclear. In this research Mn4+ is found to substitute Ti in bulk SrTiO3, but Mn2+ segregates inside grain boundaries at both Sr and interstitial sites. Mn interstitial doping has never been reported, but is found possible with the formation of Sr vacancies. This finding is significantly different from the amphoteric doping of Mn2+ substituting Sr and Mn4+ substituting Ti sites, therefore leads to different understanding on the defect mediated electrical and magnetic properties of transition metal doped perovskites.

  20. Metal-insulator transitions in LaTiO3 / CaTiO3 superlattices

    NASA Astrophysics Data System (ADS)

    Seo, Sung Seok A.; Lee, Ho Nyung

    2010-03-01

    Strongly correlated electrons at an interface of complex oxide heterostructures often show interesting behaviors that require an introduction of new physical concepts. For example, the metallic transport behavior found in the superlattices of a Mott insulator LaTiO3 and a band insulator SrTiO3 (STO) has established the concept of interfacial electronic reconstruction. In this work, we have studied the transport property of a new type of Mott/band insulator LaTiO3/CaTiO3 (LTO/CTO) superlattices grown by pulsed laser deposition (PLD). In order to rule out concerns about the PLD plume-triggered oxygen vacancies generated in STO substrates, which might influence transport measurement, and to investigate the effect of epitaxial strain, we have used insulating NdGaO3 substrates. While both LTO and CTO single films are highly insulating, we have observed intriguing metal-insulator transitions (MIT) in the LTO/CTO superlattices depending on the global LTO/CTO thickness ratio and temperature. (Note that LTO/STO superlattices are metallic at all temperatures (2-300 K)). In this talk, we will discuss the origin of the MIT in the scheme of self compensation mechanism of d-electrons at the hetero-interface between LTO and CTO.

  1. Quenching of I(2P 1/2) by O 3 and O( 3P)

    NASA Astrophysics Data System (ADS)

    Azyazov, V. N.; Antonov, I. O.; Ruffner, S.; Heaven, M. C.

    2006-02-01

    Oxygen-iodine lasers that utilize electrical or microwave discharges to produce singlet oxygen are currently being developed. The discharge generators differ from conventional chemical singlet oxygen generators in that they produce significant amounts of atomic oxygen. Post-discharge chemistry includes channels that lead to the formation of ozone. Consequently, removal of I(2P 1/2) by O atoms and O 3 may impact the efficiency of discharge driven iodine lasers. In the present study we have measured the rate constants for quenching of I(2P 1/2) by O( 3P) atoms and O 3 using pulsed laser photolysis techniques. The rate constant for quenching by O 3, 1.8x10 -12 cm 3 s -1, was found to be a factor of five smaller than the literature value. The rate constant for quenching by O( 3P) was 1.2x10 -11 cm 3 s -1. This was six times larger than a previously reported upper bound, but consistent with estimates obtained by modeling the kinetics of discharge-driven laser systems.

  2. Characterization of gamma-Ga2O3-Al2O3 prepared by solvothermal method and its performance for methane-SCR of NO.

    PubMed

    Nakatani, Tetsu; Watanabe, Tsunenori; Takahashi, Masaru; Miyahara, Yuya; Deguchi, Hiroshi; Iwamoto, Shinji; Kanai, Hiroyoshi; Inoue, Masashi

    2009-06-25

    The gamma-Ga(2)O(3)-Al(2)O(3) mixed oxides with a spinel structure were prepared by the solvothermal reaction of gallium acetylacetonate and aluminum isopropoxide in diethylenetriamine. In the crystal structures of the catalysts obtained by the calcination of these mixed oxides, Ga(3+) and Al(3+) ions preferentially occupied tetrahedral and octahedral sites, respectively. The catalysts with low Ga contents had a unique structure with high surface areas and a concentration gradient of decreasing Ga content from the surface to the bulk. In methane-selective catalytic reduction (SCR) of NO, higher NO conversion to N(2) was attained on the catalyst with high occupation of Ga(3+) ions at tetrahedral sites and Al(3+) ions at octahedral sites. For the gamma-Ga(2)O(3)-Al(2)O(3) mixed oxide with a charged Ga molar content of 0.3 (ST(0.3)), tetrahedral and octahedral sites were solely occupied by Ga(3+) and Al(3+) ions, respectively, and the catalyst exhibited the highest NO conversion to N(2). Therefore, it was concluded that the active site for methane-SCR of NO is tetrahedral Ga(3+) ion and octahedral Al(3+) ion, which are linked to each other. Nitrogen monoxide is adsorbed on the isolated hydroxyl group attached to Al(3+) ions and then oxidized by O(2) yielding surface nitrate species. Tetrahedral Ga(3+) ions work as Lewis acid sites for the activation of methane because of their coordinative unsaturation. The Ga(3+) ions in the gamma-Ga(2)O(3)-Al(2)O(3) catalyst have a redox property, which plays important roles in both the oxidation of NO to surface nitrate species and the activation of methane. The most important factor for this catalyst is that the sites for the formation of surface nitrate species reside next to the methane activation sites, which facilitates the reaction between surface nitrate species and the activated species derived from methane, thus mitigating the consumption of methane by simple combustion with O(2). Therefore, ST(0.3), which has the largest

  3. 2D-MoO3 nanosheets for superior gas sensors

    NASA Astrophysics Data System (ADS)

    Ji, Fangxu; Ren, Xianpei; Zheng, Xiaoyao; Liu, Yucheng; Pang, Liuqing; Jiang, Jiaxing; Liu, Shengzhong (Frank)

    2016-04-01

    By taking advantages of both grinding and sonication, an effective exfoliation process is developed to prepare two-dimensional (2D) molybdenum oxide (MoO3) nanosheets. The approach avoids high-boiling-point solvents that would leave a residue and cause aggregation. Gas sensors fabricated using the 2D-MoO3 nanosheets provide a significantly enhanced chemical sensor performance. Compared with the sensors using bulk MoO3, the response of the 2D-MoO3 sensor increases from 7 to 33; the sensor response time is reduced from 27 to 21 seconds, and the recovery time is shortened from 26 to 10 seconds. We attribute the superior performance to the 2D-structure with a much increased surface area and reactive sites.By taking advantages of both grinding and sonication, an effective exfoliation process is developed to prepare two-dimensional (2D) molybdenum oxide (MoO3) nanosheets. The approach avoids high-boiling-point solvents that would leave a residue and cause aggregation. Gas sensors fabricated using the 2D-MoO3 nanosheets provide a significantly enhanced chemical sensor performance. Compared with the sensors using bulk MoO3, the response of the 2D-MoO3 sensor increases from 7 to 33; the sensor response time is reduced from 27 to 21 seconds, and the recovery time is shortened from 26 to 10 seconds. We attribute the superior performance to the 2D-structure with a much increased surface area and reactive sites. Electronic supplementary information (ESI) available. See DOI: 10.1039/c6nr00880a

  4. Impedance Spectroscopic Studies of BiFeO3-Pb(ZrTi)O3 Nanocomposites

    NASA Astrophysics Data System (ADS)

    Choudhary, R. N. P.; Barik, Subrat K.; Katiyar, R. S.

    BiFeO3-Pb(ZrTi)O3 [i.e., (Bi1-xPbx)(Fe1-xZr0.6xTi0.4x)O3 (x = 0.15, 0.25, 0.40, 0.50)] nanocomposites were synthesized using mechanical activation followed by a solid-state reaction technique. The dielectric parameters (capacitance, dissipation factor D, impedance Z and phase angle Φ) of all the samples were measured in a wide range of frequencies (1 kHz-1 MHz) and temperatures (300-630 K) in air atmosphere using an impedance analyzer with low signal amplitude of 500 mV. Electrical properties of the compounds were studied using a complex impedance spectroscopy (CIS) technique. The frequency dependence of electrical data was analyzed in the framework of conductivity and modulus formalisms. AC conductivity spectrum obeys Jonscher's universal power law.

  5. Electronic and magnetic properties of RMnO3/AMnO3 heterostructures

    NASA Astrophysics Data System (ADS)

    Yu, Rong; Yunoki, Seiji; Dong, Shuai; Dagotto, Elbio

    2009-09-01

    The ground-state properties of RMnO3/AMnO3 (RMO/AMO) heterostructures (with R=La,Pr,… , a trivalent rare-earth cation and A=Sr,Ca,… , a divalent alkaline cation) are studied using a two-orbital double-exchange model including the superexchange coupling and Jahn-Teller lattice distortions. To describe the charge transfer across the interface, the long-range Coulomb interaction is taken into account at the mean-field level, by self-consistently solving the Poisson’s equation. The calculations are carried out numerically on finite clusters. We find that the state stabilized near the interface of the heterostructure is similar to the state of the bulk compound (R,A)MO at electronic density close to 0.5. For instance, a charge and orbitally ordered CE state is found at the interface if the corresponding bulk (R,A)MO material is a narrow-to-intermediate bandwidth manganite. But instead the interface regime accommodates an A-type antiferromagnetic state with a uniform x2-y2 orbital order, if the bulk (R,A)MO corresponds to a wide bandwidth manganite. We argue that these results explain some of the properties of long-period (RMO)m/(AMO)n superlattices, such as (PrMnO3)m/(CaMnO3)n and (LaMnO3)m/(SrMnO3)n . We also remark that the intermediate states in between the actual interface and the bulklike regimes of the heterostructure are dependent on the bandwidth and the screening of the Coulomb interaction. In these regions of the heterostructures, states are found that do not have an analog in experimentally known bulk phase diagrams. These new states of the heterostructures provide a natural interpolation between magnetically ordered states that are stable in the bulk at different electronic densities.

  6. Electronic and magnetic properties of RMnO3 AMnO3 heterostructures

    SciTech Connect

    Yu, Rong; Yunoki, Seiji; Dong, Shuai; Dagotto, Elbio R

    2009-01-01

    The ground-state properties of RMnO3 /AMnO3 RMO/AMO heterostructures with R=La,Pr, . . ., a trivalent rare-earth cation and A=Sr,Ca, . . ., a divalent alkaline cation are studied using a two-orbital doubleexchange model including the superexchange coupling and Jahn-Teller lattice distortions. To describe the charge transfer across the interface, the long-range Coulomb interaction is taken into account at the mean-field level, by self-consistently solving the Poisson s equation. The calculations are carried out numerically on finite clusters. We find that the state stabilized near the interface of the heterostructure is similar to the state of the bulk compound R,AMO at electronic density close to 0.5. For instance, a charge and orbitally ordered CE state is found at the interface if the corresponding bulk R,AMO material is a narrow-to-intermediate bandwidth manganite. But instead the interface regime accommodates an A-type antiferromagnetic state with a uniform x2 y2 orbital order, if the bulk R,AMO corresponds to a wide bandwidth manganite. We argue that these results explain some of the properties of long-period RMOm/ AMOn superlattices, such as PrMnO3m/ CaMnO3n and LaMnO3m/ SrMnO3n. We also remark that the intermediate states in between the actual interface and the bulklike regimes of the heterostructure are dependent on the bandwidth and the screening of the Coulomb interaction. In these regions of the heterostructures, states are found that do not have an analog in experimentally known bulk phase diagrams. These new states of the heterostructures provide a natural interpolation between magnetically ordered states that are stable in the bulk at different electronic densities.

  7. (100) facets of γ-Al2O3: the active surfaces for alcohol dehydration reactions

    SciTech Connect

    Kwak, Ja Hun; Mei, Donghai; Peden, Charles HF; Rousseau, Roger J.; Szanyi, Janos

    2011-05-01

    Temperature programmed desorption (TPD) of ethanol, and methanol dehydration reaction were studied on γ-Al2O3 in order to identify the catalytic active sites for alcohol dehydration reactions. Two high temperature (> 473 K) desorption features were observed following ethanol adsorption. Samples calcined at T≤473 K displayed a desorption feature in the 523-533 K temperature range, while those calcined at T ≥ 673 K showed a single desorption feature at 498 K. The switch from the high to low temperature ethanol desorption correlated well with the dehydroxylation of the (100) facets of γ-Al2O3 that was predicted at 550 K DFT calculations. Theoretical DFT simulations of the mechanism of dehydration. on clean and hydroxylated γ-Al2O3(100) surfaces, find that a concerted elimination of ethylene from an ethanol molecule chemisorbed at an Al3+ pentacoordinated site is the rate limiting step for catalytic cycle on both surfaces. Furthermore, titration of the pentacoordinate Al3+ sites on the (100) facets of γ-Al2O3 by BaO completely turned off the methanol dehydration reaction activity. These results unambiguously demonstrate that only the (100) facets on γ-Al2O3 are the catalytic active surfaces for alcohol dehydration.

  8. Design of n - and p -type oxide thermoelectrics in LaNiO3/SrTiO3(001 ) superlattices exploiting interface polarity

    NASA Astrophysics Data System (ADS)

    Geisler, Benjamin; Blanca-Romero, Ariadna; Pentcheva, Rossitza

    2017-03-01

    We investigate the structural, electronic, transport, and thermoelectric properties of LaNiO3/SrTiO3(001 ) superlattices containing either exclusively n - or p -type interfaces or coupled interfaces of opposite polarity by using density functional theory calculations with an on-site Coulomb repulsion term. The results show that significant octahedral tilts are induced in the SrTiO3 part of the superlattice. Moreover, the La-Sr distances and Ni-O out-of-plane bond lengths at the interfaces exhibit a distinct variation by about 7 % with the sign of the electrostatic doping. In contrast to the much studied LaAlO3/SrTiO3 system, the charge mismatch at the interfaces is exclusively accommodated within the LaNiO3 layers, whereas the interface polarity leads to a band offset and to the formation of an electric field within the coupled superlattice. Features of the electronic structure indicate an orbital-selective quantization of quantum well states. The potential- and confinement-induced multiband splitting results in complex cylindrical Fermi surfaces with a tendency towards nesting that depends on the interface polarity. The analysis of the thermoelectric response reveals a particularly large positive Seebeck coefficient (135 μ V /K) and a high figure of merit (0.35) for room-temperature cross-plane transport in the p -type superlattice that is attributed to the participation of the SrTiO3 valence band. Superlattices with either n - or p -type interfaces show cross-plane Seebeck coefficients of opposite sign and thus emerge as a platform to construct an oxide-based thermoelectric generator with structurally and electronically compatible n - and p -type oxide thermoelectrics.

  9. Impurity Enhancement of Al_2O_3/Al Adhesion

    NASA Astrophysics Data System (ADS)

    Wang, Xiao-Gang; Smith, John R.; Zhang, Wenqing; Evans, Anthony

    2003-03-01

    Our first-principles computations indicate that the clean Al_2O_3/Al interface is relatively weak - weaker than bulk Al. Fracture experiments reveal that the interface is relatively strong with observed failure in bulk Al, however. This paradox is resolved via doping effects of the common impurity C. We have found that only 1/3 of a monolayer of carbon segregated to the interface can increase the work of separation by a factor of 3. The resulting strong interface is consistent with fracture experiments. It arises due to void formation in the interface, which provides low-strain sites for the carbon to segregate to. The degree of void formation is consistent with the relatively high heat of oxide formation of Al.

  10. Vought O3U-1 'Corsair'

    NASA Technical Reports Server (NTRS)

    1931-01-01

    Vought O3U-1 'Corsair' in Full-Scale Tunnel (FST). This photograph was taken in September 1931 after the balance had been enclosed. This aircraft was also used earlier during the summer for preliminary tests in the FST and as the subject of some of the first publicity photographs taken of FST operations. NACA engineers checked the lift and drag characteristics of several aircraft with the results of earlier flight tests. Smith DeFrance concluded NACA TR No. 459, 'The agreement that has been obtained between the flight and full-scale tunnel results, together with the consistent manner in which measurements can be repeated when check tests are made, has demonstrated the accuracy and value of the equipment for aeronautical research.' (p. 298)

  11. Influence of non-magnetic and magnetic ions on the MagnetoCaloric properties of La0.7Sr0.3Mn0.9M0.1O3 doped in the Mn sites by M=Cr, Sn, Ti

    NASA Astrophysics Data System (ADS)

    Arayedh, Brahim; Kallel, Sami; Kallel, Nabil; Peña, Octavio

    2014-06-01

    We have studied the MagnetoCaloric Effect (MCE) in La0.7Sr0.3Mn0.9M0.1O3, M=Cr, Sn and Ti, prepared by a conventional solid state reaction. The temperature dependence of magnetization reveals that all compositions exhibit a ferromagnetic (FM) to paramagnetic (PM) transition at TC temperatures of 369, 326, 228 and 210 K, respectively for La0.7Sr0.3MnO3 (LSMO), La0.7Sr0.3Mn0.9Cr0.1O3 (LSMO-Cr), La0.7Sr0.3Mn0.9Sn0.1O3 (LSMO-Sn), and La0.7Sr0.3Mn0.9Ti0.1O3 (LSMO-Ti). Using Arrott plots, the phase transition from FM to PM is found to be of second order. The maximum magnetic entropy change (-ΔSM), at the applied magnetic field of 2 T, is found to be 1.27, 1.76, 0.47 and 1.45 J kg-1 K-1, respectively for LSMO, LSMO-Cr, LSMO-Sn and LSMO-Ti. The relative cooling power (RCP) for LSMO-Cr, LSMO-Sn and LSMO-Ti is in the order of 50%, 26% and 71%, respectively, compared to gadolinium (Gd). As a result, the LSMO-Cr and LSMO-Ti compounds can be considered as promising materials in magnetic refrigeration technology.

  12. Tuning the carrier density of LaAlO3/SrTiO3 interfaces by capping La1-xSrxMnO3

    NASA Astrophysics Data System (ADS)

    Shi, Y. J.; Wang, S.; Zhou, Y.; Ding, H. F.; Wu, D.

    2013-02-01

    We present a systematical study on the electronic transport properties of the insulating LaAlO3 (3 unit cells)/SrTiO3 interfaces capping with thin layers of La1-xSrxMnO3, whose formal polarization is continually tuned by Sr doping. When the Sr doping is lower than 2/3, the LaAlO3/SrTiO3 interfaces show metallic behaviors. The carrier mobility is almost independent on the Sr doping for metallic interface, indicating that the capping layer does not change the density of the oxygen vacancies and the interface intermixing. However, the sheet carrier densities monotonically decrease as increasing Sr doping, which is ascribed to the decrease of the La1-xSrxMnO3 formal polarization. These results strongly support the intrinsic mechanism of the polar catastrophe model and provide a new approach to tailor the interface states of complex oxide heterostructures.

  13. High Temperature Mechanical Characterization and Analysis of Al2O3 /Al2O3 Composition

    NASA Technical Reports Server (NTRS)

    Gyekenyesi, John Z.; Jaskowiak, Martha H.

    1999-01-01

    Sixteen ply unidirectional zirconia coated single crystal Al2O3 fiber reinforced polycrystalline Al2O3 was tested in uniaxial tension at temperatures to 1400 C in air. Fiber volume fractions ranged from 26 to 31%. The matrix has primarily open porosity of approximately 40%. Theories for predicting the Young's modulus, first matrix cracking stress, and ultimate strength were applied and evaluated for suitability in predicting the mechanical behavior of Al2O3/Al2O3 composites. The composite exhibited pseudo tough behavior (increased area under the stress/strain curve relative to monolithic alumina) from 22 to 1400 C. The rule-of-mixtures provides a good estimate of the Young's modulus of the composite using the constituent properties from room temperature to approximately 1200 C for short term static tensile tests in air. The ACK theory provides the best approximation of the first matrix cracking stress while accounting for residual stresses at room temperature. Difficulties in determining the fiber/matrix interfacial shear stress at high temperatures prevented the accurate prediction of the first matrix cracking stress above room temperature. The theory of Cao and Thouless, based on Weibull statistics, gave the best prediction for the composite ultimate tensile strength.

  14. Quantum Oscillations at LaTiO3/SrTiO3 Interfaces

    NASA Astrophysics Data System (ADS)

    Veit, Michael; Suzuki, Yuri

    Emergent metallic behavior at the interface of the Mott insulator LaTiO3 and the band insulator SrTiO3 was observed for the first time more than a decade ago. Since then the metallicity has been explained in terms of charge redistribution at the interface combined with lattice relaxation. However to date, Shubnikov de Haas oscillations have not been reported in this two dimensional metallic system. For ultrathin (3-4 unit cells) LaTiO3 thin films on SrTiO3, we report the observation of Shubnikov-de Haas oscillations whose frequency corresponds to a small Fermi pocket. Surprisingly the oscillation are only observed between 1 and 4 T. Above this range, the quantum limit is reached for this pocket so no more oscillations are observed. A Berry's phase of π is also detected in these oscillations. Additionally a strong in-plane anisotropic magnetoresistance was measured in the heterostructures which, along with the Berry's phase, is attributed to a giant Rashba coupling at the interface. This work is funded by a National Security Science Engineering Faculty Fellowship of the Department of Defense under N00014-15-1-0045.

  15. Hydrogen Incorporation in Aluminous MgSiO3-Perovskite

    NASA Astrophysics Data System (ADS)

    Smyth, J. R.; Jacobsen, S. D.; Huss, G. R.; Miyajima, N.; Pamato, M. G.

    2013-12-01

    We have synthesized hydrous, aluminum-bearing MgSiO3 perovskite samples at 25GPa and various temperatures from 1600 to 2200C in a multi-anvil press and have characterized the samples by single-crystal X-ray diffraction, Raman spectroscopy, electron microprobe (EPMA), transmission electron microscopy (TEM), and secondary ion mass spectroscopy (SIMS). Perovskite crystals range up to 100 micrometers in size and contain 1 - 2.5% by weight Al2O3. SIMS analyses with a probe spot of approximately 10 micron square indicate up to several thousand ppm by weight H2O which corresponds to one H per Al atom in the structure. Microprobe chemical analysis and crystal structure refinement from single crystal X-ray data indicates that Al substitutes in the Si site, but not in the Mg site. However, Raman spectroscopy indicates the presence of micro-inclusions of brucite, super-hydrous phase B (SHyB), magnesite, and stishovite in most samples. Some of the perovskite crystals in the samples synthesized at temperatures above 2100 C exhibit rounded inclusions that are interpreted to be melt that quenched to perovskite plus brucite, phase D, and/or stishovite. Nearly all spectra show O-H stretching bands that are associated with brucite and/or Shy-B. None of the samples show a Raman peak in the O-H stretching region (3000 to 3700 cm-1) that correlates in intensity with perovskite Raman lattice modes. Our provisional interpretation is that the MgSiO3-perovskite structure incorporates very little H2O (<100 ppmw) and that most of the H in the samples is contained in brucite, phase D, superhydrous phase B (SHyB) or aluminous stishovite. This implies that the magnesium silicate perovskite phase in the lower mantle is unlikely to be a significant host for H in the lower mantle. However, phase D may be stabilized to higher temperatures by incorporation of Al and is extremely hydrous so that two modal percent of phase D may allow the lower mantle to contain several thousand ppmw H2O. Such a small

  16. Nanosized As2O3/Fe2O3 complexes combined with magnetic fluid hyperthermia selectively target liver cancer cells

    PubMed Central

    Wang, Zi-Yu; Song, Jian; Zhang, Dong-Sheng

    2009-01-01

    AIM: To study the methods of preparing the magnetic nano-microspheres of Fe2O3 and As2O3/Fe2O3 complexes and their therapeutic effects with magnetic fluid hyperthermia (MFH). METHODS: Nanospheres were prepared by chemical co-precipitation and their shape and diameter were observed. Hemolysis, micronucleus, cell viability, and LD50 along with other in vivo tests were performed to evaluate the Fe2O3 microsphere biocompatibility. The inhibition ratio of tumors after Fe2O3 and As2O3/Fe2O3 injections combined with induced hyperthermia in xenograft human hepatocarcinoma was calculated. RESULTS: Fe2O3 and As2O3/Fe2O3 particles were round with an average diameter of 20 nm and 100 nm as observed under transmission electron microscope. Upon exposure to an alternating magnetic field (AMF), the temperature of the suspension of magnetic particles increased to 41-51°C, depending on different particle concentrations, and remained stable thereafter. Nanosized Fe2O3 microspheres are a new kind of biomaterial without cytotoxic effects. The LD50 of both Fe2O3 and As2O3/Fe2O3 in mice was higher than 5 g/kg. One to four weeks after Fe2O3 and As2O3/Fe2O3 complex injections into healthy pig livers, no significant differences were found in serum AST, ALT, BUN and Cr levels among the pigs of all groups (P > 0.05), and no obvious pathological alterations were observed. After exposure to alternating magnetic fields, the inhibition ratio of the tumors was significantly different from controls in the Fe2O3 and As2O3/Fe2O3 groups (68.74% and 82.79%, respectively; P < 0.01). Tumors of mice in treatment groups showed obvious necrosis, while normal tissues adjoining the tumor and internal organs did not. CONCLUSION: Fe2O3 and As2O3/Fe2O3 complexes exerted radiofrequency-induced hyperthermia and drug toxicity on tumors without any liver or kidney damage. Therefore, nanospheres are ideal carriers for tumor-targeted therapy. PMID:19554652

  17. Measurement and modeling of O 3 variability in Shanghai, China: Application of the WRF-Chem model

    NASA Astrophysics Data System (ADS)

    Tie, Xuexi; Geng, Fuhai; Peng, Li; Gao, Wei; Zhao, Chunsheng

    Since 2005, Shanghai Meteorological Bureau (SMB) has established an observational network for measuring VOC, NO x, O 3 and aerosols in the Shanghai region. In this study, a rapid O 3 changes from Aug/02/2007 to Aug/11/2007 was observed in the region. During this 10 day period, the noontime O 3 maximum decreased from 100 to 130 ppbv to about 20-30 ppbv. In order to analyze the processes in controlling this rapid change of O 3 during this short period, a newly developed regional chemical/dynamical model (WRF-Chem) is applied to study O 3 variability in the Shanghai region. The model performances are evaluated by comparing the model calculation to the measurement. The result shows that the calculated magnitudes and diurnal variations of O 3 are close to the measured results in city sites, but are underestimated at a rural petroleum industrial site, suggesting that the emissions from petroleum factories around this rural site are significantly underestimated and need to be improved. The calculated rapid changes of O 3 concentrations, O 3 precursors, and aerosols are consistent with the measured results, suggesting that the model is suitable to study the causes of this rapid O 3 change. The model analysis indicates that weather conditions play important roles in controlling the surface O 3 in the Shanghai region. During summer, there is a persistent sub-tropical high pressure system (SUBH) in southeast of Shanghai over Pacific Ocean. During the earlier time of the period (Aug/02-Aug/05), the SUBH system was weak, resulting in weak surface winds. With the calm winds, a noticeable noontime sea-breeze produced an inflow from ocean to land, generating a cycling pattern of wind directions. As a result, the high O 3 concentrations were trapped in the Shanghai region, with a maximum concentration of 100-130 ppbv. By contrast, during the later time of the period (Aug/06-Aug/11), the SUBH was enhanced, resulting in strong surface winds. The high O 3 concentrations formed in the

  18. Structure-Curie temperature relationships in BaTiO3-based ferroelectric perovskites: Anomalous behavior of (Ba ,Cd )TiO3 from DFT, statistical inference, and experiments

    NASA Astrophysics Data System (ADS)

    Balachandran, Prasanna V.; Xue, Dezhen; Lookman, Turab

    2016-04-01

    One of the key impediments to the development of BaTiO3-based materials as candidates to replace toxic-Pb-based solid solutions is their relatively low ferroelectric Curie temperature (TC). Among many potential routes that are available to modify TC, ionic substitutions at the Ba and Ti sites remain the most common approach. Here, we perform density functional theory (DFT) calculations on a series of A TiO3 and Ba B O3 perovskites, where A =Ba , Ca, Sr, Pb, Cd, Sn, and Mg and B =Ti , Zr, Hf, and Sn. Our objective is to study the relative role of A and B cations in impacting the TC of the tetragonal (P 4 m m ) and rhombohedral (R 3 m ) ferroelectric phases in BaTiO3-based solid solutions, respectively. Using symmetry-mode analysis, we obtain a quantitative description of the relative contributions of various divalent (A ) and tetravalent (B ) cations to the ferroelectric distortions. Our results show that Ca, Pb, Cd, Sn, and Mg have large mode amplitudes for ferroelectric distortion in the tetragonal phase relative to Ba, whereas Sr suppresses the distortions. On the other hand, Zr, Hf, and Sn tetravalent cations severely suppress the ferroelectric distortion in the rhombohedral phase relative to Ti. In addition to symmetry modes, our calculated unit-cell volume also agrees with the experimental trends. We subsequently utilize the symmetry modes and unit-cell volumes as features within a machine learning approach to learn TC via an inference model and uncover trends that provide insights into the design of new high-TCBaTiO3 -based ferroelectrics. The inference model predicts CdTiO3-BaTiO3 solid solutions to have a higher TC and, therefore, we experimentally synthesized these solid solutions and measured their TC. Although the calculated mode strength for CdTiO3 in the tetragonal phase is even larger than that for PbTiO3, the TC of CdTiO3-BaTiO3 solid solutions in the tetragonal phase does not show any appreciable enhancement. Thus, CdTiO3-BaTiO3 does not follow the

  19. Carrier-Controlled Ferromagnetism in SrTiO3

    DOE PAGES

    Moetakef, Pouya; Williams, James R.; Ouellette, Daniel G.; ...

    2012-06-27

    Magnetotransport and superconducting properties are investigated for uniformly La-doped SrTiO3 films and GdTiO3/SrTiO3 heterostructures, respectively. GdTiO3/SrTiO3 interfaces exhibit a high-density 2D electron gas on the SrTiO3 side of the interface, while, for the SrTiO3 films, carriers are provided by the dopant atoms. Both types of samples exhibit ferromagnetism at low temperatures, as evidenced by a hysteresis in the magnetoresistance. For the uniformly doped SrTiO3 films, the Curie temperature is found to increase with doping and to coexist with superconductivity for carrier concentrations on the high-density side of the superconducting dome. The Curie temperature of the GdTiO3/SrTiO3 heterostructures scales with themore » thickness of the SrTiO3 quantum well. The results are used to construct a stability diagram for the ferromagnetic and superconducting phases of SrTiO3.« less

  20. Effect of Elevated CO2, O3, and UV Radiation on Soils

    PubMed Central

    Rejšek, Klement; Vranová, Valerie

    2014-01-01

    In this work, we have attempted to review the current knowledge on the impact of elevated CO2, O3, and UV on soils. Elevated CO2 increases labile and stabile soil C pool as well as efficiency of organic pollutants rhizoremediation and phytoextraction of heavy metals. Conversely, both elevated O3 and UV radiation decrease inputs of assimilates to the rhizosphere being accompanied by inhibitory effects on decomposition processes, rhizoremediation, and heavy metals phytoextraction efficiency. Contrary to elevated CO2, O3, or UV-B decreases soil microbial biomass, metabolisable C, and soil Nt content leading to higher C/N of soil organic matter. Elevated UV-B radiation shifts soil microbial community and decreases populations of soil meso- and macrofauna via direct effect rather than by induced changes of litter quality and root exudation as in case of elevated CO2 or O3. CO2 enrichment or increased UV-B is hypothesised to stimulate or inhibit both plant and microbial competitiveness for soluble soil N, respectively, whereas O3 favours only microbial competitive efficiency. Understanding the consequences of elevated CO2, O3, and UV radiation for soils, especially those related to fertility, phytotoxins inputs, elements cycling, plant-microbe interactions, and decontamination of polluted sites, presents a knowledge gap for future research. PMID:24688424

  1. Effect of antisite-like defect in ferroelectricity of SrTiO3 films

    NASA Astrophysics Data System (ADS)

    Yang, Fang; Yang, Zhenzhong; Gu, Lin; Guo, Jiandong; Institute of Physics, Chinese Academy of Sciences Team

    2014-03-01

    Ferroelectricity in thin films of nominally nonferroelectric materials such as SrTiO3 has been widely studied. It is known that some extrinsic factors such as strain [M. P. Warusawithana et al. Science 324, 367 (2009)] and defect [H. W. Jang et al., Phys. Rev. Lett. 104, 197601 (2010), M. Choi et al., Phys. Rev. Lett. 103, 185502 (2009)] can result in the ferroelectricity of SrTiO3 thin films. The SrTiO3 thin films with ferroelectricity were prepared on Si (001) substrates by oxide molecular beam epitaxy. The energy dispersive x-ray spectroscopy (EDX) mapping measurement results demonstrate Sr diffuses to the interface of SrTiO3 and Si. The cross sectional high-resolution transmission electron microscopy (HRTEM) results show that there are interstitial Ti atoms in the unit cells. The off-centered Ti from the Sr site along [100] or [110] direction can be regarded as a polar defect pair composed of a Sr vacancy and an interstitial Ti. It is predicted that Ti antisitelike defects in SrTiO3 are responsible for the ferroelectricity . Such antisitelike defects observed in SrTiO3 films are considered as the origin of the ferroelectricity. This work is supported by ``973'' Program of China (2012CB921700) and NSFC Project 11225422.

  2. Effect of elevated CO2, O3, and UV radiation on soils.

    PubMed

    Formánek, Pavel; Rejšek, Klement; Vranová, Valerie

    2014-01-01

    In this work, we have attempted to review the current knowledge on the impact of elevated CO2, O3, and UV on soils. Elevated CO2 increases labile and stabile soil C pool as well as efficiency of organic pollutants rhizoremediation and phytoextraction of heavy metals. Conversely, both elevated O3 and UV radiation decrease inputs of assimilates to the rhizosphere being accompanied by inhibitory effects on decomposition processes, rhizoremediation, and heavy metals phytoextraction efficiency. Contrary to elevated CO2, O3, or UV-B decreases soil microbial biomass, metabolisable C, and soil N t content leading to higher C/N of soil organic matter. Elevated UV-B radiation shifts soil microbial community and decreases populations of soil meso- and macrofauna via direct effect rather than by induced changes of litter quality and root exudation as in case of elevated CO2 or O3. CO2 enrichment or increased UV-B is hypothesised to stimulate or inhibit both plant and microbial competitiveness for soluble soil N, respectively, whereas O3 favours only microbial competitive efficiency. Understanding the consequences of elevated CO2, O3, and UV radiation for soils, especially those related to fertility, phytotoxins inputs, elements cycling, plant-microbe interactions, and decontamination of polluted sites, presents a knowledge gap for future research.

  3. Structure versus properties in α-Fe2O3 nanowires and nanoblades

    NASA Astrophysics Data System (ADS)

    Wang, Chao; Wang, Yiqian; Liu, Xuehua; Yang, Huaiwen; Sun, Jirong; Yuan, Lu; Zhou, Guangwen; Rosei, Federico

    2016-01-01

    We report structure/property relationships in bicrystalline α-Fe2O3 nanowires (NWs) and nanoblades (NBs), synthesized by thermal oxidation of iron foils with different surface roughness. The electrical properties of individual nanostructures were studied by in situ transmission electron microscopy. Current-voltage (I-V) measurements using gold electrodes showed that a Schottky contact forms between α-Fe2O3 NWs whereas an ohmic contact forms between α-Fe2O3 NBs. The difference in transport properties is attributed to the existence of oxygen vacancies in the coincidence-site-lattice boundary region of α-Fe2O3 NBs. Magnetic measurements indicate that the temperature-dependent zero-field-cooled magnetization rises more rapidly near the Morin transition temperature for α-Fe2O3 NBs than that for NWs. The distinct magnetic properties of the NBs are ascribed to the enhanced magnetic order induced by the structural order in the two-dimensional NBs. These α-Fe2O3 NBs are promising building blocks for electronic and magnetic devices since their 2D geometries facilitate integration into devices with realistic pathways to manufacturing. In addition, our study shows that boundary engineering is an effective approach for tailoring the physical properties of nanomaterials.

  4. Magnetic Correlations in the Triangular Antiferromagnet TbInO3

    NASA Astrophysics Data System (ADS)

    Sala, Gabriele; Clark, Lucy; Maharaj, Dalini; Stone, Matthew B.; Knight, Kevin S.; Cheong, Sang-Wook; Gaulin, Bruce D.

    TbInO3 crystallizes with a hexagonal P63 cm structure in which layers of edge-sharing triangles of magnetic Tb3+ ions are separated by non-magnetic [InO5]7- units. TbInO3, therefore, realizes an excellent opportunity to explore the behavior of a two-dimensional magnetic triangular lattice, a canonical model of geometric frustration. Here we present our study of a polycrystalline sample of TbInO3. Our high resolution powder neutron diffraction data (HRPD, ISIS) of TbInO3 confirm that the triangular layers of Tb3+ remain undistorted to at least 0 . 46 K. Magnetic susceptibility data follow Curie-Weiss behavior over a wide range of T with θ = - 17 . 19 (3) K indicating the dominance of antiferromagnetic correlations. The susceptibility data also show an absence of conventional long-range spin order down to at least 0 . 55 K, reflecting the frustrated nature of TbInO3. Elastic magnetic diffuse neutron scattering (SEQUOIA, SNS) is observed below ~ 15 K, due to the presence of static two-dimensional spin correlations. The spectrum of crystal field excitations in TbInO3 appears to have an exotic form due to the existence of two crystallographically distinct Tb3+ sites and leads to a strong Ising anisotropy of the spin symmetry.

  5. Structural, vibrational and magnetic properties of the orthoferrites LaFeO3 and YFeO3: A comparative study

    NASA Astrophysics Data System (ADS)

    Coutinho, P. V.; Cunha, F.; Barrozo, Petrucio

    2017-02-01

    We performed this work in order to compare several properties of two orthoferrites: LaFeO3 and YFeO3. Specifically, we have concentrated on the distortions induced in the bulk material due to the exchange between elements with different atomic radii in the individual A sites of perovskite. We investigate the effect of the distortion in the structural, vibrational and magnetic properties. All samples were prepared by combustion method using citric acid as the combustible. The large difference between the ionic radii of the elements on the A site within the perovskite structure Y (r=1.10 Å) and La (r=1.36 Å) induces remarkable changes in the perovskite structure and in its properties. These changes are more noticeable in the reduction of the lattice parameters and in increase of the octahedral distortion. Changes in the Raman modes and in the magnetic properties also are observed. These studies indicate the existence of spin-phonon coupling in the LaFeO3 and YFeO3 structures. The increasing of the distortions on crystalline structure also induces an increase the canting of the spin lattice and consequently an increase of the ferromagnetic component.

  6. Structural Investigations of MnO-Bi2O3 and MnO-Bi2O3-As2O3 Glass Systems by IR Spectroscopy

    NASA Astrophysics Data System (ADS)

    Ardelean, I.; Todor, Ioana; Păşcuţă, P.; Ioncu, V.

    Glasses from xMnO . (100-x)Bi2O3 and xMnO . (100-x)[Bi2O3 . As2O3] systems, with 0<= x<= 50 mol% were obtained in the same conditions and characterized by IR spectroscopy. The influence of a gradual increase of MnO content on the glass structure and the effect of changing the glass matrix compositions, were projected. The presence and the dependence of the bismuthate structural units BiO3 and BiO6 on the MnO content was analyzed.

  7. Density functional theory study of acetaldehyde hydrodeoxygenation on MoO3

    SciTech Connect

    Mei, Donghai; Karim, Ayman M.; Wang, Yong

    2011-04-06

    Periodic spin-polarized density functional theory calculations were performed to investigate acetaldehyde (CH3CHO) hydrodeoxygenation on the reduced molybdenum trioxide (MoO3) surface. The perfect O-terminated α-MoO3(010) surface is reduced to generate an oxygen defect site in the presence of H2. H2 dissociatively adsorbs at the surface oxygen sites forming two surface hydroxyls, which can recombine into a water molecule weakly bound at the Mo site. A terminal oxygen (Ot) defect site thus forms after water desorption. CH3CHO adsorbs at the O-deficient Mo site via either the sole O-Mo bond or the O-Mo and the C-O double bonds. The possible reaction pathways of the adsorbed CH3CHO with these two configurations were thoroughly examined using the dimer searching method. Our results show that the ideal deoxygenation of CH3CHO leading to ethylene (C2H4) on the reduced MoO3(010) surface is feasible. The adsorbed CH3CHO first dehydrogenate into CH2CHO by reacting with a neighboring terminal Ot. The hydroxyl (OtH) then hydrogenates CH2CHO into CH2CH2O to complete the hydrogen transfer cycle with an activation barrier of 1.39 eV. The direct hydrogen transfer from CH3CHO to CH2CH2O is unlikely due to the high barrier of 2.00 eV. The produced CH2CH2O readily decomposes into C2H4 that directly releases to the gas phase, and regenerates the Ot atom on the Mo site. As a result, the reduced MoO3(010) surface is reoxidized to the perfect MoO3(010) surface after CH3CHO deoxygenation. Pacific Northwest National Laboratory is operated by Battelle for the US Department of Energy.

  8. Molecular beam epitaxy deposition of Gd2O3 thin films on SrTiO3 (100) substrate

    NASA Astrophysics Data System (ADS)

    Wang, Jinxing; Hao, Jinghua; Zhang, Yangyang; Wei, Hongmei; Mu, Juyi

    2016-06-01

    Gd2O3 thin films are grown on the SrTiO3 (100) substrate by molecular beam epitaxy (MBE) deposition. X-ray diffraction (XRD) analysis, conventional transmission electron microscopy (TEM) and aberration-corrected scanning transmission electron microscopy (STEM) are performed to investigate the microstructure of deposited thin films. It is found that the as-deposited thin film possesses a very uniform thickness of ∼40 nm and is composed of single cubic phase Gd2O3 grains. STEM and TEM observations reveal that Gd2O3 thin film grows epitaxially on the SrTiO3 (100) substrate with (001)Gd2O3//(100)STO and [110]Gd2O3//[001]STO orientations. Furthermore, the Gd atoms are found to diffuse into the SrTiO3 substrate for a depth of one unit cell and substitute for the Sr atoms near the interface.

  9. Enhanced photocatalytic property of BiFeO3/N-doped graphene composites and mechanism insight

    NASA Astrophysics Data System (ADS)

    Li, Pai; Li, Lei; Xu, Maji; Chen, Qiang; He, Yunbin

    2017-02-01

    A series of BiFeO3/(N-doped) graphene composites are prepared by a facile hydrothermal method. BiFeO3/N-doped graphene shows photocatalytic performance superior to that of BiFeO3/graphene and pristine BiFeO3. The enhanced photo-degradation performance of BiFeO3/N-doped graphene are mainly attributable to the improved light absorbance of the composite, abundant active adsorption sites and high electrical charge mobility of N-doped graphene, and the downward band bending of BiFeO3 at the composite interface. In particular, X-ray photoelectron spectroscopy analyses reveal that the electron energy band of BiFeO3 is downward bent by 1.0 eV at the interface of BiFeO3/N-doped graphene, because of different work functions of both materials. This downward band bending facilitates the transfer of photogenerated electrons from BiFeO3 to N-doped graphene and prompts the separation of photo-generated electron-hole pairs, leading eventually to the enhanced photocatalytic performance.

  10. PZT-like structural phase transitions in the BiFeO3-KNbO3 solid solution.

    PubMed

    Lennox, Robert C; Taylor, Daniel D; Vera Stimpson, Laura J; Stenning, Gavin B G; Jura, Marek; Price, Mark C; Rodriguez, Efrain E; Arnold, Donna C

    2015-06-21

    Despite the high prominence of the perovskites BiFeO(3) and KNbO(3) the solid solution between the two has received little attention. We report a detailed neutron and synchrotron X-ray powder diffraction, and Raman spectroscopy study which demonstrates an R3c→P4mm→Amm2 series of structural phase transitions similar to that exhibited by the PbZrO(3)-PbTiO(3) solid solution.

  11. Engineering new properties in PbTiO3 based superlattices: compositionally broken inversion symmetry and polarization rotation

    NASA Astrophysics Data System (ADS)

    Dawber, Matthew

    2013-03-01

    In this talk I will present results on two superlattice systems which contain ultra fine layers of PbTiO3 and another perovskite material. In recent years, much work has been done on the PbTiO3/SrTiO3 system, with a focus on improper ferroelectricity and the arrangement of ferroelectric domains. Here, we consider two different partner materials for PbTiO3, each of which introduces markedly different behavior in the resulting superlattice. PbTiO3/SrRuO3 superlattices with ultra-thin SrRuO3 layers were studied both experimentally and using density functional theory. Due to the superlattice geometry, the samples show a large anisotropy in their electrical resistivity, which can be controlled by changing the thickness of the PbTiO3 layers. Therefore, along the ferroelectric direction, SrRuO3 layers can act as dielectric, rather than metallic, elements. We show that, by reducing the thickness of the PbTiO3 layers, an increasingly important effect of polarization asymmetry due to compositional inversion symmetry breaking occurs. The compositional inversion symmetry breaking is seen in this bi-color superlattice due to the combined variation of A and B site ions within the superlattice. We have also achieved an experimental enhancement of the piezoelectric response and dielectric tunability in artificially layered epitaxial PbTiO3/CaTiO3 superlattices through an engineered rotation of the polarization direction. As the relative layer thicknesses within the superlattice were changed from sample to sample we found evidence for polarization rotation in multiple x-ray diffraction measurements. Associated changes in functional properties were seen in electrical measurements and piezoforce microscopy. These results demonstrate a new approach to inducing polarization rotation under ambient conditions in an artificially layered thin film. Work supported by NSF DMR1055413

  12. The Molar Volume of FeO-MgO-Fe2O3-Cr2O3-Al2O3-TiO2 Spinels

    NASA Astrophysics Data System (ADS)

    Hamecher, E. A.; Antoshechkina, P. M.; Ghiorso, M. S.; Asimow, P. D.

    2011-12-01

    will include some minor components, including Ti4+ and Cr3+. Because most constraints on the activity of garnet and pyroxene at high-P are derived from experiments with coexisting spinel, we must be confident in the ability of our spinel model to realistically reproduce thermodynamic behavior over all applicable compositions. Additionally, producing a spinel molar volume model calibrated with recent in situ high-P, T diffraction data is crucial to our ability to accurately model the spinel-garnet transition in Earth's upper mantle. For example, we recently calibrated Cr-Al exchange equilibria for garnet and spinel. When this new calibration is used with the current MELTS model, a region of garnet-spinel coexistence in lherzolites is predicted with width in pressure comparable to experimental constraints. The transition occurs, however, at the unexpectedly low pressure of ~1.7 GPa. The improved model of spinel molar volume presented here, along with a new garnet molar volume model in the system FeO-MgO-CaO-Fe2O3-Cr2O3-Al2O3-TiO2-Na2O-SiO2 currently being calibrated, will enable coupled recalibration of the garnet and pyroxene models to match both the absolute pressure and width of this key transition in mantle lithology.

  13. Crystal structure of Ln1/3NbO 3 ( Ln=Nd, Pr) and phase transition in Nd 1/3NbO 3

    NASA Astrophysics Data System (ADS)

    Zhang, Zhaoming; Howard, Christopher J.; Kennedy, Brendan J.; Knight, Kevin S.; Zhou, Qingdi

    2007-06-01

    The crystal structure of the A-site deficient perovskite Ln1/3NbO 3 ( Ln=Nd, Pr) at room temperature has been determined, for the first time, as orthorhombic in space group Cmmm using high-resolution neutron powder diffraction. Pertinent features are the alternation of unoccupied layers of A-sites and layers partly occupied by Ln cations, as well as out-of-phase tilting of the NbO 6 octahedra around an axis perpendicular to the direction of the cation/vacancy ordering. The phase transition behaviour of Nd 1/3NbO 3 has also been studied in situ. This compound undergoes a continuous phase transition at around 650 °C to a tetragonal structure in space group P4/ mmm due to the disappearance of the octahedral tilting. The analysis of spontaneous strains shows that this phase transition is tricritical in nature.

  14. LaAlO3 stoichiometry is key to electron liquid formation at LaAlO3/SrTiO3 interfaces

    NASA Astrophysics Data System (ADS)

    Warusawithana, M. P.; Richter, C.; Mundy, J. A.; Roy, P.; Ludwig, J.; Paetel, S.; Heeg, T.; Pawlicki, A. A.; Kourkoutis, L. F.; Zheng, M.; Lee, M.; Mulcahy, B.; Zander, W.; Zhu, Y.; Schubert, J.; Eckstein, J. N.; Muller, D. A.; Hellberg, C. Stephen; Mannhart, J.; Schlom, D. G.

    2013-08-01

    Emergent phenomena, including superconductivity and magnetism, found in the two-dimensional electron liquid (2-DEL) at the interface between the insulators lanthanum aluminate (LaAlO3) and strontium titanate (SrTiO3) distinguish this rich system from conventional 2D electron gases at compound semiconductor interfaces. The origin of this 2-DEL, however, is highly debated, with focus on the role of defects in the SrTiO3, while the LaAlO3 has been assumed perfect. Here we demonstrate, through experiments and first-principle calculations, that the cation stoichiometry of the nominal LaAlO3 layer is key to 2-DEL formation: only Al-rich LaAlO3 results in a 2-DEL. Although extrinsic defects, including oxygen deficiency, are known to render LaAlO3/SrTiO3 samples conducting, our results show that in the absence of such extrinsic defects an interface 2-DEL can form. Its origin is consistent with an intrinsic electronic reconstruction occurring to counteract a polarization catastrophe. This work provides insight for identifying other interfaces where emergent behaviours await discovery.

  15. LaAlO3 stoichiometry is key to electron liquid formation at LaAlO3/SrTiO3 interfaces.

    PubMed

    Warusawithana, M P; Richter, C; Mundy, J A; Roy, P; Ludwig, J; Paetel, S; Heeg, T; Pawlicki, A A; Kourkoutis, L F; Zheng, M; Lee, M; Mulcahy, B; Zander, W; Zhu, Y; Schubert, J; Eckstein, J N; Muller, D A; Hellberg, C Stephen; Mannhart, J; Schlom, D G

    2013-01-01

    Emergent phenomena, including superconductivity and magnetism, found in the two-dimensional electron liquid (2-DEL) at the interface between the insulators lanthanum aluminate (LaAlO3) and strontium titanate (SrTiO3) distinguish this rich system from conventional 2D electron gases at compound semiconductor interfaces. The origin of this 2-DEL, however, is highly debated, with focus on the role of defects in the SrTiO3, while the LaAlO3 has been assumed perfect. Here we demonstrate, through experiments and first-principle calculations, that the cation stoichiometry of the nominal LaAlO3 layer is key to 2-DEL formation: only Al-rich LaAlO3 results in a 2-DEL. Although extrinsic defects, including oxygen deficiency, are known to render LaAlO3/SrTiO3 samples conducting, our results show that in the absence of such extrinsic defects an interface 2-DEL can form. Its origin is consistent with an intrinsic electronic reconstruction occurring to counteract a polarization catastrophe. This work provides insight for identifying other interfaces where emergent behaviours await discovery.

  16. Unusual ferromagnetic YMnO3 phase in YMnO3/La2 / 3Sr1 / 3MnO3 heterostructures

    NASA Astrophysics Data System (ADS)

    Autieri, Carmine; Sanyal, Biplab

    2014-11-01

    By means of first-principles density functional calculations, we study the structural, magnetic and electronic properties of YMnO3/L{{a}2/3}S{{r}1/3}MnO3 heterostructures. Although in the bulk the ground state of YMnO3 is an antiferromagnet, the YMnO3/L{{a}2/3}S{{r}1/3}MnO3 heterostructure stabilizes the ferromagnetic (FM) phase in YMnO3 in the interface region over a wide range of Coulomb repulsion parameters. The hypothetical FM phase of bulk YMnO3 is dielectric and due to substantial differences between the lattice constants in the ab plane, a strong magnetocrystalline anisotropy is present. This anisotropy produces a high coercivity of the unusual FM YMnO3 that can explain the large vertical shift in the hysteresis loops observed in recent experiments (Paul et al 2014 J. Appl. Crystallogr. 47 1054). The correlation between weak exchange bias and the vertical shift is proposed, which calls for reinvestigation of various systems showing vertical shifts.

  17. Optical properties of LFZ grown β-Ga2O3:Eu3+ fibres

    NASA Astrophysics Data System (ADS)

    Santos, N. F.; Rodrigues, J.; Fernandes, A. J. S.; Alves, L. C.; Alves, E.; Costa, F. M.; Monteiro, T.

    2012-09-01

    Due to their relevance for electronic and optoelectronic applications, transparent conductive oxides (TCO) have been extensively studied in the last decades. Among them, monoclinic β-Ga2O3 is well known by its large direct bandgap of ˜4.9 eV being considered a deep UV TCO suitable for operation in short wavelength optoelectronic devices. The wide bandgap of β-Ga2O3 is also appropriate for the incorporation of several electronic energy levels such as those associated with the intra-4fn configuration of rare earth ions. Among these, Eu3+ ions (4f6) are widely used as a red emitting probes both in organic and inorganic compounds. In this work, undoped and Eu2O3 doped (0.1 and 3.0 mol%) Ga2O3 crystalline fibres were grown by the laser floating zone approach. All fibres were found to stabilize in the monoclinic β-Ga2O3 structure while for the heavily doped fibres the X-ray diffraction patterns show, in addition a cubic europium gallium garnet phase, Eu3Ga5O12. The spectroscopic properties of the undoped and Eu doped fibres were analysed by Raman spectroscopy, low temperature photoluminescence (PL) and photoluminescence excitation (PLE). The Eu3+ luminescence is mainly originated in the garnet, from where different europium site locations can be inferred. The spectral analysis indicates that at least one of the centres corresponds to Eu3+ ions in dodecahedral site symmetry. For the lightly doped samples, the spectral shape and intensity ratio of the 5D0 → 7FJ transitions is totally different from those on Eu3Ga5O12, suggesting that the emitting ions are placed in low symmetry sites in the β-Ga2O3 host.

  18. Variability of O3 and NO2 Profile Shapes during DISCOVER-AQ July 2011

    NASA Astrophysics Data System (ADS)

    Flynn, C.; Pickering, K. E.; Lamsal, L. N.; Herman, J. R.; Weinheimer, A. J.; Chen, G.; Liu, X.; Loughner, C.; Thompson, A. M.

    2014-12-01

    The first deployment of the NASA Earth Venture -1 DISCOVER-AQ (Deriving Information on Surface conditions from Column and Vertically Resolved Observations Relevant to Air Quality) project was conducted during July 2011 in the Baltimore-Washington region. The P-3B aircraft provided in situ vertical profiles of meteorological quantities, trace gases, and aerosols over six Maryland Department of the Environment (MDE) air quality monitoring sites over fourteen flight days. Additionally, two sites launched ozonesondes and operated tethersondes during the campaign, supplementing the P-3B profiles. A major goal of DISCOVER-AQ is to understand the processes linking column abundances to surface concentrations for O3 and NO2, which includes understanding the variability of the in situ O3 and NO2 profile shapes used to compute the lower tropospheric column abundances. In support of this goal, a hierarchical cluster analysis was performed for the O3 and NO2 P-3B and sonde profiles for the Maryland 2011 campaign, allowing classes of profile shapes to be identified at each surface site. These classes were related to differences in vertical mixing, as indicated by profiles of potential temperature, CO, and short-lived trace gas species, as well as the impact of the bay breeze at one site. Such an analysis of profile variability will also be useful to assess the representativeness of the assumed profile shapes used in satellite retrievals for O3 and NO2. Further, profile shapes for these species were compared with those from the CMAQ model to assess its performance. Lastly, the average diurnal variation of the O3 and NO2 column abundances over the July 2011 campaign was assessed at each site to elucidate the diurnal cycle for these columns and results were compared to the once-per-day OMI column observations.

  19. Accurate transport properties for O(3P)-H and O(3P)-H2

    NASA Astrophysics Data System (ADS)

    Dagdigian, Paul J.; Kłos, Jacek; Warehime, Mick; Alexander, Millard H.

    2016-10-01

    Transport properties for collisions of oxygen atoms with hydrogen atoms and hydrogen molecules have been computed by means of time-independent quantum scattering calculations. For the O(3P)-H(2S) interaction, potential energy curves for the four OH electronic states emanating from this asymptote were computed by the internally-contracted multi-reference configuration interaction method, and the R-dependent spin-orbit matrix elements were taken from Parlant and Yarkony [J. Chem. Phys. 110, 363 (1999)]. For the O(3P)-H2 interaction, diabatic potential energy surfaces were derived from internally contracted multi-reference configuration interaction calculations. Transport properties were computed for these two collision pairs and compared with those obtained with the conventional approach that employs isotropic Lennard-Jones (12-6) potentials.

  20. High Curie temperature BiInO3-PbTiO3 films.

    PubMed

    Lee, Sun Young; Wang, Wei; Trolier-McKinstry, Susan

    2014-06-14

    High Curie temperaturepiezoelectricthin films of xBiInO3-(1-x)PbTiO3 (x = 0.10, 0.15, 0.20, and 0.25) were prepared by pulsed laser deposition. It was found that the tetragonality of films decreased with increasing BI content. The dielectric constant and transverse piezoelectric coefficient (e31,f ) exhibit the highest values of 665 and -13.6 C/m(2) at x = 0.20. Rayleigh analyses were performed to identify the extrinsic contributions to dielectric nonlinearity with different x. The composition with x = 0.20 also exhibits the largest extrinsic contributions to dielectric nonlinearity. The Curie temperature (TC ) is increased with increasing x content from 558 to 633 °C; TC at x = 0.20 is about 584 °C.

  1. Negative Capacitance in BaTiO3/BiFeO3 Bilayer Capacitors.

    PubMed

    Hou, Ya-Fei; Li, Wei-Li; Zhang, Tian-Dong; Yu, Yang; Han, Ren-Lu; Fei, Wei-Dong

    2016-08-31

    Negative capacitances provide an approach to reduce heat generations in field-effect transistors during the switch processes, which contributes to further miniaturization of the conventional integrated circuits. Although there are many studies about negative capacitances using ferroelectric materials, the direct observation of stable ferroelectric negative capacitances has rarely been reported. Here, we put forward a dc bias assistant model in bilayer capacitors, where one ferroelectric layer with large dielectric constant and the other ferroelectric layer with small dielectric constant are needed. Negative capacitances can be obtained when external dc bias electric fields are larger than a critical value. Based on the model, BaTiO3/BiFeO3 bilayer capacitors are chosen as study objects, and negative capacitances are observed directly. Additionally, the upward self-polarization effect in the ferroelectric layer reduces the critical electric field, which may provide a method for realizing zero and/or small dc bias assistant negative capacitances.

  2. High Curie temperature BiInO3-PbTiO3 films

    PubMed Central

    Lee, Sun Young; Wang, Wei; Trolier-McKinstry, Susan

    2014-01-01

    High Curie temperature piezoelectric thin films of xBiInO3-(1-x)PbTiO3 (x = 0.10, 0.15, 0.20, and 0.25) were prepared by pulsed laser deposition. It was found that the tetragonality of films decreased with increasing BI content. The dielectric constant and transverse piezoelectric coefficient (e31,f) exhibit the highest values of 665 and −13.6 C/m2 at x = 0.20. Rayleigh analyses were performed to identify the extrinsic contributions to dielectric nonlinearity with different x. The composition with x = 0.20 also exhibits the largest extrinsic contributions to dielectric nonlinearity. The Curie temperature (TC) is increased with increasing x content from 558 to 633 °C; TC at x = 0.20 is about 584 °C. PMID:25316952

  3. NITROGEN SATURATION IN TEMPERATE FOREST ECOSYSTEMS: HYPOTHESES REVISITED. (R825762)

    EPA Science Inventory

    The perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Concl...

  4. Polaronic metal state at the LaAlO3/SrTiO3 interface

    PubMed Central

    Cancellieri, C.; Mishchenko, A. S.; Aschauer, U.; Filippetti, A.; Faber, C.; Barišić, O. S.; Rogalev, V. A.; Schmitt, T.; Nagaosa, N.; Strocov, V. N.

    2016-01-01

    Interplay of spin, charge, orbital and lattice degrees of freedom in oxide heterostructures results in a plethora of fascinating properties, which can be exploited in new generations of electronic devices with enhanced functionalities. The paradigm example is the interface between the two band insulators LaAlO3 and SrTiO3 that hosts a two-dimensional electron system. Apart from the mobile charge carriers, this system exhibits a range of intriguing properties such as field effect, superconductivity and ferromagnetism, whose fundamental origins are still debated. Here we use soft-X-ray angle-resolved photoelectron spectroscopy to penetrate through the LaAlO3 overlayer and access charge carriers at the buried interface. The experimental spectral function directly identifies the interface charge carriers as large polarons, emerging from coupling of charge and lattice degrees of freedom, and involving two phonons of different energy and thermal activity. This phenomenon fundamentally limits the carrier mobility and explains its puzzling drop at high temperatures. PMID:26813124

  5. Polaronic metal state at the LaAlO3/SrTiO3 interface

    NASA Astrophysics Data System (ADS)

    Cancellieri, C.; Mishchenko, A. S.; Aschauer, U.; Filippetti, A.; Faber, C.; Barišić, O. S.; Rogalev, V. A.; Schmitt, T.; Nagaosa, N.; Strocov, V. N.

    2016-01-01

    Interplay of spin, charge, orbital and lattice degrees of freedom in oxide heterostructures results in a plethora of fascinating properties, which can be exploited in new generations of electronic devices with enhanced functionalities. The paradigm example is the interface between the two band insulators LaAlO3 and SrTiO3 that hosts a two-dimensional electron system. Apart from the mobile charge carriers, this system exhibits a range of intriguing properties such as field effect, superconductivity and ferromagnetism, whose fundamental origins are still debated. Here we use soft-X-ray angle-resolved photoelectron spectroscopy to penetrate through the LaAlO3 overlayer and access charge carriers at the buried interface. The experimental spectral function directly identifies the interface charge carriers as large polarons, emerging from coupling of charge and lattice degrees of freedom, and involving two phonons of different energy and thermal activity. This phenomenon fundamentally limits the carrier mobility and explains its puzzling drop at high temperatures.

  6. Polaronic metal state at the LaAlO3/SrTiO3 interface.

    PubMed

    Cancellieri, C; Mishchenko, A S; Aschauer, U; Filippetti, A; Faber, C; Barišić, O S; Rogalev, V A; Schmitt, T; Nagaosa, N; Strocov, V N

    2016-01-27

    Interplay of spin, charge, orbital and lattice degrees of freedom in oxide heterostructures results in a plethora of fascinating properties, which can be exploited in new generations of electronic devices with enhanced functionalities. The paradigm example is the interface between the two band insulators LaAlO3 and SrTiO3 that hosts a two-dimensional electron system. Apart from the mobile charge carriers, this system exhibits a range of intriguing properties such as field effect, superconductivity and ferromagnetism, whose fundamental origins are still debated. Here we use soft-X-ray angle-resolved photoelectron spectroscopy to penetrate through the LaAlO3 overlayer and access charge carriers at the buried interface. The experimental spectral function directly identifies the interface charge carriers as large polarons, emerging from coupling of charge and lattice degrees of freedom, and involving two phonons of different energy and thermal activity. This phenomenon fundamentally limits the carrier mobility and explains its puzzling drop at high temperatures.

  7. X-ray photoelectron spectroscopy and luminescent properties of Y2O3:Bi3+ phosphor

    NASA Astrophysics Data System (ADS)

    Jafer, R. M.; Coetsee, E.; Yousif, A.; Kroon, R. E.; Ntwaeaborwa, O. M.; Swart, H. C.

    2015-03-01

    X-ray photoelectron spectroscopy (XPS) results provided proof for the blue and green emission of Bi3+ in the Y2O3:Bi3+ phosphor. The Y2O3:Bi3+ phosphor was successfully prepared by the combustion process during the investigation of down-conversion materials for Si solar cell application. The X-ray diffraction (XRD) patterns indicated that a single-phase cubic crystal structure with the Ia3 space group was formed. X-ray photoelectron spectroscopy (XPS) showed that the Bi3+ ion replaces the Y3+ ion in two different coordination sites in the Y2O3 crystal structure. The O 1s peak shows five peaks, two which correlate with the O2- ion in Y2O3 in the two different sites, two which correlate with O2- in Bi2O3 in the two different sites and the remaining peak relates to hydroxide. The Y 3d spectrum shows two peaks for the Y3+ ion in the Y2O3 structure in two different sites and the Bi 4f spectrum shows the Bi3+ ion in the two different sites in Bi2O3. The photoluminescence (PL) results showed three broad emission bands in the blue and green regions under ultraviolet excitation, which were also present for panchromatic cathodoluminescence (CL) results. These three peaks have maxima at ∼3.4, 3.0 and 2.5 eV. The PL emission ∼3.0 eV (blue emission) showed two excitation bands centered at ∼3.7 and 3.4 eV while the PL emission at ∼2.5 eV (green emission) showed a broad excitation band from ∼4 to 3.4 eV. The panchromatic CL images were obtained for selected wavelengths at (2.99 ± 0.08) eV (for blue emission) and (2.34 ± 0.06) eV (for green emission). These luminescence results correlate with the XPS results that show that there are two different Bi3+ sites in the host lattice.

  8. Strain effect on the Néel temperature of SrTcO3 from first-principles calculations

    NASA Astrophysics Data System (ADS)

    Ma, Chun-Lan; Dai, Cheng-Min; Chen, Gao-Yuan; Chen, Da; Zang, Tao-Cheng; Ge, Li-Juan; Zhou, Wei; Zhu, Yan

    2015-10-01

    Generalized gradient approximation with on-site Coulomb corrections (GGA+U) method is used to investigate the effect of biaxial strain on the Néel temperature of SrTcO3. A series of hypothetical strains on SrTcO3 are considered to simulate its being applied in SrTcO3-based devices. It is found that a tensile strain will decrease TN, while a compressive strain less than 6.6% will increase TN. At a compressive strain between 5.5% and 6.7%, a highest TN which is about 26.6% higher than that of the bulk material can be obtained. The higher TN can be experimentally achieved by growing SrTcO3 on the common substrate STO/LSAT/NGO/LAO. Our work provides a theoretical basis for the application of high-TN SrTcO3 in small devices.

  9. 2 dimensional electron gas in chemically stable SrSnO3/KTaO3 interface

    NASA Astrophysics Data System (ADS)

    Kwon, Hyukwoo; Park, Chulkwon; Char, Kookrin; Materials and Devices Physics Lab. Team

    2013-03-01

    Recent 2DEGs are mostly formed at the interface of LaAlO3/SrTiO3(LAO/STO) system, which is explained by the polar catastrophe mechanism. Because of large propensity of oxygen vacancy formation in SrTiO3, there remains a possibility that the origin of 2DEG of LAO/STO system may stem from extra charge of oxygen vacancy of SrTiO3, not from the polar layer of LaAlO3. In this presentation, we report the realization of 2DEG at the interface of SrSnO3/KTaO3(SSO/KTO), which is chemically stable due to extremely stable oxygen stoichiometry. This SrSnO3/KTaO3 heterosturcture was epitaxially grown by puled laser deposition and the interface was found atomically matched by transmission electron microscope and reciprocal space mapping. We measured the magnetic property of SSO/KTO heterostructure and acquired a large ferromagnetic signal, which is unchanged in the temperature range of 4 ~300 K by SQUID magnetometer measurement. As SrSnO3 and KTaO3 are non-magnetic materials, this ferromagnetic signal may result from 2DEG at the interface of SSO/KTO. We hope our results can shed lights on the exact mechanism of 2DEGs that are formed at oxide interfaces.

  10. Trends in (LaMnO3)n/(SrTiO3)m superlattices with varying layer thicknesses

    PubMed Central

    Jilili, J.; Cossu, F.; Schwingenschlögl, U.

    2015-01-01

    We investigate the thickness dependence of the structural, electronic, and magnetic properties of (LaMnO3)n/(SrTiO3)m (n, m = 2, 4, 6, 8) superlattices using density functional theory. The electronic structure turns out to be highly sensitive to the onsite Coulomb interaction. In contrast to bulk SrTiO3, strongly distorted O octahedra are observed in the SrTiO3 layers with a systematic off centering of the Ti atoms. The systems favour ferromagnetic spin ordering rather than the antiferromagnetic spin ordering of bulk LaMnO3 and all show half-metallicity, while a systematic reduction of the minority spin band gaps as a function of the LaMnO3 and SrTiO3 layer thicknesses originates from modifications of the Ti dxy states. PMID:26323361

  11. Evidence of rhombohedral structure within BiFeO3 thin film grown on SrTiO3

    NASA Astrophysics Data System (ADS)

    Bae, In-Tae; Naganuma, Hiroshi

    2015-03-01

    Comprehensive crystal structure analysis was performed for a BiFeO3 thin layer (∼30 nm) grown on a SrTiO3 substrate using cross-sectional transmission electron microscopy along three different zone axes. Nano-beam electron diffraction patterns combined with structure factor calculations and high-resolution transmission electron microscopy images unambiguously revealed that the BiFeO3 thin layer grew with a rhombohedral structure identical to its bulk form. No evidence of monoclinic and/or tetragonal distortion was found. The rhombohedral BiFeO3 thin layer was found to grow onto SrTiO3 by maintaining an epitaxial relationship in a manner minimizing the lattice mismatch at the BiFeO3/SrTiO3 interface.

  12. Catalytic combustion of benzene over nanosized LaMnO3 perovskite oxides.

    PubMed

    Jung, Won Young; Lim, Kwon Taek; Lee, Gun Dae; Lee, Man Sig; Hong, Seong-Soo

    2013-09-01

    In this study, LaMnO3 perovskite type oxides were successfully prepared using the malic acid method. The oxides were characterized by TG/DTA, XRD, XPS, TEM and H2-TPR and their catalytic activities for the combustion of benzene were determined. Almost all of the catalysts showed perovskite crystalline phase and had a particle size of 15-60 nm. The LaMnO3 catalysts prepared with more than 1.0 mol of malic acid showed the highest activity and the conversion reached almost 100% at 310 degrees C. The catalysts were modified to enhance the activity by substituting the metal at the A or B site of the perovskite oxides. In the LaMnO3-type catalyst, the partial substitution of Sr into site A enhanced the catalytic activity during benzene combustion. In addition, the partial substitution of Co into site B also increased the catalytic activity and the catalytic activity was in the following order: Co > Cu > Fe in the LaMn1_xBxO3(B = Co, Fe, Cu) type catalysts.

  13. Impacts of greenhouse gases on epicuticular waxes of Populus tremuloides Michx.: results from an open-air exposure and a natural O3 gradient.

    PubMed

    Mankovská, B; Percy, K E; Karnosky, D F

    2005-10-01

    Epicuticular waxes of three trembling aspen (Populus tremuloides Michx.) clones differing in O3 tolerance were examined over six growing seasons (1998-2003) at three bioindicator sites in the Lake States region of the USA and at FACTS II (Aspen FACE) site in Rhinelander, WI. Differences in epicuticular wax structure were determined by scanning electron microscopy and quantified by a coefficient of occlusion. Statistically significant increases in stomatal occlusion occurred for the three O3 bioindicator sites, with the higher O3 sites having the most affected stomata for all three clones as well as for all treatments including elevated CO2, elevated O3, and elevated CO2 + O3. We recorded statistically significant differences between aspen clones and between sampling period (spring, summer, fall). We found no statistically significant differences between treatments or aspen clones in stomatal frequency.

  14. Structural relaxation around Cr3+ in YAlO3-YCrO3 perovskites from electron absorption spectra.

    PubMed

    Cruciani, Giuseppe; Ardit, Matteo; Dondi, Michele; Matteucci, Francesco; Blosi, Magda; Dalconi, Maria Chiara; Albonetti, Stefania

    2009-12-10

    The structural relaxation around Cr(3+) in YAl(1-x)Cr(x)O(3) perovskites was investigated and compared with analogous Cr-Al joins (corundum, spinel, garnet). Eight compositions (x(Cr)((3+)) from 0 to 1) were prepared by sol-gel combustion and were analyzed by a combined X-ray diffraction (XRD) and electron absorption spectroscopy (EAS) approach. The unit cell parameters and the XRD averaged octahedral (Cr,Al)-O and ([VIII])Y-O bond distances scale linearly with the chromium fraction. The optical parameters show an expected decrease of crystal field strength (10Dq) and an increase of covalency (B(35)) and polarizability (B(55)) toward YCrO(3), but a nonlinear trend outlines some excess 10Dq below x(Cr)((3+)) approximately 0.4. The local Cr-O bond lengths, as calculated from EAS, indicate a compression from 1.98 A (x(Cr)((3+)) = 1.0) down to 1.95 A (x(Cr)((3+)) = 0.035) so that the relaxation coefficient of perovskite (epsilon = 0.54) is the lowest in comparison with garnet (epsilon = 0.74), spinel (epsilon = 0.68), and corundum (epsilon = 0.58) in contrast with its structural features. The enhanced covalent character of the Cr(3+)-O-Cr(3+) bond in the one-dimensional arrangement of corner-sharing octahedra can be invoked as a factor limiting the perovskite polyhedral network flexibility. The increased probability of Cr-O-Cr clusters for x(Cr)((3+)) greater than approximately 0.4 is associated to diverging trends of nonequivalent interoctahedral angles. The relatively low relaxation degree of Y(Al,Cr)O(3) can be also understood by considering an additional contribution to 10Dq because of the electrostatic potential of the rest of the lattice ions upon the localized electrons of the CrO(6) octahedron. Such an "excess" of 10Dq increases when the point symmetry of the Cr site is low, as in perovskite, and would be affected by the change of yttrium effective coordination number observed by XRD for x(Cr)((3+)) greater than approximately 0.4. This would justify the

  15. Elemental and lattice-parameter mapping of binary oxide superlattices of (LaNiO3)4/(LaMnO3)2 at atomic resolution

    NASA Astrophysics Data System (ADS)

    Kwon, Ji-Hwan; Lu, Ping; Hoffman, Jason; Yuan, Renliang; Yoon, Aram; Bhattacharya, Anand; Zuo, Jian-Min

    2017-01-01

    We construct the elemental distribution and lattice strain maps from the measured atomic column positions in a (LaNiO3)4/(LaMnO3)2 superlattice over a large field of view. The correlation between the distribution of B-cations and the lattice parameter in the form of Vegard’s law is validated using atomic resolution energy dispersive x-ray spectroscopy (EDS). The maps show negligible Mn intermixing in the LaNiO3 layer, while Ni intermixing in the LaMnO3 layer improves away from the substrate interface to 9.5 atomic% from the 8th period onwards, indicating that the superlattice interfacial sharpness is established as the distance from the substrate increases. The maps allow an observation of the compositional defects of the B-sites, which is not possible by Z-contrast alone. Thus, this study demonstrates a promising approach for atomic scale correlative study of lattice strain and composition, and a method for the calibration of atomic resolution EDS maps.

  16. Dielectric and AC-conductivity studies of Dy2O3 doped (K0.5Na0.5)NbO3 ceramics

    NASA Astrophysics Data System (ADS)

    Peddigari, Mahesh; Thota, Subhash; Pamu, Dobbidi

    2014-08-01

    (K0.5Na0.5)NbO3 + x wt.% Dy2O3 (x = 0-1.5) ferroelectric ceramics were prepared by conventional solid state reaction method. XRD patterns revealed that orthorhombic symmetry has transformed into psuedocubic symmetry with increasing the substitution of Dy3+ in the Na+ site. Temperature and frequency dependences of relative dielectric permittivity maximum conforms the transformation from normal ferroelectric to relaxor ferroelectric behaviour. Frequency dependence of the relative dielectric permittivity maximum temperature observed for the samples with x ≥ 1.0 and satisfied the Vogel-Fulcher law. The diffuseness exponent γ (1.27-1.95) estimated from the high temperature slopes of the diffused dielectric permittivity data reveals that the degree of relaxor behavior increases with increasing the amount of Dy2O3. The temperature dependence of AC-conductivity σAC (T) analysis in the range 310 K < T < 470 K reveals the existence of variable range hopping of charge carriers with average hopping length RH and hopping energy EH are in the range 8.5-27 Å and 48-153 meV, respectively. Voltage dependent dielectric constant measurements confirm the ferroelectric nature of KNN+ x wt% Dy2O3 ceramics.

  17. NMR spin-lattice relaxation study of 7Li and 93Nb nuclei in Ti- or Fe-doped LiNbO3:Mg single crystals

    NASA Astrophysics Data System (ADS)

    Yeom, Tae Ho; Lim, Ae Ran

    2016-04-01

    In this study, to understand the effects of paramagnetic impurities, we investigated the temperature dependent of the spin-lattice relaxation times of pure LiNbO3, LiNbO3:Mg, LiNbO3:Mg/Ti, LiNbO3:Mg/Fe, and LiNbO3:Mg/Fe (thermally treated at 500°C) single crystals. The results for the LiNbO3:Mg single crystals doped with Fe3+ or Ti3+ are discussed with respect to the site distribution and atomic mobility of Li and Nb. In addition, the effects of a thermal treatment on LiNbO3:Mg/Fe single crystals were examined based on the T1 analysis of 7Li and 93Nb. It was found that the presence of impurities in the crystals induced systematic changes of activation energies concerning atomic mobility.

  18. Impact of low level praseodymium substitution on the magnetic properties of YCrO3 orthochromites

    NASA Astrophysics Data System (ADS)

    Kumar, Surendra; Coondoo, Indrani; Rao, Ashok; Lu, Bo-Han; Kuo, Yung-Kang; Kholkin, Andrei L.; Panwar, Neeraj

    2017-04-01

    Praseodymium (Pr) modified yttrium orthochromites (YCrO3 with Pr =0% and 5% at Y-sites) have been investigated with the aim of exploring the impact of low level Pr substitution on the magnetic properties including magnetization reversal, spin reorientation, and exchange bias of YCrO3 compound. The samples exhibit a distorted orthorhombic structure with Pnma space group. A negative magnetization (or magnetization reversal) was observed under zero-field cooled (ZFC) mode for the pristine YCrO3 sample, whereas such a feature disappeared with a 5% Pr substitution. In addition, the Pr-doped samples exhibited a spin reorientation behaviour which was absent in the pristine sample. Most interestingly, the ZFC magnetic hysteresis loops revealed a left and upward shift, resembling a negative exchange bias effect. These results indicate the effectiveness of low level doping in tailoring the magnetic properties of orthochromites.

  19. Direct spectroscopic observation of a shallow hydrogenlike donor state in insulating SrTiO3.

    PubMed

    Salman, Z; Prokscha, T; Amato, A; Morenzoni, E; Scheuermann, R; Sedlak, K; Suter, A

    2014-10-10

    We present a direct spectroscopic observation of a shallow hydrogenlike muonium state in SrTiO(3) which confirms the theoretical prediction that interstitial hydrogen may act as a shallow donor in this material. The formation of this muonium state is temperature dependent and appears below ∼ 70K. From the temperature dependence we estimate an activation energy of ∼ 50 meV in the bulk and ∼ 23 meV near the free surface. The field and directional dependence of the muonium precession frequencies further supports the shallow impurity state with a rare example of a fully anisotropic hyperfine tensor. From these measurements we determine the strength of the hyperfine interaction and propose that the muon occupies an interstitial site near the face of the oxygen octahedron in SrTiO(3). The observed shallow donor state provides new insight for tailoring the electronic and optical properties of SrTiO(3)-based oxide interface systems.

  20. Magnetic and Structural Transition Properties of Niobium-Doped BiFeO3 Thin Films

    NASA Astrophysics Data System (ADS)

    Chen, H. Z.; Kao, M. C.; Young, S. L.

    2013-06-01

    Niobium-substituted BiFeO3(BiFe1-xNbxO3BFNO) thin films were successfully deposited on Pt(111)/Ti/SiO2/Si(100) substrates by spin coating with a sol-gel technology and rapid thermal annealing. The effects of Nb content (x = 0 0.08) on the microstructure, magnetic and multiferroic properties of thin films were investigated. The result of X-ray diffraction analysis shows that the BFNO thin films have rhombohedral (R3c) to tetragonal (P4mm) phase transition at x = 0.06. The Nb doping in the B-site of BiFeO3 could induce the appearance of the spontaneous magnetization and polarization by the phase transition of rhombohedral-to-tetragonal. The BFNO thin films with x = 0.06 exhibits the maximum remanent magnetization (2Mr) of 5.2 emu/g.

  1. Structural, magnetic and electrical properties of SrRuO3 films and SrRuO3/SrTiO3 superlattices.

    PubMed

    Bern, F; Ziese, M; Setzer, A; Pippel, E; Hesse, D; Vrejoiu, I

    2013-12-11

    SrRuO3 films and SrRuO3/SrTiO3 superlattices grown on SrTiO3(001) were studied by structural, magnetic, magnetoresistance and Hall effect measurements. The superlattices showed heteroepitaxial growth with coherent interfaces and a Ru/Ti diffusion region of 1-1.5 unit cells. The resistivity had metallic character above a critical thickness of 3-4 unit cells, becoming insulating below. There was no hint of conduction processes along the interfaces. Both magnetization and magnetoresistance measurements showed an increase of the magnetic anisotropy, consistent with magnetostriction effects. The magnetostriction coefficient was estimated as λ100 ∼ 1.4 × 10(-4). Three unit cell thick SrRuO3 layers in SrRuO3/SrTiO3 superlattices were found to have tetragonal crystal symmetry, as deduced from the sign change of the anomalous Hall constant.

  2. Increased phytotoxic O3 dose accelerates autumn senescence in an O3-sensitive beech forest even under the present-level O3

    NASA Astrophysics Data System (ADS)

    Kitao, Mitsutoshi; Yasuda, Yukio; Kominami, Yuji; Yamanoi, Katsumi; Komatsu, Masabumi; Miyama, Takafumi; Mizoguchi, Yasuko; Kitaoka, Satoshi; Yazaki, Kenichi; Tobita, Hiroyuki; Yoshimura, Kenichi; Koike, Takayoshi; Izuta, Takeshi

    2016-09-01

    Ground-level ozone (O3) concentrations are expected to increase over the 21st century, especially in East Asia. However, the impact of O3 has not been directly assessed at the forest level in this region. We performed O3 flux-based risk assessments of carbon sequestration capacity in an old cool temperate deciduous forest, consisting of O3-sensitive Japanese beech (Fagus crenata), and in a warm temperate deciduous and evergreen forest dominated by O3-tolerant Konara oak (Quercus serrata) based on long-term CO2 flux observations. On the basis of a practical approach for a continuous estimation of canopy-level stomatal conductance (Gs), higher phytotoxic ozone dose above a threshold of 0 uptake (POD0) with higher Gs was observed in the beech forest than that in the oak forest. Light-saturated gross primary production, as a measure of carbon sequestration capacity of forest ecosystem, declined earlier in the late growth season with increasing POD0, suggesting an earlier autumn senescence, especially in the O3-sensitive beech forest, but not in the O3-tolerant oak forest.

  3. Increased phytotoxic O3 dose accelerates autumn senescence in an O3-sensitive beech forest even under the present-level O3

    PubMed Central

    Kitao, Mitsutoshi; Yasuda, Yukio; Kominami, Yuji; Yamanoi, Katsumi; Komatsu, Masabumi; Miyama, Takafumi; Mizoguchi, Yasuko; Kitaoka, Satoshi; Yazaki, Kenichi; Tobita, Hiroyuki; Yoshimura, Kenichi; Koike, Takayoshi; Izuta, Takeshi

    2016-01-01

    Ground-level ozone (O3) concentrations are expected to increase over the 21st century, especially in East Asia. However, the impact of O3 has not been directly assessed at the forest level in this region. We performed O3 flux-based risk assessments of carbon sequestration capacity in an old cool temperate deciduous forest, consisting of O3-sensitive Japanese beech (Fagus crenata), and in a warm temperate deciduous and evergreen forest dominated by O3-tolerant Konara oak (Quercus serrata) based on long-term CO2 flux observations. On the basis of a practical approach for a continuous estimation of canopy-level stomatal conductance (Gs), higher phytotoxic ozone dose above a threshold of 0 uptake (POD0) with higher Gs was observed in the beech forest than that in the oak forest. Light-saturated gross primary production, as a measure of carbon sequestration capacity of forest ecosystem, declined earlier in the late growth season with increasing POD0, suggesting an earlier autumn senescence, especially in the O3-sensitive beech forest, but not in the O3-tolerant oak forest. PMID:27601188

  4. Transformation of dissolved organic matter in concentrated leachate from nanofiltration during ozone-based oxidation processes (O3, O3/H2O2 and O3/UV).

    PubMed

    Wang, Hua-Wei; Li, Xiao-Yue; Hao, Zhi-Peng; Sun, Ying-Jie; Wang, Ya-Nan; Li, Wei-Hua; Tsang, Yiu Fai

    2017-04-15

    In this study, the transformation of dissolved organic matter (DOM) in nanofiltration concentrated leachate during three ozone-based oxidation processes (i.e., O3, O3/H2O2 and O3/UV) was investigated. The transformation characteristics of DOM were evaluated by gel filtration chromatography (GFC), XAD-8 resin fractionation, excitation-emission matrix fluorescence spectroscopy (EEM) and Fourier transform infrared spectroscopy (FTIR). Compared with O3-alone process, the removal efficiencies of COD, TOC, and color were improved in O3-combined processes (i.e., O3/H2O2 and O3/UV) approximately by 10-15%, 7-15%, and 15-20%, respectively. Humic acid (HA) was completely degraded and preferentially reacted with the oxidants during ozonation processes. HA was first converted into fulvic acid (FA), and then the majority of these intermediates were further converted to hydrophilic fraction (HyI). The GFC results indicated that the broader molecular weight distribution of DOM was observed, and high molecular weight DOM (i.e., 0.45 μm-100 kDa) was successfully converted to low molecular weight organics in the range of 1-10 kDa after ozonation reactions. The EEM spectra also showed that HA and FA were effectively converted into HyI after ozonation for 90 min. It is suggested that ozone-based oxidation processes could effectively change the DOM distribution and fluorescence features of concentrated leachate.

  5. FixO3: Advancement towards Open Ocean Observatory Data Management Harmonisation

    NASA Astrophysics Data System (ADS)

    Behnken, Andree; Pagnani, Maureen; Huber, Robert; Lampitt, Richard

    2015-04-01

    Since 2002 there has been a sustained effort, supported as European framework projects, to harmonise both the technology and the data management of Open Ocean fixed observatories run by European nations. FixO3 started in September 2013, and for 3 more years will coordinate the convergence of data management best practice across a constellation of moorings in the Atlantic, in both hemispheres, and in the Mediterranean. To ensure the continued existence of these unique sources of oceanographic data as sustained observatories it is vital to improve access to the data collected, both in terms of methods of presentation, real-time availability, long-term archiving and quality assurance. The data management component of FixO3 improves access to marine observatory data by harmonising data management standards, formats and workflows covering the complete life cycle of data from real time data acquisition to long-term archiving. Legal and data policy aspects have been examined and discussed to identify transnational barriers to open-access to marine observatory data. As a result, a harmonised FixO3 data policy was drafted, which provides a formal basis for data exchange between FixO3 infrastructures, and also enables open access to data for the general public. FixO3 interacts with other European infrastructures such as EMODnet, SeaDataNet, PANGAEA, and especially aims to harmonise efforts with OceanSites and MyOcean. The project landing page (www.fixo3.eu) offers detailed information about every observatory as well as data visualisations and direct downloads. In addition to this, metadata for all FixO3 - relevant data are available from the searchable FixO3 metadata catalogue, which is also accessible from the project web page. This catalogue is hosted by PANGAEA and receives updates in regular intervals. The FixO3 Standards & Services registry ties in with the GEOSS Components and Services Registry (CSR) and provides additional observatory information. The data management

  6. First-Principles Calculation of Solution Energy of Alkaline-Earth Metal Elements to BaTiO3

    NASA Astrophysics Data System (ADS)

    Moriwake, Hiroki; Hirayama, Tsukasa; Ikuhara, Yuichi; Tanaka, Isao

    2007-10-01

    Quantitative analysis of the solution energy of alkaline-earth metal elements to perovskite-type BaTiO3 was carried out by a first-principles calculation combined with thermodynamics theory. The solution energies of neutral solute and a compensated solute with an oxygen vacancy were systematically calculated. They were obtained for two cation sites and four thermodynamical conditions with different chemical potentials of constituent atoms. Both Ca and Sr preferably occupy the Ba site of BaTiO3. On the other hand, Mg occupies the Ti site. This corresponds well to the widely accepted experimental findings regarding site preference. Moreover, under the condition of coexising BaO, CaO and BaTiO3, energy difference between the Ba-site solution and O-vacancy compensated Ti-site solution of Ca ions has been found to be smaller than that of Sr. Under this condition, the O-vacancy compensated Ti-site solution of Ca should be favorable compared with that of Sr. The same number of oxygen vacancies as Ca ions occupying Ti sites can be introduced. This also explains well experimental feature of the Ca-doped BaTiO3-based nonreducible multilayer ceramics capacitor (MLCC) materials regarding solution site of the Ca ion and abundance of O-vacancy.

  7. Transcriptional regulation of FoxO3 gene by glucocorticoids in murine myotubes.

    PubMed

    Kuo, Taiyi; Liu, Patty H; Chen, Tzu-Chieh; Lee, Rebecca A; New, Jenny; Zhang, Danyun; Lei, Cassandra; Chau, Andy; Tang, Yicheng; Cheung, Edna; Wang, Jen-Chywan

    2016-04-01

    Glucocorticoids and FoxO3 exert similar metabolic effects in skeletal muscle. FoxO3 gene expression was increased by dexamethasone (Dex), a synthetic glucocorticoid, both in vitro and in vivo. In C2C12 myotubes the increased expression is due to, at least in part, the elevated rate of FoxO3 gene transcription. In the mouse FoxO3 gene, we identified three glucocorticoid receptor (GR) binding regions (GBRs): one being upstream of the transcription start site, -17kbGBR; and two in introns, +45kbGBR and +71kbGBR. Together, these three GBRs contain four 15-bp glucocorticoid response elements (GREs). Micrococcal nuclease (MNase) assay revealed that Dex treatment increased the sensitivity to MNase in the GRE of +45kbGBR and +71kbGBR upon 30- and 60-min Dex treatment, respectively. Conversely, Dex treatment did not affect the chromatin structure near the -17kbGBR, in which the GRE is located in the linker region. Dex treatment also increased histone H3 and/or H4 acetylation in genomic regions near all three GBRs. Moreover, using chromatin conformation capture (3C) assay, we showed that Dex treatment increased the interaction between the -17kbGBR and two genomic regions: one located around +500 bp and the other around +73 kb. Finally, the transcriptional coregulator p300 was recruited to all three GBRs upon Dex treatment. The reduction of p300 expression decreased FoxO3 gene expression and Dex-stimulated interaction between distinct genomic regions of FoxO3 gene identified by 3C. Overall, our results demonstrate that glucocorticoids activated FoxO3 gene transcription through multiple GREs by chromatin structural change and DNA looping.

  8. A modified micrometeorological gradient method for estimating O3 dry deposition over a forest canopy

    NASA Astrophysics Data System (ADS)

    Wu, Z. Y.; Zhang, L.; Wang, X. M.; Munger, J. W.

    2015-01-01

    Small pollutant concentration gradients between levels above a plant canopy result in large uncertainties in estimated air-surface exchange fluxes when using existing micrometeorological gradient methods, including the aerodynamic gradient method (AGM) and the modified Bowen-Ratio method (MBR). A modified micrometeorological gradient method (MGM) is proposed in this study for estimating O3 dry deposition fluxes over a forest canopy using concentration gradients between a level above and a level below the canopy top, taking advantage of relatively large gradients between these levels due to significant pollutant uptake at top layers of the canopy. The new method is compared with the AGM and MBR methods and is also evaluated using eddy-covariance (EC) flux measurements collected at the Harvard Forest Environmental Measurement Site, Massachusetts during 1993-2000. All the three gradient methods (AGM, MBR and MGM) produced similar diurnal cycles of O3 dry deposition velocity (Vd(O3)) to the EC measurements, with the MGM method being the closest in magnitude to the EC measurements. The multi-year average Vd(O3) differed significantly between these methods, with the AGM, MBR and MGM method being 2.28, 1.45 and 1.18 times of that of the EC. Sensitivity experiments identified several input parameters for the MGM method as first-order parameters that affect the estimated Vd(O3). A 10% uncertainty in the wind speed attenuation coefficient or canopy displacement height can cause about 10% uncertainty in the estimated Vd(O3). An unrealistic leaf area density vertical profile can cause an uncertainty of a factor of 2.0 in the estimated Vd(O3). Other input parameters or formulas for stability functions only caused an uncertainly of a few percent. The new method provides an alternative approach in monitoring/estimating long-term deposition fluxes of similar pollutants over tall canopies.

  9. A modified micrometeorological gradient method for estimating O3 dry depositions over a forest canopy

    NASA Astrophysics Data System (ADS)

    Wu, Z. Y.; Zhang, L.; Wang, X. M.; Munger, J. W.

    2015-07-01

    Small pollutant concentration gradients between levels above a plant canopy result in large uncertainties in estimated air-surface exchange fluxes when using existing micrometeorological gradient methods, including the aerodynamic gradient method (AGM) and the modified Bowen ratio method (MBR). A modified micrometeorological gradient method (MGM) is proposed in this study for estimating O3 dry deposition fluxes over a forest canopy using concentration gradients between a level above and a level below the canopy top, taking advantage of relatively large gradients between these levels due to significant pollutant uptake in the top layers of the canopy. The new method is compared with the AGM and MBR methods and is also evaluated using eddy-covariance (EC) flux measurements collected at the Harvard Forest Environmental Measurement Site, Massachusetts, during 1993-2000. All three gradient methods (AGM, MBR, and MGM) produced similar diurnal cycles of O3 dry deposition velocity (Vd(O3)) to the EC measurements, with the MGM method being the closest in magnitude to the EC measurements. The multi-year average Vd(O3) differed significantly between these methods, with the AGM, MBR, and MGM method being 2.28, 1.45, and 1.18 times that of the EC, respectively. Sensitivity experiments identified several input parameters for the MGM method as first-order parameters that affect the estimated Vd(O3). A 10% uncertainty in the wind speed attenuation coefficient or canopy displacement height can cause about 10% uncertainty in the estimated Vd(O3). An unrealistic leaf area density vertical profile can cause an uncertainty of a factor of 2.0 in the estimated Vd(O3). Other input parameters or formulas for stability functions only caused an uncertainly of a few percent. The new method provides an alternative approach to monitoring/estimating long-term deposition fluxes of similar pollutants over tall canopies.

  10. Preparation of magnetic recoverable nanosize Cu-Fe2O3/Fe photocatalysts.

    PubMed

    Kang, Hsu-Ya; Wang, H Paul

    2013-07-02

    Iron based catalysts generally have the advantage of the easily operated magnetically recovery from application sites. In the present work, paramagnetic iron and copper core-shell nanoparticles having the iron fractions (X(Fe) = Fe/(Cu+Fe)) of 0.33-1.0 were prepared and characterized by in situ synchrotron X-ray absorption and scattering spectroscopy. During the temperature-programmed carbonization (TPC) of Cu(2+)- and Fe(3+)-β-cyclodextrin (CD) complexes, a rapid reduction of Cu(II) occurs at about 453 K together with a growth of the metallic copper (Cu). Iron proceeds in the distinct growth path. At 453-513 K, the Fe(III) → Fe(II) → Fe consecutive reduction is observed. The unreduced Fe(III) (7-13%) is coated on the surfaces of the Fe nanoparticles (as Fe2O3/Fe). Growth of the Fe nanoparticle is inhibited by the surface Fe2O3, while the steady growth in Cu is observed. The Cu has a size range of 14-18 nm in diameter, compared to the small Fe2O3/Fe ones (3-6 nm). Under the UV-visible light irradiation for four hours, methylene blue can be photocatalytically degraded (>90%) by the (Cu-Fe2O3/Fe)@C. The (Cu-Fe2O3/Fe)@C photocatalysts can effectively oxidize dye molecules, providing a promising alternative for dye degradation using solar energy. Recovery of the (Cu-Fe2O3/Fe)@C photocatalysts can be attained by applying external magnetic field to trap the ferromagnetic Cu-Fe2O3/Fe nanoparticles, which suggests an economically attractive process, especially applied in photocatalytic degradation of dye-contaminated wastewater.

  11. Impacts of Elevated Atmospheric CO 2 and O 3 on Paper Birch ( Betula papyrifera ): Reproductive Fitness

    DOE PAGES

    Darbah, Joseph N. T.; Kubiske, Mark E.; Nelson, Neil; ...

    2007-01-01

    Atmospheric CO 2 and tropospheric O 3 are rising in many regions of the world. Little is known about how these two commonly co-occurring gases will affect reproductive fitness of important forest tree species. Here, we report on the long-term effects of CO 3 and O 3 for paper birch seedlings exposed for nearly their entire life history at the Aspen FACE (Free Air Carbon Dioxide Enrichment) site in Rhinelander, WI. Elevated CO 2 increased both male and female flower production, while elevated O 3 increased female flower production compared to trees in control rings. Interestingly, very little floweringmore » has yet occurred in combined treatment. Elevated CO 2 had significant positive effect on birch catkin size, weight, and germination success rate (elevated CO 2 increased germination rate of birch by 110% compared to ambient CO 2 concentrations, decreased seedling mortality by 73%, increased seed weight by 17%, increased root length by 59%, and root-to-shoot ratio was significantly decreased, all at 3 weeks after germination), while the opposite was true of elevated O 3 (elevated O 3 decreased the germination rate of birch by 62%, decreased seed weight by 25%, and increased root length by 15%). Under elevated CO 2 , plant dry mass increased by 9 and 78% at the end of 3 and 14 weeks, respectively. Also, the root and shoot lengths, as well as the biomass of the seedlings, were increased for seeds produced under elevated CO 2 , while the reverse was true for seedlings from seeds produced under the elevated O 3 . Similar trends in treatment differences were observed in seed characteristics, germination, and seedling development for seeds collected in both 2004 and 2005. Our results suggest that elevated CO 2 and O 3 can dramatically affect flowering, seed production, and seed quality of paper birch, affecting reproductive fitness of this species.« less

  12. Distribution and budget of O3 in the troposphere calculated with a chemistry general circulation model

    NASA Astrophysics Data System (ADS)

    Roelofs, Geert-Jan; Lelieveld, Jos

    1995-10-01

    We present results of global tropospheric chemistry simulations with the coupled chemistry/atmospheric general circulation model ECHAM. Ultimately, the model will be used to study climate changes induced by anthropogenic influences on the chemistry of the atmosphere; meteorological parameters that are important for the chemistry, such as temperature, humidity, air motions, cloud and rain characteristics, and mixing processes are calculated on-line. The chemical part of the model describes background tropospheric CH4-CO-NOx-HOx photochemistry. Emissions of NO and CO, surface concentrations of CH4, and stratospheric concentrations of O3 and NOy are prescribed as boundary conditions. Calculations of the tropospheric O3 budget indicate that seasonal variabilities of the photochemical production and of injection from the stratosphere are represented realistically, although some aspects of the model still need improvement. Comparisons of calculated O3 surface concentrations and O3 profiles with available measurements show that the model reproduces O3 distributions in remote tropical and midlatitudinal sites. Also, the model matches typical profiles connected with deep convection in the Intertropical Convergence Zone (ITCZ). However, the model tends to underestimate O3 concentrations at the poles and in relatively polluted regions. These underestimates are caused by the poor representation of tropopause foldings in midlatitudes, which form a significant source of tropospheric O3 from the stratosphere, too weak transport to the poles, and the neglect of higher hydrocarbon chemistry. Also, mixing of polluted continental boundary layer air into the free troposphere may be underestimated. We discuss how these model deficiencies will be improved in the future.

  13. Non-linear Electrical Characteristics of ZnO Modified by Trioxides Sb2O3, Bi2O3, Fe2O3, Al2O3 and La2O3

    NASA Astrophysics Data System (ADS)

    Mekap, Anita; Das, Piyush R.; Choudhary, R. N. P.

    2016-08-01

    The non-linear behavior of polycrystalline-ZnO-based voltage-dependent resistors is considered in the present study. A high-temperature solid-state reaction route was used to synthesize polycrystalline samples of ZnO modified by small amounts of the trioxides Sb2O3, Bi2O3, Fe2O3, etc. in various proportions. X-ray diffraction and scanning electron microscopy techniques were used to study the structural and microstructural characteristics of modified ZnO. Detailed studies of non-linear phenomena of the I-V characteristics, dielectric permittivity ( ɛ r), impedance ( Z), etc. of the samples have provided many interesting results. All the samples exhibited dielectric anomaly. Non-linear variation in polarization with electric field for all the samples was observed. Moreover, significant non-linearity in the I-V characteristics was observed in the breakdown region of all the samples at room temperature. The non-linear coefficient ( α) in different cases, i.e. for I- V, ɛ r- f, ɛ r- T, and ɛ r- Z, was calculated and found to be appreciable. The frequency dependence of ac conductivity suggests that the material obeys Jonscher's universal power law.

  14. Structural and magnetic properties of isovalently substituted multiferroic BiFeO3: Insights from Raman spectroscopy

    NASA Astrophysics Data System (ADS)

    Bielecki, Johan; Svedlindh, Peter; Tibebu, Dessie T.; Cai, Shengzhen; Eriksson, Sten-G.; Börjesson, Lars; Knee, Christopher S.

    2012-11-01

    Raman spectra, supplemented by powder x-ray diffraction and magnetization data of isovalently A- and B-site substituted BiFeO3 in the Bi1-xLaxFeO3 (0≤x≤1), Bi1-xTbxFeO3 (0≤x≤0.2), and Bi0.9Sm0.1Fe1-xMnxO3 (0≤x≤0.3) series, are presented. A good agreement between the structural transitions observed by x-ray diffraction and the vibrational modes observed in the Raman spectra is found over the whole substitutional ranges, and in particular we find spectroscopic signatures of a PbZrO3-type structure for Bi0.8La0.2FeO3. Mode assignments in the substituted materials are made based on Raman spectra of the end-members BiFeO3 and LaFeO3. Moreover, by comparing spectra from all samples with R3c structure, the phonon assignment in BiFeO3 is revisited. A close connection between the degree of octahedral tilt and the Raman shift of the A1 oxygen a-a-a- tilt mode is established. An explanation for the strong second-order scattering observed in Bi1-xLaxFeO3 and Bi1-xTbxFeO3 is suggested, including the assignment of the previously mysterious BiFeO3 mode at 620 cm-1. Finally, the magnetization data indicates a transition from a cycloidal modulated state towards a canted antiferromagnet with increasing A-site substitution, while Bi0.9Sm0.1Fe1-xMnxO3 with x=0 and 0.15 exhibit an anomalous closing of the hysteresis loop at low temperatures. For low A-site substitution levels (x≤0.1) the decreasing Raman intensity of the Fe derived modes correlates with the partial destruction of the spin cycloid as the substitution level increases.

  15. Coherent 3D nanostructure of γ-Al2O3: Simulation of whole X-ray powder diffraction pattern

    NASA Astrophysics Data System (ADS)

    Pakharukova, V. P.; Yatsenko, D. A.; Gerasimov, E. Yu.; Shalygin, A. S.; Martyanov, O. N.; Tsybulya, S. V.

    2017-02-01

    The structure and nanostructure features of nanocrystalline γ-Al2O3 obtained by dehydration of boehmite with anisotropic platelet-shaped particles were investigated. The original models of 3D coherent nanostructure of γ-Al2O3 were constructed. The models of nanostructured γ-Al2O3 particles were first confirmed by a direct simulation of powder X-Ray diffraction (XRD) patterns using the Debye Scattering Equation (DSE) with assistance of high-resolution transmission electron microscopy (HRTEM) study. The average crystal structure of γ-Al2O3 was shown to be tetragonally distorted. The experimental results revealed that thin γ-Al2O3 platelets were heterogeneous on a nanometer scale and nanometer-sized building blocks were separated by partially coherent interfaces. The XRD simulation results showed that a specific packing of the primary crystalline blocks in the nanostructured γ-Al2O3 particles with formation of planar defects on {001}, {100}, and {101} planes nicely accounted for pronounced diffuse scattering, anisotropic peak broadening and peak shifts in the experimental XRD pattern. The identified planar defects in cation sublattice seem to be described as filling cation non-spinel sites in existing crystallographic models of γ-Al2O3 structure. The overall findings provided an insight into the complex nanostructure, which is intrinsic to the metastable γ-Al2O3 oxide.

  16. A facile fabrication of nitrogen-doped electrospun In2O3 nanofibers with improved visible-light photocatalytic activity

    NASA Astrophysics Data System (ADS)

    Lu, Na; Shao, Changlu; Li, Xinghua; Miao, Fujun; Wang, Kexin; Liu, Yichun

    2017-01-01

    Semiconductor photocatalysis demonstrates to be an effective approach for eliminating most types of environment contaminants and for producing hydrogen. Herein, a facile synthesis route combining electrospinning technique and thermal treatment method under NH3 atmosphere has been presented as a straightforward protocol for the fabrication of nitrogen-doped In2O3 (N-In2O3) nanofibers, the nitrogen content of which can be well controlled by adjusting the annealing temperature. Photocatalytic tests show that the N-In2O3 nanofibers demonstrate an improved degradation rate of Rhodamine B (RB) compared with pure In2O3 nanofibers under visible-light irradiation. This can be attributed to the nitrogen atom introducing at interstitial sites as well as the generation of oxygen vacancy on the surface of In2O3 nanofibers, resulting in the enhanced utilization of visible light for the N-In2O3 nanofibers. Furthermore, the obtained N-In2O3 nanofibers with the advantage of ultra-long one-dimensional nanostructures can be recycled several times by facile sedimentation and hence present almost no decrease in photocatalytic activity indicative of a well regeneration capability. Therefore, the as-fabricated nitrogen-doped In2O3 nanofibers as a promising photocatalyst present good photocatalytic degradation of organic pollutant in waste water for practical application.

  17. Sc2O3, Er2O3, and Y2O3 thin films by MOCVD from volatile guanidinate class of rare-earth precursors.

    PubMed

    Milanov, Andrian P; Xu, Ke; Cwik, Stefan; Parala, Harish; de los Arcos, Teresa; Becker, Hans-Werner; Rogalla, Detlef; Cross, Richard; Paul, Shashi; Devi, Anjana

    2012-12-07

    Alternative novel precursor chemistries for the vapor phase deposition of rare-earth (RE) oxide thin films were developed by synthesising the homoleptic guanidinate compounds tris(N,N'-diisopropyl-2-dimethylamidoguanidinato)-scandium(III) [Sc(DPDMG)(3)] (1), tris(N,N'-diisopropyl-2-dimethylamidoguanidinato)-erbium(III), [Er(DPDMG)(3)] (2) and tris(N,N'-diisopropyl-2-dimethylamidoguanidinato)-yttrium(III), [Y(DPDMG)(3)] (3). All three compounds are monomeric as revealed by single crystal X-ray diffraction (XRD) analysis, nuclear magnetic resonance (NMR) and electron impact mass spectrometry (EI-MS). The thermal analysis revealed that the compounds are volatile and very stable under evaporation conditions. Therefore the complexes were evaluated as precursors for the growth of Sc(2)O(3), Er(2)O(3) and Y(2)O(3) thin films, respectively, by metal-organic chemical vapor deposition (MOCVD). Uniform Sc(2)O(3), Er(2)O(3) and Y(2)O(3) films on Si(100) substrates with reproducible quality were grown by MOCVD by the combination of the respective guanidinate precursors and oxygen in the temperature range 350-700 °C. The structural, morphological, compositional and electrical properties of the films were investigated in detail. The most relevant film properties are highlighted in relation to the distinct advantages of the novel precursor chemistries in comparison to the commonly used literature known RE precursors. This study shows that compounds 1-3 are very good precursors for MOCVD yielding Sc(2)O(3), Er(2)O(3) and Y(2)O(3) thin films which are stoichiometric and display suitable electrical properties for their potential use as high dielectric constant (high-k) materials.

  18. Amphoteric doping of praseodymium Pr3+ in SrTiO3 grain boundaries

    DOE PAGES

    Yang, H.; Lee, H. S.; Kotula, P. G.; ...

    2015-03-26

    Charge Compensation in rare-earth Praseodymium (Pr3+) doped SrTiO3 plays an important role in determining the overall photoluminescence properties of the system. Here, the Pr3+ doping behavior in SrTiO3 grain boundaries (GBs) is analyzed using aberration corrected scanning transmission electron microscopy (STEM). The presence of Pr3+ induces structure variations and changes the statistical prevalence of GB structures. In contrast to the assumption that Pr3+ substitutes for A site as expected in the bulk, Pr3+ is found to substitute both Sr and Ti sites inside GBs with the highest concentration in the Ti sites. As a result, this amphoteric doping behavior inmore » the boundary plane is further confirmed by first principles theoretical calculations.« less

  19. Amphoteric Doping of Praseodymium Pr3+ in SrTiO3 Grain Boundaries

    SciTech Connect

    Yang, Hao; Lee, H. S.; Kotula, Paul G.; Sato, Yukio; Ikuhara, Yuichi; Browning, Nigel D.

    2015-03-23

    Charge Compensation in rare-earth Praseodymium (Pr3+) doped SrTiO3 plays an important role in determining the overall photoluminescence properties of the system. Here, the Pr3+ doping behavior in SrTiO3 grain boundaries (GBs) is analyzed using aberration corrected scanning transmission electron microscopy (STEM). The presence of Pr3+ induces structure variations and changes the statistical prevalence of GB structures. In contrast to the assumption that Pr3+ substitutes for A site as expected in the bulk, Pr3+ is found to substitute both Sr and Ti sites inside GBs with the highest concentration in the Ti sites. This amphoteric doping behavior in the boundary plane is further confirmed by first principles theoretical calculations.

  20. Characterization of SDC-Al2O3 solid electrolyte

    NASA Astrophysics Data System (ADS)

    Ramesh, S.; Raju, K. C. James; Reddy, C. Vishnuvardhan

    2012-06-01

    SDC20-Al2O3 materials were synthesized through the sol-gel method. Dense SDC20-Al2O3 ceramics were obtained through sintering the pellets at 1300°C. SDC20-Al2O3 materials were characterized by XRD, SEM and impedance spectroscopy. XRD measurements indicate that synthesized materials crystallized in cubic structure. Average crystallite size of the samples was in the range 11-12 nm. The relative density of SDC20-Al2O3 samples was over 95% of the theoretical density. Addition of Al2O3 promotes densification. Surface morphology was analyzed using SEM. The two-probe a.c. impedance spectroscopy was used to study the total ionic conductivity of doped and co-doped ceria in the temperature range 350-700°C. The SDC20-Al2O3 composition showed improved total ionic conductivity and minimum activation energy.

  1. Structural Behaviour of Solid Solutions in the NdAlO3-SrTiO3 System.

    PubMed

    Ohon, Natalia; Stepchuk, Roman; Blazhivskyi, Kostiantyn; Vasylechko, Leonid

    2017-12-01

    Single-phase mixed aluminates-titanates Nd1-x Sr x Al1-x Ti x O3 (x = 0.3 ÷ 0.9) were prepared from stoichiometric amounts of constituent oxides Nd2O3, Al2O3, TiO2 and strontium carbonate SrCO3 by solid-state reaction technique in air at 1773 K. Crystal structure parameters of Nd1-x Sr x Al1-x Ti x O3 were refined by full-profile Rietveld refinement in space groups R [Formula: see text] c (x = 0.3, 0.5, 0.7 and 0.8) and Pm [Formula: see text] m (x = 0.9). Comparison of the obtained structural parameters with the literature data for the end members of the system NdAlO3 and SrTiO3 revealed formation of two kinds of solid solutions Nd1-xSrxAl1-xTixO3 with the cubic and rhombohedral perovskite structure. Morphotropic rhombohedral-to-cubic phase transition in Nd1-xSrxAl1-xTixO3 series occurs at x = 0.84. Based on the results obtained as well as the literature data for the parent compounds, the tentative phase diagram of the NdAlO3-SrTiO3 pseudo-binary system have been constructed.

  2. Structural Behaviour of Solid Solutions in the NdAlO3-SrTiO3 System

    NASA Astrophysics Data System (ADS)

    Ohon, Natalia; Stepchuk, Roman; Blazhivskyi, Kostiantyn; Vasylechko, Leonid

    2017-02-01

    Single-phase mixed aluminates-titanates Nd1- x Sr x Al1- x Ti x O3 ( x = 0.3 ÷ 0.9) were prepared from stoichiometric amounts of constituent oxides Nd2O3, Al2O3, TiO2 and strontium carbonate SrCO3 by solid-state reaction technique in air at 1773 K. Crystal structure parameters of Nd1- x Sr x Al1- x Ti x O3 were refined by full-profile Rietveld refinement in space groups R overline{3} c ( x = 0.3, 0.5, 0.7 and 0.8) and Pm overline{3} m ( x = 0.9). Comparison of the obtained structural parameters with the literature data for the end members of the system NdAlO3 and SrTiO3 revealed formation of two kinds of solid solutions Nd1-xSrxAl1-xTixO3 with the cubic and rhombohedral perovskite structure. Morphotropic rhombohedral-to-cubic phase transition in Nd1-xSrxAl1-xTixO3 series occurs at x = 0.84. Based on the results obtained as well as the literature data for the parent compounds, the tentative phase diagram of the NdAlO3-SrTiO3 pseudo-binary system have been constructed.

  3. The electron-spin magnetic moments (g factors) of O3-, O3Li, and O3Na: An ab initio study

    NASA Astrophysics Data System (ADS)

    Bruna, Pablo J.; Grein, Friedrich

    1998-12-01

    The electron-spin magnetic moments of O3-, O3Li, and O3Na, as parametrized by the g factors, are studied at the uncorrelated restricted open Hartree-Fock (ROHF) and correlated multireference configuration interaction (MRCI) ab initio levels. The present method, which uses a perturbative approach complete to second order, is based on a Breit-Pauli Hamiltonian. The calculated Δg values, with Δg=g-ge, are very similar for all three species, confirming that the O3- moiety is retained in the ozonides O3M. In the standard C2v notation, Δgyy>Δgzz≫|Δgxx|. The perpendicular component Δgxx is small and negative, while the in-plane components Δgyy and Δgzz are large and positive. The MRCI results for Δgxx, Δgyy, Δgzz (in ppm) are: -475, 16 673, 10 121 for O3-; -679, 13 894, 9308 for O3Li; and -494, 12 298, 8690 for O3Na. The ROHF values of Δgyy and Δgzz are smaller than the MRCI data, due to a general overestimation of the excitation energies. The MRCI Δg values for isolated O3- reproduce the experimental results for O3- trapped in crystals or adsorbed on MgO surfaces (in ppm, -500-1200 for Δgxx, 12 400-16 400 for Δgyy, and 6900-10 000 for Δgzz). For O3Na, the experimental Δgxx, Δgyy, Δgzz data (-100, 14 200, 9800 ppm) are again satisfactorily described by our correlated results. No experimental g shifts are available for O3Li. In all systems studied here, the Δgxx component is dictated by first-order terms (ground state expectation values); Δgyy is governed by the second-order magnetic coupling between X 2B1 and 1 2A1 [electron excitation from the highest a1 molecular orbital (MO) into the b1(π*) singly occupied MO]; and Δgzz, by the coupling with two 2B2 states (excitations from the two highest b2 MOs into π*).

  4. Material properties of perovskites in the quasi-ternary system LaFeO3–LaCoO3–LaNiO3

    DOE PAGES

    Tietz, F.; Arul Raj, I.; Ma, Q.; ...

    2016-02-02

    We present an overview on the variation of electrical conductivity, oxygen permeation, oxygen surface exchange and thermal expansion coefficient as a function of the composition of perovskites in the quasi-ternary system LaFeO3–LaCoO3–LaNiO3. Powders of thirteen nominal perovskite compositions were synthesized under identical conditions by the Pechini method. The powder X-ray diffraction data of two series, namely La(Ni0.5Fe0.5)1-xCoxO3 and LaNi0.5- xFexCo0.5O3, are presented after the powders had been sintered at 1100 C for 6 h in air. The measurements revealed a rhombohedral structure for all compositions except LaNi0.5Fe0.5O3 for which 60% rhombohedral and 40% orthorhombic phase was found. Moreover, the maximummore » DC electrical conductivity value of the perovskites at 800 C was 1229 S cm-1 for the composition LaCoO3 and the minimum was 91 S cm-1 for the composition LaCo0.5Fe0.5O3. The oxygen permeation of samples with promising conductivities at 800 C was one order of magnitude lower than that of La0.6Sr0.4Co0.8Fe0.2O3 (LSCF). The highest value of 0.017 ml cm-2 min-1 at 950 C was obtained with LaNi0.5Co0.5O3. The coefficients of thermal expansion varied in the range of 13.2 x 10-6 K-1 and 21.9 x 10-6 K-1 for LaNi0.5Fe0.5O3 and LaCoO3, respectively. 57Fe M ssbauer spectroscopy was used as probe for the oxidation states, local environment and magnetic properties of iron ions as a function of chemical composition. Ultimately, the substitution had a great influence on the chemical properties of the materials.« less

  5. Study of the thermo-optical constants of Yb doped Y2O3, Lu2O3 and Sc2O3 ceramic materials.

    PubMed

    Snetkov, Ilya L; Silin, Dmitry E; Palashov, Oleg V; Khazanov, Efim A; Yagi, Hideki; Yanagitani, Takagimi; Yoneda, Hitoki; Shirakawa, Akira; Ueda, Ken-Ichi; Kaminskii, Alexander A

    2013-09-09

    Thermally induced depolarization and thermal lens of three Konoshima Chemical Co. laser-ceramics samples Yb(3+):Lu(2)O(3)(C(Yb) ≈ 1.8 at.%), Yb(3+):Y(2)O(3)(C(Yb) ≈ 1.8 at.%), and Yb(3+):Sc(2)O(3) (C(Yb) ≈ 2.5 at.%) were measured in experiment at different pump power. The results allowed us to estimate the thermal conductivity of the investigated ceramic samples and compare their thermo-optical properties. The thermo-optical constants P and Q and its sign measured for these materials at the first time.

  6. Electronic structure and optical properties of orthorhombic and rhombohedral RAlO3 (R = Sm, Nd)

    NASA Astrophysics Data System (ADS)

    Sakhya, Anup Pradhan; Dutta, Alo; Shannigrahi, Santiranjan; Sinha, T. P.

    2015-04-01

    The electronic structure and optical properties of RAlO3 (R = Sm, Nd) have been investigated by full potential linearized augmented plane wave method within the framework of density functional theory in its generalized gradient approximation. The calculations are initiated with the experimental lattice constants obtained by the Rietveld refinement of the XRD data of the synthesized samples. The band gaps of the systems are measured from the UV-visible reflectance spectra using the Kubelka-Munk function and compared with the calculated data. The spin-polarized calculation has been carried out with on-site Coulomb potential U to consider the electron-electron correlation in the system. The X-ray photoemission spectra of the systems are measured. The valence-band density-of-states spectra are generated and compared with the X-ray photoemission spectra. The chemical shifts of these compounds suggest a mixed ionic and covalent character of the bonds. It has been observed that f-state of Nd and Sm hybridizes with O-2p state near the Fermi level in valence band. The Born effective charge tensors of the constituent ions for SmAlO3 and NdAlO3 have also been calculated which shows strong hybridization and charge transfer between Sm and O in SmAlO3 and Nd and O in NdAlO3. The calculated static dielectric tensor is found to be in good agreement with the experimental values.

  7. Ion channeling study of lattice distortions in chromium-doped SrTiO3 crystals

    NASA Astrophysics Data System (ADS)

    Lavrentiev, V.; Vacik, J.; Dejneka, A.; Trepakov, V.; Jastrabik, L.

    2013-07-01

    The results of ion channeling studies of lattice distortions in SrTiO3: Cr single crystals are presented. Two types of single crystals containing the same amount of Cr impurities but differing in stoichiometry have been investigated. The single crystals grown by the Verneuil method have the compositions of standard-grown SrTiO3: Cr (0.05 at % Cr), whereas the single crystals grown with a strontium deficiency and a chromium compensating amount have the composition Sr0.9995TiO3 (0.05 at % Cr). Analysis of the angular channeling spectra indicates that, in crystals of both types, the main defects are Cr impurities located in octahedral sites. In the SrTiO3: Cr crystals, impurity atoms manifest themselves as Cr4+ with tetragonal Jahn-Teller distortions of the surrounding lattice. In the Sr0.9995TiO3: Cr crystals grown with a Sr deficiency, the characteristic displacements of Ti ions in the third coordination sphere of the Jahn-Teller center Cr4+ exhibit the effect of interaction of the center with a neighboring vacancy in the Sr sublattice.

  8. Steam Reforming of Glycerol Over Nano Size Ni-Ce/LaAlO3 Catalysts.

    PubMed

    Kim, Seong-Hak; Go, Yoo-Jin; Park, Nam-Cook; Kim, Jong-Ho; Kim, Young-Chul; Moon, Dong-Ju

    2015-01-01

    In this work, hydrogen production from glycerol by Steam Reforming (SR) was studied by Ni-Ce catalysts supported on LaAlO3 perovskite in order to effect of the cerium loading amount and the reaction conditions. Nano size Ni-Ce/LaAlO3 catalysts were prepared by precipitation method. The structure of the catalysts was characterized by XRD analysis. The morphology, dispersion and the reduction properties of catalysts was examined by SEM, TEM, H2-chemisorption and TPR, respectively. It was found that 15 wt% Ni-5 wt% Ce/LaAlO3 catalyst showed the highest glycerol conversion and hydrogen selectivity. In addition, the catalyst also showed the high carbon dioxide selectivity and the lowest methane selectivity. The results indicate that the catalyst promotes methane reforming reaction. The highest activity in the 15 wt% Ni-5 wt% Ce/LaAlO3 was attributed to the proper cerium loading amount. Moreover, the lowest metal crystal size and rise in active site were found to have an effect on catalytic activity and hydrogen selectivity. The 15 wt% Ni-5 wt% Ce/LaAlO3 catalyst exhibited excellent performance with respect to hydrogen production at reaction temperature of 450 degrees C, at atmospheric pressure, 20 wt% glycerol solution and GHSV = 6,000 mL/g-cat x hr.

  9. Understanding the interactions of CO2 with doped and undoped SrTiO3

    DOE PAGES

    Wu, Qiyuan; Cen, Jiajie; Goodman, Kenneth R.; ...

    2016-06-17

    SrTiO3 and doped SrTiO3 have a wide range of applications in different fields. For example, Rh-doped SrTiO3 has been shown to have photocatalytic activity for both hydrogen production and CO2 conversion. In this study, both undoped and Rh-doped SrTiO3 were synthesized by hydrothermal and polymerizable complex methods. Different characterizations techniques including X-ray photoelectron spectroscopy (XPS), XRD, Raman, and UV/Vis spectroscopy were utilized to establish correlations between the preparation methods and the electronic/structural properties of Rh-doped SrTiO3. The presence of dopants and oxygen vacancies substantially influenced the CO2 interactions with the surface, as revealed by the in situ infrared spectroscopic study.more » As a result, the presence of distinctly different adsorption sites was correlated to oxygen vacancies and oxidation states of Ti and Rh.« less

  10. Effect of ionic radii on the Curie temperature in Ba1-x-ySrxCayTiO3 compounds

    NASA Astrophysics Data System (ADS)

    Berenov, A.; Le Goupil, F.; Alford, N.

    2016-06-01

    A series of Ba1-x-ySrxCayTiO3 compounds were prepared with varying average ionic radii and cation disorder on A-site. All samples showed typical ferroelectric behavior. A simple empirical equation correlated Curie temperature, TC, with the values of ionic radii of A-site cations. This correlation was related to the distortion of TiO6 octahedra observed during neutron diffraction studies. The equation was used for the selection of compounds with predetermined values of TC. The effects of A-site ionic radii on the temperatures of phase transitions in Ba1-x-ySrxCayTiO3 were discussed.

  11. Effect of ionic radii on the Curie temperature in Ba1-x-ySrxCayTiO3 compounds.

    PubMed

    Berenov, A; Le Goupil, F; Alford, N

    2016-06-21

    A series of Ba1-x-ySrxCayTiO3 compounds were prepared with varying average ionic radii and cation disorder on A-site. All samples showed typical ferroelectric behavior. A simple empirical equation correlated Curie temperature, TC, with the values of ionic radii of A-site cations. This correlation was related to the distortion of TiO6 octahedra observed during neutron diffraction studies. The equation was used for the selection of compounds with predetermined values of TC. The effects of A-site ionic radii on the temperatures of phase transitions in Ba1-x-ySrxCayTiO3 were discussed.

  12. Consolidation of Al2O3 Nano-Ceramic Powders for High Power Micro-Wave Window

    DTIC Science & Technology

    2007-09-19

    Development, Korea Atomic Energy Research Institute, 150 Dukjin-dong Yuseong-gu Daejeon, 305-353, Korea 1. INTRODUCTION In material aspect, the sapphire...Al2O3) is very attractive material for window in the high power application. However, the fabrication and following process is very difficult and...much expansive. In addition, the intrinsic defects like F, F+ center in single crystalline Al2O3 act as heat generation sites during passing the high

  13. Correlated rattling-ion origins of dielectric properties in reentrant dipole glasses BaTiO3-BiScO3

    NASA Astrophysics Data System (ADS)

    Krayzman, Victor; Levin, Igor; Woicik, Joseph C.; Bridges, Frank

    2015-11-01

    The local structure of the pseudo-cubic solid solution 0.6BaTiO3-0.4BiScO3, which exhibits reentrant dipole-glass behavior, has been determined using the Reverse Monte Carlo method to simultaneously fit (1) neutron and X-ray total scattering data (including the corresponding real-space pair-distribution functions), (2) Bi and Sc extended X-ray absorption fine structure, and (3) patterns of diffuse scattering in electron diffraction. These structural refinements revealed the multi-site probability density distributions for both Bi (14-sites) and Ti (8 sites), whereas Ba and Sc featured normal unimodal distributions. Bi atoms are displaced along both the <111> and <100> directions, while Ti atoms are shifted along <111>. Correlated dynamic hopping of Bi and Ti over their corresponding split sites combined with chemical disorder is proposed as the origin of the strong frequency dispersion observed in dielectric measurements. The existence of split sites also explains the reentrant dipole-glass behavior reported for this system.

  14. The SrTiO3/BiFeO3 (001) interface: commutativity of energy band discontinuities

    NASA Astrophysics Data System (ADS)

    Schafranek, R.; Baniecki, J. D.; Ishii, M.; Kotaka, Y.; Kurihara, K.

    2013-05-01

    The interface formation between the perovskite oxides SrTiO3 and BiFeO3 was studied using in situ photoelectron spectroscopy by depositing BiFeO3 on SrTiO3 and vice versa via pulsed laser deposition. For the interfaces characterized, a type II band alignment with a valence band offset of 0.9-1.0 eV and a conduction band offset of 0.5-0.6 eV was observed. Within the margin of error the commutativity was fulfilled for the SrTiO3/BiFeO3 interface, meaning that the band alignment does not depend on the deposition sequence.

  15. Giant magnetocaloric effect in GdAlO3 and a comparative study with GdMnO3

    NASA Astrophysics Data System (ADS)

    Mahana, Sudipta; Manju, U.; Topwal, D.

    2017-01-01

    The magnetic properties and magnetocaloric effect of polycrystalline GdAlO3 and GdMnO3 have been investigated to assess their potential usage as magnetic refrigerants at cryogenic temperatures. These compounds undergo antiferromagnetic transitions at low temperatures which are associated with the giant magnetic entropy change effect (-\\bigtriangleup {{S}M} )  ˜40.9 J Kg · K-1 under a field change of 0-9 T for GdAlO3 while the moderate effect of 18 J Kg · K-1 is observed for polycrystalline GdMnO3. Though the relative cooling power of both the stated materials is similar however, the absence of magnetic and thermal hysteresis makes GdAlO3 a more efficient magnetic refrigerant than GdMnO3.

  16. Ionic liquid-based hydrothermal synthesis of Lu2O3 and Lu2O3:Eu3+ microcrysals

    NASA Astrophysics Data System (ADS)

    Li, Yinyan; Xu, Shiqing

    2016-09-01

    Uniform and well-defined Lu2O3 and Lu2O3:Eu3+ microarchitectures have been successfully synthesized via a green and facile ionic liquid-based hydrothermal method followed by a subsequent calcination process. Novel 3D micro-rodbundles and 1D microrods of Lu2O3 and Lu2O3:Eu3+ were controllably obtained through this method. X-ray powder diffraction, scanning electron microscopy, transmission electron microscopy and photoluminescence spectra were used to characterize the micromaterials. The proposed formation mechanisms have been investigated on the basis of a series of SEM studies of the products obtained at different hydrothermal durations. The results indicated that hydrothermal temperature and the ionic liquid-tetrabutylammonium hydroxide were two key factors for the formation as well as the morphology control of the Lu2O3 and Lu2O3:Eu3+ microarchitectures.

  17. Calculation of Phase Equilibria in the Y2O3-Yb2O3-ZrO2 System

    NASA Technical Reports Server (NTRS)

    Jacobson, Nathan S.; Liu, Zi-Kui; Kaufman, Larry; Zhang, Fan

    2001-01-01

    Rare earth oxide stabilized zirconias find a wide range of applications. An understanding of phase equilibria is essential to all applications. In this study, the available phase boundary data and thermodynamic data is collected and assessed. Calphad-type databases are developed to completely describe the Y2O3-ZrO2, Yb2O3-ZrO2, and Y2O3-Yb2O3 systems. The oxide units are treated as components and regular and subregular solution models are used. The resultant calculated phase diagrams show good agreement with the experimental data. Then the binaries are combined to form the database for the Y2O3-Yb2O3-ZrO2 psuedo-ternary.

  18. Study on catalytic incineration of methane using Cr2O3/gamma-Al2O3 as the catalyst.

    PubMed

    Wang, Ching-Huei; Lin, Shiow-Shyung

    2004-01-01

    A fixed bed reactor was employed to investigate the catalytic incineration of CH4 by various supported transition metal oxide catalysts, with a view of finding the optimal one. Results indicated that the active species, the support, the metal content, the weight hourly space velocity (WHSV), and the inlet CH4 concentration were all important factors affecting CH4 oxidation. Cr2O3/gamma-Al2O3 was found to be the most active catalyst among the seven gamma-Al2O3-supported metal oxide catalysts tested. With Cr2O3 as the active species, gamma-Al2O3 was the most suitable of six supports tested. Furthermore, the optimal Cr content of Cr2O3/ gamma-Al2O3 was 9 wt.%. X-ray diffraction (XRD) patterns showed that it was formation of CrO3 crystals that caused a decline in catalyst activity at Cr content above 9wt.%. Using the optimal Cr2O3/gamma-Al2O3 catalyst, CH4 was completely oxidized at about 390 degrees C. much lower than the temperature required by noble metal catalysts for the same outcome. The stability of Cr2O3/gamma-Al2O3 was good and was not affected by the reaction temperature, demonstrated by a nearly constant conversion rate of CH4 of 57% at 350 degrees C and 97% at 380 degrees C during a 20 h on-stream test. However, WHSV and inlet concentration of CH4 did affect CH4 conversion noticeably. For complete oxidation of CH4, the reaction temperature required increased with WHSV and inlet CH4 concentration.

  19. Non-uniform magnetization in LaAlO3/SrTiO3 superlattices.

    NASA Astrophysics Data System (ADS)

    Fitzsimmons, M. R.; Zhernenkov, M.; Hengartner, N.; Sharoni, A.; Schuller, Ivan K.; Garcia-Barriocanal, J.; Bruno, F. Y.; Santamaria, J.

    2009-03-01

    Recently, Brinkman et al., [Nature 6, 493 (2007)] reported magnetism induced at the interface between LaAlO3 (LAO) and SrTiO3 (STO)inferred from transport measurements. They found the magnetization to be greatly enhanced at low temperatures (i.e., liquid He temperature) and by application of high (10+ T) fields. We report polarized neutron reflectometry measurements of the magnetization depth profile of two LAO/STO superlattices with the same number of bilayer repeats. For low temperatures and a field of 11 T, the intensities of the superlattice Bragg reflections for both samples exhibited a dependence upon neutron beam polarization. The spin dependence was much weaker at small field (and low temperature) and disappeared altogether at 11 T and 300 K. These observations demonstrate that the magnetization depth profile has the period of the LAO/STO superlattice. The neutron spin dependence was more pronounced for the sample with a thin LAO layer compared to one with a thick LAO layer, suggesting that the magnetism may be interfacial in origin.

  20. BiScO3 -PbTiO3 Nanoceramics Prepared by Spark Plasma Sintering

    NASA Astrophysics Data System (ADS)

    Wang, Xiaohui

    2015-11-01

    Highly dense 0.37 BiScO3 -0.63 PbTiO3 (BS-PT) ceramics with nano-sized grains were prepared by combination of Spark Plasma Sintering and two-step sintering method. The microstructures, phase and piezoelectric behaviors of BS-PT nanoceramics were investigated. TEM observations clearly showed that the average grain sizes of the ceramic samples were 23, 33 and 70 nm respectively. The contrasting morphologies of grain boundary region under different magnifications were caused by different contrast and imaging mechanisms. HRTEM image confirmed that the samples had dense and thin grain boundary regions. Perovskite phase was demonstrated for all the samples by XRD and SAED data. Local SPM measurements recorded well-formed butterfly and piezoelectric hysteresis loops for all the samples, suggesting that BS-PT nanoceramics retained a ferroelectric state and the polarizations were switchable with the average grain size as fine as 23 nm. There was a comparatively large fluctuation of local piezoelectric responses. A significant difference between local and macro piezoelectric coefficients was observed. The grain boundary regions with complex internal stress and charges/defects were the key factor to understand these unusual properties in ferroelectric nanoceramics.

  1. Al2O3/GdAlO3 fiber for dental porcelain reinforcement.

    PubMed

    Medeiros, Igor S; Luz, Luciana A; Yoshimura, Humberto N; Cesar, Paulo F; Hernandes, Antonio C

    2009-10-01

    The aim of this study was to test the hypothesis that the addition of continuous or milled GdAlO3/Al2O3 fibers to a dental porcelain increases its mechanical properties. Porcelain bars without reinforcement (control) were compared to those reinforced with long fibers (30 vol%). Also, disk specimens reinforced with milled fibers were produced by adding 0 (control), 5 or 10 vol% of particles. The reinforcement with continuous fibers resulted in significant increase in the uniaxial flexural strength from 91.5 to 217.4 MPa. The addition of varied amounts of milled fibers to the porcelain did not significantly affect its biaxial flexural strength compared to the control group. SEM analysis showed that the interface between the continuous fiber and the porcelain was free of defects. On the other hand, it was possible to note the presence of cracks surrounding the milled fiber/porcelain interface. In conclusion, the reinforcement of the porcelain with continuous fibers resulted in an efficient mechanism to increase its mechanical properties; however the addition of milled fibers had no significant effect on the material because the porcelain was not able to wet the ceramic particles during the firing cycle.

  2. External voltage control of LaAlO3/SrTiO3 interface structure

    NASA Astrophysics Data System (ADS)

    Fujii, Hiromasa; Minohara, Makoto; Bell, Christopher; Hikita, Yasuyuki; Hwang, Harold Y.; Kimura, Tsuyoshi; Wakabayashi, Yusuke

    2015-03-01

    Physical properties of the LaAlO3 (LAO)/ SrTiO3 (STO) interface are controlled by external voltage such as voltage-induced metal-insulator transition and superconductivity-insulator transition. The modulated parameters by external voltage are not only the carrier density but also the Hall mobility. In order to clarify local electric field and polarization around the interface, we have investigated the effect of external voltage on the interface structure at room temperature by means of a surface x-ray diffraction technique, crystal truncation rod (CTR) scattering. Our measurements were performed at BL-4C of the Photon Factory, KEK, Japan. A 5-unit-cell thick sample was prepared using the pulsed laser deposition technique. The scattered x-ray intensity profile shows slight external voltage dependence, which means that the interface structure is changed by the external voltage. We also found that the voltage dependence of the scattering intensity exhibits hysteresis. Least squares refinement revealed that main atomic displacement induced by the eternal voltage occur in the LAO. The displacements in STO at the interface are of the order of sub-pm, which is much larger than expected for bulk STO (~ 0.01pm).

  3. Doping of BiScO3-PbTiO3 Ceramics for Enhanced Properties

    NASA Technical Reports Server (NTRS)

    Sehirlioglu, Alp; Sayir, Ali; Dynys, Fred

    2008-01-01

    High-temperature piezoelectrics are a key technology for aeronautics and aerospace applications such as fuel modulation to increase the engine efficiency and decrease emissions. The principal challenge for the insertion of piezoelectric materials is the limitation on upper use temperature which is due to low Curie-Temperature (T(sub c) and increasing electrical conductivity. BiScO3 -PbTiO3 (BS-PT) system is a promising candidate for improving the operating temperature for piezoelectric actuators due to its high TC (>400 C). Effects of Zr and Mn doping of the BS-PT ceramics have been studied and all electrical and electromechanical properties for Sc-deficient and Ti-deficient BS- PT ceramics are reported as a function of electrical field and temperature. Donor doping with Zr and Mn (in Sc deficient compositions) increased the DC-resistivity and decreased tan at all temperatures. Resulting ceramics exhibited saturated hysteresis loops with low losses and showed no dependence on the applied field (above twice the coercive field) and measurement frequency.

  4. EXAFS simulations in Zn-doped LiNbO3 based on defect calculations

    NASA Astrophysics Data System (ADS)

    Valerio, Mário E. G.; Jackson, Robert A.; Bridges, Frank G.

    2017-02-01

    Lithium niobate, LiNbO3, is an important technological material with good electro-optic, acousto-optic, elasto-optic, piezoelectric and nonlinear properties. EXAFS on Zn-doped LiNbO3 found strong evidences that Zn substitutes primarily at the Li site on highly doped samples. In this work the EXAFS results were revisited using a different approach where the models for simulating the EXAFS results were obtained from the output of defect calculations. The strategy uses the relaxed positions of the ions surrounding the dopants to generate a cluster from where the EXAFS oscillations can be calculated. The defect involves not only the Zn possible substitution at either Li or Nb sites but also the charge compensating defects, when needed. From previous defect modelling, a subset of defects was selected based on the energetics of the defect production in the LiNbO3 lattice. From them, all possible clusters were generated and the simulated EXAFS were computed. The simulated EXAFS were them compared to available EXAFS results in the literature. Based on this comparison different models could be proposed to explain the behaviour of Zn in the LiNbO3 matrix.

  5. Synthesis and several features of the Na2O-B2O3-Bi2O3-MoO3 glasses

    NASA Astrophysics Data System (ADS)

    Saddeek, Yasser B.; Abousehly, A. M.; Hussien, Shaban I.

    2007-08-01

    Glasses in the system Na2-2xB4-4xBixMo0.5xO7-4x, 0 <= x <= 0.4, have been prepared by the melt quenching technique. Elastic properties and IR spectroscopic studies have been employed to study the role of Bi2O3 and MoO3 on the structure of Na2B4O7 glass. Elastic properties and Debye temperature have been investigated using sound velocity measurements at 4 MHz. The results showed that the density and the molar volume increase while both sound velocities and the determined glass transition temperatures decrease with increase in x. Infrared spectra of the glasses reveal that the strong borate network consists of diborate units and is affected by the increase in the concentration of Bi2O3, and MoO3. These results are interpreted in terms of the increase in the number of non-bridging oxygen atoms, substitution of longer bond lengths of Bi-O, and Mo-O in place of shorter B-O bond and the change in Na+ ion concentration. The results indicate that bismuth and molybdenum ions have been substituted for boron ions as network modifier ions. The elastic moduli are observed to increase with the increase in Bi2O3 and MoO3 content. This contradiction in the elastic moduli-molar volume relation is attributed to the role of the respective bonds.

  6. MgSiO3-FeSiO3-Al2O3 in the Earth's lower mantle: Perovskite and garnet at 1200 km depth

    NASA Technical Reports Server (NTRS)

    O'Neill, Bridget; Jeanloz, Raymond

    1994-01-01

    Natural pyroxene and garnet starting material are used to study the effects of joint Fe and Al substitution into MgSiO3 perovskite at approxmiately 50 GPa. Garnet is found to coexist with perovskite in samples containing both Fe and Al to pressures occurring deep into the lower mantel (approximately 1200 km depth). The volume of the perovskite unit cell is V(sub o(Angstrom(exp 3)) = 162.59 + 5.95x(sub FeSiO3) + 10.80x(sub Al2O3) with aluminum causing a significant increase in the distortion from the ideal cubic cell. On the basis of a proposed extension of the MgSiO3-Al2O3 high-pressure phase diagram toward FeSiO3, Fe is shown to partition preferentially into the garnet phase. The stability of garnet deep into the lower mantel may hinder the penetration of subducted slabs below the transition zone.

  7. Elasticity of single-crystal SmAlO 3, GdAlO 3 and ScAlO 3 perovskites

    NASA Astrophysics Data System (ADS)

    Bass, Jay D.

    1984-12-01

    The adiabatic single-crystal elastic moduli of SmAlO 3, GdAlO 3 and ScAlO 3, all with the orthorhombic perovskite structure, have been measured by Brillouin spectroscopy under ambient conditions. These 3 compounds display various degrees of crystallographic distortion from the ideal cubic perovskite structure. We find that longitudinal moduli in directions parallel to the axes of a pseudocubic subcell are nearly equal and insensitive to distortions of the crystal structure from cubic symmetry, whereas, the moduli C 11 and C 22, parallel to the orthorhombic axes, display pronounced anisotropy with the exception of ScAlO 3. The shear moduli also correlate with distortion from cubic symmetry, as measured by rotation, or tilt angles, of the AlO 6 octahedra. Our data support the observations of Liebermann et al. that perovskite-structure compounds define consistent elasticity trends relating bulk modulus and molar volume, and sound speed and mean atomic weight. These relationships have been used to estimate bulk and shear moduli for the high-pressure polymorphs of CaSiO 3 and MgSiO 3 with the perovskite structure.

  8. Potential Fluctuations at Low Temperatures in Mesoscopic-Scale SmTiO3/SrTiO3/SmTiO3 Quantum Well Structures.

    PubMed

    Hardy, Will J; Isaac, Brandon; Marshall, Patrick; Mikheev, Evgeny; Zhou, Panpan; Stemmer, Susanne; Natelson, Douglas

    2017-03-28

    Heterointerfaces of SrTiO3 with other transition metal oxides make up an intriguing family of systems with a bounty of coexisting and competing physical orders. Some examples, such as LaAlO3/SrTiO3, support a high carrier density electron gas at the interface whose electronic properties are determined by a combination of lattice distortions, spin-orbit coupling, defects, and various regimes of magnetic and charge ordering. Here, we study electronic transport in mesoscale devices made with heterostructures of SrTiO3 sandwiched between layers of SmTiO3, in which the transport properties can be tuned from a regime of Fermi-liquid like resistivity (ρ ∝ T(2)) to a non-Fermi liquid (ρ ∝ T(5/3)) by controlling the SrTiO3 thickness. In mesoscale devices at low temperatures, we find unexpected voltage fluctuations that grow in magnitude as T is decreased below 20 K, are suppressed with increasing contact electrode size, and are independent of the drive current and contact spacing distance. Magnetoresistance fluctuations are also observed, which are reminiscent of universal conductance fluctuations but not entirely consistent with their conventional properties. Candidate explanations are considered, and a mechanism is suggested based on mesoscopic temporal fluctuations of the Seebeck coefficient. An improved understanding of charge transport in these model systems, especially their quantum coherent properties, may lead to insights into the nature of transport in strongly correlated materials that deviate from Fermi liquid theory.

  9. Epitaxial BiFeO3 nanostructures fabricated by differential etching of BiFeO3 films

    NASA Astrophysics Data System (ADS)

    Johann, Florian; Morelli, Alessio; Vrejoiu, Ionela

    2011-08-01

    We report on differential etching behavior of the different orientations of the polarization in BiFeO3 (BFO), similar to other ferroelectrics, such as LiNbO3. We show how this effect can be used to fabricate epitaxial BiFeO3 nanostructures. By means of piezoresponse force microscopy (PFM) domains of arbitrary shape and size can be poled in an epitaxial BiFeO3 film, which are then reproduced in the film morphology by differential etching. Structures with a lateral size smaller than 200 nm were fabricated and very good retention properties as well as a highly increased piezoelectric response were detected by PFM.

  10. Voltage-controlled ferromagnetism and magnetoresistance in LaCoO3/SrTiO3 heterostructures

    NASA Astrophysics Data System (ADS)

    Hu, Chengqing; Park, Keun Woo; Posadas, Agham; Jordan-Sweet, Jean L.; Demkov, Alexander A.; Yu, Edward T.

    2013-11-01

    A LaCoO3/SrTiO3 heterostructure grown on Si (001) is shown to provide electrically switchable ferromagnetism, a large, electrically tunable magnetoresistance, and a vehicle for achieving and probing electrical control over ferromagnetic behavior at submicron dimensions. Fabrication of devices in a field-effect transistor geometry enables application of a gate bias voltage that modulates strain in the heterostructure via the converse piezoelectric effect in SrTiO3, leading to an artificial inverse magnetoelectric effect arising from the dependence of ferromagnetism in the LaCoO3 layer on strain. Below the Curie temperature of the LaCoO3 layer, this effect leads to modulation of resistance in LaCoO3 as large as 100%, and magnetoresistance as high as 80%, both of which arise from carrier scattering at ferromagnetic-nonmagnetic interfaces in LaCoO3. Finite-element numerical modeling of electric field distributions is used to explain the dependence of carrier transport behavior on gate contact geometry, and a Valet-Fert transport model enables determination of spin polarization in the LaCoO3 layer. Piezoresponse force microscopy is used to confirm the existence of piezoelectric response in SrTiO3 grown on Si (001). It is also shown that this structure offers the possibility of achieving exclusive-NOR logic functionality within a single device.

  11. Stoichiometry, defects, and the polar catastrophe in LaAlO3 thin films on SrTiO3

    NASA Astrophysics Data System (ADS)

    Hellberg, C. Stephen

    2013-03-01

    Careful growth of LaAlO3 thin films on SrTiO3 by molecular beam epitaxy has shown that the La/Al ratio of the nominal LaAlO3 layer is key to the formation of a two-dimensional electron liquid at the interface--metallic conductivity is only observed in Al-rich films. The interfacial electron liquid forms due to the polar catastrophe, the diverging potential caused by the atomic layer arrangement at the interface when polar LaAlO3 is grown on TiO2-terminated non-polar SrTiO3. The system eventually reconstructs, moving negative charges to the interface to screen the diverging potential. I will present density functional calculations of the defects that form in LaAlO3 on SrTiO3 to accomodate variations in stoichiometry. In La-rich films, the lowest energy defects are extended and allow cation vacancies to move to the interface to screen the diverging potential. Thus the interface between La-rich LaAlO3 and SrTiO3 remains insulating. In Al-rich films, the defects are localized and block cation motion. In this case a conducting electron liquid forms to screen the diverging potential.

  12. The electronic level structure of lanthanide impurities in REPO4, REBO3, REAlO3, and RE2O3 (RE = La, Gd, Y, Lu, Sc) compounds

    NASA Astrophysics Data System (ADS)

    Dorenbos, Pieter

    2013-06-01

    The vacuum referred binding energies of electrons in divalent and trivalent lanthanide impurity states and host band states in the rare earth (RE = La, Gd, Y, Lu, Sc) orthophosphates REPO4, orthoborates REBO3, aluminum perovskites REAlO3, and sesqui-oxides RE2O3 have been determined by combining the recently developed chemical shift model with spectroscopic data from the archival literature. The main trends in impurity and host band level locations with changing type of RE, which determines the site size, and with changing P, B, Al, or RE cation, which determines the strength of bonding with the oxygen ligands, are identified. Sc3+-based compounds are characterized by a relatively low energy for the conduction band bottom, or equivalently a high electron affinity, which is attributed to a relatively strong electron bonding in the 3d-shell of Sc2+.

  13. Distinct responses of soil microbial communities to elevated CO2 and O3 in a soybean agro-ecosystem.

    PubMed

    He, Zhili; Xiong, Jinbo; Kent, Angela D; Deng, Ye; Xue, Kai; Wang, Gejiao; Wu, Liyou; Van Nostrand, Joy D; Zhou, Jizhong

    2014-03-01

    The concentrations of atmospheric carbon dioxide (CO2) and tropospheric ozone (O3) have been rising due to human activities. However, little is known about how such increases influence soil microbial communities. We hypothesized that elevated CO2 (eCO2) and elevated O3 (eO3) would significantly affect the functional composition, structure and metabolic potential of soil microbial communities, and that various functional groups would respond to such atmospheric changes differentially. To test these hypotheses, we analyzed 96 soil samples from a soybean free-air CO2 enrichment (SoyFACE) experimental site using a comprehensive functional gene microarray (GeoChip 3.0). The results showed the overall functional composition and structure of soil microbial communities shifted under eCO2, eO3 or eCO2+eO3. Key functional genes involved in carbon fixation and degradation, nitrogen fixation, denitrification and methane metabolism were stimulated under eCO2, whereas those involved in N fixation, denitrification and N mineralization were suppressed under eO3, resulting in the fact that the abundance of some eO3-supressed genes was promoted to ambient, or eCO2-induced levels by the interaction of eCO2+eO3. Such effects appeared distinct for each treatment and significantly correlated with soil properties and soybean yield. Overall, our analysis suggests possible mechanisms of microbial responses to global atmospheric change factors through the stimulation of C and N cycling by eCO2, the inhibition of N functional processes by eO3 and the interaction by eCO2 and eO3. This study provides new insights into our understanding of microbial functional processes in response to global atmospheric change in soybean agro-ecosystems.

  14. Exploring the Role of La Codoping beyond Charge Compensation for Enhanced Hydrogen Evolution by Rh-SrTiO3.

    PubMed

    Modak, Brindaban; Ghosh, Swapan K

    2015-08-27

    In this theoretical study, we investigate recent observation of enhancement of hydrogen evolution efficiency of Rh-doped SrTiO3 due to codoping with La at the Sr lattice site. Using hybrid density functional theory, we have systematically studied the electronic structure of (Rh, La)-codoped SrTiO3 and compared with that of Rh-doped SrTiO3, La-doped SrTiO3, and undoped SrTiO3. The aim of the present study has been to explore the role of different factors toward the observed enhanced photoactivity of (Rh, La)-codoped SrTiO3. Doping with only Rh significantly reduces the photoabsorption energy by introducing localized acceptor states between the valence band and conduction band. Unfortunately, these states act as efficient sources for charge carrier trapping. Besides, the oxygen vacancy found to be present in the Rh-doped SrTiO3 as a charge compensating defect also accelerates the electron-hole recombination rate. We have shown that codoping with La and Rh leads to the formation of clean band structure without encountering any midgap states. Introduction of La into the Rh-doped SrTiO3 not only reduces the quantity of Rh(4+) species but also suppresses the oxygen vacancy due to formation of a charge-compensated system. The presence of La favors Rh doping into the crystal structure of SrTiO3 by reducing the formation energy. Moreover, the conduction band minima are found to be shifted in the upward direction significantly due to codoping with Rh and La, thereby increasing the reducing behavior at the conduction band. This leads to enhancement of hydrogen evolution activity of SrTiO3 during photocatalytic water splitting under visible light.

  15. Microstructural development of protective Al2O3 scales

    NASA Technical Reports Server (NTRS)

    Smialek, J. L.

    1984-01-01

    Microstructural characteristics of Al2O3 scales grown as protective coatings on NiCrAl alloys used in jet engines are described. The alloys were pure or doped with 0.3 percent Zr or Y and oxidized in 1 atm air at 1100 C for 0.1, 1 or 20.0 hr. The scales were then examined under a microscope. Transient epitaxial scales, formed during the 0.1 hr treatment and containing Ni, Cr and Al, consisted of a mosaic of subgrains and precipitates of different phases. The Y and Zr dopants had no effect on the nucleation site locations. The appearance of intergranular porosity at 0.1 hr was exacerbated after the 1 hr treatment. A bimodal void distribution appeared after 20 hr, when no porosity was evident. The detection of local areas of preferred orientation is taken as a spur to further studies of scale growth to gain control of the grain size or even to produce single crystal scales.

  16. Technetium incorporation into hematite (alpha-Fe2O3).

    PubMed

    Skomurski, Frances N; Rosso, Kevin M; Krupka, Kenneth M; McGrail, B Pete

    2010-08-01

    Quantum-mechanical methods were used to evaluate mechanisms for possible structural incorporation of Tc species into the model iron oxide, hematite (alpha-Fe2O3). Using periodic supercell models, energies for charge-neutral incorporation of Tc4+ or TcO4- ions were calculated using either a Tc4+/Fe2+ substitution scheme on the metal sublattice, or by insertion of TcO4- as an interstitial species within a hypothetical vacancy cluster. Although pertechnetate incorporation is found to be invariably unfavorable, incorporation of small amounts of Tc4+ (at least 2.6 wt %) is energetically feasible. Energy minimized bond distances around this impurity are provided to aid in future spectroscopic identification of these impurity species. The calculations also show that Fe2+ and Tc4+ prefer to cluster in the hematite lattice, attributed to less net Coulombic repulsion relative to that of Fe3+-Fe3+. These modeling predictions are generally consistent with observed selective association of Tc with iron oxide under reducing conditions, and in residual waste solids from underground storage tanks at the U.S. Department of Energy Hanford Site (Washington, U.S.). Here, even though relatively high pH and oxidizing conditions are dominant, Tc incorporation into iron oxides and (oxy)hydroxides is prospectively enabled by prior reduction of TcO4- to Tc4+ via interaction with radiolytic species.

  17. 26 CFR 301.6501(o)-3 - Partnership items.

    Code of Federal Regulations, 2013 CFR

    2013-04-01

    ... 26 Internal Revenue 18 2013-04-01 2013-04-01 false Partnership items. 301.6501(o)-3 Section 301... § 301.6501(o)-3 Partnership items. (a) Partnership item defined. For purposes of section 6501(o) (as it..., and § 301.6511(g)-1, the term “partnership item” means— (1) Any item required to be taken into...

  18. 26 CFR 301.6501(o)-3 - Partnership items.

    Code of Federal Regulations, 2014 CFR

    2014-04-01

    ... 26 Internal Revenue 18 2014-04-01 2014-04-01 false Partnership items. 301.6501(o)-3 Section 301... § 301.6501(o)-3 Partnership items. (a) Partnership item defined. For purposes of section 6501(o) (as it..., and § 301.6511(g)-1, the term “partnership item” means— (1) Any item required to be taken into...

  19. 26 CFR 301.6501(o)-3 - Partnership items.

    Code of Federal Regulations, 2012 CFR

    2012-04-01

    ... 26 Internal Revenue 18 2012-04-01 2012-04-01 false Partnership items. 301.6501(o)-3 Section 301... § 301.6501(o)-3 Partnership items. (a) Partnership item defined. For purposes of section 6501(o) (as it..., and § 301.6511(g)-1, the term “partnership item” means— (1) Any item required to be taken into...

  20. Diurnal and phenological variations of O 3 and CO 2 fluxes of rice canopy exposed to different O 3 concentrations

    NASA Astrophysics Data System (ADS)

    Tong, Lei; Wang, Xiaoke; Geng, Chunmei; Wang, Wei; Lu, Fei; Song, Wenzhi; Liu, Hongjie; Yin, Baohui; Sui, Lihua; Wang, Qiong

    2011-10-01

    A dynamic chamber system was designed to measure simultaneously the diurnal and phenological canopy ozone (O 3) and carbon dioxide (CO 2) fluxes in the paddy field under different O 3 concentrations (0, 40, 80 and 120 nmol mol -1). On the diurnal timescale, a decreasing trend of canopy O 3 flux was observed from morning to evening and the O 3 flux increased with increasing O 3 concentration, while canopy CO 2 flux generally followed the track of photosynthetic active radiation, with higher values at noon except at the end of the growing season when rice was senescent. The constant CO 2 flux among different O 3 treatments in this experiment suggested that the photosynthesis of the rice canopy was not affected by short-duration (ca. 10 min) O 3 exposure of elevated concentration. The daily mean O 3 and CO 2 fluxes increased with rice growth until the dough stage and the late jointing stage, respectively, then decreased with rice aging. The peak values of O 3 flux appeared later than those of CO 2 flux because the latter was closely synchronized with the leaf area index of the rice canopy. Diurnal mean canopy O 3 flux varied from 18.7 to 43.3 nmol m -2 s -1, and nocturnal mean canopy O 3 flux varied from 2.7 to 17.8 nmol m -2 s -1 and from 7.0 to 25.4 nmol m -2 s -1 for the 40 and 80 nmol mol -1 O 3 treatments, respectively. The considerable amount of nocturnal O 3 flux indicated a significant contribution of non-stomatal factors to canopy O 3 uptake. The adjusted Jarvis multiplicative models were used and well parameterized to fit the measured O 3 and CO 2 fluxes of our rice cultivar from environmental variables. Although more validation work is needed, the present results suggest that the models can be considered as a tool for canopy flux predictions in the paddy field.

  1. Structural and electronic properties of SrZrO3 and Sr(Ti,Zr)O3 alloys

    NASA Astrophysics Data System (ADS)

    Weston, L.; Janotti, A.; Cui, X. Y.; Himmetoglu, B.; Stampfl, C.; Van de Walle, C. G.

    2015-08-01

    Using hybrid density functional calculations, we study the electronic and structural properties of SrZrO3 and ordered Sr (Ti ,Zr )O3 alloys. Calculations were performed for the ground-state orthorhombic (P n m a ) and high-temperature cubic (P m 3 m ) phases of SrZrO3. The variation of the lattice parameters and band gaps with Ti addition was studied using ordered SrTixZr1 -xO3 structures with x =0 , 0.25, 0.5, 0.75, and 1. As Ti is added to SrZrO3, the lattice parameter is reduced and closely follows Vegard's law. On the other hand, the band gap shows a large bowing and is highly sensitive to the Ti distribution. For x =0.5 , we find that arranging the Ti and Zr atoms into a 1 ×1 SrZrO3/SrTiO3 superlattice along the [001] direction leads to interesting properties, including a highly dispersive single band at the conduction-band minimum (CBM), which is absent in both parent compounds, and a band gap close to that of pure SrTiO3. These features are explained by the splitting of the lowest three conduction-band states due to the reduced symmetry of the superlattice, lowering the band originating from the in-plane Ti 3 dx y orbitals. The lifting of the t2 g orbital degeneracy around the CBM suppresses scattering due to electron-phonon interactions. Our results demonstrate how short-period SrZrO3/SrTiO3 superlattices could be exploited to engineer the band structure and improve carrier mobility compared to bulk SrTiO3.

  2. Mesoscopic-scale structure and dynamics near the morphotropic phase boundary of (1 -x ) PbTiO3-x BiScO3

    NASA Astrophysics Data System (ADS)

    Datta, K.; Richter, A.; Göbbels, M.; Neder, R. B.; Mihailova, B.

    2015-07-01

    A range of compelling information on the local structure and dynamics of the ferroelectric perovskite-type (ABO3) system (1 -x ) PbTiO3-x BiScO3 has been revealed through analyzing room-temperature x-ray pair distribution functions and temperature-dependent Raman scattering data for compositions ranging across the morphotropic phase boundary (MPB). Raman scattering data have provided exclusive evidence for distinct dynamical responses from the A-site Pb/Bi and the B-site Ti/Sc cations as a function of composition and temperature. Both pair distribution function and Raman scattering analyses indicate improved coherence between the A-site and B-site off-center displacements for x above the MPB composition. The distinguishable dynamical features were spotted between two sets of compositional range from which x =0.34 could be assigned as a critical composition of "local" MPB: the composition at which the pathway of mesoscopic-scale temperature-driven coupling and transformation processes changes. This differs from the previous reports based on the analysis of the average structure, suggesting the response function of a system may not necessarily follow the evolution of the average structure from which however the MPB has so far been ascribed for a particular system. The individual features of the cations revealed here will further help in understanding the structure-property correlations for similar ferroelectric solid solutions.

  3. La-doped Al2O3 supported Au nanoparticles: highly active and selective catalysts for PROX under PEMFC operation conditions.

    PubMed

    Lin, Qingquan; Qiao, Botao; Huang, Yanqiang; Li, Lin; Lin, Jian; Liu, Xiao Yan; Wang, Aiqin; Li, Wen-Cui; Zhang, Tao

    2014-03-14

    La-doped γ-Al2O3 supported Au catalysts show high activity and selectivity for the PROX reaction under PEMFC operation conditions. The superior performance is attributed to the formation of LaAlO3, which suppresses H2 oxidation and strengthens CO adsorption on Au sites, thereby improving competitive oxidation of CO at elevated temperature.

  4. Methylene blue removal from contaminated waters using O3, natural zeolite, and O3/zeolite.

    PubMed

    Valdés, H; Tardón, R F; Zaror, C A

    2009-01-01

    This paper compares experimental results on methylene blue (MB) removal systems based on ozone oxidation, zeolite adsorption, and simultaneous adsorption-oxidation using ozone in the presence of natural zeolite. The effect of pH (2-8), and the presence of radical scavengers (sodium acetate) on process rates and removal efficiencies are assessed at laboratory scale. The experimental system consisted of a 1 L differential circular flow reactor and an ozone generator rated at 5 g O3/h. Results show that ozone oxidation combined with zeolite adsorption increases the overall MB oxidation rate with respect to ozonation process and zeolite adsorption. In presence of free radical scavenger, only a 25% of reduction on MB removal rate are observed in the simultaneous treatment, as compared with 70% when ozonation treatment is used, suggesting that MB oxidation reactions take mainly place on the zeolite surface.

  5. Oxygen evolution on a SrFeO3 anode - Mechanistic considerations from molecular orbital theory

    NASA Technical Reports Server (NTRS)

    Mehandru, S. P.; Anderson, Alfred B.

    1989-01-01

    Various pathways proposed in the literature for the evolution of O2 in electrochemical oxidations are explored using the atom superposition and electron delocalization molecular orbital (ASED-MO) theory and the cluster models of the SrFeO3 surface as a prototype material. Calculations indicate that oxygen atoms can be easily formed on the (100) surface as well as on the edge cation sites of a SrFeO3 anode by the discharge of OH(-), followed by its deprotonation and electron transfer to the electrode. The O atoms can form O2 on the edge and corner sites, where the Fe(4+) is coordinated to four and three bulk oxygen anions, respectively. The calculations strongly disfavor mechanisms involving coupling of oxygen atoms adsorbed on different cations as well as a mechanism featuring an ozone intermediate.

  6. Anisotropic two-dimensional electron gas at the LaAlO3/SrTiO3 (110) interface

    PubMed Central

    Annadi, A.; Zhang, Q.; Renshaw Wang, X.; Tuzla, N.; Gopinadhan, K.; Lü, W. M.; Roy Barman, A.; Liu, Z. Q.; Srivastava, A.; Saha, S.; Zhao, Y. L.; Zeng, S. W.; Dhar, S.; Olsson, E.; Gu, B.; Yunoki, S.; Maekawa, S.; Hilgenkamp, H.; Venkatesan, T.; Ariando

    2013-01-01

    The observation of a high-mobility two-dimensional electron gas between two insulating complex oxides, especially LaAlO3/SrTiO3, has enhanced the potential of oxides for electronics. The occurrence of this conductivity is believed to be driven by polarization discontinuity, leading to an electronic reconstruction. In this scenario, the crystal orientation has an important role and no conductivity would be expected, for example, for the interface between LaAlO3 and (110)-oriented SrTiO3, which should not have a polarization discontinuity. Here we report the observation of unexpected conductivity at the LaAlO3/SrTiO3 interface prepared on (110)-oriented SrTiO3, with a LaAlO3-layer thickness-dependent metal-insulator transition. Density functional theory calculation reveals that electronic reconstruction, and thus conductivity, is still possible at this (110) interface by considering the energetically favourable (110) interface structure, that is, buckled TiO2/LaO, in which the polarization discontinuity is still present. The conductivity was further found to be strongly anisotropic along the different crystallographic directions with potential for anisotropic superconductivity and magnetism, leading to possible new physics and applications. PMID:23673623

  7. The Vaporization of B2O3(l) to B2O3(g) and B2O2(g)

    NASA Technical Reports Server (NTRS)

    Jacobson, Nathan S.; Myers, Dwight L.

    2011-01-01

    The vaporization of B2O3 in a reducing environment leads to formation of both B2O3(g) and B2O2(g). While formation of B2O3(g) is well understood, many questions about the formation of B2O2(g) remain. Previous studies using B(s) + B2O3(l) have led to inconsistent thermodynamic data. In this study, it was found that after heating, B(s) and B2O3(l) appear to separate and variations in contact area likely led to the inconsistent vapor pressures of B2O2(g). To circumvent this problem, an activity of boron is fixed with a two-phase mixture of FeB and Fe2B. Both second and third law enthalpies of formation were measured for B2O2(g) and B2O3(g). From these the enthalpies of formation at 298.15 K are calculated to be -479.9 +/- 41.5 kJ/mol for B2O2(g) and -833.4 +/- 13.1 kJ/mol for B2O3(g). Ab initio calculations to determine the enthalpies of formation of B2O2(g) and B2O3(g) were conducted using the W1BD composite method and show good agreement with the experimental values.

  8. Tailoring the Two Dimensional Electron Gas at Polar ABO3/SrTiO3 Interfaces for Oxide Electronics

    PubMed Central

    Li, Changjian; Liu, Zhiqi; Lü, Weiming; Wang, Xiao Renshaw; Annadi, Anil; Huang, Zhen; Zeng, Shengwei; Ariando; Venkatesan, T.

    2015-01-01

    The 2D electron gas at the polar/non-polar oxide interface has become an important platform for several novel oxide electronic devices. In this paper, the transport properties of a wide range of polar perovskite oxide ABO3/SrTiO3 (STO) interfaces, where ABO3 includes LaAlO3, PrAlO3, NdAlO3, NdGaO3 and LaGaO3 in both crystalline and amorphous forms, were investigated. A robust 4 unit cell (uc) critical thickness for metal insulator transition was observed for crystalline polar layer/STO interface while the critical thickness for amorphous ones was strongly dependent on the B site atom and its oxygen affinity. For the crystalline interfaces, a sharp transition to the metallic state (i.e. polarization catastrophe induced 2D electron gas only) occurs at a growth temperature of 515 °C which corresponds to a critical relative crystallinity of ~70 ± 10% of the LaAlO3 overlayer. This temperature is generally lower than the metal silicide formation temperature and thus offers a route to integrate oxide heterojunction based devices on silicon. PMID:26307382

  9. Tailoring the Two Dimensional Electron Gas at Polar ABO3/SrTiO3 Interfaces for Oxide Electronics.

    PubMed

    Li, Changjian; Liu, Zhiqi; Lü, Weiming; Wang, Xiao Renshaw; Annadi, Anil; Huang, Zhen; Zeng, Shengwei; Ariando; Venkatesan, T

    2015-08-26

    The 2D electron gas at the polar/non-polar oxide interface has become an important platform for several novel oxide electronic devices. In this paper, the transport properties of a wide range of polar perovskite oxide ABO3/SrTiO3 (STO) interfaces, where ABO3 includes LaAlO3, PrAlO3, NdAlO3, NdGaO3 and LaGaO3 in both crystalline and amorphous forms, were investigated. A robust 4 unit cell (uc) critical thickness for metal insulator transition was observed for crystalline polar layer/STO interface while the critical thickness for amorphous ones was strongly dependent on the B site atom and its oxygen affinity. For the crystalline interfaces, a sharp transition to the metallic state (i.e. polarization catastrophe induced 2D electron gas only) occurs at a growth temperature of 515 °C which corresponds to a critical relative crystallinity of ~70 ± 10% of the LaAlO3 overlayer. This temperature is generally lower than the metal silicide formation temperature and thus offers a route to integrate oxide heterojunction based devices on silicon.

  10. Tailoring the Two Dimensional Electron Gas at Polar ABO3/SrTiO3 Interfaces for Oxide Electronics

    NASA Astrophysics Data System (ADS)

    Li, Changjian; Liu, Zhiqi; Lü, Weiming; Wang, Xiao Renshaw; Annadi, Anil; Huang, Zhen; Zeng, Shengwei; Ariando; Venkatesan, T.

    2015-08-01

    The 2D electron gas at the polar/non-polar oxide interface has become an important platform for several novel oxide electronic devices. In this paper, the transport properties of a wide range of polar perovskite oxide ABO3/SrTiO3 (STO) interfaces, where ABO3 includes LaAlO3, PrAlO3, NdAlO3, NdGaO3 and LaGaO3 in both crystalline and amorphous forms, were investigated. A robust 4 unit cell (uc) critical thickness for metal insulator transition was observed for crystalline polar layer/STO interface while the critical thickness for amorphous ones was strongly dependent on the B site atom and its oxygen affinity. For the crystalline interfaces, a sharp transition to the metallic state (i.e. polarization catastrophe induced 2D electron gas only) occurs at a growth temperature of 515 °C which corresponds to a critical relative crystallinity of ~70 ± 10% of the LaAlO3 overlayer. This temperature is generally lower than the metal silicide formation temperature and thus offers a route to integrate oxide heterojunction based devices on silicon.

  11. Enhanced Dielectric Properties and High-Temperature Microwave Absorption Performance of Zn-Doped Al2O3 Ceramic

    NASA Astrophysics Data System (ADS)

    Wang, Yuan; Luo, Fa; Wei, Ping; Zhou, Wancheng; Zhu, Dongmei

    2015-07-01

    To improve the dielectric and microwave absorption properties of Al2O3 ceramic, Zn-doped Al2O3 ceramic was prepared by conventional ceramic processing. X-ray diffraction analysis confirmed that Zn atoms successfully entered the Al2O3 ceramic lattice and occupied Al sites. The complex permittivity increased with increasing Zn concentration, which is mainly attributed to the increase in charged vacancy defects and densification of the Al2O3 ceramic. In addition, the temperature-dependent complex permittivity of 3% Zn-doped Al2O3 ceramic was determined in the temperature range from 298 K to 873 K. Both the real and imaginary parts of the complex permittivity increased monotonically with increasing temperature, which can be ascribed to the shortened relaxation time and increasing electrical conductivity. The increased complex permittivity leads to a great improvement in microwave absorption. In particular, when the temperature is up to 873 K, the 3% Zn-doped Al2O3 ceramic exhibited the best absorption performance with a maximum peak (-12.1 dB) and broad effective absorption bandwidth (reflection loss less than -10 dB from 9.3 GHz to 12.3 GHz). These results reveal that Zn-doped Al2O3 ceramic is a promising candidate for use as a kind of high-temperature microwave absorption material.

  12. Native defects and Pr impurities in orthorhombic CaTiO3 by first-principles calculations

    NASA Astrophysics Data System (ADS)

    Zhu, Ailing; Wang, Jianchuan; Zhao, Dongdong; Du, Yong

    2011-07-01

    Formation energies of native defects and Pr impurities in orthorhombic CaTiO3 are explored using the first-principles calculations. The Ca vacancy (VCa), Ti vacancy (VTi) and Ca antisite (CaTi) are found to be energetically preferable. The Ti antisite (TiCa) and O vacancy (VO) are not energetically favorable in the wide range of Fermi level. In Pr-doped CaTiO3, Pr substituting for Ca (PrCa) is likely to form under condition A in which CaTiO3 is in equilibrium with CaO and O2. Under condition B (TiO2, CaTiO3 and O2 are in equilibrium), PrTi defect is energetically preferable depending on the Fermi levels. Several native defects and the two sites of Pr impurities in CaTiO3 are coincided with several different defects in Pr-doped CaTiO3 reported in the literature. Based on the present calculations, we can elucidate that the Ca deficiency design of the traditional formula Ca1-xVCa(x/2)PrxTiO3 is not the best for efficient red photoluminescence, which is realized via the experimental measurements.

  13. Dry deposition of O3 and SO2 estimated from gradient measurements above a temperate mixed forest.

    PubMed

    Wu, Zhiyong; Staebler, Ralf; Vet, Robert; Zhang, Leiming

    2016-03-01

    Vertical profiles of O3 and SO2 concentrations were monitored at the Borden Forest site in southern Ontario, Canada from May 2008 to April 2013. A modified gradient method (MGM) was applied to estimate O3 and SO2 dry deposition fluxes using concentration gradients between a level above and a level below the canopy top. The calculated five-year mean (median) dry deposition velocity (Vd) were 0.35 (0.27) and 0.59 (0.54) cm s(-1), respectively, for O3 and SO2. Vd(O3) exhibited large seasonal variations with the highest monthly mean of 0.68 cm s(-1) in August and the lowest of 0.09 cm s(-1) in February. In contrast, seasonal variations of Vd(SO2) were smaller with monthly means ranging from 0.48 (May) to 0.81 cm s(-1) (December). The different seasonal variations between O3 and SO2 were caused by the enhanced SO2 uptake by snow surfaces in winter. Diurnal variations showed a peak value of Vd in early morning in summer months for both O3 and SO2. Canopy wetness increased the non-stomatal uptake of O3 while decreasing the stomatal uptake. This also applied to SO2, but additional factors such as surface acidity also played an important role on the overall uptake.

  14. Crystalline orientations of Tl2Ba2Ca2Cu3O(x) grains on MgO, SrTiO3, and LaAlO3 substrates

    NASA Technical Reports Server (NTRS)

    Liou, S. H.; Wu, C. Y.

    1992-01-01

    Crystalline orientations of Tl2Ba2Ca2Cu3O(x) grains in magnetron sputtered films on MgO (001), SrTiO3 (001), and LaAlO3 (001) substrates were investigated by scanning electron microscopy. In contrast to the nearly single crystalline films on the lattice matched substrates SrTiO3 and LaAlO3, films on the MgO (001) substrate, being polycrystalline in nature, exhibit several preferred in-plane grain orientations. These orientations agree well with a simplified theory of near-coincidence site lattices between Tl2Ba2Ca2Cu3O(x) and MgO.

  15. Bipolar resistive switching in YMnO3/Nb:SrTiO3 pn-heterojunctions

    NASA Astrophysics Data System (ADS)

    Bogusz, Agnieszka; Bürger, Danilo; Skorupa, Ilona; Schmidt, Oliver G.; Schmidt, Heidemarie

    2016-11-01

    Resistively switching oxides are promising materials for use in electronic applications such as nonvolatile memories, logic gates, and artificial synapses. This work presents the bipolar resistive switching (BRS) in YMnO3/Nb:SrTiO3 pn-heterojunctions. A thermally driven electroforming process is required prior to the observed BRS. Results indicate that the BRS in YMnO3/Nb:SrTiO3 originates from the combined effects of charge trapping and detrapping processes along with the electro-migration of charged point defects in the depletion layer of the pn-heterojunction. It is shown that the built-in voltage of the pn-heterojunctions can be tuned by the oxygen partial pressure during growth of the YMnO3 thin film and impacts the working parameters of the resistively switching cell. This study provides a guideline for material engineering of bipolar resistive switches based on pn-heterojunctions.

  16. Impact of structural transitions on electron transport at LaAlO3/SrTiO3 heterointerfaces

    NASA Astrophysics Data System (ADS)

    Schoofs, Frank; Egilmez, Mehmet; Fix, Thomas; MacManus-Driscoll, Judith L.; Blamire, Mark G.

    2012-02-01

    We have studied conductive LaAlO3/SrTiO3 heterostructures deposited at different oxygen pressures. Photoluminescence spectra confirm the presence of a significant amount of oxygen vacancies in samples deposited at low oxygen pressures. Power law fitting of resistance versus temperature measurements reveals fundamental characteristics of the conduction mechanism at the interface. A distinct non-Fermi-liquid behavior is observed for samples grown in higher oxygen pressure, which give two-dimensionally confined conducting interfaces, whereas characteristic electron-electron scattering is observed for samples grown in lower oxygen pressures, as seen in bulk doped SrTiO3 (i.e., oxygen deficient SrTiO3). Transitions between different conduction modes occur throughout the studied temperature range (10-270 K) as a result of structural transformations in the near-surface region of the SrTiO3.

  17. Structural Transformation of Hexagonal (0001)BaTiO3 Ceramics to Tetragonal (111)BaTiO3 Ceramics

    NASA Astrophysics Data System (ADS)

    Watanabe, Takayuki; Shimada, Mikio; Aiba, Toshiaki; Yabuta, Hisato; Miura, Kaoru; Oka, Kengo; Azuma, Masaki; Wada, Satoshi; Kumada, Nobuhiro

    2011-09-01

    A ceramic slurry that contains a 6H-type Ba(Ti0.95Mn0.05)O3 powder was casted into a plaster mold under 10 T magnetic field to form a green compact of (0001)-oriented Ba(Ti0.95Mn0.05)O3. After sintering the green compact at 1300 °C in air, it was confirmed that the (0001)-oriented 6H-type perovskite structure transformed to a (111)-oriented 3C-type perovskite structure. The structural transformation was again examined using hexagonal BaTiO3 prepared by reducing pseudo-cubic BaTiO3 powder in H2 atmosphere. In this case, the preferred (0001) orientation was not confirmed for the green compacts. After sintering the green compacts at 1300 °C in air, mixed crystal orientations of (100)/(001) and (111) were observed for the resultant tetragonal BaTiO3 ceramics. This (100)/(001) orientation was suppressed by annealing the hexagonal BaTiO3 powder at 1000 °C before slip-casting, leading to highly (111)-oriented ceramics. It was found that the green compacts of (0001)-oriented hexagonal BaTiO3 can transform into (111)-oriented tetragonal BaTiO3 ceramics, maintaining the macroscopic crystal orientations due to a similar atomic stacking along [0001] of 6H-type BaTiO3 and [111] of 3C-type BaTiO3.

  18. Investigation of hyperfine interactions in GdCrO3 perovskite oxide using PAC spectroscopy

    NASA Astrophysics Data System (ADS)

    Silva, Renilson A. Da; Saxena, R. N.; Carbonari, A. W.; Cabrera-Pasca, G. A.

    2010-04-01

    Perturbed angular correlation (PAC) measurements have been carried out in the antiferromagnetic GdCrO3 perovskite oxide using 111In (111Cd) and 181Hf(181Ta) nuclear probes. The radioactive parent nuclei 111In and 181Hf were introduced in the compound through a chemical process during sample preparation. The PAC measurements were carried out in the temperature range 20-300 K. Measurements with the 181Ta indicated a unique quadrupole interaction above 170 K and a combined electric quadrupole and magnetic dipole interactions below this temperature. The observed interaction was assigned to the probe nuclei substituting Cr sites. Measurements with 111Cd showed two quadrupole interactions. Only one of the fractions however, showed a combined electric and magnetic interaction in the temperature rage 20-170 K which was assigned to 111Cd probe substituting Cr site. The other fraction was attributed to the Gd site. The present results are compared with those of LaCrO3 and NdCrO3.

  19. Molecular Dynamics Simulations of Chemically Disordered Ferroelectric (Ba,Sr)TiO3 with a Semi-Empirical Effective Hamiltonian

    NASA Astrophysics Data System (ADS)

    Nishimatsu, Takeshi; Grünebohm, Anna; Waghmare, Umesh V.; Kubo, Momoji

    2016-11-01

    We present a semi-empirical effective Hamiltonian to capture effects of disorder associated with Ba and Sr cations occupying A sites in (BaxSr1-x)TiO3 on its ferroelectric phase transition. Averaging between the parameters of first-principles effective Hamiltonians of end members BaTiO3 and SrTiO3, we include a term with an empirical parameter to capture the local polarization and strains arising from the difference between ionic radii of Ba and Sr. Using mixed-space molecular dynamics of the effective Hamiltonian, we determine T-dependent ferroelectric phase transitions in (BaxSr1-x)TiO3 which are in good agreement with experiment. Our scheme of determination of semi-empirical parameters in effective Hamiltonian should be applicable to other perovskite-type ferroelectric solid solutions.

  20. Moessbauer Effect Study of Bi2O3. Na2O. B2O3. Fe2O3 Glass System

    SciTech Connect

    Salah, S.H.; Kashif, I.; Salem, S.M.; Mostafa, A.G.; El-Manakhly, K.A.

    2005-04-26

    Sodium-tetra-borate host glass containing both bismuth and iron cations were prepared obeying the composition (Na2B4O7)0.75 (Fe2O3)0.25-x (Bi2O3)x [where x = 0.0, 0.05, 0.10, 0.15, 0.20, and 0.25 mol.%]. X-ray diffraction indicated that all samples were in a homogeneous glassy phase. Moessbauer effect results showed that all iron ions appeared as Fe3+ ions occupying tetrahedral coordination state. The covalency of the Fe-O bond increased as bismuth oxide was gradually increased. IR measurements indicated the presence of some non-bridging oxygens and confirmed that iron ions occupy the tetrahedral coordination state. It was found also that, as Bi2O3 was gradually increased both magnetic susceptibility and specific volume decreased, while both density and molar volume increased.

  1. Formation of hexagonal-molybdenum trioxide (h-MoO3) nanostructures and their pseudocapacitive behavior

    NASA Astrophysics Data System (ADS)

    Kumar, Vipin; Wang, Xu; Lee, Pooi See

    2015-07-01

    The crystallographic structure and morphology of redox active transition metal oxides have a pronounced effect on their electrochemical properties. In this work, h-MoO3 nanostructures with three distinct morphologies, i.e., pyramidal nanorod, prismatic nanorod and hexagonal nanoplate, were synthesized by a facile solvothermal method. The morphologies of h-MoO3 nanostructures were tailored by a controlled amount of hexamethylenetetramine. An enhanced specific capacitance about 230 F g-1 at an applied current density of 0.25 A g-1 was achieved in h-MoO3 pyramidal nanorods. Electrochemical studies confirmed that the h-MoO3 pyramidal nanorods exhibit superior charge-storage ability. This improved performance can be ascribed to the coexistence of its well exposed crystallographic planes with abundant active sites, i.e., hexagonal window (HW), trigonal cavity (TC) and four-coordinated square window (SW). The mechanism of charge-storage is likely facilitated by the vehicle mechanism of proton transportation due to the availability of the vehicles, i.e., NH4+ and H2O. The promising, distinct and unexploited features of h-MoO3 nanostructures reveal a strong candidate for pseudocapacitive electrode materials.The crystallographic structure and morphology of redox active transition metal oxides have a pronounced effect on their electrochemical properties. In this work, h-MoO3 nanostructures with three distinct morphologies, i.e., pyramidal nanorod, prismatic nanorod and hexagonal nanoplate, were synthesized by a facile solvothermal method. The morphologies of h-MoO3 nanostructures were tailored by a controlled amount of hexamethylenetetramine. An enhanced specific capacitance about 230 F g-1 at an applied current density of 0.25 A g-1 was achieved in h-MoO3 pyramidal nanorods. Electrochemical studies confirmed that the h-MoO3 pyramidal nanorods exhibit superior charge-storage ability. This improved performance can be ascribed to the coexistence of its well exposed

  2. New epsilon-Bi2O3 metastable polymorph.

    PubMed

    Cornei, Nicoleta; Tancret, Nathalie; Abraham, Francis; Mentré, Olivier

    2006-06-26

    The new metastable epsilon-Bi2O3 polymorph has been prepared by hydrothermal treatment and structurally characterized. It shows strong relationships with the room temperature alpha form and the metastable beta form through rearrangements of [Bi2O3] columns formed by edge-sharing OBi4 tetrahedra. Its fully ordered crystal structure yields an ionic insulating character. It irreversibly transforms at 400 degrees C to the alpha form. The chemical analysis indicates its undoped bismuth oxide nature, then leading to the fifth characterized Bi2O3 polymorph to date.

  3. Current status of Ga2O3 power devices

    NASA Astrophysics Data System (ADS)

    Higashiwaki, Masataka; Murakami, Hisashi; Kumagai, Yoshinao; Kuramata, Akito

    2016-12-01

    Gallium oxide (Ga2O3) is an emerging wide-bandgap semiconductor for high-power, low-loss transistors and diodes by virtue of its excellent material properties and suitability for mass production. In this paper, we begin by discussing the material properties of Ga2O3 that make it an attractive alternative to not only Si but also other wide-bandgap materials such as SiC and GaN. State-of-the-art Ga2O3-based devices that have been fabricated to date demonstrate the performance potential for power electronics applications.

  4. Investigation of luminescence and laser transition of Dy3+ in Li2O-Gd2O3-Bi2O3-B2O3 glasses

    NASA Astrophysics Data System (ADS)

    Zaman, F.; Kaewkhao, J.; Srisittipokakun, N.; Wantana, N.; Kim, H. J.; Rooh, G.

    2016-05-01

    The aim of this study is to develop Li2O-Gd2O3-Bi2O3-B2O3 glass doped with different concentration of Dy3+ ions by melt quenching technique for different applications in photonics and laser devices. From the experimental oscillator strength (fexp) of the absorption spectra the JO intensity parameters (Ω λ = 2, 4, 6) have been calculated, and by using these JO intensity parameters various radiative parameters were calculated. By using JO theory the radiative transition probability (AR), radiative lifetime (τR) and branching ratio (βR) for Dy3+ ion have been found. A decrease in lifetimes of the prepared glass by increasing concentration of Dy3+ is because of the energy transfer through cross relaxation and resonant energy transfer channels in the present glass matrix. Using experimental and calculated lifetimes, the quantum efficiency (η) and non-radiative relaxation rates (WNR) of 4F9/2 excited state have been calculated. From emission spectra, effective bandwidths (Δλeff) and emission stimulated emission cross section σ (λp) were found for 4F9/2 → 6HJ (J = 15/2, 13/2, 11/2 and 9/2). Chromaticity results revealed that the CCT values of the LGBiBDy glass samples are in between to those of day light and commercial white light LED sources. Further investigations are under way for the optimization of dopant concentration in the Li2O-Gd2O3-Bi2O3-B2O3 glass.

  5. Fiber optic thermometer using Cr-doped GdAlO3 broadband emission decay

    NASA Astrophysics Data System (ADS)

    Eldridge, Jeffrey I.; Chambers, Matthew D.

    2015-09-01

    Luminescence decay temperature measurements are performed from 800 to 1200 °C using a Cr-doped GdAlO3 (Cr:GdAlO3) sensor tip on a YAG single crystal fiber. As a thermographic phosphor, Cr:GdAlO3 combines the intense luminescence of transition metal dopants with the high temperature long decay times usually exhibited only by rare earth dopants. The proposed mechanism is emission by the Cr3+ dopant via the spin-allowed 4T2  →  4A2 transition supported by a reservoir state in 2E which populates {}4{{\\text{T}}2} (2E  →  {}4{{\\text{T}}2} ) through thermal equilibration. The relative energy levels and transition probabilities associated with the strong crystal field at the Al3+ site in the perovskite structure of GdAlO3 are favorable for suppressing thermal quenching of luminescence. Results from a single-fiber configuration sensor, based on a YAG fiber for its low background luminescence, are presented. Using a decay curve fitting procedure that accounts for background fluorescence, accuracies of better than  ±5 °C are demonstrated.

  6. Infrared and Raman spectroscopy of [Pb(Zn1/3Nb2/3)O3]0.92-[PbTiO3]0.08 and [Pb(Mg1/3Nb2/3)O3]0.71-[PbTiO3]0.29 single crystals

    NASA Astrophysics Data System (ADS)

    Kamba, S.; Buixaderas, E.; Petzelt, J.; Fousek, J.; Nosek, J.; Bridenbaugh, P.

    2003-01-01

    Far-infrared reflectivity spectra of [Pb(Zn1/3Nb2/3)O3]0.92-[PbTiO3]0.08 and [Pb(Mg1/3Nb2/3)O3]0.71-[PbTiO3]0.29 single crystals were investigated between 10 and 530 K, micro-Raman spectra were recorded between 300 and 800 K. No phonon softening was observed near either of the ferroelectric phase transitions. The low-frequency dielectric anomaly in the paraelectric phase is caused by contribution of dynamic polar nanoclusters with the main dispersion in the microwave range. Infrared and Raman spectra confirm the locally doubled unit cell (Zprim=2) in the paraelectric and ferroelectric phases due to the ordering in the perovskite B sites and occurrence of polar nanoclusters in the paraelectric phase. The lowest-frequency transverse optical (TO1) phonon mode active in the infrared spectra is underdamped in contrast to the recent result of inelastic neutron scattering, where no TO1 mode could be observed for the wave vectors q⩽0.2 Å-1. This discrepancy was explained by different q vectors probed in infrared and neutron experiments. The infrared probe couples with very long-wavelength phonons (q≈10-5 Å-1) which see the homogeneous medium averaged over the nanoclusters, whereas the neutron probe couples with phonons whose wavelength is comparable to the nanocluster size (q⩾10-2 Å-1).

  7. Raman effect and magnetic properties of doped TbMnO3

    NASA Astrophysics Data System (ADS)

    Kumar, A.; Shahi, P.; Kumar, S.; Shukla, K. K.; Singh, Ranjan Kr; Ghosh, A. K.; Nigam, A. K.; Chatterjee, Sandip

    2013-03-01

    The room temperature Raman scattering, structural and temperature variation of magnetic properties of Y- and Ni-doped TbMnO3 are investigated. Both for Y and Ni doping, the Néel temperature (TN) decreases. Y doping reduces effectively both the JTb-Tb and JMn-Mn exchange interactions, whereas Ni doping on the Mn site decreases only the JMn-Mn exchange interaction. The reduction in TN in the Ni-doped sample cannot be explained with simple exchange integral. It might be the case that Ni2+ doping changes the polarization flop observed in TbMnO3 which in effect may change the exchange interaction. In the room temperature Raman spectra for TbMnO3 and Y-doped TbMnO3 eight modes are observed. When Ni is doped, modes due to MnO6 bending and in-plane O2 stretching broaden and few modes disappear due to the induced lattice disorder.

  8. Cation Intermixing And Electronic Deviations At The Insulating LaCrO3/SrTiO3(001) Interface

    SciTech Connect

    Colby, Robert J.; Qiao, Liang; Zhang, Hongliang; Shutthanandan, V.; Ciston, Jim; Kabius, Bernd C.; Chambers, Scott A.

    2013-10-29

    The interface between polar perovskite LaCrO3 (LCO) and non-polar SrTiO3(001) (STO), grown by molecular beam epitaxy, is examined using a combination of electron microscopy, spectroscopy, and Rutherford backscattering spectrometry. The LCO/STO(001) interface is insulating, a potential counter example for the claim that polar/nonpolar perovskite interfaces should be conductive by virtue of an electronic reconstruction to alleviate the polar discontinuity. The A-site cations of these ABO3 perovskites are found to diffuse across the interface to a greater extent than the B-site cations, based on high angle annular dark field scanning transmission electron microscopy (HAADF-STEM), energy dispersive x-ray spectroscopy (EDS) and electron energy loss spectroscopy (EELS). The B-site cation valences are shown to be partially reduced near the interface by analysis of EELS near-edge structures. The location and direction of these electronic modifications do not intuitively compensate the charge imbalance imposed by uneven cation inter-diffusion, and yet both the film and interface are insulating. These results highlight the importance of both the physical and electronic structure of such complex interfaces in determining their characteristics. Furthermore, the extent of inter-diffusion is shown to increase with increasing LCO film thickness, suggesting a potential mechanism behind the critical thickness for interfacial conductivity in other polar/non-polar oxide systems, and a fundamental limitation on the formation of abrupt interfaces in LCO/STO(001).

  9. Synthesis of A12O3 Nanoparticles from Local Bauxite for Water- A12O3 Nanofluids egy

    NASA Astrophysics Data System (ADS)

    Gustaman Syarif, Dani; Hadi Prajitno, Djoko; Umar, Efrizon

    2017-01-01

    A study on synthesis and characterization of A12O3 nanoparticles from bauxite for water-A12O3 nanofluids as an alternative coolant for nuclear and non-nuclear applications has been done. The A12O3 nanoparticles were synthesized by heating AlOOH as a precursor derived from local bauxite. The Al2O3 nanoparticles were dispersed in water and ultrasonicated to produce nanofluids. XRD data showed that the A12O3 nanoparticles crystallized in gamma alumina with crystallite size of 4.5 nm (Debye Scherrer method). Surface area of the A12O3 nanoparticles was 195 m2/gram. Data of TEM showed that the particle size was smaller than 10 nm. According to zeta potential data, the nanofluids were stable at neutral pH of 7.3 with zeta potential of 28-51 mV. The height of the nanofluid surface decreased about 13 % after 6 days. In addition, the CHF of the water-A12O3 nanofluids produced in this study increased about 55-161 % compared to that of water.

  10. Retardation mechanism of ultrathin Al2O3 interlayer on Y2O3 passivated gallium nitride surface.

    PubMed

    Quah, Hock Jin; Cheong, Kuan Yew

    2014-05-28

    A systematic investigation was carried out by incorporating an ultrathin aluminum oxide (Al2O3) as an interlayer between yttrium oxide (Y2O3) passivation layer and GaN substrate. The sandwiched samples were then subjected to postdeposition annealing in oxygen ambient from 400 to 800 °C. The Al2O3 interlayer was discovered to play a significant role in slowing down inward diffusion of oxygen through the Y2O3 passivation layer as well as in impeding outward diffusion of Ga(3+) and N(3-) from the decomposed GaN surface. These beneficial effects have suppressed subsequent formation of interfacial layer. A mechanism in association with the function of Al2O3 as an interlayer was suggested and discussed. The mechanism was explicitly described on the basis of the obtained results from X-ray diffraction, X-ray photoelectron spectroscopy, energy-filtered transmission electron microscopy (TEM), high resolution TEM, and electron energy loss spectroscopy line scan. A correlation between the proposed mechanism and metal-oxide-semiconductor characteristics of Y2O3/Al2O3/GaN structure has been proposed.

  11. High-mobility two-dimensional electron gas in SrGeO3- and BaSnO3-based perovskite oxide heterostructures: an ab initio study.

    PubMed

    Wang, Yaqin; Tang, Wu; Cheng, Jianli; Nazir, Safdar; Yang, Kesong

    2016-11-23

    We explored the possibility of producing a high-mobility two-dimensional electron gas (2DEG) in the LaAlO3/SrGeO3 and LaGaO3/BaSnO3 heterostructures using first-principles electronic structure calculations. Our results show that the 2DEG occurs at n-type LaAlO3/SrGeO3 and LaGaO3/BaSnO3 interfaces. Compared to the prototype LaAlO3/SrTiO3, LaAlO3/SrGeO3 and LaGaO3/BaSnO3 systems yield comparable total interfacial charge carrier density but much lower electron effective mass (nearly half the value of LaAlO3/SrTiO3), thus resulting in about twice larger electron mobility and enhanced interfacial conductivity. This work demonstrates that SrGeO3 and BaSnO3 can be potential substrate materials to achieve a high-mobility 2DEG in the perovskite-oxide heterostructures.

  12. Thermodynamic stability of stoichiometric LaFeO3 and BiFeO3: a hybrid DFT study.

    PubMed

    Heifets, Eugene; Kotomin, Eugene A; Bagaturyants, Alexander A; Maier, Joachim

    2017-02-01

    BiFeO3 perovskite attracts great attention due to its multiferroic properties and potential use as a parent material for Bi1-xSrxFeO3-δ and Bi1-xSrxFe1-yCoyO3-δ solid solutions in intermediate temperature cathodes of oxide fuel cells. Another iron-based LaFeO3 perovskite is the end member for well-known solid solutions (La1-xSrxFe1-yCoyO3-δ) used for oxide fuel cells and other electrochemical devices. In this study an ab initio hybrid functional approach was used for the study of the thermodynamic stability of both LaFeO3 and BiFeO3 with respect to decompositions to binary oxides and to elements, as a function of temperature and oxygen pressure. The localized (LCAO) basis sets describing the crystalline electron wave functions were carefully re-optimized within the CRYSTAL09 computer code. The results obtained by considering Fe as an all-electron atom and within the effective core potential technique are compared in detail. Based on our calculations, the phase diagrams were constructed allowing us to predict the stability region of stoichiometric materials in terms of atomic chemical potentials. This permits determining the environmental conditions for the existence of stable BiFeO3 and LaFeO3. These conditions were presented as contour maps of oxygen atoms' chemical potential as a function of temperature and partial pressure of oxygen gas. A similar analysis was also performed using the experimental Gibbs energies of formation. The obtained phase diagrams and contour maps are compared with the calculated ones.

  13. Efficient regioselective O3-monodesilylation by hydrochloric acid in cyclodextrins.

    PubMed

    Gu, Jiamin; Chen, Tong; Wang, Qifang; Chen, Tieyu; Ling, Chang-Chun

    2015-06-17

    An efficient O3-monodesilylation method has been developed for the derivatization of per-3-O-silylated cyclodextrin (CD) derivatives. Using hydrochloric acid as a reagent, the O3-monodesilylation was found to be regioselective, mild, practical and general as it can be applied to all α-, β- and γ-CDs. The advantage of the methodology is that the acid-catalyzed O3-desilylation can be carried out in a stepwise manner so that different types of functional groups can be introduced to a CD molecule at different stage of the O3-desilylations. This makes the current methodology flexible and versatile. This current methodology constitutes one of the few methodologies available for the regioselective modification of CDs at the secondary face.

  14. Electronic excitations in γ -Li2IrO3

    NASA Astrophysics Data System (ADS)

    Li, Ying; Winter, Stephen M.; Jeschke, Harald O.; Valentí, Roser

    2017-01-01

    We investigate the electronic properties of the three-dimensional stripyhoneycomb γ -Li2IrO3 via relativistic density functional theory calculations as well as exact diagonalization of finite clusters and explore the details of the optical conductivity. Our analysis of this quantity reveals the microscopic origin of the experimentally observed (i) optical transitions and (ii) anisotropic behavior along the various polarization directions. In particular, we find that the optical excitations are overall dominated by transitions between jeff=1 /2 and 3/2 states and the weight of transitions between jeff=1 /2 states at low frequencies can be correlated to deviations from a pure Kitaev description. We furthermore reanalyze within this approach the electronic excitations in the known two-dimensional honeycomb systems α -Li2IrO3 and Na2IrO3 and discuss the results in comparison to γ -Li2IrO3 .

  15. Towards positive feedbacks between vegetation and tropospheric O3

    NASA Astrophysics Data System (ADS)

    VanLoocke, A. D.; Bernacchi, C. J.; Ainsworth, E. A.; Betzelberger, A. M.

    2011-12-01

    The concentration of tropospheric ozone ([O3]) has approximately doubled since 1900 and is projected to continue increasing. The extent of this increase depends strongly on the emission of ozone precursors as well as changing temperature and humidity. The responses of vegetation to O3 may also have the potential to positively feedback on regional climate and on the cycle of O3 formation and destruction. Plant productivity is linked to feedbacks in the climate indirectly through the carbon cycle as well as directly through the partitioning of radiation into sensible and latent heat fluxes. In the troposphere, O3 reduces plant productivity, an effect that is pronounced in soybean, the 4th most important food crop in the world. The soybean-maize agro-ecosystem is the largest ecosystem in the contiguous U.S., therefore changes in productivity and water use by soybean under increasing [O3] could impact the regional climate and hydrologic cycle in Midwestern U.S. with feedback effects on tropospheric O3 production and cycling. To assess the response to increasing [O3], soybeans were grown under open-air agricultural conditions at the SoyFACE research facility. During the 2009 growing season, eight 20 m diameter plots were exposed to different [O3] ranging from 40 to 200 ppb. Measurements of leaf-level gas exchange were made on four dates throughout the growing season and non-destructive measurements of Leaf Area Index were made weekly. Canopy latent and sensible heat fluxes were measured continuously throughout the growing season (day of year 197-245) using a residual energy balance micrometeorological technique. Results show that as [O3] increased, rates of photosynthesis and stomatal conductance decreased. Productivity, (i.e. seed yield) decreased by over 60% from 40 to 200 ppb while canopy evapotranspiration decreased by 30%. Sensible heat flux increased by 30%, while the growing season average canopy temperatures increased by 1 °C and with peak increases of 2

  16. Anharmonic phonons and magnons in BiFeO3

    SciTech Connect

    Delaire, Olivier A; Ma, Jie; Stone, Matthew B; Huq, Ashfia; Gout, Delphine J; Brown, Craig; Wang, Kefeng; Ren, Zhifeng

    2012-01-01

    The phonon density of states (DOS) and magnetic excitation spectrum of polycrystalline BiFeO3 were measured for temperatures 200 < T < 750K , using inelastic neutron scattering (INS). Our results indicate that the magnetic spectrum of BiFeO3 closely resembles that of similar Fe perovskites, such as LaFeO3, despite the cycloid modulation in BiFeO3. We do not find any evidence for a spin gap. A strong T-dependence of the phonon DOS was found, with a marked broadening of the whole spectrum, providing evidence of strong anharmonicity. This anharmonicity is corroborated by large amplitude motions of Bi and O ions observed with neutron diffraction. These results highlight the importance of spin-phonon coupling in this material.

  17. Advanced treatment of benzothiazole contaminated waters: comparison of O3, AC, and O3/AC processes.

    PubMed

    Valdés, H; Zaror, C A

    2005-01-01

    Benzothiazole (BT) is a toxic and poorly biodegradable contaminant, usually found in wastewater from rubber related applications. This compound could be effectively eliminated using advanced treatment processes. This paper compares experimental results on detoxification systems based on ozone oxidation, activated carbon adsorption, and simultaneous adsorption-oxidation using ozone in the presence of activated carbon. The effect of pH (2-11), and the presence of radical scavengers (tert-butyl alcohol and sodium carbonate) on process rates and removal efficiencies are assessed at laboratory scale. The experimental system consisted of a 1 L differential circular flow reactor and an ozone generator rated at 5 g O3/h. Results show that ozone oxidation combined with activated carbon adsorption increases the overall BT oxidation rate with respect to the ozonation process and activated carbon adsorption. In the presence of free radical scavenger, only a 44% reduction in BT removal rate is observed in the simultaneous treatment, as compared with 72% when ozonation treatment is used, suggesting that BT oxidation reactions mainly take place on the activated carbon surface.

  18. Preparation and surface characterization of CuO and Fe2O3 catalyst

    NASA Astrophysics Data System (ADS)

    Kosa, Samia A.; Maksod, Islam Hamdy Abd El; Alkhateeb, Lateefa; Hegazy, Eman Z.

    2012-07-01

    Aromatic hydroxylation, using novel effective catalysts was developed by loading CuO and Fe2O3 nanoparticles onto Egyptian kaolin. The H2O2 was used as a green and environmentally benign oxidizing agent. The resulting catalysts were subjected to several characterization methods, including XRD, SEM, and EDX analysis. Next, the catalytic activity of these species in effecting the hydroxylation of benzene was evaluated. The compounds were loaded using two methods: impregnation and precipitation deposition. A detailed comparison between the two methods has been undertaken. EDX analysis enables us to differentiate between two types of active sites - surface and bulk active sites.

  19. Residual stresses and clamped thermal expansion in LiNbO3 and LiTaO3 thin films

    NASA Astrophysics Data System (ADS)

    Bartasyte, A.; Plausinaitiene, V.; Abrutis, A.; Murauskas, T.; Boulet, P.; Margueron, S.; Gleize, J.; Robert, S.; Kubilius, V.; Saltyte, Z.

    2012-09-01

    Residual stresses in LiNbO3 and LiTaO3 epitaxial thin films were evaluated taking into account Li nonstoichiometry by means of Raman spectroscopy and x-ray diffraction. The epitaxial films were grown on C-cut sapphire substrates by pulsed injection metal organic chemical vapour deposition. Clamping of the epitaxial films by the substrate induced a transfer from the in plane thermal expansion to the out of plane component. The temperature of the phase transition of clamped LiTaO3 films was close to that expected for a bulk sample.

  20. Interfacial Control of Magnetic Properties at LaMnO3/LaNiO3 Interfaces.

    PubMed

    Gibert, M; Viret, M; Torres-Pardo, A; Piamonteze, C; Zubko, P; Jaouen, N; Tonnerre, J-M; Mougin, A; Fowlie, J; Catalano, S; Gloter, A; Stéphan, O; Triscone, J-M

    2015-11-11

    The functional properties of oxide heterostructures ultimately rely on how the electronic and structural mismatches occurring at interfaces are accommodated by the chosen materials combination. We discuss here LaMnO3/LaNiO3 heterostructures, which display an intrinsic interface structural asymmetry depending on the growth sequence. Using a variety of synchrotron-based techniques, we show that the degree of intermixing at the monolayer scale allows interface-driven properties such as charge transfer and the induced magnetic moment in the nickelate layer to be controlled. Further, our results demonstrate that the magnetic state of strained LaMnO3 thin films dramatically depends on interface reconstructions.

  1. The loading effect of silver nanoparticles prepared by impregnation and solution plasma methods on the photocatalysis of Ga2O3

    NASA Astrophysics Data System (ADS)

    Yamamoto, Muneaki; Yoshida, Tomoko; Yamamoto, Naoto; Nomoto, Toyokazu; Yagi, Shinya

    2015-09-01

    Ag loaded Ga2O3 (Ag/Ga2O3) photocatalysts for the reduction of CO2 with water have been prepared by impregnation (IMP) and two types of solution plasma methods (SPM1 and SPM2). Using X-ray absorption near edge structure (XANES) and Fourier transform infrared (FT-IR) spectroscopies, we have investigated the local electronic structures of Ag/Ga2O3 photocatalysts as well as the adsorption behaviors of CO2 during the reaction. Both Ag L3-edge and O K-edge XANES analyses reveal the Ag-Ga2O3 interaction, i.e., the charge-transfer from O atoms to Ag atoms, by demonstrating the decrease in the unoccupied Ag 4d-state density and increase in the unoccupied O 2p-state density. The strength of the interaction depends on the preparation method, and increases in the order of Ag/Ga2O3 (SPM2), Ag/Ga2O3 (SPM1) and Ag/Ga2O3 (IMP). In addition, FT-IR measurements have disclosed that Ag/Ga2O3 (IMP) obtains a larger amount of strongly basic sites as a result of the strongest interaction between Ag and Ga2O3. Although the amount of the adsorbed CO2 is different in each Ag/Ga2O3 sample, in the following formation process of bidentate formate species, no remarkable difference is detected among all samples. The bidentate formate species are likely to interact with H2O molecules to produce CO under photoirradiation, and this process would be affected by the strength of the Ag-Ga2O3 interaction, because this reaction hardly proceeds over Ag/Ga2O3 (SPM2) having the weakest Ag-Ga2O3 interaction.

  2. Structure-Directing Effect of Alkali Metal Cations in New Molybdenum Selenites, Na2Mo2O5(SeO3)2, K2Mo2O5(SeO3)2, and Rb2Mo3O7(SeO3)3.

    PubMed

    Bang, Seong-eun; Ok, Kang Min

    2015-09-08

    Both single crystals and pure polycrystalline samples of three new quaternary alkali metal molybdenum selenites, Na2Mo2O5(SeO3)2, K2Mo2O5(SeO3)2, and Rb2Mo3O7(SeO3)3, have been synthesized through hydrothermal and solid-state reactions using A2CO3 (A = Na, K, and Rb), MoO3, and SeO2 as reagents. The frameworks of all three materials consist of both families of second-order Jahn-Teller distortive cations, i.e., the d(0) cation (Mo(6+)) and the lone pair cation (Se(4+)). Although the extent of framework distortions and the resulting occupation sites of alkali metal cations are dissimilar, Na2Mo2O5(SeO3)2 and K2Mo2O5(SeO3)2 exhibit similar three-dimensional networks that are composed of highly asymmetric Mo2O11 dimers and SeO3 polyhedra. Rb2Mo3O7(SeO3)3 reveals a two-dimensional structure that is built with Mo3O15 trimers and SeO3 intralayer linkers. Close structural examinations suggest that the structure-directing effect of alkali metal cations is significant in determining the framework distortions and the dimensions of the molybdenum selenites. UV-vis diffuse reflectance and infrared spectroscopy, thermogravimetric analyses, and ion-exchange reactions are reported, as are out-of-center distortion and dipole moment calculations.

  3. Halogen chemistry reduces tropospheric O3 radiative forcing

    NASA Astrophysics Data System (ADS)

    Sherwen, Tomás; Evans, Mat J.; Carpenter, Lucy J.; Schmidt, Johan A.; Mickley, Loretta J.

    2017-01-01

    Tropospheric ozone (O3) is a global warming gas, but the lack of a firm observational record since the preindustrial period means that estimates of its radiative forcing (RFTO3) rely on model calculations. Recent observational evidence shows that halogens are pervasive in the troposphere and need to be represented in chemistry-transport models for an accurate simulation of present-day O3. Using the GEOS-Chem model we show that tropospheric halogen chemistry is likely more active in the present day than in the preindustrial. This is due to increased oceanic iodine emissions driven by increased surface O3, higher anthropogenic emissions of bromo-carbons, and an increased flux of bromine from the stratosphere. We calculate preindustrial to present-day increases in the tropospheric O3 burden of 113 Tg without halogens but only 90 Tg with, leading to a reduction in RFTO3 from 0.43 to 0.35 Wm-2. We attribute ˜ 50 % of this reduction to increased bromine flux from the stratosphere, ˜ 35 % to the ocean-atmosphere iodine feedback, and ˜ 15 % to increased tropospheric sources of anthropogenic halogens. This reduction of tropospheric O3 radiative forcing due to halogens (0.087 Wm-2) is greater than that from the radiative forcing of stratospheric O3 (˜ 0.05 Wm-2). Estimates of RFTO3 that fail to consider halogen chemistry are likely overestimates (˜ 25 %).

  4. Phonon dispersion relation in PbTiO3

    NASA Astrophysics Data System (ADS)

    Tomeno, Izumi; Fernandez-Baca, Jaime; Marty, Karol; Oka, Kunihiko; Tsunoda, Yorihiko

    2013-03-01

    The phonon dispersion relations for cubic PbTiO3 (Tc = 763 K) have been determined along the high symmetry directions at T = 793 K using inelastic neutron scattering. A set of the TO branches drops significantly toward the zone center. This is quite different from the soft mode anomaly in the Pb-based relaxors, named as the waterfall phenomenon. The zone-center TO mode energy softens with decreasing temperature from 1173 to 793 K. The TA branch along [ ξ , ξ , ξ ] shows significant softening around ξ = 0.25 and 0.5. These two anomalies persist up to 1173 K and are weakly temperature dependent. Moreover, the TA branches along [1,0,0] and [1,1,0] soften in the entire q range as the temperature approaches Tc. Although the phonon softening occurs simultaneously, the softening of the zone center TO mode plays an important role in the single phase transition. The phonon dispersion relations for cubic and tetragonal PbTiO3 are discussed in connection with BaTiO3, KTaO3, Pb(Zn1/3Nb2/3)O3, and Pb(Mg1/3Nb2/3)O3. U.S.-Japan cooperative program on neutron scattering

  5. Silicon solar cells with Al2O3 antireflection coating

    NASA Astrophysics Data System (ADS)

    Dobrzański, Leszek; Szindler, Marek; Drygała, Aleksandra; Szindler, Magdalena

    2014-09-01

    The paper presents the possibility of using Al2O3 antireflection coatings deposited by atomic layer deposition ALD. The ALD method is based on alternate pulsing of the precursor gases and vapors onto the substrate surface and then chemisorption or surface reaction of the precursors. The reactor is purged with an inert gas between the precursor pulses. The Al2O3 thin film in structure of the finished solar cells can play the role of both antireflection and passivation layer which will simplify the process. For this research 50×50 mm monocrystalline silicon solar cells with one bus bar have been used. The metallic contacts were prepared by screen printing method and Al2O3 antireflection coating by ALD method. Results and their analysis allow to conclude that the Al2O3 antireflection coating deposited by ALD has a significant impact on the optoelectronic properties of the silicon solar cell. For about 80 nm of Al2O3 the best results were obtained in the wavelength range of 400 to 800 nm reducing the reflection to less than 1%. The difference in the solar cells efficiency between with and without antireflection coating was 5.28%. The LBIC scan measurements may indicate a positive influence of the thin film Al2O3 on the bulk passivation of the silicon.

  6. Addition of NH3 to Al3O3-

    NASA Astrophysics Data System (ADS)

    Wyrwas, Richard B.; Jarrold, Caroline Chick; Das, Ujjal; Raghavachari, Krishnan

    2006-05-01

    Recent computational studies on the addition of ammonia (NH3) to the Al3O3- cluster anion [A. Guevara-Garcia, A. Martinez, and J. V. Ortiz, J. Chem. Phys. 122, 214309 (2005)] have motivated experimental and additional computational studies, reported here. Al3O3- is observed to react with a single NH3 molecule to form the Al3O3NH3- ion in mass spectrometric studies. This is in contrast to similarly performed studies with water, in which the Al3O5H4- product was highly favored. However, the anion PE spectrum of the ammoniated species is very similar to that of Al3O4H2-. The adiabatic electron affinity of Al3O3NH3 is determined to be 2.35(5)eV. Based on comparison between the spectra and calculated electron affinities, it appears that NH3 adds dissociatively to Al3O3-, suggesting that the time for the Al3O3-•NH3 complex to either overcome or tunnel through the barrier to proton transfer (which is higher for NH3 than for water) is short relative to the time for collisional cooling in the experiment.

  7. Stomata open at night in pole-sized and mature ponderosa pine: implications for O3 exposure metrics.

    PubMed

    Grulke, N E; Alonso, R; Nguyen, T; Cascio, C; Dobrowolski, W

    2004-09-01

    Ponderosa pine (Pinus ponderosa Dougl. ex Laws.) is widely distributed in the western USA. We report the lack of stomatal closure at night in early summer for ponderosa pine at two of three sites investigated. Trees at a third site with lower nitrogen dioxide and nitric acid exposure, but greater drought stress, had slightly open stomata at night in early summer but closed stomata at night for the rest of the summer. The three sites had similar background ozone exposure during the summer of measurement (2001). Nighttime stomatal conductance (gs) ranged from one tenth to one fifth that of maximum daytime values. In general, pole-sized trees (< 40 years old) had greater nighttime gs than mature trees (> 250 years old). In late summer, nighttime gs was low (< 3.0 mmol H2O m(-2) s(-1)) for both tree size classes at all sites. Measurable nighttime gs has also been reported in other conifers, but the values we observed were higher. In June, nighttime ozone (O3) uptake accounted for 9, 5 and 3% of the total daily O3 uptake of pole-sized trees from west to east across the San Bernardino Mountains. In late summer, O3 uptake at night was < 2% of diel uptake at all sites. Nocturnal O3 uptake may contribute to greater oxidant injury development, especially in pole-sized trees in early summer.

  8. Orbital Inversion and Carrier Confinement in SrTiO3/LaAlO3 Interfaces Grown on NdGaO3 Substrates

    NASA Astrophysics Data System (ADS)

    Golden, Mark; Slooten, E.; Shi, B.; Zwartsenberg, B.; Huang, Z.; Venkatesan, T.; Annandi, A.; Gorgoi, M.; Radu, F.; Abrudan, R.; Miedema, P.; Schuessler, C.; Goedkoop, J.; Doennig, D.; Munding, J.; Pentcheva, R.; Ariando, A.

    2014-03-01

    We investigate the role of the SrTiO3 thickness on the electronic properties of heterointerfaces comprised of NdGaO3 (bulk) / SrTiO3 (n uc) / LaAlO3 (15 uc) using X-ray linear dichroism (XLD) in absorption, Hard X-ray Photoemission Spectroscopy (HAXPES) and DFT +U calculations. XLD shows an orbital inversion for all STO thicknesses: the lowest energy d-orbitals are of xz/yz character, unlike `regular' STO/LAO, in which the xy orbitals are lowest in energy. For n<6 transport shows the carriers to be localized, HAXPES data showing electronic confinement to the NGO/STO interface. For STO thickness >=8 uc, only weak localization is seen in transport, the STO/LAO interface becomes populated and carrier concentrations approaching half an electron per unit cell are deduced from both Hall measurements and HAXPES. Data from layer-resolved DFT +U calculations on STO/LAO and STO/NGO superlattices, and from NGO/STO/LAO are presented and compared to the experimental data, thereby providing a complete picture of the orbital polarization in these systems.

  9. Preparation and radar-absorbing properties of Al2O3/TiO2/Fe2O3/Yb2O3 composite powder

    NASA Astrophysics Data System (ADS)

    Zhang, Yi-fan; Ji, Zhen; Chen, Ke; Jia, Cheng-chang; Yang, Shan-wu; Wang, Meng-ya

    2017-02-01

    Al2O3/TiO2/Fe2O3/Yb2O3 composite powder was synthesized via the sol-gel method. The structure, morphology, and radar-absorption properties of the composite powder were characterized by transmission electron microscopy, X-ray diffraction analysis and RF impedance analysis. The results show that two types of particles exist in the composite powder. One is irregular flakes (100-200 nm) and the other is spherical Al2O3 particles (smaller than 80 nm). Electromagnetic wave attenuation is mostly achieved by dielectric loss. The maximum value of the dissipation factor reaches 0.76 (at 15.68 GHz) in the frequency range of 2-18 GHz. The electromagnetic absorption of waves covers 2-18 GHz with the matching thicknesses of 1.5-4.5 mm. The absorption peak shifts to the lower-frequency area with increasing matching thickness. The effective absorption band covers the frequency range of 2.16-9.76 GHz, and the maximum absorption peak reaches -20.18 dB with a matching thickness of 3.5 mm at a frequency of 3.52 GHz.

  10. The gas sensitive material Cr (2-x) Ti (x) O3

    NASA Astrophysics Data System (ADS)

    Niemeyer, Dirk

    multiplet splitting, proposed to originate from local magnetic moments at the Cr site. A CrVI state is also detected. Substituting titanium decreases the proportion of surface CrVI and reduces the splitting of the Cr 2p3/2 state. A reappearance of the splitting at higher Ti concentrations was observed, speculatively attributed to ordering of the surface structure. Although currently used solely in oxygen-containing environments CTO can also detect gases in a nitrogen atmosphere. Decreasing oxygen partial pressure caused a large decline in conductivity that is explained by removal of oxygen surface acceptor states. Whilst carbon monoxide and ethanol react with the few remaining acceptor states causing a large gas response, H2S sulphates the surface. The stable gas response to H2S is caused by reversible adsorption of H2S molecules on a CrIII site, forming a new surface trap state. Replacing titanium in CTO by vanadium, iron, magnesium or manganese resulted in a significantly reduced gas response to carbon monoxide. These elements did not form a solid solution with the Cr2O3 lattice. However, if introduced as additional elements in CTO manganese and iron dopants crystallised as MnCr2O4 and (Cr0.4Fe0.6)2O3 impurity phases and reduced the amount of chromium. A significantly reduced response to water vapour relative to the response to carbon monoxide was observed with these materials.

  11. BaTiO3-Based Non-Reducible Low-Loss Dielectric Ceramics

    NASA Astrophysics Data System (ADS)

    Nakamura, Tomoyuki; Sano, Harunobu; Konoike, Takehiro; Tomono, Kunisaburo

    1999-09-01

    Dielectrics composed of BaTiO3-rare earth oxide-MgO havebeenstudied to design a non-reducible low-loss dielectricmaterial. Curie temperatures of dielectrics composed ofBaTiO3 Gd2O3 MgO were lowered by Gd2O3, which provided thedielectrics with low power loss. It was found that the addition ofBaZrO3 to BaTiO3 Gd2O3 MgO decreased the capacitance change withtemperature. Gd2O3 diffused easily into BaTiO3, but, it could noteasily diffuse into BaTiO3 to which BaZrO3 had been added. It wasconsidered that BaZrO3 prevented the Gd2O3 diffusion into BaTiO3,resulting the remains of ferroelectricity and reduced capacitancechange. Thus non-reducible and low power loss X7R dielectricceramics were developed.

  12. Crystal structures of (Mg1-x,Fe(x))SiO3 postperovskite at high pressures.

    PubMed

    Yamanaka, Takamitsu; Hirose, Kei; Mao, Wendy L; Meng, Yue; Ganesh, P; Shulenburger, Luke; Shen, Guoyin; Hemley, Russell J

    2012-01-24

    X-ray diffraction experiments on postperovskite (ppv) with compositions (Mg(0.9)Fe(0.1))SiO(3) and (Mg(0.6)Fe(0.4))SiO(3) at Earth core-mantle boundary pressures reveal different crystal structures. The former adopts the CaIrO(3)-type structure with space group Cmcm, whereas the latter crystallizes in a structure with the Pmcm (Pmma) space group. The latter has a significantly higher density (ρ = 6.119(1) g/cm(3)) than the former (ρ = 5.694(8) g/cm(3)) due to both the larger amount of iron and the smaller ionic radius of Fe(2+) as a result of an electronic spin transition observed by X-ray emission spectroscopy (XES). The smaller ionic radius for low-spin compared to high-spin Fe(2+) also leads to an ordered cation distribution in the M1 and M2 crystallographic sites of the higher density ppv structure. Rietveld structure refinement indicates that approximately 70% of the total Fe(2+) in that phase occupies the M2 site. XES results indicate a loss of 70% of the unpaired electronic spins consistent with a low spin M2 site and high spin M1 site. First-principles calculations of the magnetic ordering confirm that Pmcm with a two-site model is energetically more favorable at high pressure, and predict that the ordered structure is anisotropic in its electrical and elastic properties. These results suggest that interpretations of seismic structure in the deep mantle need to treat a broader range of mineral structures than previously considered.

  13. Micrometer-Scale Ballistic Transport of Electron Pairs in LaAlO3/SrTiO3 Nanowires

    NASA Astrophysics Data System (ADS)

    Tomczyk, Michelle; Cheng, Guanglei; Lee, Hyungwoo; Lu, Shicheng; Annadi, Anil; Veazey, Joshua P.; Huang, Mengchen; Irvin, Patrick; Ryu, Sangwoo; Eom, Chang-Beom; Levy, Jeremy

    2016-08-01

    High-mobility complex-oxide heterostructures and nanostructures offer new opportunities for extending the paradigm of quantum transport beyond the realm of traditional III-V or carbon-based materials. Recent quantum transport investigations with LaAlO3/SrTiO3 -based quantum dots reveal the existence of a strongly correlated phase in which electrons form spin-singlet pairs without becoming superconducting. Here, we report evidence for the micrometer-scale ballistic transport of electron pairs in quasi-1D LaAlO3/SrTiO3 nanowire cavities. In the paired phase, Fabry-Perot-like quantum interference is observed, in sync with conductance oscillations observed in the superconducting regime (at a zero magnetic field). Above a critical magnetic field Bp, the electron pairs unbind and the conductance oscillations shift with the magnetic field. These experimental observations extend the regime of ballistic electronic transport to strongly correlated phases.

  14. Are lithium niobate (LiNbO3) and lithium tantalate (LiTaO3) ferroelectrics bioactive?

    PubMed

    Vilarinho, Paula Maria; Barroca, Nathalie; Zlotnik, Sebastian; Félix, Pedro; Fernandes, Maria Helena

    2014-06-01

    The use of functional materials, such as ferroelectrics, as platforms for tissue growth in situ or ex situ, is new and holds great promise. But the usage of materials in any bioapplication requires information on biocompatibility and desirably on bioactive behavior when bone tissue engineering is envisaged. Both requirements are currently unknown for many ferroelectrics. Herein the bioactivity of LiNbO3 and LiTaO3 is reported. The formation of apatite-like structures on the surface of LiNbO3 and LiTaO3 powders after immersion in simulated body fluid (SBF) for different soaking periods indicates their bioactive potential. The mechanism of apatite formation is suggested. In addition, the significant release of lithium ions from the ferroelectric powders in the very first minutes of soaking in SBF is examined and ways to overcome this likely hurdle addressed.

  15. Ferroelectric Metal in Tetragonal BiCoO3/BiFeO3 Bilayers and Its Electric Field Effect

    PubMed Central

    Yin, Li; Mi, Wenbo; Wang, Xiaocha

    2016-01-01

    By first-principles calculations we investigate the electronic structure of tetragonal BiCoO3/BiFeO3 bilayers with different terminations. The multiferroic insulator BiCoO3 and BiFeO3 transform into metal in all of three models. Particularly, energetically favored model CoO2-BiO exhibits ferroelectric metallic properties, and external electric field enhances the ferroelectric displacements significantly. The metallic character is mainly associated to eg electrons, while t2g electrons are responsible for ferroelectric properties. Moreover, the strong hybridization between eg and O p electrons around Fermi level provides conditions to the coexistence of ferroelectric and metallic properties. These special behaviors of electrons are influenced by the interfacial electronic reconstruction with formed Bi-O electrovalent bond, which breaks OA-Fe/Co-OB coupling partially. Besides, the external electric field reverses spin polarization of Fe/Co ions efficiently, even reaching 100%. PMID:26839049

  16. Theoretical insight into Cobalt subnano-clusters adsorption on α-Al2O3 (0001)

    NASA Astrophysics Data System (ADS)

    Gao, Fen-e.; Ren, Jun; Wang, Qiang; Li, Debao; Hou, Bo; Jia, Litao; Cao, Duanlin

    2017-02-01

    The investigation on the structural stability, nucleation, growth and interaction of cobalt cluster Con(n=2-7) on the α-Al2O3(0001) surface by using density functional theory methods has been reported. Energetically, the most favorable adsorption sites were identified and the strongest adsorption energy cluster is the tetrahedral Co4 cluster. On the other hand, the nucleation of Con(n=2-7) clusters on the surface is exothermic and thermodynamically favorable. Moreover, even-odd alternation was found with respect to clusters nucleation as a function of the number of cobalt atoms (for n=1-7). Meanwhile, the Con clusters can be adsorbed on the surface stably owing to the charge transfer from Co atoms to Al and O atoms of the Al2O3 substrate. In addition, we establish the crucial importance of monomer, dimer and trimer diffusion on the surface. The diffusion of the monomer cobalt from Al(3) to O(5) or O(5) to Al(4) site is quite easy on the Al2O3(0001) surface, whereas the diffusion of the Co2 dimer is thermodynamically unfavorable by compared with that of the Co adatom and Co3 trimer.

  17. Seasonal cycles of O3 in the marine boundary layer: Observation and model simulation comparisons

    NASA Astrophysics Data System (ADS)

    Parrish, D. D.; Galbally, I. E.; Lamarque, J.-F.; Naik, V.; Horowitz, L.; Shindell, D. T.; Oltmans, S. J.; Derwent, R.; Tanimoto, H.; Labuschagne, C.; Cupeiro, M.

    2016-01-01

    We present a two-step approach for quantitatively comparing modeled and measured seasonal cycles of O3: (1) fitting sine functions to monthly averaged measurements and model results (i.e., deriving a Fourier series expansion of these results) and (2) comparing the phase and amplitude of the statistically significant terms between the models and measurements. Two and only two sine terms are sufficient to quantify the O3 seasonal cycle in the marine boundary layer (MBL) in both the measurements and the model results. In addition to the expected fundamental (one sine cycle per year), a second harmonic term (i.e., two sine cycles per year) is identified as a ubiquitous feature of O3 in the MBL. Three chemistry climate models (Community Atmosphere Model with chemistry, GFDL-CM3, and GISS-E2-R) approximately reproduce many features of the measured seasonal cycles at MBL surface sites throughout the globe, with some notable quantitative disagreements, but give divergent results that do not agree with O3 sonde measurements above the MBL. This disagreement and divergence of results between models indicate that the treatment of the MBL dynamics in the chemistry-climate models is not adequate to reproduce the isolation of the MBL indicated by the observations. Within the MBL the models more accurately reproduce the second harmonic term than the fundamental term. We attribute the second harmonic term to the second harmonic of opposite phase in the photolysis rate of O3, while the fundamental term evidently has many influences. The parameters derived from the Fourier series expansion of the measurements are quantitative metrics that can serve as the basis for future model-measurement comparisons.

  18. Room-Temperature Quantum Transport Signatures in Graphene/LaAlO3 /SrTiO3 Heterostructures.

    PubMed

    Jnawali, Giriraj; Huang, Mengchen; Hsu, Jen-Feng; Lee, Hyungwoo; Lee, Jung-Woo; Irvin, Patrick; Eom, Chang-Beom; D'Urso, Brian; Levy, Jeremy

    2017-03-01

    High mobility graphene field-effect devices, fabricated on the complex-oxide heterostructure LaAlO3 /SrTiO3 , exhibit quantum interference signatures up to room temperature. The oxide material is believed to play a critical role in suppressing short-range and phonon contributions to scattering. The ability to maintain pseudospin coherence at room temperature holds promise for the realization of new classical and quantum information technologies.

  19. Growth of Nanoscale BaTiO3/SrTiO3 Superlattices by Molecular-Beam Epitaxy

    DTIC Science & Technology

    2008-05-01

    Daimon: Fabrication of barium titanate /strontium titanate artificial superlattice by atomic layer epitaxy. Jpn. J. Appl. Phys., Pt. 1 33, 5192 (1994...GdScO3, and (101) SmScO3 substrates by reactive MBE. The strontium and barium fluxes were produced by sublimat- ing elemental strontium and barium ...QCM) located directly in front of the substrate was used to get a rough (±5%) idea of the barium , strontium, and titanium mo- lecular beam fluxes

  20. Interfacial Ferromagnetism and Exchange Bias in CaRuO3/CaMnO3 Superlattices

    DTIC Science & Technology

    2012-11-07

    and the interface region is consistent with double exchange interaction among the Mn ions at the interface. Polarized neutron reflectivity and the...CaMnO3 thickness dependence of the exchange bias field together indicate that the interfacial 1. REPORT DATE ( DD -MM-YYYY) 4. TITLE AND SUBTITLE 13...consistent with double exchange interaction among the Mn ions at the interface. Polarized neutron reflectivity and the CaMnO3 thickness dependence of the

  1. Stoichiometry-driven metal-to-insulator transition in NdTiO3/SrTiO3 heterostructures

    NASA Astrophysics Data System (ADS)

    Xu, Peng; Phelan, Daniel; Seok Jeong, Jong; Andre Mkhoyan, K.; Jalan, Bharat

    2014-02-01

    By controlling stoichiometry via a hybrid molecular beam epitaxy approach, we report on the study of thin film growth and the electronic transport properties of phase-pure, epitaxial NdTiO3/SrTiO3 heterostructures grown on (001) (La0.3Sr0.7)(Al0.65Ta0.35)O3 (LSAT) substrates as a function of cation stoichiometry in NdTiO3. Despite the symmetry mismatch between bulk NdTiO3 and the substrate, NdTiO3 films grew in an atomic layer-by-layer fashion over a range of cation stoichiometry; however amorphous films resulted in cases of extreme cation non-stoichiometry. Temperature-dependent sheet resistance measurements were consistent with Fermi-liquid metallic behavior over a wide temperature range, but revealed a remarkable crossover from metal-to-insulator (M-I) type behavior at low temperatures for all compositions. A direct correlation between cation stoichiometry, transport behavior, and the temperature of M-I transition is established.

  2. Epitaxial strain and its relaxation at the LaAlO3/SrTiO3 interface

    NASA Astrophysics Data System (ADS)

    Liu, Guozhen; Lei, Qingyu; Wolak, Matthäus A.; Li, Qun; Chen, Long-Qing; Winkler, Christopher; Sloppy, Jennifer; Taheri, Mitra L.; Xi, Xiaoxing

    2016-08-01

    A series of LaAlO3 thin films with different thicknesses were deposited by pulsed laser deposition at temperatures from 720 °C to 800 °C. The results from grazing incidence x-ray diffraction and reciprocal space mapping indicate that a thin layer of LaAlO3 adjacent to the SrTiO3 substrate remains almost coherently strained to the substrate, while the top layer starts to relax quickly above a certain critical thickness, followed by a gradual relaxation at larger film thickness when they are grown at lower temperatures. The atomic force microscopy results show that the fast relaxation is accompanied by the formation of cracks on the film surface. This can be ascribed to the larger energy release rate when compared with the resistance of LaAlO3 to cracking, according to calculations from the Griffith fracture theory. For films grown at 720 °C, a drop in sheet resistance by two orders of magnitude is observed when the top layer starts to relax, indicating a relationship between the strain and the conductivity of the two-dimensional electron gas at the LaAlO3/SrTiO3 interface. The strain engineered by growth temperature provides a useful tool for the manipulation of the electronic properties of oxide heterointerfaces.

  3. Stabilization of metastable ɛ-Fe2O3 thin films using a GaFeO3 buffer

    NASA Astrophysics Data System (ADS)

    Thai, Trang Minh Nguyen; Nguyen, Dong Tri; Lee, Nam-Suk; Rhyee, Jong-Soo; Song, Jonghyun; Kim, Heon-Jung

    2016-11-01

    This paper reports a simple and robust route to stabilize metastable ɛ-Fe2O3 as an epitaxial thin film using a GaFeO3 (GFO) buffer in pulsed laser deposition. The use of an isostructural GFO buffer widens the range of film growth, allowing for stabilization on a range of substrates even with different surface symmetries, such as Al2O3 (0001), SrTiO3 (111), and Y:ZrO2 (100). All films grown on these substrates were c-axis oriented with the characteristic in-plane domain structures. Magnetization of these buffered thin films showed considerable magnetic anisotropy at 350 K. In particular, in-plane magnetization was found to be relatively larger in the films grown on the Y:ZrO2 (100) compared to the other cases. Heterostructuring ɛ-Fe2O3 on GFO is promising in the applications of ɛ-Fe2O3 for magnetic and multiferroic devices in that it provides a larger growth window and an effective means to optimize the film properties beyond the simple substitution of Fe with Ga.

  4. Stoichiometry of LaAlO3 films grown on SrTiO3 by pulsed laser deposition

    NASA Astrophysics Data System (ADS)

    Golalikhani, M.; Lei, Q. Y.; Chen, G.; Spanier, J. E.; Ghassemi, H.; Johnson, C. L.; Taheri, M. L.; Xi, X. X.

    2013-07-01

    We have studied the stoichiometry of epitaxial LaAlO3 thin films on SrTiO3 substrate grown by pulsed laser deposition as a function of laser energy density and oxygen pressure during the film growth. Both x-ray diffraction (θ-2θ scan and reciprocal space mapping) and transmission electron microscopy (geometric phase analysis) revealed a change of lattice constant in the film with the distance from the substrate. Combined with composition analysis using x-ray fluorescence we found that the nominal unit-cell volume expanded when the LaAlO3 film was La-rich, but remained near the bulk value when the film was La-poor or stoichiometric. La excess was found in all the films deposited in oxygen pressures lower than 10-2 Torr. We conclude that the discussion of LaAlO3/SrTiO3 interfacial properties should include the effects of cation off-stoichiometry in the LaAlO3 films when the deposition is conducted under low oxygen pressures.

  5. Chemistry, growth kinetics, and epitaxial stabilization of Sn2+ in Sn-doped SrTiO3 using (CH3)6Sn2 tin precursor

    NASA Astrophysics Data System (ADS)

    Wang, Tianqi; Pitike, Krishna Chaitanya; Yuan, Yakun; Nakhmanson, Serge M.; Gopalan, Venkatraman; Jalan, Bharat

    2016-12-01

    PbTiO3-based ferroelectrics have impressive electroactive properties, originating from the Pb2+ 6s2 electron lone-pair, which cause large elastic distortion and electric polarization due to cooperative pseudo Jahn-Teller effect. Recently, tin-based perovskite oxide (SnTiO3) containing Sn2+ and a chemistry similar to that of the 6s2 lone-pair has been identified as a thermally stable, environmentally friendly substitute for PbTiO3-based ferroelectrics. However experimental attempts to stabilize Sn2+ on the A-site of perovskite ATiO3 have so far failed. In this work, we report on the growth of atomically smooth, epitaxial, and coherent Sn-alloyed SrTiO3 films on SrTiO3 (001) substrates using a hybrid molecular beam epitaxy approach. With increasing Sn concentration, the out-of-plane lattice parameter first increases in accordance with the Vegard's law and then decreases for Sn(Sr+Ti+Sn/) at. % ratio > 0.1 due to the incorporation of Sn2+ at the A-site. Using a combination of high-resolution X-ray photoelectron spectroscopy and density functional calculations, we show that while majority of Sn is on the B-site, there is a quantitatively unknown fraction of Sn being consistent with the A-site occupancy making SrTiO3 polar. A relaxor-like ferroelectric local distortion with monoclinic symmetry, induced by A-site Sn2+, was observed in Sn-doped SrTiO3 with Sn(Sr+Ti+Sn/) at. % ratio = 0.1 using optical second harmonic generation measurements. The role of growth kinetics on the stability of Sn2+ in SrTiO3 is discussed.

  6. Impact of Fe on structural modification and room temperature magnetic ordering in BaTiO3

    NASA Astrophysics Data System (ADS)

    Rajan, Soumya; Gazzali, P. M. Mohammed; Chandrasekaran, G.

    2017-01-01

    Ba1 - xFexTiO3 (x = 0, 0.005, 0.01) polycrystalline ceramics are prepared using solid state reaction method. Structural studies through XRD, Raman and XPS confirm single tetragonal phase for BaTiO3 whereas a structural disorder tends to intervene with the introduction of smaller Fe ions which reduces the tolerance factor and tetragonality ratio. Grain size of the samples is estimated using SEM micrographs with ImageJ software and chemical composition is confirmed using EDX spectra. Raman spectra measured in the temperature range of 303 K to 573 K showers light on the structural phase transition exploiting a significant disappearance of the 306 cm- 1 mode. Further, structural analyses suggest the entry of Fe into the B-site upon increasing its concentration in BaTiO3. The dopant sensitive modes lying at around 640 cm- 1 and 650 cm- 1 are assigned to lattice strain. A reduction in ferroelectric to paraelectric transition temperature is observed with a transformation from diffused type to normal ferroelectric upon the increased Fe content. The oxidation state of Fe in the BaTiO3 lattice has been decided using EPR Spectra precisely. Room temperature magnetic ordering is observed in Fe substituted BaTiO3 using PPMS. The coexistence of ferroelectric and magnetic ordering is established in the present study for optimized Fe substituted BaTiO3.

  7. The effect of strontium doping on the structural and magnetic transition of YMnO3

    NASA Astrophysics Data System (ADS)

    Thakur, Rajesh K.; Thakur, Rasna; Awasthi, A. M.; Ganesan, V.; Gaur, N. K.

    2012-06-01

    A systematic study on the effect of strontium (Sr) doping in YMnO3 has been undertaken. Polycrystalline samples with composition Y1-xSrxMnO3 (x=0, 0.01) were synthesized by using high temperature solid state reaction method. The structural and thermal properties of the prepared samples have been carried out in the wide range of temperature. Our XRD reveals the single phase formation of the reported compounds in hexagonal structure with space group P63cm (JCPDS: 25-1079). The observed pointed kinks in the specific heat study are symptomatic of the probable coupling in between the electric and magnetic orders. Our specific heat curves show that the AFM transition temperature (TN) shifts to higher value with minute Sr doping to Y-site. Further, low temperature study shows independence of specific heat on magnetic field at 8T and 12T.

  8. Investigation of optical photorefractive properties of Zr:Fe:LiNbO 3 crystals

    NASA Astrophysics Data System (ADS)

    Zhou, Zifan; Wang, Biao; Lin, Shaopeng; Li, Yilun; Wang, Kun

    2012-03-01

    A series of Zr:Fe:LiNbO 3 crystals with various levels of ZrO 2 doping were grown by Czochraski technique. The optical damage resistance and photorefractive properties were deeply explored. The results showed that the ability optical damage resistance increased remarkably when the concentration of ZrO 2 is over threshold concentration, but which is lower than that of traditional damage resistant additive MgO. While, the holographic storage properties can be greatly enhanced by proper level of ZrO 2 doping in Fe:LiNbO 3. In terms of ions' site occupation model, the photo-damage resistant ability enhancement and the change of the photorefractive properties were discussed.

  9. Reducing the In2O3(111) Surface Results in Ordered Indium Adatoms

    SciTech Connect

    Wagner, Margareta; Seiler, Steffen; Meyer, Bernd; Boatner, Lynn A; Schmid, M.; Diebold, U.

    2014-01-01

    The In2O3(111) surface can be transformed from an oxidized bulk termination to one that is covered by single In adatoms. As each adatom sits at one specific site within the surface unit cell they form a well-ordered (1 1) superstructure. Annealing at 500 C in O2 or in ultrahigh vacuum results in a fully reversible conversion between these two surface terminations; this transformation and intermediate stages were followed with Scanning Tunneling Microscopy (STM). Formation of this novel surface structure under reducing conditions is corroborated by Density Functional Theory (DFT). The reduced adatom-covered and the oxidized In2O3(111) surfaces are expected to exhibit different chemical and electronic properties, which can easily be exploited by the facile and reversible switching between the two terminations.

  10. Effect of dopant concentration on photoluminescence properties of Gd2O3:Eu3+

    NASA Astrophysics Data System (ADS)

    Selvalakshmi, T.; Bose, A. Chandra

    2013-02-01

    Red-emitting Gd2-xO3:Eux3+(x = 2,4,6at%) was synthesized by sol-gel method and its optical properties were studied. The formation of Gd2O3 and the presence of metal oxygen bond were confirmed from X-ray diffraction (XRD) and fourier transform infrared (FTIR) spectroscopy studies. Incorporation of Eu3+ in Gd3+ site was proved qualitatively by Energy dispersive X-ray analysis (EDX). A strong charge transfer band (CTB) at 254 nm was observed in the excitation spectra with varying intensity for different dopant concentrations. Photoluminescence (PL) spectra reported red emission peak at 611 nm corresponding to 5D0-7F2 transition between Eu3+ energy levels. Concentration quenching occurred at 2 at % and its critical distance was calculated. Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM) studies was carried out to study the morphological variations.

  11. Magneto-structural study of a Cr-doped CaRuO3

    NASA Astrophysics Data System (ADS)

    Ranjan, Rajeev; Garg, Rohini; Senyshyn, Anatoliy; Hegde, M. S.; Ehrenberg, Helmut; Boysen, Hans

    2009-08-01

    Temperature-dependent neutron powder diffraction, magnetization and XPS studies were carried out on an optimally Cr-doped CaRuO3, i.e. CaRu0.85Cr0.15O3 (CRC-15). XPS data revealed that Cr exist in 3+ and 6+ oxidation states. The charge dissociation preserves the overall 4+ nominal charge of the Ru site. Although ferromagnetic correlations develop around 100 K, the system exhibits a large coercive field below 50 K. The unit cell volume exhibits negative thermal expansion below 50 K since the lattice expansion due to the magnetostrictive effect outweighs the thermal contraction due to the phonon-driven mechanism.

  12. Complex spin glass behavior in Ga2-xFexO3

    NASA Astrophysics Data System (ADS)

    Mahana, Sudipta; Topwal, D.

    2017-03-01

    We report the results of the dc magnetization and ac susceptibility measurements on solid solutions of Ga2-xFexO3 (with x = 0.75, 1.0, and 1.25). Magnetic behavior in this series of compounds could broadly be explained by the molecular-field-approximation of a three-sublattice ferrimagnetic model considering three inequivalent octahedral sites. Analysis of frequency dispersion of ac susceptibility reveals a transition from the cluster-glass-like phase to the spin-glass-like phase with decreasing temperature for the x = 0.75 composition. Mentioned glassy behavior is found to gradually evolve with the composition (x) from the Ising type character to Heisenberg type behavior to unconventional glassy behavior for the x = 1.25 composition. Ga2-xFexO3 can hence serve as an ideal system for modeling complex spin glasses.

  13. Effect of Zn doping on the photoluminescence properties of LiNbO3 single crystals

    NASA Astrophysics Data System (ADS)

    Murillo, J. G.; Herrera, G.; Vega-Rios, A.; Flores-Gallardo, S.; Duarte-Moller, A.; Castillo-Torres, J.

    2016-12-01

    An extraordinary violet luminescence at 418 nm together with the intrinsic blue band at 440 nm with excitation in the UV region (380 nm) was observed in a series of LiNbO3 single crystals doped with Zn. Structural and photoluminescence properties were studied by Raman, UV reflectance, and fluorospectrometry, respectively. The emission peaks in PL spectra varied in amplitude according to the level of concentration of Zn in LiNbO3 crystals. It was found, from Raman spectroscopy studies, a connection between the appearance of the new emission band centered at 418 nm and a diminishing in the Li concentration in crystals, which suggest the displacement of the Li ions from their regular sites by the Zn ions. The maximum peak intensity of each one of the three PL emission components found from a deconvolution process shows a linear dependence on the Zn concentration present in the crystals studied.

  14. Density functional theory investigation of the interaction of water with α-Al2O3 and α-Fe2O3(11̲02) surfaces: Implications for surface reactivity

    NASA Astrophysics Data System (ADS)

    Aboud, Shela; Wilcox, Jennifer; Brown, Gordon E., Jr.

    2011-03-01

    Density functional theory calculations were performed in conjunction with ab initio thermodynamics, bond valence calculations, and density of states studies to investigate the chemical reactivity of α-Al2O3 and α-Fe2O3 (11¯02) surfaces in a humid environment. Isostructural α-Fe2O3 (11¯02) displays a much higher degree of surface reactivity with respect to water adsorption and aqueous heavy metal ions than α-Al2O3. The reason for these differences has not been fully explained. We have found that, while both metal oxides exhibit a similar stable (11¯02) surface at and below room temperature, corresponding to a stoichiometric surface with the first layer of metal ions missing, the degree of hydroxylation of the surface oxygen atoms leads to differences in the atomic layer relaxation in α-Al2O3 (11¯02) compared to α-Fe2O3 (11¯02), which has also been confirmed previously by crystal truncation rod x-ray diffraction studies. Also in agreement with these experimental studies, we find the atomic layer spacing of the most energetically stable (11̲02) Al2O3 surface is relatively insensitive to the inclusion of multiple layers of physisorbed water. This is in contrast to previously reported density functional theory studies of hydrated (11̲02) α-Fe2O3 surfaces, the results of which are confirmed in this work, that a monolayer of water is required for good agreement with experimental measurements of the atomic layer relaxation. These changes in atomic spacing result in changes in electron charge distributions and in Lewis and Brønsted acid/base properties of surface sites, which influence the relative reactivities of the two surfaces. However, the higher reactivity of the hydrated (11¯02) surface of α-Fe2O3 can be attributed mainly to the empty d states of the surface Fe atoms, which exhibit a first peak at ˜1 eV above the Fermi level and act as very strong Lewis acid sites. In comparison, the empty p states of Al in the hydrated (11¯02) α-Al2O3 surface

  15. Electronic properties of LaAlO3/SrTiO3 n-type interfaces: a GGA+U study

    NASA Astrophysics Data System (ADS)

    Piyanzina, I. I.; Kopp, T.; Lysogorskiy, Yu V.; Tayurskii, D. A.; Eyert, V.

    2017-03-01

    The role of electronic correlation effects for a realistic description of the electronic properties of \\text{LaAl}{{\\text{O}}3} /\\text{SrTi}{{\\text{O}}3} heterostructures as covered by the on-site Coulomb repulsion within the GGA+U approach is investigated. Performing a systematic variation of the values of the Coulomb parameters applied to the Ti 3d and La 4f orbitals we put previous suggestions to include a large value for the La 4f states into perspective. Furthermore, our calculations provide deeper insight into the band gap landscape in the space spanned by these Coulomb parameters and the resulting complex interference effects. In addition, we identify important correlations between the local Coulomb interaction within the La 4f shell, the band gap, and the atomic displacements at the interface. In particular, these on-site Coulomb interactions influence buckling within the LaO interface layer, which via its strong coupling to the electrostatic potential in the LAO overlayer causes considerable shifts of the electronic states at the surface and eventually controls the band gap.

  16. Mechanisms of charge transfer and redistribution in LaAlO3/SrTiO3 revealed by high-energy optical conductivity

    NASA Astrophysics Data System (ADS)

    Asmara, T. C.; Annadi, A.; Santoso, I.; Gogoi, P. K.; Kotlov, A.; Omer, H. M.; Motapothula, M.; Breese, M. B. H.; Rübhausen, M.; Venkatesan, T.; Ariando; Rusydi, A.

    2014-04-01

    In condensed matter physics the quasi two-dimensional electron gas at the interface of two different insulators, polar LaAlO3 on nonpolar SrTiO3 (LaAlO3/SrTiO3) is a spectacular and surprising observation. This phenomenon is LaAlO3 film thickness dependent and may be explained by the polarization catastrophe model, in which a charge transfer of 0.5e- from the LaAlO3 film into the LaAlO3/SrTiO3 interface is expected. Here we show that in conducting samples (≥4 unit cells of LaAlO3) there is indeed a ~0.5e- transfer from LaAlO3 into the LaAlO3/SrTiO3 interface by studying the optical conductivity in a broad energy range (0.5-35 eV). Surprisingly, in insulating samples (≤3 unit cells of LaAlO3) a redistribution of charges within the polar LaAlO3 sublayers (from AlO2 to LaO) as large as ~0.5e- is observed, with no charge transfer into the interface. Hence, our results reveal the different mechanisms for the polarization catastrophe compensation in insulating and conducting LaAlO3/SrTiO3 interfaces.

  17. Chemical strain-dependent two-dimensional transport at R AlO3/SrTiO3 interfaces (R =La,Nd,Sm,and Gd)

    NASA Astrophysics Data System (ADS)

    Li, Chen; Shen, Xuan; Yang, Yurong; Bai, Yuhang; Yuan, Zhoushen; Su, Dong; Li, Aidong; Zhang, Shantao; Wang, Peng; Bellaiche, Laurent; Wu, Di

    2016-12-01

    Perovskite R AlO3 (R =La ,Nd,Sm,and Gd) films have been deposited epitaxially on (001) TiO2-terminated SrTiO3 substrates. It is observed that the two-dimensional transport characteristics at the R AlO3/SrTiO3 interfaces are very sensitive to the species of rare-earth element, that is to chemical strain. Although electron energy loss spectroscopy measurements show that electron transfer occurs in all the four polar/nonpolar heterostructures, the amount of electrons transferred across SmAlO3/SrTiO3 and GdAlO3/SrTiO3 interfaces are much less than those across LaAlO3/SrTiO3 and NdAlO3/SrTiO3 interfaces. First-principles calculations reveal the competition between ionic polarization and electronic polarization in the polar layers in compensating the build-in polarization due to the polar discontinuity at the interface. In particular, a large ionic polarization is found in SmAlO3/SrTiO3 and GdAlO3/SrTiO3 systems (which experience the largest tensile epitaxial strain), hence reducing the amount of electrons transferred.

  18. Chemical strain-dependent two-dimensional transport at RAlO3/SrTiO3 interfaces (R=La,Nd,Sm,and Gd)

    DOE PAGES

    Li, Chen; Shen, Xuan; Yang, Yurong; ...

    2016-12-27

    Perovskite RAlO3 (R = La, Nd, Sm, and Gd) films have been deposited epitaxially on (001) TiO2-terminated SrTiO3 substrates. In this paper, it is observed that the two-dimensional transport characteristics at the RAlO3/SrTiO3 interfaces are very sensitive to the species of rare-earth element, that is to chemical strain. Although electron energy loss spectroscopy measurements show that electron transfer occurs in all the four polar/nonpolar heterostructures, the amount of electrons transferred across SmAlO3/SrTiO3 and GdAlO3/SrTiO3 interfaces are much less than those across LaAlO3/SrTiO3 and NdAlO3/SrTiO3 interfaces. First-principles calculations reveal the competition between ionic polarization and electronic polarization in the polar layersmore » in compensating the build-in polarization due to the polar discontinuity at the interface. Finally, in particular, a large ionic polarization is found in SmAlO3/SrTiO3 and GdAlO3/SrTiO3 systems (which experience the largest tensile epitaxial strain), hence reducing the amount of electrons transferred.« less

  19. Foliar quality influences tree-herbivore-parasitoid interactions: effects of elevated CO2, O3, and plant genotype.

    PubMed

    Holton, M Kim; Lindroth, Richard L; Nordheim, Erik V

    2003-10-01

    This study examined the effects of carbon dioxide (CO2)-, ozone (O3)-, and genotype-mediated changes in quaking aspen (Populus tremuloides) chemistry on performance of the forest tent caterpillar (Malacosoma disstria) and its dipteran parasitoid (Compsilura concinnata) at the Aspen Free-Air CO2 Enrichment (FACE) site. Parasitized and non-parasitized forest tent caterpillars were reared on two aspen genotypes under elevated levels of CO2 and O3, alone and in combination. Foliage was collected for determination of the chemical composition of leaves fed upon by forest tent caterpillars during the period of endoparasitoid larval development. Elevated CO2 decreased nitrogen levels but had no effect on concentrations of carbon-based compounds. In contrast, elevated O3 decreased nitrogen and phenolic glycoside levels, but increased concentrations of starch and condensed tannins. Foliar chemistry also differed between aspen genotypes. CO2, O3, genotype, and their interactions altered forest tent caterpillar performance, and differentially so between sexes. In general, enriched CO2 had little effect on forest tent caterpillar performance under ambient O3, but reduced performance (for insects on one aspen genotype) under elevated O3. Conversely, elevated O3 improved forest tent caterpillar performance under ambient, but not elevated, CO2. Parasitoid larval survivorship decreased under elevated O3, depending upon levels of CO2 and aspen genotype. Additionally, larval performance and masses of mature female parasitoids differed between aspen genotypes. These results suggest that host-parasitoid interactions in forest systems may be altered by atmospheric conditions anticipated for the future, and that the degree of change may be influenced by plant genotype.

  20. Thermodynamic studies on SrThO 3(s)

    NASA Astrophysics Data System (ADS)

    Prasad, R.; Dash, Smruti; Parida, S. C.; Singh, Ziley; Venugopal, V.

    2003-01-01

    The Gibbs energy of formation of SrThO 3(s) has been determined using e.m.f. and manometric techniques. In the e.m.f. method, two fluoride cells have been constructed to determine Δ fG0m(SrThO 3,s, T) using CaF 2(s) as a solid electrolyte. The cells used are: (-) O2( g), Pt/ SrO( s)+ SrF2( s)// CaF2//( SrThO3( s)+ ThO2( s)+ SrF2( s)/ Pt, O2( g)(+), ( I) (-) O2( g), Pt/ SrThO3( s)+ SrF2( s)+ ThO2( s)// CaF2( s)// CaO( s)+ CaF2( s)/ Pt, O2( g)(+). ( II) The observed e.m.f. values are represented by following respective expressions: E ( V)±0.0001=0.0998+3.254×10 -5T ( K), ( Cell I) E ( V)±0.0001=0.0285-6.37×10 -5T ( K). ( Cell II) From the measured e.m.f. values of the cells and the Δ fG0m( T) values from the literature, Δ fG0m(SrThO 3,s, T) have been calculated and are respectively given as ΔfG 0m( SrThO3, s,T)±10 kJ mol-1=-1829.2+0.2735T ( K) (978⩽T ( K)⩽1154), ( Cell I) ΔfG 0( SrThO3, s,T)±20 kJ mol-1=-1853.5+0.2867T ( K) (1008⩽T ( K)⩽1168). ( Cell II) In the manometric technique, equilibrium CO 2(g) pressures are measured over the three phase mixture: {SrThO 3(s)+SrCO 3(s)+ThO 2(s)} using a mercury manometer from 1075 to 1197 K. The corresponding Gibbs energy as a function of temperature is given by ΔfG 0m( SrThO3, s,T)( kJ mol-1)±14=-1865.4+0.3086T ( K).

  1. Quasi-Two-Dimensional Electron Gas Behavior in Doped LaAlO3 Thin Films on SrTiO3 Substrates

    DTIC Science & Technology

    2013-04-03

    REPORT Quasi-two-dimensional electron gas behavior in doped LaAlO3 thin films on SrTiO3 substrates 14. ABSTRACT 16. SECURITY CLASSIFICATION OF: We have...demonstrated the growth of Tm and Lu doped LaAlO3 epitaxial thin films on single crystal (001) SrTiO3 substrates. These rare-earth dopants...gas behavior in doped LaAlO3 thin films on SrTiO3 substrates Report Title ABSTRACT We have demonstrated the growth of Tm and Lu doped LaAlO3 epitaxial

  2. Microstructural evolution in NaNbO3-based antiferroelectrics

    NASA Astrophysics Data System (ADS)

    Guo, Hanzheng; Shimizu, Hiroyuki; Randall, Clive A.

    2015-11-01

    Our recent study found that CaZrO3 doping can effectively enhance the antiferroelectric P phase in NaNbO3 ceramics, leading to a double polarization hysteresis loop characteristic of a reversible antiferroelectric ↔ ferroelectric phase transition [Shimizu et al., Dalton Trans. 44, 10763 (2015)]. Here, a thorough transmission electron microscope study was performed to illustrate the CaZrO3 doping-assisted antiferroelectricity stabilization. In parallel to the bright-field imaging and selected area electron diffraction from multiple zone axes, detailed dark-field imaging was utilized to determine the superlattice structural origins, from either oxygen octahedral tilting or antiparallel cation displacements. By analogy with Pb(Zr1-xTix)O3 and rare-earth doped BiFeO3 systems, the chemical substitutions are such as to an induced polar-to-antipolar transition that is consistent with a tolerance factor reduction. The resultant chemical pressure has a similar effect to the compressive hydrostatic pressure where the antiferroelectric state is favored over the ferroelectric state.

  3. High-Temperature Thermometer Using Cr-Doped GdAlO3 Broadband Luminescence

    NASA Technical Reports Server (NTRS)

    Eldridge, Jeffrey; Chambers, Matthew

    2011-01-01

    A new concept has been developed for a high-temperature luminescence-based optical thermometer that both shows the desired temperature sensitivity in the upper temperature range of present state-of-the-art luminescence thermometers (above 1,300 C), while maintaining substantial stronger luminescence signal intensity that will allow these optical thermometers to operate in the presence of the high thermal background radiation typical of industrial applications. This objective is attained by using a Cr-doped GdAlO3 (Cr:GdAlO3) sensor with an orthorhombic perovskite structure, resulting in broadband luminescence that remains strong at high temperature due to the favorable electron energy level spacing of Cr:GdAlO3. The Cr:GdAlO3 temperature (and pressure) sensor can be incorporated into, or applied onto, a component s surface when a non-contact surface temperature measurement is desired, or alternatively, the temperature sensor can be attached to the end of a fiber-optic probe that can then be positioned at the location where the temperature measurement is desired. In the case of the fiber-optic probe, both the pulsed excitation and the luminescence emission travel through the fiber-optic light guide. In either case, a pulsed light source provides excitation of the luminescence, and the broadband luminescence emission is collected. Real-time temperature measurements are obtain ed using a least-squares fitting algorithm that determines the luminescence decay time, which has a known temperature dependence established by calibration. Due to the broad absorption and emission bands for Cr:GdAlO3, there is considerable flexibility in the choice of excitation wavelength and emission wavelength detection bands. The strategic choice of the GdAlO3 host is based on its high crystal field, phase stability, and distorted symmetry at the Cr3+ occupation sites. The use of the broadband emission for temperature sensing at high temperatures is a key feature of the invention and is

  4. Electromechanical properties of tetragonal Pb(In(12)Nb(12))O(3)-Pb(Mg(13)Nb(23))O(3)-PbTiO(3) ferroelectric crystals.

    PubMed

    Li, Fei; Zhang, Shujun; Xu, Zhuo; Wei, Xiaoyong; Luo, Jun; Shrout, Thomas R

    2010-03-01

    The ferroelectric, dielectric, elastic, piezoelectric, and electromechanical properties of tetragonal Pb(In(12)Nb(12))O(3)-Pb(Mg(13)Nb(23))O(3)-PbTiO(3) (PIN-PMN-PT) crystals were investigated. The single domain piezoelectric coefficients d(33), d(15), and d(31) were found to be 530, 2350, and -200 pCN, respectively, with electromechanical coupling factors k(33), k(15), and k(31) being on the order of 0.84, 0.85, and 0.58. The mechanical quality factor Q for longitudinal mode was found to be >700, with high coercive field (E(c)) being on the order of 10 kVcm. The temperature and dc bias electric-field characteristics of single domain tetragonal PIN-PMN-PT crystals were also investigated. In contrast to [001] oriented domain engineered rhombohedral crystals, tetragonal PIN-PMN-PT crystals exhibited broader temperature usage range and higher thermalelectric field stability, with improved coercive field and mechanical quality factor.

  5. Optical properties of epitaxial BiFeO3 thin film grown on SrRuO3-buffered SrTiO3 substrate.

    PubMed

    Xu, Ji-Ping; Zhang, Rong-Jun; Chen, Zhi-Hui; Wang, Zi-Yi; Zhang, Fan; Yu, Xiang; Jiang, An-Quan; Zheng, Yu-Xiang; Wang, Song-You; Chen, Liang-Yao

    2014-01-01

    The BiFeO3 (BFO) thin film was deposited by pulsed-laser deposition on SrRuO3 (SRO)-buffered (111) SrTiO3 (STO) substrate. X-ray diffraction pattern reveals a well-grown epitaxial BFO thin film. Atomic force microscopy study indicates that the BFO film is rather dense with a smooth surface. The ellipsometric spectra of the STO substrate, the SRO buffer layer, and the BFO thin film were measured, respectively, in the photon energy range 1.55 to 5.40 eV. Following the dielectric functions of STO and SRO, the ones of BFO described by the Lorentz model are received by fitting the spectra data to a five-medium optical model consisting of a semi-infinite STO substrate/SRO layer/BFO film/surface roughness/air ambient structure. The thickness and the optical constants of the BFO film are obtained. Then a direct bandgap is calculated at 2.68 eV, which is believed to be influenced by near-bandgap transitions. Compared to BFO films on other substrates, the dependence of the bandgap for the BFO thin film on in-plane compressive strain from epitaxial structure is received. Moreover, the bandgap and the transition revealed by the Lorentz model also provide a ground for the assessment of the bandgap for BFO single crystals.

  6. Mn2O3 Slurry Achieving Reduction of Slurry Waste

    NASA Astrophysics Data System (ADS)

    Kishii, Sadahiro; Nakamura, Ko; Hanawa, Kenzo; Watanabe, Satoru; Arimoto, Yoshihiro; Kurokawa, Syuhei; Doi, Toshiro K.

    2012-04-01

    Fumed silica is widely used for SiO2 chemical mechanical polishing (CMP). In semiconductor processes, only fresh slurry is used, the used slurry being disposed of. We have demonstrated that Mn2O3 abrasive slurry polishes dielectric SiO2 film, giving 4 times the removal rate of conventional fumed silica slurry. The higher removal rate reduces the total amount of slurry used, consequently reducing the amount of used slurry waste. The removal rate of Mn2O3 slurry remains constant for solid concentrations between l and 10 wt %, and stays constant without pad conditioning. These characteristics are very useful for slurry reuse. Remanufacture of Mn2O3 slurry from used slurry has been demonstrated, and the removal rates of the remanufactured and fresh slurries are the same. Reuse and remanufacturing drastically reduce the amount of waste.

  7. Raman tensor elements of β-Ga2O3

    PubMed Central

    Kranert, Christian; Sturm, Chris; Schmidt-Grund, Rüdiger; Grundmann, Marius

    2016-01-01

    The Raman spectrum and particularly the Raman scattering intensities of monoclinic β-Ga2O3 are investigated by experiment and theory. The low symmetry of β-Ga2O3 results in a complex dependence of the Raman intensity for the individual phonon modes on the scattering geometry which is additionally affected by birefringence. We measured the Raman spectra in dependence on the polarization direction for backscattering on three crystallographic planes of β-Ga2O3 and modelled these dependencies using a modified Raman tensor formalism which takes birefringence into account. The spectral position of all 15 Raman active phonon modes and the Raman tensor elements of 13 modes were determined and are compared to results from ab-initio calculations. PMID:27808113

  8. Quantum chemical study of the O 3-HONO complex

    NASA Astrophysics Data System (ADS)

    Roohi, Hossein; Ashuri, Masomeh

    2009-07-01

    Gas phase hydrogen-bonded isomers of the O 3-HONO complex have been investigated by means of DFT(B3LYP), MP2, MP4(SDTQ), CCSD(T) and QCISD(T) methods in conjunction with the 6-311++G(2d,2p), 6-311++G(df,pd), AUG-cc-pVDZ and AUG-cc-pVTZ basis sets. Ten isomers were found for the O 3-HONO complex. The O⋯H and O⋯O interactions are predicted that participate in the formation of non-planar ring structure of the most stable isomer. The AIM calculations reveal that the O⋯H interaction in the most stable complex is stronger than others. In addition, both O⋯H and O⋯O interactions in O 3-HONO complexes are electrostatic in nature.

  9. Products and yields from O3 photodissociation at 1576 A

    NASA Technical Reports Server (NTRS)

    Taherian, M. R.; Slanger, T. G.

    1985-01-01

    An analysis has been made of the primary atomic and molecular products arising from O3 photodissociation at 1576 A. The yield of oxygen atoms is 1.90 + or - 0.30, of which 71 percent are O(3P) and 29 percent are O(1D). Since a primary yield greater than unity can only be a consequence of three-fragment dissociation, these results suggest that fragmentation into three O(3P) atoms, and production of O(1D) plus a singlet oxygen molecule, have comparable yields. Observation of prompt emission in the 7300-8100 A spectral region indicates that the singlet O2 is O2(b 1Sigma + g). Vibrational levels in the range v = 0-6 have been detected, the distribution corresponding to a vibrational temperature of 1000 K.

  10. Photocatalytic activity of zinc modified Bi 2O 3

    NASA Astrophysics Data System (ADS)

    Hameed, Abdul; Gombac, Valentina; Montini, Tiziano; Felisari, Laura; Fornasiero, Paolo

    2009-12-01

    The surface of α-Bi 2O 3 was modified by either impregnating Zn acetate or coating with a sol-gel containing Zn hydroxide. The surface modified Bi 2O 3 powders were evaluated by UV-Visible spectroscopy, Scanning Electron Microscopy (SEM), X-ray diffraction (XRD) and surface area analysis (BET). The photocatalytic performances were evaluated for the degradation of phenol, methylene blue and methyl orange. The variations in photocatalytic activity were correlated with morphology change. The presence of ZnO does not significantly prevent the progressive formation of photocatalytically inactive (BiO) 2CO 3, while the dye decolourization capability of nanocomposite is significantly preserved with respect to that of bare Bi 2O 3.

  11. CVD Lu(2)O(3):Eu coatings For Advanced Scintillators.

    PubMed

    Topping, Stephen G; Sarin, V K

    2009-03-01

    Currently Lu(2)O(3):Eu(3+) scintillators can only be fabricated via hot-pressing and pixelization, which is commercially not viable, thus restricting their use. Chemical vapor deposition is being developed as an alternative manufacturing process. Columnar coatings of Lu(2)O(3):Eu(3+) have been achieved using the halide-CO(2)-H(2) system, clearly signifying feasibility of the CVD process. Characterization of the coatings using high resolution scanning electron microscopy (SEM) and x-ray diffraction (XRD) analysis have been used as an aid to optimize process parameters and attain highly oriented and engineered coating structures. These results have clearly demonstrated that this process can be successfully used to tailor sub-micron columnar growth of Lu(2)O(3):Eu(3+), with the potential of ultra high resolution x-ray imaging.

  12. Electrostatic model of the LiTaO3 ferroelectric

    NASA Astrophysics Data System (ADS)

    Yatsenko, A. V.

    2017-01-01

    Possible combinations of the electronic polarizability tensor components for oxygen and tantalum ions have been established based on the analysis of the refraction coefficients of LiTaO3 crystal in the far-IR region. The local electric field on structurally nonequivalent ions in the LiTaO3 unit cell was calculated within the modified point-multipole model. A combination of the electronic polarizability tensor components for oxygen and tantalum ions and their effective charges is established, which provides a good correspondence of the calculation results with the experimental data on LiTaO3 crystals obtained by 7Li nuclear magnetic resonance and 181Ta nuclear quadrupole resonance and with the known value of the crystal spontaneous polarization.

  13. Synthesis and thermal characterization of Al2O3 nanoparticles

    NASA Astrophysics Data System (ADS)

    Ismardi, A.; Rosadi, O. M.; Kirom, M. R.; Syarif, D. G.

    2016-11-01

    Al2O3 nanoparticle has been successfully synthesized using sol gel method from AlCl3. The obtained nanoparticles was then characterized for grain size measurement, the size of nanoparticles was 6 nm by using surface area meter (SAM) and Transmission Electron Microscopy (TEM). The crystallinity property of the product was then checked with XRD spectroscopy, the result shows that the diffraction peaks were match with the 10-0425 JCPDS database. Thermal property of the Al2O3 nanoparticles was then studied by mixing it with engine base fluid as nanofluid. The usage of nanofluid was expected to be heat absorber and woulo increase cooling process in cooling machine. The results showed that cooling time increases when the concentration of nanofluid was increased. Finally, it is concluded that thermal property of Al2O3 was studied and applicable to be mixed with engine coolant of cooler machine to reduce cooling time process.

  14. Local Structure of La1-xSrxCoO3 determined from EXAFS and neutron PDF studies

    SciTech Connect

    Sundaram, N.; Jiang, Y.; Anderson, I. E.; Belanger, D. P.; Booth, C. H.; Bridges, F.; Mitchell, J. F.; Proffen, Th.; Zheng, H.

    2009-01-26

    The combined local structure techniques, extended x-ray absorption fine structure (EXAFS) and neutron pair distribution function analysis, have been used for temperatures 4<= T<= 330 K to rule out a large Jahn-Teller (JT) distortion of the Co-O bond in La1?xSrxCoO3 for a significant fraction of Co sites (x<= 0.35), indicating few, if any, JT-active, singly occupied eg Co sites exist.

  15. Roles of Fe2+, Fe3+, and Cr3+ Surface Sites in the Oxidation of NO on the (Fe,Cr)3O4(1 1 1) Surface Termination of an α-(Fe,Cr)2O3(0 0 0 1) Mixed Oxide

    SciTech Connect

    Henderson, Michael A.

    2014-10-01

    The oxidation and photooxidation reactions of nitric oxide were explored on a mixed Fe and Cr mixed oxide surface using temperature programmed desorption (TPD). The mixed oxide surface examined initially had a corundum (0001) structure with a nominal cation composition of 75% Fe and 25% Cr, but after sputter/anneal cleaning was transformed into a magnetite-like (111) surface structure enriched with Cr (~40%). TPD studies of nitric oxide on the (Fe,Cr)3O4(111) surface revealed two main desorption states at 220 and 370 K, along with a third minor desorption state at ~310 K. Similarly, O2 TPD occurred in two main TPD states (100 and 230 K) and a minor state (155 K). The more strongly and weakly bound NO and O2 molecules were assigned to adsorption at Fe2+ and Fe3+ sites, respectively, with the minor desorption states assigned to Cr3+ sites. No thermal decomposition or surface chemistry was detected in TPD for adsorbed NO (e.g., no N2 or N2O formation), whereas ~10% of the adsorbed O2 irreversibly dissociated at Fe2+ sites. These dissociated oxygen species did not react with coadsorbed NO, but instead blocked NO adsorption at the Fe2+ sites, but had no effect on NO adsorption at Fe3+ sites. In contrast, NO reacted with preadsorbed O2 molecules to generate an adsorbed nitrate/nitrite species that decomposed in TPD to liberate NO at 425 K, leaving an O atom on the surface. Coadsorption of 15N18O with 16O2 suggests the oxidized species was a nitrate based on the detected level of oxygen scrambling. Preadsorption of O2 was required for nitrate formation as preadsorbed NO blocked both O2 adsorption and the oxidation reaction. Irradiation of adsorbed NO with 460 nm light at 40 K resulted in rapid photodesorption of NO without generation of any new surface species. Irradiation of the coadsorbed NO+O2 system did not promote additional NO oxidation, but limited the extent of thermal NO oxidation (in subsequent TPD) by photodepleting the surface of adsorbed NO. Preheating the NO

  16. Oxidation of the GaAs semiconductor at the Al2O3/GaAs junction.

    PubMed

    Tuominen, Marjukka; Yasir, Muhammad; Lång, Jouko; Dahl, Johnny; Kuzmin, Mikhail; Mäkelä, Jaakko; Punkkinen, Marko; Laukkanen, Pekka; Kokko, Kalevi; Schulte, Karina; Punkkinen, Risto; Korpijärvi, Ville-Markus; Polojärvi, Ville; Guina, Mircea

    2015-03-14

    Atomic-scale understanding and processing of the oxidation of III-V compound-semiconductor surfaces are essential for developing materials for various devices (e.g., transistors, solar cells, and light emitting diodes). The oxidation-induced defect-rich phases at the interfaces of oxide/III-V junctions significantly affect the electrical performance of devices. In this study, a method to control the GaAs oxidation and interfacial defect density at the prototypical Al2O3/GaAs junction grown via atomic layer deposition (ALD) is demonstrated. Namely, pre-oxidation of GaAs(100) with an In-induced c(8 × 2) surface reconstruction, leading to a crystalline c(4 × 2)-O interface oxide before ALD of Al2O3, decreases band-gap defect density at the Al2O3/GaAs interface. Concomitantly, X-ray photoelectron spectroscopy (XPS) from these Al2O3/GaAs interfaces shows that the high oxidation state of Ga (Ga2O3 type) decreases, and the corresponding In2O3 type phase forms when employing the c(4 × 2)-O interface layer. Detailed synchrotron-radiation XPS of the counterpart c(4 × 2)-O oxide of InAs(100) has been utilized to elucidate the atomic structure of the useful c(4 × 2)-O interface layer and its oxidation process. The spectral analysis reveals that three different oxygen sites, five oxidation-induced group-III atomic sites with core-level shifts between -0.2 eV and +1.0 eV, and hardly any oxygen-induced changes at the As sites form during the oxidation. These results, discussed within the current atomic model of the c(4 × 2)-O interface, provide insight into the atomic structures of oxide/III-V interfaces and a way to control the semiconductor oxidation.

  17. Structural study of radiolytic catalysts Ni-Ce/Al2O3 and Ni-Pt/Al2O3

    NASA Astrophysics Data System (ADS)

    Seridi, F.; Chettibi, S.; Keghouche, N.; Beaunier, P.; Belloni, J.

    2017-01-01

    Ni-Ce and Ni-Pt bimetallic catalysts supported over α-Al2O3 are synthesized by using co-impregnation method, and then reduced, each via radiolytic process or thermal H2-treatment. For Ni-Ce/Al2O3, the structural study reveals that Ce is alloyed with Ni as Ce2Ni7 nanoparticles in the radiation-reduced catalysts, while it segregates to the surface in the form of CeO2 in the H2-reduced catalysts. For Ni-Pt/Al2O3 radiolytic catalysts, Ni, Pt, NiPt and Ni3Pt nanoparticles, which size is 3.5 nm, are observed. When the radiation-reduced samples are tested in the benzene hydrogenation, they both display high conversion rate. However, the Ni-Pt/Al2O3 is more efficient than Ni-Ce/Al2O3. The performance of the catalysts is correlated with the high dispersion of the metal and the presence of intermetallic Ni-Pt and Ni-Ce phases. It is compared to that of other radiolytic monometallic/oxide catalysts of the literature.

  18. Electric Field Control of the Ferromagnetic CaRuO3 /CaMnO3 Interface

    NASA Astrophysics Data System (ADS)

    Grutter, Alexander; Kirby, Brian; Gray, Matthew; Flint, Charles; Suzuki, Yuri; Borchers, Julie

    2015-03-01

    Electric field control of magnetism has been recognized as one of the most important goals in nanoscale magnetics research. The most popular routes towards achieving magnetoelectric (ME) coupling have focused on heterostructures incorporating multiferroics or ferroelectrics. Such studies often rely on voltage induced distortion to induce strain in the magnetic film and alter the magnetic properties. However, successful attempts to induce ME coupling without multiferroicity or magnetoelasticity remain relatively rare. The ferromagnetic interface between the antiferromagnetic insulator CaMnO3 and the paramagnetic metal CaRuO3 is a promising candidate for direct magnetization control. This interfacial ferroagnetism is stabilized through the competition between interfacial double exchange and antiferromagnetic superexchange between adjacent Mn4+ so that the system is expected to be very sensitive to small changes in interfacial carrier density. Using polarized neutron reflectometry, we have probed the electric field dependence of the interfacial magnetization of CaRuO3/CaMnO3 bilayers deposited on SrTiO3. We find that electric fields of +/-8 kV/m are sufficient to switch the interfaces from largely ferromagnetic to completely antiferromagnetic.

  19. Epitaxial growth and thermodynamic stability of SrIrO3/SrTiO3 heterostructures

    NASA Astrophysics Data System (ADS)

    Groenendijk, D. J.; Manca, N.; Mattoni, G.; Kootstra, L.; Gariglio, S.; Huang, Y.; van Heumen, E.; Caviglia, A. D.

    2016-07-01

    Obtaining high-quality thin films of 5d transition metal oxides is essential to explore the exotic semimetallic and topological phases predicted to arise from the combination of strong electron correlations and spin-orbit coupling. Here, we show that the transport properties of SrIrO3 thin films, grown by pulsed laser deposition, can be optimized by considering the effect of laser-induced modification of the SrIrO3 target surface. We further demonstrate that bare SrIrO3 thin films are subject to degradation in air and are highly sensitive to lithographic processing. A crystalline SrTiO3 cap layer deposited in-situ is effective in preserving the film quality, allowing us to measure metallic transport behavior in films with thicknesses down to 4 unit cells. In addition, the SrTiO3 encapsulation enables the fabrication of devices such as Hall bars without altering the film properties, allowing precise (magneto)transport measurements on micro- and nanoscale devices.

  20. Gas sensing behaviour of Cr2O3 and W6+: Cr2O3 nanoparticles towards acetone

    NASA Astrophysics Data System (ADS)

    Kohli, Nipin; Hastir, Anita; Singh, Ravi Chand

    2016-05-01

    This paper reports the acetone gas sensing properties of Cr2O3 and 2% W6+ doped Cr2O3 nanoparticles. The simple cost-effective hydrolysis assisted co-precipitation method was adopted. Synthesized samples were characterized by X-ray diffraction (XRD) and field emission scanning electron microscopy (FESEM) techniques. XRD revealed that synthesized nanoparticles have corundum structure. The lattice parameters have been calculated by Rietveld refinement; and strain and crystallite size have been calculated by using the Williamson-Hall plots. For acetone gas sensing properties, the nanoparticles were applied as thick film onto alumina substrate and tested at different operating temperatures. The results showed that the optimum operating temperature of both the gas sensors is 250°C. At optimum operating temperature, the response of Cr2O3 and 2% W6+ doped Cr2O3 gas sensor towards 100 ppm acetone was found to be 25.5 and 35.6 respectively. The investigations revealed that the addition of W6+ as a dopant enhanced the sensing response of Cr2O3 nanoparticles appreciably.

  1. Ferromagnetic interactions in chromium (III) doped YMnO3

    NASA Astrophysics Data System (ADS)

    Thakur, Rajesh K.; Thakur, Rasna; Kaurav, N.; Okram, G. S.; Gaur, N. K.

    2016-05-01

    Both of the reported compounds with compositions YMn1-xCrxO3 (x = 0.1 and 0.2) are synthesized by using the conventional solid state reaction method and their magnetic properties are analyzed vigilantly. The XRD pattern reveals the hexagonal structure of the reported compounds with space group P63cm (25-1079). The in-depth analysis of the magnetic measurements reveals the enhancement in the ferromagnetic character with Cr doping in YMnO3 compounds. The observed enhancement in the ferromagnetism is found to be due to the increased double exchange interactions among the Cr3+ and Mn3+ ions with Cr doping.

  2. Magnetic properties of the (LaMnO3)N/(SrTiO3)N atomic layer superlattices

    NASA Astrophysics Data System (ADS)

    Zhai, Xiaofang; Mohapatra, Chandra S.; Shah, Amish B.; Zuo, Jian-Min; Eckstein, James N.

    2013-05-01

    We studied the magnetic properties of atomic layer superlattices of (LaMnO3)N/(SrTiO3)N (N = 1,2,8) fabricated by ozone-assisted atomic layer-by-layer molecular beam epitaxy. Compared to a reference LaMnO3 thin film, the N = 8 superlattice exhibits enhanced magnetization, while the N = 1 and 2 superlattices exhibit suppressed magnetization. The onset temperature of the ferromagnetic transition is lowered in all superlattices. Moreover, the Brillouin function fits to the magnetic hysteresis curves indicate that the ground state of the superlattices consists of non-uniform spin interactions. The electric transport measurements suggest a very small variation of Mn valence (˜±0.015) that may not be enough to induce the observed large change in the magnetic property.

  3. Influence of interfacial coherency on ferroelectric switching of superlattice BaTiO3/SrTiO3

    SciTech Connect

    Wu, Pingping; Ma, Xingqiao; Li, Yulan; Eom, C. B.; Schlom, Darrell G.; Gopalan, Venkatraman; Chen, Long-Qing

    2015-04-11

    Switching behavior of (BaTiO3)8/ (SrTiO3)4 heterostructure superlattice grown on SrTiO3 substrate was studied by employing the phase field method. To investigate the constraint effect of the substrate on switching, three types of superlattice/substrate interface mechanical relaxation conditions were considered, i.e. the fully ommensurate, partially relaxed and fully relaxed. Our simulation results demonstrated that the hysteresis loops under the three types of constraints were very different. The interfacial coherency affects dramatically the coercivity and remanence of the superlattice films. The mechanism of the hysteresis loop varying with interfacial coherency was analyzed by the ferroelectric domain configuration and its evolution during the switching process. The hysteresis loop of fully relaxed superlattice shows application potential on ferroelectric energy storage materials.

  4. EPITAXIAL STRAIN CONTROLLED ?CHARGE LEAKAGE? AT LaMnO3 / SrTiO3 INTERFACES

    SciTech Connect

    Garcia-Barriocanal, Javier; Bruno, Flavio Y.; Rivera-Calzada, Alberto; Sefrioui, Z.; Garcia-Hernandez, M; Rubio-Zuazo, J.; Castro, G.; Varela del Arco, Maria; Pennycook, Stephen J; Leon, C.; Santamaria, J.

    2010-01-01

    We report on the charge transfer at the interface between a band (SrTiO3) and a Mott insulator (LaMnO3) in epitaxial superlattices. We have used combined atomic resolution electron microscopy and spectroscopy, synchrotron X ray reciprocal space maps and magneto transport measurements, to characterize the interface properties. The LaMnO3 layers are always started and terminated in (LaO) planes, giving an overall electron doping to the system. However, the direction of charge leakage is determined by the manganite to titanate thickness ratio in a way controlled by the different epitaxial strain patterns. This result may provide a clue to optimize oxide devices such as magnetic tunnel junctions and field effect transistors whose operation is determined by the interface properties.

  5. Bethe-Salpeter calculation of optical-absorption spectra of In2O3 and Ga2O3

    NASA Astrophysics Data System (ADS)

    Varley, Joel B.; Schleife, André

    2015-02-01

    Transparent conducting oxides keep attracting strong scientific interest not only due to their promising potential for ‘transparent electronics’ applications but also due to their intriguing optical absorption characteristics. Materials such as In2O3 and Ga2O3 have complicated unit cells and, consequently, are interesting systems for studying the physics of excitons and anisotropy of optical absorption. Since currently no experimental data is available, for instance, for their dielectric functions across a large photon-energy range, we employ modern first-principles computational approaches based on many-body perturbation theory to provide theoretical-spectroscopy results. Using the Bethe-Salpeter framework, we compute dielectric functions and we compare to spectra computed without excitonic effects. We find that the electron-hole interaction strongly modifies the spectra and we discuss the anisotropy of optical absorption that we find for Ga2O3 in relation to existing theoretical and experimental data.

  6. Modulation-Doped SrTiO3/SrTi1-xZrxO3 Heterostructures

    NASA Astrophysics Data System (ADS)

    Kajdos, Adam Paul

    Two-dimensional electron gases (2DEGs) in SrTiO3 have attracted considerable attention for exhibiting a variety of interesting physical phenomena, such as superconductivity and magnetism. So far, most of the literature has focused on interfaces between nonpolar SrTiO3 and polar perovskite oxides (e.g. LaAlO3 or rare-earth titanates), where high carrier density 2DEGs (˜3 x 1014 cm-2) are generated by polar discontinuity. Modulation doping is an alternative approach to generating a 2DEG that has been explored extensively in III-V semiconductors but has not heretofore been explored in complex oxides. This approach involves interfacing an undoped semiconductor with a doped semiconductor whose conduction band edge lies at a higher energy, which results in electrons diffusing into the undoped semiconductor transport channel, where scattering from ionized dopants is minimized. Realizing a high-mobility modulation-doped structure with a SrTiO3 transport channel therefore requires both the optimization of the transport channel by minimizing native defects as well as the development of a perovskite oxide which has a suitable band offset with SrTiO3 and can be electron-doped. The growth of high electron mobility SrTiO3 as a suitable transport channel material was previously demonstrated using the hybrid molecular beam epitaxy (MBE) approach, where Sr is delivered via a solid source and Ti is delivered using a metal-organic precursor, titanium (IV) tetra-isopropoxide (TTIP). Expanding on this, in-situ reflection high-energy electron diffraction (RHEED) is used to track the surface and resulting film cation stoichiometry of homoepitaxial SrTiO3 (001) thin films grown by hybrid MBE. It is shown that films with lattice parameters identical to bulk single-crystal substrates within the detection limit of high-resolution X-ray diffraction (XRD) measurements exhibit an evolution in surface reconstruction with increasing TTIP beam-equivalent pressure. The change in the observed

  7. Self-assembled monolayer modified MoO3/Au/MoO3 multilayer anodes for high performance OLEDs

    NASA Astrophysics Data System (ADS)

    Jeong, Daekyun; Lim, Chefwi; Kim, Myeonggi; Jeong, Kyunghoon; Kim, Jae-Hun; Kim, Jiyoung; Park, Jin-Goo; Min, Kyeong-Sik; Lee, Jaegab

    2017-01-01

    We control the work function and the surface energy of the MoO3/Au/MoO3 (MAM) anode of OLEDs by modifying the top MoO3 layer via vapor phase deposition. The performance and stability of the device are significantly altered depending on the dipole direction of the selfassembled monolayer (SAM) with permanent dipole moment inserted between N,N'-Bis(naphthalen-1-yl)-N,N'-bis(phenyl)benzidine (NPB) film and a MAM anode as well as on the interfacial wetting between the SAM and NPB layer. A CF3-terminated monolayer on a MAM electrode improved the performance and stability of the OLEDs relative to a reference device with only a MAM electrode, demonstrating that coating with SAMs via vapor phase deposition is an effective method to engineer the interface of MAM electrode optoelectronic devices. [Figure not available: see fulltext.

  8. Evolution of the interfacial structure of LaAlO3 on SrTiO3.

    PubMed

    Pauli, S A; Leake, S J; Delley, B; Björck, M; Schneider, C W; Schlepütz, C M; Martoccia, D; Paetel, S; Mannhart, J; Willmott, P R

    2011-01-21

    The evolution of the atomic structure of LaAlO_{3} grown on SrTiO_{3} was investigated using surface x-ray diffraction in conjunction with model-independent, phase-retrieval algorithms between two and five monolayers film thickness. A depolarizing buckling is observed between cation and oxygen positions in response to the electric field of polar LaAlO_{3}, which decreases with increasing film thickness. We explain this in terms of competition between elastic strain energy, electrostatic energy, and electronic reconstructions. Based on these structures, the threshold for formation of a two-dimensional electron system at a film thickness of 4 monolayers is quantitatively explained. The findings are also qualitatively reproduced by density-functional-theory calculations.

  9. Research Update: Conductivity and beyond at the LaAlO3/SrTiO3 interface

    NASA Astrophysics Data System (ADS)

    Gariglio, S.; Gabay, M.; Triscone, J.-M.

    2016-06-01

    In this review, we focus on the celebrated interface between two band insulators, LaAlO3 and SrTiO3, that was found to be conducting, superconducting, and to display a strong spin-orbit coupling. We discuss the formation of the 2-dimensional electron liquid at this interface, the particular electronic structure linked to the carrier confinement, the transport properties, and the signatures of magnetism. We then highlight distinctive characteristics of the superconducting regime, such as the electric field effect control of the carrier density, the unique tunability observed in this system, and the role of the electronic subband structure. Finally we compare the behavior of Tc versus 2D doping with the dome-like behavior of the 3D bulk superconductivity observed in doped SrTiO3. This comparison reveals surprising differences when the Tc behavior is analyzed in terms of the 3D carrier density for the interface and the bulk.

  10. Unexpected ordering at the atomic scale interface of SrRuO3 and BaTiO3

    NASA Astrophysics Data System (ADS)

    Baddorf, Arthur P.

    2011-03-01

    Atomically engineered oxide multilayers and superlattices display unique properties responsive to the electronic and atomic structures of the interfaces. Interfaces can exhibit not only two-dimensional functionality, but have the power to dictate the properties of thin films. A clear example is found in ferroelectric thin films, where the domain size, orientation, and transport properties are controlled by top and buried interfaces. We have explored a prototypical ferroelectric - bottom electrode interface by characterizing BaTi O3 grown on SrRu O3 . Films were grown on SrTi O3 substrates by pulsed laser deposition, monitored by high-pressure reflection high-energy diffraction, exhibited high crystalline quality in electron diffraction and cross-sectional transmission electron microscopy (STEM), and were flat according to atomic force microscopy. Despite multiple indicators commonly accepted to confirm a sharp interface, atomically the structure is more complex. When grown in a typical oxygen pressure, at or below 10 mTorr, in situ scanning tunneling microscopy (STM) revealed the SrRu O3 surface is littered with oxygen vacancies. For growth or post-annealing above ~ 100 mtorr, vacancies were removed, but STM and low energy electron diffraction (LEED) disclosed a surface reconstruction consisting of parallel rows with periodicity doubled in one direction. Density function theory (DFT) suggests these rows are chains of Sr and O raised by excess oxygen. Both LEED and cross-sectional STEM revealed that this reconstruction persists at the buried interface and modifies the structure of subsequent BaTi O3 layers. By four layers, the BaTi O3 surface returns to a bulk-like structure with upward polar distortion. This study emphasizes the importance of atomic scale structural studies of what may otherwise appear as sharp interfaces. Research at ORNL's CNMS was sponsored by the Scientific User Facilities Division, Office of Basic Energy Sciences, U.S. DOE.

  11. Structural, magnetic, and dielectric properties of solid solutions between BiMnO3 and YMnO3

    NASA Astrophysics Data System (ADS)

    Belik, Alexei A.

    2017-02-01

    Bi1-xYxMnO3 (0.1≤x≤0.9) solid solutions were prepared by the high-pressure high-temperature method at 6 GPa and 1573 K. They crystallize in the GdFeO3-type perovskite structure with the Pnma symmetry. Crystal structures of Bi0.9Y0.1MnO3 and Bi0.5Y0.5MnO3 are studied by synchrotron X-ray powder diffraction at room temperature. Only one Néel temperature, TN, is found in samples with 0.1≤x≤0.9 in comparison with two Néel temperatures observed in YMnO3 (TN=29 and 39 K). Samples with 0.5≤x≤0.9 have almost constant TN=44 K, while TN starts to increase linearly for other compositions: TN=46 K for x=0.3, TN=58 K for x=0.2, and TN=68 K for x=0.1. Field-induced transitions from canted-antiferromagnetic states to antiferromagnetic states are detected at about 30 kOe for x=0.2 and 70 kOe for x=0.1. Dielectric constant increases below TN in samples with 0.5≤x≤1, while it decreases below TN in samples with 0.1≤x≤0.3. Our data suggest that a magnetic structure changes near x=0.4. By extrapolation, we could estimate lattice parameters (a=5.9221 Å, b=7.5738 Å, and c=5.4157 Å) and TN=79 K for a hypothetical Pnma modification of BiMnO3.

  12. Comparison of H 2O 2 and O 3 content in atmospheric samples in the San Bernardino mountains, Southern California

    NASA Astrophysics Data System (ADS)

    Sakugawa, Hiroshi; Kaplan, Isaac R.

    Concentrations of atmospheric H 2O 2 were measured in air, rain, cloud and dew samples in forested areas of the San Bernardino Mountains, southern California, from spring through fall of 1987-1990 O 3 measurements in air were also conducted for comparison. Typical ranges of H 2O 2 concentrations measured were 1-3 ppb in air, 10-90 μM in rain and cloud water, and < μM in dew. The results show that gas-phase H 2O 2 concentrations were slightly higher at nighttime than at daytime or nearly constant throughout a 24-hr period, whereas O 3 concentrations were highest during the afternoon, when polluted air masses from Los Angeles carried by daily sea breezes reached the mountain region. Afternoon concentrations of gaseous H 2O 2 and O 3 in the mountain region were compared with those measured in Los Angeles urban sites to elucidate the regional variation of these oxidants. The results show that ambient concentrations of H 2O 2 and O 3 were about 50-100% higher at the mountains sites than at the Los Angeles sites.

  13. Seasonal variation of the O3-CO correlation derived from remote sensing measurements over western Japan

    NASA Astrophysics Data System (ADS)

    Ohyama, Hirofumi; Kawakami, Shuji; Uchino, Osamu; Sakai, Tetsu; Morino, Isamu; Nagai, Tomohiro; Shiomi, Kei; Sakashita, Masanori; Akaho, Taiga; Okumura, Hiroshi; Arai, Kohei

    2016-12-01

    We used a lower tropospheric ozone column (LTOC) and column-averaged dry-air mole fraction of carbon monoxide (XCO) data observed in the area around Saga, which is located in western Japan and is close to the Asian continent, with an aim to investigate whether these data can characterize the seasonal variation of the photochemical ozone (O3) formation in the northeast Asian Pacific rim region. The LTOC data after April 2009 were retrieved from thermal infrared spectra measured by the Thermal and Near Infrared Sensor for Carbon Observation-Fourier Transform Spectrometer (TANSO-FTS) onboard the Greenhouse Gases Observing Satellite (GOSAT). The XCO data after July 2011 were obtained from ground-based high-resolution FTS measurements at Saga. The retrieved LTOCs were validated with those derived from a differential absorption lidar for O3 at Saga. The LTOCs showed a distinct seasonal variation that reached a maximum in late spring (May or June) and a local minimum in winter. In addition to the general seasonal pattern, we observed pronounced minimums in July or August. The XCO concentrations showed a maximum in spring and a minimum in summer. These seasonal patterns are consistent with those observed from mountainous sites in Japan. The origins of the air masses reaching Saga were characterized for each season according to backward trajectories, and the factors causing the temporal variations of the LTOCs and the XCO were identified based on the transport paths of the air masses. The enhancement of the LTOC relative to the XCO (ΔO3/ΔCO ratio) reveals significant positive correlations in the spring and summer seasons with slopes of 0.21 and 0.45 ppb/ppb, respectively. The effects of stratospheric air intrusion on the observed ΔO3/ΔCO ratio in spring were investigated using meteorological data (backward trajectory and potential vorticity) and column-averaged hydrogen fluoride data derived from the ground-based FTS measurements. It was found that there was little

  14. Oxygen ion conduction in barium doped LaInO3 perovskite oxides

    NASA Astrophysics Data System (ADS)

    Kim, Hye-Lim; Kim, Shin; Lee, Kyu-Hyung; Lee, Hong-Lim; Lee, Ki-Tae

    2014-12-01

    Oxygen ion conduction behaviors of the 0-5 mol% excess Ba-doped La0.6Ba0.4InO3-δ cubic perovskite oxides have been investigated to elucidate their potential as electrolyte materials. The highest conductivity, 5.6 × 10-2 S cm-1 at 800 °C, is obtained at the 3 mol% excess Ba-doped composition benefiting from a supplementation of Ba2+ ions on the vacant A-site generated by the volatilization during the heat-treatment processes. Interestingly, all the samples except the undoped composition show curved electrical conductivity behavior in the Arrhenius plot. The activation energy is 0.50-0.52 eV in the high-temperature region above 900 °C, which is slightly lower than that of the doped LaGaO3 system. Moreover, all the samples show significantly lower activation energy values of both the high- and low-temperature regions compared with yttria-stabilized zirconia. The 3 mol% excess Ba-doped La1-xBaxInO3-δ (0.4 ≤ x ≤ 0.8) sample has also been studied. All of the compositions show a cubic perovskite structure and a nearly pure oxygen ion conduction behavior in a dry atmosphere even when p(O2) = 1atm. The composition of x = 0.4 exhibits the highest oxygen ion conductivities.

  15. Enhanced spin - Reorientation temperature and origin of magnetocapacitance in HoFeO3

    NASA Astrophysics Data System (ADS)

    Kotnana, Ganesh; Jammalamadaka, S. Narayana

    2016-11-01

    We report on the increase in the spin reorientation temperature in HoFe0.5Cr0.5O3 compound by isovalent substitution (Cr3+) at the Fe-site and the magnetocapacitance in the HoFeO3 compound. Spin reorientation transition is evident around 50 K and 150 K for the x=0 and x=0.5 compounds respectively. The increase in the spin reorientation transition temperature in case of x=0.5 compound can be attributed to the domination of the Ho3+-Fe3+ interaction over the Fe3+-Fe3+ interaction. Decrease in Néel temperature from 643 K (x=0) to 273 K (x=0.5) can be ascribed to the decrease in the interaction between antiferromagnetically aligned Fe3+ moments as a result of the dilution of the Fe3+ moments with the Cr3+ addition. From the magnetization M vs. magnetic field H variation it is evident that the coercivity, HC decreases for x=0.5 compound, hinting the magnetic softening of the HoFeO3 compound. Observed magnetocapacitance could be due to lossy dielectric mechanism in the present compound. Indeed, present results would be helpful in understanding the physics behind rare-earth orthoferrites.

  16. Blending Cr2O3 into a NiO-Ni electrocatalyst for sustained water splitting.

    PubMed

    Gong, Ming; Zhou, Wu; Kenney, Michael James; Kapusta, Rich; Cowley, Sam; Wu, Yingpeng; Lu, Bingan; Lin, Meng-Chang; Wang, Di-Yan; Yang, Jiang; Hwang, Bing-Joe; Dai, Hongjie

    2015-10-05

    The rising H2 economy demands active and durable electrocatalysts based on low-cost, earth-abundant materials for water electrolysis/photolysis. Here we report nanoscale Ni metal cores over-coated by a Cr2 O3 -blended NiO layer synthesized on metallic foam substrates. The Ni@NiO/Cr2 O3 triphase material exhibits superior activity and stability similar to Pt for the hydrogen-evolution reaction in basic solutions. The chemically stable Cr2 O3 is crucial for preventing oxidation of the Ni core, maintaining abundant NiO/Ni interfaces as catalytically active sites in the heterostructure and thus imparting high stability to the hydrogen-evolution catalyst. The highly active and stable electrocatalyst enables an alkaline electrolyzer operating at 20 mA cm(-2) at a voltage lower than 1.5 V, lasting longer than 3 weeks without decay. The non-precious metal catalysts afford a high efficiency of about 15 % for light-driven water splitting using GaAs solar cells.

  17. Blending Cr2O3 into a NiO-Ni electrocatalyst for sustained water splitting

    DOE PAGES

    Gong, Ming; Zhou, Wu; Kenney, Michael James; ...

    2015-08-24

    The rising H2 economy demands active and durable electrocatalysts based on low-cost, earth-abundant materials for water electrolysis/photolysis. Here we report nanoscale Ni metal cores over-coated by a Cr2O3-blended NiO layer synthesized on metallic foam substrates. The Ni@NiO/Cr2O3 triphase material exhibits superior activity and stability similar to Pt for the hydrogen-evolution reaction in basic solutions. The chemically stable Cr2O3 is crucial for preventing oxidation of the Ni core, maintaining abundant NiO/Ni interfaces as catalytically active sites in the heterostructure and thus imparting high stability to the hydrogen-evolution catalyst. The highly active and stable electrocatalyst enables an alkaline electrolyzer operating at 20more » mA cm–2 at a voltage lower than 1.5 V, lasting longer than 3 weeks without decay. Thus, the non-precious metal catalysts afford a high efficiency of about 15 % for light-driven water splitting using GaAs solar cells.« less

  18. Magnetism and metal-insulator transition in oxygen deficient SrTiO3

    NASA Astrophysics Data System (ADS)

    Lopez-Bezanilla, Alejandro; Ganesh, P.; Littlewood, Peter

    2015-03-01

    We report new findings in the electronic structure and magnetism of oxygen vacancies in SrTiO3. By means of first-principles calculations we show that the appearance of magnetism in oxygen-deficient SrTiO3 is not determined solely by the presence of a single oxygen vacancy but by the density of free carriers and the relative proximity of the vacant sites. While an isolated vacancy behaves as a non-magnetic double donor, manipulation of the doping conditions allows the stability of a single donor state with emergent local moments. Strong local lattice distortions enhance the binding of this state. Consequently we find that the free-carrier density and strain are fundamental components to obtaining trapped spin-polarized electrons in oxygen-deficient SrTiO3, which may have important implications in the design of switchable magneto-optic devices. AL-B and PBL were supported by DOE-BES under Contract No. DE-AC02-06CH11357. PG was sponsored by the Laboratory Directed Research and Development Program of Oak Ridge National Laboratory, managed by UT- Battelle, LLC, for the US Department of Energy.

  19. Magnetocaloric properties in La1-xCaxMnO3 thin films: Monte Carlo simulations

    NASA Astrophysics Data System (ADS)

    Restrepo-Parra, E.; Ramos-Rivera, L.; Londoño-Navarro, J.

    2014-02-01

    The magnetocaloric effect (MCE) of La1-xCaxMnO3 was analyzed when varying the stoichiometry (x=0.2, 0.33, 0.4 and 0.5) and the external applied magnetic field. Simulations were carried out using the Monte Carlo method having a configuration ascribed by the set Sz of all-site spin projections, under the Metropolis algorithm. La1-xCaxMnO3 is characterized for three types of magnetic ions corresponding to Mn4+ (S=3/2), which are bonded to Ca2+, and Mn3+(eg) and Mn3+(eg', S=2), which are both bonded to La3+. Different interactions must be considered depending on the type of interacting ions. The entropy change ΔS in an isothermal process as well as the temperature change ΔT in an adiabatic process was determined with this model. Both ΔS and ΔT show stoichiometry-dependent maximums near the paramagnetic-ferromagnetic transition temperature (TC), confirming the order-disorder change at this temperature. The strong dependence in La1-xCaxMnO3 of the MCE on the stoichiometry and the external magnetic field makes this phenomenon important for different technological applications, particularly in refrigeration.

  20. Insight into the effects of different ageing protocols on Rh/Al2O3 catalyst

    NASA Astrophysics Data System (ADS)

    Zhao, Baohuai; Ran, Rui; Cao, Yidan; Wu, Xiaodong; Weng, Duan; Fan, Jun; Wu, Xueyuan

    2014-07-01

    In this work, a catalyst of Rh loaded on Al2O3 was prepared by impregnating method with rhodium nitrate aqueous solution as the Rh precursor. The catalyst was aged under different protocols (lean, rich, inert and cyclic) to obtain several aged samples. All the Rh/Al2O3 samples were characterized by X-ray diffraction (XRD), Brunauer-Emmett-Teller (BET) method, CO-chemisorption, H2-temperature programmed reduction (H2-TPR), transmission electron microscope (TEM) and X-ray photoelectron spectroscopy (XPS). It was found that a specific ageing treatment could strongly affect the catalytic activity. The N2 aged and the H2 aged samples had a better catalytic activity for CO + NO reaction than the fresh sample while the air aged and the cyclic aged samples exhibited much worse activity. More surface Rh content and better reducibility were obtained in the N2 and the H2 aged samples and the Rh particles existed with an appropriate size, which were all favorable to the catalytic reaction. However, the air and the cyclic ageing protocols induced a strong interaction between Rh species and the Al2O3 support, which resulted in a severe sintering of particles of Rh species and the loss of active sites. The structure evolution scheme of the catalysts aged in different protocols was also established in this paper.

  1. Isovalent Bi3+ substitution induced structural and magnetic transitions in LaMnO3

    NASA Astrophysics Data System (ADS)

    Joseph, D. Paul; Lin, J. W.; Kumar, N. Pavan; Chen, W. C.; Lin, J. G.

    2016-11-01

    Rare earth perovskite manganites have attracted renewed attention due to scientific aspect and prospective device applications. This work explores the structural and magnetic properties of La(1-x)BixMnO3 (x=0-0.5) with isovalent Bi3+ ions substituted at the La3+site synthesized through solid state reaction method. Doping of 'Bi3+' in LaMnO3 induces transition from orthorhombic to cubic phase for x≥ 0.3. Decrease in the magnetic transition temperature in ZFC-FC data is correlated to the distortion induced by 'Bi3+' doping. Spin glass like feature is witnessed in orthorhombic phase and it diminished appreciably for x≥0.3 in the cubic symmetry. At 10 K, coercivity decreases in orthorhombic phase, whereas it increases marginally in cubic phase. Thus, isovalent Bi3+ doping in LaMnO3 is found to induce structural change from orthorhombic to cubic which is also reflected in the magnetic properties as a change over from hard to soft magnetic phase. In addition, a phenomenological model is applied for fitting the field cooled magnetization data. The results of fitting and the related magneto-caloric effect are also discussed in this paper.

  2. A Pyrolitic Lower Mantle with (Mg,Fe3+)(Si,Al3+)O3 Bridgmanite

    NASA Astrophysics Data System (ADS)

    Wang, X.; Tsuchiya, T.

    2014-12-01

    To better understand the Earth's lower mantle (LM), thermodynamic properties (TDPs) of LM minerals should be illustrated clearly. We have so far reported the TDPs of Fe (and Al)-bearing MgO, MgSiO3 bridgmanite (Br) and post bridgmanite [1-5] by using the internally consistent LSDA+U method and the lattice dynamics method. In this work, two spin states, the high (HS) and low spin (LS) state, and several possible distribution configurations are considered in the LM pressure range. For Fe incorporated in Br, only Fe3+ at the Si site undergoes a HS to LS transition. However, this is suppressed by Al incorporation, because Al3+ prefers the Si site and attracts HS Fe3+ at the adjacent Mg site forming Fe3+-Al3+ pair. Br with geophysically relevant 6.25 mol% Fe2+ or Fe3+-Al3+ pair is found vibrationally stable. Incorporation of these elements increases the Br volume a little but gives marginal effects on the TDPs. Simulated densities, adiabatic bulk moduli, and bulk sound velocities of possible LM mineral aggregations show that a composition close to pyrolite with (Mg,Fe3+)(Si,Al3+)O3 Br is accountable for the reference Earth model, while Fe2+-bearing Br instead gives unignorable disagreements in deeper part. Neither Si-richer nor Si-poorer composition improves the disagreements. This indicates that Fe in LM bridgmanite should predominantly be ferric acquiring the HS state, and pyrolitic composition with (Mg,Fe3+)(Si,Al3+)O3 Br is a reasonable LM model. References:[1] A. Metsue, and T. Tsuchiya, J. Geophys. Res. 116, B08207 (2011). [2] A. Metsue, and T. Tsuchiya, Geophys. J. Int. 190, 310 (2012). [3] H. Fukui, T. Tsuchiya, and A. Q. R. Baron, J. Geophys. Res. 117, B12202 (2012). [4] T. Tsuchiya, and X. Wang, J. Geophys. 118, 83 (2013). [5] X. Wang, and T. Tsuchiya, under reviewing.

  3. Epitaxial growth and electric properties of γ-Al2O3(110) films on β-Ga2O3(010) substrates

    NASA Astrophysics Data System (ADS)

    Hattori, Mai; Oshima, Takayoshi; Wakabayashi, Ryo; Yoshimatsu, Kohei; Sasaki, Kohei; Masui, Takekazu; Kuramata, Akito; Yamakoshi, Shigenobu; Horiba, Koji; Kumigashira, Hiroshi; Ohtomo, Akira

    2016-12-01

    Epitaxial growth and electrical properties of γ-Al2O3 films on β-Ga2O3(010) substrates were investigated regarding the prospect of a gate oxide in a β-Ga2O3-based MOSFET. The γ-Al2O3 films grew along the [110] direction and inherited the oxygen sublattice from β-Ga2O3 resulting in the unique in-plane epitaxial relationship of γ-Al2O3 [\\bar{1}10] ∥ β-Ga2O3[001]. We found that the γ-Al2O3 layer had a band gap of 7.0 eV and a type-I band alignment with β-Ga2O3 with conduction- and valence-band offsets of 1.9 and 0.5 eV, respectively. A relatively high trap density (≅ 2 × 1012 cm-2 eV-1) was found from the voltage shift of photoassisted capacitance-voltage curves measured for a Au/γ-Al2O3/β-Ga2O3 MOS capacitor. These results indicate good structural and electric properties and some limitations hindering the better understanding of the role of the gate dielectrics (a γ-Al2O3 interface layer naturally crystallized from amorphous Al2O3) in the β-Ga2O3 MOSFET.

  4. High-temperature degradation in plasma-enhanced chemical vapor deposition Al2O3 surface passivation layers on crystalline silicon

    NASA Astrophysics Data System (ADS)

    Kühnhold, Saskia; Saint-Cast, Pierre; Kafle, Bishal; Hofmann, Marc; Colonna, Francesco; Zacharias, Margit

    2014-08-01

    In this publication, the activation and degradation of the passivation quality of plasma-enhanced chemical vapor deposited aluminum oxide (Al2O3) layers with different thicknesses (10 nm, 20 nm, and 110 nm) on crystalline silicon (c-Si) during long and high temperature treatments are investigated. As indicated by Fourier Transform Infrared Spectroscopy, the concentration of tetrahedral and octahedral sites within the Al2O3 layer changes during temperature treatments and correlates with the amount of negative fixed charges at the Si/Al2O3 interface, which was detected by Corona Oxide Characterization of Semiconductors. Furthermore, during a temperature treatment at 820 °C for 30 min, the initial amorphous Al2O3 layer crystallize into the γ-Al2O3 structure and was enhanced by additional oxygen as was proven by x-ray diffraction measurements and underlined by Density Functional Theory simulations. The crystallization correlates with the increase of the optical density up to 20% while the final Al2O3 layer thickness decreases at the same time up to 26%. All observations described above were detected to be Al2O3 layer thickness dependent. These observations reveal novel aspects to explain the temperature induced passivation and degradation mechanisms of Al2O3 layers at a molecular level like the origin of the negative fixe charges at the Si/SiOx/Al2O3 interface or the phenomena of blistering. Moreover, the crystal phase of Al2O3 does not deliver good surface passivation due to a high concentration of octahedral sites leading to a lower concentration of negative fixed charges at the interface.

  5. Study of electronic structure and magnetism at the relaxed SrTiO3/LaAlO3 interface

    NASA Astrophysics Data System (ADS)

    Ghosh, Soham; Manousakis, Efstratios

    2013-03-01

    The SrTiO3/LaAlO3 interface has been found experimentally to be metallic and magnetic, with bandstructure calculations linking both phenomena to polar catastrophe and surface oxygen vacancies. In this work, we use LDA+U to study the properties of this interface, allowing the ionic structure to be fully relaxed, and investigate the 2-dimensional nature of the electron gas formed at the junction. We present an effort to understand the role of electron-electron correlation on the interfacial collective phenomena, by constructing extended Hubbard-like models based on bandstructure calculation.

  6. Vapor Pressures in the Al(I)+Al2O3(s) System: Reconsidering Al2O3(s) Condensation

    NASA Technical Reports Server (NTRS)

    Copland, Evan

    2005-01-01

    The vaporization behavior of the A1-O system has been studied on numerous occasions but significant uncertainties remain. The origin of this uncertainty must be understood before A1-O vaporization behavior can be accurately determined. The condensation of A12O3 and clogging of the effusion orifice is a difficult problem for the Knudsen effusion technique that influences the measured vaporization behavior but has only received limited attention. This study reconsiders this behavior in detail. A new theory for A12O3 condensation is proposed together with procedures that will improve the measured thermodynamic properties of A1-O vaporization.

  7. Thin film processing of photorefractive BaTiO3

    NASA Technical Reports Server (NTRS)

    Schuster, Paul R.; Potember, Richard S.

    1991-01-01

    The principle objectives of this ongoing research involve the preparation and characterization of polycrystalline single-domain thin films of BaTiO3 for photorefractive applications. These films must be continuous, free of cracks, and of high optical quality. The two methods proposed are sputtering and sol-gel related processing.

  8. Bismuthates: BaBiO3 and related superconducting phases

    NASA Astrophysics Data System (ADS)

    Sleight, Arthur W.

    2015-07-01

    BaBiO3 has the perovskite structure, but tilting of the BiO6 octahedra destroy the ideal cubic symmetry except at temperatures above 820 K. BaBiO3 is a diamagnetic semiconductor due to a charge density wave (CDW), which is equivalent to a Ba2Bi3+Bi5+O6 representation. Recent calculations and experimental results confirm that there is no significant deviation from the oxidation states of 3+ and 5+. Superconductivity with a Tc as high as 13 K occurs for BaPb1-xBixO3 phases where the 6s band is about 25% filled, and superconductivity with a Tc as high as 34 K occurs for Ba1-xKxBiO3 phases where the 6s band is about 35% filled. Structures in these two solid solutions can have cubic, tetragonal, orthorhombic, or monoclinic symmetry. However, superconductivity has only been observed when the symmetry is tetragonal.

  9. Recent progress in Ga2O3 power devices

    NASA Astrophysics Data System (ADS)

    Higashiwaki, Masataka; Sasaki, Kohei; Murakami, Hisashi; Kumagai, Yoshinao; Koukitu, Akinori; Kuramata, Akito; Masui, Takekazu; Yamakoshi, Shigenobu

    2016-03-01

    This is a review article on the current status and future prospects of the research and development on gallium oxide (Ga2O3) power devices. Ga2O3 possesses excellent material properties, in particular for power device applications. It is also attractive from an industrial viewpoint since large-size, high-quality wafers can be manufactured from a single-crystal bulk synthesized by melt-growth methods. These two features have drawn much attention to Ga2O3 as a new wide bandgap semiconductor following SiC and GaN. In this review, we describe the recent progress in the research and development on fundamental technologies of Ga2O3 devices, covering single-crystal bulk and wafer production, homoepitaxial thin film growth by molecular beam epitaxy and halide vapor phase epitaxy, as well as device processing and characterization of metal-semiconductor field-effect transistors, metal-oxide-semiconductor field-effect transistors and Schottky barrier diodes.

  10. Single-domain multiferroic BiFeO3 films

    DOE PAGES

    Kuo, Chang -Yang; Hu, Z.; Yang, J. C.; ...

    2016-09-01

    The strong coupling between antiferromagnetism and ferroelectricity at room temperature found in BiFeO3 generates high expectations for the design and development of technological devices with novel functionalities. However, the multi-domain nature of the material tends to nullify the properties of interest and complicates the thorough understanding of the mechanisms that are responsible for those properties. Here we report the realization of a BiFeO3 material in thin film form with single-domain behaviour in both its magnetism and ferroelectricity: the entire film shows its antiferromagnetic axis aligned along the crystallographic b axis and its ferroelectric polarization along the c axis. With thismore » we are able to reveal that the canted ferromagnetic moment due to the Dzyaloshinskii–Moriya interaction is parallel to the a axis. Moreover, by fabricating a Co/BiFeO3 heterostructure, we demonstrate that the ferromagnetic moment of the Co film does couple directly to the canted moment of BiFeO3.« less

  11. Interface Structure of MoO3 on Organic Semiconductors

    PubMed Central

    White, Robin T.; Thibau, Emmanuel S.; Lu, Zheng-Hong

    2016-01-01

    We have systematically studied interface structure formed by vapor-phase deposition of typical transition metal oxide MoO3 on organic semiconductors. Eight organic hole transport materials have been used in this study. Ultraviolet photoelectron spectroscopy and X-ray photoelectron spectroscopy are used to measure the evolution of the physical, chemical and electronic structure of the interfaces at various stages of MoO3 deposition on these organic semiconductor surfaces. For the interface physical structure, it is found that MoO3 diffuses into the underlying organic layer, exhibiting a trend of increasing diffusion with decreasing molecular molar mass. For the interface chemical structure, new carbon and molybdenum core-level states are observed, as a result of interfacial electron transfer from organic semiconductor to MoO3. For the interface electronic structure, energy level alignment is observed in agreement with the universal energy level alignment rule of molecules on metal oxides, despite deposition order inversion. PMID:26880185

  12. Electronic Structure of Oxide Interfaces: A Comparative Analysis of GdTiO3/SrTiO3 and LaAlO3/SrTiO3 Interfaces

    PubMed Central

    Banerjee, Hrishit; Banerjee, Sumilan; Randeria, Mohit; Saha-Dasgupta, Tanusri

    2015-01-01

    Emergent phases in the two-dimensional electron gas (2DEG) formed at the interface between two insulating oxides have attracted great attention in the past decade. We present ab-initio electronic structure calculations for the interface between a Mott insulator GdTiO3 (GTO) and a band insulator SrTiO3 (STO) and compare our results with those for the widely studied LaAlO3/SrTiO3 (LAO/STO) interface between two band insulators. Our GTO/STO results are in excellent agreement with experiments, but qualitatively different from LAO/STO. We find an interface carrier density of 0.5 e−/Ti, independent of GTO thickness in both superlattice and thin film geometries, in contrast to LAO/STO. The superlattice geometry in LAO/STO offers qualitatively the same result as in GTO/STO. On the other hand, for a thin film geometry, the interface carrier density builds up only beyond a threshold thickness of LAO. The positive charge at the vacuum surface that compensates the 2DEG at the interface also exhibits distinct behaviors in the two systems. The compensating positive charge at the exposed surface of GTO charge disproportionates due to correlation effect making the surface insulating as opposed to that in LAO which remains metallic within band theory and presumably becomes insulating due to surface disorder or surface reconstruction. PMID:26689360

  13. Multidimentional Normal Mode Calculations for the OH Vibrational Spectra of (H_2O)_3^+, (H_2O)_3^+Ar, H^+(H_2O)_3, and H^+(H_2O)_3Ar

    NASA Astrophysics Data System (ADS)

    Li, Ying-Cheng; Chuang, Hsiao-Han; Tan, Jake Acedera; Takahashi, Kaito; Kuo, Jer-Lai

    2014-06-01

    Recent experimental observations of (H_2O)_3^+, (H_2O)_3^+Ar, H^+(H_2O)_3, and H^+(H_2O)_3Ar clusters in the region 1400-3800 wn show that the OH stretching vibration has distinct characteristics. Multidimensional normal mode calculations were carried out for OH stretching vibrations in the 1200-4000 wn photon energy range. The potential energy and dipole surfaces were evaluated by using first-principles methods. By comparing the calculated frequencies and intensities of OH stretching vibration with experimental spectra, we found that the assignment of OH strecthing of H_3O^+ moiety and free OH strectching vibration have resonable agreement with experimental data. Jeffrey M. Headrick, Eric G. Diken, Richard S. Walters, Nathan I. Hammer, Richard A. Christie, Jun Cui, Evgeniy M. Myshakin, Michael A. Duncan, Mark A. Johnson, Kenneth D. Jordan, Science, 2005, 17, 1765. Kenta Mizuse, Jer-Lai Kuo and Asuka Fujii, Chem. Sci., 2011, 2, 868 Kenta Mizuse and Asuka Fujii, J. Phys. Chem. A, 2013, 117, 929.

  14. Arabidopsis transcriptional responses differentiate between O3 and herbicides

    EPA Science Inventory

    Using published data based on Affymetrix ATH1 Gene-Chips we characterized the transcriptional response of Arabidopsis thaliana Columbia to O3 and a few other major environmental stresses including oxidative stress . A set of 101 markers could be extracted which provided a compo...

  15. Single-domain multiferroic BiFeO3 films

    PubMed Central

    Kuo, C.-Y.; Hu, Z.; Yang, J. C.; Liao, S.-C.; Huang, Y. L.; Vasudevan, R. K.; Okatan, M. B.; Jesse, S.; Kalinin, S. V.; Li, L.; Liu, H. J.; Lai, C.-H.; Pi, T. W.; Agrestini, S.; Chen, K.; Ohresser, P.; Tanaka, A.; Tjeng, L. H.; Chu, Y. H.

    2016-01-01

    The strong coupling between antiferromagnetism and ferroelectricity at room temperature found in BiFeO3 generates high expectations for the design and development of technological devices with novel functionalities. However, the multi-domain nature of the material tends to nullify the properties of interest and complicates the thorough understanding of the mechanisms that are responsible for those properties. Here we report the realization of a BiFeO3 material in thin film form with single-domain behaviour in both its magnetism and ferroelectricity: the entire film shows its antiferromagnetic axis aligned along the crystallographic b axis and its ferroelectric polarization along the c axis. With this we are able to reveal that the canted ferromagnetic moment due to the Dzyaloshinskii–Moriya interaction is parallel to the a axis. Furthermore, by fabricating a Co/BiFeO3 heterostructure, we demonstrate that the ferromagnetic moment of the Co film does couple directly to the canted moment of BiFeO3. PMID:27581797

  16. Electronic Structure of Oxide Interfaces: A Comparative Analysis of GdTiO3/SrTiO3 and LaAlO3/SrTiO3 Interfaces

    NASA Astrophysics Data System (ADS)

    Banerjee, Hrishit; Banerjee, Sumilan; Randeria, Mohit; Saha-Dasgupta, Tanusri

    2015-12-01

    Emergent phases in the two-dimensional electron gas (2DEG) formed at the interface between two insulating oxides have attracted great attention in the past decade. We present ab-initio electronic structure calculations for the interface between a Mott insulator GdTiO3 (GTO) and a band insulator SrTiO3 (STO) and compare our results with those for the widely studied LaAlO3/SrTiO3 (LAO/STO) interface between two band insulators. Our GTO/STO results are in excellent agreement with experiments, but qualitatively different from LAO/STO. We find an interface carrier density of 0.5 e-/Ti, independent of GTO thickness in both superlattice and thin film geometries, in contrast to LAO/STO. The superlattice geometry in LAO/STO offers qualitatively the same result as in GTO/STO. On the other hand, for a thin film geometry, the interface carrier density builds up only beyond a threshold thickness of LAO. The positive charge at the vacuum surface that compensates the 2DEG at the interface also exhibits distinct behaviors in the two systems. The compensating positive charge at the exposed surface of GTO charge disproportionates due to correlation effect making the surface insulating as opposed to that in LAO which remains metallic within band theory and presumably becomes insulating due to surface disorder or surface reconstruction.

  17. Strain effects on oxygen vacancy energetics in KTaO3

    DOE PAGES

    Xi, Jianqi; Xu, Haixuan; Zhang, Yanwen; ...

    2017-02-07

    Due to lattice mismatch between epitaxial films and substrates, in-plane strain fields are produced in the thin films, with accompanying structural distortions, and ion implantation can be used to controllably engineer the strain throughout the film. Because of the strain profile, local defect energetics are changed. In this study, the effects of in-plane strain fields on the formation and migration of oxygen vacancies in KTaO3 are investigated using first-principles calculations. In particular, the doubly positive charged oxygen vacancy (V2+O) is studied, which is considered to be the main charge state of the oxygen vacancy in KTaO3. We find that themore » formation energies for oxygen vacancies are sensitive to in-plane strain and oxygen position. The local atomic configuration is identified, and strong relaxation of local defect structure is mainly responsible for the formation characteristics of these oxygen vacancies. Based on the computational results, formation-dependent site preferences for oxygen vacancies are expected to occur under epitaxial strain, which can result in orders of magnitude differences in equilibrium vacancy concentrations on different oxygen sites. In addition, all possible migration pathways, including intra- and inter-plane diffusions, are considered. In contrast to the strain-enhanced intra-plane diffusion, the diffusion in the direction normal to the strained plane is impeded under the epitaxial strain field. Lastly, these anisotropic diffusion processes can further enhance site preferences.« less

  18. Effect of Gd-substitution on the ferroelectric and magnetic properties of BiFeO3 processed by high-energy ball milling

    NASA Astrophysics Data System (ADS)

    Sharma, Shiwani; Mishra, Alok; Saravanan, P.; Pandey, O. P.; Sharma, Puneet

    2016-11-01

    Multiferroic BiFeO3 was synthesized by means of high-energy ball milling (HEBM) followed by thermal annealing at various temperatures and the effect of Gd3+ substitution (x=0.0-0.20) at Bi3+ site was investigated in this study. It is found that the Gd-substitution tends to decrease the impurity phases and the crystallization of single phase BiFeO3 is observed at x=0.1. Scanning electron micrograph of Bi1-xGdxFeO3 sintered sample indicated a decrease in particle size and change in shape with increasing x. For all the studied samples, the measured dielectric constant values tend to increase from 110 (x=0.0) to 250 (x=0.10). The dielectric loss is found to be more for the pure BiFeO3 as compared to the Bi1-xGdxFeO3. Ferroelectric loops show a maximum polarization of 1.63 μC/cm2 for the Bi0.9Gd0.1FeO3. Magnetization (M) versus magnetic field (H) hysteresis loops at 300 K BiFeO3 and Bi0.9Gd0.1FeO3 demonstrated non-saturated loops, suggesting the antiferromagnetic nature of the samples. The M-H behavior of the Bi1-xGdxFeO3 at 300 K shows the antiferromagnetic nature of the samples. The estimated magnetization value at 10 kOe for the Bi0.9Gd0.1FeO3 sample (0.23 emu/g) is found to be higher than that of the pure BiFeO3 (0.037 emu/g).

  19. Experimental studies on equilibrium adsorption isosteres and determination of the thermodynamic quantities of polar media on alumina Al2O3

    NASA Astrophysics Data System (ADS)

    Yonova, Albena

    2017-03-01

    The present work is a revieif of theoretical and experimental study on the adsorption performance of the adsorbent Alumina (Al2O3) used in the adsorption system. An experimental investigation on the equilibrium adsorption isosteres at low pressure (< 1 atm) of working pairs Al2O3/H2O and Al2O3/C2H6O2 is carried out. The isovolume measurement method is adopted in the test setup to directly measure the saturated vapor pressures of working pairs at vapor-liquid equilibrium (dG=0 and dμi=0). Quantity adsorbed is determined from pressure, volume and temperature using gas law. The isosteric heat of adsorption is calculated from the slope of the plot of lnP versus 1/T different amounts of adsorbate onto adsorbent as follows: 0,01 vol% Al2O3/H2O; 0,03 vol% Al2O3/H2O; 0,1 vol% Al2O3/H2O; 0,01 vol% Al2O3/C2H6O2; 0,03 vol% Al2O3/C2H6O2; 0,1 vol% Al2O3/C2H6O2. This study shows that adsorption working pair Al2O3 C2H6O2 has better adsorption performances than those of the A2O3/H2O. Surface acidity! is a most important property! far both adsorption and catalysis and therefore is examined structure of active sites of alumina surface. Thermodynamic parameters such as isosteric heat of adsorption, isosteric enthalpy and entropy of adsorption are critical design variables in estimating the performance and predicting the mechanism of an adsorption process and are also one of the basic requirements for the characterization and optimization of an adsorption process

  20. Theoretical study of oxidation-reduction reaction of Fe2O3 supported on MgO during chemical looping combustion

    NASA Astrophysics Data System (ADS)

    Qin, Wu; Chen, Qiuluan; Wang, Yang; Dong, Changqing; Zhang, Junjiao; Li, Wenyan; Yang, Yongping

    2013-02-01

    We applied density-functional theory (DFT) in periodic system to investigate the two reactions (CO + Fe2O3/MgO → CO2 + Fe2O2/MgO, O2 + Fe2O2/MgO → O + Fe2O3/MgO) in chemical looping combustion system. While Fe2O3 was supported on MgO(1 0 0) surface Fe2O3 gathered together to form a cluster shape on MgO(1 0 0), denoted as Fe2O3/MgO, where the Fe2O3 was activated by MgO(1 0 0). Then CO interacted with Fe2O3/MgO and carbonate generated during a stepwise reaction with the calculated maximum barrier energy of 0.95 eV, far less than that of the reaction between CO and the pure Fe2O3 cluster (2.59 eV). CO was oxidized by Fe2O3/MgO and then Fe2O3/MgO transformed into the reduced state Fe2O2/MgO, corresponding to the reaction in the fuel reactor in the CLC system. Then the breaking of the adsorbed O2 molecule on Fe2O2/MgO made an O atom bind to a Fe site with the barrier energy of 0. 20 eV, which played as the key step for the oxidizing of Fe2O2/MgO by O2 into Fe2O3/MgO, corresponding to the reaction in the air reactor in the CLC system.

  1. Magnetic characterization of iron oxides formed after thermal treatment of nontronite and the formation of three polymorphs of Fe2O3: α-Fe2O3, γ-Fe2O3, ɛ-Fe2O3

    NASA Astrophysics Data System (ADS)

    Berquo, T. S.; Moskowitz, B. M.

    2011-12-01

    Nontronite is an Fe-rich smectite clay that occurs widely in terrestrial soils, sediments and weathering formations and may also be present in the Martian regolith. The thermal decomposition of nontronite is known to form various magnetic iron oxides but their compositions, magnetic properties, and formation pathways remain poorly understood. The magnetic alteration products of nontronite have been proposed as a source for the magnetic phases in the surface layers and dust on Mars as well as in some archeological fired-bricks and ceramic pottery. One alteration product of nontronite is ɛ-Fe2O3 which is ferrimagnetic with a Curie temperature of ~ 500 K and extremely large coercivity (HC ~ 1-2 T) at 300 K. In this work nontronite samples from eight source localities were heated to 1000°C in air for one hour. The magnetic properties of the alteration products were investigated with low-temperature (LT) magnetization and AC susceptibility curves, hysteresis loops, Mossbauer spectroscopy, and X-ray diffraction. The thermal treatment was effective in converting the nontronite to a combination of different polymorphs of ferric oxide depending on source locality and included: hematite (α-Fe2O3), ɛ-Fe2O3, and a cubic spinel phase that suggest the presence of maghemite (γ-Fe2O3). Mossbauer spectra at 300 K identified hematite and ɛ-Fe2O3 as the main phases in 7 samples with amounts ranging from 26-100% for hematite 0-69% for ɛ-Fe2O3. One sample showed a paramagnetic Fe3+ doublet and a broad sextet characteristic of magnetic relaxation effects. Upon cooling to 4.2 K, the Mossbauer spectrum was consistent with maghemite. In all samples except one, the magnetic hyperfine fields for the hematite phase are slightly reduced as compared with its stoichiometric form indicating some iron substitution with ions such as Al. This is consistent with the observation that all but one sample lacked the characteristic Morin transition for pure hematite on LT-remanence warming curves

  2. Moessbauer spectroscopy of Mg(0.9)Fe(0.1)SiO3 perovskite

    NASA Technical Reports Server (NTRS)

    Jeanloz, Raymond; O'Neill, Bridget; Pasternak, Moshe P.; Taylor, R. D.; Bohlen, Steven R.

    1992-01-01

    Ambient pressure Moessbauer spectra of Mg(0.9)Fe-57(0.1)SiO3 perovskite synthesized at pressure-temperature conditions of about 50 GPa and 1700 K show that the iron is entirely high-spin Fe(2+) and appears to be primarily located in the octahedral site within the crystal structure. We observe broad Moessbauer lines, suggesting a distribution of electric-field gradients caused by disorder associated with the Fe ions. Also, the perovskite exhibits magnetic ordering at temperatures lower than 5 K, implying that there is a magnetic contribution to the absolute ('third-law') entropy of this phase.

  3. Anomalous enhancement of Neel temperature and magnetic coupling for Bi0.9Ca0.1FeO3-δ and Bi0.9Pb0.1FeO3

    NASA Astrophysics Data System (ADS)

    Dwivedi, Gopeshmwar-Dhar; Yang, Kung-Shang; Chen, Bo-Yu; Chou, Hsiung

    Temperature dependent neutron diffraction patterns of the Ca-doped BiFeO3 and Pb-doped BiFeO3 show that their Neel temperatures (TN) increase to 710 K and 680 K, while pure BiFeO3 has a TN ~643 K. X-ray absorption spectra clearly shows that there is no evidence of mixed valence states despite divalent cation doping in trivalent Bi-sites. X-ray photoemission spectroscopy study revealed that divalent doping has introduced oxygen vacancies in the system. Oxygen deficiency plays a significant role in contracting Fe-O bond length in Fe-O6 octahedra and hence increasing the Fe-O-Fe bond angle in Bi0.9Ca0.1FeO3-δ and Bi0.9Pb0.1FeO3-δ. The decreased Fe-O bond length and increased Fe-O-Fe bond angle favors the Goodenough-Kanamori-Anderson (GKA) coupling. The GKA coupling increases the magnetic interaction between the spins and hence increases the TN. Additionally, doping of divalent cations (Ca2+ and Pb2+) results in the destruction of cycloidal spin structure and formation of a simple antiferromagnetic (AFM) structure. This structure can easily be canted near the heterogeneous interface with a ferromagnetic layer to induce the Dzyaloshinskii-Moriya (DM) interaction and enhance the magneto-electric (M-E) coupling. Corresponding Author.

  4. Modulated two-dimensional charge-carrier density in LaTiO3-layer-doped LaAlO3/SrTiO3 heterostructure.

    PubMed

    Nazir, Safdar; Bernal, Camille; Yang, Kesong

    2015-03-11

    The highly mobile two-dimensional electron gas (2DEG) formed at the polar/nonpolar LaAlO3/SrTiO3 (LAO/STO) heterostructure (HS) is a matter of great interest because of its potential applications in nanoscale solid-state devices. To realize practical implementation of the 2DEG in device design, desired physical properties such as tuned charge carrier density and mobility are necessary. In this regard, polar perovskite-based transition metal oxides can act as doping layers at the interface and are expected to tune the electronic properties of 2DEG of STO-based HS systems dramatically. Herein, we investigated the doping effects of LaTiO3(LTO) layers on the electronic properties of 2DEG at n-type (LaO)(+1)/(TiO2)(0) interface in the LAO/STO HS using spin-polarized density functional theory calculations. Our results indicate an enhancement of orbital occupation near the Fermi energy, which increases with respect to the number of LTO unit cells, resulting in a higher charge carrier density of 2DEG than that of undoped system. The enhanced charge carrier density is attributed to an extra electron introduced by the Ti 3d(1) orbitals from the LTO dopant unit cells. This conclusion is consistent with the recent experimental findings (Appl. Phys. Lett. 2013, 102, 091601). Detailed charge density and partial density of states analysis suggests that the 2DEG in the LTO-doped HS systems primarily comes from partially occupied dyz and dxz orbitals.

  5. Catalytic Oxidation of Benzene Over LaCoO3 Perovskite-Type Oxides Prepared Using Microwave Process.

    PubMed

    Jung, Won Young; Song, Young In; Lim, Kwon Taek; Lee, Gun Dae; Lee, Man Sig; Hong, Seong-Soo

    2015-01-01

    LaCoO3 perovskite type oxides were successfully prepared using microwave-assisted method, characterized by TG/DTA, XRD, XPS and H2-TPR and their catalytic activities for combustion of benzene were determined. Almost of catalyst showed perovskite crystalline phase and 13-84 nm particle size. LaCoO3 catalysts prepared by microwave-assisted method showed the highest activity and the conversion reached almost 100% at 360 degrees C. In the LaCoO3-type catalyst, the partial substitution of Sr into site A enhanced the catalytic activity on the combustion of benzene. The higher amount of the chemisorbed oxygen was, the better the performance of the combustion catalyst. The catalytic activity of perovskite-type oxides showed a good relationship with the results of H2-TPR and XPS measurement.

  6. Effect of Li/Nb Ratio on Growth and Spectrometric Characterization of Hf:Fe:LiNbO3 Crystals

    NASA Astrophysics Data System (ADS)

    Dai, Li; Wu, Shi-Ping; Guo, Jing-Jie; Xu, Chao; Su, Yan-Qing; Xu, Yu-Heng

    Hf:Fe:LiNbO3 crystals were grown by the Czochralski technique with various ratios of Li/Nb = 0.946, 1.05, 1.20 and 1.38 in the melt. The crystal composition and defect structure were analyzed by XRD, UV-Vis and IR spectroscopy. The results show that the threshold concentration of Hf in LiNbO3 crystals decrease with the increasing of the Li/Nb ratio; when the Li/Nb ratio is 1.05, the threshold concentration of Hf is less than 2 mol%, largely under the threshold concentration of Hf ions in congruent Hf:Fe:LiNbO3 crystal (4 mol).1-3 With the increase of Li/Nb, Hf ions first replace the Nb4+ Li; when the concentration of Hf ions is higher than the threshold value, Hf ions occurs on normal Nb and Li sites.

  7. Structural, morphological and optical investigations on electron-beam irradiated PbF2-TeO2-B2O3-Eu2O3 glasses

    NASA Astrophysics Data System (ADS)

    Wagh, Akshatha; Petwal, Vikash; Dwivedi, Jishnu; Upadhyaya, V.; Raviprakash, Y.; Kamath, Sudha D.

    2016-09-01

    Combined structural, optical and morphological studies were carried out on Eu2O3 doped PbF2-TeO2-B2O3 glass samples, before and after being subjected to electron beam of energy 7.5 MeV. XRD confirmed the amorphous nature of the glasses even after 150 kGy electron beam irradiation. Densities of the irradiated samples showed slightly greater values when compared to their respective values before irradiation, which proved the increase in the compaction of the network. The intensities of the three prominent bands; B-O-B linkages, BO4 units and BO3 units of FT-IR spectra, of the titled glasses, showed slight decrease after electron beam irradiation. The decrement in the values of energy band gap and shift in cut-off wavelength towards red edge, proved the formation of color centers in the glass network after irradiation. The change in Hunter L values, through color measurement was a proof for the Farbe/color/absorption centers created in the glass sites after irradiation.

  8. Ab initio study of nontrivial topological phases in corundum-structured (M2O3)/ (Al2O3)5 multilayers

    NASA Astrophysics Data System (ADS)

    Afonso, Juan F.; Pardo, Victor

    2015-12-01

    Ab initio calculations have been performed on hexagonal layers of M2O3 (M being several transition metals of the 5 d series) sandwiched by a band insulator such as Al2O3 that provides the honeycomb lattice where the 5 d electrons reside. This corundum-structure-based superlattice is a way to design a honeycomb lattice with transition metal cations avoiding the use of largely polar surfaces. We find that this system supports the presence of Dirac cones at the Fermi level that open up with the introduction of spin-orbit coupling at various fillings of the 5 d band. The DFT calculations performed in this paper show that the 5 d5 situation is always a trivial insulator, whereas the 5 d8 filling presents topological insulating configurations which evolve into a trivial state with increasing tensile strain or on-site Coulomb potential U . However, LDA + U calculations show a stable antiferromagnetic solution for the 5 d8 case at every U value, which would break time reversal symmetry and could affect the topological properties of the system. We also discuss the similarities with the buckled honeycomb lattice obtained using perovskite (111) bilayers previously studied in literature, in particular for the 5 d5 and 5 d8 configurations. This paper provides some clues on the stability of topological phases using metal oxides in general.

  9. Effect of ionic radii on the Curie temperature in Ba1-x-ySrxCayTiO3 compounds

    PubMed Central

    Berenov, A.; Le Goupil, F.; Alford, N.

    2016-01-01

    A series of Ba1-x-ySrxCayTiO3 compounds were prepared with varying average ionic radii and cation disorder on A-site. All samples showed typical ferroelectric behavior. A simple empirical equation correlated Curie temperature, TC, with the values of ionic radii of A-site cations. This correlation was related to the distortion of TiO6 octahedra observed during neutron diffraction studies. The equation was used for the selection of compounds with predetermined values of TC. The effects of A-site ionic radii on the temperatures of phase transitions in Ba1-x-ySrxCayTiO3 were discussed. PMID:27324841

  10. Anomalous phase diagram of ferroelectric (Ba,Ca)TiO3 single crystals with giant electromechanical response.

    PubMed

    Fu, Desheng; Itoh, Mitsuru; Koshihara, Shin-ya; Kosugi, Taichi; Tsuneyuki, Shinji

    2008-06-06

    We report the anomalous phase evolution in ferroelectric single crystals Ba1-xCaxTiO3 (0.02site atom and oxygen but also by the substitution of A site with small ions with off-centering nature. Theoretical calculations support the idea that the off-center displacements of the smaller Ca ions in the Ba-site play an important role in the exotic natures of Ba1-xCaxTiO3.

  11. Microwave dielectric properties of Na(x)Nd((2-x)/3)TiO(3) solid solutions.

    PubMed

    Kagomiya, Isao; Yamada, Yuko; Kakimoto, Ken-ichi; Ohsato, Hitoshi

    2008-12-01

    Na(x)Nd((2-x)/3)TiO(3) solid solutions possess tetragonal or orthorhombic perovskite structure, where the A-sites are characterized by 2 kinds of cations (Na(+), Nd(3+)) and vacancies. We have measured microwave dielectric properties of Na(x)Nd((2-x)/3)TiO(3) solid solutions (x = 0.05 to 0.5) to investigate an effect of the compositional ordering in the A-sites of the perovskite structure. According to powder x-ray diffraction, the A-site is disordered in the composition range of x = 0.29 to 0.5. A compositional ordering (Na(+), vacancy / Nd(3+)) in A-sites appeared when x = 0.05 to 0.2. The quality factor (Q x f), where Q is the inverse of dielectric loss and f is frequency, was found to be slightly improved with decreasing Na content in the range of x = 0.05 to 0.2, suggesting that the Q x f of the Na(x)Nd((2-x)/3)TiO(3) solid solutions depends on the compositional ordering in A-sites.

  12. Fundamental Bulk/Surface Structure Photoactivity Relationships of Supported (Rh2-yCryO3)/GaN Photocatalysts

    SciTech Connect

    Phivilay, Somphonh; Roberts, Charles; Puretzky, Alexander A; Domen, Kazunari Domen; Wachs, Israel

    2013-01-01

    ABSTRACT. The supported (Rh2-yCryO3)/GaN photocatalyst was examined as a model nitride photocatalyst system to assist in the development of fundamental structure photoactivity relationships for UV activated water splitting. Surface characterization of the outermost surface layers by High Sensitivity-LEIS and High Resolution-XPS revealed for the first time that the GaN support consists of a GaOx outermost surface layer and a thin film of GaOxNy in the surface region. HR-XPS also demonstrates that the supported (Rh2-yCryO3) mixed oxide nanoparticles (NPs) exclusively consist of Cr+3 and Rh+3 cations and are surface enriched for the supported (Rh2-yCryO3)/GaN photocatalyst. Bulk analysis by Raman and UV-vis spectroscopy show that the bulk molecular and electronic structures, respectively, of the GaN support are not perturbed by the deposition of the (Rh2-yCryO3) mixed oxide NPs. The function of the GaN bulk lattice is to generate photoexcited electrons/holes, with the electrons harnessed by the surface Rh+3 sites for evolution of H2 and the holes trapped at the Ga oxide/oxynitride surface sites for splitting of water and evolving O2. These new structure-photoactivity relationships for supported (Rh2-yCryO3)/GaN also extend to the best performing visible light activated supported (Rh2-yCryO3)/(Ga1-xZnx)(N1-xOx) photocatalyst.

  13. Ab initio calculations of SrTiO3, BaTiO3, PbTiO3, CaTiO3, SrZrO3, PbZrO3 and BaZrO3 (001), (011) and (111) surfaces as well as F centers, polarons, KTN solid solutions and Nb impurities therein

    NASA Astrophysics Data System (ADS)

    Eglitis, R. I.

    2014-03-01

    In this paper, the review of recent results of calculations of surface relaxations, energetics, and bonding properties for ABO3 perovskite (001), (011) and (111) surfaces using mostly a hybrid description of exchange and correlation is presented. Both AO and BO2-terminations of the nonpolar (001) surface and A, BO, and O terminations of the polar (011) surface, as well as B and AO3-terminations of the polar (111) surface were considered. On the AO-terminated (001) surface, all upper-layer A atoms relax inwards, while all second layer atoms relax outwards. For the BO2-terminated (001) surface, in most cases, the largest relaxations are on the second-layer metal atoms. For almost all ABO3 perovskites, the surface rumpling is much larger for the AO-terminated than for the BO2-terminated (001) surface, but their surface energies are always quite similar. In contrast, different terminations of the (011) ABO3 surface lead to very different surface energies for the O-terminated, A-terminated, and BO-terminated (011) surface, respectively. A considerable increase in the Ti-O or Zr-O, respectively, chemical bond covalency near the (011) surface as compared both to the bulk and to the (001) surface in ABO3 perovskites were predicted. According to the results of ab initio calculations for Nb doped SrTiO3, Nb is a shallow donor; six nearest O ions are slightly displaced outwards from the Nb ion. The F center in ABO3 perovskites resembles electron defects in the partially-covalent SiO2 crystal rather than usual F centers in ionic crystals like MgO and alkali halides. The results of calculations for several perovskite KNbxTa1-xO3 (KTN) solid solutions, as well as hole and electron polarons in ABO3 perovskites are analyzed.

  14. High thermal stability of La2O3 and CeO2-stabilized tetragonal ZrO2

    DOE PAGES

    Wang, Shichao; Xie, Hong; Lin, Yuyuan; ...

    2016-02-15

    Catalyst support materials of tetragonal ZrO2, stabilized by either La2O3 (La2O3-ZrO2) or CeO2 (CeO2-ZrO2), were synthesized under hydrothermal conditions at 200 °C with NH4OH or tetramethylammonium hydroxide as the mineralizer. From In Situ synchrotron powder X-ray diffraction and small-angle X-ray scattering measurements, the calcined La2O3-ZrO2 and CeO2-ZrO2 supports were nonporous nanocrystallites that exhibited rectangular shapes with thermal stability up to 1000 °C in air. These supports had an average size of ~10 nm and a surface area of 59-97 m2/g. The catalysts Pt/La2O3-ZrO2 and Pt/CeO2-ZrO2 were prepared by using atomic layer deposition with varying Pt loadings from 6.3-12.4 wt %.more » Mono-dispersed Pt nanoparticles of ~3 nm were obtained for these catalysts. As a result, the incorporation of La2O3 and CeO2 into the t-ZrO2 structure did not affect the nature of the active sites for the Pt/ZrO2 catalysts for the water-gas-shift (WGS) reaction.« less

  15. Interaction of SO2 and CO with the Ti2O3(101¯2) surface

    NASA Astrophysics Data System (ADS)

    Smith, Kevin E.; Henrich, Victor E.

    1985-10-01

    The interaction of sulfur dioxide with the nearly perfect (101¯2) surface of the corundum transition-metal oxide Ti2O3 has been studied using ultraviolet and x-ray photoemission spectroscopies and low-energy electron diffraction. The reaction of SO2 with Ti2O3 is found to be extremely vigorous, with SO2 adsorbing dissociatively and catalyzing the complete oxidation of the surface to TiO2 and TiS2. This result is significant since exposure to large amounts of O2 does not result in the production of large amounts of TiO2 at the Ti2O3 surface. Dissociative adsorption of SO2 continues for exposures up to at least 104 L (1 L=10-6Torr sec). The reaction is accompanied by large scale surface disorder and by an increase in the work function of 1.32 eV. In contrast, CO adsorbs molecularly for exposures >=105 L, with an extramolecular relaxation-polarization shift of 3.0 eV. For CO exposures <=104 L, the chemisorption mechanism is tentatively identified as dissociative adsorption at defect sites. Inclusive of this study, the interaction of four oxygen-containing molecules (SO2, CO, H2O, and O2) with Ti2O3(101¯2) surfaces has been studied, and their behavior is compared and trends isolated with a view to understanding the oxidation of Ti2O3.

  16. Photocatalytic hydrogen production over solid solutions between BiFeO3 and SrTiO3

    NASA Astrophysics Data System (ADS)

    Lu, Lingwei; Lv, Meilin; Liu, Gang; Xu, Xiaoxiang

    2017-01-01

    Constituting solid solutions has been an appealing means to gain control over various physicochemical properties. In this work, we synthesized a series of SrTiO3-BiFeO3 solid solutions and systematically explored their structural, optical and photocatalytic properties. Our results show that all solid solutions crystallize in a primitive cubic structure and their band gap values can be easily tuned by adjusting molar ratios between SrTiO3 and BiFeO3. Photocatalytic hydrogen production under both full range and visible light irradiation is greatly improved after forming solid solutions. The highest hydrogen production rate obtained is ∼180 μmol/h under full range irradiation (λ ≥ 250 nm) and ∼4.2 μmol/h under visible light irradiation (λ ≥ 400 nm), corresponding to apparent quantum efficiency ∼2.28% and ∼0.10%, respectively. The activity is found to be strongly influenced by surface area and light absorption. Theoretical calculation suggests that Fe contributes to the formation of spin-polarized bands in the middle of original band gap and is responsible for the band gap reduction and visible light photocatalytic activity.

  17. Electronic and magnetic properties of SrTiO(3)/LaAlO(3) interfaces from first principles.

    PubMed

    Chen, Hanghui; Kolpak, Alexie M; Ismail-Beigi, Sohrab

    2010-07-20

    A number of intriguing properties emerge upon the formation of the epitaxial interface between the insulating oxides LaAlO(3) and SrTiO(3). These properties, which include a quasi two-dimensional conducting electron gas, low temperature superconductivity, and magnetism, are not present in the bulk materials, generating a great deal of interest in the fundamental physics of their origins. While it is generally accepted that the novel behavior arises as a result of a combination of electronic and atomic reconstructions and growth-induced defects, the complex interplay between these effects remains unclear. In this report, we review the progress that has been made towards unraveling the complete picture of the SrTiO(3)/LaAlO(3) interface, focusing primarily on present ab initio theoretical work and its relation to the experimental data. In the process, we highlight some key unresolved issues and discuss how they might be addressed by future experimental and theoretical studies.

  18. Electronic structure of interfaces between insulating LaAlO3 and SrTiO3 perovskite oxides

    NASA Astrophysics Data System (ADS)

    Park, Min Sik; Rhim, S. H.; Freeman, A. J.

    2006-03-01

    Since heteroepitaxial structures of perovskite oxides are potent candidates for multifunctional devices, understanding their interface properties is very important for applications, because they often show completely different properties from bulk. Recently, interfaces between the wide-band gap insulators of LaAlO3 and SrTiO3, were found to be insulating when hole-doped, and conducting when electron-doped. First-principles calculations with the highly precise full-potential linearized augmented plane wave (FLAPW) method for the stoichiometric compounds on [001] superlattices composed of perovskite unit cells of LaAlO3 and SrTiO3, show metallicity in both the hole-doped AlO2/SrO and electron-doped LaO/TiO2 interfaces, even with inclusion of geometry relaxation. Only by considering oxygen vacancies is the experimental result of insulating behavior in the hole-doped AlO2/SrO interface obtained. A. Ohtommo and H. Y. Hwang, Nature 427, 423 (2004). Wimmer, Krakauer, Weinert, Freeman, Phys.Rev.B, 24, 864 (1981)

  19. Infrared and UV-visible spectroscopic studies of gamma-irradiated Sb2O3-B2O3 glasses

    NASA Astrophysics Data System (ADS)

    Marzouk, Samir Y.; Elbatal, Fatma H.

    2014-04-01

    Glasses from the binary Sb2O3-B2O3 system were prepared in the compositional range 90-30 Sb2O3 mol%. UV-visible spectroscopic measurements were carried out in the range 190-1100 nm before and after successive gamma rays irradiation (1, 3, 4 Mrad). Infrared absorption of the samples was measured by the KBr technique in the range 4000-400 cm-1 and the same measurements were repeated after gamma irradiation with 4 kGy. Experimental results indicate that antimony borate glasses reveal quite shielding behavior towards gamma rays irradiation as observed with heavy metal cations bearing glasses such as Bi3+ and Pb2+. Infrared absorption spectra reveal characteristic absorption bands specific for the glass-forming borate units and Sb-O units. Glasses containing high antimony oxide content can thus be recommended as promising radiation-shielding material because they show resistant to gamma irradiation due to the presence of high percent of heavy metal oxide (Sb2O3).

  20. Light induced suppression of Kondo effect at amorphous LaAlO3/SrTiO3 interface

    NASA Astrophysics Data System (ADS)

    Liu, G. Z.; Qiu, J.; Jiang, Y. C.; Zhao, R.; Yao, J. L.; Zhao, M.; Feng, Y.; Gao, J.

    2016-07-01

    We report photoelectric properties of two-dimensional electron gas (2DEG) at an amorphous LaAlO3/SrTiO3 interface. Under visible light illumination (650 nm), an enhancement of electric conductivity is observed over the temperature range from 2 to 300 K. Particularly, a resistance upturn appearing below 25 K, which is further proved to from the Kondo effect, is suppressed by the 650 nm visible light. From the results of light-assisted Hall measurements, light irradiation increases the carrier mobility rather than carrier density in the Kondo regime. It is suggested that light induces the decoherence effect of localized spin states, hence the electron scattering is weakened and the carrier mobility is improved accordingly. Moreover, the enhancement of electrical conductivity by visible light verifies that in-gap states located in the SrTiO3 side of the interface play an important role in the electrical transport of the amorphous SrTiO3-based oxide 2DEG system. Our results provide deeper insight into the photoinduced effects in the 2DEG system, paving the way for the design of optoelectronic devices based on oxides.

  1. LaAlO3 thickness window for electronically controlled magnetism at LaAlO3/SrTiO3 heterointerfaces

    NASA Astrophysics Data System (ADS)

    Bi, Feng; Huang, Mengchen; Lee, Hyungwoo; Eom, Chang-Beom; Irvin, Patrick; Levy, Jeremy

    2015-08-01

    Complex-oxide heterostructures exhibit rich physical behavior such as emergent conductivity, superconductivity, and magnetism that are intriguing for scientific reasons as well as for potential technological applications. It was recently discovered that in-plane magnetism at the LaAlO3/SrTiO3 (LAO/STO) interface can be electronically controlled at room temperature. Here, we employ magnetic force microscopy to investigate electronically controlled ferromagnetism at the LAO/STO interface with LAO thickness t varied from 4 unit cell (u.c.) to 40 u.c. Magnetic signatures are observed only within a thickness window 8 u.c. ≤ t ≤ 25 u.c. Within this window, the device capacitance corresponds well to the expected geometric value, while for thicknesses outside this window, the capacitance is strongly suppressed. The ability to modulate electronic and magnetic properties of LAO/STO devices depends on the ability to control carrier density, which is in turn constrained by intrinsic tunneling mechanisms.

  2. Structural properties of Y2O3–Al2O3 liquids and glasses: An overview

    SciTech Connect

    Wilding, Martin C.; Wilson, Mark; McMillan, Paul F.; Benmore, Chris J.; Weber, J. K.R.; Deschamps, Thierry; Champagnon, Bernard

    2015-01-01

    Liquids in the system Y2O3- Al2O3 have been the subject of considerable study because of the reported occurrence of a first-order density and entropy-driven liquid-liquid phase transition (LLPT) in the supercooled liquid state. The observations have become controversial because of the presence of crystalline material that can be formed simultaneously and that can mask the nucleation and growth of the lower density liquid. The previous work is summarized here along with arguments for and against the different viewpoints. Also two studies have been undertaken to investigate the LLPT in this refractory system with emphasis on determining the structure of unequivocally amorphous materials. These include the in situ high energy X-ray diffraction (HEXRD) of supercooled Y2O3 - Al2O3 liquids and the low frequency vibrational dynamics of recovered glasses. Manybody molecular dynamics simulations are also used to interpret the results of both studies. The HEXRD measurements, combined with aerodynamic levitation and rapid data acquisition techniques, show that for the 20 mol% Y2O3 (i.e. AlY20) liquid there is a shift in the position of the first peak in the diffraction pattern over a narrow temperature range (2100-1800 K) prior to crystallization. Microbeam Raman spectroscopy measurements made on AlY20 glasses clearly show contrasting spectra in the low frequency part of the spectrum for low(LDA) and high-density (HDA) glassy regions. The molecular dynamics simulations identify contrasting coordination environments around oxygen anions for the high- (HDL) and low-density (LDL) liquids. (C) 2014 Elsevier B.V. All rights reserved.

  3. Subsolidus phase equilibria and properties in the system Bi 2O 3:Mn 2O 3±x:Nb 2O 5

    NASA Astrophysics Data System (ADS)

    Vanderah, T. A.; Lufaso, M. W.; Adler, A. U.; Levin, I.; Nino, J. C.; Provenzano, V.; Schenck, P. K.

    2006-11-01

    Subsolidus phase relations have been determined for the Bi-Mn-Nb-O system in air (750-900 °C). Phases containing Mn 2+, Mn 3+, and Mn 4+ were all observed. Ternary compound formation was limited to pyrochlore (A 2B 2O 6O'), which formed a substantial solid solution region at Bi-deficient stoichiometries (relative to Bi 2(Mn,Nb) 2O 7) suggesting that ≈14-30% of the A-sites are occupied by Mn (likely Mn 2+). X-ray powder diffraction data confirmed that all Bi-Mn-Nb-O pyrochlores form with structural displacements, as found for the analogous pyrochlores with Mn replaced by Zn, Fe, or Co. A structural refinement of the pyrochlore 0.4000:0.3000:0.3000 Bi 2O 3:Mn 2O 3±x:Nb 2O 5 using neutron powder diffraction data is reported with the A and O' atoms displaced (0.36 and 0.33 Å, respectively) from ideal positions to 96g sites, and with Mn 2+ on A-sites and Mn 3+ on B-sites (Bi 1.6Mn 2+0.4(Mn 3+0.8Nb 1.2)O 7, Fd3¯m (♯227), a=10.478(1) Å); evidence of A or O' vacancies was not found. The displacive disorder is crystallographically analogous to that reported for Bi 1.5Zn 0.92Nb 1.5O 6.92, which has a similar concentration of small B-type ions on the A-sites. EELS spectra for this pyrochlore were consistent with an Mn oxidation between 2+ and 3+. Bi-Mn-Nb-O pyrochlores exhibited overall paramagnetic behavior with negative Curie-Weiss temperature intercepts, slight superparamagnetic effects, and depressed observed moments compared to high-spin, spin-only values. At 300 K and 1 MHz the relative dielectric permittivity of Bi 1.600Mn 1.200Nb 1.200O 7 was ≈128 with tan δ=0.05; however, at lower frequencies the sample was conductive which is consistent with the presence of mixed-valent Mn. Low-temperature dielectric relaxation such as that observed for Bi 1.5Zn 0.92Nb 1.5O 6.92 and other bismuth-based pyrochlores was not observed. Bi-Mn-Nb-O pyrochlores were readily obtained as single crystals and also as textured thin films using pulsed laser deposition.

  4. Impedance-based interpretations in 2-dimensional electron gas conduction formed in the LaAlO3/SrxCa1-xTiO3/SrTiO3 system

    NASA Astrophysics Data System (ADS)

    Park, Chan-Rok; Moon, Seon Young; Park, Da-Hee; Kim, Shin-Ik; Kim, Seong-Keun; Kang, Chong-Yun; Baek, Seung-Hyub; Choi, Jung-Hae; Kim, Jin-Sang; Choi, Eunsoo; Hwang, Jin-Ha

    2016-06-01

    Frequency-dependent impedance spectroscopy was applied to the 2-dimensioanl conduction transport in the LaAlO3/SrxCa1-xTiO3/SrTiO3 system. The 2-dimensional conduction modifies the electrical/dielectric responses of the LaAlO3/SrxCa1-xTiO3/SrTiO3 depending on the magnitude of the interfacial 2-dimensional resistance. The high conduction of the 2-dimensional electron gas (2DEG) layer can be described using a metallic resistor in series with two parallel RC circuits. However, the high resistance of the 2-dimensional layer drives the composite system from a finite low resistor in parallel with the surrounding dielectrics composed of LaAlO3 and SrTiO3 materials to a dielectric capacitor. This change in the resistance of the 2-dimensional layers modifies the overall impedance enabled by the presence of the interfacial layer due to SrxCa1-xTiO3, which alters the charge transport of the 2-dimensional layer from metallic to semiconducting conduction. A noticeable change is observed in the capacitance Bode plots, indicating highly amplified dielectric constants compared with the pristine SrTiO3 substrates and SrxCa1-xTiO3 with a greater Ca content.

  5. Aggregation and Colloidal Stability of Commercially Available Al2O3 Nanoparticles in Aqueous Environments

    PubMed Central

    Mui, Julie; Ngo, Jennifer; Kim, Bojeong

    2016-01-01

    The aggregation and colloidal stability of three, commercially-available, gamma-aluminum oxide nanoparticles (γ-Al2O3 NPs) (nominally 5, 10, and 20–30 nm) were systematically examined as a function of pH, ionic strength, humic acid (HA) or clay minerals (e.g., montmorillonite) concentration using dynamic light scattering and transmission electron microscopy techniques. NPs possess pH-dependent surface charges, with a point of zero charge (PZC) of pH 7.5 to 8. When pH < PZC, γ-Al2O3 NPs are colloidally stable up to 100 mM NaCl and 30 mM CaCl2. However, significant aggregation of NPs is pronounced in both electrolytes at high ionic strength. In mixed systems, both HA and montmorillonite enhance NP colloidal stability through electrostatic interactions and steric hindrance when pH ≤ PZC, whereas their surface interactions are quite limited when pH > PZC. Even when pH approximates PZC, NPs became stable at a HA concentration of 1 mg·L−1. The magnitude of interactions and dominant sites of interaction (basal planes versus edge sites) are significantly dependent on pH because both NPs and montmorillonite have pH-dependent (conditional) surface charges. Thus, solution pH, ionic strength, and the presence of natural colloids greatly modify the surface conditions of commercial γ-Al2O3 NPs, affecting aggregation and colloidal stability significantly in the aqueous environment. PMID:28335218

  6. In2O3 based perovskite solar cells

    NASA Astrophysics Data System (ADS)

    Dong, Qi; Liu, Fangzhou; Wong, Man Kwong; Djurišić, Aleksandra B.; Ren, Zhiwei; Shen, Qian; Ng, Annie; Surya, Charles; Chan, Wai Kin

    2016-02-01

    Hybrid organic-inorganic perovskite solar cells have attracted lots of attention in recent years. Growth and properties of perovskite layer and its relationship to photovoltaic performance have been extensively studied. Comparably less attention was devoted to the research of the influence of electron transporting layer (ETL). Conventionally, TiO2 is selected as ETL. However, photocatalytic property of this transparent conductive metal oxide reduces the stability of perovskite solar cells under illumination. To realize the commercialization, the stability of perovskite solar cell must be improved. In this study, we replace TiO2 by In2O3, which is not only transparent and conductive, but also has little photocatalytic effect and it has higher electron mobility than TiO2. Investigation on different solution process methods of In2O3 as ETL is demonstrated.

  7. Doping and Hall effect in SrTiO3

    NASA Astrophysics Data System (ADS)

    Stemmer, Susanne

    2015-03-01

    Electron-doped SrTiO3 has generated renewed interest because of reports of coexisting magnetism and superconductivity, and of superconducting transitions at extremely low carrier densities. In this talk, we will present new insights into doping and its electronic structure obtained using very high quality SrTiO3 films grown by molecular beam epitaxy. We discuss the arrangements and imaging of individual La dopant atoms and clusters using quantitative scanning transmission electron microscopy. We present studies of the temperature dependence of the Hall coefficient, Hall mobility, and of Shubnikov-de Haas oscillations. We will particularly discuss the significance of the regime in which the resistance follows a T2 temperature-dependence over a wide range of temperatures and doping. This work was performed in collaboration with Evgeny Mikheev, Adam Kajdos, Jinwoo Hwang, Jack Zhang, and Jim Allen.

  8. Intrinsic polarization switching mechanisms in BiFeO3

    NASA Astrophysics Data System (ADS)

    Xu, Bin; Garcia, Vincent; Fusil, Stéphane; Bibes, Manuel; Bellaiche, L.

    2017-03-01

    A first-principles-based effective Hamiltonian technique is used to investigate the polarization switching mechanisms in two polymorphic phases of BiFeO3 having no defects. The switching mechanism is homogeneous for any switching field in the rhombohedral phase, while in the supertetragonal phase it changes from the classical nucleation and domain-wall motion to nucleation-limited switching with virtually no propagation, and then to homogeneous switching with increasing electric field. The first two inhomogeneous switching mechanisms of the supertetragonal phase of BiFeO3 are thus intrinsic in nature, and can be well described by the classical and nucleation-limited switching models, respectively. The reason behind their absence in the rhombohedral phase is also indicated. Moreover, the field-induced changes of switching mechanism within the supertetragonal phase are further elucidated from an energetic point of view.

  9. Molecular Dynamics Simulation of MgSiO3 Perovskite

    NASA Astrophysics Data System (ADS)

    Lin-xiang, Zhou; L, Zhou X.; J, Hardy R.; Xin, Xu; X, Xu

    1998-06-01

    Using molecular dynamics to simulate MgSiO3 perovskite is performed to investigate its phase transitions and superionicity. These simulations has used parameter-free Gordon-Kim potentials and a novel technique to monitor the motion of ions which clearly demonstrates the sublattice melting of ions O2- and the rotations of SiO6 octahedra. MgSiO3 has to undergo a few of phase transitions, then enter into the cubic phase. In particular, there is a transitional phase between orthorhombic phase and cubic phase. There are a superionic phase and the cubic phase in magnesium-rich silicate perovskite. This superionic phase occurs after the onset of cubic phase before the melting point. The onset temparature Tc for superionicity is about 200-700 K below the melting point Tm, Tc / Tm similar 0.92.

  10. Growth, structure, and magnetic properties of γ-Fe2O3 epitaxial films on MgO

    NASA Astrophysics Data System (ADS)

    Gao, Y.; Kim, Y. J.; Thevuthasan, S.; Chambers, S. A.; Lubitz, P.

    1997-04-01

    Single-crystal epitaxial thin films of γ-Fe2O3(001) have been grown on MgO(001) using oxygen-plasma-assisted molecular beam epitaxy. The structure and magnetic properties of these films have been characterized by a variety of techniques, including reflection high-energy electron diffraction (RHEED), low-energy electron diffraction (LEED), x-ray photoelectron spectroscopy and x-ray photoelectron/Auger electron diffraction (XPD/AED), vibrating sample magnetometry, and ferromagnetic resonance. Real-time RHEED reveals that the film growth occurs in a layer-by-layer fashion. The γ-Fe2O3(001) film surface exhibits a (1×1) LEED pattern. The growth of γ-Fe2Ooverflow="scroll">3 films at 450 °C is accompanied by significant Mg outdiffusion. AED of Mg KLL Auger emission reveals that Mg substitutionally incorporates in the γ-Fe2O3 lattice, occupying the octahedral sites. Magnetic moments are ˜2300 G and ˜4500 G for γ-Fe2O3 films grown at 250 °C and 450 °C, respectively. The high magnetic moment for the films grown at 450 °C could be attributed to the high degree of structural order of the films and Mg substitution at octahedral sites.

  11. Defect structures and optical characteristics of Er3+ ion in Er:LiNbO3 crystals

    NASA Astrophysics Data System (ADS)

    Qian, Yannan; Wang, Rui; Wang, Biao; Xu, Chao; Xing, Lili; Xu, Yanling

    2013-03-01

    Congruent Er:LiNbO3 crystals were grown by Czochraski method. The OH- absorption and UV-vis-near infrared absorption spectra indicated that Er3+ cluster sites were formed in LiNbO3 crystal doped with 3 mol% Er3+ ions. Studies on the stokes and anti-stokes spectra showed that the formation of Er3+ cluster sites could increase the rate of cross relaxation processes. Judd-Ofelt theory was carried out to discuss the spectral characteristics of Er3+ ions in Er:LiNbO3 crystals. Based on Füchtbauer-Ladenburg and McCumber theory, the emission cross section of the 4I13/2 → 4I15/2 transition of Er3+ ion was calculated, and the potential laser performance was evaluated by the gain cross section spectra. Er:LiNbO3 crystal codoped with Zn2+ ions was also grown to discuss the relation between the defect structure and optical characteristics of Er3+ ion.

  12. High-field magnetization of Dy2O3

    NASA Technical Reports Server (NTRS)

    Flood, D. J.

    1974-01-01

    The magnetization of powdered samples of Dy2O3 has been measured at temperatures between 1.45 and 4.2 K, in applied magnetic fields ranging to 70 kilogauss. A linear dependence of magnetization on applied field is observable in the high-field region, the slope of which is independent of temperature over the range investigated. The extrapolated saturation magnetic moment is about 2.77 Bohr magnetons per ion.

  13. High-field magnetization of Dy2O3

    NASA Technical Reports Server (NTRS)

    Flood, D. J.

    1974-01-01

    The magnetization of powdered samples of Dy2O3 has been measured at temperatures between 1.45 deg and 4.2 K, in applied magnetic fields ranging to 7 Teslas. A linear dependence of magnetization on applied field is observable in high field region, the slope of which is independent of temperature over the range investigated. The extrapolated saturation magnetic moment is 2.77 + or - 0.08 Bohr magnetons per ion.

  14. Magnetoresistance in Sn-Doped In2O3Nanowires

    PubMed Central

    2009-01-01

    In this work, we present transport measurements of individual Sn-doped In2O3nanowires as a function of temperature and magnetic field. The results showed a localized character of the resistivity at low temperatures as evidenced by the presence of a negative temperature coefficient resistance in temperatures lower than 77 K. The weak localization was pointed as the mechanism responsible by the negative temperature coefficient of the resistance at low temperatures. PMID:20596280

  15. Conductivity enhancement in mechanosynthesized Bi2O3

    NASA Astrophysics Data System (ADS)

    Bandyopadhyay, S.; Anirban, Sk.; Sinha, A.; Pradhan, S. K.; Dutta, A.

    2016-05-01

    Nanostructured Bi2O3 was prepared through mechanical alloying method. Detailed microstructural information was obtained after Rietveld refinement of the prepared samples. The Transmission Electron Microscope images confirmed the crystallinity of the sample. The average crystallite size decreases whereas microstrain increases due to milling. The ionic conductivity of the milled sample was found to have increased few orders than the unmilled sample. The change in structural and electrical properties due to milling were discussed and correlated.

  16. Sensitivity of Stratospheric Dynamics to Uncertainty in O3 Production

    NASA Astrophysics Data System (ADS)

    Hsu, J. C.; Prather, M. J.; Bergmann, D. J.; Cameron-Smith, P. J.

    2013-12-01

    Some key photochemical uncertainties that cannot be readily eliminated by current observations translate into a range of stratospheric O3 abundances in the tens of percent. The uncertainty in O3 production due to that in the cross sections for O2 in the Hertzberg continuum is studied here with the NCAR Community Atmosphere Model, which allows for interactive climate and ozone chemistry. A min-max range in the O2 cross sections of 30%, consistent with current uncertainties, changes O3 abundances in the lower tropical stratosphere by up to 30%, with a relatively smaller and opposite change above 30 hPa. Here we have systematically examined the changes in the time-mean state, the seasonal cycle, and the interannual variability of the temperature and circulation associated with the +/-30% change in O2 cross sections. This study points to the important role of O3 in the lower tropical stratosphere in determining the physical characteristics of the tropical tropopause layer. Reducing O2 cross sections by 30% increases ozone abundances which warms the lower stratosphere (60S -60N; 2K maximum at equator) and lowers the tropopause height by 100-200m (30S -30N). The large-scale warming leads to enhanced stratification near the tropopause which reduces upward wave propagation everywhere except for high latitudes. The lowermost tropical stratosphere is better ventilated during austral winter. The annual cycle of ozone is amplified. The interannual variability of the winter stratospheric polar vortices also increases, but the mechanism involves wave-mean flow interaction and the exact role of ozone in it needs further investigation.

  17. Electric-field-induced Shift in the Threshold Voltage in LaAlO3/SrTiO3 Heterostructures

    PubMed Central

    Kim, Seong Keun; Kim, Shin-Ik; Lim, Hyungkwang; Jeong, Doo Seok; Kwon, Beomjin; Baek, Seung-Hyub; Kim, Jin-Sang

    2015-01-01

    The two-dimensional electron gas (2DEG) at the interface between insulating LaAlO3 and SrTiO3 is intriguing both as a fundamental science topic and for possible applications in electronics or sensors. For example, because the electrical conductance of the 2DEG at the LaAlO3/SrTiO3 interface can be tuned by applying an electric field, new electronic devices utilizing the 2DEG at the LaAlO3/SrTiO3 interface could be possible. For the implementation of field-effect devices utilizing the 2DEG, determining the on/off switching voltage for the devices and ensuring their stability are essential. However, the factors influencing the threshold voltage have not been extensively investigated. Here, we report the voltage-induced shift of the threshold voltage of Pt/LaAlO3/SrTiO3 heterostructures. A large negative voltage induces an irreversible positive shift in the threshold voltage. In fact, after the application of such a large negative voltage, the original threshold voltage cannot be recovered even by application of a large positive electric field. This irreversibility is attributed to the generation of deep traps near the LaAlO3/SrTiO3 interface under the negative voltage. This finding could contribute to the implementation of nanoelectronic devices using the 2DEG at the LaAlO3/SrTiO3 interface. PMID:25620684

  18. Epitaxially grown crystalline Al2O3 interlayer on β-Ga2O3(010) and its suppressed interface state density

    NASA Astrophysics Data System (ADS)

    Kamimura, Takafumi; Krishnamurthy, Daivasigamani; Kuramata, Akito; Yamakoshi, Shigenobu; Higashiwaki, Masataka

    2016-12-01

    Al2O3 films were deposited on β-Ga2O3(010) and β-Ga2O3 (\\bar{2}01) substrates by atomic layer deposition at 250 °C, and their interface state densities (D it) at shallow energies were evaluated using a high-low capacitance-voltage (C-V) method. Al2O3/β-Ga2O3(010) showed lower D it values (5.9 × 1010 to 9.3 × 1011 cm-2 eV-1) than Al2O3/β-Ga2O3 (\\bar{2}01) (2.0 × 1011 to 2.0 × 1012 cm-2 eV-1) in an energy range of -0.8 to -0.1 eV. Cross-sectional transmission electron microscopy analysis indicated the formation of a uniform amorphous Al2O3 layer on the β-Ga2O3 (\\bar{2}01) substrate. In contrast, a crystalline Al2O3 interlayer with a thickness of 3.2 ± 0.7 nm with an amorphous Al2O3 top layer was formed on the β-Ga2O3(010) substrate, which effectively decreased D it. Moreover, thicker interlayers showing lower D it values at deep state levels were formed at deposition temperatures higher than 100 °C, which were evaluated by shifts in the C-V curves.

  19. Photoconductivity of Graphene in Proximity to La AlO3 /Sr TiO3 Heterostructures: Phenomenon and Photosensor Applications

    NASA Astrophysics Data System (ADS)

    Cheng, Long; Fan, Xiaodong; Wei, Laiming; Lu, Juanjuan; Liang, Haixing; Qi, Ji; Zeng, Changgan

    2016-07-01

    The proximal coupling between graphene and transition-metal-oxide heterostructures may integrate their unique features and further generate emergent states. Using the photoconductivity of graphene as an effective probe, we demonstrate the existence of a built-in polar field within the La AlO3 layer of the La AlO3 /Sr TiO3 heterostructures for both conducting and insulating La AlO3 /Sr TiO3 interfaces. Such a polar field is a prerequisite for the validity of the electronic reconstruction mechanism for the interfacial conductivity. The built-in polar field is reflected by the hole doping in the graphene in proximity to the La AlO3 /Sr TiO3 induced by pulsed deep-ultraviolet illumination regardless of the graphene's carrier type. These photoresponse characteristics also render the graphene /La AlO3 /Sr TiO3 hybrid system a convenient deep-ultraviolet sensor. Moreover, we design an efficient broad-spectrum photodetector benefiting from the large in-plane electric field in graphene across the boundary between the graphene/La AlO3 /Sr TiO3 and graphene/Sr TiO3 . Our findings may provide clues to the design of photosensors based on the hybrid structures of graphene and oxide heterostructures.

  20. Absence of ferroelectricity in BiMnO3 ceramics

    NASA Astrophysics Data System (ADS)

    Goian, V.; Kamba, S.; Savinov, M.; Nuzhnyy, D.; Borodavka, F.; Vaněk, P.; Belik, A. A.

    2012-10-01

    We performed factor-group analysis of all phonons in possible monoclinic C2/c and C2 structures of BiMnO3 and compared it with our experimental infrared and Raman spectra. We conclude that the crystal structure is centrosymmetric C2/c in the whole investigated temperature range from 10 to 550 K, therefore BiMnO3 cannot be ferroelectric. We revealed a dielectric relaxation in THz spectra above the structural phase transition taking place at TC1 = 475 K giving evidence in strong lattice anharmonicity and a large dynamical disorder of Bi cations above TC1. Step-like dielectric anomaly observed at TC1 in THz permittivity reminds antiferroelectric phase transition. Nevertheless, the low-temperature dielectric studies did not reveal any antiferroelectric or ferroelectric hysteresis loop. Our experimental results support theoretical paper of Baettig et al. (J. Am. Chem. Soc. 129, 9854 (2007)) claiming that BiMnO3 is not multiferroic but only antipolar ferromagnet.

  1. Ferroelectric functionality in SrTiO3/Si heterojunctions

    NASA Astrophysics Data System (ADS)

    Yu, H. L.; Wu, Y. Z.; Jiang, X. F.; Cai, M. Q.; Gu, L. P.; Yang, G. W.

    2013-11-01

    By the first-principles calculations, various SrTiO3/Si interface architectures have been studied in this work and the computed results showed that the stable ferroelectricity can be realized in the SrTiO3/Si system. The Si/SrO interface architecture with the Si-O configuration showed predominately the ferroelectric nature and the height of the potential barrier between the negative and positive poled states (0.77 eV per interfacial unit cell). The presence of the covalent bond between the substrate Si and O of SrO layer adjacent to the substrate Si leads to the disappearance of the electronic dipoles at the interface, and the reason is that the Si-O configuration of the Si/SrO interface architecture exhibits ferroelectric nature. In order to further understand the influence of the interfacial bonding nature on the ferroelectricity of the oxide layer, the BaTiO3/Si heterojunction with the same interface architectures also have been studied. Indeed, the Si/BaO interface architecture with the Si-O configuration showed predominately the ferroelectric nature too. Certainly, a full SrO (or BaO) layer directly grown on the substrate Si is benefit to the realization of the ferroelectric functionality in the ferroelectric-Si heterojunction. These findings are useful for the understanding of the basic physics of the ferroelectric-Si heterojunction and the silicon-based functional oxide device design.

  2. Tunneling spectroscopy in engineered SrTiO3 heterostructures

    NASA Astrophysics Data System (ADS)

    Swartz, Adrian; Inoue, Hisashi; Merz, Tyler; Hikita, Yasuyuki; Hwang, Harold

    Despite decades of intense research on the topic, superconductivity in the dilute high- k semiconductor SrTiO3 (STO) has posed a long-standing problem. In light of the recent reports of unconventional 2D superconductivity in STO-based heterostructures, this problem deserves renewed attention in the bulk limit. Tunneling spectroscopy, which directly measures the electronic density of states, is a powerful tool to investigate the superconducting ground state as well as the relevant electron-phonon couplings. A limiting obstacle for employing this technique is the long depletion lengths formed when semiconducting SrTiO3 is contacted with a metal in Schottky junctions, which obstructs access to the intrinsic bulk electronic properties. Here, using band alignment engineered planar tunneling junctions to minimize these long depletion lengths, we experimentally re-examine canonical tunneling experiments in Nb-doped STO. We discuss our results on the extraction of the electron-phonon coupling in SrTiO3 and it's relevance to the superconducting condensate.

  3. Electrical phase diagram of bulk BiFeO3

    NASA Astrophysics Data System (ADS)

    Stengel, Massimiliano; Íñiguez, Jorge

    2015-12-01

    We study the electrical behavior of multiferroic BiFeO3 by means of first-principles calculations. We do so by constraining a specific component of the electric displacement field along a variety of structural paths, and by monitoring the evolution of the relevant physical properties of the crystal along the way. We find a complex interplay of ferroelectric, antiferroelectric, and antiferrodistortive degrees of freedom that leads to an unusually rich electrical phase diagram, which strongly departs from the paradigmatic double-well model of simpler ferroelectric materials. In particular, we show that many of the structural phases that were recently reported in the literature, e.g., those characterized by a giant aspect ratio, can be in principle accessed via application of an external electric field starting from the R 3 c ground state. Our results also reveal ways in which nonpolar distortions (e.g., the antiferrodistortive ones associated with rotations of the oxygen octahedra in the perovskite lattice) can be controlled by means of applied electric fields, as well as the basic features characterizing the switc