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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. PMID:16005765

  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. NITROGEN SATURATION IN NORTHERN FOREST ECOSYSTEMS

    EPA Science Inventory

    In this article we provide a formal definition of nitrogen saturation and set forth a series of testable hypotheses regarding the states of forest ecosystem response to chronic nitrogen deposition. hese hypotheses are used to suggest early indicators of nitrogen saturation and to...

  4. Role of Tricoordinate Al Sites in CH3ReO3/Al2O3 Olefin Metathesis Catalysts.

    PubMed

    Valla, Maxence; Wischert, Raphael; Comas-Vives, Aleix; Conley, Matthew P; Verel, René; Copéret, Christophe; Sautet, Philippe

    2016-06-01

    Re2O7 supported on γ-alumina is an alkene metathesis catalyst active at room temperature, compatible with functional groups, but the exact structures of the active sites are unknown. Using CH3ReO3/Al2O3 as a model for Re2O7/Al2O3, we show through a combination of reactivity studies, in situ solid-state NMR, and an extensive series of DFT calculations, that μ-methylene structures (Al-CH2-ReO3-Al) containing a Re═O bound to a tricoordinated Al (AlIII) and CH2 bound to a four-coordinated Al (AlIVb) are the precursors of the most active sites for olefin metathesis. The resting state of CH3ReO3/Al2O3 is a distribution of μ-methylene species formed by the activation of the C-H bond of CH3ReO3 on different surface Al-O sites. In situ reaction with ethylene results in the formation of Re metallacycle intermediates, which were studied in detail through a combination of solid-state NMR experiments, using labeled ethylene, and DFT calculations. In particular, we were able to distinguish between metallacycles in TBP (trigonal-bipyramidal) and SP (square-pyramidal) geometry, the latter being inactive and detrimental to catalytic activity. The SP sites are more likely to be formed on other Al sites (AlIVa/AlIVa). Experimentally, the activity of CH3ReO3/Al2O3 depends on the activation temperature of alumina; catalysts activated at or above 500 °C contain more active sites than those activated at 300 °C. We show that the dependence of catalytic activity on the Al2O3 activation temperature is related to the quantity of available AlIII-defect sites and adsorbed H2O. PMID:27140286

  5. Growing season loss of nitrate at three northeastern hardwood forests: A regional indicator of nitrogen saturation

    SciTech Connect

    Pardo, L.H.; Murdoch, P.E.; Mitchell, M.J.; Driscoll, C.T.; Likens, G.E. )

    1994-06-01

    Nitrogen is typically tightly retained in terrestrial ecosystems in the Northeast. In ecosystems with episodic nitrogen losses, nitrate export during the summer period of high biotic demand remains low. Increasing nitrate loss during the growing season is an early indicator of ecosystems shifting from episodic to chronic nitrogen loss (nitrogen saturation). Studies of nitrogen cycling from Biscuit Brook, Catskills, NY, Huntington Forest, Adirondacks, NY and Hubbard Brook Experimental Forest, White Mountains, NH, showed high nitrate loss at each site during the summer of 1990. This regional pattern many be caused by anthropogenic (higher nitrogen deposition), climatic (temperature and weather interactions), and/or natural (eg. pest outbreaks) disturbance. High nitrate loss causes surface water quality deterioration and may be linked to forest decline. The pattern also demonstrates the need for surface water monitoring on a regional scale to assess the effects of air pollution emissions legislation.

  6. 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

  7. First-Principles Investigations of Pb Anti-Site Defects in PbZrO3 and Pb(Zr, Ti)O3 Perovskites

    NASA Astrophysics Data System (ADS)

    Kagimura, Ricardo; Singh, David J.

    2008-03-01

    Lead zirconate (PZ) and lead zirconate titanate (PZT) have the perovskite type structure, ABO3. Bivalent lead (Pb^+2) ions occupy the A site, while tetravalent titanium and zirconium (Zr^+4, Ti^+4) ions occupy the B site at random of the PZT solid solution. Also, lead can be tetravalent (Pb^+4), such as in PbO2 structure. Recent experimental work has reported that tetravalent Pb ions can locate at the B site of the PZT perovskite forming a lead zirconate-titanate-plumbate solid solution. The experimental results suggest that, based on a PbZrO3-PbTiO3-PbPbO3 ternary solution phase diagram [G. Suchaneck et al., Ferroelectrics 318, 3 (2005)], the substitutional Pb atom prefers to occupy the Zr site instead of the Ti one. In this work, we report density functional supercell calculations for pure PbZrO3 perovskite and for ordered Pb(Zr1/2Ti1/2)O3 solid solution with different configurations for the Zr and Ti atoms. We investigate the anti-site defect energies and the effects on the electronic structure.

  8. 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.

  9. 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.

  10. Temporal characterization and regional contribution to O3 and NOx at an urban and a suburban site in Nanjing, China.

    PubMed

    Xie, Min; Zhu, Kuanguang; Wang, Tijian; Chen, Pulong; Han, Yong; Li, Shu; Zhuang, Bingliang; Shu, Lei

    2016-05-01

    To improve our understanding of the interplay among local and regional photochemical pollutants in the typical city of the Yangtze River Delta (YRD) region, the concurrent observation of O3 and NOx concentrations at an urban and a suburban site in Nanjing during 2008 is presented. In general, the annual mean O3 concentration is 2.35ppbv lower in the downtown than at suburban due to higher NOx pollution levels correlated with heavy traffic. At both sites, O3 shows a distinct seasonality with the spring maximum and the winter minimum, while the minimum concentration of NOx appears in summertime. Besides the chemical processes of O3 sensitivity in the daytime and the NOx titration at night, meteorological conditions also play an essential role in these monthly and diurnal variations. The ozone weekend effect that can be attributed to the weekly routine of human activities is observed in the urban atmosphere of Nanjing as well, with O3 concentrations 2.09ppbv higher and NOx concentrations 6.20ppbv lower on weekends than on weekdays. The chemical coupling of NO, NO2 and O3 is investigated to show that the OX-component (O3 and NO2) partitioning point occurs at about 35ppbv for NOx, with O3 being the dominant form at lower levels and NO2 dominating at higher levels. And it is also discovered that the level of OX is made up of two contributions, including the regional contribution affected by regional background O3 level and the local contribution correlated with the level of primary pollution. The diurnal peak of regional contribution appears 2-5h after the peak of local contribution, implying that OX in Nanjing might prominently affected by the pollutants from a short distance. The highest regional contribution and the second highest local contribution lead to the spring peak of O3 observed in Nanjing, whereas the highest local contribution and the moderate regional contribution make the O3 concentrations in summer higher than those in autumn and winter. Our results

  11. 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.

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

    DOE PAGESBeta

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

    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.

  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

    2015-11-01

    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. PMID:26398359

  14. 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.

  15. Site preference of cation vacancies in Mn-doped Ga2O3 with defective spinel structure

    NASA Astrophysics Data System (ADS)

    Hayashi, Hiroyuki; Huang, Rong; Oba, Fumiyasu; Hirayama, Tsukasa; Tanaka, Isao

    2012-12-01

    A strong site preference of intrinsic cation vacancies in Mn-doped Ga2O3 with a defective spinel structure is revealed using a combination of high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) and first-principles calculations. The intensity profile analysis of HAADF-STEM images clearly indicates that the cation vacancies prefer the octahedral sites. Systematic first-principles calculations for 698 atomic configurations suggest that the Mn ions and cation vacancies are energetically favorable at the tetrahedral and octahedral sites, respectively. The site preference of the cation vacancies is found to correlate with the electrostatic energy.

  16. Investigation into relationships among NO, NO2, NOx, O3, and CO at an urban background site in Delhi, India

    NASA Astrophysics Data System (ADS)

    Tiwari, Suresh; Dahiya, Anita; Kumar, Nandini

    2015-04-01

    High resolution concentrations of nitric oxide (NO), nitrogen dioxide (NO2), oxides of nitrogen (NOx), and Ozone (O3) were measured at a urban site (urban background) in New Delhi, India for a period of two years from September 2010 to August 2012. During the study period, the mean concentrations of NO, NO2, NOx, O3 (ppb), and CO (ppm) were observed to be 17.2, 12.5, 29.3, 23.6, and 1.97, respectively. This data was then employed to investigate the relationships between NO, NO2, and O3 as a function of NOx. The highest mean concentrations of NO were observed from midnight 00:00 to 05:00 h local time (LT) in the morning as a result of an increase in traffic emissions and a reduction in boundary layer height during the night. The total levels of oxidant [OX], which are considered to be the sum of O3 and NO2, were determined. A study of variation of [OX] and NOx identified two distinct contributions to ambient OX concentrations, i.e., NOx independent and NOx dependent. The NOx-dependent contribution corresponds to the local production of ozone, and the NOx-independent contribution corresponds to regional concentrations, which at this site is the background level of ozone. The monthly and diurnal variations of [OX] are discussed. Wind directions were used to identify possible regional sources of [OX]. The analysis suggests that [OX] concentrations were about six times higher with winds originating from the Northwest direction (NW) compared to those from the East.

  17. 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

  18. 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.

  19. 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

    2016-01-01

    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

  20. 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.

  1. Tuning of magnetic ordering by Y substitution onto Tb site in the nanocrystalline TbMnO3

    NASA Astrophysics Data System (ADS)

    Chakraborty, Keka R.; Shukla, Rakesh; Kaushik, S. D.; Mukadam, M. D.; Siruguri, V.; Tyagi, A. K.; Yusuf, S. M.

    2015-10-01

    We report the magnetic properties, of nano-crystalline powders Tb1-xYxMnO3 (x = 0, 0.1, 0.2, 0.3 and 0.4), as perceived by neutron diffraction, and elucidate the effect of Tb site substitution on the magnetic structure of TbMnO3. All samples crystallized in the orthorhombic structure conforming to space group Pnma, and exhibited an incommensurate collinear antiferromagnetic ordering of the Mn ions below ˜40 K. Furthermore, at T ≤ 20 K, all these samples showed a change in magnetic structure (of Mn moments) to a spiral ordering down to 2 K, the lowest measured temperature. For the samples with x = 0, 0.1, and 0.2, a short-ranged two dimensional (2D) ordering of Tb moments was also observed at 2 K. However, for the other samples (x = 0.3 and 0.4), no magnetic ordering of Tb moments was found down to 2 K. So with Y substitution, a crossover from 2D ordering to a disordering of Tb moments was observed. The moments at the Mn site were found to be lower than the full Mn3+ (4μB) moment for all the samples below 40 K. The magnetic properties of all the samples studied by us in nano form are more pronounced than those of the reported single crystals of same compositions [V. Yu. Ivanov et al., JETP Lett. 91, 392-397 (2010)].

  2. 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.

  3. Summer to Early Fall O3\\ and CO Measurements in the North Atlantic Ocean at a Mountaintop Site in the Azores Islands

    NASA Astrophysics Data System (ADS)

    Edlin, C. L.; Honrath, R. E.

    2001-12-01

    A system for the continuous ground-based measurement of ozone (O3) and carbon monoxide (CO) was recently installed at a mountaintop site in the Portuguese Azores Islands in the central north Atlantic Ocean{}. The main objective of this site will be the determination of the frequency and impact of transport events bringing O3\\ and O3\\ precursors from North America and Europe to the central north Atlantic Ocean region. These measurements are a part of the PICO-NARE study (Pico International atmospheric Chemistry Observatory - North Atlantic Research Experiment). The measurement site is located on the top of Pico mountain at an altitude of 2225 meters, allowing frequent sampling of free tropospheric air. Frequency and magnitude of long-range pollution events to the north Atlantic from continental sources are determined through analysis of correlation between O3\\ and CO and the use of back-trajectory data. Data obtained from July to October, 2001 will be presented here. The measurements will be analyzed to assess ambient levels of O3\\ and CO in the remote central north Atlantic region. Additionally, these measurements will be utilized to identify and quantify O3\\ import and en route production associated with polluted air masses transported to the north Atlantic region. Meteorological data will also be analyzed and presented, to begin characterization of the PICO-NARE site for determination of the frequency of the free tropospheric observations at the site.

  4. Enhanced piezoelectricity in (1 -x)Bi1.05Fe1-yAyO3-xBaTiO3 lead-free ceramics: site engineering and wide phase boundary region.

    PubMed

    Zheng, Ting; Jiang, Zhenggen; Wu, Jiagang

    2016-07-28

    Site engineering has been employed to modulate the piezoelectric activity of high temperature (1 -x)Bi1.05Fe1-yScyO3-xBaTiO3 lead-free ceramics fabricated by a conventional solid-state method together with a quenching technique. The effects of x and y content on the phase structure, microstructure, and electrical properties have been investigated in detail. A wide rhombohedral (R) to pseudo-cubic (C) phase boundary was formed in the ceramics with x = 0.30 and 0 ≤y≤ 0.07, thus leading to enhanced piezoelectricity (d33 = 120-180 pC N(-1)), ferroelectricity (Pr = 19-22 μC cm(-2)) and a high Curie temperature (TC = 478-520 °C). In addition, the influence of different element substitutions for Fe(3+) on phase structure and electrical behavior was also investigated. Improved piezoelectricity (d33 = 160-180 pC N(-1)) and saturated P-E loops can be simultaneously achieved in the ceramics with A = Sc, Ga, and Al due to the R-C phase boundary. As a result, site engineering may be an efficient way to modulate the piezoelectricity of BiFeO3-BaTiO3 lead-free ceramics. PMID:27357104

  5. Effects of A-site nonstoichiometry on oxide ion conduction in 0.94Bi0.5Na0.5TiO3-0.06BaTiO3 ceramics

    NASA Astrophysics Data System (ADS)

    Prasertpalichat, Sasiporn; Schmidt, Whitney; Cann, David P.

    2016-06-01

    Lead free 0.94(Bi0.5Na0.5)TiO3-0.06BaTiO3 ceramics were prepared by conventional solid-state mixed oxide route with the A-site stoichiometry modified to incorporate donor-doping (through Bi-excess) and acceptor-doping (through Na-excess). Both stoichiometric and nonstoichiometric ceramics exhibited a single perovskite phase with pseudo-cubic symmetry. A significant improvement in the dielectric properties was observed in Bi-excess compositions and a deterioration in the dielectric properties was observed in Na-excess compositions. Impedance spectroscopy was utilized to analyze the effects of A-site nonstoichiometry on conduction mechanisms. Compositions with Bi-excess resulted in an electrically homogeneous microstructure with an increase in resistivity by ˜3-4 orders of magnitude and an associated activation energy of 1.57eV which was close to half of the optical bandgap. In contrast, an electrically heterogeneous microstructure was observed in both the stoichiometric and Na-excess compositions. In addition, the Na-excess compositions exhibited low resistivities (ρ˜103Ω-cm) with characteristic peaks in the impedance data comparable to the recent observations of oxide ion conduction in (Bi0.5Na0.5)TiO3. Long term annealing studies were also conducted at 800∘C to identify changes in crystal structure and electrical properties. The results of this study demonstrates that the dielectric and electrical properties of 0.94(Bi0.5Na0.5)TiO3-0.06BaTiO3 ceramics are very sensitive to Bi/Na stoichiometry.

  6. A DFT+U study of A-site and B-site substitution in BaFeO3-δ.

    PubMed

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

    2015-09-28

    BaFeO3-δ (BFO)-based perovskites have emerged as cheap and effective oxygen electrocatalysts for oxygen reduction reaction at high temperatures. The BFO cubic phase facilitates a high oxygen deficiency and is commonly stabilised by partial substitution. Understanding the electronic mechanisms of substitution and oxygen deficiency is key to rational material design, and can be realised through DFT analysis. In this work an in-depth first principle DFT+U study is undertaken to determine site distinctive characteristics for 12.5%, Y, La and Ce substitutions in BFO. In particular, it is shown that B-site doped structures exhibit a lower energy cost for oxygen vacancy formation relative to A site doping and pristine BFO. This is attributed to the stabilisation of holes in the oxygen sub-lattice and increased covalency of the Fe-O bonds of the FeO6 octahedra in B-site-substituted BFO. Charge analysis shows that A-site substitution amounts to donor doping and consequently impedes the accommodation of other donors (i.e. oxygen vacancies). However, A-site substitution may also exhibit a higher electronic conductivity due to less lattice distortion for oxygen deficiency compared to B-site doped structures. Furthermore, analysis of the local structural effects provides physical insight into stoichiometric expansions observed for this material. PMID:26295283

  7. Electronic structures and optical properties of Zn-doped β-Ga2O3 with different doping sites

    NASA Astrophysics Data System (ADS)

    Li, Chao; Yan, Jin-Liang; Zhang, Li-Ying; Zhao, Gang

    2012-12-01

    The electronic structures and optical properties of intrinsic β-Ga2O3 and Zn-doped β-Ga2O3 are investigated by first-principles calculations. The analysis about the thermal stability shows that Zn-doped β-Ga2O3 remains stable. The Zn doping does not change the basic electronic structure of β-Ga2O3, but only generates an empty energy level above the maximum of the valence band, which is shallow enough to make the Zn-doped β-Ga2O3 a typical p-type semiconductor. Because of Zn doping, absorption and reflectivity are enhanced in the near infrared region. The higher absorption and reflectivity of ZnGa(2) than those of ZnGa(1) are due to more empty energy states of ZnGa(2) than those of ZnGa(1) near Ef in the near infrared region.

  8. Synthesis and characterization of A-site deficient rare-earth doped BaZr xTi 1- xO 3 perovskite-type compounds

    NASA Astrophysics Data System (ADS)

    Ostos, C.; Mestres, L.; Martínez-Sarrión, M. L.; García, J. E.; Albareda, A.; Perez, R.

    2009-05-01

    A-site deficient rare-earth doped BaZr xTi 1- xO 3 (BZT) ceramics were prepared from a soft-chemistry route and by solid-state reaction (SSR). Perovskite-like single-phase diagrams for the BaTiO 3-La 2/3TiO 3-BaZrO 3 system were constructed for each method of synthesis. Infrared spectroscopy on (Ba 1- yLa 2 y/3 )Zr xTi 1- xO 3 solid solution revealed a dramatic stress on the M-O (M = Ti, Zr) bonds due to the combined effect of A-site vacancies and the lower ionic radius of La 3+ than that of Ba 2+. A relationship between the M-O stretching vibration ( υ) and the tolerance factor ( t) was determined. (Ba 1- yLn 2 y/3 )Zr 0.09Ti 0.91O 3 (Ln = La, Pr, Nd) samples synthesized by SSR were selected for detailed studies. X-ray diffraction data were refined by the Rietveld method. Scanning electron microscopy on sintered compacts detected abnormal crystal growth and grain sizes in the range of about 1 μm up to 10 μm when the dopant concentration is 6.7 at. %. Impedance measurements exhibited that ferroelectric to paraelectric phase-transition temperature shifted to lower values as increasing rare-earth content. (Ba 1- yLn 2 y/3 )Zr 0.09Ti 0.91O 3 system showed a diffuse phase transition with a relaxor-like ferroelectric behaviour. Furthermore, the dielectric constant was enhanced with respect to non-doped BZT system.

  9. 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.

  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. 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.

  12. Tailoring ergodicity through selective A-site doping in the Bi1/2Na1/2TiO3-Bi1/2K1/2TiO3 system

    NASA Astrophysics Data System (ADS)

    Acosta, Matias; Liu, Na; Deluca, Marco; Heidt, Sabrina; Ringl, Ines; Dietz, Christian; Stark, Robert W.; Jo, Wook

    2015-04-01

    The morphotropic phase boundary composition Bi1/2Na1/2TiO3-20 mol. % Bi1/2K1/2TiO3 was chosen as initial material to do selective A-site aliovalent doping replacing Na and K by 1 at. % La, respectively. The materials were studied macroscopically by measuring dielectric and electromechanical properties. The Na-replaced material has a lower freezing temperature Tfr, lower remanent polarization and remanent strain, and thus a higher degree of ergodicity than the K-replaced material. These results are contrasted with local poling experiments and hysteresis loops obtained from piezoresponse force microscopy. The faster relaxation of the tip-induced local polarization and the lower remanent state in bias-on and -off loops confirm the higher degree of ergodicity of the Na-replaced material. The difference in functional properties is attributed to small variations in chemical pressure achieved through selective doping. Raman results support this working hypothesis.

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

    NASA Astrophysics Data System (ADS)

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

    2015-10-01

    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.

  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. A case study of nitrogen saturation in western U.S. forests.

    PubMed

    Fenn, M E; Poth, M A

    2001-11-01

    Virtually complete nitrification of the available ammonium in soil and nitrification activity in the forest floor are important factors predisposing forests in the San Bernardino Mountains of southern California to nitrogen (N) saturation. As a result, inorganic N in the soil solution is dominated by nitrate. High nitrification rates also generate elevated nitric oxide (NO) emissions from soil. High-base cation saturation of these soils means that soil calcium depletion or effects associated with soil acidification are not an immediate risk for forest health as has been postulated for mesic forests in the eastern U.S. Physiological disturbance (e.g., altered carbon [C] cycling, reduced fine root biomass, premature needle abscission) of ozone-sensitive ponderosa pine trees exposed to high N deposition and high ozone levels appear to be the greater threat to forest sustainability. However, N deposition appears to offset the aboveground growth depression effects of ozone exposure. High nitrification activity reported for many western ecosystems suggests that with chronic N inputs these systems are prone to N saturation and hydrologic and gaseous losses of N. High runoff during the winter wet season in California forests under a Mediterranean climate may further predispose these watersheds to high nitrate leachate losses. After 4 years of N fertilization at a severely N saturated site in the San Bernardino Mountains, bole growth unexpectedly increased. Reduced C allocation below- ground at this site, presumably in response to ozone or N or both pollutants, may enhance the bole growth response to added N. PMID:12805801

  16. Theoretical investigations of EPR g factors for Ce3+ ion at monoclinic Cs site in YAlO3 crystal

    NASA Astrophysics Data System (ADS)

    Liu, Hong-Gang; Zheng, Wen-Chen

    2015-01-01

    Three EPR principal g values (gx, gy and gz) for monoclinic (Cs) Ce3+ center in YAlO3 crystal are calculated by the complete diagonalization (of energy matrix) method (CDM) based on the superposition model (SPM) analysis. The calculated g factors are more reasonably closer to experimental results reported by Asatryan et al. (2002) than their same work in 1997. The reliability of fitted crystal-field parameters of YAP:Ce3+ crystal is also analyzed. In SPM calculations, the seeming abnormal negative power-law exponent t6 is found to be actually reasonable and its underlying cause may be explained by future ab initio studies.

  17. Electronic and structural properties, and hyperfine interactions at Sc sites in the semiconductor Sc2O3 : TDPAC and ab initio study

    NASA Astrophysics Data System (ADS)

    Richard, D.; Muñoz, E. L.; Butz, T.; Errico, L. A.; Rentería, M.

    2010-07-01

    The time-differential γ-γ perturbed-angular-correlation (TDPAC) technique using T44i→S44c tracers was applied to study the nuclear quadrupole interaction of the first excited I=1 state of S44c in the cubic bixbyite structure of scandium sesquioxide (Sc2O3) . In addition, ab initio calculations of electronic and structural properties and hyperfine parameters at the cationic sites of the Sc2O3 structure were performed using the full-potential augmented plane wave plus local-orbital (APW+lo) method. The accuracy of the calculations and the excellent agreement of the predicted electric-field-gradient (EFG) tensors and the structural properties (lattice parameters, internal positions) with the experimental results enable us to identify the observed hyperfine interactions and to infer the EFG sign that cannot be measured in conventional TDPAC experiments. Additionally, the APW+lo calculations show that the EFG at Sc sites is originated in the population of Sc3p states and give an explanation for the preferential occupation of the asymmetric cationic site C of the structure by the T44i doping impurities. Finally, the validity of the ionic model, usually used to describe the EFG at native cation sites, is discussed.

  18. A-site ordering in colossal magnetoresistance manganite La(1-x)Sr(x)MnO3? Molecular dynamics simulations and quantum mechanics calculations.

    PubMed

    Jang, Yun Hee; Gervais, François; Lansac, Yves

    2009-09-01

    Recent experiments have called into question the assumption of a random A-site distribution in mixed-valence colossal magnetoresistance (CMR) manganites. We explored the possibility of an A-site (La(3+)/Sr(2+)) ordering in a CMR manganite La(3/4)Sr(1/4)MnO(3) using molecular dynamics (MD) simulations with a newly developed force field (FF) and quantum mechanics (QM) (density functional theory with the generalized gradient approximation) calculations of the relative stability of structures obtained from MD. Both methods suggest that the degree of stabilization (enthalpy gain) of A-site ordering is not sufficient to overcome the accompanying entropy loss, supporting the assumption of a random A-site distribution in La(3/4)Sr(1/4)MnO(3). This approach combining MD and QM as well as the versatile FF developed in this study should be useful for investigating the structure and functionality of magnetic tunnel junction devices involving composite materials of mixed-valence manganites. PMID:19739857

  19. Heterogeneous distribution of B-site cations in BaZrxTi1-xO3 epitaxial thin films grown on (0 0 1) SrTiO3 by pulsed laser deposition

    NASA Astrophysics Data System (ADS)

    Ventura, J.; Polo, M. C.; Ferrater, C.; Hernández, S.; Sancho-Parramón, J.; Coy, L. E.; Rodríguez, L.; Canillas, A.; Fábrega, L.; Varela, M.

    2016-09-01

    The isovalent susbstitution of Ti4+ by Zr4+ in BaZrxTi1-xO3 modifies the dielectric character of ferroelectric BaTiO3 yielding different behaviours such as relaxor, polar cluster, etc. The dynamic coupling between BaTiO3 polar nanoregions and BaZrO3 nonpolar ones as well as microstrain between them are thought to be behind such a rich phase diagram. However, these short-range compositonal variations are elusive to detect and this topic is thus rarely addressed. We have grown epitaxial thin films of BaZrxTi1-xO3 on (0 0 1)-oriented SrTiO3 substrates by pulsed laser deposition sweeping the entire composition range between BaTiO3 and BaZrO3 in increments of 0.1 in x. Several characterization techniques (AFM, TEM, XRD, Raman spectroscopy) were used for this research in order to understand the morphological and structural properties of the deposited films. Ellipsometric measurements allowed the calculation of the band gap energy of the films. This work demonstrates the existence of a heterogeneous distribution in the substitution of titanium by zirconium yielding relaxor and polar cluster nanoregions.

  20. 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

  1. Transmission electron microscopy study of B-site cation configurations in perovskite-structured Pb(Mg1/2W1/2)O3- Pb(Ni1/3Nb2/3)O3- PbTiO3 ceramics

    NASA Astrophysics Data System (ADS)

    Furuya, M.; Mori, T.; Ochi, A.

    1994-04-01

    Configurations of B-site cations in the perovskite-structured ternary system Pb(Mg1/2W1/2)O3-Pb(Ni1/3Nb2/3)O3-PbTiO3 (PMW-PNN-PT) of interest for multilayer ceramic capacitors were studied by transmission electron microscopy. The evaluated specimens were four PMW/PNN/PT compositions: 10/30/60, 30/30/40, 50/30/20, and 70/30/0 on a compositional line with 30 mol % PNN content. A ``core-shell-type'' microstructure was seen in the 10/30/60 specimen composition, which has a ``normal'' ferroelectric characteristic, along with typical ferroelectric domain structures. The B-site cation ordering in the 10/30/60 composition was not detectable in the selected-area electron diffraction pattern. On the other hand, an ``island-type'' microstructure, consisting of clusters (˜1-2 nm) with B-site cations 1:1 ordered, was observed in the 30/30/40, 50/30/20, and 70/30/0 compositions, which have relaxor-type characteristics. In the 70/30/0 composition, larger stripe-shaped ordered regions (˜20-200 nm) were also observed. These ordered regions extended from the center of the grain to the boundary. On the basis of the results obtained, origins of the dielectric behaviors for this system, that is, a ``normal'' ferroelectric, a relaxor ferroelectric, and an antiferroelectric, were discussed from the point of view of the B-site cation configurations. The PMW component plays two roles in this ternary system, corresponding to its content. When the PMW content is low, Mg and W ions are disordered in the B-site sublattice, and interrupt the ferroelectricity. With increasing PMW content, small ordered clusters (˜1-2 nm) are formed, which are believed to localize superparaelectric potentials effectively and dominate a degree of a diffuse phase transition in the solid-solution system.

  2. Co-doping of (Bi0.5Na0.5)TiO3: secondary phase formation and lattice site preference of Co

    NASA Astrophysics Data System (ADS)

    Schmitt, V.; Staab, T. E. M.

    2012-11-01

    Bismuth sodium titanate (Bi0.5Na0.5)TiO3 (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. (Bi0.5Na0.5)TiO3 + 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 Co2TiO4 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.

  3. Effect of heterovalent substitution at Mn site on the magnetic and transport properties of La0.67Sr0.33MnO3

    NASA Astrophysics Data System (ADS)

    Priolkar, K. R.; Rawat, R.

    Magnetic and transport properties of Ti substituted La0.67Sr0.33MnO3 are drastically affected with a change in preparation conditions. Low temperature infra-red absorption measurements reveal that this is perhaps due to inhomogeniety in substitution of Ti on Mn sites. It is found that, in the high temperature annealed samples, the substitution of Ti supresses the double exchange interaction due to the formation of Mn-O- Ti chains. While in the low temperature annealed case substitution of Ti causes formation of isolated ferromagnetic clusters linked to each other by a variable range hopping polaron.

  4. 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

  5. The effect of A-site and B-site substitution on BaFeO3-δ: An investigation as a cathode material for intermediate-temperature solid oxide fuel cells

    NASA Astrophysics Data System (ADS)

    Wang, Jian; Saccoccio, Mattia; Chen, Dengjie; Gao, Yang; Chen, Chi; Ciucci, Francesco

    2015-11-01

    This work systematically investigates the effects of single A-site dopant (5 mol% La3+, Sm3+ and Gd3+) and single B-site dopant (5 mol% Zr4+ and Ce4+) on the structure and oxygen reduction reaction of BaFeO3-δ (BFO) used as a cathode for solid oxide fuel cells. The materials are prepared by solid-state method and their structural, electronic, electrocatalytic properties are characterized and compared. X-ray diffraction reveals 5 mol% A-site or B-site dopant is sufficient to stabilize the cubic phase of BFO, as predicted by the lattice calculation. X-ray photoelectron spectroscopy and iodometric titration demonstrates that neither of the two doping sites has obvious advantage over the other towards the formation of additional oxygen vacancies. B-site doped BFO shows a lower electrical conductivity than A-site doped ones, however, they have much quicker response to electrical conductivity relaxation, likely originating from the expanded lattice size. With the largest oxygen vacancy concentrations, Ba0.95La0.05FeO3-δ and BaFe0.95Zr0.05O3-δ stand out from the A-site and B-site doped BFO, respectively, and polarization resistances of 0.029 Ω cm2 and 0.020 Ω cm2 are achieved at 700 °C, PO2 = 0.2atm . With a similar amount of oxygen vacancies, B-site doping is more advantageous for enhancing oxygen bulk diffusion kinetics, and thus ORR activity.

  6. 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.

  7. Lattice site investigations for Mg in LiNbO 3 by combined RBS-PIXE-NRA channeling experiments

    NASA Astrophysics Data System (ADS)

    Kling, A.; Kollewe, D.; Grabmaier, B. C.

    1992-02-01

    The lattice position of magnesium in lithium niobate has been investigated for single crystals doped with MgO (between 0 and 9 mol% in the congruent melt) using a combination of RBS, PIXE and NRA with channeling. Mg seems to be collinear with the niobium and lithium in the c-axis for the whole concentration range. Concentration dependent effects with a threshold of about 1 mol% MgO for other axes have been observed. For low concentrations experimental results and computer simulations performed with our recently developed program CASSIS indicate that magnesium occupies an octahedral site near lithium while for higher concentrations the regular lithium site and an octahedral position near niobium is found to be occupied.

  8. 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.

  9. 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

  10. 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

    2016-11-01

    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. PMID:27318729

  11. Site Redistribution, Partial Frozen-in Defect Chemistry, and Electrical Properties of Ba1-x(Zr,Pr)O3-δ.

    PubMed

    Antunes, Isabel; Mikhalev, Sergey; Mather, Glenn Christopher; Kharton, Vladislav Vadimovich; Figueiras, Fábio Gabriel; Alves, Adriana; Rodrigues, Joana; Correia, Maria Rosário; Frade, Jorge Ribeiro; Fagg, Duncan Paul

    2016-09-01

    Changes in nominal composition of the perovskite (ABO3) solid solution Ba1-x(Zr,Pr)O3-δ and adjusted firing conditions at very high temperatures were used to induce structural changes involving site redistribution and frozen-in point defects, as revealed by Raman and photoluminescence spectroscopies. Complementary magnetic measurements allowed quantification of the reduced content of Pr. Weak dependence of oxygen stoichiometry with temperature was obtained by coulometric titration at temperatures below 1000 °C, consistent with a somewhat complex partial frozen-in defect chemistry. Electrical conductivity measurements combined with transport number and Seebeck coefficient measurements showed prevailing electronic transport and also indicated trends expected for partial frozen-in conditions. Nominal Ba deficiency and controlled firing at very high temperatures allows adjustment of structure and partial frozen-in defect chemistry, opening the way to engineer relevant properties for high-temperature electrochemical applications. PMID:27509311

  12. Influence of Ni substitution at B-site for Fe3+ ions on morphological, optical, and magnetic properties of HoFeO3 ceramics

    NASA Astrophysics Data System (ADS)

    Habib, Zubida; Majid, Kowsar; Ikram, Mohd.; Sultan, Khalid; Mir, Sajad Ahmad; Asokan, K.

    2016-05-01

    Present study reports the effect of Ni substitution at B-site in HoFeO3 on the morphological, optical and magnetic properties. These compounds were prepared by solid-state reaction method. Scanning electron microscope reveals an increase in average grain sizes with Ni concentration. Absorption and emission spectra show redshift in band gap with increase in Ni ion concentrations. The Tauc plots show direct allowed transitions. Temperature-dependent magnetization studies on these compounds revealed the transition from ferromagnetism to paramagnetism. There is separation between temperature at which zero-field-cooled and field-cooled occurs at varied temperature with Ni substitution. The separation effect is related to the impact of the paramagnetic Ho3+ ions, whose magnitude becomes more prominent at higher temperature. The value of squareness ratio in these materials is below 0.5 indicating presence of multidomain structures.

  13. 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. PMID:22648346

  14. Effect of A Site and Oxygen Vacancies on the Structural and Electronic Properties of Lead-Free KTa0.5Nb0.5O3 Crystal

    NASA Astrophysics Data System (ADS)

    Yang, Wenlong; Wang, Li; Lin, Jiaqi; Li, Xiaokang; Xiu, Hanjiang; Shen, Yanqing

    2016-04-01

    The structural and electronic properties of lead-free potassium tantalite niobate KTa0.5Nb0.5O3 (KTN) with A site vacancies V_{{K}}0 , V_{{K}}^{1 - } and oxygen vacancies V_{{O}}0 , V_{{O}}^{2 + } , were investigated by first-principles calculations, which indicated that A site vacancies V_{{K}}0 are likely to form in the KTN compared with V_{{K}}^{1 - } , and oxygen vacancies V_{{O}}^{2 + } are likely to form compared with V_{{O}}0 in the KTN according to the investigation of formation energy. The results show that K and O vacancies have significant influence on the atomic interactions of the atoms and the electronic performance of the materials. And Ta atoms are more easily influenced by the K and O vacancies than the Nb atoms from the atomic displacements in KTN with K and O vacancies. The investigation of density of state indicates that the compensation of electrons in KTN with vacancies make the hybridization become stronger among Ta d, Nb d and O p orbitals. Besides, Mulliken population of all the Ta and Nb atoms in KTN with charged vacancies are influenced by complement electrons. The strength of the Nb-O bond is stronger than Ta-O based on the changes of bond lengths and Mulliken population.

  15. Effect of A Site and Oxygen Vacancies on the Structural and Electronic Properties of Lead-Free KTa0.5Nb0.5O3 Crystal

    NASA Astrophysics Data System (ADS)

    Yang, Wenlong; Wang, Li; Lin, Jiaqi; Li, Xiaokang; Xiu, Hanjiang; Shen, Yanqing

    2016-07-01

    The structural and electronic properties of lead-free potassium tantalite niobate KTa0.5Nb0.5O3 (KTN) with A site vacancies V_{{K}}0 , V_{{K}}^{1 - } and oxygen vacancies V_{{O}}0 , V_{{O}}^{2 + } , were investigated by first-principles calculations, which indicated that A site vacancies V_{{K}}0 are likely to form in the KTN compared with V_{{K}}^{1 - } , and oxygen vacancies V_{{O}}^{2 + } are likely to form compared with V_{{O}}0 in the KTN according to the investigation of formation energy. The results show that K and O vacancies have significant influence on the atomic interactions of the atoms and the electronic performance of the materials. And Ta atoms are more easily influenced by the K and O vacancies than the Nb atoms from the atomic displacements in KTN with K and O vacancies. The investigation of density of state indicates that the compensation of electrons in KTN with vacancies make the hybridization become stronger among Ta d, Nb d and O p orbitals. Besides, Mulliken population of all the Ta and Nb atoms in KTN with charged vacancies are influenced by complement electrons. The strength of the Nb-O bond is stronger than Ta-O based on the changes of bond lengths and Mulliken population.

  16. 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.

  17. Lead-free and lead-based ABO3 perovskite relaxors with mixed-valence A-site and B-site disorder: Comparative neutron scattering structural study of (Na1/2Bi1/2)TiO3 and Pb(Mg1/3Nb2/3)O3

    NASA Astrophysics Data System (ADS)

    Ge, Wenwei; Devreugd, Christopher P.; Phelan, D.; Zhang, Qinhui; Ahart, Muhtar; Li, Jiefang; Luo, Haosu; Boatner, Lynn A.; Viehland, Dwight; Gehring, Peter M.

    2013-11-01

    We report the results of neutron elastic-scattering measurements made between -250 °C and 620 °C on the lead-free relaxor (Na1/2Bi1/2)TiO3 (NBT). Strong, anisotropic, elastic diffuse scattering intensity decorates the (100), (110), (111), (200), (210), and (220) Bragg peaks at room temperature. The wave-vector dependence of this diffuse scattering is compared to that in the lead-based relaxor Pb(Mg1/3Nb2/3)O3 (PMN) to determine if any features might be common to relaxors. Prominent ridges in the elastic diffuse scattering intensity contours that extend along ⟨110⟩ are seen that exhibit the same zone dependence as those observed in PMN and other lead-based relaxors. These ridges disappear gradually on heating above the cubic-to-tetragonal phase transition temperature TCT = 523 °C, which is also near the temperature at which the dielectric permittivity begins to deviate from Curie-Weiss behavior. We thus identify the ⟨110⟩-oriented ridges as a relaxor-specific property. The diffuse scattering contours also display narrower ridges oriented along ⟨100⟩ that are consistent with the x-ray results of Kreisel [Phys. Rev. BPRBMDO1098-012110.1103/PhysRevB.68.014113 68, 014113 (2003)]; these vanish near 320 °C, indicating that they have a different physical origin. The ⟨100⟩-oriented ridges are not observed in PMN. We observe no equivalent relaxor-specific elastic diffuse scattering from the homovalent relaxor analogues K0.95Li0.05TiO3 (A-site disordered) and KTa0.95Nb0.05O3 (B-site disordered). This suggests that the ⟨110⟩-oriented diffuse scattering ridges are correlated with the presence of strong random electric fields and invites a reassessment of what defines the relaxor phase. We find that doping NBT with 5.6% BaTiO3, a composition close to the morphotropic phase boundary with enhanced piezoelectric properties, increases the room-temperature correlation length along [11¯0] from 40 to 60 Å while doubling the associated integrated diffuse

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

    DOE PAGESBeta

    Sergey Y. Smolin; Sfeir, Matthew Y.; Scafetta, Mark D.; Choquette, Amber K.; Baxter, Jason B.; May, Steven J.

    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

  19. 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.

  20. 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

  1. O3 stars

    SciTech Connect

    Walborn, N.R.

    1982-03-01

    A brief review of the 10 known objects in this earliest spectral class is presented. Two new members are included: HD 64568 in NGC 2467 (Puppis OB2), which provides the first example of an O3 V((f*)) spectrum; and Sk -67/sup 0/22 in the Large Magellanic Cloud, which is intermediate between types O3 If* and WN6-A. In addition, the spectrum of HDE 269810 in the LMC is reclassified as the first of type O3 III (f*). The absolute visual magnitudes of these stars are rediscussed.

  2. Atmospheric inputs and nitrogen saturation status in and adjacent to Class I wilderness areas of the northeastern US.

    PubMed

    Templer, Pamela H; Weathers, Kathleen C; Lindsey, Amanda; Lenoir, Katherine; Scott, Lindsay

    2015-01-01

    Atmospheric inputs of N and S in bulk deposition (open collectors) and throughfall (beneath canopy collectors) were measured in and adjacent to two Class 1 wilderness areas of the northeastern US. In general, atmospheric S inputs followed our expectations with throughfall S fluxes increasing with elevation in the White Mountains, New Hampshire and throughfall S fluxes being greater in coniferous than deciduous stands in both sites. In contrast, throughfall N fluxes decreased significantly with elevation. Throughfall NO3 (-) fluxes were greater in coniferous than deciduous stands of Lye Brook, Vermont, but were greater in deciduous than coniferous stands of the White Mountains. We found overlap in the range of values for atmospheric N inputs between our measurements and monitoring data [National Atmospheric Deposition Program (NADP) and Clean Air Status and Trends Network (CASTNET)] for wet and total (wet + dry) deposition at Lye Brook. However, our measurements of total S deposition in the White Mountains and bulk (wet) deposition at both Lye Brook and the White Mountains were significantly lower than NADP plus CASTNET, and NADP data, respectively. Natural abundance (18)O in throughfall and bulk deposition were not significantly different, suggesting that there was no significant biological production of [Formula: see text] via nitrification in the canopy. NO3 (-) concentrations in streams were low and had natural abundance (18)O values consistent with microbial production, demonstrating that atmospheric N is being biologically transformed while moving through these watersheds and that these forested watersheds are unlikely to be N saturated. PMID:25407620

  3. A-site-deficiency effect on critical behavior in the Pr0.6Sr0.4MnO3 compound.

    PubMed

    Elleuch, F; Bekri, M; Hussein, M; Triki, M; Dhahri, E; Hlil, E K; Bessais, L

    2015-10-28

    We present the effect of vacancy in Pr0.6Sr0.4MnO3via dc magnetisation measurements. Using various techniques such as modified Arrott plots, the Kouvel-Fisher method, and Widom scaling relationship the values of TC (ferromagnetic transition temperature), as well as the β, γ and δ (critical exponents) are estimated. Critical exponents for the stoichiometric sample and the strontium deficient sample match well with those predicted for the tricritical mean field model. The vacancy in Pr0.5□0.1Sr0.4MnO3 changes the universal class. The estimated critical exponents of the praseodymium deficient sample are close to those found out by the 3D-Ising model. PMID:26395805

  4. Catchment nitrogen saturation drives ecological change in an alpine lake in SW China (eastern margin of Tibet)

    NASA Astrophysics Data System (ADS)

    Anderson, N. J.; Hu, Z.; Yang, X.; Zhang, E.

    2011-12-01

    There is substantial evidence for recent (last ca. 120 years) ecological change in remote arctic and alpine lakes (increased productivity, altered biological structure). Initially, these changes were attributed to global warming which has altered the heat budgets of these lakes (stronger stratification, longer ice free periods). The emphasis on temperature, however, ignores that global environmental change is driven by a range of multiple stressors (e.g. altered biogeochemical cycles, land cover change). One of the characteristics of the observed change in remote lakes is the expansion of small species of the planktonic diatom genus Cyclotella. It is increasingly obvious that the recent success of this diatom genus is driven by other factors (nutrients, light, mixing depth) as much as temperature. SE Asia is a major hotspot for the emission of reactive nitrogen as a result of intensive agriculture and fossil fuel combustion. In this study we report recent ecological change in a small, oligotrophic alpine lake (ShadeCo; altitude 4423 m) located in Sichuan Province (SW China), one of many relatively unstudied alpine lakes on the eastern margin of Tibet. The lake is located above the tree-line and there is no cultural land-use; the catchment vegetation is dominated by alpine shrub (predominantly Rhododendron). We used a multi-proxy palaeolimnological approach (diatom, geochemical and stable isotope analyses of a 210-Pb dated core) coupled with regional long-term climate data to understand the pronounced 20th century changes in the diatom record, notably an expansion of Cyclotella spp from around 1920. This initial increase is coincident with warming in SW China but the maximum Cyclotella abundance occurs in in the 1970s and 1980s, a period of regional cooling and major changes in catchment-lake biogeochemistry as indicated by geochemical analyses. The possible drivers of the observed changes (nitrogen deposition, temperature) at this site are discussed in the context

  5. 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).

  6. The effect of A-site substitution of Ce and La on the magnetic and electronic properties of Sr(Ti0.6Fe0.4)O(3-δ) films.

    PubMed

    Jiang, Peng; Bi, Lei; Sun, Xueyin; Kim, Dong Hun; Jiang, Daming; Wu, Gaohui; Dionne, G F; Ross, C A

    2012-12-17

    The structure and magnetic properties of epitaxial (Ce(x)Sr(1-x))(Ti(0.6)Fe(0.4))O(3-δ) (x = 0, 0.1, 0.2 and 0.3) and (La(x)Sr(1-x))(Ti(0.6)Fe(0.4))O(3-δ) (x = 0, 0.1, 0.2, 0.3 and 0.4) perovskite-structure thin films deposited by pulsed laser deposition on (LaAlO(3))(0.3)(Sr(2)AlTaO(6))(0.7) (LSAT) substrates are reported. Both La and Ce ions showed a dominant 3+ valence state and acted as donors on the Sr(2+) site (A site) in the perovskite lattice. The optical band gap widened, and the Fermi level moved toward the vacuum level with increased Ce or La content; meanwhile the Ti and particularly the Fe ions were driven to a lower valence state, resulting in a higher Fe(2+) concentration. The materials were magnetic at room temperature with up to 0.8 μ(B)/Fe and a magnetoelastic out-of-plane anisotropy. Ce and La lowered the coercivity while raising both the Faraday rotation at 1550 nm and the optical absorption at near-infrared wavelengths. PMID:23210609

  7. Bulk modulus and specific heat of B-site doped (La0.3Pr0.7)0.65Ca0.35Mn1-xBxO3 (B=Fe, Cr, Ru, Al, Ga)

    NASA Astrophysics Data System (ADS)

    Srivastava, Archana; Thakur, Rasna; Gaur, N. K.

    2014-04-01

    Specific heat (Cp) thermal expansion (α) and Bulk modulus (BT) of lightly doped Rare Earth manganites (La0.3Pr0.7)0.65Ca0.35Mn1-xBxO3 (B3+ = Fe3+,Cr3+,Ga3+,Al3+,Ru4+); (0.3site cation by other transition / Group IIIA elements of different size, mass and valence introduces large size and charge mismatch at B-site affecting the bulk modulus and thermal properties. Lattice specific heat (Cp)lat of (La0.3Pr0.7)0.65Ca0.35Mn0.97Fe0.03O3 as a function of temperature (10K≤T≤ 200K) is found to be in agreement with the published data. The trend of variation of Debye temperature with B-site cationic radius is predicted probably for the first time for the B-site doped rare earth manganites.

  8. Direct observation of B-site ordering in LSAT: (La0.3Sr0.7)(Al0.65Ta0.35)O3 single crystal

    NASA Astrophysics Data System (ADS)

    Okada, S.; Kobayashi, S.; Ohashi, K.; Nishikawa, N.; Tokunaga, T.; Sasaki, K.; Yamamoto, T.

    2016-06-01

    B-site atomic column regularity was directly observed in (La0.3Sr0.7)(Al0.65Ta0.35)O3 single crystals by Z-contrast imaging during high-angle annular dark-field scanning transmission electron microscopy. Two types of areas with different B-site regularity were found. One of the ordered structures, which was similar to a previously reported structure, was several tens of nanometers in size and had a rock salt-like regularity owing to variation in the B-site Al/Ta ratio. The other structure existed as disordered-like domains in the (La0.3Sr0.7)(Al0.65Ta0.35)O3 crystal. Fourier transform processing revealed that the disordered-like domains consisted of very fine ordered domains of several nanometers in size. These very fine ordered structures had a different B-site Al/Ta ratio variation with a rock salt-like regularity.

  9. 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. PMID:19793616

  10. Effect of Nb doping at Mn site on thermal expansion of Pr0.7Sr0.3MnO3

    NASA Astrophysics Data System (ADS)

    Rao, Ashok; Poornesh, P.; Wu, K. K.; Kuo, Y. K.; Agarwal, S. K.

    2013-10-01

    In this study we present results on effect of Nb doping on thermal expansion of Pr0.7Sr0.3MnO3. Thermal expansion measurements were done using three terminal capacitance method. The pure sample shows a jump at the insulator-metal (I-M) transition temperature, and with Nb doping, a fourfold decrease in the jump is found. Since thermal expansion is a bulk property, this suggests that the dopants are not in the form of local clusters; rather they are distributed uniformly throughout the sample. Temperature variation of Gruniesen ratio α/CP shows that for temperatures below I-M transition, the ratio is weakly dependent on temperature. Pressure dependence on the transition temperature, dTP/dP and jump in compressibility, Δβ, of these samples has been estimated using well-known Ehrenfest equations. The present results are in fairly good agreement with those reported in the literature.

  11. 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.

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

    PubMed

    Tsuchiya, Jun; Tsuchiya, Taku

    2008-12-01

    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. PMID:19036928

  13. 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.

  14. Effect of A - Site disorder on the bonding mechanism and optical properties of Smx(Al2O3)1-x system

    NASA Astrophysics Data System (ADS)

    Wahab, Hassan

    2016-01-01

    Samples of varying samarium (Sm) concentration doped alumina (Al2O3) were prepared by the solid state reaction method and were characterized using x-ray diffraction and Raman spectroscopy for phase identification and local structural disorder respectively. The lattice disorder induced by varying composition and the enhancement of Raman intensities in the lower wavenumber side confirms the successful incorporation of dopant ions into the host matrix. The addition of dopant ions changes the unit cell volume and crystal structure to orthorhombic with Pbnm symmetry. The extent of non-bridging oxygen atoms vary with increasing dopant concentration, which shows the varying covalent character of the titled material. This is believed to induce a substantial destabilization in the octahedral environment leading to the tilting and bending of the BO6 octahedra. UV-vis diffuse reflectance spectroscopy data analysis confirms that changing covalent character of the material induced by the destabilization in the octahedral environment. The optical band gap energy decreases, while the Urbach energy decreases with increasing non-bridging oxygen atoms.

  15. 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.

  16. Microwave property improvement of Ca[(Li1/3Nb2/3)0.95Zr0.15]O3+δ perovskite by A-site substitution

    NASA Astrophysics Data System (ADS)

    Hu, Mingzhe; Xiong, Gang; Ding, Zhao

    2016-04-01

    The crystal structure and microwave dielectric properties of Ca[(Li1/3Nb2/3)0.95Zr0.15]O3+δ ceramic (CLNZ) are tuned by A-site substitution of Sr2+ and Ba2+ ions in the present paper. The tuning effect on the crystal structure is investigated by the X-ray diffraction (XRD) pattern and it illustrates that single phase of orthorhombic perovskite structure is formed, however, minor amount of BaNb2O6-type second phase is also detected in (Ca1‑xBax)[(Li1/3Nb2/3)0.95Zr0.15]O3+δ ceramics (CBLNZ) in the range of x ≥ 0.025, while pure perovskite phase is obtained in (Ca1‑xSrx)[(Li1/3Nb2/3)0.95Zr0.15]O3+δ ceramics (CSLNZ) in the whole investigation range of 0 ≤ x ≤ 0.2. With the increase of x value, the unit cell volumes of both CBLNZ and CSLNZ perovskites gradually expand, which results in the degradation of the vibration bond strength between the B-site ions and oxygen in the perovskites. The microscopic structure related thermal parameters in CSLNZ and CBLNZ perovskites are analyzed in terms of Clausius-Mossotti equation to reveal the original contributors in the temperature coefficients. The results show that both Sr2+ and Ba2+ substitution can effectively improve the permittivity and Qf value, especially, improve the temperature coefficient of CLNZ ceramic in a certain range.

  17. 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

    2016-02-01

    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 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. PMID:26742465

  18. 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.

  19. 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.

  20. Effects of site substitutions and concentration on the structural, optical and visible photoluminescence properties of Er doped BaTiO3 thin films prepared by RF magnetron sputtering

    NASA Astrophysics Data System (ADS)

    Maneeshya, L. V.; Thomas, P. V.; Joy, K.

    2015-08-01

    The structural, optical and visible photoluminescence of the Erbium (Er) doped BaTiO3 (BT:Er) thin films were studied in terms of Er3+ substitutions for Ba and Ti sites with different Er3+ doping concentrations (0, 1, 3 and 5 wt%). X-ray diffraction pattern of BT:Er films with different Er3+ concentration showed tetragonal phase with preferred orientation along (1 0 1) plane. The lattice constant of BT:Er film of 1 wt% Er3+ shrank and then expanded for higher concentration. This indicates that Er3+ ions are completely incorporated into the host lattice by substituting for Ba2+ sites for 1 wt% Er3+ and then Ti4+ sites for higher Er3+ concentration in the BaTiO3 host. The crystallite size decreased for 1 wt% and then increased for higher Er (3 and 5 wt%) concentrations. The Scanning electron microscopy images revealed well patterned arrangement of larger spherical grains with neck formation. X-ray photoelectron spectroscopy analysis confirmed the presence of barium, titanium, erbium and oxygen in BT:Er films. An average transmittance >80% in visible region were observed for all the films. Optical band gap energy of BT:Er films were found to vary with increase in Er3+ concentration. The high refractive index >2 of these films can be used in optical application and anti-reflection coatings. Photoluminescence spectra of the films exhibited an increase in the emission intensity up to 3 wt% of Er3+ and then a decrease, due to self quenching. The improved optical properties of BT:Er films makes suitable for optical applications.

  1. Remarkable Strontium B-Site Occupancy in Ferroelectric Pb(Zr(1-X)Ti(X))O(3) Solid Solutions Doped With Cryolite-Type Strontium Niobate

    SciTech Connect

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

    2009-06-03

    New high-performance ferroelectric solid solutions based on Pb(Zr{sub 1-x}Ti{sub x})O{sub 3} (PZT), which 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 O;1-y} with 0{<=}y{<=}1) and hence denoted PZT:SNO, and their microscopic structure and defect chemistry are described. Extended X-ray absorption fine-structure (EXAFS) analyses of PZT:SNO samples revealed that -10% of Sr{sup 2+} occupy the nominal B-sites of the perovskite-type PZT host lattice. This result is 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{sup 2+} on B-sites are ruled out. A clear Sr-Pb peak in Fourier-transformed EXAFS data visually confirms 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 material properties of PZT:SNO. As a result, ferroelectric PZT:SNO solid solutions are very attractive for use in new and innovative piezoelectric actuator and transducer applications.

  2. 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.

  3. Effect of A-site La and Ba doping on threshold field and characteristic temperatures of PbSc0.5Ta0.5O3 relaxor studied by acoustic emission

    NASA Astrophysics Data System (ADS)

    Dul'kin, E.; Mihailova, B.; Gospodinov, M.; Roth, M.

    2012-09-01

    The structural transitions in Pb1-xLaxSc(1+x)/2Ta(1-x)/2O3, x = 0.08 (PLST) relaxor crystals were studied by means of acoustic emission (AE) under an external electric field (E) and compared with those observed in pure PbSc0.5Ta0.5O3 (PST) and Pb0.78Ba0.22Sc0.5Ta0.5O3 (PBST) [E. Dul'kin et al., EPL 94, 57002 (2011)]. Similar to both the PST and PBST compounds, in zero field PLST exhibits AE corresponding to a para-to-antiferroelectric incommensurate phase transition at Tn = 276 K, lying in the vicinity of dielectric temperature maximum (Tm). This AE signal exhibits a nontrivial behavior when applying E resembling the electric-field-dependence of Tn previously observed for both the PST and PBST, namely, Tn initially decreases with the increase of E, attains a minimum at a threshold field Eth = 0.5 kV/cm, accompanied by a pronounced maximum of the AE count rate Ṅ = 12 s-1, and then starts increasing as E enhances. The similarities and difference between PST, PLST, and PBST with respect to Tn, Eth, and Ṅ are discussed from the viewpoint of three mechanisms: (i) chemically induced random local electric field due to the extra charge on the A-site ion, (ii) disturbance of the system of stereochemically active lone-pair electrons of Pb2+ by the isotropic outermost electron shell of substituting ion, and (iii) change in the tolerance factor and elastic field to the larger ionic radius of the substituting A-site ion due to the different radius of the substituting ion. The first two mechanisms influence the actual values of Tn and Eth, whereas the latter is shown to affect the normalized Ṅ, indicating the fractions undergoing a field-induced crossover from a modulated antiferroelectric to a ferroelectric state. Creation of secondary random electric field, caused by doping-induced A-site-O ionic chemical bonding, is discussed.

  4. Co-ordinatively Unsaturated Al3+ Centers as Binding Sites for Active Catalyst Phases of Platinum on -Al2O3

    SciTech Connect

    Kwak, Ja Hun; Hu, Jiangzhi; Mei, Donghei; Yi, Cheol-Woo; Kim, Do Heui; Peden, Charles; Allard Jr, Lawrence Frederick; Szanyi, Janos

    2009-01-01

    In many heterogeneous catalysts, the interaction of metal particles with their oxide support can alter the electronic properties of the metal and can play a critical role in determining particle morphology and maintaining dispersion. We used a combination of ultrahigh magnetic field, solid-state magic-angle spinning nuclear magnetic resonance spectroscopy, and high-angle annular dark-field scanning transmission electron microscopy coupled with density functional theory calculations to reveal the nature of anchoring sites of a catalytically active phase of platinum on the surface of a {gamma}-Al{sub 2}O{sub 3} catalyst support material. The results obtained show that coordinatively unsaturated pentacoordinate Al{sup 3+} (Al{sub penta}{sup 3+}) centers present on the (100) facets of the {gamma}-Al{sub 2}O{sub 3} surface are anchoring Pt. At low loadings, the active catalytic phase is atomically dispersed on the support surface (Pt/Al{sub penta}{sup 3+} = 1), whereas two-dimensional Pt rafts form at higher coverages.

  5. The A-site driven phase transition procedure of (Pb0.97La0.02)(Zr0.42Sn0.40Ti0.18)O3 ceramics: An evidence from electronic structure variation

    NASA Astrophysics Data System (ADS)

    Chen, X.; Jiang, P. P.; Duan, Z. H.; Hu, Z. G.; Chen, X. F.; Wang, G. S.; Dong, X. L.; Chu, J. H.

    2013-11-01

    The transition of (Pb0.97La0.02)(Zr0.42Sn0.40Ti0.18)O3 (PLZST) ceramic has been investigated by temperature-dependent X-ray diffraction (XRD) and spectroscopic ellipsometry (SE). The rhombohedral and tetragonal symmetries are confirmed by XRD analysis. Two interband transitions (Ecp1 and Ecp2) located at about 3.7 and 5.2 eV can be derived from the second derivative of the complex dielectric functions using the standard critical point (SCP) model. Except for the negative temperature coefficient parts, the transitions present additional parts corresponding to appearance of the antiferroelectric (AFE) phase. The phenomena can be attributed to variation of the electronic structure during A-site driven phase transition.

  6. Effect of Ionic Radius of the A Site on EPR Line in Paramagnetic and Ferromagnetic Phase of La0.7- xRxCa0.3MnO3

    NASA Astrophysics Data System (ADS)

    Rao, G. Narsinga; Babu, Y.; Sastry, M. D.; Babu, D. Suresh

    The effects of partial substitution of La by a smaller Lanthanide element (R) in La0.7-xRxCa0.3MnO3 (R=Ce, Pr, Nd Sm, Gd, Dy with x=0 and 0.1) ceramic pellets on the electron paramagnetic resonance has been investigated. The line width increased with decrease in ionic radius of the A site in paramagnetic phase, which is explained on the basis of tolerance factor. The observed increase in g-value and line width with increase in in ferromagnetic phase explained qualitatively by Mn-O-Mn bond angle distortion and Mn-O orbital overlap which in turn is governed by the size of the substitution ion.

  7. 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.

  8. 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.

  9. 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.

  10. 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

  11. 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

    2015-10-01

    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. PMID:26381280

  12. 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.

  13. Magnetic properties of Fe substituted SrRuO3 thin films and SrRuO3/Fe2O3 superlattices

    NASA Astrophysics Data System (ADS)

    Chmaissem, Omar; Kolesnik, Stanislaw; Dabrowski, Bogdan; Choi, Yongseong; Haskel, Daniel

    2010-03-01

    In recent years, SrRuO3 thin films have received considerable interest because of their potential for use as electrodes in oxide-based spintronic applications. SrRuO3 bulk materials are known to exhibit good room temperature thermal and electrical conductivity, a stable perovskite crystal structure, and itinerant ferromagnetic properties at temperatures below 163 K. To the best of our knowledge, attempts to enhance the magnetic properties of SrRuO3 through chemical substitutions of transition metal elements (e.g., Fe, Co, Mn, Cu, Zn, Ti, Cr, etc) at the Ru site, all failed except for the case of Cr substitutions in which TC was successfully raised to 190 K. In this work, we will demonstrate the drastically different effects of Fe on the magnetic properties of SrRuO3 bulk materials and thin films. We will also show and discuss the magnetic properties of SrRuO3/Fe2O3 superlattices. Work supported by the NSF (DMR-0706610) and the DOE-Office of Science (DEAC-02-06CH11357).

  14. 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.

  15. Phonons in La-Substituted BiFeO3-PbTiO3

    NASA Astrophysics Data System (ADS)

    Mishra, K. K.; Sivasubramanian, V.; Sarguna, R. M.; Ravindran, T. R.; Arora, A. K.

    2010-12-01

    (Bi1-xLax)0.5Pb0.5Fe0.5Ti0.5O3 (BF-PT) ceramics were prepared for x = 0.0, 0.2, 0.3, 0.4 and 0.5 using solid state reaction method. x = 0.0 samples were found to have tetragonal perovskite structure, same as that of PbTiO3 (PT), while in La-substituted samples tetragonal distortion reduced and system turned cubic at 40% La-concentration. Raman spectroscopic investigations reveal 10 modes in pure BF-PT which were assigned by comparing with those in PT. Although in the cubic phase no Raman active phonons are expected, 7 modes are found that have correspondence with those of the tetragonal phase. The modes in the cubic phase are activated due to substitutional disorder at cation site.

  16. 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.

  17. Structural properties of Ge on SrTiO3 (001) surface and Ge/SrTiO3 interface

    NASA Astrophysics Data System (ADS)

    Pu, Long; Wang, Jianli; Tang, Gang; Zhang, Junting

    2015-03-01

    Germanium-perovskite oxide heterostructures have a strong potential for next-generation low-voltage and low-leakage metal-oxide semiconductor field-effect transistors. We investigated the atomic structure and electronic properties of Ge on perfect and defective (001) SrTiO3 by first-principle calculations. The specific adsorption sites at the initial growth stage and the atomic structure of Ge on the SrTiO3 (001) substrate have been systematically investigated. The surface grand potential was calculated and compared as a function of the relative chemical potential. The complete surface phase diagram was presented. The energetically favorable interfaces were pointed out among the atomic arrangements of the Ge/SrTiO3 (001) interfaces. The atomic structure and electronic properties of the intrinsic point defects were calculated and analyzed for the Ge/SrTiO3 (001) interfaces.

  18. 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.

  19. Ferromagnetic CaRuO3

    PubMed Central

    Tripathi, Shivendra; Rana, Rakesh; Kumar, Sanjay; Pandey, Parul; Singh, R. S.; Rana, D. S.

    2014-01-01

    The non-magnetic and non-Fermi-liquid CaRuO3 is the iso-structural analog of the ferromagnetic (FM) and Fermi-liquid SrRuO3. We show that an FM order in the orthorhombic CaRuO3 can be established by the means of tensile epitaxial strain. The structural and magnetic property correlations in the CaRuO3 films formed on SrTiO3 (100) substrate establish a scaling relation between the FM moment and the tensile strain. The strain dependent crossover from non-magnetic to FM CaRuO3 was observed to be associated with switching of non-Fermi liquid to Fermi-liquid behavior. The intrinsic nature of this strain-induced FM order manifests in the Hall resistivity too; the anomalous Hall component realizes in FM tensile-strained CaRuO3 films on SrTiO3 (100) whereas the non-magnetic compressive-strained films on LaAlO3 (100) exhibit only the ordinary Hall effect. These observations of an elusive FM order are consistent with the theoretical predictions of scaling of the tensile epitaxial strain and the magnetic order in tensile CaRuO3. We further establish that the tensile strain is more efficient than the chemical route to induce FM order in CaRuO3. PMID:24464302

  20. Structural investigations of (Ca,Sr)ZrO3 and Ca(Sn,Zr)O3 perovskite compounds

    NASA Astrophysics Data System (ADS)

    Tarrida, Martine; Larguem, H.; Madon, M.

    2009-07-01

    (Ca x ,Sr1- x )ZrO3 and Ca(Sn y ,Zr1- y )O3 solid solutions were synthesized by solid-state reaction at high temperature before to be studied by powder X-ray diffraction and Raman Spectroscopy. Diffraction data allow the distortion of the ABO3 perovskite structure to be investigated according to cations substitution on A and B-sites. It is shown that distortion, characterized by Φ, the tilt angle of BO6 octahedra, slightly increases with decreasing y content in Ca(Sn y ,Zr1- y )O3 compounds and strongly decreases with decreasing x content in (Ca x ,Sr1- x )ZrO3 compounds. Such results are discussed in view of the relative A and B cation sizes. Raman data show that vibrational spectra are strongly affected by the cation substitution on A-site; the frequencies of most vibrational modes increase with increasing x content in (Ca x ,Sr1- x )ZrO3 compounds, i.e. with the decreasing mean size of the A-cation; the upper shift is observed for the 358 cm-1 mode (∂ ν/∂r = -60.1 cm-1/Å). On the other hand, the cation substitution on B-sites, slightly affect the spectra; it is shown that in most cases, the frequency of vibrational modes increases with increasing y content in Ca(Sn y ,Zr1- y )O3 compounds, i.e. with the decreasing mean size of the B-cation, but that two modes (287 and 358 cm-1) behave differently: their frequencies decrease with the decreasing mean size of the B-cation, with a shift respectively equal to +314 and +162 cm-1/Å. Such results could be used to predict the location of different elements such as trivalent cations or radwaste elements on A- or B-site, in the perovskite structure.

  1. 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.

  2. EPR Theoretical Study of the Local Lattice Structure of Fe3+ Doped in MgTiO3 and LiTaO3

    NASA Astrophysics Data System (ADS)

    Pan, Lei-Lei; Kuang, Xiao-Yu; Li, Guang-Dong; Wang, Hui

    2007-02-01

    The EPR zero-field splittings of Fe3+ doped in MgTiO3 and LiTaO3 are studied by diagonalizing the complete energy matrices of the electron-electron repulsion, ligand-field and spin-orbit coupling interactions for a d5 configuration ion in a trigonal ligand-field. It is shown that, when Fe3+ is doped in aMgTiO3 or LiTaO3 crystal, the local lattice structure around the octahedral Fe3+ center has an obvious distortion along the C3 axis. By simulating the second- and fourth-order EPR parameters D and (a-F) simultaneously, the local structure parameters of Fe3+ doped inMgTiO3 and LiTaO3 crystals are determined, which reveal that Fe3+ occupies both the Mg2+ and Ti4+ sites in the MgTiO3:Fe3+ system and occupies the Li+ site rather than the Ta5+ site in the LiTaO3:Fe3+ system. The results accord with the ENDOR and EPR experiments. - PACS numbers: 71.70.Gm; 75.30.Et; 71.70.Ch.

  3. Tailoring LaAlO3/SrTiO3 Interface Metallicity by Oxygen Surface Adsorbates.

    PubMed

    Dai, Weitao; Adhikari, Sanjay; Garcia-Castro, Andrés Camilo; Romero, Aldo H; Lee, Hyungwoo; Lee, Jung-Woo; Ryu, Sangwoo; Eom, Chang-Beom; Cen, Cheng

    2016-04-13

    We report an oxygen surface adsorbates induced metal-insulator transition at the LaAlO3/SrTiO3 interfaces. The observed effects were attributed to the terminations of surface Al sites and the resultant electron-accepting surface states. By controlling the local oxygen adsorptions, we successfully demonstrated the nondestructive patterning of the interface two-dimensional electron gas (2DEG). The obtained 2DEG structures are stable in air and also robust against general solvent treatments. This study provides new insights into the metal-insulator transition mechanism at the complex oxide interfaces and also a highly efficient technique for tailoring the interface properties. PMID:26928809

  4. Direction-dependent RBS channelling studies in ion implanted LiNbO3

    NASA Astrophysics Data System (ADS)

    Wendler, E.; Becker, G.; Rensberg, J.; Schmidt, E.; Wolf, S.; Wesch, W.

    2016-07-01

    Damage formation in ion implanted LiNbO3 was studied by Rutherford backscattering spectrometry (RBS) along various directions of the LiNbO3 crystal. From the results obtained it can be unambiguously concluded that Nb atoms being displaced during ion implantation preferably occupy the free octahedron sites of the LiNbO3 lattice structure and most likely also form NbLi antisite defects.

  5. Effect of cation substitution at the B site on the oxygen semi-permeation flux in La0.5Ba0.5Fe0.7B0.3O3-δ dense perovskite membranes with B = Al, Co, Cu, Mg, Mn, Ni, Sn, Ti and Zn (part II)

    NASA Astrophysics Data System (ADS)

    Reichmann, M.; Geffroy, P.-M.; Fouletier, J.; Richet, N.; Del Gallo, P.; Chartier, T.

    2015-03-01

    The aim of this paper is to provide insight into the effect of cation substitution at the B site on the oxygen semi-permeation performances. Particular attention is given here to identify the impact of cation substitution at the B site on oxygen diffusion and oxygen surface-exchange kinetics in the La0.5Ba0.5Fe0.7B0.3O3-δ perovskite membrane series with B = Al, Co, Cu, Mg, Mn, Ni, Sn, Ti and Zn. This study clearly shows that the prediction of the oxygen semi-permeation performances of membrane materials from the nature of cation at the A or B sites in perovskite structure is quite complex. The cation substitution at the B-site has a low impact on the nature of rate-determining step and a significant impact on oxygen semi-permeation performances, contrary to the cation substitution at A-site. Unfortunately, it is not possible to establish a relevant trend about the effect of the nature of cation in the A or B sites in perovskite structure on oxygen diffusion and the oxygen surface-exchange kinetics.

  6. 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.

  7. 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

    2015-01-01

    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+) 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. PMID:26272264

  8. 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

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

    NASA Astrophysics Data System (ADS)

    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.

    2015-08-01

    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.

  10. Hyperfine interaction measurements in LaCrO3 and LaFeO3 perovskites using perturbed angular correlation spectroscopy

    NASA Astrophysics Data System (ADS)

    Dogra, R.; Junqueira, A. C.; Saxena, R. N.; Carbonari, A. W.; Mestnik-Filho, J.; Moralles, M.

    2001-06-01

    The perturbed angular correlation (PAC) technique was used to study the hyperfine interactions in the antiferromagnetic and paramagnetic regions of the distorted perovskites LaCrO3 and LaFeO3. The dilute 111In-->111Cd nuclear probes were introduced into the samples through a chemical process. The present measurements cover the temperature ranges from 15 to 848 K for LaCrO3 and 77 to 1324 K for LaFeO3. Two distinct electric-quadrupole interactions were observed in each compound. The lower quadrupole frequency was assigned to the transition-metal atom site while the higher frequency was attributed to the lanthanum site in both cases. Temperature dependence of the electric-quadrupole interaction parameters indicated structural phase transitions at around 512 and 1223 K, respectively, in LaCrO3 and LaFeO3. The phase transitions were associated with the change from an orthorhombic to rhombohedral structure and characterized by a sudden increase in the electric field gradient Vzz and a decrease in the asymmetry parameter η for both sites. PAC spectra measured below the Néel temperature revealed that at 0 K the supertransferred magnetic hyperfine field on 111Cd at the Cr site in LaCrO3 (2.4 T) is much smaller than at the Fe site in LaFeO3 (19.4 T). The magnetic field on 111Cd at La sites in both compounds is of the order of 0.3 T. Additional measurements were made to determine the magnetic hyperfine field using the probe nucleus 140La-->140Ce. The result reconfirmed that a relatively weak hyperfine field is supertransferred to the probe atoms at La sites.

  11. Excellent ethanol sensing properties based on Er2O3-Fe2O3 nanotubes

    NASA Astrophysics Data System (ADS)

    Liu, Chang-Bai; He, Ying; Wang, Sheng-Lei

    2015-11-01

    In this work, pure α-Fe2O3 and Er2O3-Fe2O3 nanotubes were synthesized by a simple single-capillary electrospinning technology followed by calcination treatment. The morphologies and crystal structures of the as-prepared samples were characterized by scanning electron microscopy and x-ray diffraction, respectively. The gas-sensing properties of the as-prepared samples have been researched, and the result shows that the Er2O3-Fe2O3 nanotubes exhibit much better sensitivity to ethanol. The response value of Er2O3-Fe2O3 nanotubes to 10 ppm ethanol is 21 at the operating temperature 240°, which is 14 times larger than that of pure α-Fe2O3 nanotubes (response value is 1.5). The ethanol sensing properties of α-Fe2O3 nanotubes are remarkably enhanced by doping Er, and the lowest detection limit of Er2O3-Fe2O3 nanotubes is 300 ppb, to which the response value is about 2. The response and recovery times are about 4 s and 70 s to 10 ppm ethanol, respectively. In addition, the Er2O3-Fe2O3 nanotubes possess good selectivity and long-term stability. Project supported by Jilin Provincial Science and Technology Department, China (Grant No. 20140204027GX) and the Challenge Cup for College Students, China (Grant No. 450060497053).

  12. Dependence of catalytic properties of Al/Fe2O3 thermites on morphology of Fe2O3 particles in combustion reactions

    NASA Astrophysics Data System (ADS)

    Zhao, Ningning; He, Cuicui; Liu, Jianbing; Gong, Hujun; An, Ting; Xu, Huixiang; Zhao, Fengqi; Hu, Rongzu; Ma, Haixia; Zhang, Jinzhong

    2014-11-01

    Three Fe2O3 particle samples with the same crystal structure but different morphologies were prepared by the hydrothermal method and then combined with Al nanoparticles to produce Al/Fe2O3 thermites using ultrasonic mixing. The properties of Fe2O3 and Al/Fe2O3 were studied using a combination of experimental techniques including scanning electron microscopy (SEM), energy dispersive spectrometer (EDS), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and differential scanning calorimetry (DSC). The influences of the three Al/Fe2O3 thermites on the combustion properties of the AP/HTPB (ammonium perchlorate/hydroxyl-terminated polybutadiene) composite propellant were investigated in comparison to those of Fe2O3. The results show that the Al/Fe2O3 thermites are better than Fe2O3 in enhancing the combustion performance of AP/HTPB. Furthermore, the surface area, which depends on size and mophology, of Fe2O3 particles was found to play a vital role in improving the burning rate of the thermites-containing propellant formulation, with the smallest particles with the largest surface-to-volume (S/V) ratio performing the best. The enhanced catalytic property of the granular-shape Fe2O3 and the corresponding thermite is attributed to the large specific surface area of Fe2O3. The different thermal behaviors of these three superthemites were supposed to be attributed to the surface site of Fe2O3 particles. This work provides a better understanding on the catalytic properties of thermites that are important for combustion applications.

  13. Muonium Diffusion in In2O3

    NASA Astrophysics Data System (ADS)

    Baker, Brittany; Lichti, Roger; Celebi, Y. Gurkan; Mengyan, Patrick

    2015-03-01

    Indium oxide (In2O3) is a transparent conducting oxide (TCO) commonly found in mixtures used as windows and transparent electrodes in optical semiconductor devices (i.e. LEDs and solar cells). Hydrogen diffusion in the TCO layer and across the interface between the TCO and the semiconductor device plays an important role in the degradation of the transparency of TCO windows or electrodes. Theoretical calculations show positive H as the only stable, interstitial H charge state above the neutral H ionization temperature. Muon Spin Relaxation measurements were performed to investigate positive muon (Mu+) diffusion which are an experimentally accessible analog to H+. Three distinct Mu+ states are identified between 2 K and 1000 K; a static low temperature state, a dynamic state above room temperature, and a trapping state from 400 K to 800 K. The trap component creates complex dynamics and has been modeled assuming the Mu+ transfers between the dynamic state and the trapping state. Fits of the model to the data provide information about capture and release rates and energy barriers into and out of the trap state. Here we present and discuss results from these fits, possible site locations for each state and likely diffusion paths.

  14. B-site Mo-doped perovskite Pr0.4Sr0.6 (Co0.2Fe0.8)1-xMoxO3-σ (x = 0, 0.05, 0.1 and 0.2) as electrode for symmetrical solid oxide fuel cell

    NASA Astrophysics Data System (ADS)

    Zhang, Peng; Guan, Guoqing; Khaerudini, Deni S.; Hao, Xiaogang; Xue, Chunfeng; Han, Minfang; Kasai, Yutaka; Abudula, Abuliti

    2015-02-01

    Pr0.4Sr0.6(Co0.2Fe0.8)1-xMoxO3-σ (PSCFMx, x = 0, 0.05, 0.1 and 0.2), which obtained by doping molybdenum at the B site of Pr0.4Sr0.6Co0.2Fe0.8O3-σ (PSCF) cathode, have been synthesized by a solid state reaction method and studied towards the application as symmetrical electrode materials for symmetrical SOFCs (SSOFCs) in this study. It is found that cubic perovskite phase of PSCFM in the Pm/3 m space group is formed after sintered at 1100 °C for PSCFMx (x = 0, 0.05 and 0.1) samples, and the main phase is converted to K2NiF4 structure identified as SrPrFeO4 in the I4/m space group, and some new phases of Pr2O3 and CoFe-alloy appear after PSCFMx is heat-treated in dry H2 at 900 °C for 2 h. The K2NiF4 structure SrPrFeO4 can be transferred to a pure cubic structure of PSCFMx again by calcining it in air at 900 °C. The maximum power densities of a single SSOFC based on the PSCFM0.05 symmetrical electrode, which shows the lowest polarization resistances (Rp), are 493 and 160 mW cm-2 at 850 °C in H2 and CH4, respectively. No obvious degradation is observed during a 100 h stability test in CH4, which suggests that PSCFM material is a potential symmetrical electrode for SSOFCs.

  15. Mössbauer and magnetic studies of bulk and fine-powder SrRu O3 and Sr-Cu-Ru O3 systems

    NASA Astrophysics Data System (ADS)

    Felner, Israel; Nomura, Kiyoshi; Nowik, Israel

    2006-02-01

    SrRuO3 is a ferromagnet, TC=165K . Due to difference in grain sizes, ceramic bulk and fine-powder (prepared by the sol-gel procedure) of SrRuO3 , have different coercive fields. The Fe57 doped Mössbauer effect spectra (MS) of powder SrRuO3 exhibit distinct magnetic hyperfine sextets up to TC , while none is observed at 90K in the bulk material. This is probably a result of the fact that the Fe57 probe resides in the Sr and Ru sites for powder and bulk SrRuO3 , respectively. Due to the shorter Sr-Ru distance, the Fe57 ions in the Sr site are exposed to an exchange field from the Ru magnetically ordered ions, much more than the iron in the Ru site. The Fe57 MS spectra of Sr1-xCuxRuO3 and SrRu1-yCuyO3 systems behave similarly to powder and bulk SrRuO3 , respectively. The magnetic properties of the two systems are discussed. The above results served as the basic explanation for the peculiar magnetic behavior of the magneto superconducting RuEu1.5Ce0.5Sr2Cu2O10 in the temperature range 90-165K .

  16. Growth and optical properties of Mg, Fe Co-doped LiTaO3 crystal

    NASA Astrophysics Data System (ADS)

    Fang, Shuangquan; Ma, Decai; Zhang, Tao; Ling, Furi; Wang, Biao

    2006-02-01

    Mg, Fe double-doped LiTaO3 and LiNbO3 crystals have been grown by Czochralski method. The optical properties were measured by two-beam coupling experiments and transmitted facula distortion method. The results showed that the photorefractive response speed of Mg:Fe:LiTaO3 was about three times faster than that of Fe:LiTaO3, whereas the photo-damage resistance was two orders of magnitude higher than that of Fe:LiTaO3. In this paper, site occupation mechanism of impurities was also discussed to explain the high photo-damage resistance and fast response speed in Mg:Fe:LiTaO3 crystal.

  17. The influence of local circulations on vertical profiles of NO2 and O3 at semi-rural sites during DISCOVER-AQ campaigns in California, Texas, and Colorado

    NASA Astrophysics Data System (ADS)

    Stein Zweers, D. C.; Pickering, K. E.; Clark, R. D.; Weinheimer, A. J.; Flynn, C.; Mazzuca, G.; Spinei, E.

    2014-12-01

    Through use of the Millersville University tethersonde balloon an NO2-sonde, developed at the Royal Netherlands Meteorological Institute (KNMI), profiled the lower boundary layer as part of the larger NASA Earth Venture program funded mission. This campaign known as DISCOVER-AQ stands for 'Deriving Information on Surface Conditions from Column and Vertically Resolved Observations Relevant to Air Quality'. Recent results from the California, Texas, and Colorado deployments of DISCOVER-AQ highlight the importance of semi-continuous, daytime measurement of the vertical distribution of ozone and NO2 in the lower boundary layer. The balloon profiles, typically from the surface to 500m above ground level, fill an important gap between surface measurements and the lowest extent of aircraft measurements. This near-surface region of the atmosphere is highly variable and local circulation features including land-sea breezes and mountain-valley breezes were observed. These circulations altered local transport patterns and led to changes in the chemical regime at each site. These processes were especially apparent at Smith Point, Texas during an extreme pollution event on 25 September 2013. The extent to which these local circulations influenced diurnal variation and vertical distribution of NO2 and ozone is evaluated and compared for each semi-rural site using wind direction and other meteorological data. NO2-sonde profile data is compared to ground station trace gas analyzers and where available, column and profile measurements from PANDORA spectrometer instruments. These data measured in the segment of the near-surface atmosphere most critical for human health are unique and crucial for validation of satellite columns and atmospheric chemical models.

  18. 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.

  19. Two-dimensional conductivity at LaAlO3/SrTiO 3 interfaces

    NASA Astrophysics Data System (ADS)

    Raslan, Amany

    Experiments have observed a two-dimensional electron gas at the interface of two insulating oxides: strontium titanate (SrTiO3) and lanthanum aluminate (LaAlO3). These interfaces exhibit metallic, superconducting, and magnetic behaviours, which are strongly affected by impurities. Motivated by experiments, we introduce a simple model in which impurities lie at the interface. We treat the LaAlO3 as an insulator and model the SrTiO 3 film. By solving a set of self-consistent Hartree equations for the charge density, we obtain the band structure of the SrTiO3 film. We then study the relative contributions made by the occupied bands to the two-dimensional conductivity of the LaAlO3/SrTiO 3 interface. We find that the fractional conductivity of each band depends on several parameters: the mass anisotropy, the filling, and the impurity potential.

  20. Ferroelectric properties of RbNbO3 and RbTaO3

    NASA Astrophysics Data System (ADS)

    Lebedev, A. I.

    2015-02-01

    Phonon spectra of cubic rubidium niobate and rubidium tantalate with the perovskite structure are calculated from first principles within the density functional theory. Based on the analysis of unstable modes in phonon spectra, symmetries of possible distorted phases are determined, their energies are calculated, and it is shown that R3 m is the ground-state structure of RbNbO3. In RbTaO3, the ferroelectric instability is suppressed by zero-point lattice vibrations. For ferroelectric phases of RbNbO3, spontaneous polarization, piezoelectric, nonlinear optical, electro-optical, and other properties as well as the energy band gap in the LDA and GW approximations are calculated. The properties of rhombohedral RbNbO3 are compared with those of rhombohedral KNbO3, LiNbO3, and BaTiO3.

  1. Spectral Weight Redistribution in (LaNiO3)n/(LaMnO3)2 Superlattices from Optical Spectroscopy.

    PubMed

    Di Pietro, P; Hoffman, J; Bhattacharya, A; Lupi, S; Perucchi, A

    2015-04-17

    We have studied the optical properties of four (LaNiO3)n/(LaMnO3)2 superlattices (SL) (n=2,3,4,5) on SrTiO3 substrates. We have measured the reflectivity at temperatures from 20 to 400 K, and extracted the optical conductivity through a fitting procedure based on a Kramers-Kronig consistent Lorentz-Drude model. With increasing LaNiO3 thickness, the SLs undergo an insulator-to-metal transition (IMT) that is accompanied by the transfer of spectral weight from high to low frequency. The presence of a broad midinfrared band, however, shows that the optical conductivity of the (LaNiO3)n/(LaMnO3)2 SLs is not a linear combination of the LaMnO_{3} and LaNiO3 conductivities. Our observations suggest that interfacial charge transfer leads to an IMT due to a change in valence at the Mn and Ni sites. PMID:25933327

  2. 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.

  3. Excellent performance of gas sensor based on In2O3-Fe2O3 nanotubes

    NASA Astrophysics Data System (ADS)

    Li, Liu; Shouchun, Li; Xin, Guo; Yue, He; Lianyuan, Wang

    2016-01-01

    In2O3-Fe2O3 nanotubes are synthesized by an electrospinning method. The as-synthesized materials are characterized by scanning electron microscope and X-ray powder diffraction. The gas sensing results show that In2O3-Fe2O3 nanotubes exhibit excellent sensing properties to acetone and formaldehyde at different operating temperatures. The responses of gas sensors based on In2O3-Fe2O3 nanotubes to 100 ppm acetone and 100 ppm formaldehyde are 25 (240 °C) and 15 (260 °C), and the response/recovery times are 3/7 s and 4/7 s, respectively. The responses of In2O3-Fe2O3 nanotubes to 1 ppm acetone (240 °C) and formaldehyde (260 °C) are 3.5 and 1.8, respectively. Moreover, the gas sensor based on In2O3-Fe2O3 nanotubes also possesses an excellent selectivity to acetone and formaldehyde. Project supported by the Jilin Provincial Science and Technology Department (No. 20140204027GX).

  4. The remarkable enhancement of CO-pretreated CuO-Mn2O3/γ-Al2O3 supported catalyst for the reduction of NO with CO: the formation of surface synergetic oxygen vacancy.

    PubMed

    Li, Dan; Yu, Qiang; Li, Shan-Shan; Wan, Hai-Qin; Liu, Lian-Jun; Qi, Lei; Liu, Bin; Gao, Fei; Dong, Lin; Chen, Yi

    2011-05-01

    NO reduction by CO was investigated over CuO/γ-Al2O3, Mn2O3/γ-Al2O3, and CuOMn2O3/γ-Al2O3 model catalysts before and after CO pretreatment at 300 °C. The CO-pretreated CuO-Mn2O3/γ-Al2O3 catalyst exhibited higher catalytic activity than did the other catalysts. Based on X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), UV/Vis diffuse reflectance spectroscopy (DRS), Raman, and H2-temperature-programmed reduction (TPR) results, as well as our previous studies, the possible interaction model between dispersed copper and manganese oxide species as well as γ-Al2O3 surface has been proposed. In this model, Cu and Mn ions occupied the octahedral vacant sites of γ-Al2O3, with the capping oxygen on top of the metal ions to keep the charge conservation. For the fresh CuO/γ-Al2O3 and Mn2O3/γ-Al2O3 catalysts, the -Cu-O-Cu- and -Mn-O-Mn- species were formed on the surface of γ-Al2O3, respectively; but for the fresh CuO-Mn2O3/γ-Al2O3 catalyst, -Cu-O-Mn- species existed on the surface of -Al2O3. After CO pretreatment, -Cu-□-Cu- and -Mn-□-Mn- (□ represents surface oxygen vacancy (SOV)) species would be formed in CO-pretreated CuO/γ-Al2O3 and CO-pretreated Mn2O3/γ-Al2O3 catalysts, respectively; whereas -Cu-□-Mn- species existed in CO-pretreated CuO-Mn2O3/γ-Al2O3. Herein, a new concept, surface synergetic oxygen vacancy (SSOV), which describes the oxygen vacancy formed between the individual Mn and Cu ions, is proposed for CO-pretreated CuO-Mn2O3/γ-Al2O3 catalyst. In addition, the role of SSOV has also been approached by NO temperature-programmed desorption (TPD) and in situ FTIR experiments. The FTIR results of competitive adsorption between NO and CO on all the CO-pretreated CuO/γ-Al2O3, Mn2O3/γ-Al2O3, and CuO-Mn2O3/γ-Al2O3 samples demonstrated that NO molecules mainly were adsorbed on Mn2+ and CO mainly on Cu+ sites. The current study suggests that the properties of the SSOVs in CO-pretreated CuO-Mn2O3/γ-Al2O3 catalyst were significantly

  5. Local structure in BaTi O3-BiSc O3 dipole glasses

    NASA Astrophysics Data System (ADS)

    Levin, I.; Krayzman, V.; Woicik, J. C.; Bridges, F.; Sterbinsky, G. E.; Usher, T.-M.; Jones, J. L.; Torrejon, D.

    2016-03-01

    Local structures in cubic perovskite-type (B a0.6B i0.4) (T i0.6S c0.4) O3 solid solutions that exhibit reentrant dipole glass behavior have been studied with variable-temperature x-ray/neutron total scattering, extended x-ray absorption fine structure, and electron diffraction methods. Simultaneous fitting of these data using a reverse Monte Carlo algorithm provided instantaneous atomic configurations, which have been used to extract local displacements of the constituent species. The smaller Bi and Ti atoms exhibit probability density distributions that consist of 14 and 8 split sites, respectively. In contrast, Ba and Sc feature single-site distributions. The multisite distributions arise from large and strongly anisotropic off-center displacements of Bi and Ti. The cation displacements are correlated over a short range, with a correlation length limited by chemical disorder. The magnitudes of these displacements and their anisotropy, which are largely determined by local chemistry, change relatively insignificantly on cooling from room temperature. The structure features a nonrandom distribution of local polarization with low-dimensional polar clusters that are several unit cells in size. In situ measurements of atomic pair-distribution function under applied electric field were used to study field-induced changes in the local structure; however, no significant effects besides lattice expansion in the direction of the field could be observed up to electric-field values of 4 kV m m-1 .

  6. Transparent Conducting Properties of SrSnO3 and ZnSnO3

    DOE PAGESBeta

    Ong, Khuong P.; Fan, Xiaofeng; Subedi, Alaska; Sullivan, Michael B.; Singh, David J.

    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.

  7. Dielectric response of BaZrO3/BaTiO3 superlattice

    NASA Astrophysics Data System (ADS)

    Wang, D.; Jiang, Z.

    2016-06-01

    We use the first-principles-based molecular dynamic approach to simulate dipolar dynamics of BaZrO3/BaTiO3 superlattice, and obtain its dielectric response. The dielectric response is decomposed into its compositional, as well as the in-plane and out-of-plane parts, which are then discussed in the context of chemical ordering of Zr/Ti ions. We reveal that, while the in-plane dielectric response of BaZrO3/BaTiO3 superlattice also shows dispersion over probing frequency, it shall not be categorized as relaxor.

  8. 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

  9. Photoresponse dynamics in amorphous-LaAlO3/SrTiO3 interfaces

    NASA Astrophysics Data System (ADS)

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

    2015-02-01

    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.

  10. Metastable honeycomb SrTiO3/SrIrO3 heterostructures

    NASA Astrophysics Data System (ADS)

    Anderson, T. J.; Ryu, S.; Zhou, H.; Xie, L.; Podkaminer, J. P.; Ma, Y.; Irwin, J.; Pan, X. Q.; Rzchowski, M. S.; Eom, C. B.

    2016-04-01

    Recent theory predictions of exotic band topologies in (111) honeycomb perovskite SrIrO3 layers sandwiched between SrTiO3 have garnered much attention in the condensed matter physics and materials communities. However, perovskite SrIrO3 film growth in the (111) direction remains unreported, as efforts to synthesize pure SrIrO3 on (111) perovskite substrates have yielded films with monoclinic symmetry rather than the perovskite structure required by theory predictions. In this study, we report the synthesis of ultra-thin metastable perovskite SrIrO3 films capped with SrTiO3 grown on (111) SrTiO3 substrates by pulsed laser deposition. The atomic structure of the ultra-thin films was examined with scanning transmission electron microscopy (STEM), which suggests a perovskite layering distinct from the bulk SrIrO3 monoclinic phase. In-plane 3-fold symmetry for the entire heterostructure was confirmed using synchrotron surface X-ray diffraction to measure symmetry equivalent crystal truncation rods. Our findings demonstrate the ability to stabilize (111) honeycomb perovskite SrIrO3, which provides an experimental avenue to probe the phenomena predicted for this material system.

  11. Comparison of sludge treatment by O3 and O3/H2O2.

    PubMed

    Yuxin, Zhao; Liang, Wang; Helong, Yu; Baojun, Jiang; Jinming, Jiang

    2014-01-01

    This work focuses on the comparison of sludge decomposition caused by ozone (O3) alone and by ozone/hydrogen peroxide (O3/H2O2). The content of carbonaceous organic materials, nitrogenous compounds and phosphoric substances in sludge supernatant were measured. The release of soluble chemical oxygen demand, total nitrogen (TN) and total phosphorus (TP) caused by O3/H2O2 treatment were more than by O3 alone. As a result, it can be concluded that the efficiency of sludge breakup in O3/H2O2 was better than that in O3 alone. However, a peak appeared in both systems for the biodegradable substances such as carbohydrate. Carbohydrate could be used as the carbon source for denitrification, and the releasing of TN and TP may become an additional burden for a subsequent biological system. So, it was of benefit for the enhancement of cryptic growth and cost reduction by raising and maintaining the content of biodegradable substance and reducing the concentrations of the nitrogenous and phosphoric substances as far as possible. Therefore, sludge treated by O3/H2O2 with lower O3 dose would be more suitable than O3 alone. PMID:25026588

  12. Transparent conducting properties of SrSnO3 and ZnSnO3

    NASA Astrophysics Data System (ADS)

    Ong, Khuong P.; Fan, Xiaofeng; Subedi, Alaska; Sullivan, Michael B.; Singh, David J.

    2015-06-01

    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.

  13. Systematic investigation of chemical substitution in BaSnO3 using the combinatorial approach

    NASA Astrophysics Data System (ADS)

    Takeuchi, Ichiro; Shin, Jongmoon; Lee, Seunghun; Zhang, Xiaohang; Jaim, H. M. Iftekhar; Jeong, Se-Young

    BaSnO3 has been regarded as a possible material for photo-catalysis, dielectric capacitors, and transparent conductors. We are systematically investigating the effect of chemical substitution for A and B sites in BaSnO3 using a high-throughput methodology. We have thus far investigated the effect of substituting La and Sr for the Ba-site and Pb and Bi for the Sn-site. The composition spread films were prepared on MgO, SrTiO3 and LaAlO3 using combinatorial pulsed laser deposition. The lattice parameters and band-gap energies were found to continually change as a function of the concentration of each substitutional dopant. We find that the band gap can be tuned from 2.8 eV for BaSn0.05Pb0.95O3 to 4.5 eV for Ba0.05La0.95SnO3. Especially for Ba1-xLaxSnO3 with x in the range of 0.05

  14. Interface exchange processes in LaAlO3/Sr TiO3 induced by oxygen vacancies

    NASA Astrophysics Data System (ADS)

    Behrmann, Malte; Lechermann, Frank

    2015-09-01

    Understanding the role of defects in oxide heterostructures is crucial for future materials control and functionalization. We hence study the impact of oxygen vacancies (OVs) at variable concentrations on orbital and spin exchange in the LaAlO3/Sr TiO3 interface by first-principles many-body theory and real-space model-Hamiltonian techniques. Intricate interplay between the Hubbard U and Hund's coupling JH for OV-induced correlated states is demonstrated. Orbital polarization towards an effective eg state with predominant local antiferromagnetic alignment on Ti sites near OVs is contrasted with t2 g(x y ) states with ferromagnetic tendencies in the defect-free regions. Different magnetic phases are identified, giving rise to distinct net-moment behavior at low and high OV concentrations. This provides a theoretical basis for prospective tailored magnetism by defect manipulation in oxide interfaces.

  15. Dependence of electrostatic potential distribution of Al2O3/Ge structure on Al2O3 thickness

    NASA Astrophysics Data System (ADS)

    Wang, Xiaolei; Xiang, Jinjuan; Wang, Wenwu; Zhao, Chao; Zhang, Jing

    2016-09-01

    Electrostatic potential distribution of Al2O3/Ge structure is investigated vs. Al2O3 thickness by X-ray photoelectron spectroscopy (XPS). The electrostatic potential distribution is found to be Al2O3 thickness dependent. This interesting phenomenon is attributed to the appearance of gap states on Al2O3 surface (GSAl2O3) and its higher charge neutrality level (CNL) compared with the CNL of gap states at Al2O3/Ge interface (GSAl2O3/Ge), leading to electron transfer from GSAl2O3 to GSAl2O3/Ge. In the case of thicker Al2O3, fewer electrons transfer from GSAl2O3 to GSAl2O3/Ge, resulting in a larger potential drop across Al2O3 and XPS results.

  16. 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.

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

    PubMed Central

    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. PMID:26742878

  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

    2016-01-01

    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. PMID:26742878

  19. 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)

  20. Growth and photorefractive properties of Zn, Fe double-doped LiTaO 3 crystal

    NASA Astrophysics Data System (ADS)

    Fang, Shuangquan; Wang, Biao; Zhang, Tao; Ling, Furi; Wang, Rui

    2006-02-01

    Zn, Fe double-doped LiTaO3 crystals have been grown by the Czochralski method. The photorefractive properties and optical damage resistance were measured by the two-beam coupling experiments and transmitted facula distortion method, respectively. The results showed that the photorefractive response speed of Zn:Fe:LiTaO3 was about four times faster than that of Fe:LiTaO3, whereas the optical damage resistance was two orders of magnitude higher than that of Fe:LiTaO3. In this paper, site occupation mechanism of impurities was also discussed to explain the high optical damage resistance and fast response speed of Zn:Fe:LiTaO3 crystal.

  1. 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.

  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. 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.

  4. Massive symmetry breaking in LaAlO3/SrTiO3(111) quantum wells: a three-orbital strongly correlated generalization of graphene.

    PubMed

    Doennig, David; Pickett, Warren E; Pentcheva, Rossitza

    2013-09-20

    Density functional theory calculations with an on-site Coulomb repulsion term reveal competing ground states in (111)-oriented (LaAlO(3))(M)/(SrTiO(3))(N) superlattices with n-type interfaces, ranging from spin, orbitally polarized (with selective e(g)('), a(1g), or d(xy) occupation), Dirac point Fermi surface, to charge-ordered flat band phases. These phases are steered by the interplay of (i) Hubbard U, (ii) SrTiO(3) quantum well thickness, and (iii) crystal field splitting tied to in-plane strain. In the honeycomb lattice bilayer N = 2 under tensile strain, inversion symmetry breaking drives the system from a ferromagnetic Dirac point (massless Weyl semimetal) to a charge-ordered multiferroic (ferromagnetic and ferroelectric) flat band massive (insulating) phase. With increasing SrTiO(3) quantum well thickness an insulator-to-metal transition occurs. PMID:24093290

  5. 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.

  6. Emergent ferromagnetism in NdMnO3 /SrMnO3 superlattices

    NASA Astrophysics Data System (ADS)

    Glavic, Artur; Calder, Stuart; Cooper, Valentino; Dixit, Hemant

    2015-03-01

    The phenomenon of ferromagnetism evolving in digital superlattices of two antiferromagnets LaMnO3[2n]/SrMnO3[n] has been well established. We show that this interface effect can be observed in systems with different rare earth manganites as well, exemplified in the Nd system grown on LSAT and TbScO3 substrates. With polarized neutron reflectometry we prove that not only 2/1 unit cell samples become ferromagnetic but that interface ferromagnetism can be induced whenever a single layer of SrMnO3 is introduced in the NdMnO3 system. These results show that the strain state of the superlattice system is of much less importance for the induced magnetization then the Mn3+/Mn4+ electronic state.

  7. Methylation by Set9 modulates FoxO3 stability and transcriptional activity.

    PubMed

    Calnan, Daniel R; Webb, Ashley E; White, Jamie L; Stowe, Timothy R; Goswami, Tapasree; Shi, Xiaobing; Espejo, Alexsandra; Bedford, Mark T; Gozani, Or; Gygi, Steven P; Brunet, Anne

    2012-07-01

    The FoxO family of transcription factors plays an important role in longevity and tumor suppression by regulating the expression of a wide range of target genes. FoxO3 has recently been found to be associated with extreme longevity in humans and to regulate the homeostasis of adult stem cell pools in mammals, which may contribute to longevity. The activity of FoxO3 is controlled by a variety of post-translational modifications that have been proposed to form a 'code' affecting FoxO3 subcellular localization, DNA binding ability, protein-protein interactions and protein stability. Lysine methylation is a crucial post-translational modification on histones that regulates chromatin accessibility and is a key part of the 'histone code'. However, whether lysine methylation plays a role in modulating FoxO3 activity has never been examined. Here we show that the methyltransferase Set9 directly methylates FoxO3 in vitro and in cells. Using a combination of tandem mass spectrometry and methyl-specific antibodies, we find that Set9 methylates FoxO3 at a single residue, lysine 271, a site previously known to be deacetylated by Sirt1. Methylation of FoxO3 by Set9 decreases FoxO3 protein stability, while moderately increasing FoxO3 transcriptional activity. The modulation of FoxO3 stability and activity by methylation may be critical for fine-tuning cellular responses to stress stimuli, which may in turn affect FoxO3's ability to promote tumor suppression and longevity. PMID:22820736

  8. Polarization in RMnO3 multiferroics.

    PubMed

    Pirogov, A N

    2016-02-01

    Some comments on the review by Sim et al. [(2016). Acta Cryst. B72, 3-19] are given. The review is devoted to hexagonal multiferroics RMnO3, in which there are ferroelectric and magnetic orders. Strong interaction between these orders causes a series of interesting properties of multiferroics. PMID:26830791

  9. Photolysis of O3 at 3130A

    NASA Technical Reports Server (NTRS)

    Simonaitis, R.; Braslavsky, S.; Heicklen, J.; Nicolet, M.

    1972-01-01

    The photolysis of O3 at 3130 A and 25 C has been studied in the presence of a large excess of N2O to react with any O(1D) atoms produced. From the N2 produced, the quantum efficiency for O(1D) production was found to be 0.50 + or - 0.03.

  10. 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

  11. 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.

  12. Enhanced piezoelectric and ferroelectric properties in the BaZrO3 substituted BiFeO3-PbTiO3

    NASA Astrophysics Data System (ADS)

    Fan, Longlong; Chen, Jun; Li, Sha; Kang, Huajun; Liu, Laijun; Fang, Liang; Xing, Xianran

    2013-01-01

    BiFeO3-PbTiO3 (BF-PT) compounds possess very high Curie temperature and tetragonality compared to other PbTiO3-based piezoceramics. The BaZrO3 (BZ), with weakly ferroelectric active cations, was introduced into the BiFeO3-PbTiO3 to reduce the tetragonality (c/a) and improve the piezoelectric property. For the (0.8-x)BiFeO3-0.2BaZrO3-xPbTiO3, the BaZrO3 substitution can effectively decrease the tetragonality (c/a) from 1.18 to 1.02 for those compositions near the morphotropic phase boundary. The piezoelectric property of BiFeO3-PbTiO3 can be much enhanced with an optimal piezoelectric constant ˜270 pC/N with a reduced TC of 270 °C. Both the temperature dependent dielectric properties and polarization loops verified the existence of antiferroelectric relaxor, which was not observed in previous reported BiFeO3-PbTiO3 based materials.

  13. 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.

  14. The variations of CO and O3 concentrations in a region subject to biomass burning

    NASA Technical Reports Server (NTRS)

    Kirchhoff, V. W. J. H.; Rasmussen, R. A.

    1990-01-01

    Carbon monoxide (CO) and ozone (O3) concentrations have been observed in the Brazilian Amazon region, at a site strongly affected by biomass burning (Cuiaba, 16 deg S, 58 deg W). Time variations are described for the first long-term program of studying the effect of biomass burning on O3 and CO over a complete seasonal cycle, including the seasonal maxima of 1987 and 1988. In order to obtain elements for comparison, an identical observational program was maintained at a site totally outside of the direct influence of biomass burning (Natal, 6 deg S, 35 deg W). The biomass burning contribution to the Cuiaba concentrations of CO and O3 is very large. Diurnal maxima concentrations exceeded 90 ppbv O3 in 1987 and 120 ppbv O3 in 1988, in September. For the wet season, the monthly average ozone concentration in March-April is about 10 ppbv. During the month of maxima, September, the O3 concentration average was 41 ppbv for 1987 and 71 ppbv for 1988. The CO concentrations are about 90 ppbv in the wet season. In September, 460 ppbv and 660 ppbv of CO were observed for 1987 and 1988, respectively. At Natal the seasonal variation is of the order of a factor of 2. During the wet season, the concentrations of CO and O3 at both stations are about the same.

  15. Improved Piezoelectric Properties of LiTaO3 Family Solid Solution Ceramics with Modified Composition

    NASA Astrophysics Data System (ADS)

    Bamba, Noriko; Takaoka, Junpei; Chino, Takashi; Fukami, Tatsuo; Elouadi, Brahim

    2006-09-01

    Nonstoichiometric LiTaO3 ceramics doped with 15 mol % CaTiO3 have been prepared to improve the piezoelectricity of LiTaO3 ceramics and iron doping has been investigated to obtain a high mechanical quality factor, Qm. By increasing the ratio of B sites (Ta and Ti) from 49.5 to 52.0 mol %, crack generation was suppressed and resonance frequency in the radial vibration mode shifted. (Li0.84Ca0.15)(Ta0.86Ti0.15)O3 ceramics whose A and B site ratios were 49.5 and 50.5 mol %, respectively, caused a higher resonance frequency and a high piezoelectric activity than the stoichiometric LiTaO3. The optimum composition for the piezoelectric properties was obtained from the nonstoichiometric LiTaO3 expressed as (Li0.832Ca0.158)(Ta0.856Ti0.15Fe0.004)O3; the phase shift was 73° and the quality factor Qm was 7872 in the radial vibration mode. Although the phase shift is still not sufficiently high, it is expected to approach 90° by fixing it under better poling conditions. One of the possible applications of this material is as an oscillator element for signal processing circuits.

  16. 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.

  17. 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.

  18. Thermodynamic properties of Ba1-xLaxCoO3

    NASA Astrophysics Data System (ADS)

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

    2016-05-01

    We have predicted the thermodynamic behavior of Ba1-xLaxCoO3 family at temperature 1K≤T≤300K using the Modified Rigid Ion Model (MRIM). The specific heat of BaCoO3 with La doping in the perovskite structure at A-site has been reported. Also, the cohesive energy (ϕ), molecular force constant (f), Reststrahlen frequency (υ), Debye temperature (θD), specific heat (C) and Gruneisen parameter (γ) of Ba1-xLaxCoO3 compounds are discussed.

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

    DOE PAGESBeta

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

    2016-01-21

    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

  20. 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

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

    NASA Astrophysics Data System (ADS)

    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.

  2. Engineered Mott ground state in a LaTiO(3+δ)/LaNiO3 heterostructure.

    PubMed

    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 LaTiO(3+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 e(g) 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

  3. Polarity and the Metal-Insulator Transition in ultrathin LaNiO3 on SrTiO3

    NASA Astrophysics Data System (ADS)

    Freeland, J. W.; Tung, I. C.; Luo, G.; Zhou, H.; Lee, J. H.; Chang, S. H.; Morgan, D.; Bedzyk, M. J.; Fong, D. D.

    Dimensionality and strain control of nickelates has been shown as a route for control of interesting electronic and magnetic phases. However, little is know about the evolution of atomic structure in these layered architectures and the interplay with these states. Here we present, a detailed study of lattice structures measured real time during the layer-by-layer growth of LaNiO3 on SrTiO3. Using hard X-rays coupled with oxide MBE, we have tracked the lattice structure evolution as a function of depth across the regime where transport shows a clear metal to insulator transition. At the same time X-ray absorption shows the films are closer to LaNiO2.5 when thin and evolve to LaNiO3 by 10 unit cells thickness. Analysis of the structure during growth displays a very complex evolution throughout the film of the lattice parameter and displacement of the B-site from the unit cell center, which theory connects with pathways of compensating the polar mismatch at the surface and interface. Work at the APS, Argonne is supported by the U.S. Department of Energy, Office of Science, and Office of Basic Energy Sciences, under Contract No. DE-AC02-06CH11357.

  4. Weak ferromagnetism in the ferroelectric BiFeO3-ReFeO3-BaTiO3 solid solutions (Re=Dy,La)

    NASA Astrophysics Data System (ADS)

    Kim, Jeong Seog; Cheon, Chae Il; Lee, Chang Hee; Jang, Pyung Woo

    2004-07-01

    The binary and ternary solid solutions, BiFeO3-BaTiO3, BiFeO3-ReFeO3-BaTiO3 (Re=Dy,Pr,La), and BiFeO3-BaFeO2.5-BaTiO3 have been explored for attaining ferromagnetic ferroelectrics in bulk ceramics and understanding the effect of rare earth orthoferrites ReFeO3 on the spontaneous magnetization. The coexistence of ferromagnetism and ferroelectricity has been observed over the composition range of 0.2⩽x⩽0.4 in the (1-x)BiFeO3-xBaTiO3 at room temperature. The introduction of DyFeO3 and LaFeO3 expands the composition range of the coexistence. The most superior ferromagnetic ferroelectrics obtained in this study are the 0.65BiFeO3-0.025DyFeO3-0.325BaTiO3 (Pr=5 μC/cm2,Mr=0.1 emu/g), 0.4875BiFeO3-0.025DyFeO3-0.4875BaTiO3 (Pr=7 μC/cm2,Mr=0.06 emu/g), and 0.475BiFeO3-0.05LaFeO3-0.475BaTiO3 (Pr=3.2 μC/cm2,Mr=0.2 emu/g). The spontaneous magnetization strongly depends on both the type and amount of the substitution components, DyFeO3, LaFeO3, PrFeO3, and BaFeO2.5 rather than the degree of G-type antiferromagnetic ordering. The origin of the spontaneous magnetization has been discussed in terms of antiferromagnetic ordering and charge carrier mediation.

  5. Human Immunodeficiency Virus Type 1 Resistance to the Small Molecule Maturation Inhibitor 3-O-(3′,3′-Dimethylsuccinyl)-Betulinic Acid Is Conferred by a Variety of Single Amino Acid Substitutions at the CA-SP1 Cleavage Site in Gag▿ †

    PubMed Central

    Zhou, Jing; Chen, Chin Ho; Aiken, Christopher

    2006-01-01

    The compound 3-O-(3′,3′-dimethylsuccinyl)-betulinic acid (DSB) potently and specifically inhibits human immunodeficiency virus type 1 (HIV-1) replication by delaying the cleavage of the CA-SP1 junction in Gag, leading to impaired maturation of the viral core. In this study, we investigated HIV-1 resistance to DSB by analyzing HIV-1 mutants encoding a variety of individual amino acid substitutions in the CA-SP1 cleavage site. Three of the substitutions were lethal to HIV-1 replication owing to a deleterious effect on particle assembly. The remaining mutants exhibited a range of replication efficiencies; however, each mutant was capable of replicating in the presence of concentrations of DSB that effectively inhibited wild-type HIV-1. Mutations conferring resistance to DSB also led to impaired binding of the compound to immature HIV-1 virions and loss of DSB-mediated inhibition of cleavage of Gag. Surprisingly, two of the DSB-resistant mutants retained an intermediate ability to bind the compound, suggesting that binding of DSB to immature HIV-1 particles may not be sufficient for antiviral activity. Overall, our results indicate that Gag amino acids L363 and A364 are critical for inhibition of HIV-1 replication by DSB and suggest that these residues form key contacts with the drug in the context of the assembling HIV-1 particle. These results have implications for the design of and screening for novel inhibitors of HIV-1 maturation. PMID:17035324

  6. Transport properties of a quasi-two-dimensional electron system formed in LaAlO3/EuTiO3/SrTiO3 heterostructures

    NASA Astrophysics Data System (ADS)

    De Luca, G. M.; Di Capua, R.; Di Gennaro, E.; Granozio, F. Miletto; Stornaiuolo, D.; Salluzzo, M.; Gadaleta, A.; Pallecchi, I.; Marrè, D.; Piamonteze, C.; Radovic, M.; Ristic, Z.; Rusponi, S.

    2014-06-01

    We study the structural, magnetic, and transport properties of LaAlO3/EuTiO3/SrTiO3 heterostructures grown by pulsed laser deposition. The samples are characterized in situ by electron diffraction and scanning probe microscopy and ex situ by transport measurements and x-ray absorption spectroscopy. LaAlO3/EuTiO3/SrTiO3 films show a ferromagnetic transition at T ≤7.5 K, related to the ordering of Eu2+ spins, even in samples characterized by just two EuTiO3 unit cells. A finite metallic conductivity is observed only in the case of samples composed by one or two EuTiO3 unit cells and, simultaneously, by a LaAlO3 thickness greater than or equal to four unit cells. The effect of ferromagnetic EuTiO3 on the transport properties of δ-doped LaAlO3/EuTiO3/SrTiO3 is critically discussed.

  7. Universal magnetic behavior the electron-doped SrMnO3 cubic perovskite

    NASA Astrophysics Data System (ADS)

    Kolesnik, S.; Dabrowski, B.; Chmaissem, O.

    2009-03-01

    SrMnO3 is the end member of a widely explored family of colossal magnetoresistive manganites RxSr1-xMnO3 (R=rare earth elements). Low-level R^3+ substitutions change the antiferromagnetic order from G-type in cubic SrMnO3 to C-type in tetragonal RxSr1-xMnO3 through first-order resistive and structural transitions. From the magnetization, transport, and neutron diffraction experiments we observe that a similar change can be induced by B-site substitutions in SrMn1-xMxO3 (M=Ru^5+,Mo^6+) both generating Mn^3+ in the Mn^4+ matrix. For both A-site and B-site substitutions, the N'eel temperature is dependent on the Mn^3+ concentration in a universal way. These observations reveal that the magnetic and electronic properties of low-level substituted SrMnO3 are controlled by the band filling throughout the increasing role of local distortions of Mn^3+O6 octahedra changing from randomly diluted to cooperative character of the entire lattice. Work at NIU was supported by the NSF (DMR-0706610) and at ANL by the U.S. DOE under contract No. DE-AC02-06CH11357.

  8. 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. PMID:20422673

  9. 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.

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

    PubMed

    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 Fe(2+) and Fe(3+) 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

  11. 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

  12. Strain dynamics during La2O3/Lu2O3 superlattice and alloy formation

    NASA Astrophysics Data System (ADS)

    Proessdorf, André; Niehle, Michael; Grosse, Frank; Rodenbach, Peter; Hanke, Michael; Trampert, Achim

    2016-06-01

    The dynamics of strain relaxation and intermixing during molecular beam epitaxy of La2O3 and Lu2O3 superlattices and alloys consisting of both binaries on Si(111) have been studied by real-time in situ grazing incidence x-ray diffraction and high resolution transmission electron microscopy. The presence of both hexagonal and cubic polymorphs of La2O3 influences the epitaxial formation within the superlattice. The process of strain relaxation is closely related to the presence of a (La,Lu)2O3 alloy adopting a cubic symmetry. It is formed by interdiffusion of La and Lu atoms reducing internal lattice mismatch within the superlattice. An interface thickness dominated by interdiffusion regions of about 3 monolayers is determined by high-angle annular dark field scanning transmission electron microscopy.

  13. [Advanced Treatment of Incineration Leachate with O3-BAC and Double O3-BAC].

    PubMed

    Du, An-jing; Fan, Ju-hong; Liu, Rui; Qiu, Song-kai; Wen, Xiao-gang; Chen, Lü-jun

    2015-11-01

    Ozone-biological activated carbon (O3-BAC) process and double O3-BAC process were respectively used for advanced treatment of the biologically treated effluent of incineration leachate, and their pollutant removal performances were compared. The results showed that the double O3-BAC removed 75.9% ± 2.1% of chemical oxygen demand (COD), 78.8% ± 2.9% of UV254 and 96.8% ± 0.9% of color at ozone dosage of 200 mg x L(-1). The treated effluent was with COD of below 100 mg x L(-1) and color of below 40 times, meeting the emission requirements of GB 16889-2008. At the same ozone dosage, however, the O3-BAC removed 68.2% ± 1.3% of COD, 69.7% ± 0.5% of UV254 and 92.5% ± 1.1% of color. The treated effluent was with COD of around 150 mg x L(-1) and color of about 60 times, failing to meet the emission requirements. Namely, ozone of 290 mg x L(-1) was required by O3-BAC in order to achieve similar pollutant removals as those in double O3-BAC at O3 dosage of 200 mg x L(-1). In double O3-BAC at ozone dosage of 200 mg x L(-1), total phosphorus was removed by 63.5% ± 4.4%, and the phosphorus concentration in the effluent was remained 1 mg x L(-1) or less, directly meeting the emission requirement of GB 16889-2008. PMID:26911003

  14. 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:  Reverb:   Order Data Guide ...

  15. Theory of Valence Transition in BiNiO3

    NASA Astrophysics Data System (ADS)

    Naka, Makoto; Seo, Hitoshi; Motome, Yukitoshi

    2016-02-01

    Motivated by the colossal negative thermal expansion recently found in BiNiO3 , the valence transition accompanied by the charge transfer between the Bi and Ni sites is theoretically studied. We introduce an effective model for Bi -6 s and Ni -3 d orbitals taking into account the valence skipping of Bi cations, and investigate the ground-state and finite-temperature phase diagrams within the mean-field approximation. We find that the valence transition is caused by commensurate locking of the electron filling in each orbital associated with charge and magnetic orderings, and the critical temperature and the nature of the transitions are strongly affected by the relative energy between the Bi and Ni levels and the effective electron-electron interaction in the Bi sites. The obtained phase diagram well explains the temperature- and pressure-driven valence transitions in BiNiO3 and the systematic variation of valence states for a series of Bi and Pb perovskite oxides.

  16. Theory of Valence Transition in BiNiO_{3}.

    PubMed

    Naka, Makoto; Seo, Hitoshi; Motome, Yukitoshi

    2016-02-01

    Motivated by the colossal negative thermal expansion recently found in BiNiO_{3}, the valence transition accompanied by the charge transfer between the Bi and Ni sites is theoretically studied. We introduce an effective model for Bi-6s and Ni-3d orbitals taking into account the valence skipping of Bi cations, and investigate the ground-state and finite-temperature phase diagrams within the mean-field approximation. We find that the valence transition is caused by commensurate locking of the electron filling in each orbital associated with charge and magnetic orderings, and the critical temperature and the nature of the transitions are strongly affected by the relative energy between the Bi and Ni levels and the effective electron-electron interaction in the Bi sites. The obtained phase diagram well explains the temperature- and pressure-driven valence transitions in BiNiO_{3} and the systematic variation of valence states for a series of Bi and Pb perovskite oxides. PMID:26894723

  17. Intermixtures at LaAlO3/SrTiO3 interfaces

    NASA Astrophysics Data System (ADS)

    Chen, Hanghui; Kolpak, Alexie; Ismail-Beigi, Sohrab

    2010-03-01

    The intriguing transport properties observed at the LaAlO3/SrTiO3 n-type interface have precipitated numerous studies in the past few years. However, it remains uncertain whether the interface obtained experimentally is atomically sharp, and if not, what role the disorder plays in the unique behavior of this system. We use first principles density functional theory to find the energetics of cation intermixing, specifically La-Sr and Al-Ti, at the LaAlO3/SrTiO3 n-type interface. We find that an ideal interface with no intermixing is not thermodynamically stable. Ti-Al intermixing reduces the total energy while Sr-La intermixing increases the total energy. We explain the energetics and this asymmetry in terms of a simple electrostatic model, which is able to accurately describe the DFT results. We also discuss how intermixing affects the polar field in the LaAlO3, the ``polar catastrophe'', and the critical thickness of LaAlO3 needed to induce a metal-insulator transition.

  18. Dielectric and Electrical Properties of BiFeO3-LiTaO3 Systems

    NASA Astrophysics Data System (ADS)

    Mohanty, Suchismita; Choudhary, R. N. P.

    2015-07-01

    Materials of general formula (Bi1- x Li x )(Fe1- x Ta x )O3 ( x = 0.0, 0.5) were prepared from polycrystalline BiFeO3 and LiTaO3 by solid-state reaction. Analysis of the basic structural properties of the materials by room-temperature x-ray diffraction revealed the formation of single-phase tetragonal crystals for (Bi0.5Li0.5)(Fe0.5Ta0.5)O3. Scanning electron micrographs confirmed the polycrystalline nature of the materials. The microstructure of the materials comprised uniformly distributed grains of unequal size. Studies of the temperature-frequency dependence of dielectric did not reveal any dielectric anomaly or phase transition in the temperature range studied. The presence of hysteresis loops at room temperature confirmed the known ferroelectricity of BiFeO3 and (Bi0.5Li0.5)(Fe0.5Ta0.5)O3. Complex impedance spectroscopic analysis revealed the materials had negative temperature coefficient of resistance (NTCR)-type behavior. The electrical conductivity and relaxation characteristics of the materials suggested the presence of a thermally activated process, and their values suggested the materials had similar types of conductivity and relaxation species. The frequency dependence of the ac conductivity obeyed Jonscher's universal power law.

  19. 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.

  20. 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. PMID:27514235

  1. Structure and magnetism of FeMnO3

    NASA Astrophysics Data System (ADS)

    Rayaprol, S.; Kaushik, S. D.; Babu, P. D.; Siruguri, V.

    2013-02-01

    The compound FeMnO3 crystallizing in the mineral bixbyite structure has been prepared by mechanochemical synthesis achieved by high energy ball milling of starting compounds. The structure and magnetism have been studied using powder neutron diffraction and magnetization measurements. Magnetization measurements exhibits ferrimagnetism at 300 K and antiferromagnetic (TN) ordering around 36 K. Magnetic structure has been determined from the Rietveld analysis of the neutron diffraction pattern recorded at 300 K. Fe and Mn occupy both 8b and 24d sites in 1:1 ratio. Interaction between Fe and Mn atoms is antiferromagnetic. The ferrimagnetism arises due to anti-parallel alignment of unequal moments on 8b and 24d sites.

  2. Doping and defects by design: Ga2O3

    NASA Astrophysics Data System (ADS)

    Lany, Stephan

    Density functional supercell calculations are widely employed to describe the defect physics in semiconductors and insulators. Due to a variety of challenges such as finite size effects for charged defects and the band gap error of DFT, results were often controversial in the past. With developments over the past decade, defect theory should hopefully be truly predictive, and be able to guide experimental efforts. The present work on n-type doping in Ga2O3 compares different potential doping routes via anion-site doping with F, and cation site doping with group IV elements (C, Si, Ge, Sn). The study addresses dopant solubility, electrical activity, and compensation by native defects, including non-equilibrium effects due to supersaturated dopant concentrations and the mechanism of dopant-defect pair formation. Supported by DOE-SC-BES as part of an Energy Frontier Research Center.

  3. Transition-metal ion impurities in KTaO3

    NASA Astrophysics Data System (ADS)

    Leung, Kevin

    2002-01-01

    A systematic study of transition-metal impurity centers in pervoskites is undertaken by considering isolated Co2+, Fe3+, and Cu2+ point defects in KTaO3. Within the generalized gradient approximation (GGA), the defect center magnetic moments agree with experiments, except for A-site Fe3+ complexes which exhibit 3μB and 5μB structures competitive in energies. It is argued that the anomaly is an artifact of GGA, which underestimates Fe3+ 3d electron correlations. Large (~1 Å) off-center displacements of K-substituting impurities obtain due to metal-oxygen covalent bonding. These A-site dipoles exhibit relaxation dynamics barriers which agree well with experiments. The Fe3+-OI 2- complex is considered in some detail; it exhibits Fe-O bonds considerably shorter than shell-model predictions.

  4. 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.

  5. 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. PMID:25895623

  6. 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.

  7. 2D-MoO3 nanosheets for superior gas sensors.

    PubMed

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

    2016-04-28

    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. PMID:27053379

  8. 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.

  9. Defect mechanisms in high resistivity BaTiO3-Bi(Zn1/2Ti1/2)O3 ceramics

    NASA Astrophysics Data System (ADS)

    Raengthon, Natthaphon; DeRose, Victoria J.; Brennecka, Geoffrey L.; Cann, David P.

    2012-09-01

    The defect mechanisms that underpin the high energy density dielectric 0.8BaTiO3-0.2Bi(Zn1/2Ti1/2)O3 were investigated. Characterization of the nominally stoichiometric composition revealed the presence of a Ti3+-related defect center, which is correlated with lower resistivities and an electrically heterogeneous microstructure. In compositions with 2 mol. % Ba-deficiency, a barium vacancy-oxygen vacancy pair (VBa-VO), acted as an electron-trapping site. This defect was responsible for a significant change in the transport behavior with a high resistivity and an electrically homogeneous microstructure.

  10. Chemical and meteorological characteristics associated with rapid increases of O3 in Houston, Texas

    NASA Astrophysics Data System (ADS)

    Berkowitz, Carl M.; Jobson, Tom; Jiang, Guangfeng; Spicer, Chester W.; Doskey, Paul V.

    2004-05-01

    We report here on measurements made from the 62nd story of the Williams Tower on the west side of Houston, Texas between 15 August and 15 September 2000. The time series of trace gases differ from those at many other urban sites in having very rapidly increasing spikes of O3, HCHO, and PAN. Measurements show that the highest O3 levels in Houston are not always those measured at the surface, and the extreme values may occur aloft. Plumes with high O3 appear to be produced largely from local sources and to have the potential to form additional O3. The ozone production efficiency (7 molecules of O3 produced per molecule of NOx consumed) when ΔO3/Δt ≥ 20 ppb per 15 min was found to be smaller than estimates made from observations directly downwind of the Ship Channel petrochemical plants (e.g., ˜12). Back trajectories show that simple straight line flow was associated with mean O3 levels of 56 ppb, in contrast to flow patterns associated with a decrease in wind speed or flow reversal, which were associated with mean values of 63 ppb and extremes in excess of 125ppb. VOC samples taken during periods when ΔO3/Δt ≥ 20 ppb per 15 min were elevated and in particular light olefins were more than a factor of 7 greater than the corresponding samples collected on other occasions. No significant increase in isoprene at the Williams Tower was associated with these episodes. When air passed over stack emissions in eastern Houston, rich in VOCs, a Lagrangian model simulated O3 production rates of ˜50 ppb hr-1.

  11. Interface enhanced functionalities in BaTiO3/CaTiO3 superlattices

    NASA Astrophysics Data System (ADS)

    Wu, Xifan

    2014-03-01

    Interface engineering of oxide thin films has led to the development of many intriguing physical properties and new functionalities, in which the oxygen rotation and tilting take an crucial role. The oxygen octahedral tilt has been considered to be a coherent motion in the oxide thin-films, based on which the tilt is often neglected in the modeling of ABO3 superlattices. However, combined with state-of-art experimental high-resolution electron microscopic image, our first-principles results clearly show that oxygen octahedral tilt should be more appropriately defined by the tilting angles of two individual pyramids. Each pyramid will tilt rather independently as a function of its local chemical environment. Considering the oxygen octahedral rotation at the same time, the new picture of oxygen octahedral tilting will induce a novel interface effect, in which an unstable structure in bulk CaTiO3 will be stabilized at the interface in BaTiO3/CaTiO3 superlattice. This novel interface effect induces large polarizations both in-plane and out-of-plane with a corresponding enhanced piezoelectricity. The above scenario successfully explains the recent experimental discoveries in BaTiO3/CaTiO3 superlattices by H. Lee's and P. Evan's groups respectively.

  12. Structural and Magnetic Properties of LaCoO3/SrTiO3 Multilayers.

    PubMed

    Zhang, Hongrui; Zhang, Jing; Yang, Huaiwen; Lan, Qianqian; Hong, Deshun; Wang, Shufang; Shen, Xi; Khan, Tahira; Yu, Richeng; Sun, Jirong; Shen, Baogen

    2016-07-20

    Structural and magnetic properties of the LaCoO3/SrTiO3 (LCO/STO) multilayers (MLs) with a fixed STO layer of 4 nm but varied LCO layer thicknesses have been systematically studied. The MLs grown on Sr0.7La0.3Al0.65Ta0.35O3 (LSAT) and SrTiO3 (STO) exhibit the in-plane lattice constant of the substrates, but those on LaAlO3 (LAO) show the in-plane lattice constant between those of the first two kinds of MLs. Compared with the LCO single layer (SL), the magnetic order of the MLs is significantly enhanced, as demonstrated by a very slow decrease, which is fast for the SL, of the Curie temperature and the saturation magnetization as the LCO layer thickness decreases. For example, clear ferromagnetic order is observed in the ML with the LCO layer of ∼1.5 nm, whereas it vanishes below ∼6 nm for the LCO SL. This result is consistent with the observation that the dark stripes, which are believed to be closely related to the magnetic order, remain clear in the MLs while they are vague in the corresponding LCO SL. The present work suggests a novel route to tune the magnetism of perovskite oxide films. PMID:27377147

  13. Switchable Induced Polarization in LaAlO3/SrTiO3 Heterostructures

    SciTech Connect

    Bark, C; Sharma, P.; Wang, Y.; Baek, Seung Hyub; Lee, S.; Ryu, S.; Folkman, C H; Paudel, Tula R; Kumar, Amit; Kalinin, Sergei V; Sokolov, A.; Tsymbal, E Y; Rzchowski, M; Gruverman, Alexei; Eom, Professor Chang-Beom

    2012-01-01

    Demonstration of a tunable conductivity of the LaAlO3/SrTiO3 interfaces drew significant attention to the development of oxide electronic structures where electronic confinement can be reduced to the nanometer range. While the mechanisms for the conductivity modulation are quite different and include metal insulator phase transition and surface charge writing, generally it is implied that this effect is a result of electrical modification of the LaAlO3 surface (either due to electrochemical dissociation of surface adsorbates or free charge deposition) leading to the change in the twodimensional electron gas (2DEG) density at the LaAlO3/SrTiO3 (LAO/STO) interface. In this paper, using piezoresponse force microscopy we demonstrate a switchable electromechanical response of the LAO overlayer, which we attribute to the motion of oxygen vacancies through the LAO layer thickness. These electrically induced reversible changes in bulk stoichiometry of the LAO layer are a signature of a possible additional mechanism for nanoscale oxide 2DEG control on LAO/STO interfaces.

  14. Oxygen Octahedral Rotations in BaTiO3/CaTiO3 Superlattices

    NASA Astrophysics Data System (ADS)

    Cosgriff, Margaret; Chen, Pice; Corey, Nathaniel; Wu, Xifan; Mehta, Apurva; Tajiri, Hiroo; Lee, Ho Nyung; Evans, Paul

    2013-03-01

    Complex oxide superlattices have a wide range of electronic and magnetic properties, which are affected by the structure of the interfaces between different components of the superlattice. The magnitude, coherence, and electric field response of oxygen displacements in three different BaTiO3/CaTiO3 superlattice compositions are measured using x-ray diffraction. The displacements are greater in compositions with more consecutive CaTiO3 layers. The pattern of layer-by-layer alternating displacements is coherent over less than two superlattice unit cells. The net in-phase rotation of the oxygen octahedra gives rise to an x-ray reflection at (3/2 1/2 1). Density functional theory calculations for a 2(BaTiO3) /4(CaTiO3) composition predict a decrease in displacements of oxygen octahedra between barium and calcium layers when an electric field is applied, causing an intensity increase in this reflection. We found the intensity of this reflection for this composition increases by 1.6% when a 12.5 V pulse is applied, a weaker response than the 11% increase predicted. When a 20 V pulse is applied, the reflection intensity actually decreases by 3%, indicating a more complicated response.

  15. Tensile Behavior of Al2o3/feal + B and Al2o3/fecraly Composites

    NASA Technical Reports Server (NTRS)

    Draper, S. L.; Eldridge, J. I.; Aiken, B. J. M.

    1995-01-01

    The feasibility of Al2O3/FeAl + B and Al2O3/FeCrAlY composites for high-temperature applications was assessed. The major emphasis was on tensile behavior of both the monolithics and composites from 298 to 1100 K. However, the study also included determining the chemical compatibility of the composites, measuring the interfacial shear strengths, and investigating the effect of processing on the strength of the single-crystal Al2O3 fibers. The interfacial shear strengths were low for Al203/FeAl + B and moderate to high for Al203/FeCrAlY. The difference in interfacial bond strengths between the two systems affected the tensile behavior of the composites. The strength of the Al203 fiber was significantly degraded after composite processing for both composite systems and resulted in poor composite tensile properties. The ultimate tensile strength (UTS) values of the composites could generally be predicted with either rule of mixtures (ROM) calculations or existing models when using the strength of the etched-out fiber. The Al2O3/FeAl + B composite system was determined to be unfeasible due to poor interfacial shear strengths and a large mismatch in coefficient of thermal expansion (CTE). Development of the Al2O3/FeCrAlY system would require an effective diffusion barrier to minimize the fiber strength degradation during processing and elevated temperature service.

  16. Emergent phenomena and magnetism in high-density electron gases in SrTiO3

    NASA Astrophysics Data System (ADS)

    Stemmer, Susanne

    2013-03-01

    GdTiO3/SrTiO3 interfaces grown by molecular beam epitaxy exhibit mobile carrier densities that are remarkably well predicted by the electrostatic requirements of the compensation of the polar discontinuity at the interface. Carrier densities are ~3x1014 cm-2, or ~0.5 electron per surface unit cell. By sandwiching few-unit-cell-thick SrTiO3 layers between GdTiO3, carrier concentrations in the SrTiO3 approach densities under which on-site Coulomb interactions may appear. By changing the width of the quantum well, the 3D electron density can be varied, which allows for a systematic study of interaction effects. In this presentation, we discuss evidence for short-range Coulomb interactions, and associated phenomena, in ultrathin, confined the SrTiO3 quantum wells containing extreme charge densities. We show that narrow SrTiO3 quantum wells exhibit ferromagnetism at low temperatures, as evidenced by a hysteresis in the magnetoresistance. The Curie temperature scales with the thickness of the SrTiO3 quantum well. We discuss evidence for on-site Mott-Hubbard-type correlation physics in the temperature-dependent transport in metallic quantum wells. With increasing 3D carrier densities we observe a correlation-induced mass enhancement, followed by a transition to a correlated insulator at the highest 3D densities. We also discuss the role of disorder in the insulating state. This work was done in collaboration with Pouya Moetakef, Clayton A. Jackson, Leon Balents, Jim Allen, Jimmy Williams and David Goldhaber-Gordon.

  17. 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

  18. 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.

  19. 2DEGs at Perovskite Interfaces between KTaO3 or KNbO3 and Stannates

    PubMed Central

    Fan, Xiaofeng; Zheng, Weitao; Chen, Xin; Singh, David J.

    2014-01-01

    We report density functional studies of electron rich interfaces between KTaO3 or KNbO3 and CaSnO3 or ZnSnO3 and in particular the nature of the interfacial electron gasses that can be formed. We find that depending on the details these may occur on either the transition metal or stannate sides of the interface and in the later case can be shifted away from the interface by ferroelectricity. We also present calculations for bulk KNbO3, KTaO3, CaSnO3, BaSnO3 and ZnSnO3, showing the different transport and optical properties that may be expected on the two sides of such interfaces. The results suggest that these interfaces may display a wide range of behaviors depending on conditions, and in particular the interplay with ferroelectricity suggests that electrical control of these properties may be possible. PMID:24626191

  20. Magnetic interactions in BiFe0.5Mn0.5O3 films and BiFeO3/BiMnO3 superlattices

    PubMed Central

    Xu, Qingyu; Sheng, Yan; Khalid, M.; Cao, Yanqiang; Wang, Yutian; Qiu, Xiangbiao; Zhang, Wen; He, Maocheng; Wang, Shuangbao; Zhou, Shengqiang; Li, Qi; Wu, Di; Zhai, Ya; Liu, Wenqing; Wang, Peng; Xu, Y. B.; Du, Jun

    2015-01-01

    The clear understanding of exchange interactions between magnetic ions in substituted BiFeO3 is the prerequisite for the comprehensive studies on magnetic properties. BiFe0.5Mn0.5O3 films and BiFeO3/BiMnO3 superlattices have been fabricated by pulsed laser deposition on (001) SrTiO3 substrates. Using piezoresponse force microscopy (PFM), the ferroelectricity at room temperature has been inferred from the observation of PFM hysteresis loops and electrical writing of ferroelectric domains for both samples. Spin glass behavior has been observed in both samples by temperature dependent magnetization curves and decay of thermo-remnant magnetization with time. The magnetic ordering has been studied by X-ray magnetic circular dichroism measurements, and Fe-O-Mn interaction has been confirmed to be antiferromagnetic (AF). The observed spin glass in BiFe0.5Mn0.5O3 films has been attributed to cluster spin glass due to Mn-rich ferromagnetic (FM) clusters in AF matrix, while spin glass in BiFeO3/BiMnO3 superlattices is due to competition between AF Fe-O-Fe, AF Fe-O-Mn and FM Mn-O-Mn interactions in the well ordered square lattice with two Fe ions in BiFeO3 layer and two Mn ions in BiMnO3 layer at interfaces. PMID:25766744

  1. (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.

  2. Enhanced magnetization and polarization in chemically modified multiferroic (1-x)BiFeO3-xDyFeO3 solid solution

    NASA Astrophysics Data System (ADS)

    Zhu, W.-M.; Su, L. W.; Ye, Z.-G.; Ren, W.

    2009-04-01

    In order to develop multiferroics with large magnetization and polarization, we have prepared the (1-x)BiFeO3-xDyFeO3 (BF-DF) solid solution and systematically studied its properties. A morphotropic phase transition from rhombohedral perovskite (R3c) to orthorhombic orthoferrite (Pbnm) was found at x around 0.1. The magnetic properties of BiFeO3 were improved by the introduction of Dy3+ on the perovskite A site. Chemically modified Bi0.9Dy0.1Fe1-xTixO3+x/2 ceramics by aliovalent ionic substitution of Ti4+ for Fe3+ with excess Bi2O3 exhibit weak ferromagnetism and a typical ferroelectric hysteresis loop with a large remnant polarization of 23 μC/cm2 at room temperature and a large saturated magnetization (Ms=0.5 μB/f.u.) at 2 K. These properties entitle the BF-DF solid solution one of few multiferroic materials that exhibit both decent magnetization and electric polarization.

  3. 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

  4. High frequency elastic losses in LaAlO3 and its importance for LaAlO3/SrTiO3 heterojunctions

    NASA Astrophysics Data System (ADS)

    Salje, Ekhard K. H.; Carpenter, Michael A.

    2011-08-01

    Cooling heterojunctions on LaAlO3 substrates or thick layers of LaAlO3 on SrTiO3 substrates below 820 K lead to a ferroelastic phase transition Pm3-m→ R3-c in LaAlO3, with extensive twinning and elastic softening. Twin boundaries add to structural disorder near the heterojunction and generate partially localized carriers. Resonant Ultrasound Spectroscopy data relating to the elastic instability in LaAlO3 show that elastic Cole-Cole circles and the background autocorrelation function follow Vogel-Fulcher behaviour, with a Vogel-Fulcher temperature of 230 K. An extremely low activation energy, 0.02 eV, would promote the formation of highly structured, "glassy" LaAlO3 near the junction.

  5. Electron paramagnetic resonance of Cr3+ in near-stoichiometric LiTaO3

    NASA Astrophysics Data System (ADS)

    Loyo-Menoyo, M.; Keeble, D. J.; Furukawa, Y.; Kitamura, K.

    2005-06-01

    Electron-paramagnetic-resonance (EPR) experiments on the dominant Cr3+ center in near-stoichiometric LiTaO3 crystals, grown by the double crucible Czochralski method, are reported. A near complete roadmap of EPR positions was obtained allowing an accurate determination of the spin-Hamiltonian parameters. Newman superposition model calculations of zero-field splitting term were performed and support the model of Cr3+ incorporation within the Li octahedron. Calculations were also made for Cr3+ in LiNbO3, again good agreement with a Li site model was obtained for the main EPR center. The temperature dependence of the zero-field splitting parameter for Cr3+ in LiTaO3 was found to show anomalous behavior in the region of 40 K, suggesting the presence local structural instability at the ion site.

  6. 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)

  7. Hybrid improper ferroelectricity in SrZrO3/BaZrO3 superlattice.

    PubMed

    Zhang, Yajun; Wang, Jie; Sahoo, M P K; Wang, Xiaoyuan; Shimada, Takahiro; Kitamura, Takayuki

    2016-08-24

    Incipient ferroelectrics, which show a unique dielectric property, arouse tremendous interests due to their potential application in microwave dielectric devices. However, ferroelectric transition in incipient ferroelectrics is suppressed entirely by quantum fluctuation. Here, by means of first-principles calculations, we demonstrate that there exists hybrid improper ferroelectricity in a layered artificial superlattice composed of the incipient ferroelectrics of SrZrO3 and BaZrO3. The hybrid improper ferroelectric polarization stems from oxygen octahedral rotation and coexists with the strain-induced ferroelectric distortion. The coexistence of oxygen octahedral rotation and ferroelectric distortion results in an enhanced polarization in the superlattice. It is further found that the total polarization in the superlattice is mainly contributed by the oxygen octahedral rotation for zero or small strain, whereas the contribution from strain-induced ferroelectric distortion gradually becomes predominant as the strain increases. The phonon dispersion, energy surface and atomic displacements are calculated to shed light on the underlying mechanism of the hybrid improper ferroelectricity in the SrZrO3/BaZrO3 superlattice. PMID:27523881

  8. 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.

  9. 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.

  10. Dielectric and Electrical Properties of BiFeO3-PbZrO3 Composites

    NASA Astrophysics Data System (ADS)

    Satpathy, S. K.; Mohanty, N. K.; Behera, A. K.; Sen, S.; Behera, Banarji; Nayak, P.

    2015-11-01

    The dielectric and electrical properties of composites prepared by addition of two different amounts of PbZrO3 (PZO) to BiFeO3 (BFO) are discussed. The composites (1 - x)(BiFeO3)- x(PbZrO3) ( x = 0.5, 0.7; i.e., 0.5BF-0.5PZ and 0.3BF-0.7PZ) were synthesized by solid-state reaction. X-ray diffraction analysis confirmed formation of composites with a rhombohedral structure at room temperature. Scanning electron microscopy revealed homogeneously distributed grains. Dielectric constants and dielectric loss increased with decreasing PZO content whereas the transition temperature shifted to higher temperature with decreasing PZO content. Hysteresis loops confirmed the ferroelectric nature of the materials. The Nyquist plot was indicative of the contribution of the bulk effect and a small contribution from the grain boundary effect. Temperature-dependent relaxation occurred for both materials. Non-Debye type electrical impedance was confirmed by asymmetric peak broadening and a spread of relaxation times. Activation energies were calculated from plots of ac conductivity as a function of temperature by linear fitting. Dc and ac conductivity increased with increasing temperature. Activation energies calculated from the complex impedance plot and from the fitted Jonscher power law were very similar, implying conduction by a similar type of charge carrier in both composites.

  11. 26 CFR 301.6501(o)-3 - Partnership items.

    Code of Federal Regulations, 2011 CFR

    2011-04-01

    ... 26 Internal Revenue 18 2011-04-01 2011-04-01 false Partnership items. 301.6501(o)-3 Section 301.6501(o)-3 Internal Revenue INTERNAL REVENUE SERVICE, DEPARTMENT OF THE TREASURY (CONTINUED) PROCEDURE AND ADMINISTRATION PROCEDURE AND ADMINISTRATION Limitations Limitations on Assessment and Collection § 301.6501(o)-3 Partnership items....

  12. Carrier-Controlled Ferromagnetism in SrTiO3

    DOE PAGESBeta

    Moetakef, Pouya; Williams, James R.; Ouellette, Daniel G.; Kajdos, Adam P.; Goldhaber-Gordon, David; Allen, S. James; Stemmer, Susanne

    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

  13. Band alignment at epitaxial BaSnO3/SrTiO3(001) and BaSnO3/LaAlO3(001) heterojunctions

    NASA Astrophysics Data System (ADS)

    Chambers, Scott A.; Kaspar, Tiffany C.; Prakash, Abhinav; Haugstad, Greg; Jalan, Bharat

    2016-04-01

    We have spectroscopically determined the optical bandgaps and band offsets at epitaxial interfaces of BaSnO3 with SrTiO3(001) and LaAlO3(001). 28 u.c. BaSnO3 epitaxial films exhibit direct and indirect bandgaps of 3.56 ± 0.05 eV and 2.93 ± 0.05 eV, respectively. The lack of a significant Burstein-Moss shift corroborates the highly insulating, defect-free nature of the BaSnO3 films. The conduction band minimum is lower in electron energy in 5 u.c. films of BaSnO3 than in SrTiO3 and LaAlO3 by 0.4 ± 0.2 eV and 3.7 ± 0.2 eV, respectively. This result bodes well for the realization of oxide-based, high-mobility, two-dimensional electron systems that can operate at ambient temperature, since electrons generated in the SrTiO3 by modulation doping, or at the BaSnO3/LaAlO3 interface by polarization doping, can be transferred to and at least partially confined in the BaSnO3 film.

  14. Gd-doped BaSnO3: A transparent conducting oxide with localized magnetic moments

    NASA Astrophysics Data System (ADS)

    Alaan, Urusa S.; Shafer, Padraic; N'Diaye, Alpha T.; Arenholz, Elke; Suzuki, Y.

    2016-01-01

    We have synthesized transparent, conducting, paramagnetic stannate thin films via rare-earth doping of BaSnO3. Gd3+ (4f7) substitution on the Ba2+ site results in optical transparency in the visible regime, low resistivities, and high electron mobilities, along with a significant magnetic moment. Pulsed laser deposition was used to stabilize epitaxial Ba0.96Gd0.04SnO3 thin films on (001) SrTiO3 substrates, and compared with Ba0.96La0.04SnO3 and undoped BaSnO3 thin films. Gd as well as La doping schemes result in electron mobilities at room temperature that exceed those of conventional complex oxides, with values as high as 60 cm2/V.s (n = 2.5 × 1020 cm-3) and 30 cm2/V.s (n = 1 × 1020 cm-3) for La and Gd doping, respectively. The resistivity shows little temperature dependence across a broad temperature range, indicating that in both types of films the transport is not dominated by phonon scattering. Gd-doped BaSnO3 films have a strong magnetic moment of ˜7 μB/Gd ion. Such an optically transparent conductor with localized magnetic moments may unlock opportunities for multifunctional devices in the design of next-generation displays and photovoltaics.

  15. Sodium ion diffusion in Al2O3: a distinct perspective compared with lithium ion diffusion.

    PubMed

    Jung, Sung Chul; Kim, Hyung-Jin; Choi, Jang Wook; Han, Young-Kyu

    2014-11-12

    Surface coating of active materials has been one of the most effective strategies to mitigate undesirable side reactions and thereby improve the overall battery performance. In this direction, aluminum oxide (Al2O3) is one of the most widely adopted coating materials due to its easy synthesis and low material cost. Nevertheless, the effect of Al2O3 coating on carrier ion diffusion has been investigated mainly for Li ion batteries, and the corresponding understanding for emerging Na ion batteries is currently missing. Using ab initio molecular dynamics calculations, herein, we first find that, unlike lithiation, sodiation of Al2O3 is thermodynamically unfavorable. Nonetheless, there can still exist a threshold in the Na ion content in Al2O3 before further diffusion into the adjacent active material, delivering a new insight that both thermodynamics and kinetics should be taken into account to describe ionic diffusion in any material media. Furthermore, Na ion diffusivity in NaxAl2O3 turns out to be much higher than Li ion diffusivity in LixAl2O3, a result opposite to the conventional stereotype based on the atomic radius consideration. While hopping between the O-rich trapping sites via an Na-O bond breaking/making process is identified as the main Na ion diffusion mechanism, the weaker Na-O bond strength than the Li-O counterpart turns out to be the origin of the superior diffusivity of Na ions. PMID:25286155

  16. Search for half-metallic ferromagnetism in orthorhombic Ce(Fe/Cr)O3 perovskites

    NASA Astrophysics Data System (ADS)

    Abbad, A.; Benstaali, W.; Bentounes, H. A.; Bentata, S.; Benmalem, Y.

    2016-02-01

    The full-potential linearized augmented plane wave (FPLAPW) method based on the density functional theory within the GGA and GGA+U, is used to investigate the structural, magnetic and half-metallic properties of the Pnma orthorhombic Cerium orthoferrite (CeFeO3) and Cerium orthochromite (CeCrO3). The calculated densities of states presented in this study identify the metallic behavior CeFeO3 when we use the GGA scheme, whereas when we use the GGA+U, we see that its exhibits half-metallic character with an integer magnetic moment of 24 μB per formula unit at its equilibrium volume. CeCrO3 is half-metallic for both approaches and of n type conductivity for GGA but p type conductivity for GGA+U. It is found that the majority of the magnetic moments of both compounds originate from the cerium sites since the f states of Ce are spin polarized. From the band structure and the densities of states analysis, we find that CeCrO3 and CeFeO3 are strong candidates for spintronic applications.

  17. 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. PMID:24688424

  18. 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

  19. 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.

  20. Dielectric and electromechanical properties of LiNbO3-modified (BiNa)TiO3-(BaCa)TiO3 lead-free piezoceramics

    NASA Astrophysics Data System (ADS)

    Zaman, Arif; Hussain, Ali; Malik, Rizwan Ahmed; Maqbool, Adnan; Nahm, Sahn; Kim, Myong-Ho

    2016-05-01

    The dielectric and electromechanical properties of LiNbO3-modified (1-x) [0.91Na0.5Bi0.5TiO3-0.09Ba0.70Ca0.30TiO3]-xLiNbO3 (abbreviated as (BiNa)TiO3-(BaCa)TiO3-LN) lead-free piezoceramics were investigated. The electrical properties revealed that the addition of LiNbO3 (LN) induces a phase transition from a non-ergodic relaxor to an ergodic relaxor in the (BiNa)TiO3-(BaCa)TiO3-LN system. A large electrostrain of ~0.418% with a normalized strain of ~690 pm V-1 at 6 kV mm-1 was observed at the coexistence of the non-ergodic relaxor and ergodic relaxor phases for LN 0.020, where a field-assisted reversible phase transition between metastable ferroelectric and stable ergodic relaxor phases occurs. Subsequently, a gradual enhancement in the temperature stability of the dielectric constant was observed. At 3 mol.% LN, a nearly constant temperature and a frequency-invariant permittivity of ɛ r ~ 3300 over a broad temperature range of 147 °C-306 °C was observed along with small losses from room temperature up to 400 °C.

  1. Semitransparent inverted polymer solar cells with MoO3/Ag/MoO3 as transparent electrode

    NASA Astrophysics Data System (ADS)

    Tao, Chen; Xie, Guohua; Liu, Caixia; Zhang, Xindong; Dong, Wei; Meng, Fanxu; Kong, Xiangzi; Shen, Liang; Ruan, Shengping; Chen, Weiyou

    2009-08-01

    Semitransparent inverted polymer solar cells were developed using thermally evaporable MoO3/Ag/MoO3 as transparent anode. The ultrathin inner MoO3 layer was introduced as a buffer layer to improve hole collection, while the outer MoO3 layer served as a light coupling layer to enhance optical transmittance of the device. The dependence of the device performances on the thickness of the outer MoO3 layer was investigated. The results showed that the addition of the outer MoO3 layer improves the transmittance of the anode compared to MoO3/Ag anode and the performances of the semitransparent devices with the outer MoO3 layer are improved due to the reduced series resistance.

  2. 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.

  3. Al atom on MoO3(010) surface: adsorption and penetration using density functional theory.

    PubMed

    Wu, Hong-Zhang; Bandaru, Sateesh; Wang, Da; Liu, Jin; Lau, Woon Ming; Wang, Zhenling; Li, Li-Li

    2016-03-14

    Interfacial issues, such as the interfacial structure and the interdiffusion of atoms at the interface, are fundamental to the understanding of the ignition and reaction mechanisms of nanothermites. This study employs first-principle density functional theory to model Al/MoO3 by placing an Al adatom onto a unit cell of a MoO3(010) slab, and to probe the initiation of interfacial interactions of Al/MoO3 nanothermite by tracking the adsorption and subsurface-penetration of the Al adatom. The calculations show that the Al adatom can spontaneously go through the topmost atomic plane (TAP) of MoO3(010) and reach the 4-fold hollow adsorption-site located below the TAP, with this subsurface adsorption configuration being the most preferred one among all plausible adsorption configurations. Two other plausible configurations place the Al adatom at two bridge sites located above the TAP of MoO3(010) but the Al adatom can easily penetrate below this TAP to a relatively more stable adsorption configuration, with a small energy barrier of merely 0.2 eV. The evidence of subsurface penetration of Al implies that Al/MoO3 likely has an interface with intermixing of Al, Mo and O atoms. These results provide new insights on the interfacial interactions of Al/MoO3 and the ignition/combustion mechanisms of Al/MoO3 nanothermites. PMID:26899169

  4. 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. PMID:25859922

  5. Ferroelectricity in (BaTiO3)n/(SrTiO3)m Superlattices Containing as Few as one BaTiO3 Layer (n=1)

    NASA Astrophysics Data System (ADS)

    Schlom, Darrell

    2007-03-01

    The question of how thin a ferroelectric can be and still be ferroelectric has been the source of an intensive research effort over the past decade. Several studies, both theoretical and experimental, have concluded that with appropriate boundary conditions ferroelectricity can exist in superlattices containing BaTiO3 or PbTiO3 layers as thin as one unit cell. In this talk I will show the results of experiment and theory for BaTiO3/SrTiO3 superlattices grown by reactive molecular-beam epitaxy (MBE) on three different substrates: TiO2-terminated (001) SrTiO3, (110) DyScO3, and (110) GdScO3. With the aid of reflection high-energy electron diffraction (RHEED), precise single-monolayer doses of BaO, SrO, and TiO2 were deposited sequentially to create commensurate BaTiO3/SrTiO3 superlattices with a variety of periodicities. The superlattices consist of an n unit-cell-thick slab of BaTiO3 followed by an m unit-cell-thick slab of SrTiO3, which are designated [(BaTiO3)n/(SrTiO3)m]q, where q is the number of times the bilayer is repeated. X-ray diffraction (XRD) measurements exhibit clear superlattice peaks and the narrowest rocking curves ever reported for oxide superlattices. High-resolution transmission electron microscopy reveals nearly atomically abrupt interfaces. UV Raman results show that the BaTiO3 in these [(BaTiO3)n/(SrTiO3)m]q superlattices is tetragonal and the SrTiO3 is polar due to strain. Temperature-dependent UV Raman and XRD reveal the paraelectric-to-ferroelectric transition temperature (TC). Our results* demonstrate (1) that [(BaTiO3)n/(SrTiO3)m]q superlattices containing as few as one strained BaTiO3 layer (n=1) are ferroelectric and (2) the sensitivity of TC to the boundary conditions. Comparisons to ab initio and phase-field modeling of the properties of these [(BaTiO3)n/(SrTiO3)m]q ferroelectric superlattices will be made and the importance of strain demonstrated. In addition to probing finite size effects and the importance of mechanical boundary

  6. 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.

  7. Structure and negative thermal expansion in the PbTiO3-BiFeO3 system

    NASA Astrophysics Data System (ADS)

    Chen, J.; Xing, X. R.; Liu, G. R.; Li, J. H.; Liu, Y. T.

    2006-09-01

    The structures of (1-x)PbTiO3-xBiFeO3 (x =0.3 and 0.6) were investigated by means of the neutron powder diffraction. A splitting shift between Fe and Ti atoms was found along the c axis in 0.7PbTiO3-0.3BiFeO3; however, this splitting does not appear in 0.4PbTiO3-0.6BiFeO3. The tetragonal phase of PbTiO3-BiFeO3 exhibits a large spontaneous polarization. The negative thermal expansion of PbTiO3 is significantly enhanced in a wide temperature range by the BiFeO3 substitution. The average bulk thermal expansion coefficient of 0.4PbTiO3-0.6BiFeO3 is a¯v=-3.92×10-5°C-1, which is much strong in the known negative thermal expansion oxides.

  8. NOx versus VOC limitation of O3 production in the Po valley: Local and integrated view based on observations

    NASA Astrophysics Data System (ADS)

    Spirig, Christoph; Neftel, Albrecht; Kleinman, Lawrence I.; Hjorth, Jens

    2002-11-01

    We characterize the local O3 production at an urban and a rural site in the northern part of the Po valley (Italy) during the Pianura Padana Produzione di Ozono experiment (PIPAPO). A steady state calculation based on observations is performed to determine the local O3 production rate, P(O3), and its sensitivity to precursor concentrations. The urban site exhibited a strongly VOC sensitive O3 production rate, while both VOC and NOx sensitive conditions were observed at the rural site. In addition to the local steady state analysis, we performed one-dimensional Lagrangian model calculations that simulate conditions in the Po valley. These calculations show that the P(O3) at the surface tends to be more VOC sensitive than the average in the mixed layer. The Lagrangian calculations are also used to determine the response of O3 concentration to an emissions change. We compare emission control information with information on sensitivities from the local analysis. It is concluded that a local analysis of P(O3) within the mixing layer offers useful qualitative information but tends to overestimate VOC sensitivity as judged by a comparison with an emissions-based Lagrangian model.

  9. 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.

  10. The origin of two-dimensional electron gas formed in LaGaO3/SrTiO3

    NASA Astrophysics Data System (ADS)

    Wang, Funing; Li, Jichao; Du, Yanling; Zhang, Xinhua; Liu, Hanzhang; Liu, Jian; Wang, Chunlei; Mei, Liangmo

    2015-11-01

    The first-principles calculations are employed to investigate the electrical properties of (0 0 1) epitaxial LaGaO3/SrTiO3 heterostructure. It is found that the interface remains metallic and the atomic displacements occur mostly in the SrTiO3 side after atomic relaxation. The interface crystal field induces the Ti t2g orbitals to split into the nondegenerate dxy and two-fold degenerate dxz/yz orbitals. The partly filled nondegenerate dxy orbitals are the origin of two-dimensional electron gas at the interface of LaGaO3/SrTiO3 (0 0 1).

  11. Electric dipole sheets in BaTiO3/BaZrO3 superlattices

    NASA Astrophysics Data System (ADS)

    Jiang, Zhijun; Xu, Bin; Li, Fei; Wang, Dawei; Jia, C.-L.

    2015-01-01

    We investigate two-dimensional electric dipole sheets in the superlattice made of BaTiO3 and BaZrO3 using first-principles-based Monte Carlo simulations and density functional calculations. Electric dipole domains and complex patterns are observed and complex dipole structures with various symmetries (e.g., P m a 2 ,C m c m , and P m c 21 ) are further confirmed by density functional calculations, which are found to be almost degenerate in energy with the ferroelectric ground state of the A m m 2 symmetry, therefore strongly resembling magnetic sheets. More complex dipole patterns, including vortices and antivortices, are also observed, which may constitute the intermediate states that overcome the high-energy barrier of different polarization orientations previously predicted by A. I. Lebedev [Phys. Solid State 55, 1198 (2013), 10.1134/S1063783413060218]. We also show that such system possesses large electrostrictive effects that may be technologically important.

  12. Charge reorganization in LaMnO3 /LaNiO3 superlattice interfaces

    NASA Astrophysics Data System (ADS)

    Iori, Federico; Gloter, Alexandre; Unravel Project Team; Stem Group Team

    Functional properties of oxide heterostructurecan recently be controlled and tuned through the electronic and structural mismatch at the interface. Artificial superlattices thin film can thus present complex magnetic structure at the interface different from their corresponding bulk building blocks. In this scenario when an antiferromagnetic buk LMO and the paramagnetic bulk LNO are combined in thin filmssuperlattices, LaMnO3/LaNiO3, strong exchange bias, new metal-insulator transition or antiferromagnetic order at the interface appear. In this work we study by ab initio Density Functional Theory how the induced magnetic moments in LNO films in LMO/LMO (111)-oriented can lead to charge transfer and reorganization at the interface among the Ni and Mn metal ions for different periodicities of the superlattices (3/3, 5/5, 7/7) and how it is possible to control them through atomic intermixing at the interface.

  13. Multiferroic BiFeO3/BiCrO3 superlattices

    NASA Astrophysics Data System (ADS)

    Huijben, Mark; Kantner, Colleen; Zhan, Qian; Orenstein, Joseph; Ramesh, Ramamoorthy

    2007-03-01

    There is currently an increasing interest into multiferroic materials. Although a large number of potential applications can be envisaged, there are currently no known single-phase materials that show large, robust magnetization and polarization at room temperature. Theoretical calculations of artificially constructed (111) layered double perovskite Bi2FeCrO6 predict them to be ferrimagnetic (with a magnetic moment of 2 μB per formula unit) and ferroelectric (with a polarization of ˜80 μC/cm^2). A high degree of control over the layer composition is required to accomplish this. In this work we fabricated such epitaxial BiFeO3/BiCrO3 superlattices by laser-MBE during which the growth was controlled on the atomic scale by reflection high energy electron diffraction. We will report results of structural, chemical, electrical and magnetic measurements of such superlattices.

  14. Quasi-two-dimensional ferroelectricity in KNbO3/KTaO3 superlattices

    NASA Astrophysics Data System (ADS)

    Lebedev, A. I.

    2011-12-01

    First-principles density functional theory is used to calculate the phonon spectrum in the paraelectric phase, the ground-state structure and polarization distribution in the polar phase, and energies of ferro- and antiferroelectrically ordered phases of free-standing (KNbO3)1(KTaO3) n ferroelectric superlattices with n = 1-7. It is established that quasi-two-dimensional ferroelectricity with polarization oriented in the layer plane, which weakly interacts with polarization in neighboring layers, appears in potassium niobate layers with a thickness of one unit cell in the superlattices. The possibility of using of such ferroelectric superlattices as a medium for three-dimensional information recording is shown.

  15. 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. PMID:27502999

  16. Holmium-doped Lu2O3, Y2O3, and Sc2O3 for lasers above 2.1 μm.

    PubMed

    Koopmann, Philipp; Lamrini, Samir; Scholle, Karsten; Schäfer, Michael; Fuhrberg, Peter; Huber, Günter

    2013-02-11

    Efficient room-temperature laser operation was obtained in the wavelength range from 2117 nm to 2134 nm with Ho:Lu(2)O(3) and Ho:Y(2)O(3) as the active materials. With an FBG-stabilized Tm-doped fiber laser as the pump source, the maximum slope efficiency and output power of the Ho:Y(2)O(3) laser were 63% and 18.8 W, respectively. With Ho:Lu(2)O(3) the respective values were 76% and 25.2 W. With Ho:Sc(2)O(3) as the active material the accessible wavelength range could be expanded to 2158 nm in a diode-pumped setup. PMID:23481849

  17. 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.

  18. The magnetic properties of Bi(Fe0.95Co0.05)O3 ceramics

    NASA Astrophysics Data System (ADS)

    Xu, Qingyu; Zai, Haifa; Wu, D.; Qiu, T.; Xu, M. X.

    2009-09-01

    Bi(Fe0.95Co0.05)O3 bulk ceramics were prepared by rapid sintering using sol-gel derived fine powders. Bi(Fe0.95Co0.05)O3 crystallized in a rhombohedrally distorted BiFeO3 structure with compressive lattice distortion induced by the Co substitution at Fe sites from Raman study. Compared with BiFeO3 prepared under similar conditions, the magnetic properties were significantly enhanced, with saturate magnetization of 1.6 emu/g and remnant magnetization of 0.7 emu/g at 300 K. Clear metamagnetism was observed in Bi(Fe0.95Co0.05)O3.

  19. Phase separation, crystallization and polyamorphism in the Y(2)O(3)-Al(2)O(3) system.

    PubMed

    Skinner, Lawrie B; Barnes, Adrian C; Salmon, Philip S; Crichton, Wilson A

    2008-05-21

    A detailed study of glass formation from aerodynamically levitated liquids in the (Y(2)O(3))(x)(Al(2)O(3))(1-x) system for the composition range 0.21≤x≤0.41 was undertaken by using pyrometric, optical imaging and x-ray diffraction methods. Homogeneous and clear single-phase glasses were produced over the composition range [Formula: see text]. For Y(2)O(3)-rich compositions ([Formula: see text]), cloudy materials were produced which contain inclusions of crystalline yttrium aluminium garnet (YAG) of diameter up to 40 µm in a glassy matrix. For Y(2)O(3)-poor compositions around x = 0.24, cloudy materials were also produced, but it was not possible to deduce whether this resulted from (i) sub-micron inclusions of a nano-crystalline or glassy material in a glassy matrix or (ii) a glass formed by spinodal decomposition. For x = 0.21, however, the sample cloudiness results from crystallization into at least two phases comprising yttrium aluminium perovskite and alumina. The associated pyrometric cooling curve shows slow recalescence events with a continuous and slow evolution of excess heat which contrasts with the sharp recalescence events observed for the crystallization of YAG at compositions near x = 0.375. The materials that are the most likely candidates for demonstrating homogeneous nucleation of a second liquid phase occur around x = 0.25, which corresponds to the limit for formation of a continuous random network of corner-shared AlO(4) tetrahedra. PMID:21694284

  20. 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.

  1. Study on Viscosity of the La2O3-SiO2-Al2O3 Slag System

    NASA Astrophysics Data System (ADS)

    Deng, Yong-chun; Wu, Sheng-li; Jiang, Yin-ju; Jia, Su-qi

    2016-08-01

    The viscosities and free-running temperatures of slag in a La2O3-SiO2-Al2O3 slag system were measured using an internal rotating cylinder method. For different La2O3 mass contents (45, 50, and 55 pct) in the La2O3-SiO2-Al2O3 ternary slag, the slag viscosity and free-running temperature decreased with a decrease in SiO2 content and an increase in Al2O3 content, and decreased with an increase in La2O3 content. Minor components B2O3, FeO, and MnO could decrease the viscosity and free-running temperature of La2O3-SiO2-Al2O3 ternary slag, especially FeO, and a small amount of FeO and B2O3 had an additive effect on slag viscosity and free-running temperature reduction.

  2. 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.

  3. Towards electrical spin injection into LaAlO3-SrTiO3.

    PubMed

    Bibes, M; Reyren, N; Lesne, E; George, J-M; Deranlot, C; Collin, S; Barthélémy, A; Jaffrès, H

    2012-10-28

    Future spintronics devices will be built from elemental blocks allowing the electrical injection, propagation, manipulation and detection of spin-based information. Owing to their remarkable multi-functional and strongly correlated character, oxide materials already provide such building blocks for charge-based devices such as ferroelectric field-effect transistors (FETs), as well as for spin-based two-terminal devices such as magnetic tunnel junctions, with giant responses in both cases. Until now, the lack of suitable channel materials and the uncertainty of spin-injection conditions in these compounds had however prevented the exploration of similar giant responses in oxide-based lateral spin transport structures. In this paper, we discuss the potential of oxide-based spin FETs and report magnetotransport data that suggest electrical spin injection into the LaAlO(3)-SrTiO(3) interface system. In a local, three-terminal measurement scheme, we analyse the voltage variation associated with the precession of the injected spin accumulation driven by perpendicular or longitudinal magnetic fields (Hanle and 'inverted' Hanle effects). The spin accumulation signal appears to be much larger than expected, probably owing to amplification effects by resonant tunnelling through localized states in the LaAlO(3). We give perspectives on how to achieve direct spin injection with increased detection efficiency, as well on the implementation of efficient top gating schemes for spin manipulation. PMID:22987038

  4. 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

    2016-01-01

    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

    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

  6. Large refractive index in BiFeO3-BiCoO3 epitaxial films

    NASA Astrophysics Data System (ADS)

    Shima, Hiromi; Nishida, Ken; Yamamoto, Takashi; Tadokoro, Toshiyasu; Tsutsumi, Koichi; Suzuki, Michio; Naganuma, Hiroshi

    2013-05-01

    Rhombohedral (R-) and tetragonal (T-) Bi(Fe,Co)O3 (BFCO) films were epitaxially grown on the SrTiO3 (100) substrates, and the optical properties of the BFCO films were evaluated by spectroscopic ellipsometry. It was revealed that the refractive indexes of R- and T-BFCO epitaxial films were 2.93 and 2.86 at wavelength of 600 nm, and 2.65 and 2.59 at 1550 nm, respectively, which are comparable to the pure BiFeO3. The refractive index of the R-BFCO film was totally larger than that of the T-BFCO film; it might be caused by structural strain and local symmetry breaking. It was confirmed that the extinction coefficients of both films were almost zero at wavelengths larger than 600 nm. In addition, the optical band gaps of the R- and T-BFCO films were estimated to be 2.78 and 2.75 eV, respectively. It can expect that the BFCO film has a possibility to use optical-magnetic field sensor working at room temperature.

  7. Metal-insulator transition in nanostructured SrTiO3/LaAlO3

    NASA Astrophysics Data System (ADS)

    Zhuang, Houlong; Cooper, Valentino R.; Ganesh, P.; Xu, Haixuan; Kent, P. R. C.

    2015-03-01

    It is well known that an insulator-to-metal transition occurs at SrTiO3/LaAlO3 epitaxial heterostructures when the number of LaAlO3 layers reaches a critical value of four. With first-principles calculations, we show that instead of requiring the threshold number of layers to trigger metallicity, the so-called 1+2 overlayer heterostructure also exhibits metallic states. Interestingly, we demonstrate that these metallic states form a two-dimensional electron gas at the overlayer heterostructure. We understand that these fascinating phenomena originate from a modified ``polar catastrophe'' model, where the overlayer heterostructure accumulates an electrostatic potential more rapidly than regular heterostructures, leading to the reduction of number of LAO layers. Using this model, we further show that the thinner 1+1 overlayer heterostructure exhibits a similar 2DEG. Our work provides a novel approach of inducing 2DEGs in oxide heterostructures, which are beneficial for modern electronics applications. HZ, PRCK, VRC and PG were sponsored by the LDRD at ORNL for the U.S. DOE and HX by the University of Tennessee JDRD and UT/ORNL-JIAM programs.

  8. Band alignment and electrical properties of Al2O3/β-Ga2O3 heterojunctions

    NASA Astrophysics Data System (ADS)

    Kamimura, Takafumi; Sasaki, Kohei; Hoi Wong, Man; Krishnamurthy, Daivasigamani; Kuramata, Akito; Masui, Takekazu; Yamakoshi, Shigenobu; Higashiwaki, Masataka

    2014-05-01

    The band alignment of Al2O3/n-Ga2O3 was investigated by x-ray photoelectron spectroscopy (XPS). With a band gap of 6.8 ± 0.2 eV measured for Al2O3, the conduction and valence band offsets at the interface were estimated to be 1.5 ± 0.2 eV and 0.7 ± 0.2 eV, respectively. The conduction band offset was also obtained from tunneling current in Al2O3/n-Ga2O3 (2¯01) metal-oxide-semiconductor (MOS) diodes using the Fowler-Nordheim model. The electrically extracted value was in good agreement with the XPS data. Furthermore, the MOS diodes exhibited small capacitance-voltage hysteresis loops, indicating the successful engineering of a high-quality Al2O3/Ga2O3 interface.

  9. The metallic interface between insulating NdGaO3 and SrTiO3 perovskites

    NASA Astrophysics Data System (ADS)

    Li, Chen; Xu, Qinfang; Wen, Zheng; Zhang, Shantao; Li, Aidong; Wu, Di

    2013-11-01

    Perovskite NdGaO3 (NGO) films, 2-20 unit cells in thickness, have been deposited epitaxially on {001} TiO2-terminated SrTiO3 substrates at different O2 pressures. The {001} NdGaO3/SrTiO3 (STO) interface becomes metallic as the NdGaO3 overlayer is more than 4 unit cells in thickness. The sheet carrier density is above 1013 cm-2 and temperature-independent from 300 down to 7 K. Similar metallic interface has also been achieved in {111} NdGaO3/SrTiO3. Post-annealing in O2 does not change the transport characteristics significantly. These indicate that oxygen vacancies may not have a predominant contribution to the observed interfacial conduction in NGO/STO heterostructures deposited at high oxygen pressure.

  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. Enhanced switching characteristics and piezoelectric response in epitaxial BiFeO3-TbMnO3 thin films

    NASA Astrophysics Data System (ADS)

    Li, Wei; Wang, Yiping; Nie, Pengxiao; Hu, Querui; Yang, Ying; Yuan, Guoliang

    2015-06-01

    High-quality (001) oriented epitaxial 0.9BiFeO3-0.1TbMnO3 thin films were grown on La2/3Sr1/3MnO3 and SrRuO3 buffered SrTiO3 substrate using pulsed laser deposition. X-ray diffraction showed that the films are single-phase perovskite without secondary impurity phases. Domain structures and upward ferroelectric self-poling phenomenon were distinctly observed in both films with compressive epitaxial strains. Furthermore, the upward self-poling disappears in polycrystalline 0.9BiFeO3-0.1TbMnO3 thin film on Pt/TiO2/SiO2/Si substrates. Through local switching spectroscopy measurements, the evidence of enhanced ferroelectric switching and piezoelectric response characteristics have been provided.

  12. Structure evolution of nanoparticulate Fe2O3

    NASA Astrophysics Data System (ADS)

    Erlebach, Andreas; Kurland, Heinz-Dieter; Grabow, Janet; Müller, Frank A.; Sierka, Marek

    2015-02-01

    The atomic structure and properties of nanoparticulate Fe2O3 are characterized starting from its smallest Fe2O3 building unit through (Fe2O3)n clusters to nanometer-sized Fe2O3 particles. This is achieved by combining global structure optimizations at the density functional theory level, molecular dynamics simulations by employing tailored, ab initio parameterized interatomic potential functions and experiments. With the exception of nearly tetrahedral, adamantane-like (Fe2O3)2 small (Fe2O3)n clusters assume compact, virtually amorphous structures with little or no symmetry. For n = 2-5 (Fe2O3)n clusters consist mainly of two- and three-membered Fe-O rings. Starting from n = 5 they increasingly assume tetrahedral shape with the adamantane-like (Fe2O3)2 unit as the main building block. However, the small energy differences between different isomers of the same cluster-size make precise structural assignment for larger (Fe2O3)n clusters difficult. The tetrahedral morphology persists for Fe2O3 nanoparticles with up to 3 nm in diameter. Simulated crystallization of larger nanoparticles with diameters of about 5 nm demonstrates pronounced melting point depression and leads to formation of ε-Fe2O3 single crystals with hexagonal morphology. This finding is in excellent agreement with the results obtained for Fe2O3 nanopowders generated by laser vaporization and provides the first direct indication that ε-Fe2O3 may be thermodynamically the most stable phase in this size regime.The atomic structure and properties of nanoparticulate Fe2O3 are characterized starting from its smallest Fe2O3 building unit through (Fe2O3)n clusters to nanometer-sized Fe2O3 particles. This is achieved by combining global structure optimizations at the density functional theory level, molecular dynamics simulations by employing tailored, ab initio parameterized interatomic potential functions and experiments. With the exception of nearly tetrahedral, adamantane-like (Fe2O3)2 small (Fe2O3)n

  13. NMR study of a 17O enriched LaMnO3 stoichiometric crystal

    NASA Astrophysics Data System (ADS)

    Pinsard-Gaudart, L.; Trokiner, A.; Verkhovskii, S.; Gerashenko, A.; Dragoe, N.

    2011-12-01

    We present the synthesis and the NMR characterization of a 17O enriched LaMnO 3 crystalline sample. We checked that it is single phase and, more important, stoichiometric in oxygen. Its 17O enrichment estimated by NMR is about 5.5%. These first 17O NMR results obtained at T=415 K in an undoped parent LaMnO 3 manganite demonstrate that the two oxygen sites of the structure probe very different Mn spin correlations in the paramagnetic orbital ordered phase. This work opens the way to study experimentally the interactions responsible for the orbital order.

  14. 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.

  15. Regional and Local Influences on Surface O3 over Beijing: Constraints from Integrated Surface observations and Modeling

    NASA Astrophysics Data System (ADS)

    Wang, Y.; McElroy, M. B.; Munger, W.; Hao, J.; Ma, H.; Chen, Y.

    2007-05-01

    Beijing, the Chinese capital, faces the challenge of improving its atmospheric environment while seeing an annual growth rate of 15% in the number of personal vehicles on the road. Among many pollutants, surface ozone is of particular concern for Beijing as it will host the "green" Olympics Games in summer 2008. Continuous measurements of surface O3 and CO at Miyun (a rural site 50km northeast of Beijing) in 2006 are analyzed using a 3-dimensional chemical transport model (GEOS-Chem) to improve our understanding of regional and local factors contributing to changes in tropospheric O3 in the Beijing area. The location of the site was selected to sample both clean continental air and pollution included in the plume from Beijing. To our knowledge, this is the first station in mainland China providing continuous measurements of O3 and related species (CO and CO2) over a relatively long period (years). Observations show that O3 peaks in June and September, while CO has a broad maximum in winter. Using updated emissions for China, the model successfully reproduces the seasonal variability in O3, CO, and their correlations observed at Miyun. Regional O3 levels representative of north China are identified from observations using concurrent measurements of CO. Events with daytime peak O3 concentrations exceeding 100 ppb were observed mainly in summer (JJA) and in September. A major discrepancy of the model is an overestimate of O3 in July. Observations show a decrease of 16 ppb in mean (median) O3 from June to July, presumably associated with enhanced precipitation and cloudiness in July. Implications of high levels of O3 for crop production will be discussed.

  16. Recovery of ectomycorrhiza after 'nitrogen saturation' of a conifer forest.

    PubMed

    Högberg, Peter; Johannisson, Christian; Yarwood, Stephanie; Callesen, Ingeborg; Näsholm, Torgny; Myrold, David D; Högberg, Mona N

    2011-01-01

    Trees reduce their carbon (C) allocation to roots and mycorrhizal fungi in response to high nitrogen (N) additions, which should reduce the N retention capacity of forests. The time needed for recovery of mycorrhizas after termination of N loading remains unknown. Here, we report the long-term impact of N loading and the recovery of ectomycorrhiza after high N loading on a Pinus sylvestris forest. We analysed the N% and abundance of the stable isotope (15) N in tree needles and soil, soil microbial fatty acid biomarkers and fungal DNA. Needles in N-loaded plots became enriched in (15) N, reflecting decreased N retention by mycorrhizal fungi and isotopic discrimination against (15) N during loss of N. Meanwhile, needles in N-limited (control) plots became depleted in (15) N, reflecting high retention of (15) N by mycorrhizal fungi. N loading was terminated after 20yr. The δ(15) N and N% of the needles decreased 6yr after N loading had been terminated, and approached values in control plots after 15yr. This decrease, and the larger contributions compared with N-loaded plots of a fungal fatty acid biomarker and ectomycorrhizal sequences, suggest recovery of ectomycorrhiza. High N loading rapidly decreased the functional role of ectomycorrhiza in the forest N cycle, but significant recovery occurred within 6-15yr after termination of N loading. PMID:20880225

  17. 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...

  18. A statistical approach to estimate O3 uptake of ponderosa pine in a mediterranean climate.

    PubMed

    Grulke, N E; Preisler, H K; Fan, C C; Retzlaff, W A

    2002-01-01

    In highly polluted sites, stomatal behavior is sluggish with respect to light, vapor pressure deficit, and internal CO2 concentration (Ci) and poorly described by existing models. Statistical models were developed to estimate stomatal conductance (gs) of 40-year-old ponderosa pine at three sites differing in pollutant exposure for the purpose of calculating O3 uptake. Gs was estimated using julian day, hour of day, pre-dawn xylem potential and photosynthetic photon flux density (PPFD). The median difference between estimated and observed field gs did not exceed 10 mmol H2O m(-2) s(-1), and estimated gs within 95% confidence intervals. 03 uptake was calculated from hourly estimated gs, hourly O3 concentration, and a constant to correct for the difference in diffusivity between water vapor and 03. The simulation model TREGRO was also used to calculate the cumulative 03 uptake at all three sites. 03 uptake estimated by the statistical model was higher than that simulated by TREGRO because gas exchange rates were proportionally higher. O3 exposure and uptake were significantly correlated (r2>0.92), because O3 exposure and gs were highly correlated in both statistical and simulation models. PMID:12152824

  19. Role of codoping on multiferroic properties at room temperature in BiFeO3 ceramic

    NASA Astrophysics Data System (ADS)

    Ghosh, Anup K.; Dwivedi, G. D.; Chatterjee, B.; Rana, B.; Barman, A.; Chatterjee, S.; Yang, H. D.

    2013-07-01

    Role of codoping (20% La in Bi-site and 10% Mn in Fe-site) on mutiferroic properties in insulating BiFeO3 ceramic have been investigated. The X-ray diffraction (XRD) with Rietveld refinement shows that the structure of Bi0.8La0.2FeO3 is orthorhombic (Pnma). Furthermore, it shows that on substitution of 10% Mn-ions in Fe-site, no structural change occurs which has been supported by micro-Raman study. DTA study shows that ferroelectric transition temperature (TC) decreases very fast due with La-doping and slowly with the Mn-doping. Measurement on magnetization vs. applied magnetic field (M-H) shows increase of magnetization due to codoping of La and Mn in BiFeO3. This may be due to partly destruction or suppression of the spin cycloid structure in it and/ or the introduction of the mixed valance state. P-E measurement shows high leakage in Bi0.8La0.2Fe0.9Mn0.1O3.

  20. Eu doping in multiferroic BiFeO3 ceramics studied by Mossbauer and EXAFS spectroscopy.

    PubMed

    Kothari, Deepti; Raghavendra Reddy, V; Gupta, Ajay; Meneghini, Carlo; Aquilanti, Giuliana

    2010-09-01

    Bismuth ferrite ceramics (BiFeO(3)) are multifunctional materials classified as multiferroics for their special magnetic and electric properties that can be modified by substitutional doping at the Bi and/or Fe sites. Understanding the relation between magnetoelectric response and structural/electronic modification upon doping is a relevant issue. In this work, the structure of Eu-doped multiferroic systems (Bi(1-x)Eu(x)FeO(3), x = 0, 0.5, 0.1, 0.15) as well as the valence state of Fe and Eu ions have been investigated combining Mossbauer and x-ray absorption fine structure (XAFS) spectroscopy techniques. The Eu(3+) doping at the Bi site results in better magnetic properties. High temperature (57)Fe Mossbauer data and Fe K-edge XAFS results show that FeO(6) octahedron distortions reduce with Eu(3+) doping. It is conclusively shown that the observed magnetic properties in BiFeO(3) with chemical substitution (Eu) are mainly due to the structural distortions and not due to Fe multiple valence. (151)Eu Mossbauer measurements show that the Eu(3+)(Bi(3+)) site is magnetically inactive in BiFeO(3). PMID:21403301

  1. Eu doping in multiferroic BiFeO3 ceramics studied by Mossbauer and EXAFS spectroscopy

    NASA Astrophysics Data System (ADS)

    Kothari, Deepti; Raghavendra Reddy, V.; Gupta, Ajay; Meneghini, Carlo; Aquilanti, Giuliana

    2010-09-01

    Bismuth ferrite ceramics (BiFeO3) are multifunctional materials classified as multiferroics for their special magnetic and electric properties that can be modified by substitutional doping at the Bi and/or Fe sites. Understanding the relation between magnetoelectric response and structural/electronic modification upon doping is a relevant issue. In this work, the structure of Eu-doped multiferroic systems (Bi1 - xEuxFeO3, x = 0, 0.5, 0.1, 0.15) as well as the valence state of Fe and Eu ions have been investigated combining Mossbauer and x-ray absorption fine structure (XAFS) spectroscopy techniques. The Eu3 + doping at the Bi site results in better magnetic properties. High temperature 57Fe Mossbauer data and Fe K-edge XAFS results show that FeO6 octahedron distortions reduce with Eu3 + doping. It is conclusively shown that the observed magnetic properties in BiFeO3 with chemical substitution (Eu) are mainly due to the structural distortions and not due to Fe multiple valence. 151Eu Mossbauer measurements show that the Eu3 + (Bi3 + ) site is magnetically inactive in BiFeO3.

  2. Efficient n-type doping of MoO3

    NASA Astrophysics Data System (ADS)

    Peelaers, Hartwin; van de Walle, Chris G.

    MoO3 is a layered material that has shown great promise as a transparent contact to organic photovoltaics and organic light-emitting diodes. It also exhibits photo- and electrochromic properties, and can be used as catalyst or sensor material. Due to its capability to reversibly accommodate Li it can be used in Li batteries. Despite these interesting properties, remarkably little is known about the properties of native defects and the possibilities of controlling the properties by intentional doping. We have used advanced hybrid functional calculations within density functional theory to investigate efficient doping strategies for this material. In particular, we explored the role of native defects in the conductivity of this material. To control the n-type conductivity and to obtain a larger amount of free carriers, intentional dopants can be used. We show that substitutional Re (on a Mo site) is a shallow donor. In contrast, substitutional doping with Mn, which also has one additional electron compared to Mo, leads to compensating behavior. Halogen impurities on the O site also act as shallow donors. This work was supported by NSF and DOE.

  3. 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

  4. FixO3 : Early progress towards Open Ocean observatory Data Management Harmonisation

    NASA Astrophysics Data System (ADS)

    Pagnani, Maureen; Huber, Robert; Lampitt, Richard

    2014-05-01

    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 4 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 will improve access to marine observatory data by harmonizing data management standards and workflows covering the complete life cycle of data from real time data acquisition to long-term archiving. Legal and data policy aspects will be examined to identify transnational barriers to open-access to marine observatory data. A harmonised FixO3 data policy is being synthesised from the partner's existing policies, which will overcome the identified barriers, and provide a formal basis for data exchange between FixO3 infrastructures. Presently, the interpretation and implementation of accepted standards has considerable incompatibilities within the observatory community, and these different approaches will be unified into the FixO3 approach. Further, FixO3 aims to harmonise data management and standardisation efforts with other European and international marine data and observatory infrastructures. The FixO3 synthesis will build on the standards established in other European infrastructures such as EDMONET, SEADATANET, PANGAEA, EuroSITES (European contribution to JCOMMP OceanSITES programme), and MyOcean (the Marine Core Service for GMES) infrastructures as well as relevant international infrastructures and data centres such as the ICOS Ocean Thematic Centre

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

    DOE PAGESBeta

    Darbah, Joseph N. T.; Kubiske, Mark E.; Nelson, Neil; Oksanen, Elina; Vaapavuori, Elina; Karnosky, David F.

    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

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

    PubMed

    Kang, Hsu-Ya; Wang, H Paul

    2013-07-01

    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. PMID:23790076

  7. 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.

  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. Indications of strong neutral impurity scattering in Ba(Sn,Sb)O3 single crystals

    NASA Astrophysics Data System (ADS)

    Kim, Hyung Joon; Kim, Jiyeon; Kim, Tai Hoon; Lee, Woong-Jhae; Jeon, Byung-Gu; Park, Ju-Young; Choi, Woo Seok; Jeong, Da Woon; Lee, Suk Ho; Yu, Jaejun; Noh, Tae Won; Kim, Kee Hoon

    2013-09-01

    It was recently discovered that a transparent n-type (Ba,La)SnO3 system has electrical mobility as high as 320 cm2 V-1 s-1 at room temperature and superior thermal stability up to ˜500 °C. To understand comparatively the carrier-scattering mechanism in the doped BaSnO3, we investigate the physical properties of the single crystals of BaSn1-xSbxO3 (x = 0.03, 0.05, and 0.10), which also show the n-type characters via the Sn site doping by Sb. Transmittance of the grown single crystals in the visible spectral region turn out to be similar to that of the (Ba,La)SnO3 system, maintaining optical transparency. Temperature-dependent Hall effect measurements reveal that the electrical mobility at room temperature reaches as high as 79.4 cm2 V-1 s-1 at a carrier density of 1.02×1020 cm-3, and upon increasing carrier density further, it systematically decreases nearly proportional to the inverse of the carrier density. The overall reduced mobility of the Ba(Sn,Sb)O3 system as compared to the (Ba,La)SnO3 system is attributed to the enhanced scattering caused by the Sb ions located in the direct conduction path. Based on the inverse proportionality between the carrier density and the electrical mobility, we suggest that the neutral impurity scattering becomes particularly strong in the Ba(Sn,Sb)O3.

  10. 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. PMID:26758684

  11. Phase Structure, Piezoelectric and Multiferroic Properties of SmCoO3-Modified BiFeO3-BaTiO3 Lead-Free Ceramics

    NASA Astrophysics Data System (ADS)

    Jiang, Na; Tian, Mijie; Luo, Lingling; Zheng, Qiaoji; Shi, Dongliang; Lam, Kwok Ho; Xu, Chenggang; Lin, Dunmin

    2016-01-01

    (0.75- x)BiFeO3-0.25BaTiO3- xSmCoO3 + 1 mol.% MnO2 lead-free multiferroic ceramics were synthesized by a conventional ceramic fabrication technique. The effects of SmCoO3 on phase structure, piezoelectricity and multiferroicity of the ceramics were studied. All the ceramics can be well sintered at a low sintering temperature of 960°C. The crystalline structure of the ceramics is transformed from rhombohedral to tetragonal symmetry with increasing the amount of SmCoO3. A morphotropic phase boundary of rhombohedral and tetragonal phases is formed at x = 0.01-0.04. A small amount of SmCoO3 is shown to improve the ferroelectric, piezoelectric and magnetoelectric properties of the ceramics. For the ceramics with x = 0.01-0.03, enhanced resistivity ( R ˜ 1.2 × 109 Ω cm to 2.1 × 109 Ω cm), piezoelectricity ( d 33 ˜ 65 pC/N to 106 pC/N) and ferroelectricity ( P r ˜ 6.38 μC/cm2 to 22.89 μC/cm2) are obtained. The ferromagnetism of the materials is greatly enhanced by the doping of SmCoO3 such that a very high magnetoelectric coefficient of ˜742 mV/(cm Oe) is obtained at x = 0.01, suggesting a promising potential in multiferroic devices.

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

    PubMed

    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 21(st) 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

  13. 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

  14. Direct Spectroscopic Observation of a Shallow Hydrogenlike Donor State in Insulating SrTiO3

    NASA Astrophysics Data System (ADS)

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

    2014-10-01

    We present a direct spectroscopic observation of a shallow hydrogenlike muonium state in SrTiO3 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 ˜70 K. 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 SrTiO3. The observed shallow donor state provides new insight for tailoring the electronic and optical properties of SrTiO3-based oxide interface systems.

  15. Studies on structural and electrical properties of pure and doped h-YMnO3

    NASA Astrophysics Data System (ADS)

    Rathod, K. N.; Rajyaguru, Bhargav; Solanki, Sapana; Shrimali, V. G.; Sagapariya, Khushal; Markna, J. H.; Solanki, P. S.; Shah, N. A.

    2016-05-01

    In the present communication, we report the results of the structural and electrical studies on pure YMnO3 (YMO) and Zr doped Y0.95Zr0.05MnO3 (YZMO) samples, synthesized using low cost sol-gel technique. To understand the structural properties, structural phases present and effect of doping on the structural behavior, X-ray diffraction (XRD) measurements were carried out for both the samples understudy. XRD results reveal the single phasic nature of both the samples having hexagonal unit cell structure. Improved crystal structure has been observed for pure YMnO3 sample while doping of Zr at Y-site degrades the structure of the sample. Improved dielectric constant and enhanced AC conductivity (σa) have been discussed on the basis of charge carrier polarization and correlated barrier hopping due to the localized state.

  16. XAFS analysis for quantification of the gallium coordinations in Al2O3-supported Ga2O3 photocatalysts

    NASA Astrophysics Data System (ADS)

    Akatsuka, M.; Yoshida, T.; Yamamoto, N.; Yamamoto, M.; Ogawa, S.; Yagi, S.

    2016-05-01

    Ga2O3 loaded Al2O3 samples (Ga2O3/Al2O3) were prepared to change coordination structures around Ga atoms. Ga K-edge XANES spectra of the Ga2O3/Al2O3 samples showed two peaks assigned to Ga atoms having tetrahedral coordination structure (Ga(t)) and octahedral one (Ga(o)). Curve-fitting analysis of XANES spectra was carried out with a set of pseudo- Voight and arctangent functions, and the fractions of Ga(t) and Ga(o) were quantitatively estimated from the ratio of the peak areas. EXAFS curve-fitting analysis also evaluated the fractions of Ga(t) and Ga(o) and they were in good agreement with those obtained by XANES analysis. It was revealed that the fraction of Ga(t) increased with the decrease in the loading amount of Ga2O3 due to the interaction of Ga species with Al2O3. The fractions of Ga(t) and Ga(o) might relate to the photocatalytic activity for CO2 reduction with H2O over the Ga2O3/Al2O3 samples.

  17. 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.

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

    DOE PAGESBeta

    Tietz, F.; Arul Raj, I.; Ma, Q.; Baumann, S.; Mahmoud, A.; Hermann, R. P.

    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

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

    SciTech Connect

    Tietz, Frank; Raj, I. Arul; Ma, Q.; Baumann, S.; Mahmoud, A.; Hermann, Raphael P

    2016-01-01

    An overview is presented 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. The maximum 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. The substitution had a great influence on the chemical properties of the materials.

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

    NASA Astrophysics Data System (ADS)

    Tietz, F.; Arul Raj, I.; Ma, Q.; Baumann, S.; Mahmoud, A.; Hermann, R. P.

    2016-05-01

    An overview is presented on the variation of electrical conductivity, oxygen permeation, 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. The maximum 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 13.2×10-6 K-1 and 21.9×10-6 K-1 for LaNi0.5Fe0.5O3 and LaCoO3, respectively. 57Fe Mössbauer spectroscopy was used as probe for the oxidation states, local environment and magnetic properties of iron ions as a function of chemical composition. The substitution had a great influence on the chemical properties of the materials.

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

    DOE PAGESBeta

    Tietz, Frank; Raj, I. Arul; Ma, Q.; Baumann, S.; Mahmoud, A.; Hermann, Raphael P

    2016-01-01

    An overview is presented 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. The maximum DCmore » 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. The substitution had a great influence on the chemical properties of the materials.« less

  2. Laboratory Measurement of O3(v) + O Vibrational Energy Transfer

    NASA Astrophysics Data System (ADS)

    Castle, K. J.; Hwang, E. S.; Dodd, J. A.

    2007-12-01

    Photochemical reactions involving O3 play a key role in determining the thermal and radiative structure of the upper mesosphere/lower thermosphere. Emission detected in NASA's TIMED/SABER 9.6-μm channel is dominated by the O3(ν3) asymmetric stretch mode, including hot band and combination band emission arising from vibrationally-excited O3(v) populated by O + O2 + M three-body recombination. Rate coefficients kM(O3) for the relaxation of O3(v) by O2, N2, and O must be known to confidently model the O3 photochemistry in this region. Measurements of O3( v) quenching by O2 and N2 have been performed by several groups, including the temperature dependence. On the other hand, rate coefficients kO(O3) for quenching of O3(ν2,ν3) by O were only reported in a single published paper some 30 years ago. Those measurements were performed at room temperature, and yielded rate coefficients with factor-of-two precision. The data suggest that quenching of O3(v) by O could make a significant contribution especially at higher altitudes, motivating an updated measurement. The goal of the present work is to measure the quenching of several excited O3(v) levels by O using a temperature-jump/transient diode laser absorption experiment similar to the ongoing CO2(ν2)-O study. Ultimately a variable-temperature reaction cell will be used to measure temperature-dependent O3(v)-O relaxation rates for the first time.

  3. Emission of NO and deposition of O3 in a tropical forest system

    NASA Technical Reports Server (NTRS)

    Kaplan, W. A.; Wofsy, S. C.; Keller, M.; Da Costa, Jose Maria

    1988-01-01

    Rates for emission of NO and deposition of O3 were measured at a tropical forest site in Reserve Adolfo Ducke, near Manaus, Brazil. Two independent techniques were used to determine the NO flux: (1) a soil enclosure method and (2) a method based on simultaneous observations of NO and O3 vertical profiles at night, when NO is irreversibly removed by reaction with O3. Results obtained using the two techniques agreed well, giving an average NO flux of 5.2 + or - 1.7 x 10 to the 10th molecules/sq cm per sec and an average vertical exchange coefficient of 2.2 x 10 to the 3rd cu cm/sec. Sources of NO from tropical forest soils may be important for global atmospheric chemistry. Rapid removal of O3 was observed in the lowest levels of the forest. The nocturnal deposition rate was estimated to be 5.6 + or - 2.5 x 10 to the 11th molecules/sq cm per sec through the 6-m level. The large deposition rate for O3 is consistent with the strong sink inferred from observations of ozone in the Amazon region.

  4. Structural and multiferroic properties of La-modified BiFeO3 ceramics

    NASA Astrophysics Data System (ADS)

    Das, S. R.; Choudhary, R. N. P.; Bhattacharya, P.; Katiyar, R. S.; Dutta, P.; Manivannan, A.; Seehra, M. S.

    2007-02-01

    The coexistence of the magnetic and the electrical properties in lanthanum (La)-modified bismuth ferrite (Bi1-xLaxFeO3, x =0.05, 0.1, 0.15, and 0.2) ceramics was studied and compared with those of bismuth ferrite (BiFeO3). The presence of a small secondary phase of BiFeO3 (arises due to excess Bi2O3) was removed on La substitution at the Bi site, as observed in x-ray diffraction (XRD). The effect of La substitution on dielectric constant, loss tangent, and remnant polarization of the samples was studied in a wide range of temperature (77-400K ) and frequency (1kHz-1MHz). The variation of magnetization, coercive field, and exchange bias with temperature (2-300K) and La concentration were investigated. These changes in the magnetic parameters with La doping along with those of the electron magnetic resonance parameters measured at 300K and 9.28GHz are understood in terms of increase in the magnetic anisotropy and magnetization. These results also show that stabilization of crystal structure and nonuniformity in spin cycloid structure by La substitution enhances the multiferroic properties of BiFeO3.

  5. Photodissociation dynamics of O 3- at 523 nm

    NASA Astrophysics Data System (ADS)

    Garner, M. C.; Sherwood, C. R.; Hanold, K. A.; Continetti, R. E.

    1996-01-01

    The photodissociation dynamics of O 3- at 523 nm have been studied using fast-ion-beam translational energy spectroscopy. Translational energy and angular distributions of coincident O - + O 2 products from the process O 3- + hv → O - + O 2 were measured. O 3- was generated by electron-impact in a pulsed beam from two precursors — neat O 2 and a seeded beam of O 3. The observed photodissociation dynamics are very different in the two cases, indicating a great difference in internal excitation of ozonide in the two sources.

  6. Silicon diffusion control in atomic-layer-deposited Al2O3/La2O3/Al2O3 gate stacks using an Al2O3 barrier layer.

    PubMed

    Wang, Xing; Liu, Hong-Xia; Fei, Chen-Xi; Yin, Shu-Ying; Fan, Xiao-Jiao

    2015-01-01

    In this study, the physical and electrical characteristics of Al2O3/La2O3/Al2O3/Si stack structures affected by the thickness of an Al2O3 barrier layer between Si substrate and La2O3 layer are investigated after a rapid thermal annealing (RTA) treatment. Time of flight secondary ion mass spectrometry (TOF-SIMS) and X-ray photoelectron spectroscopy (XPS) tests indicate that an Al2O3 barrier layer (15 atomic layer deposition (ALD) cycles, approximately 1.5 nm) plays an important role in suppressing the diffusion of silicon atoms from Si substrate into the La2O3 layer during the annealing process. As a result, some properties of La2O3 dielectric degenerated by the diffusion of Si atoms are improved. Electrical measurements (C-V, J-V) show that the thickness of Al2O3 barrier layer can affect the shift of flat band voltage (V FB) and the magnitude of gate leakage current density. PMID:25897303

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

    DOE PAGESBeta

    Yang, H.; Lee, H. S.; Kotula, P. G.; Sato, Y.; Ikuhara, Y.; Browning, N. D.

    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

  8. 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.

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

    NASA Astrophysics Data System (ADS)

    Yang, H.; Lee, H. S.; Kotula, P. G.; Sato, Y.; Ikuhara, Y.; Browning, N. D.

    2015-03-01

    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. The presence of Pr3+ induces structural variations and changes the statistical prevalence of the GB structures. In contrast to the assumption that Pr3+ substitutes on the Sr site in the bulk, Pr3+ is found to substitute on both Sr and Ti sites inside the GBs, with the highest concentration at the Ti sites. This amphoteric doping behavior in the boundary plane is further confirmed by first principles theoretical calculations.

  10. Measurements of CO and O3 at Shemya, Alaska

    NASA Astrophysics Data System (ADS)

    Jaffe, Dan; Yurganov, Leonid; Pullman, Eric; Reuter, Joseph; Mahura, Alexander; Novelli, Paul

    1998-01-01

    In situ measurements of surface CO were conducted from June 1994 to May 1995, and surface ozone was measured from February to May, 1995, at Shemya, Alaska (52o44'N, 174o06'E) using nondispersive infrared-gas filter correlation (GFC) and UV absorption spectroscopy, respectively. Over the same period, air samples were collected in flasks for analysis of CO and other trace gases as part of the NOAA-CMDL cooperative air sampling network. We compared the continuous GFC measurements with the National Oceanic and Atmospheric Administration Climate Monitoring and Diagnostics Laboratory (NOAA-CMDL) flask data. Over this 1-year period, CO mixing ratios varied between 60 and 250 parts per billion by volume (ppbv). Within this range, the comparison between the two measurements is quite good, with an overall R2 of 0.953 and an average difference of 3.1%. A seasonal cycle is apparent in the CO data, with a springtime maximum and a summer minimum. Synoptic influences on the data include transport from the lower-latitude Pacific, bringing air with very low CO mixing ratios to Shemya, and, occasionally, transport from industrial areas in east Asia, including northern China, Japan, and eastern Russia. A scatterplot of CO versus O3 using all the data shows essentially no relationship at this remote site. This result implies that the primary sources and sinks for these trace gases are different at this location. However, during a few 12- to 48-hour periods in fall and late spring, enhancements in CO or in both CO and O3 were observed. During these periods, isentropic back trajectories indicate transport from the west and southwest. However, the trajectories are often difficult to interpret due to looping and are of short duration due to impact at the surface. These complexities are associated with the presence of cyclonic systems in the region. The local meteorological data suggest that the enhanced concentrations occurred around the time when these cyclonic systems passed near the

  11. Electro-mechanical response of top-gated LaAlO3/SrTiO3

    NASA Astrophysics Data System (ADS)

    Bi, Feng; Huang, Mengchen; Bark, Chung-Wung; Ryu, Sangwoo; Lee, Sanghan; Eom, Chang-Beom; Irvin, Patrick; Levy, Jeremy

    2016-01-01

    LaAlO3/SrTiO3 heterostructures are known to exhibit a sharp, hysteretic metal-insulator transition (MIT) with large enhanced capacitance near depletion. To understand the physical origin of this behavior, the electromechanical response of top-gated LaAlO3/SrTiO3 heterostructures is probed using two simultaneous measurement techniques: piezoresponse force microscopy (PFM) and capacitance spectroscopy. The observed hysteretic PFM responses show strong correlation with the capacitance signals, suggesting an interfacial carrier-mediated structural distortion associated with the gate-tuned MIT. In addition, the frequency dependence of the capacitance enhancement in LaAlO3/SrTiO3 is found to be well-matched to local PFM measurements. Our experimental results provide a fuller understanding of the top-gate tuned MIT in oxide heterostructure, which could be helpful for the development of future oxide-based nanoelectronics.

  12. Thermal conductivity of K1-xLixTaO3 and KTa1-xNbxO3

    NASA Astrophysics Data System (ADS)

    Tachibana, Makoto

    2015-11-01

    Thermal conductivity data between 1.8 and 300 K are reported for K1-xLixTaO3 (0≤x≤0.03) and KTa1-xNbxO3 (0≤x≤0.16) single crystals. Whereas lightly Li- and Nb-doped crystals exhibit relaxor-like behavior in dielectric susceptibility, they do not show the glasslike thermal transport found in conventional relaxors such as PbMg1/3Nb2/3O3 and Na1/2Bi1/2TiO3. The lack of glasslike behavior in K1-xLixTaO3 and KTa1-xNbxO3 is confirmed by the absence of temperature-linear contribution in heat capacity.

  13. 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.

  14. Generic Representation of Y( s o(3)) Based on the Lie Algebraic Basis of s o(3)

    NASA Astrophysics Data System (ADS)

    Zhang, Hong-Biao; Wang, Gang-Cheng

    2016-05-01

    We focus on constructing a generic representation of Y( s o(3)) based on the Lie algebraic basis of s o(3) basis, and further developing transition of Yangian operator hat Y. As an application of Y( s o(3)), we calculate all the matrix elements of unit vector operators hat n in angular momentum basis. It is also discovered that the Yangian operator hat Y may work in quantum vector space. In addition, some shift operators hat {O}^{(± )}_{μ } are naturally built on the basis of the representation of Y( s o(3)). As an another application of Y( s o(3)), we can derive the CG cofficients of two coupled angular momenta from the down-shift operator hat {O}^{(-)}_{-1} acting on a s o(3)-coupled tensor basis. This not only explores that Yangian algebras can work in quantum tensor space, but also provides a novel approach to solve CG coefficients for two coupled angular momenta.

  15. 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.

  16. Ferroelectric memristor based on Pt/BiFeO3/Nb-doped SrTiO3 heterostructure

    NASA Astrophysics Data System (ADS)

    Hu, Zhongqiang; Li, Qian; Li, Meiya; Wang, Qiangwen; Zhu, Yongdan; Liu, Xiaolian; Zhao, Xingzhong; Liu, Yun; Dong, Shuxiang

    2013-03-01

    We report a continuously tunable resistive switching behavior in Pt/BiFeO3/Nb-doped SrTiO3 heterostructure for ferroelectric memristor application. The resistance of this memristor can be tuned up to 5 × 105% by applying voltage pulses at room temperature, which exhibits excellent retention and anti-fatigue characteristics. The observed memristive behavior is attributed to the modulation effect of the ferroelectric polarization reversal on the width of depletion region and the height of potential barrier of the p-n junction formed at the BiFeO3/Nb-doped SrTiO3 interface.

  17. Studies on the properties of Al2O3:Cr2O3 (50:50) thin film

    NASA Astrophysics Data System (ADS)

    Ponmudi, S.; Sivakumar, R.; Sanjeeviraja, C.

    2016-05-01

    Aluminium oxide (Al2O3) and chromium oxide (Cr2O3) thin films have received great attention of researchers because of their unique properties of corrosion/oxidation resistance and high dielectric constant. In addition, chromium aluminium oxide has been considered as a best candidate for deep-ultraviolet optical masks. In the present work, thin films of Al2O3:Cr2O3 (50:50) were deposited on pre-cleaned microscopic glass substrate by RF magnetron sputtering technique. The substrate temperature and RF power induced changes in structural, surface morphological, compositional and optical properties of the films have been studied.

  18. Growth and properties of chemical solution deposited BiInO3-PbTiO3 films

    NASA Astrophysics Data System (ADS)

    Ko, S. W.; Yeo, H. G.; Trolier-McKinstry, S.

    2009-10-01

    The dielectric, ferroelectric, and piezoelectric properties of chemical solution deposited xBiInO3-(1-x)PbTiO3 (0.10≤x ≤0.35) thin films on platinized silicon substrates were investigated. Using a PbTiO3 seed layer, phase pure xBiInO3-(1-x)PbTiO3 (0.10≤x ≤0.35) thin films were prepared. For a 470 nm thick 0.15BiInO3-0.85PbTiO3 film, the room temperature permittivity was 650, while the dielectric loss tangent was below 2%. The coercive field and remanent polarization were 73 kV/cm and 22 μC/cm2, respectively. The ferroelectric transition temperatures of the xBiInO3-(1-x)PbTiO3 (x =0.10-0.20) films were all in excess of 550 °C. For x=0.15, the e31,f piezoelectric coefficient was -2.7 C/m2.

  19. 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.

  20. 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.

  1. 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.

  2. Small polarons and point defects in LaFeO3

    NASA Astrophysics Data System (ADS)

    Zhu, Zhen; Peelaers, Hartwin; van de Walle, Chris G.

    The proton-conductive perovskite-type LaFeO3 is a promising negative-electrode material for Ni/metal-hydride (Ni-MH) batteries. It has a discharge capacity up to 530 mAhg-1 at 333 K, which is significantly higher than commercialized AB5-type alloys. To elucidate the underlying mechanism of this performance, we have investigated the structural and electronic properties of bulk LaFeO3, as well as the effect of point defects, using hybrid density functional methods. LaFeO3 is antiferromagnetic in the ground state with a band gap of 3.54 eV. Small hole and electron polarons can form through self- or point-defect-assisted trapping. We find that La vacancies and Sr substitutional on La sites are shallow acceptors with the induced holes trapped as small polarons, while O and Fe vacancies are deep defect centers. Hydrogen interstitials behave like shallow donors, with the donor electrons localized on nearby iron sites as electron polarons. With a large trapping energy, these polarons can act as electron or hole traps and affect the electrical performance of LaFeO3 as the negative electrode for Ni-MH batteries. We acknowledge DOE for financial support.

  3. Interface properties of Ge on cubic SrHfO3 (001)

    NASA Astrophysics Data System (ADS)

    Wang, Jianli; Wang, Chenxiang; Tang, Gang; Zhang, Junting; Guo, Sandong; Han, Yujia

    2016-06-01

    High quality Ge-on-high-k oxide interface is essential to facilitate the high performance metal-oxide semiconductor field-effect transistors and monolithically integrated optoelectronics device performance. The atomic structure and electronic properties of Ge on perfect and defective (001) SrHfO3 are investigated by first-principle calculations. The amplitude of the surface rumpling for the SrO-terminated surface is much larger than that for HfO2-terminated surface, although both SrO- and HfO2-terminated surfaces are stable for a comparable range of the HfO2 chemical potential. The distance between the first and second planes compresses while that of the second and third planes expands due to the relaxation of the slab. We investigated systematically the specific adsorption sites and the atomic structure at the initial growth stage of Ge on the SrHfO3 (001) substrate. The top sites of the oxygen atoms are favorable for 1/2 (1/3) monolayer Ge adsorbate at SrO (HfO2)-terminated surface. We calculated the surface grand potential and presented the complete surface phase diagram. We also pointed out the energetically favorable interfaces among the atomic arrangements of the Ge/SrHfO3 (001) interfaces. The atomic structure and electronic properties of the intrinsic point defects were calculated and analyzed for the Ge/SrHfO3 (001) interfaces.

  4. 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. PMID:26125518

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

    PubMed Central

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

    2014-01-01

    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. PMID:24108327

  6. 26 CFR 301.6501(o)-3 - Partnership items.

    Code of Federal Regulations, 2010 CFR

    2010-04-01

    ... 26 Internal Revenue 18 2010-04-01 2010-04-01 false Partnership items. 301.6501(o)-3 Section 301.6501(o)-3 Internal Revenue INTERNAL REVENUE SERVICE, DEPARTMENT OF THE TREASURY (CONTINUED) PROCEDURE AND ADMINISTRATION PROCEDURE AND ADMINISTRATION Limitations Limitations on Assessment and...

  7. Dielectric, piezoelectric, and electromechanical phenomena in (K0.5Na0.5)NbO3-LiNbO3-BiFeO3-SrTiO3 ceramics

    NASA Astrophysics Data System (ADS)

    Li, Enzhu; Suzuki, Ryo; Hoshina, Takuya; Takeda, Hiroaki; Tsurumi, Takaaki

    2009-03-01

    The effect of the substitutions of BiFeO3 (BF) and SrTiO3 (ST) to (Na0.5K0.5)NbO3-LiNbO3 (KNN-LN) ceramics was studied as a candidate of lead-free piezoceramics. The piezoelectric property is enhanced near the phase transition composition caused by the distortion of crystal lattice by Li+ and also the strong ferroelectric nature of BF. The ST was found to be effective in improving the temperature dependence of the KNN ceramics. Small amount of ST also promoted the incorporation of LN and BF into the crystal lattice, and enhanced the piezoelectric performance furthermore. The 94.5(Na0.5K0.5)NbO3-4.5LiNbO3-0.5SrTiO3-0.5BiFeO3 ceramics showed excellent piezoelectric properties of d15=231 pC/N, d33=155 pC/N, and d31=70 pC/N.

  8. Effects of electron correlations application to Ti atoms on physical properties of (LaMnO3)m/(SrTiO3)n superlattices

    NASA Astrophysics Data System (ADS)

    Aezami, A.; Abolhassani, M.; Elahi, M.

    2016-05-01

    Magnetic structures and Curie temperatures of the (LaMnO3)m/(SrTiO3)n superlattices (SLm-n) with m=1, 2, 3 and n=1, 2, 3, 8 were investigated, using density functional theory implemented in Quantum-Espresso open source code. By applying on-site coulomb interaction (Hubbard term U) to Ti atoms for all of these superlattices, using Stoner-Wolfarth model, it was found that the magnetic order of interfacial atoms of these superlattices changed to ferromagnetic by implying U=5 eV on Ti atoms. The inclusion of electron-electron correlation with U=5 eV on the Ti atoms for all of the superlattices made the two dimensional electron gas (2DEG) formed at the interfaces, half-metallic. The obtained values of Curie temperature, calculated within mean field approximation with U=5 eV on the Ti atoms, are in good agreement with the experimental results.

  9. Crystal structure and dielectric properties of Ca(0.85)Nd(0.1)TiO(3) - LnAlO(3) ceramics.

    PubMed

    Eung, S; Dong, H; Yang, Jun-Mo; Hyung, S; Nur, I; Ohsato, Hitoshi

    2008-05-01

    The microwave dielectric properties of Ca(0.85)Nd(0.1)TiO(3) - LnAlO(3) (Ln = Sm, Gd, Dy, Er) ceramics are investigated in this paper. The structural characteristics of the specimens were evaluated by Rietveld refinement of Xray diffraction (XRD) patterns and high-resolution transmission electron microscopy (HRTEM). Solid solution limits were dependent on the ionic radius of Ln(3+) ions. With the decrease of the ionic radius of the Ln(3+) ions, the thermal stability of the resonant frequency decreases. This can be attributed to the increased level of oxygen octahedral distortion caused by the increase in the B-site bond valence in the ABO(3) perovskite structure. The dielectric constant (K) and the quality factor (Qf) of the specimens were dependent on the polarizability and grain size, respectively. PMID:18519215

  10. Metastable extension of the fluorite phase field in Y2O3-ZrO3-ZrO2 and its effect on grain growth

    NASA Astrophysics Data System (ADS)

    Jayaram, V.; Degraef, M.; Levi, C. G.

    1994-06-01

    Pure Y2O3 and Y2O3-ZrO2 solid solutions have been prepared by melt atomization and by pyrolysis of nitrate solutions. Extended solubility is readily achieved in both techniques for the entire composition range investigated: melts with 0.30% ZrO2 and precursors with 0.50% ZrO2. However, solidification of under cooled droplets yields almost exclusively single phase powders with the structure of cubic yttria (D5(sub 3)). In contrast, the pyrolysis route leads to a sequence of metastable microstructures beginning with a nanocrystalline disordered fluorite-based (C1) solid solution. Further heating leads to the evolution of much larger (micron size) flake crystals with a (001) texture, concurrent with partial ordering of the oxygen ions to the sites occupied in the D5(sub 3) addition.

  11. Surface structure and catalytic properties of MoO3/CeO2 and CuO/MoO3/CeO2.

    PubMed

    Yu, Wujiang; Zhu, Jie; Qi, Lei; Sun, Chuanzhi; Gao, Fei; Dong, Lin; Chen, Yi

    2011-12-15

    XRD, LRS, TPR and in situ NH(3) adsorption FT-IR were used to investigate the dispersion state of the copper oxide and molybdena species of MoO(3)/CeO(2) and CuO/MoO(3)/CeO(2) catalysts as well as their surface acidity. The results showed that the molybdena monolayer modification promoted the dispersion of CuO due to the formation of new tetrahedral vacancies. Meanwhile, CuO changed the structure of molybdenum species and then influenced the surface acidity of the samples. A detail discussion about the possible model of the surface structure of the catalyst was presented. In addition, combining with the in situ NH(3) adsorption FT-IR, the relationships between the activities for ''NO + NH(3) + O(2)'' reaction and surface acid properties (Brønsted and Lewis acid sites) of the catalysts were discussed. PMID:21930282

  12. The Impacts of Cation Stoichiometry and Substrate Surface Quality on Nucleation, Structure, Defect Formation, and Intermixing in Complex Oxide Heteroepitaxy–LaCrO3 on SrTiO3(001)

    SciTech Connect

    Qiao, Liang; Zhang, Hongliang; Bowden, Mark E.; Varga, Tamas; Shutthanandan, V.; Colby, Robert J.; Du, Yingge; Kabius, Bernd C.; Sushko, P. V.; Biegalski, Michael D.; Chambers, Scott A.

    2013-06-20

    Our ability to design and fabricate electronic devices with reproducible properties using complex oxides is critically dependent on our ability to controllably synthesize these materials in thin-film form. Structure-property relationships are intimately tied to film and interface composition. Here we report on the effects of cation stoichiometry in LaCrO3 heteroepitaxial films prepared using molecular beam epitaxy. We show that LaCrO3 films grow pseudomorphically on SrTiO3(001) over an wide range of La-to-Cr atom ratios. However, the growth mode and structural quality are sensitive to the La-to-Cr ratio, with La-rich films being of considerably lower structural quality than Cr-rich films. Cation mixing occurs at the interface for all La-to-Cr ratios investigated, and is not quenched by deposition at ambient temperature. Indiffused La atoms occupy Sr sites in the substrate. The presence of defects in the SrTiO3 substrate is implicated in promoting La indiffusion by comparing the properties of LaCrO3/SrTiO3 with those of LaCrO3/Si, both prepared at ambient temperature. Additionally, pulsed laser deposition is shown to result in more extensive interfacial mixing than molecular beam epitaxy for deposition at ambient temperature on Si.

  13. Is hexagonal InMnO3 ferroelectric?

    NASA Astrophysics Data System (ADS)

    Huang, Fei-Ting; Horibe, Yoichi; Wang, Xueyun; Cheong, Sang-Wook; Mori, Shigeo

    2013-03-01

    Hexagonal manganite (h-REMnO3; RE=rare earths) shows a unique improper ferroelectricity, accompanying a structural trimerization. RE can be replaced by In, which is much smaller than any RE ions. Recently, Oak et al. suggested InMnO3 is ferroelectric from the results of first-principles calculations, while Kumagai et al. proposed a non-ferroelectric ground state. In this talk, we will report the results of our investigation on the structural domains and local structural distortions of InMnO3 using dark-field transmission electron microscopy. We demonstrate that InMnO3 shows a distinct √{ 3} ×√{ 3} -type superstructure from the high-temperature paraelectric phase (P63/mmc), and the domain structure can be delicately controlled by varying the synthesis and annealing conditions. The correlation between physical properties and local structural distortions in the InMnO3 will be discussed in detail.

  14. 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.

  15. 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. PMID:20666557

  16. Solid-state synthesis of Bi2O3/BaTiO3 heterostructure: preparation and photocatalytic degradation of methyl orange

    NASA Astrophysics Data System (ADS)

    Ren, Pengrong; Fan, Huiqing; Wang, Xin

    2013-06-01

    In this work, Bi2O3/BaTiO3 heterostructure were prepared through a solid milling and annealing process. It was found that Bi3+ dissolved in the BaTiO3 lattice and the chemical bond was constructed between the interface of Bi2O3 and BaTiO3 after annealing process. Powder X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and UV-visible absorption spectra were used to characterize the Bi2O3/BaTiO3 heterostructure. Furthermore, UV-induced catalytic activities of the Bi2O3/BaTiO3 heterostructure was studied by a degradation reaction of methyl orange (MO) dye. The band gap of the Bi2O3/BaTiO3 heterostructure was estimated to be 3.0 eV. Compared with pure Bi2O3 powders, the Bi2O3/BaTiO3 heterostructure had a much higher catalytic activity. An excellent performance of the photocatalytic property of the Bi2O3/BaTiO3 heterostructure is ascribed to high mobility of species and effective separation of photogenerated carriers driven by the photoinduced potential difference generated at the Bi2O3/BaTiO3 junction interface, demonstrating that the Bi2O3/BaTiO3 heterostructure is a promising candidate as a photocatalyst.

  17. Effects of the substitution of P2O5 by B2O3 on the structure and dielectric properties in (90-x) P2O5-xB2O3-10Fe2O3 glasses.

    PubMed

    Sdiri, N; Elhouichet, H; Dhaou, H; Mokhtar, F

    2014-01-01

    90%[xB2O3 (1-x) P2O5] 10%Fe2O3, glass systems where (x=0 mol%, 5 mol%, 10 mol%, 15 mol%, 20 mol%) was prepared via a melt quenching technique. The structure of glass is investigated at room temperature by, Raman and EPR spectroscopy. Raman studies have been performed on these glasses to examine the distribution of different borate and phosphate structural groups. We have noted an increase from 3 to 4 in the coordination number of the boron atoms from 3 to 4, i.e., the conversion of the BO3 triangular structural units into BO4 tetrahedra. The samples have been investigated by means of electron paramagnetic resonance (EPR). The results obtained from the gef=4.28 EPR line are typical of the occurrence of iron (III) occupying substitutional sites. Moreover, the dielectric sizes such as ε'(ω), ε″(ω), imaginary parts of the electrical modulus, M(*)(ω) and the loss tanδ, their variation with frequency at room temperature show a decrease in relaxation intensity with an increase in the concentration of (B2O3). On the present work, we have found a weak extinction index with our new glass. PMID:23995605

  18. Gene expression responses of paper birch to elevated O3 and CO2 during leaf maturation and senescence

    NASA Astrophysics Data System (ADS)

    Kontunen-Soppela, S.; Parviainen, J.; Ruhanen, H.; Brosché, M.; Keinanen, M.; Thakur, R. C.; Kolehmainen, M.; Kangasjarvi, J.; Oksanen, E.; Karnosky, D. F.; Vapaavuori, E.

    2009-12-01

    Forest trees are exposed to increasing concentrations of O3 and CO2 simultaneously. The rise of concentration in these gases causes changes in the gene expression of trees, which can be small in acclimated trees, but yet pivotal for the metabolism of the trees. We have studied the response of paper birch (Betula papyrifera) leaf gene expression to elevated O3 and CO2 concentrations during leaf maturation and senescence. The hypotheses were:(1) Elevated O3 induces oxidative stress in leaves. During long O3-exposure repair mechanisms are activated. Because chemical defense requires energy and carbon uptake is reduced, leaf senescence is activated earlier. Alternatively, the senescence-associated processes, remobilization and storage of carbohydrates and nutrients, may not be completed. (2) In the combination of elevated CO2+O3, the O3-caused damages are not seen or they are smaller, due to closure of the stomata under elevated CO2 and decreased O3 uptake by the leaves. On the other hand, elevated CO2 may provide energy and increase defense chemicals, enabling leaves to repair the O3-caused damages. Gene expression responses of paper birch leaves to elevated O3 and CO2 were studied with microarray analyses. Samples were collected from the long-term O3 and CO2 fumigation experiment Aspen FACE in Rhinelander, WI, USA (http://aspenface.mtu.edu/). The site contains 12 FACE rings receiving CO2, O3, CO2+O3, and ambient air (controls). Birches have been exposed to elevated CO2 (550ppm) and O3 (1.5X ambient) since 1998. Leaf samples were collected in July, August and September 2004. The cDNA-microarrays used for hybridizations consisted of Populus euphratica ESTs representing ca 6500 different genes. In order to detect similar gene expression patterns within samplings and treatments, the microarray data was analyzed with multivariate methods; clustering with Self-Organizing Map, finding optimal cluster grouping by K-means clustering and visualizing the results with Sammon

  19. Magnetic exchange interactions and antiferromagnetism of ATcO3 (A= Ca, Sr, Ba) studied from first principles

    NASA Astrophysics Data System (ADS)

    Borisov, V. S.; Maznichenko, I. V.; Böttcher, D.; Ostanin, S.; Ernst, A.; Henk, J.; Mertig, I.

    2012-04-01

    The magnetic properties of ATcO3 (A = Ca, Sr, Ba) perovskites were studied from first principles using multiple-scattering theory. For each system, the most preferable magnetic order is antiferromagnetic where the magnetic moments of the nearest Tc atoms are aligned antiparallel to each other. In the case of CaTcO3 and SrTcO3, their recently observed antiferromagnetism is supported by our calculation of the Tc-Tc exchange coupling parameters. The Néel temperatures TN estimated for CaTcO3 and SrTcO3 are in a good agreement with experiment. For BaTcO3, which is not synthesized so far, we predict a fundamental band gap of 0.3 eV and TN below 900 K. In general, TN increases with volume expansion, whereas the presence of vacancies on both the oxygen and cation sites of ATcO3 should significantly suppress the critical temperature as well as the magnetic moment of Tc. Electronic correlations play a minor role in the formation of the magnetic state, although they may improve the calculated value of TN.

  20. First-Principles Study on Electronic Structure and Thermodynamic Stability of Sr(Ti,Ru)O3

    NASA Astrophysics Data System (ADS)

    Shimizu, Tatsuo; Kawakubo, Takashi

    2001-02-01

    Not only the electronic structure but also the thermodynamic stability of Sr(Ti,Ru)O3 is investigated using the first-principles method. For the electronic structure with small Ru concentration, the Ru t2g states appear below the middle of the band gap of SrTiO3. In this case, the wave functions of the Ru t2g states are localized at the Ru site. As a Ru concentration increases to more than 50 mol%, the inside-gap states gradually become delocalized. Therefore, a conductive Sr(Ti,Ru)O3 thin film is expected. On the other hand, thermodynamic stability of a Sr(Ti,Ru)O3 thin film is enhanced drastically relative to that of SrRuO3, as Ru concentration decreases. Sr(Ti,Ru)O3 with Ru concentration of more than 60 mol% may oxidize the neighboring (Ti,Al)N layer, which is often used as a barrier metal in memory-cell capacitors. In short, Sr(Ti,Ru)O3 with Ru concentration of about 50 mol% is proposed as a promising candidate material for new electrodes.

  1. 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.

  2. 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.

  3. High electron density 2DEGs at 111 SrTiO3/SmTiO3 interfaces

    NASA Astrophysics Data System (ADS)

    Raghavan, Santosh; Stemmer, Susanne; Stemmer Research Group Team

    2015-03-01

    (001) SrTiO3 quantum wells formed in structures such as RTiO3/SrTiO3/RTiO3 (R = Gd or Sm) exhibit two dimensional electron gases (2DEGs) that exhibit ferromagnetism and non-Fermi-liquid behavior. 2DEGs are also expected for (111) quantum wells, which furthermore form a honeycomb lattice that is susceptible to geometric frustration and nontrivial band structures. In this work, we present the growth of high quality SrTiO3 and SmTiO3 layers on (111) LSAT substrates using a hybrid molecular beam epitaxy technique. Structural and electrical characterization show atomically sharp (111) interfaces between SrTiO3 and SmTiO3, and the presence of a high charge carrier density of ~ 3 × 1014 cm-2. We will discuss results of magneto-transport studies in highly confined quantum wells that are only a few atomic planes thick and compare them with results from (001) interfaces.

  4. 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.

  5. 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

  6. Localization of the Two-dimensional Electron Gas in LaAlO3/SrTiO3 Heterostructures

    NASA Astrophysics Data System (ADS)

    Hernandez, Tomas; Wung Bark, Chung; Eom, Chang-Beom; Rzchowski, Mark S.

    2012-02-01

    We use low temperature magnetotransport measurements to compare the quasi 2-dimensional electron gas (2DEG) at the LaAlO3/SrTiO3 interface in heterostructures grown on (LaAlO3)0.3-(Sr2AlTaO3)0.7 (LSAT) substrates to the 2DEG at the LaAlO3/single crystal SrTiO3 interface. All heterostructures were grown by pulsed laser deposition with in-situ reflection high-energy electron diffraction. For the samples on LSAT, we find that increasing the carrier concentration by growing at lower oxygen partial pressures changes the conductivity mechanism, from strongly localized transport at low carrier concentrations to metallic conductivity with indications of weak localization at higher concentrations. We interpret this as an increasing occupation of Ti 3d bands of layers near the interface, changing the spatial extent of the conduction region and its susceptibility to localization by disorder and point defects at the interface. On the other hand, the 2DEG of similarly grown LaAlO3 on single crystal SrTiO3 shows metallic behavior and low temperature measurements display Kohler scaling of the out-of-plane magnetoresistance, consistent with classical orbital transport.

  7. Superior high-temperature oxidation resistance of a novel (Al2O3-Y2O3)/Pt laminated coating

    NASA Astrophysics Data System (ADS)

    Ma, Xiaoxu; He, Yedong; Wang, Deren; Zhang, Jin

    2012-03-01

    A 7-layer (Al2O3-Y2O3)/Pt laminated coating was successfully prepared on a Ni-based superalloy by magnetron sputtering methods. It is observed that the as-prepared coating has dense and refined brittle/ductile laminated nanostructure. Cyclic oxidation tests were adopted to investigate the oxidation and spallation resistance of this novel laminated coating. The results revealed that the 7-layer (Al2O3-Y2O3)/Pt laminated coating can significantly improve the high-temperature oxidation resistance and spallation resistance of the Ni-based superalloy. In such laminated coating, the multi-sealed (Al2O3-Y2O3) and Pt layers can effectively suppress the inward diffusion of oxygen to an extremely low level, providing super oxidation resistance at 1200 °C for 1000 h. In addition, the excellent high-temperature mechanical properties of the (Al2O3-Y2O3)/Pt laminated coating are mainly induced by the increased thermal expansion coefficient and the brittle/ductile laminated composite structure by means of energy release mechanisms.

  8. 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.

  9. 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.

  10. First-principles study of the electronic structure and magnetism of CaIrO3

    NASA Astrophysics Data System (ADS)

    Subedi, Alaska

    2012-01-01

    I study the electronic structure and magnetism of postperovskite CaIrO3 using first-principles calculations. The density functional calculations within the local density approximation without the combined effect of spin-orbit coupling and on-site Coulomb repulsion show the system to be metallic, which is in disagreement with the recent experimental evidences that show CaIrO3 to be an antiferromagnetic Mott insulator in the Jeff=1/2 state. However, when spin-orbit coupling is taken into account, the Ir t2g bands split into fully filled Jeff=3/2 bands and half-filled Jeff=1/2 bands. I find that spin-orbit coupling along with a modest on-site Coulomb repulsion opens a gap leading to a Mott insulating state. The ordering is antiferromagnetic along the c axis with total moments aligned antiparallel along the c axis and canted along the b axis.

  11. Electronic Structure near the Interface of Complex Oxide Heterostructure SmTiO3/SrTiO3

    NASA Astrophysics Data System (ADS)

    Mori, Ryo; Isaac, Brandon; Marshall, Patrick; Denlinger, Jonathan; Stemmer, Susanne; Lanzara, Alessandra

    Quantum wells created from oxide heterostructures induce quantum confinement systems at the heterostructure interface, which show unique properties, such as strong electron correlation, two-dimensional superconductivity, high carrier densities and mobility, and/or magnetism. The rare earth titanate, SmTiO3, and the transition metal oxide, SrTiO3, create such confined electron systems at their interface, which has a controllable quantum well length by changing the number of SrO layers in SrTiO3. By Varying the number of SrO layers, we will present the layer-dependent electronic structure of the SmTiO3/SrTiO3 interface system from angle-resolved photoemission spectroscopy (ARPES) measurements and discuss these results in terms of strong correlations.

  12. Upconversion luminescence in Er3+/Yb3+ codoped PbO-Bi2O3-AI2O3-B2O3 glasses

    NASA Astrophysics Data System (ADS)

    Appa Rao, B.; Raja Rao, Y.; Krishnamurthy Goud, K.; Srinivas, M.

    2015-02-01

    Er3+/Yb3+ co-doped glasses with the composition PbO-Bi2O3-Al2O3-B2O3 were prepared by melt quenching method. Optical absorption (OA) and photoluminescence (PL) and FT-IR spectra of all the glasses were recorded at room temperature. Green and red upconversion emissions centered at 525, 545 and 654 nm corresponding to 2H11/2 → 4I15/2, 4S3/2 → 4I15/2 and 4F9/2 → 4I15/2 transitions of Er3+ ions have been obtained under the excitation of 980 nm laser at room temperature. From emission spectra it was observed that the intensity of red emission increases with increasing the concentration of Er3+ ions upto 0.8 mol% and decreases with the further increase in the concentration of Er3+ ions. The spectra have been analyzed in the light of structural modifications in the vicinity of the dopant rare earth ions, due to relative variations in the concentration of Al2O3 and B2O3 in the glass network.

  13. Quantifying the electronic reconstruction in LaTiO3/LaNiO3/(LaAlO3)3 heterostructures using RIXS

    NASA Astrophysics Data System (ADS)

    Fabbris, Gilberto; Disa, Ankit S.; Ismail-Beigi, Sohab; Walker, Frederick J.; Ahn, Charles H.; Pelliciari, Jonathan; Huang, Yaobo; Schmitt, Thorsten; Xu, Lei; Hozoi, Liviu; van den Brink, Jeroen; Dean, Mark

    A novel approach for manipulating the 3d state in transition metal oxide heterostructures has emerged with the growth of trilayer nickelate LaTiO3/LaNiO3/(LaAlO3)3 (LTNAO). This heterostructure induces a striking reconstruction of the LaNiO3 electronic structure, which is due to a combination of charge transfer from Ti's 3d state and octahedral elongation along the c axis. We use resonant inelastic x-ray scattering (RIXS) experiments at Ni L2,3 and O K edges to spectroscopically resolve the LTNAO electronic structure. Surprisingly, our results show that the octahedral elongation generates minor changes in crystal fields at Ni's 3d state compared to bulk LaNiO3. Instead, heterostructuring creates an anisotropic reconstruction of the Ni 3d - O 2p hybridization. The x2-y2 orbital is significantly more hybridized with O p, leading to a 3z2-r2/x2-y2 hole ratio of ~0.55 and large orbital polarization as measured by x-ray absorption spectroscopy. This work establishes RIXS as an ultra-sensitive probe of complex oxide heterostructures. Work at BNL was supported by the US Department of Energy under Award No DEAC02-98CH10886 and under Early Career Award No 20878.

  14. High temperature carbon dioxide capture on nano-structured MgO-Al2O3 and CaO-Al2O3 adsorbents: an experimental and theoretical study.

    PubMed

    Bang, Yongju; Han, Seung Ju; Kwon, Soonchul; Hiremath, Vishwanath; Song, In Kyu; Seo, Jeong Gil

    2014-11-01

    Nano-structured alkaline-earth metal oxide adsorbents (denoted as MgO-Al2O3 and CaO-Al2O3) were prepared by an epoxide-driven one-pot sol-gel method, and they were applied to the dynamic and static CO2 adsorption. For comparison, a nano-structured aluminum oxide adsorbent (denoted as Al2O3) was also prepared by a similar method. MgO-Al2O3 adsorbent exhibited a well-developed mesopore structure through the formation of MgAl2O4 spinel phase, whereas CaO-Al2O3 adsorbent was composed of nano-sized CaO and CaAl2O4, resulting in a pore plugging. It was revealed that total basicity increased in the order of Al2O3 (0.11 mmol-CO2/g) < MgO-Al2O3 (0.37 mmol-CO2/g) < CaO-Al2O3, (1.21 mmol-CO2/g), which is in concurrent with adsorption energy obtained from DFT calculations. However, it was found that both basicity and base strength of the adsorbents played an important role in determining the CO2 adsorptive performance at different operating temperature. Among the adsorbents tested, MgO-Al2O3, which mostly retained medium basic sites, exhibited a best CO2 adsorptive performance at 200 degrees C. Furthermore, the experimental results are well supported by theoretical estimation, suggesting a useful design method of adsorbents for facile and regenerative adsorption in the applications of CO2 capture. PMID:25958558

  15. Novel gold nanocluster electrochemiluminescence immunosensors based on nanoporous NiGd-Ni2O3-Gd2O3 alloys.

    PubMed

    Lv, Xiaohui; Ma, Hongmin; Wu, Dan; Yan, Tao; Ji, Lei; Liu, Yixin; Pang, Xuehui; Du, Bin; Wei, Qin

    2016-01-15

    Herein, three-dimensional nanoporous NiGd alloy (NP-NiGd) was prepared by selectively dealloy Al from NiGdAl alloy in mild alkaline solution, then Ni2O3 and Gd2O3 grew further on the surface of NP-NiGd to obtain the NP-NiGd-Ni2O3-Gd2O3. On this basis, NP-NiGd-Ni2O3-Gd2O3 was further functionalized with gold nanoparticles (NP-NiGd-Ni2O3-Gd2O3@Au) and acted as sensor platform to fabricate a novel electrochemiluminescence (ECL) immunosensor. Bovine serum albumin protected gold nanoclusters (AuNCs@BSA) were prepared and acted as illuminant. AuNCs@BSA modified graphene oxide (GO/AuNCs@BSA) were used as labels of second antibody. In order to characterize the performance of the ECL immunosensor, carcino embryonie antigen (CEA) was used as the model to complete the experiments. Due to the good performances of NP-NiGd-Ni2O3-Gd2O3@Au (high surface area, excellent electron conductivity) and AuNCs@BSA (low toxicity, biocompatibility, easy preparation and good water solubility), the ECL immunosensor exhibited a wide range from 10(-4) to 5ng/mL with a detection limit of 0.03pg/mL (S/N=3). The immunosensor with excellent stability, acceptable repeatability and selectivity provided a promising method to detect CEA in human serum sample sensitively. PMID:26318782

  16. Zn2(TeO3)Br2

    PubMed Central

    Zhang, Dong; Johnsson, Mats

    2008-01-01

    Single crystals of dizinc tellurium dibromide trioxide, Zn2(TeO3)Br2, were synthesized via a transport reaction in sealed evacuated silica tubes. The compound has a layered crystal structure in which the building units are [ZnO4Br] distorted square pyramids, [ZnO2Br2] distorted tetra­hedra, and [TeO3 E] tetra­hedra (E being the 5s 2 lone pair of Te4+) joined through sharing of edges and corners to form layers of no net charge. Bromine atoms and tellurium lone pairs protrude from the surfaces of each layer towards adjacent layers. This new compound Zn2(TeO3)Br2 is isostructural with the synthetic compounds Zn2(TeO3)Cl2, CuZn(TeO3)2, Co2(TeO3)Br2 and the mineral sophiite, Zn2(SeO3)Cl2. PMID:21202162

  17. Study of coexisting phases in Bi doped La0.67Sr0.33MnO3

    NASA Astrophysics Data System (ADS)

    Kambhala, Nagaiah; Chen, Miaoxiang; Li, Peng; Zhang, Xi-xiang; Rajesh, Desapogu; Bhagyashree, K. S.; Goveas, Lora Rita; Bhat, S. V.; Kumar, P. Anil; Mathieu, Roland; Angappane, S.

    2016-05-01

    We report the remarkable phase separation behavior in La0.67Sr0.33MnO3 doped with Bi3+ ion at La site. The temperature dependent resistivity and magnetization of La0.67-xBixSr0.33MnO3 (x>0) show the presence of phase separation of ferromagnetic metallic and charge ordered antiferromagnetic insulating phases. Markedly, the field dependant magnetization studies of La0.67-xBixSr0.33MnO3 (x=0.3) show the metamagnetic nature of ferromagnetic metallic state implying the competition of coexisting ferromagnetic metallic and charge ordered antiferromagnetic phases. The electron spin resonance and exchange bias studies of La0.67-xBixSr0.33MnO3 (x=0.4 and 0.5) substantiate the coexistence of ferromagnetic clusters in antiferromagnetic matrix.

  18. 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.

  19. Substrate effects on V 2O 3 thin films

    NASA Astrophysics Data System (ADS)

    Schwingenschlögl, Udo; Frésard, Raymond; Eyert, Volker

    2009-01-01

    We apply density functional theory and the augmented spherical wave method to analyze the electronic structure of V 2O 3 in the vicinity of an interface to Al 2O 3. The interface is modeled by a heterostructure setup of alternating vanadate and aluminate slabs. We focus on the possible modifications of the V 2O 3 electronic states in this geometry, induced by the presence of the aluminate layers. In particular, we find that the tendency of the V 3 d states to localize is enhanced and may even cause a metal-insulator transition.

  20. Superposition model calculation of zero-field splitting of Fe3+ in LiTaO3 crystal

    NASA Astrophysics Data System (ADS)

    Yeom, T. H.

    2001-11-01

    The second-order zero-field splitting (ZFS) parameter b20 of the Fe3+ ion centre at the Li site, the Ta site and the structural vacancy site in the LiTaO3 crystal are calculated using the empirical superposition model. The fourth-order ZFS parameters b40, b43 and b4-3 are also calculated at the Li and Ta site, respectively. The calculated b20 of Fe3+ ion at the Li site agrees well with the experimental one. It is concluded that the Fe3+ replaces the Li+ ion rather than the Ta5+ ion in the LiTaO3 crystal. This conclusion confirms the site assignment from the electron nuclear double resonance experiments.

  1. 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.

  2. Magnetic properties of mixed spinel BaTiO3-NiFe2O4 composites

    NASA Astrophysics Data System (ADS)

    Sarkar, Babusona; Dalal, Biswajit; Dev Ashok, Vishal; Chakrabarti, Kaushik; Mitra, Amitava; De, S. K.

    2014-03-01

    Solid solution of nickel ferrite (NiFe2O4) and barium titanate (BaTiO3), (100-x)BaTiO3-(x) NiFe2O4 has been prepared by solid state reaction. Compressive strain is developed in NiFe2O4 due to mutual structural interaction across the interface of NiFe2O4 and BaTiO3 phases. Quantitative analysis of X-ray diffraction and X-ray photo electron spectrum suggest mixed spinel structure of NiFe2O4. A systematic study of composition dependence of composite indicates BaTiO3 causes a random distribution of Fe and Ni cations among octahedral and tetrahedral sites during non-equilibrium growth of NiFe2O4. The degree of inversion decreases monotonically from 0.97 to 0.75 with increase of BaTiO3 content. Temperature dependence of magnetization has been analyzed by four sublattice model to describe complex magnetic exchange interactions in mixed spinel phase. Curie temperature and saturation magnetization decrease with increase of BaTiO3 concentration. Enhancement of strain and larger occupancy of Ni2+ at tetrahedral site increase coercivity up to 200 Oe. Magnetostructual coupling induced by BaTiO3 improves coercivity in NiFe2O4. An increase in the demagnetization and homogeneity in magnetization process in NiFe2O4 is observed due to the interaction with diamagnetic BaTiO3.

  3. Octahedral rotation patterns in strained EuFeO3 and other Pbnm perovskite films: Implications for hybrid improper ferroelectricity

    NASA Astrophysics Data System (ADS)

    Choquette, A. K.; Smith, C. R.; Sichel-Tissot, R. J.; Moon, E. J.; Scafetta, M. D.; Di Gennaro, E.; Miletto Granozio, F.; Karapetrova, E.; May, S. J.

    2016-07-01

    We report the relationship between epitaxial strain and the crystallographic orientation of the in-phase rotation axis and A -site displacements in Pbnm-type perovskite films. Synchrotron diffraction measurements of EuFeO3 films under strain states ranging from 2% compressive to 0.9% tensile on cubic or rhombohedral substrates exhibit a combination of a-a+c- and a+a-c- rotational patterns. We compare the EuFeO3 behavior with previously reported experimental and theoretical work on strained Pbnm-type films on nonorthorhombic substrates, as well as additional measurements from LaGaO3,LaFeO3, and Eu0.7Sr0.3MnO3 films on SrTiO3. Compiling the results from various material systems reveals a general strain dependence in which compressive strain strongly favors a-a+c- and a+a-c- rotation patterns and tensile strain weakly favors a-a-c+ structures. In contrast, EuFeO3 films grown on Pbnm-type GdScO3 under 2.3% tensile strain take on a uniform a-a+c- rotation pattern imprinted from the substrate, despite strain considerations that favor the a-a-c+ pattern. These results point to the use of substrate imprinting as a more robust route than strain for tuning the crystallographic orientations of the octahedral rotations and A -site displacements needed to realize rotation-induced hybrid improper ferroelectricity in oxide heterostructures.

  4. Effect of nonmagnetic dilution in the honeycomb-lattice iridates Na2IrO3 and Li2IrO3

    NASA Astrophysics Data System (ADS)

    Manni, S.; Tokiwa, Y.; Gegenwart, P.

    2014-06-01

    We have synthesized single crystals of Na2(Ir1-xTix)O3 and polycrystals of Li2(Ir1-xTix)O3 and studied the effect of magnetic depletion on the magnetic properties by measurements of the magnetic susceptibility, specific heat, and magnetocaloric effect at temperatures down to 0.1 K. In both systems, the nonmagnetic substitution rapidly changes the magnetically ordered ground state into a spin glass, indicating strong frustration. While for the Li system the Weiss temperature ΘW remains unchanged up to x =0.55, a strong decrease |ΘW| is found for the Na system. This suggests that only for the former system magnetic exchange beyond nearest neighbors is dominating. This is also corroborated by the observation of a smeared quantum phase transition in Li2(Ir1-xTix)O3 near x =0.5, i.e., much beyond the site percolation threshold of the honeycomb lattice.

  5. Mn-doped 0.15BiInO3-0.85PbTiO3 piezoelectric films deposited by pulsed laser deposition

    NASA Astrophysics Data System (ADS)

    Lee, Sun Young; Ko, Song Won; Lee, Soonil; Trolier-McKinstry, Susan

    2012-05-01

    Undoped, 0.5 and 1.0 mol. % Mn-doped 0.15BiInO3-0.85PbTiO3 films were grown on PbTiO3/Pt/Ti/SiO2/Si substrates by pulsed laser deposition. Phase-pure perovskite films were obtained at a substrate temperature of 585 °C irrespective of Mn doping level. The 0.5 mol. % Mn-doped films showed a room temperature permittivity of 480 and a dielectric loss tangent of 0.015 at 100 kHz after 650 °C post-deposition annealing. The coercive field and remanent polarization were 80 kV/cm and 29 µC/cm2, respectively. The ferroelectric transition temperature of the films ranged from 535 to 585 °C. The e31,f piezoelectric coefficient was -7.1 C/m2. X-ray diffraction and phase transition temperature data showed that the Mn atoms substitute on the Ti-site as Mn3+; the resulting films have p-type conduction characteristics.

  6. The transformation of γ Fe 2O 3 to α Fe 2O 3: thermal activation and the effect of elevated pressure

    NASA Astrophysics Data System (ADS)

    Adnan, J.; O'Reilly, W.

    1999-01-01

    The transformation of acicular γ Fe 2O 3 particles to α Fe 2O 3 has been monitored using magnetic properties as a proxy for γ Fe 2O 3 concentration during the inversion process. The transformation is thermally activated, the height of the barrier opposing inversion being 3.7 eV at atmospheric pressure and 0.5 eV at a pressure of about 100 MPa. The barrier arises from the combination of a term representing the reduction in lattice energy in an inverted region, and the strain energy associated with the interface between the inverted and non-inverted phases. The sensitivity of the inversion process to pressure can be understood in terms of the dependence of these energy terms, and the energy barrier, on interatomic spacing. Extrapolation of these laboratory data to the conditions of the submarine crust at Site 504B of the Deep Sea Drilling Project is consistent with the inferred magnetic mineralogy of the recovered material.

  7. Microemulsion mediated synthesis of nanocrystalline (K x,Na 1-x)NbO 3 powders

    NASA Astrophysics Data System (ADS)

    Pithan, Christian; Shiratori, Yosuke; Dornseiffer, Jürgen; Haegel, Franz-Hubert; Magrez, Arnaud; Waser, Rainer

    2005-06-01

    The present study reports on the synthesis of nanocrystalline (K x,Na 1-x)NbO 3 powders prepared via microemulsion mediated hydrolytic decomposition of mixed alkoxide solutions. Compositions with different K/Na ratios ranging between the two end members KNbO 3 and NaNbO 3 have been synthesized and characterized with respect to stoichiometry, purity, crystalline structure, particle size and powder morphology using X-ray diffraction, Raman spectroscopy and inductively coupled plasma with optical emission spectroscopy. Both raw as well as calcined powders were investigated. For the technically relevant and piezoelectric most active composition (K 0.50,Na 0.50)NbO 3 the results are presented and discussed in comparison to micron-sized and submicron-sized powders, that have been prepared by solid state reaction for reference. The study of the crystallographic structure of these reference powders by XRD and Raman spectroscopy confirms the size induced phase transition between the thermodynamically stable monoclinic modification for large particles towards a new triclinic polymorph, which has been reported for nano-powders of this composition by us previously. As possible origin for this phenomenon, internal OH - groups, variations in K-/Na-site occupancy and mechanical stresses arising from the large surface curvature of the nanocrystalline powders are addressed.

  8. Relaxor behavior of (Ba,Bi)(Ti,Al)O3 ferroelectric ceramic

    NASA Astrophysics Data System (ADS)

    Cui, Lei; Hou, Yu-Dong; Wang, Sai; Wang, Chao; Zhu, Man-Kang

    2010-03-01

    Perovskite type (Ba0.9Bi0.1)(Ti0.9Al0.1)O3 (BBTA) ceramics have been prepared through solid state reaction route. The room temperature x-ray diffraction study suggests that BBTA ceramics have single phase tetragonal symmetry with space group P4mm. In contrast to the sharp dielectric transition of pure BaTiO3, a broad dielectric anomaly coupled with the shift in dielectric maxima toward a higher temperature with increasing frequency has been observed in BBTA. The quantitative characterization based on empirical parameters (ΔTm, γ, ΔTrelax, and ΔTdiffuse(1 kHz)) confirms its relaxor nature. The dielectric relaxation which follows the Vogel-Fulcher relationship with Eα=0.011 eV, Tf=356 K, and f0=1.38×1010 Hz, further supports spin-glass-like characteristics. In this system, the relaxor behavior can be attributed to the dynamic response of the polar clusters induced by the combined substitutions of Bi3+ and Al3+ on the Ba2+ and Ti4+ site. Moreover, the curie temperature of BBTA shows the decreasing trend compared to that of pure BaTiO3, which doesn't follow the normal Vegard's law, confirming that no BiAlO3 sublattice formed in BBTA. All these features indicate that BBTA is a promising candidate for lead-free relaxors.

  9. Phase and structural behaviour of the PrAlO3-LaAlO3 pseudo-binary system

    NASA Astrophysics Data System (ADS)

    Basyuk, T.; Vasylechko, L.; Fadeev, S.; Syvorotka, I. I.; Trots, D.; Niewa, R.

    2009-10-01

    High-resolution in situ X-ray powder diffraction applying synchrotron radiation has been used to examine the occurring crystal structures and the thermal behaviour of the solid solution Pr1-xLaxAlO3 in a wide temperature range 12-1173 K. At room temperature all studied samples in the whole composition range of the pseudo-binary system PrAlO3-LaAlO3 adopt a rhombohedral perovskite structure. The phases Pr1-xLaxAlO3 with x=0.56 and 0.66 undergo a sequence of three phase transitions I2/m↔Imma↔R3¯c↔Pm3¯m. For the sample with x=0.24 a series of four (I4/mcm↔I2/m↔Imma↔R3¯c↔Pm3¯m) phase transitions has been observed and for x=0.86 two transformations were apparent (I2/m↔R3¯c↔Pm3¯m). Crystal structure parameters for all studied compositions Pr1-xLaxAlO3 have been determined. Based on in situ powder diffraction and DTA/DSC data, the phase diagram of the pseudo-binary system PrAlO3-LaAlO3 has been constructed.

  10. Conducting and insulating LaAlO3/SrTiO3 interfaces: A comparative surface photovoltage investigation

    NASA Astrophysics Data System (ADS)

    Beyreuther, E.; Paparo, D.; Thiessen, A.; Grafström, S.; Eng, L. M.

    2013-12-01

    Surface photovoltage (SPV) spectroscopy, which is a versatile method to analyze the energetic distribution of electronic defect states at surfaces and interfaces of wide-bandgap semiconductor (hetero-)structures, is applied to comparatively investigate heterostructures made of 5-unit-cell-thick LaAlO3 films grown either on TiO2- or on SrO-terminated SrTiO3. As shown in a number of experimental and theoretical investigations in the past, these two interfaces exhibit dramatically different properties with the first being conducting and the second insulating. Our present SPV investigation reveals clearly distinguishable interface defect state distributions for both configurations when interpreted within the framework of a classical semiconductor band scheme. Furthermore, bare SrTiO3 crystals with TiO2 or mixed SrO/TiO2 terminations show similar SPV spectra and transients as do LaAlO3-covered samples with the respective termination of the SrTiO3 substrate. This is in accordance with a number of recent works that stress the decisive role of SrTiO3 and the minor role of LaAlO3 with respect to the electronic interface properties.

  11. 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.

  12. Diffusion control of an ion by another in LiNbO3 and LiTaO3 crystals

    PubMed Central

    Zhang, De-Long; Zhang, Qun; Qiu, Cong-Xian; Wong, Wing-Han; Yu, Dao-Yin; Yue-Bun Pun, Edwin

    2015-01-01

    Diffusion-doping is an effective, practical method to improve material properties and widen material application. Here, we demonstrate a new physical phenomenon: diffusion control of an ion by another in LiNbO3 and LiTaO3 crystals. We exemplify Ti4+/Xn+ (Xn+ = Sc3+, Zr4+, Er3+) co-diffusion in the widely studied LiNbO3 and LiTaO3 crystals. Some Ti4+/Xn+-co-doped LiNbO3 and LiTaO3 plates were prepared by co-diffusion of stacked Ti-metal and Er-metal (Sc2O3 or ZrO2) films coated onto LiNbO3 or LiTaO3 substrates. The Ti4+/Xn+-co-diffusion characteristics were studied by secondary ion mass spectrometry. In the Xn+-only diffusion case, the Xn+ diffuses considerably slower than the Ti4+. In the Ti4+/Xn+ co-diffusion case, the faster Ti4+ controls the diffusion of the slower Xn+. The Xn+ diffusivity increases linearly with the initial Ti-metal thickness and the increase depends on the Xn+ species. The phenomenon is ascribed to the generation of additional defects induced by the diffusion of faster Ti4+ ions, which favors and assists the subsequent diffusion of slower Xn+ ion. For the diffusion system studied here, it can be utilized to substantially shorten device fabrication period, improve device performance and produce new materials. PMID:25941037

  13. Interface Structure of MoO3 on Organic Semiconductors

    NASA Astrophysics Data System (ADS)

    White, Robin T.; Thibau, Emmanuel S.; Lu, Zheng-Hong

    2016-02-01

    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.

  14. Thermoelectric properties of doped BaHfO3

    NASA Astrophysics Data System (ADS)

    Dixit, Chandra Kr.; Bhamu, K. C.; Sharma, Ramesh

    2016-05-01

    We have studied the structural stability, electronic structure, optical properties and thermoelectric properties of doped BaHfO3 by full potential linearized augmented plane wave (FP-LAPW) method. The electronic structure of BaHfO3 doped with Sr shows enhances the indirect band gaps of 3.53 eV, 3.58 eV. The charge density plots show strong ionic bonding in Ba-Hf, and ionic and covalent bonding between Hf and O. Calculations of the optical spectra, viz., the dielectric function, refractive index and extinction coefficient are performed for the energy range are calculated and analyzed. Thermoelectric properties of semi conducting are also reported first time. The doped BaHfO3 is approximately wide band gap semiconductor with the large p-type Seebeck coefficient. The power factor of BaHfO3 is increased with Sr doping, decreases because of low electrical resistivity and thermal conductivity.

  15. 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.

  16. 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

  17. New High-Pressure Phase in Fe2O3

    NASA Astrophysics Data System (ADS)

    Tsuchiya, T.; Nishiyama, N.; Yusa, H.; Tsuchiya, J.; Funakoshi, K.

    2009-12-01

    Hematite Fe2O3, a prototype of trivalent transition metal oxides, crystallizes in the antiferromagnetic (AFM) insulating phase with the corundum structure at ambient conditions. Extensive studies have been carried out to clarify its structural, magnetic, and electronic evolutions under high pressure due to the broad interests in hematite from condensed matter physics to geosciences. The high-pressure phase relation in Fe2O3 is also substantial to understand geophysically important MgSiO3-Fe2O3 phase equilibria. Those are however still yet to be clarified as for example, some in situ X-ray diffraction measurements using the diamond anvil cell (DAC) reported a phase change from Rh2O3(II) (or orthorhombic Pv) to the CaIrO3-type structure over 60 GPa, while an experiment using the Kawai-type apparatus with sintered diamond (SD) anvils suggested to stabilize a different phase with an unidentified orthorhombic structure at much lower pressure of 40~45 GPa. On the other hand, recent theoretical and experimental investigations of non-magnetic sesquioxide compounds have revealed an emerging systematics of their high-pressure phase sequence (Tsuchiya et al., 2005; Tsuchiya et al., 2007; Yusa et al., 2008; Yusa et al., 2009). While the CaIrO3-type phase with six and eight disproportionate coordination polyhedra was found to stabilize in Al2O3 and Ga2O3 at megabar pressure, several other compounds such as In2O3 and Sc2O3 were reported to transform directly to a further denser phase with the α-Gd2S3 structure composed only of high eight-fold coordination polyhedra at much lower pressure. Similarly to these studies, we searched for a stable form of Fe2O3 under pressure theoretically by means of the density-functional structurally consistent LDA+U method and succeeded to discover a new phase transformation from Rh2O3(II) at the pressure fairly close to that reported by the SD experiment. The high-pressure phase however has different lattice constants suggested experimentally and

  18. 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.

  19. Bipolaron dynamics in pure and doped SrTiO3 and KTaO3 perovskite systems

    NASA Astrophysics Data System (ADS)

    Levstik, A.; Filipič, C.; Bobnar, V.; Pirc, R.

    2002-11-01

    The dielectric relaxation in SrTiO3, Sr0.942Ca0.058TiO3, and K0.989Li0.011TaO3 was analyzed. While at higher temperatures the characteristic relaxation frequency follows the Arrhenius behavior, its value is temperature independent at low temperatures. It is shown that such a behavior is a consequence of the dynamic properties of bipolarons, which undergo a transition from thermally activated hopping to a tunneling regime.

  20. Evolution of the electronic and lattice structure with carrier injection in BiFeO3

    NASA Astrophysics Data System (ADS)

    He, Xu; Jin, Kui-juan; Guo, Hai-zhong; Ge, Chen

    2016-05-01

    We report a density-functional study on the evolution of the electronic and lattice structure in BiFeO3 with injected electrons and holes. First, the self-trapping of electrons and holes was investigated. We found that the injected electrons tend to be localized on Fe sites due to the local lattice expansion, the on-site Coulomb interaction of Fe 3 d electrons, and the antiferromagnetic order in BiFeO3. The injected holes tend to be delocalized if the on-site Coulomb interaction of O 2 p is weak (in other words, UO is small). Single-center polarons and multicenter polarons are formed with large and intermediate UO, respectively. With intermediate UO, multicenter polarons can be formed. We also studied the lattice distortion with the injection of carriers by assuming the delocalization of these carriers. We found that the ferroelectric off-centering of BiFeO3 increases with the concentration of the electrons injected and decreases with that of the holes injected. It was also found that a structural phase transition from R 3 c to the nonferroelectric P b n m occurs, with the hole concentration over 8.7 ×1019cm-3 . The change of the off-centering is mainly due to the change of the lattice volume. The understanding of the carrier localization mechanism can help to optimize the functionality of ferroelectric diodes and the ferroelectric photovoltage devices, while the understanding of the evolution of the lattice with carriers can help tune the ferroelectric properties by the carriers in BiFeO3.

  1. FoxO3a and disease progression

    PubMed Central

    Nho, Richard Seonghun; Hergert, Polla

    2014-01-01

    The Forkhead box O (FoxO) family has recently been highlighted as an important transcriptional regulator of crucial proteins associated with the many diverse functions of cells. So far, FoxO1, FoxO3a, FoxO4 and FoxO6 proteins have been identified in humans. Although each FoxO family member has its own role, unlike the other FoxO families, FoxO3a has been extensively studied because of its rather unique and pivotal regulation of cell proliferation, apoptosis, metabolism, stress management and longevity. FoxO3a alteration is closely linked to the progression of several types of cancers, fibrosis and other types of diseases. In this review, we will examine the function of FoxO3a in disease progression and also explore FoxO3a’s regulatory mechanisms. We will also discuss FoxO3a as a potential target for the treatment of several types of disease. PMID:25225602

  2. FoxO3 suppresses Myc-driven lymphomagenesis

    PubMed Central

    Vandenberg, C J; Motoyama, N; Cory, S

    2016-01-01

    This study demonstrates, for the first time, that loss of a single forkhead box class O (FoxO) transcription factor, can promote lymphomagenesis. Using two different mouse models, we show that FoxO3 has a significant tumour-suppressor function in the context of Myc-driven lymphomagenesis. Loss of FoxO3 significantly accelerated myeloid tumorigenesis in vavP-MYC10 transgenic mice and B lymphomagenesis in Eμ-myc transgenic mice. Tumour analysis indicated that the selective pressure for mutation of the p53 pathway during Eμ-myc lymphomagenesis was not altered. Frank tumours were preceded by elevated macrophage numbers in FoxO3−/− vavP-MYC10 mice but, surprisingly, pre-B-cell numbers were relatively normal in healthy young FoxO3−/−Eμ-myc mice. In vitro assays revealed enhanced survival capacity of Myc-driven cells lacking FoxO3, but no change in cell cycling was detected. The loss of FoxO3 may also be affecting other tumour-suppressive functions for which FoxO1/4 cannot fully compensate. PMID:26764572

  3. Er3+ diffusion in LiTaO3 crystal

    NASA Astrophysics Data System (ADS)

    Zhang, De-Long; Zhang, Qun; Wong, Wing-Han; Pun, Edwin Yue-Bun

    2015-12-01

    Some Er3+-doped LiTaO3 plates were prepared by in-diffusion of Er-metal film locally coated onto congruent Z-cut substrate in air at a wide temperature range from 1000 to 1500 °C. After diffusion, Er3+-doping effect on LiTaO3 refractive index and Li2O out-diffusion arising from Er3+ in-diffusion were studied at first. Refractive indices at the doped and undoped surface parts were measured by prism coupling technique and the surface composition was estimated. The results show that Er3+ dopant has small contribution to the LiTaO3 index. Li2O out-diffusion is slight (Li2O content loss <0.3 mol%) for the temperature below 1300 °C while is moderate (Li2O content loss <0.6 mol%) for the temperature above 1400 °C. The Er3+ profile was studied by secondary ion mass spectrometry. The study shows that the diffused Er3+ ions follow either a complementary error function or a Gaussian profile. Characteristic parameters including diffusivity, diffusion constant, activation energy, solubility, solubility constant and heat of solution were obtained and compared with the LiNbO3 case. The comparison shows that the diffusivity and solubility in LiTaO3 are considerably smaller than in LiNbO3 because of the difference of Ta and Nb in atomic weight.

  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. Structural and magnetic characterization of the ball-milled α-Fe 2O 3-Mn 2O 3 and α-Fe-Mn 2O 3 systems

    NASA Astrophysics Data System (ADS)

    de Medeiros, S. N.; Luciano, A.; Cótica, L. F.; Santos, I. A.; Paesano, A.; da Cunha, J. B. M.

    2004-10-01

    In this work, the (Fe2O3)x(Mn2O3)1-x and Fey(Mn2O3)1-y systems were mechanically processed in a high-energy ball-mill. The as-milled powders were structurally and magnetically characterized by X-ray diffraction, Mössbauer spectroscopy and magnetic measurements. Under similar milling settings and conditions, dissimilar behaviors were observed in the studied systems. In the oxide-oxide system, only the bixbyite (Mn,Fe)2O3 phase was obtained in all the analysed samples, whereas in the metal-oxide system, a sharp compositional dependence for the final milling products was observed. For y⩽0.40, the FeMn2O4 spinel phase was detected and, for y>0.40, a wustite-like phase of the (Fe, Mn)1-yO type was formed. It was observed that magnetization in both systems increased with the nominal concentration, x or y, of the magnetic precursors, up to half of the concentration maximum and then it decreased as a result of structural phase transformations.

  6. 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.

  7. Electron paramagnetic resonance of Fe3+ in near-stoichiometric LiTaO3

    NASA Astrophysics Data System (ADS)

    Loyo-Menoyo, M.; Keeble, D. J.; Furukawa, Y.; Kitamura, K.

    2004-12-01

    Electron paramagnetic resonance (EPR) experiments on the dominant Fe3+ centre in near-stoichiometric LiTaO3 crystals grown by the double crucible Czochralski method are reported. A near complete roadmap of EPR positions was obtained, and transitions from two magnetically non-equivalent sites clearly resolved in the zx plane, perpendicular to the glide plane. This allowed accurate determination of C3 symmetry spin Hamiltonian parameters. Newman superposition model analyses of second and fourth order zero field splitting term parameters were performed to give further insight into the site of incorporation. The second order calculations provide evidence for Fe3+ substitution within the Li octahedron.

  8. Photoinduced melting of magnetic order in the correlated electron insulator NdNiO3

    NASA Astrophysics Data System (ADS)

    Caviglia, A. D.; Först, M.; Scherwitzl, R.; Khanna, V.; Bromberger, H.; Mankowsky, R.; Singla, R.; Chuang, Y.-D.; Lee, W. S.; Krupin, O.; Schlotter, W. F.; Turner, J. J.; Dakovski, G. L.; Minitti, M. P.; Robinson, J.; Scagnoli, V.; Wilkins, S. B.; Cavill, S. A.; Gibert, M.; Gariglio, S.; Zubko, P.; Triscone, J.-M.; Hill, J. P.; Dhesi, S. S.; Cavalleri, A.

    2013-12-01

    Using ultrafast resonant soft x-ray diffraction, we demonstrate photoinduced melting of antiferromagnetic order in the correlated electron insulator NdNiO3. Time-dependent analysis of the resonant diffraction spectra allows us to follow the temporal evolution of the charge imbalance between adjacent Ni sites. A direct correlation between the melting of magnetic order and charge rebalancing is found. Furthermore, we demonstrate that the magnetic ordering on the Ni and Nd sites, which are locked together in equilibrium, become decoupled during this nonthermal process.

  9. 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. PMID:15234897

  10. Characterization and optical properties of Fe2O3-PbO-B2O3 glasses

    NASA Astrophysics Data System (ADS)

    Sanjay, Kishore, N.; Kundu, R.; Dahiya, S.; Pal, I.; Dhankhar, S.; Punia, R.

    2016-05-01

    Heavy metal-based oxide glasses of compositions xFe2O3.(40-x)PbO.60B2O3 have been synthesized by the standard melt-quenching technique. The amorphous nature of these samples is ascertained by XRD patterns. Scanning Electron Microscope is used to study the microstructure of the samples. The absorption edge (λcut-off) shifts toward longer wavelengths with an increase in Fe2O3 content in the glass matrix. Study of absorption edge signifies the glassy nature of the samples. The values of optical band gap energy for indirect allowed and forbidden transitions have been determined and it is found that it decreases with increasing Fe2O3 content. The Urbach's energy is used to characterize the degree of disorder in the studied samples.

  11. Optically excited multi-band conduction in LaAlO3/SrTiO3 heterostructures

    NASA Astrophysics Data System (ADS)

    Guduru, V. K.; Granados del Aguila, A.; Wenderich, S.; Kruize, M. K.; McCollam, A.; Christianen, P. C. M.; Zeitler, U.; Brinkman, A.; Rijnders, G.; Hilgenkamp, H.; Maan, J. C.

    2013-02-01

    The low-temperature resistance of a conducting LaAlO3/SrTiO3 interface with a 10 nm LaAlO3 film decreases by more than 50% after illumination with light of energy higher than the SrTiO3 band-gap. We explain our observations by optical excitation of an additional high mobility electron channel, which is spatially separated from the photo-excited holes. After illumination, we measure a strongly non-linear Hall resistance which is governed by the concentration and mobility of the photo-excited carriers. This can be explained within a two-carrier model where illumination creates a high mobility electron channel in addition to a low mobility electron channel which exists before illumination.

  12. 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

  13. Micrometer-Scale Ballistic Transport of Electron Pairs in LaAlO_{3}/SrTiO_{3} Nanowires.

    PubMed

    Tomczyk, Michelle; Cheng, Guanglei; Lee, Hyungwoo; Lu, Shicheng; Annadi, Anil; Veazey, Joshua P; Huang, Mengchen; Irvin, Patrick; Ryu, Sangwoo; Eom, Chang-Beom; Levy, Jeremy

    2016-08-26

    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 LaAlO_{3}/SrTiO_{3}-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 LaAlO_{3}/SrTiO_{3} 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 B_{p}, 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. PMID:27610871

  14. Ferroelectric Metal in Tetragonal BiCoO3/BiFeO3 Bilayers and Its Electric Field Effect.

    PubMed

    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

  15. Ferroelectric Metal in Tetragonal BiCoO3/BiFeO3 Bilayers and Its Electric Field Effect

    NASA Astrophysics Data System (ADS)

    Yin, Li; Mi, Wenbo; Wang, Xiaocha

    2016-02-01

    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%.

  16. Mechanism of the ferroelectric phase transitions in LiNbO3 and LiTaO3

    NASA Astrophysics Data System (ADS)

    Ohkubo, Y.; Murakami, Y.; Saito, T.; Yokoyama, A.; Uehara, S.; Kawase, Y.

    2002-02-01

    The temperature dependences of the nuclear-electric-quadrupole frequency ωQ of 117In doped in LiTaO3 (TC=938 K) and Li1-xInx/3TaO3 with x=0.2 (TC=818 K) show that the order-disorder of the Li ions is not the driving mechanism for the ferroelectric instability in LiNbO3 and LiTaO3 systems, and imply that the oxygen order-disorder is the driving mechanism. The significantly different temperature dependences of ωQ of 111Cd in these materials compared, to those of 117In, demonstrate that this order-disorder is of dynamic character.

  17. Field effect tuning of superconductivity at the LaAlO3/SrTiO3 interface

    NASA Astrophysics Data System (ADS)

    Triscone, Jean-Marc

    2008-03-01

    At interfaces between complex oxides, electronic systems with unusual properties can be generated [1]. As reported first by Ohtomo and Hwang [2], a highly mobile electron gas is formed at the interface between LaAlO3 and SrTiO3, two insulating dielectric perovskite oxides. It will be shown that the ground state of this system is superconducting [3]. The superconducting critical temperature is about 200mK. The field effect allows the normal state and superconducting state properties to be spectacularly tuned. The characteristics of the observed superconducting transitions are consistent with a superconducting sheet as thin as a few nm. [1] ``When oxides meet face to face''. E. Dagotto, Science 318, 1076 (2007) [2] ``A high mobility electron gas at the LaAlO3/SrTiO3 heterointerface''. A. Ohtomo, H. Y. Hwang, Nature 427, 423 (2004). [3] ``Superconducting interfaces between insulating oxides''. N. Reyren, et al., Science 317, 1196 (2007).

  18. Pair distribution function (PDF) analysis of mesoporous α-Fe2O3 and Cr2O3.

    PubMed

    Hill, Adrian H; Allieta, Mattia

    2013-06-14

    We have measured atomic pair distribution functions of novel mesoporous metal oxides, α-Fe2O3 and Cr2O3. These have an ordered pore mosaic as well as crystalline structure within the pore walls, making them an interesting class of materials to characterise. Comparison of "bulk" and mesoporous data sets has allowed an estimate of long range structural coherence to be derived; ≈125 Å and ≈290 Å for α-Fe2O3 and Cr2O3 respectively. Further "box-car" analysis has shown that above ≈40 Å both mesoporous samples deviate greatly from their bulk counterparts. This is attributed to the pores of the mesoporous structure creating voids in the pair-correlations, disrupting long range order. PMID:23619834

  19. Magnetism, Superconductivity and Pseudogap at the LaAlO3-SrTiO3 Interface

    NASA Astrophysics Data System (ADS)

    Mannhart, Jochen

    2014-03-01

    The electron liquid at the LaAlO3-SrTiO3 interface is a two-dimensional superconductor and simultaneously displays magnetic order. To experimentally explore the fundamental properties of this state, we developed a planar tunnel junction technology that allows to measure the spectral density-of-states of the superconducting liquid while its carrier density can be altered by the electric-field effect. These studies yield surprising results, as key features of the superconducting electron liquid at the LaAlO3-SrTiO3 interface are found to be analogous to features deemed characteristic for the high-Tc cuprates. This work was performed in collaboration with C. Richter, H. Boschker, W. Dietsche, E. Fillis-Tsirakis, R. Jany, F. Loder, L.F. Kourkoutis, D.A. Muller, J.R. Kirtley, and C.W. Schneider.

  20. 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.

  1. Structural, EPR, optical and Raman studies of Nd2O3:Cu2+ nanophosphors.

    PubMed

    Umesh, B; Eraiah, B; Nagabhushana, H; Sharma, S C; Nagabhushana, B M; Shivakumara, C; Rao, J L; Chakradhar, R P S

    2012-08-01

    Nanocrystalline Nd(2)O(3):Cu(2+) (2mol %) phosphors have been prepared by a low temperature solution combustion technique. Powder X-ray diffraction (PXRD) results confirm that hexagonal A-type Nd(2)O(3) (900°C, 3h) and the lattice parameters have been evaluated by Rietveld refinement. Surface morphology of as-formed and Cu(2+) doped Nd(2)O(3) phosphors show that the particles are irregular in shape and porous in nature. TEM results also confirm the nature and size of the particles. The EPR spectrum exhibits two resonance signals with effective g values at g(ǀǀ)≈2.12 and g(⊥)≈2.04. The g values indicate that the site symmetry of Cu(2+) ions is octahedral symmetry with elongated tetragonal distortion. Raman studies show major peaks, which are assigned, to F(g) and combination of A(g)+E(g) modes. It is observed that the Raman peaks and intensity have been reduced in Cu(2+) doped samples. UV-Visible absorption spectra exhibit a strong and broad absorption band at ∼240nm. Further, the absorption peak shifts to ∼14nm in Cu(2+) doped samples. The optical band gap is estimated to be 5.28eV for Cu doped Nd(2)O(3) nanoparticles which are higher than the bulk Nd(2)O(3) (4.7eV). This can be attributed to the quantum confinement effect of the nanoparticles. PMID:22579331

  2. Engineering LaAlO3/SrTiO3 quantum wells by selective orbital occupancy

    NASA Astrophysics Data System (ADS)

    Herranz, Gervasi

    2015-03-01

    The two-dimensional confinement of electrons in quantum wells (QWs) along the interface between two semiconductors such as Si or GaAs has been fundamental for technology as well for the development of new fundamental concepts. More recently, the discovery of 2D-QWs in oxides, with the flagship interface between LaAlO3 and SrTiO3, has been heralded as a milestone in the research of 2D electron systems. Unlike more conventional 2D-QWs based on III-V or II-VI semiconductors, carriers at LaAlO3/SrTiO3 populate narrow 3d-bands, where strong correlations underlie complex phases not present in conventional semiconductors. In LaAlO3/SrTiO3 not all the electrons reside in the same QW subband and, indeed, they behave differently depending on which orbital are they occupying. Here we demonstrate that the symmetry of the conduction band inside the QWs can be selected, disclosing unprecedented ways to tailor the electron properties. More specifically, we show that the spatial extension and anisotropy of the 2D-superconductivity and the Rashba spin-orbit field can be largely modulated by controlling the 2D-QWsubband filling. Our results indicate a route to manipulate selectively the electronic properties of QWs at the LaAlO3/SrTiO3 interface, opening new prospects to understand the link between orbital symmetry and 2D-superconductivity and to achieve enhanced properties suitable for spin-dependent transport.

  3. Impedance spectroscopy of V2O5-Bi2O3-BaTiO3 glass-ceramics

    NASA Astrophysics Data System (ADS)

    Al-syadi, Aref M.; Yousef, El Sayed; El-Desoky, M. M.; Al-Assiri, M. S.

    2013-12-01

    The glasses within composition as: (80 - x)V2O5/20Bi2O3/xBaTiO3 with x = 2.5, 5, 7.5 and 10 mol% have been prepared. The glass transition (Tg) increases with increasing BaTiO3 content. Synthesized glasses ceramic containing BaTi4O9, Ba3TiV4O15 nanoparticles of the order of 25-35 nm and 30-46 nm, respectively were estimated using XRD. The dielectric properties over wide ranges of frequencies and temperatures were investigated as a function of BaTiO3 content by impedance spectroscopy measurements. The hopping frequency, ωh, dielectric constant, ɛ', activation energies for the DC conduction, Eσ, the relaxation process, Ec, and stretched exponential parameter β of the glasses samples have been estimated. The, ωh,β, decrease from 51.63 to 0.31 × 106 (s-1), 0.84 to 0.79 with increasing BaTiO3 respectively. Otherwise, the Eσ, increase from 0.279 to 0.306 eV with increasing BaTiO3. The value of dielectric constant equal 9.5·103 for the 2.5BaTiO3/77.5V2O5/20Bi2O3 glasses-ceramic at 330 K for 1 KHz which is ten times larger than that of same glasses composition. Finally the relaxation properties of the investigated glasses are presented in the electric modulus formalism, where the relaxation time and the respective activation energy were determined.

  4. The nature of magnetoelectric coupling in Pb(Zr,Ti)O3 -Pb(Fe,Ta)O3.

    PubMed

    Evans, Donald M; Alexe, Marin; Schilling, Alina; Kumar, Ashok; Sanchez, Dilsom; Ortega, Nora; Katiyar, Ram S; Scott, James F; Gregg, J Marty

    2015-10-21

    The coupling between magnetization and polarization in a room temperature multiferroic (Pb(Zr,Ti)O3 -Pb(Fe,Ta)O3 ) is explored by monitoring the changes in capacitance that occur when a magnetic field is applied in each of three orthogonal directions. Magnetocapacitance effects, consistent with P(2) M(2) coupling, are strongest when fields are applied in the plane of the single crystal sheet investigated. PMID:26351267

  5. Research Update: Plentiful magnetic moments in oxygen deficient SrTiO3

    NASA Astrophysics Data System (ADS)

    Lopez-Bezanilla, Alejandro; Ganesh, P.; Littlewood, Peter B.

    2015-10-01

    Correlated band theory is employed to investigate the magnetic and electronic properties of different arrangements of oxygen di- and tri-vacancy clusters in SrTiO3. Hole and electron doping of oxygen deficient SrTiO3 yields various degrees of magnetization as a result of the interaction between localized magnetic moments at the defect sites. Different kinds of Ti atomic orbital hybridization are described as a function of the doping level and defect geometry. We find that magnetism in SrTiO3-δ is sensitive to the arrangement of neighbouring vacancy sites, charge carrier density, and vacancy-vacancy interaction. Permanent magnetic moments in the absence of vacancy doping electrons are observed. Our description of the charged clusters of oxygen vacancies widens the previous descriptions of mono- and multi-vacancies and points out the importance of the controlled formation at the atomic level of defects for the realization of transition metal oxide based devices with a desirable magnetic performance.

  6. Correlation between oxygen vacancies and magnetism in Fe-doped In2O3 films

    NASA Astrophysics Data System (ADS)

    An, Yukai; Wang, Shiqi; Feng, Deqiang; Wu, Zhonghua; Liu, Jiwen

    2013-07-01

    Correlation between oxygen vacancies and magnetic property in the as-deposited and annealed (In0.93Fe0.07)2O3 films has been investigated by X-ray diffraction, magnetization measurement, X-ray absorption near-edge structure and extend X-ray absorption fine structure. Magnetic measurement reveals that clear room temperature ferromagnetism is observed for the as-deposited film, in which the doped Fe ions substitute for In sites of the In2O3 lattice and Fe-related secondary phases or clusters as the source of ferromagnetism is safely ruled out. After high-temperature annealing in air, the crystalline structure of film and occupation sites of Fe ions keep unchanged, whereas the magnetic property has a dramatic decrease. Based on X-ray absorption near-edge spectroscopy analysis and multiple-scattering theoretical calculations, it is found that the content of oxygen vacancy of film remarkably decreases, even disappears by annealing in air, which resulting in greatly decreasing the ferromagnetism. These results further provide strong evidence that the oxygen vacancies play an important role in activating the ferromagnetic interactions in Fe-doped In2O3.

  7. Non-linear second harmonic generation (SHG) studies of BaTiO3/SrTiO3 superlattices

    NASA Astrophysics Data System (ADS)

    Vlahos, Eftihia; Lee, Che-Hui; Wu, Pingping; Wung Bark, Chung; Jang, Ho Won; Folkman, Chad; Hyub Baek, Seung; Park, J. W.; Biegalski, Mike; Tenne, Dmitri; Schlom, Darrell; Chen, Long-Qing; Eom, Chang-Beom; Gopalan, Venkatraman

    2010-03-01

    Theoretical phase-field simulations predict that certain types of superlattices consisting of alternating (BaTiO3)n/(SrTiO3)n layers have novel vortex domain wall configurations which give rise to exceptionally high polarization tunability combined with negligible polarization hysteresis. Optical second harmonic generation (SHG) was used to probe the phase and transition temperatures of multilayer (BaTiO3)m/(SrTiO3)n superlattices, as a function of epitaxial strain. In addition, in-plane electro-optic measurements were carried out. The experimental results are in excellent agreement both with theoretical predictions, as well as the temperature-strain phase diagram obtained experimentally from UV Raman studies. The ferroelectric, in-plane SHG signal, from the tensile strained SrTiO3 layers reveals an mm2 point group symmetry, whereas the point group symmetry of the compressively strained BaTiO3 layers, was determined to be 4mm.

  8. Ultrafast magneto-optical spectroscopy of BiFeO3-BaTiO3 based structures

    NASA Astrophysics Data System (ADS)

    Magill, Brenden A.; Bishop, Michael; McGill, Stephen A.; Zhou, Yuon; Chopra, Anuj; Maurya, Deepam; Song, Hyun-Cheol; Priya, Shashank; Khodaparast, Giti A.

    2015-09-01

    Ultrafast optical spectroscopy can provide insight into fundamental microscopic interactions, dynamics and the coupling of several degrees of freedom. Pump/ probe studies can reveal the answer to questions like "What are the achievable switching speeds in multiferroics?", "What is the influence of the crystallographic orientation and domain states on the available switching states?", and "What is the effect of the hetrostructure on promoting the coupling between the varying field excitations?". In this presentation, we report on two color (400/800nm) ultrafast pump-probe differential reflectance spectroscopy of BiFeO3-BaTiO3 structures to probe the coupling between optical and acoustic phonons to spin waves. The data presented here is a combination of different transient reflectivity measurements to probe both the carrier and spin dynamics. The (001)-BiFeO3-BaTiO3 thin films were prepared using pulsed laser deposition on vicinal SrTiO3 substrates using La0.70 Sr0.30MnO3 bottom electrodes. Crystal orientation and topography were analyzed by x-ray diffraction and atomic force microscopy. . Our results are important to developing devices on the basis of this material system. This work was supported by the AFOSR through grant FA9550-14-1-0376,NSF-Career Award DMR-0846834, and the Virginia Tech Institute for Critical Technology and Applied Science.

  9. 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.

  10. Capacitance-voltage analysis of high-carrier-density SrTiO3/GdTiO3 heterostructures

    NASA Astrophysics Data System (ADS)

    Jackson, Clayton A.; Moetakef, Pouya; James Allen, S.; Stemmer, Susanne

    2012-06-01

    We report on capacitance-voltage (C-V) analysis of SrTiO3/GdTiO3 heterostructures that contain a high-density, two-dimensional electron gas (2DEG) at the interface. The complex admittance was measured as a function of frequency for different gate biases applied to a Schottky contact on the SrTiO3. A one-dimensional, complex impedance transmission line model was used to extract C-V characteristics from the frequency dependent admittance. The extracted capacitance was nearly independent of the gate voltage (up to -0.5 V), indicating a fully depleted SrTiO3 layer. The results are used to estimate the dielectric constant of the SrTiO3, the degree of modulation of the 2DEG by the maximum applied voltage (˜2.5%), and to establish an upper limit of the residual carrier density in the bulk of the SrTiO3 film (˜9 × 1018 cm-3).

  11. Spin injection and spin-charge conversion in LaAlO3/SrTiO3

    NASA Astrophysics Data System (ADS)

    Bibes, Manuel; Lesne, Edouard; Rojas Sanchez, Juan Carlos; Oyarzun, Simon; Fu, Yu; Reyren, Nicolas; Jamet, Mathieu; Jacquet, Eric; Barthelemy, Agnes; George, Jean-Marie; Fert, Albert; Jaffres, Henri; Vila, Laurent

    2015-03-01

    The perovskite oxides family provides materials to efficiently generate and control spin polarized currents using respectively half-metallic ferromagnets such as mixed-valence manganites or ferroelectrics and multiferroics. More recently channel materials to transport spin information have also emerged. These include the LaAlO3/SrTiO3 two-dimensional electron system (2DES) which, in addition, possesses a gate-tunable spin-orbit coupling. A limitation of this system is however the minimum LaAlO3 thickness of 4 uc required for 2DES formation. In this presentation we will show that this thickness can be reduced if the LaAlO3 is capped by appropriate metals. We will also present different approaches to inject spins in these engineered LaAlO3/SrTiO3 2DES and introduce detection schemes taking advantage of efficient spin-charge conversion via interfacial spin-orbit effects. Support by ERC Consolidator Grant MINT (No. 615759) is acknowledged.

  12. Spectrum and phase mapping across the epitaxial γ-Al2O3/SrTiO3 interface

    NASA Astrophysics Data System (ADS)

    Lu, Sirong; Kormondy, Kristy J.; Ngo, Thong Q.; Aoki, Toshihiro; Posadas, Agham; Ekerdt, John G.; Demkov, Alexander A.; McCartney, Martha R.; Smith, David J.

    2016-02-01

    Epitaxial heterostructures of γ - Al 2 O 3 / SrTiO 3 , grown by atomic layer deposition (ALD) and molecular beam epitaxy, have been characterized by advanced electron microscopy techniques, including aberration-corrected negative-Cs imaging, electron-energy-loss near-edge fine-structure analysis, and off-axis electron holography. Analysis of two-dimensional spectrum maps from samples that previously showed highly conductive interfacial layers revealed partial reduction of the Ti oxidation state in the SrTiO3 layer from Ti4+ to Ti3+, which was confined to within ˜1-2 unit cells of the interface. Electron holography of an ALD-grown sample revealed a phase profile within the SrTiO3 layer that rose sharply over a distance of about 1 nm moving away from the interface. Taken together, these results suggest a strong connection between reduction of oxidation state, which could be caused by oxygen vacancies and the quasi-two-dimensional electron gas present at the γ - Al 2 O 3 / SrTiO 3 interface.

  13. Lattice crossover and phase transitions in NdAlO3-GdAlO3 system

    NASA Astrophysics Data System (ADS)

    Vasylechko, L.; Shmanko, H.; Ohon, N.; Prots, Yu.; Hoffmann, S.; Ubizskii, S.

    2013-02-01

    Phase and structural behaviour in the (1-x)NdAlO3-xGdAlO3 system in a whole concentration range has been studied by means of in situ high-resolution X-ray synchrotron powder diffraction technique and differential thermal analysis. Two kinds of solid solutions Nd1-xGdxAlO3 have been found at room temperature: one with rhombohedral (x<0.15) and one with orthorhombic (x≥0.20) symmetry. A morphotropic phase transition occurs at x≈0.15, where the co-existence of both phases was observed. Peculiarity of the orthorhombic solid solution is the lattice parameter crossover at the compositions with x=0.33, 0.49 and 0.62. First-order structural transition Pbnm↔R3¯с has been detected both from in situ powder diffraction and thermal analysis data. Continuous phase transformation R3¯с↔Pm3¯m above 2140 K has been predicted for Nd-rich sample Nd0.85Gd0.15AlO3 from the extrapolation of high-temperature behaviour of the lattice parameter ratio of the rhombohedral phase. Based on the experimental data, the phase diagram of the pseudo-binary system NdAlO3-GdAlO3 has been constructed.

  14. 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.

  15. Emergent phenomena in LaAlO3 /GdAlO3 superlattices by breaking inversion symmetry

    NASA Astrophysics Data System (ADS)

    Zhang, Hai-Tian; Haislmaier, Ryan; Lapano, Jason; Gopalan, Venkatraman; Engel-Herbert, Roman

    2015-03-01

    Recently, tremendous interest has been focused on materials by design, where hybrid improper ferroelectricity was proposed from first principles predictions in perovskite superlattice structures (ABO3)n/(A'BO3)m , which is directly coupled to the oxygen octahedral rotations [1]. Such oxygen octahedron rotations are anticipated stable at high temperatures, thus being a potential materials candidate for high temperature piezoelectric sensor and transducer applications. In this talk we will present the homoepitaxial growth of LaAlO3 and GaAlO3 by hybrid molecular beam epitaxy, where a volatile aluminium alkoxide precursor and elemental La/Gd (flux 2 × 1013 cm-2s-1) were co-supplied in the presence of an oxygen plasma (RF plasma power 250 W). Growth mode, film surface morphology and defect type for films grown under La/Gd-rich and Al-rich growth conditions will be discussed and directly related to structure and properties characterization of the LaAlO3 and GaAlO3. Changes in the octahedral tilts, probed by scanning transmission electron microscopy in the proximity of GdAlO3/LaAlO3 interface are discussed and compared to first principle predictions.

  16. Structural transformation and multiferroic properties of Ba-Mn co-doped BiFeO3

    NASA Astrophysics Data System (ADS)

    Rout, Jyoshna; Choudhary, R. N. P.

    2016-01-01

    Pure BiFeO3 and Bi1-xBaxFe1-xMnxO3 (x = 0.10, 0.20) fine ceramics were synthesized using mechano-synthesis route. The influence of co-doping (Ba-Mn) on structural and multiferroic properties of BiFeO3 has been studied in different experimental conditions. X-ray diffraction patterns, Rietveld structural refinement of XRD patterns and Fourier transform infrared (FTIR) spectra reveal the structural transition from rhombohedral (R3c) to the biphasic structure (R3c + P4mm) on co-doping. The co-doping improves surface morphology and also reduces the particle size. The room temperature M-H loops of all samples showed antiferromagnetic/weak ferromagnetic behavior. Magnetoelectric coupling coefficient determination is carried out to reveal extent of intimate interaction between electric and magnetic dipoles interaction in the samples. Room temperature occurrence of ferromagnetism, ferroelectricity and magnetoelectric effect supports the observation of multiferroism and magnetoelectric coupling in BiFeO3. Thus, co-doping at Bi- and Fe-sites of BiFeO3 can improve multiferroic properties of BiFeO3 for various applications.

  17. Low temperature hydrothermal synthesis, structure and magnetic properties of RECrO3 (RE = La, Pr, Nd, Sm).

    PubMed

    Wang, Shan; Huang, Keke; Hou, Changmin; Yuan, Long; Wu, Xiaofeng; Lu, Dayong

    2015-10-21

    Perovskite structured rare-earth chromites (RECrO3) are an interesting family of functional materials due to their wide application in numerous areas. Various methods have been used to synthesize this family of materials; however, such methods usually need a high temperature crystallization process above 800 °C, and only produce polycrystalline ceramics. Herein, a series of RECrO3 single crystal samples with uniform particle sizes were prepared via a mild hydrothermal method with temperatures as low as 240-260 °C, and the synthesis conditions were studied in detail. Samples of LaCrO3, PrCrO3, and NdCrO3 were indexed to the Pnma space group, whereas SmCrO3 was indexed to Pbnm. The shapes of the crystals changed from cubic to plate as a result of the crystal lattice distortions induced by the reduction in the size of the A-site rare-earth cation. Raman spectra of the samples showed characteristic vibration modes of CrO6 clusters. Temperature dependent magnetization studies showed a transition from antiferromagnetism to paramagnetism in all the samples. Higher maximum and residual magnetization was achieved in all the hydrothermally prepared samples compared with those prepared by other methods. PMID:26374249

  18. Infrared spectroscopy and surface chemistry of beta-Ga(2)O(3) nanoribbons.

    PubMed

    Bermudez, V M; Prokes, S M

    2007-12-01

    The structure and surface chemistry of crystalline beta-Ga2O3 nanoribbons (NRs), deposited in a thin layer on various metallic and dielectric substrates (mainly on Au), have been characterized using vibrational spectroscopy. The results have been analyzed with the aid of a previous ab initio theoretical model for the beta-Ga2O3 surface structure. Raman spectra and normal-incidence infrared (IR) transmission data show little if any difference from corresponding results for bulk single crystals. For a layer formed on a metallic substrate, IR reflection-absorption spectroscopy (IRRAS) shows longitudinal-optic (LO) modes that are red-shifted by approximately 37 cm-1 relative to those of a bulk crystal. Evidence is also seen for a bonding interaction at the Ga2O3/Au interface following heating in room air. Polarization-modulated IRRAS has been used to study the adsorption of pyridine under steady-state conditions in ambient pressures as high as approximately 5 Torr. The characteristic nu19b and nu8a modes of adsorbed pyridine exhibit little or no shift from the corresponding gas-phase values. This indicates that the surface is only weakly acidic, consistent with the theoretical prediction that singly unsaturated octahedral Ga sites are the only reactive cation sites on the NR surface. However, evidence for adsorption at defect sites is seen in the form of more strongly shifted modes that saturate in intensity at low pyridine coverage. The effect of H atoms, formed by thermal cracking of H2, has also been studied. No Ga-H or O-H bonds are observed on the pristine NR surface. This suggests that the previously reported presence of such species on Ga2O3 powders heated in H2 is a result of a partial reduction of the oxide surface. The heat of adsorption of atomic H on the pristine beta-Ga2O3(100) surface at 0 K is computed to be -1.79 eV per H at saturation (average of Ga-H and O-H sites), whereas a value of +0.45 eV per H is found for the dissociative adsorption of H2. This

  19. Electronic structure and surface properties of PrMnO3 (001): A density functional theory study

    NASA Astrophysics Data System (ADS)

    Zhou, Yongjun; Lü, Zhe; Wei, Bo; Wang, Zhihong; Zhu, Xingbao

    2015-01-01

    In this paper, the surface properties of the (001) surface in PrMnO3 are investigated using the projector augmented plane wave (PAW) methods within the spin-polarization generalized gradient approximation (GGA+U), where U is on-site Coulomb interaction correction. The result of the total density of states shows a half-metallic ground state for PrMnO3 in GGA+U treatment. The optimized structure parameters of both cubic and orthorhombic bulk phases are obtained. The electronic properties of the cubic PrMnO3 (001) surface with PrO- and MnO2-terminations are discussed. Based on the results of the calculated surface energies, we predict the surface energies of three low-index surfaces follows the sequence of (001)<(111)<(110). The rumpling for the PrO-terminated surface is much larger than that of the MnO2-terminated surface. Both the PrO- and MnO2-terminated surfaces display a reduction of d12 interlayer distance and an expansion of d23. Bader effective charge of the ion is much smaller than its formal charge which is due to the partial Mn-O bond covalency. The oxygen-vacancy formation energy in bulk PrMnO3 is found to be smaller than other perovskites, e.g. LaMnO3 and SrTiO3. We find that the formation energy of oxygen-vacancy on MnO2-terminated surface is lower than the formation energy of oxygen-vacancy on PrO-terminated surface and Sr-doped PrMnO3 makes oxygen-vacancy formation more easily compared pure PrMnO3.

  20. 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. PMID:12898383

  1. 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.

  2. 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.

  3. 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.

  4. Observation of room temperature saturated ferroelectric polarization in Dy substituted BiFeO3 ceramics

    NASA Astrophysics Data System (ADS)

    Zhang, Shuxia; Wang, Lei; Chen, Yao; Wang, Dongliang; Yao, Yingbang; Ma, Yanwei

    2012-04-01

    High quality Bi1-xDyxFeO3 (0 ≤ x ≤ 0.15) ceramics have been fabricated by sintering Dy-doped BiFeO3 (BFO) precursor powders at a low temperature of 780 °C. The magnetic properties of BFO were improved by the introduction of Dy on the Bi-site. More importantly, well saturated ferroelectric hysteresis loops and polarization switching currents have been observed at room temperature. A large remnant polarization (2Pr) value of 62 μC/cm2 is achieved, which is the highest value reported so far for rare-earth-doped BFO ceramics. Moreover, mechanisms for improved multiferroic properties depending on chemical doping-caused structure evolutions have also been discussed.

  5. Raman Scattering in LaMnO3 Systems

    NASA Astrophysics Data System (ADS)

    Podobedov, V. B.; Weber, A.; Rice, J. P.; Romero, D. B.; Drew, H. D.

    1997-03-01

    Polarized Raman spectra of undoped and doped LaMnO3 single crystals have been studied in the temperature range from 5 K to 325 K. The spectra are mainly related to optical phonons at q_ 0. The analysis of the vibrational spectra was carried out within the orthorhombic, rhombohedral and cubic symmetries of LaMnO3 systems. The P_nma lattice structure of undoped LaMnO3 crystal distorted by the static Jahn-Teller effect has four perovskite formula units in the primitive cell and belongs to the orthorhombic D_2h^16 space group. Most of the predicted Raman active modes (7Ag + 5B_1g + 7B_2g + 5B_3g) were detected at different polarizations of both excitation and scattered radiation in the frequency range 30-700 cm-1. Raman spectra of the LaMnO3 crystals doped with Sr or Ca (x=0.3) have weakly-resolved features and intensities comparable to those of the second-order spectra in the cubic media. We have measured temperature dependencies of both the intensity and position of Raman modes that follow the symmetry conditions. The Raman modes show both ordinary and anomalous frequency shifts with a temperature. The most intense Bg mode in LaMnO3 has an abrupt frequency shift near T_c=140 K; this may be associated with a paramagnetic-canted antiferromagnetic phase transition.

  6. 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.

  7. Cr2O3 Films for Magnetoelectric Gate Applications

    NASA Astrophysics Data System (ADS)

    Stuart, Sean; Sachet, Edward; Maria, J. P.; Rowe, J. E. (Jack); Ulrich, Marc C.; Dougherty, Dan

    2014-03-01

    The magnetoelectric properties of Cr2O3 have been extensively studied, including recent reports of a robust electrically switched magnetic surface state. We have identified Cr2O3 as a material whose magnetoelectric properties would enable voltage controlled switching of the exchange interaction with graphene, as in the Field Effect Transistor proposed by Semenov et al. (Appl. Phys. Lett. 91, 153105). We used pulsed laser deposition to grow thin Cr2O3 films directly on HOPG and sapphire. Atomic force microscopy for films grown on HOPG show closely packed Cr2O3 islands, with a smooth surface interrupted by grain boundaries. X-Ray Diffraction shows that the film has a (0001) texture for films grown at 650 deg. C, which is the ideal orientation for magnetoelectric gating. X-Ray photoelectron spectroscopy on incomplete films suggest strong chemical interactions between the graphite and Cr2O3. Films grown on sapphire have improved crystallinity and surface morphology, which allow for measurement of the surface magnetization by magnetic force microscopy after magneto-electric annealing.

  8. High-Pressure Polymorph of NaBiO3.

    PubMed

    Naa, Octavianti; Kumada, Nobuhiro; Miura, Akira; Takei, Takahiro; Azuma, Masaki; Kusano, Yoshihiro; Oka, Kengo

    2016-06-20

    A new high-pressure polymorph of NaBiO3 (hereafter β-NaBiO3) was synthesized under the conditions of 6 GPa and 600 °C. The powder X-ray diffraction pattern of this new phase was indexed with a hexagonal cell of a = 9.968(1) Å and c = 3.2933(4) Å. Crystal structure refinement using synchrotron powder X-ray diffraction data led to RWP = 8.53% and RP = 5.55%, and the crystal structure was closely related with that of Ba2SrY6O12. No photocatalytic activity for phenol decomposition was observed under visible-light irradiation in spite of a good performance for its mother compound, NaBiO3. The optical band-gap energy of β-NaBiO3 was narrower than that of NaBiO3, which was confirmed with density of states curves simulated by first-principles density functional theory calculation. PMID:27243818

  9. Origin of Polarity in Amorphous SrTiO3

    NASA Astrophysics Data System (ADS)

    Frenkel, Anatoly I.; Ehre, David; Lyahovitskaya, Vera; Kanner, Leah; Wachtel, Ellen; Lubomirsky, Igor

    2007-11-01

    Although neither SrTiO3 nor BaZrO3 has any polar crystalline polymorphs, they may form noncrystalline pyro- and piezoelectric phases [Adv. Mater.ADVMEW0935-9648 19, 1515 (2007)10.1002/adma.200602149]. These phases and the similar phase of BaTiO3 have been called quasiamorphous. In this Letter, the structure of the quasiamorphous phase of SrTiO3 is examined by the x-ray absorption fine structure technique and found to be built of a random network of polar octahedral TiO6 local bonding units. While in crystalline SrTiO3 all TiO6 octahedra are apex sharing only, in its amorphous and quasiamorphous phases, some octahedra share edges. The polarity of the quasiamorphous phase is due to the partial alignment of the TiO6 octahedra. Such a mechanism is completely different from that of inorganic polar crystals. This mechanism should be possible in a large variety of other compounds that contain similar local bonding units.

  10. Critical current density of YBa2Cu3O7-x films with BaZrO3 inclusions on SrTiO3 and Al2O3 substrates

    NASA Astrophysics Data System (ADS)

    Augieri, A.; Galluzzi, V.; Celentano, G.; Fabbri, F.; Mancini, A.; Rufoloni, A.; Vannozzi, A.; Gambardella, U.; Padeletti, G.; Cusmà, A.; Petrisor, T.; Ciontea, L.

    2008-02-01

    Recently, many efforts have been dedicated to the development of a reliable technology for the introduction of artificial pinning sites in YBa2Cu3O7-x (YBCO) films with the aim of improving the in-field Jc performances. One of the most effective technique resulted to be the inclusion of BaZrO3 (BZO) second phase embedded in the YBCO films. In this contribution we present Jc measurements on BZO-added YBCO films deposited on SrTiO3 (STO) and CeO2-buffered-Al2O3 (ALO) substrates. Samples were deposited by pulsed laser ablation technique using a composite YBCO + 5mol.% BZO target at the optimum conditions for fully oxygenated c-axis oriented YBCO films. Despite of a slight Tc reduction, BZO addition in YBCO-STO films resulted in an improvement of in-field performances with the appearance of a Jc plateau in the low field region which extends up to about 2.5 Tesla irrespective of the temperature at least in the investigated range (down to 65K). On the other hand, samples deposited on ALO did not exhibit any remarkable difference neither in the Jc value nor in the magnetic field dependences as compared with pure YBCO. The presence of 0° (magnetic field parallel to the c-axis) peaks in the Jc. angular behaviour revealed a c-axis correlated character of the pinning forces in BZO added YBCO films grown on both STO and ALO substrates. X-ray diffraction measurements and AFM investigations were carried out in order to determine the influence of BZO addition on films crystalline quality and microstructure.

  11. High temperature neutron diffraction studies of PrInO3 and the measures of perovskite structure distortion.

    PubMed

    Baszczuk, A; Dabrowski, B; Avdeev, M

    2015-06-21

    The crystal structure of PrInO(3) was investigated in the temperature range 303-1123 K by high-resolution neutron-powder diffraction. The PrInO(3) adopts a highly distorted variant of the perovskite structure with the orthorhombic Pnma space group in the whole temperature range investigated. The bond length and bond-angle analysis revealed a very slow tendency to decrease structural distortion with increasing temperature. Comparison of different parameters quantifying perovskite structure distortion calculated for PrInO(3) and the similar PrAlO(3) and PrGaO(3) shows the advantage of using the tolerance factor t12 calculated for the 12-fold coordinated Pr by geometrical averaging of the individual interatomic distances. An additional advantage of the tolerance factor method results from the possibility of extending it to predict the average structural distortion and the geometrical stability of the perovskites at various temperatures once the accurate dependence of t(x,T,d) on the composition, temperature and oxygen content is found. By comparing PrInO(3) with several AMO(3) perovskites containing ions in the fixed oxidation state on the A and M crystal sites it was found that structural distortion and the tolerance factor t12 for PrInO(3) are consistent with the empirical thermal expansion coefficient based on the bond strength calculation [R. M. Hazen, and C. T. Prewitt, Am. Mineral., 1977, 62(3-4), 309]. In contrast to perovskites AMO(3-d) containing mixed-valent M ions, which allow for a wide range of changes of the tolerance factor t(12)(T,d) as a function of oxygen content, perovskites AMO(3) with M ions in the fixed oxidation state show much less flexibility. This flexibility is further reduced for the A(3+)M(3+)O(3) perovskites like PrInO(3) for which even a large change of the synthesis temperature has a minor effect on controlling the resulting t(12)(T) and the structural phase in comparison with A(2+)M(4+)O3 perovskites. The only parameter left for A(3+)M

  12. Volcanic Ash a Sink for Atmospheric Trace Species? A Laboratory Study of SO2 and O3 Uptake by Ash

    NASA Astrophysics Data System (ADS)

    Maters, E. C.; Delmelle, P.; Rossi, M. J.

    2015-12-01

    The impacts of volcanic activity on atmospheric chemistry have dominantly been viewed in relation to sulphur and halogen gas and aerosol emissions, while volcanic ash has been largely overlooked. However, solid particles in the atmosphere are increasingly recognised to be important in providing surfaces for heterogeneous reaction with trace gases such as SO2, NOx, O3 and organic compounds. Average annual emissions of ash, the <2 mm aluminosilicate particles generated during explosive eruptions, correspond to a surface area roughly equivalent to one-third to one-half of Earth's geometric surface area. Despite the substantial surface presented by airborne ash particles, interactions between ash and gases at ambient temperature have seldom been investigated. Laboratory studies with volcanic ash similar to those conducted with mineral dust from arid and semi-arid regions are much needed to understand and quantify the kinetics and mechanisms involved in heterogeneous reactions. Addressing this gap in knowledge is fundamental to better assess the capacity of ash emissions to affect atmospheric chemistry. We determined the initial uptake coefficient (γM) and the total uptake capacity (NiM) for gaseous SO2 and O3 by a compositional range of ash and glass powders in a Knudsen flow reactor. The volcanic materials exhibited γSO2 and NiSO2 values ranging from 10-3 to 10-2 and from 1011 to 1013 molecules cm-2, respectively. The solids samples also showed γO3 and NiO3 values ranging from 10-3 to 10-2 and from 1012 to 1013 molecules cm-2, respectively. Results of sequential exposure trials (SO2 then O3, O3 then SO2) suggest that SO2 and O3 do not compete for surface sites on the aluminosilicate materials, although O3 may participate in redox reactions with surface adsorbed sulphur species, enhancing the total capacity for O3 uptake by the solid. Differences in reactivity of the samples towards SO2 and O3 may be interpreted in light of variations in types and abundances of

  13. 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

  14. Photochromic centers and impurities in nominally pure KTaO3 and K1-xLixTaO3

    NASA Astrophysics Data System (ADS)

    Laguta, V. V.; Glinchuk, M. D.; Bykov, I. P.; Rosa, J.; Jastrabík, L.; Klein, R. S.; Kugel, G. E.

    1995-09-01

    Investigations of photochromic centers and impurities in nominally pure single crystals of KTaO3 and K1-xLixTaO3 (KTL) have been carried out by the ESR method. In all investigated KTL samples (x=0.016, 0.02, 0.03) the axial symmetry spectrum of Fe3+ substituted for K+ [Fe3+ax(K)], cubic symmetry spectrum of Fe3+ substituted for K+ [Fe3+c(K)], and that of Ni3+ substituted for Ta5+ [Ni3+c(Ta)] have been observed at T<=60 K. After light illumination with 365<=λ<=436 nm, several ESR spectra appeared, each one with the characteristic temperature of its annealing in the region 25<=T<=120 K. In KTL samples simultaneously the Fe3+ax(K) spectrum disappeared and intensities of Fe3+c(K) and Ni3+c(Ta) spectra decreased. In nominally pure KTaO3 the spectra Fe3+ax(K) and Fe+ax(K), observed before illumination, disappeared after it. The gradual restoration of these aforementioned spectra in both KTaO3 and KTL was observed at T>25 K when some of the photoinduced spectra disappeared. One of the photoinduced spectra was shown to be that of O- in both KTaO3 and KTL. A scheme of local electronic levels of impurities in the band gap of nominally pure KTaO3 and KTL was proposed. This scheme and especially the shallow O- level in it made it possible to explain some peculiarities of photosensitive phenomena observed in nominally pure KTaO3 and KTL in recent years.

  15. NOx versus VOC limitation of O3 production in the Po valley: Local and integrated view based on observations

    NASA Astrophysics Data System (ADS)

    Spirig, Christoph; Neftel, Albrecht; Kleinman, Lawrence I.; Hjorth, Jens

    2002-09-01

    We characterize the local O3 production at an urban and a rural site in the northern part of the Po valley (Italy) during the Pianura Padana Produzione di Ozono experiment (PIPAPO). A steady state calculation based on observations is performed to determine the local O3 production rate, P(O3), and its sensitivity to precursor concentrations. The urban site exhibited a strongly VOC sensitive O3 production rate, while both VOC and NOx sensitive conditions were observed at the rural site. In addition to the local steady state analysis, we performed one-dimensional Lagrangian model calculations that simulate conditions in the Po valley. These calculations show that the P(O3) at the surface tends to be more VOC sensitive than the average in the mixed layer. The Lagrangian calculations are also used to determine the response of O3 concentration to an emissions change. We compare emission control information with information on sensitivities from the local analysis. It is concluded that a local analysis of P(O3) within the mixing layer offers useful qualitative information but tends to overestimate VOC sensitivity as judged by a comparison with an emissions-based Lagrangian model.

  16. Upconversion Properties of the Er-Doped Y2O3, Bi2O3 and Sb2O3 Nanoparticles Fabricated by Pulsed Laser Ablation in Liquid Media

    NASA Astrophysics Data System (ADS)

    Reza, Zamiri; Hamid-Reza, Bahari-Poor; Azmi, Zakaria; Raheleh, Jorfi; Golnoush, Zamiri; Avito, Rebelo; Akrajas, Ali Omar

    2013-11-01

    Er-doped Y2O3, Bi2O3 and Sb2O3 nanoparticles are synthesized using pulsed laser ablation in a liquid. Ceramic targets of Y2O3:Er3+, Bi2O3:Er3+ and Sb2O3:Er3+ for ablation process are prepared by standard solid-state reaction technique and ablation is carried out in 5-ml distilled water using nanosecond Q-switched Nd:YAG laser. The morphology and size of the fabricated nanoparticles are evaluated by transmission electron microscopy and the luminescence emission properties of the prepared samples are investigated under different excitation wavelengths.

  17. Enhanced ferromagnetism in co-doped BiFeO3 ceramics

    NASA Astrophysics Data System (ADS)

    Trivedi, Harsh; Singh, Deepa; Gupta, Rajeev; Garg, Ashish

    2012-02-01

    BiFeO3 (BFO) is the most studied multiferroic material with high ferroelectric polarization as well above room temperature transition temperatures. Studies have shown significant improvements in the electrical and magnetic properties of BFO upon atomic substitutions at Bi (A) and Fe (B) sites. While enhanced ferromagnetism upon A-site doping is attributed to the suppression of cycloidal spin ordering of Fe moments, B site substitution reduces leakage current by eliminating oxygen vacancies. This study aims to combine these two aspects by co-doping the material at A- and B- sites using La^3+ and V^3+/V^+5 respectively and to investigate the electrical and magnetic characteristics of co-doped BFO. La-doped LaxBi1-xFeO3 and co-doped LaxBi1-xVyFe1-yO3 (x = .05, 0.1, 0.15, 0.2; y = 0.03) samples were prepared solid-state reaction method. While La-doped samples show only reduced leakage without any discernible change in the magnetic characteristics, co-doped samples (La^3+ & V^5+ ) show significant enhancements in magnetic properties in addition to reduced leakage attributed to the elimination of oxygen vacancies. Improvement in the magnetic characteristics can be understood as a consequence of enhanced double exchange interaction between adjacent Fe ions. This argument is further strengthened by our observation that co-doped samples made by substitution of Fe with V^+3 show a magnetic response equivalent to that of only La-doped BFO samples.

  18. Hardening of the soft phonon in bulk SrTiO3 interfaced with LaAlO3 and SrRuO3

    NASA Astrophysics Data System (ADS)

    Nucara, A.; Ortolani, M.; Baldassarre, L.; Mohamed, W. S.; Schade, U.; Aurino, P. P.; Kalaboukhov, A.; Winkler, D.; Khare, A.; Miletto Granozio, F.; Calvani, P.

    2016-06-01

    The low-temperature softening of the TO1 phonon of SrTiO3 (STO), which determines its incipient ferroelectricity, is known to be partially hindered either in the bulk under strong electric fields, or in thin STO films. Here we show, by terahertz (THz) reflectivity measurements, that a similar effect is produced in bulk STO and at zero static field by ultrathin metallic films on its surface, like a 10-nm-thick film of SrRuO3 (SRO), or the two-dimensional electron system (2DES) present at the interface with LaAlO3. In SRO/STO, the observed hardening is well explained by the depolarizing action of the SRO free electrons which follow adiabatically the ion motion. In LAO/STO, a weaker TO1 hardening could be detected by patterning the 2DES in the form of microstripes and using a polarized THz field parallel (E⃗∥) or orthogonal (E⃗⊥) to the stripes. At 10 K, when TO1 is excited together with the free electrons by E⃗∥, its absorbance is harder by about 7 cm-1 than that measured when TO1 is coupled to the plasmon-polariton confined within the stripes, being excited by E⃗⊥.

  19. Optical properties of epitaxial BiFeO3 thin film grown on SrRuO3-buffered SrTiO3 substrate

    PubMed Central

    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. PMID:24791162

  20. 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. PMID:24791162

  1. Structural study of yttrium substituted BiFeO3

    NASA Astrophysics Data System (ADS)

    Mejía Gómez, J. A.; Canaria, C.; Ochoa Burgos, R.; Ortiz, C. A.; Supelano, G. I.; Parra Vargas, C. A.

    2016-02-01

    Yttrium-substituted Bi1-xYxFeO3 (x=0, 0.03, 0.07, 0.15, 0.2 and 0.5) samples were prepared by solid state reaction technique. Morphological analysis was obtained by Scanning Electron Microscopy (SEM) technique indicating mainly granular behaviour. In addition, the substitution of yttrium promotes smaller particle size of BiFeO3. The obtained samples were also studied by X-ray diffraction (XRD). The crystal structure and the lattice parameters were confirmed by XRD. Rietveld refinement of experimental X-ray diffraction patterns showed that substituted BiFeO3 compounds crystallize in a R3c type structure and the lattice parameters decrease as Y concentration increases.

  2. 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.

  3. Observation of strontium segregation in LaAlO3/SrTiO3 and NdGaO3/SrTiO3 oxide heterostructures by X-ray photoemission spectroscopy

    NASA Astrophysics Data System (ADS)

    Treske, Uwe; Heming, Nadine; Knupfer, Martin; Büchner, Bernd; Koitzsch, Andreas; Di Gennaro, Emiliano; Scotti di Uccio, Umberto; Miletto Granozio, Fabio; Krause, Stefan

    2014-01-01

    LaAlO3 and NdGaO3 thin films of different thicknesses have been grown by pulsed laser deposition on TiO2-terminated SrTiO3 single crystals and investigated by soft X-ray photoemission spectroscopy. The surface sensitivity of the measurements has been tuned by varying photon energy hν and emission angle Θ. In contrast to the core levels of the other elements, the Sr 3d line shows an unexpected splitting for higher surface sensitivity, signaling the presence of a second strontium component. From our quantitative analysis we conclude that during the growth process Sr atoms diffuse away from the substrate and segregate at the surface of the heterostructure, possibly forming strontium oxide.

  4. 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.

  5. Resistive switching in polycrystalline YMnO3 thin films

    NASA Astrophysics Data System (ADS)

    Bogusz, A.; Müller, A. D.; Blaschke, D.; Skorupa, I.; Bürger, D.; Scholz, A.; Schmidt, O. G.; Schmidt, H.

    2014-10-01

    We report a unipolar, nonvolatile resistive switching in polycrystalline YMnO3 thin films grown by pulsed laser deposition and sandwiched between Au top and Ti/Pt bottom electrodes. The ratio of the resistance in the OFF and ON state is larger than 103. The observed phenomena can be attributed to the formation and rupture of conductive filaments within the multiferroic YMnO3 film. The generation of conductive paths under applied electric field is discussed in terms of the presence of grain boundaries and charged domain walls inherently formed in hexagonal YMnO3. Our findings suggest that engineering of the ferroelectric domains might be a promising route for designing and fabrication of novel resistive switching devices.

  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. The magnetism of BiFeO3 powders

    NASA Astrophysics Data System (ADS)

    Luo, Xi; Tseng, Li-Ting; Li, Sean; Yi, Jiabao

    2015-12-01

    Conventional sintering and direct ball milling of Bi2O3 + Fe2O3 mixture were used for the fabrication of BiFeO3 powders. The fabricated powders were performed annealing or high energy ball milling to vary the grain size from bottom-up or top-down. It was found that the magnetization of the powders synthesized by both methods plotted with the reciprocal of the grain size could be linearly fitted, indicating that the magnetism is from the finite size effect. Exchange bias phenomenon was observed after field cooling (FC) of the powders, confirming the magnetization is due to the uncompensated or canted surface spins. No spin glass behavior was found in these powders.

  8. Disproportionation, dopant incorporation, and defect clustering in Perovskite-structured NdCoO3.

    PubMed

    Tealdi, Cristina; Malavasi, Lorenzo; Fisher, Craig A J; Islam, M Saiful

    2006-03-23

    Atomistic simulation techniques are used to examine the defect chemistry of perovskite-structured NdCoO(3), a material whose electrochemical properties make it attractive for use in heterogeneous oxidation catalysis, as well as in gas sensors and mixed ionic/electronic conductors. In practice, dopants are added to NdCoO(3) to obtain the desired properties, such as high electrical conductivity and rapid gas adsorption/desorption; thus, a wide range of dopants substituted on both Nd and Co sites are examined. Charge compensation for aliovalent dopants is predicted to occur via formation of oxide ion vacancies; these are understood to be key sites with respect to catalytic and sensor activity. Low activation energies calculated for oxide ion migration are consistent with high oxygen mobilities measured experimentally. Sr and Ca, which occupy Nd sites in the lattice, are found to be the most soluble of the alkaline earth metals, in agreement with experiment. These two dopant ions also have the weakest binding energies for dopant-vacancy cluster formation. Mechanisms of electronic defect formation, critical to the overall transport properties of the material, are also considered. The results suggest that disproportionation of the Co ion to form small polaron species is the most favorable intrinsic defect process. In doped compounds, formation of electronic holes via uptake of oxygen at vacant sites is found to be a low energy process. PMID:16539474

  9. Role of atomic radius and d -states hybridization in the stability of the crystal structure of M2O3 (M =Al , Ga, In) oxides

    NASA Astrophysics Data System (ADS)

    Sabino, F. P.; de Oliveira, Luiz Nunes; Da Silva, Juarez L. F.

    2014-10-01

    We study the stability of the corundum, gallia, and bixbyite structures of Al2O3,Ga2O3 , and In2O3 with density functional theory calculations. To artificially control the relative position of the d states within the band structure, we add a Hubbard-like on-site Coulomb interaction to the d states. We quantitatively show that smaller (larger) atomic radii favor the corundum (bixbyte) structure, which supports empirical models based on the atomic radius ratio between the cation and anions and the spacing-filling condition. Thus, Al2O3 and In2O3 crystallizes in the corundum and bixbyite structures, which is consistent with experimental observations. The empirical models based on atomic radius and space filling would predict a corundum or bixbyite structure for Ga2O3 . However, as expected from experimental observations, we find gallia to be the most stable structure for Ga2O3 . Our results explain why Ga2O3 crystallizes in the gallia structures instead of the corundum or bixbyite as follows. The stability of gallia increases as the hybridization of the Ga d states with the O 2 s states grows and the p -d splitting increases, which is maximized by the presence of fourfold cation sites. The presence of the fourfold cation sites in gallia is a key structural feature that increases its relative stability compared with the corundum and bixbyite structures for Ga2O3 , which contain only sixfold cation sites, so that the effect of the d states is unimportant.

  10. Ultrasonic microspectroscopy of congruent LiNbO3 crystals

    NASA Astrophysics Data System (ADS)

    Kushibiki, Jun-ichi; Ohashi, Yuji; Hirohashi, Junji

    2005-12-01

    Experimental procedures for evaluating the compositional homogeneity of LiNbO3 single crystals were developed using the line-focus-beam ultrasonic material characterization system, and the true congruent composition was determined. First, the relationships among leaky surface acoustic wave (LSAW) velocities (VLSAW), chemical compositions, Curie temperatures, densities, and lattice constants were investigated for crystal evaluation, using X-, Y-, and Z-cut substrates prepared from three LiNbO3 crystals grown along the crystallographic Z axis with different Li2O contents of 48.0, 48.5, and 49.0mol%. We selected VLSAW for Z-cut Y-axis propagating (ZY ) LiNbO3 with the highest sensitivity to chemical composition changes [0.0253Li2Omol%/(m/s)], and also VLSAW for Y-cut X-axis propagating (YX ) LiNbO3 [0.0464Li2Omol%/(m/s)] that was advantageous for detailed evaluation of distributions in the chemical composition along the pulling direction as well as the diameter direction.The congruent composition was estimated to be 48.477Li2Omol%. Next, the homogeneities of the three above-mentioned crystals and a commercially available LiNbO3 crystal with a nominally congruent composition were evaluated using data for YX-LiNbO3 specimens. Consequently, compositional changes were observed clearly as VLSAW changes. The commercial crystal specimen had a gradient of -0.0046(m /s)/mm from top to bottom. The VLSAW variations for the entire examined region (60×36mm2) exhibited a maximum change of 0.55m/s, corresponding to the chemical composition change of 0.025Li2Omol%. The relationships between the chemical compositions and the acoustical physical constants (the elastic, piezoelectric, and dielectric constants, and density) were also provided.

  11. 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. PMID:25686555

  12. High mobility conduction at (110) and (111) LaAlO3/SrTiO3 interfaces

    PubMed Central

    Herranz, G.; Sánchez, F.; Dix, N.; Scigaj, M.; Fontcuberta, J.

    2012-01-01

    In recent years, striking discoveries have revealed that two-dimensional electron liquids (2DEL) confined at the interface between oxide band-insulators can be engineered to display a high mobility transport. The recognition that only few interfaces appear to suit hosting 2DEL is intriguing and challenges the understanding of these emerging properties not existing in bulk. Indeed, only the neutral TiO2 surface of (001)SrTiO3 has been shown to sustain 2DEL. We show that this restriction can be surpassed: (110) and (111) surfaces of SrTiO3 interfaced with epitaxial LaAlO3 layers, above a critical thickness, display 2DEL transport with mobilities similar to those of (001)SrTiO3. Moreover we show that epitaxial interfaces are not a prerequisite: conducting (110) interfaces with amorphous LaAlO3 and other oxides can also be prepared. These findings open a new perspective both for materials research and for elucidating the ultimate microscopic mechanism of carrier doping. PMID:23091698

  13. 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.

  14. Phase equilibria investigations and thermodynamic modeling of the system Bi2O3-Al2O3

    NASA Astrophysics Data System (ADS)

    Oudich, F.; David, N.; Mathieu, S.; Vilasi, M.

    2015-02-01

    The system Bi2O3-Al2O3 has been experimentally investigated above 600 °C by DTA, XRD and EPMA under air and low oxygen pressure. Only two compounds were found to exist in equilibrium, which are Bi2Al4O9(1Bi2O3:2Al2O3) and Bi25AlO39(25:1). The latter exhibits a sillenite structure and does not contain pentavalent bismuth. A peritectoid decomposition of (25:1) and a peritectic melting of (1:2) occur at 775 °C and 1075 °C respectively, while an eutectic transformation was observed at 815 °C for 97 mol% Bi2O3. On the basis of the results obtained within the present work as well as experimental data provided from literature, a thermodynamic modeling where the liquid phase is described by the two-sublattice ionic liquid model was performed according to the Calphad approach. The resulting thermodynamic optimization yielded good agreement with experimental results in the investigated region.

  15. Phase transition and magneto-electric coupling of BiFeO3-YMnO3 multiferroic nanoceramics

    NASA Astrophysics Data System (ADS)

    Narayan Tripathy, Satya; Mishra, K. K.; Sen, S.; Mishra, B. G.; Pradhan, Dhiren K.; Palai, R.; Pradhan, Dillip K.

    2013-10-01

    We report the crystal structure, dielectric, magnetic, and magneto-electric properties of (1-x) BiFeO3-xYMnO3 (0.00 ≤ x ≤ 0.2) multiferroic nanoceramics prepared by auto-combustion technique. YMnO3 substitution is found to induce a structural phase transition from R3c to R3c+Pbnm after x ≈ 0.1 using Rietveld refinement technique. Field emission scanning electron micrographs show decrease in grain size with increase in YMnO3 content. The dielectric permittivity and loss tangent are found to be increased with composition x. The anomalies noticed from the temperature dependent dielectric analysis reveal the signature of magneto-electric coupling in the system. A decrease in magnetic ordering temperature as a function of composition is found from dielectric study. At room temperature, the dielectric permittivity of all the YMnO3 modified samples decrease with increasing magnetic field. The maximum value of magneto-electric coupling coefficient (ɛ(H)-ɛ(0))/ɛ(0) is found to be ˜ -5.5% at H = 2 T for x = 0.2. The behaviour of the magnetic hysteresis loop observed at room temperature suggests the suppression of space modulated spin structure.

  16. 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.

  17. 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.

  18. Magnetic properties of Eu doped BiGdO3

    NASA Astrophysics Data System (ADS)

    Nithya, R.; Yadagiri, K.; Shukla, Neeraj

    2016-05-01

    Bulk Bismuth Gadolinium Oxide, BiGdO3 and Eu doped BiGdO3 compounds were synthesized by the conventional solid state reaction in air. Phase formation of these compounds was tracked using powder X-ray characterization technique since single phase formation was found to be sensitive to thermal treatment parameters such as cooling and heating rates. Analysis of X-ray diffraction patterns revealed cubic structure with Pm-3m symmetry. An antiferromagnetic transition around 3.8K was observed in the pristine compound whereas doped samples showed paramagnetic nature in the whole measured temperature range.

  19. Phase Transitions in Nanoscale SrTiO3

    NASA Astrophysics Data System (ADS)

    Yu, Tian; Zhang, Han; Croft, Mark; Scofield, Megan; Bobb-Semple, Dara; Tao, Jing; Jaye, Cherno; Fisher, Daniel; Wong, Stanislaus; Tyson, Trevor

    Free standing SrTiO3 has recently been shown to be polar for ~10 nm particles (APL 105, 091901 (2014). We have conducted pressure dependent x-ray diffraction on monodispersed nanoscale samples with varying particle size. Distinctly different behavior is found in the diffraction patterns for sample with reduced size. The nature of the low temperature polar state under pressure will be discussed. The results are compared with reported work on bulk SrTiO3. This work is supported by DOE Grant DE-FG02-07ER46402.

  20. Room-Temperature Multiferroic Hexagonal LuFeO3

    SciTech Connect

    Cheng, Xuemei; Balke, Nina; Chi, Miaofang; Gai, Zheng; Keavney, David; Lee, Ho Nyung; Shen, Jian; Snijders, Paul C; Wang, Wenbin; Ward, Thomas Z; Xu, Xiaoshan; Yi, Jieyu; Zhu, Leyi; Christen, Hans M; Zhao, Jun

    2013-01-01

    We observed the coexistence of ferroelectricity and weak ferromagnetism at room temperature in the hexagonal phase of LuFeO3 stabilized by epitaxial thin film growth. While the ferroelectricity in hexagonal LuFeO3 can be understood as arising from its polar structure, the observation of weak ferromagnetism at room temperature is remarkable considering the frustrated triangular spin structure. An explanation of the room temperature weak ferromagnetism is proposed in terms of a subtle lattice distortion revealed by the structural characterization. The combination of ferroelectricity and weak ferromagnetism in epitaxial films at room temperature offers great potential for the application of this novel multiferroic material in next generation devices.

  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. Catalytic Methane Decomposition over Fe-Al2 O3.

    PubMed

    Zhou, Lu; Enakonda, Linga Reddy; Saih, Youssef; Loptain, Sergei; Gary, Daniel; Del-Gallo, Pascal; Basset, Jean-Marie

    2016-06-01

    The presence of a Fe-FeAl2 O4 structure over an Fe-Al2 O3 catalysts is demonstrated to be vital for the catalytic methane decomposition (CMD) activity. After H2 reduction at 750 °C, Fe-Al2 O3 prepared by means of a fusion method, containing 86.5 wt % FeAl2 O4 and 13.5 wt % Fe(0) , showed a stable CMD activity at 750 °C for as long as 10 h. PMID:27159367

  3. 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.

  4. Structural evidence for enhanced polarization in a commensurate short-period BaTiO3/SrTiO3 superlattice

    NASA Astrophysics Data System (ADS)

    Tian, W.; Jiang, J. C.; Pan, X. Q.; Haeni, J. H.; Li, Y. L.; Chen, L. Q.; Schlom, D. G.; Neaton, J. B.; Rabe, K. M.; Jia, Q. X.

    2006-08-01

    A short-period (BaTiO3)6/(SrTiO3)5 superlattice was characterized by x-ray diffraction and transmission electron microscopy. The superlattice is epitaxially oriented with the c axes of BaTiO3 and SrTiO3 normal to the (001) surface of the SrTiO3 substrate. Despite the large in-plane lattice mismatch between BaTiO3 and SrTiO3 (˜2.2%), the superlattice interfaces were found to be nearly commensurate. The crystallographic c /a ratio of the superlattice was measured and the results agree quantitatively with first-principles calculations and phase-field modeling. The agreement supports the validity of the enhanced spontaneous polarization predicted for short-period BaTiO3/SrTiO3 superlattices.

  5. 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. PMID:26484628

  6. Anisotropic superconducting properties of nanowires at the LaAlO3/SrTiO3 (110) interface

    NASA Astrophysics Data System (ADS)

    Irvin, Patrick; Huang, Mengcheng; Annadi, Anil; Cheng, Guanglei; Levy, Jeremy; Gopinadhan, Kalon; Venkatesan, Thirumalai; Ariando, Ariando

    2015-03-01

    The superconducting properties of nanowires created on anisotropic SrTiO3 (110) surfaces were investigated. Nanowires are created using conductive AFM (c-AFM) lithography at the LaAlO3/SrTiO3(110) interface along the (001) and (1 1 0) crystallographic directions. In these devices we observe anisotropic superconductivity. The upper critical magnetic field along the (001) and (1 1 0) directions are found to be markedly different with a superconducting dome that is shifted for the two orientations. These observations can be explained by anisotropic orbital binding of Ti and O atoms or the differences in the spin-orbit coupling along the two different directions. We gratefully acknowledge support for this work from NSF (DMR-1124131, DMR-1104191), AFOSR (FA9550-12-1-0057, FA9550-12-1-0268), and CRP-NRF (Tailoring Oxide Electronics).

  7. 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.

  8. 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

  9. Tunnel and electrostatic coupling in graphene-LaAlO3/SrTiO3 hybrid systems

    NASA Astrophysics Data System (ADS)

    Aliaj, I.; Torre, I.; Miseikis, V.; di Gennaro, E.; Sambri, A.; Gamucci, A.; Coletti, C.; Beltram, F.; Granozio, F. M.; Polini, M.; Pellegrini, V.; Roddaro, S.

    2016-06-01

    We report on the transport properties of hybrid devices obtained by depositing graphene on a LaAlO3/SrTiO3 oxide junction hosting a 4 nm-deep 2-dimensional electron system. At low graphene-oxide inter-layer bias, the two electron systems are electrically isolated, despite their small spatial separation. A very efficient reciprocal gating of the two neighboring 2-dimensional systems is shown. A pronounced rectifying behavior is observed for larger bias values and ascribed to the interplay between electrostatic field-effects and tunneling across the LaAlO3 barrier. The relevance of these results in the context of strongly coupled bilayer systems is discussed.

  10. 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.

  11. Ferroelectricity driven magnetism at domain walls in LaAlO3/PbTiO3 superlattices

    PubMed Central

    Zhou, P. X.; Dong, S.; Liu, H. M.; Ma, C. Y.; Yan, Z. B.; Zhong, C. G.; Liu, J. -M.

    2015-01-01

    Charge dipole moment and spin moment rarely coexist in single-phase bulk materials except in some multiferroics. Despite the progress in the past decade, for most multiferroics their magnetoelectric performance remains poor due to the intrinsic exclusion between charge dipole and spin moment. As an alternative approach, the oxide heterostructures may evade the intrinsic limits in bulk materials and provide more attractive potential to realize the magnetoelectric functions. Here we perform a first-principles study on LaAlO3/PbTiO3 superlattices. Although neither of the components is magnetic, magnetic moments emerge at the ferroelectric domain walls of PbTiO3 in these superlattices. Such a twist between ferroelectric domain and local magnetic moment, not only manifests an interesting type of multiferroicity, but also is possible useful to pursuit the electrical-control of magnetism in nanoscale heterostructures. PMID:26269322

  12. Ferroelectricity driven magnetism at domain walls in LaAlO3/PbTiO3 superlattices.

    PubMed

    Zhou, P X; Dong, S; Liu, H M; Ma, C Y; Yan, Z B; Zhong, C G; Liu, J-M

    2015-01-01

    Charge dipole moment and spin moment rarely coexist in single-phase bulk materials except in some multiferroics. Despite the progress in the past decade, for most multiferroics their magnetoelectric performance remains poor due to the intrinsic exclusion between charge dipole and spin moment. As an alternative approach, the oxide heterostructures may evade the intrinsic limits in bulk materials and provide more attractive potential to realize the magnetoelectric functions. Here we perform a first-principles study on LaAlO3/PbTiO3 superlattices. Although neither of the components is magnetic, magnetic moments emerge at the ferroelectric domain walls of PbTiO3 in these superlattices. Such a twist between ferroelectric domain and local magnetic moment, not only manifests an interesting type of multiferroicity, but also is possible useful to pursuit the electrical-control of magnetism in nanoscale heterostructures. PMID:26269322

  13. LaCrO3 heteroepitaxy on SrTiO3(001) by molecular beam epitaxy

    SciTech Connect

    Qiao, Liang; Droubay, Timothy C.; Bowden, Mark E.; Shutthanandan, V.; Kaspar, Tiffany C.; Chambers, Scott A.

    2011-08-09

    Stoichiometric, epitaxial LaCrO3 films have been grown on TiO2-terminated SrTiO3(001) substrates by molecular beam epitaxy using O2 as the oxidant. Film growth occurred in a layer-by-layer fashion, giving rise to structurally excellent films and surfaces which preserve the step-terrace structure of the substrate. The critical thickness is in excess of 500 Å. Near-surface Cr(III) is highly susceptible to further oxidation to Cr(V), leading to the formation of a disordered phase upon exposure to atomic oxygen. Recovery of the original epitaxial LaCrO3 phase is readily achieved by vacuum annealing.

  14. Large piezoelectric response of BiFeO3/BaTiO3 polycrystalline films induced by the low-symmetry phase.

    PubMed

    Hou, Y F; Li, W L; Zhang, T D; Wang, W; Cao, W P; Liu, X L; Fei, W D

    2015-05-01

    BaTiO3, BiFeO3 and BiFeO3/BaTiO3 polycrystalline films were prepared by the radio frequency magnetron sputtering on the Pt/Ti/SiO2/Si substrate. The phase structure, converse piezoelectric coefficient and domain structure of BaTiO3, BiFeO3 and BiFeO3/BaTiO3 thin films are characterized by XRD and PFM, respectively. The converse piezoelectric coefficient d33 of BiFeO3/BaTiO3 thin films is 119.5 pm V(-1), which is comparable to that of lead-based piezoelectric films. The large piezoelectric response of BiFeO3/BaTiO3 thin films is ascribed to the low-symmetry T-like phase BiFeO3, because the spontaneous polarization vector of T-like phase (with monoclinic symmetry) BiFeO3 can rotate easily under external field. In addition, the reduced leakage current and major domains with upward polarization are also attributed to the large piezoelectricity. PMID:25866266

  15. Tuning polarization states and interface properties of BaTiO3/SrTiO3 heterostructure by metal capping layers

    NASA Astrophysics Data System (ADS)

    Zhou, Jun; Yang, Ming; Shen, Lei; Wu, Qing Yun; Xu, Lei; Feng, Yuan Ping; Rusydi, Andrivo

    2016-04-01

    How to tune two-dimensional electron gas at interface of heterostructures is becoming an important question for both fundamental physics and electronic applications. Here, using density functional theory calculations, we find that the polarization state of BaTiO3 in metal capped BaTiO3/SrTiO3 heterostructures changes dramatically, depending on the termination of BaTiO3 and the different metal layers (M =Al , Fe, Pt Au). Most interestingly, for Pt on the BaO-terminated BaTiO3/SrTiO3, interface conductivity can be tuned. With a paraelectric state in BaTiO3, Pt_BaTiO 3 /SrTiO3 remains insulating at interface, while when BaTiO3 is ferroelectric, a hole- or electron-conducting BaTiO3/SrTiO3 interface can be realized, depending on its polarization direction in BaTiO3. This conducting interface and the top Pt layer screen the depolarization field, and thus stabilize the ferroelectricity in BaTiO3. Our result provides important clues for the reversibly tunable conductivity at oxide interfaces.

  16. Synthesis and Piezoelectric Properties Nd2O3-doped BaTiO3-Bi0.5(Na, K)0.5TiO3 by a Novel Composite-hydroxide-mediated Approach

    NASA Astrophysics Data System (ADS)

    Kimura, T.; Yin, S.; Hashimoto, T.; Sasaki, A.; Tokano, Y.; Sato, T.

    2011-10-01

    High purity Nd2O3-doped (1-x)BaTiO3-xBi0.5(Na, K)0.5TiO3 (x = 0.00-0.08) were synthesized by a composite-hydroxide-mediated approach at 200°C using a hydrothermal reaction apparatus with a rolling system. The powders with an average size of 100 nm in diameter were produced and were sintered to almost full theoretical density at low temperature such as 1200°C for 2 h. Although (1--x)BaTiO3-xBi0.5(Na, K)0.5TiO3 could not be poled, Nd2O3 additive was useful to proceed the polarization of (1-x)BaTiO3-xBi0.5(Na, K)0.5TiO3 ceramics.

  17. Concentration- and Temperature-Induced Phase Transitions in PrAlO3-SrTiO3 System.

    PubMed

    Vasylechko, Leonid; Stepchuk, Roman; Prots, Yuri; Rosner, Helge

    2016-12-01

    Single-phase mixed aluminates-titanates Pr1-x Sr x Al1-x Ti x O3 (x = 0.1, 0.2, 0.3, 0.5, 0.7) with rhombohedral perovskite structure were prepared by solid-state reaction technique at 1823-1873 K. Morphotropic rhombohedral-to-cubic phase transition in Pr1-x Sr x Al1-x Ti x O3 series is predicted to occur at x = 0.88. The temperature-induced structural phase transition R  [Formula: see text]  с - Pm [Formula: see text]  m in Pr0.5Sr0.5Al0.5Ti0.5O3, detected at 930 K by in situ high-temperature X-ray synchrotron powder diffraction, occurs at considerably lower temperature as the corresponding transformation in the parent compound PrAlO3 (1770 K). Such remarkable drop of the transition temperature is explained by gradual decrease of the perovskite structure deformation in the Pr1-x Sr x Al1-x Ti x O3 series with increasing Sr and Ti contents as a consequence of the increasing Goldschmidt tolerance factor. For Pr0.3Sr0.7Al0.3Ti0.7O3 phase, a sequence of the low-temperature phase transformation R  [Formula: see text]  с - Immb(C2/m) - I4/mcm was detected. PMID:26759353

  18. Determination of magnetic parameters in La0.7Sr0.3MnO3/SrTiO3 thin films using EMCD

    NASA Astrophysics Data System (ADS)

    Li, Gen; Song, Dongsheng; Li, Zhi Peng; Zhu, Jing

    2016-06-01

    It is well known that the magnetic state of the La0.7Sr0.3MnO3 (LSMO) thin-film heterostructure is strongly correlated with the lattice, spin, orbital, and charge states, since these influence the electric and magnetic transport properties even on the unit-cell level. Therefore, understanding the material's magnetic properties on the nanoscale is important for the development of novel applications. The recently developed electron magnetic-circular dichroism (EMCD) technique allows the determination of atomic site-specific magnetic information via the use of transmitted electrons; however, its sensitivity is not high enough to quantitatively acquire magnetic information in many weak magnetism systems. Here, we utilized a dynamical diffraction-effect assisted EMCD technique to quantitatively determine the spin and orbital magnetic moment of LSMO/SrTiO3 thin films on the nanometer scale using a transmission electron microscope. Further, data processing was optimized to enhance the intensity of the EMCD signals for manganese, which have very weak magnetism at room temperature. High signal-to-noise ratio and accurate quantitative magnetic measurement are eventually achieved. Finally, the spin magnetic moments (0.73 ± 0.26 μB) are derived, and we also limited the ratio of the orbital to spin magnetic moment within an interval of (-0.03, 0.01). Our results not only present the nanoscale magnetic parameters of LSMO/SrTiO3, but also demonstrate how the measurement limit of the spin (or orbital) magnetic moment can be achieved, which is via the developed dynamical diffraction effect assisted EMCD technique.

  19. TDPAC measurements in pure and Fe-doped In 2 O 3

    NASA Astrophysics Data System (ADS)

    Sena, C.; Costa, M. S.; Cabrera-Pasca, G. A.; Saxena, R. N.; Carbonari, A. W.

    2013-05-01

    Measurements of the electric quadrupole interactions were used to characterize pure and Fe-doped In2O3 samples using perturbed γ- γ angular correlation (PAC) technique with 111In-111Cd radioactive probe. The samples of pure as well as 1 % and 5 % Fe-doped In2O3 were prepared by sol-gel method and characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy dispersive x-ray spectroscopy (EDS). The PAC measurements were carried out with a conventional fast-slow coincidence set-up using four BaF2 detectors as a function of temperature from 295 K to 1073 K. The powder XRD spectra analyzed with Rietveld method as well as SEM and EDS results showed that Fe-doped samples are homogeneous without any secondary iron oxide phases. The PAC spectra of pure and 1 % Fe-doped In2O3 show well-known characteristic quadrupole frequencies for the two non-equivalent sites in the bixbyte structure. The hyperfine parameters in these cases change little with temperature. For the 5 % Fe-doped sample however the PAC spectra changed significantly and a third frequency with large η appears.

  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. Pressure-driven changes in electronic structure of BiCoO3

    NASA Astrophysics Data System (ADS)

    Kanungo, Sudipta; Saha-Dasgupta, Tanusri

    2012-02-01

    Using first-principles DFT based calculations, carried out on the recently measured crystal structure data [Oka et.al. J.Am.Chem.Soc.132, 9438 (2010)], we study the changes in the electronic structure of BiCoO3 between the ambient-pressure and the high-pressure conditions. Our study shows that the application of high pressure drives the high-spin-to-low-spin transition at the Co site. The obtained results for the ambient pressure phase shows C-type AFM alignment of Co high spins, while the electronic structure at the high-pressure phase shows the presence of a finite energy gap at Ef in contrast with previously reported metallic or semimetallic character with low-spin state of Co. This semiconducting behavior in the nonmagnetic BiCoO3 with LS state of Co is found to be driven by the presence of the GdFeO3 type of orthorhombic distortion which arises due to finite mixing of Bi lone-pair states with O-p states, as opposed to previously predicted cubic or tetragonal symmetry of the high-pressure. The ambient pressure phase shows an order of magnitude larger energy gap arising due to the AFM alignment of Co in the high-spin state than the energy gap at the high pressure phase, explains the observed 3-order of magnitude jump in resistivity.

  2. Electron paramagnetic resonance and optical spectroscopy of Er-doped β-Ga2O3

    NASA Astrophysics Data System (ADS)

    Vincent, J.; Guillot-Noël, O.; Binet, L.; Aschehoug, P.; Le Du, Y.; Beaudoux, F.; Goldner, P.

    2008-08-01

    Conducting β-Ga2O3 single crystals doped with Er3+ were grown using the floating zone method. Electron paramagnetic resonance (EPR) showed that conduction electrons can coexist with the Er3+ dopant. Optical and EPR characterizations of samples nominally doped with 0.5% and 1.5% were performed at low temperature showing that erbium substitution into β-Ga2O3 can only be achieved effectively at the lower concentration because of the appearance of an erbium gallium garnet phase when the erbium concentration is increased. Despite the existence of two cationic sites in β-Ga2O3, EPR measurements demonstrate that Er incorporation occurs at a single crystallographic position. Optical spectroscopy of 0.5% doped samples of the 1.5μm transition allowed us to determine some crystal field levels of the I15/24 and I13/24 multiplets. A lifetime of about 12ms was found for the 1.5μm emission, indicating a high quantum yield for the I13/24 multiplet.

  3. 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

    2015-10-01

    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. PMID:26307213

  4. Importance of anisotropic Coulomb interaction in LaMnO3

    NASA Astrophysics Data System (ADS)

    Mellan, Thomas A.; Corà, Furio; Grau-Crespo, Ricardo; Ismail-Beigi, Sohrab

    2015-08-01

    In low-temperature antiferromagnetic LaMnO3, strong and localized electronic interactions among Mn 3 d electrons prevent a satisfactory description from standard local density and generalized gradient approximations in density functional theory calculations. Here, we show that the strong on-site electronic interactions are described well only by using direct and exchange corrections to the intraorbital Coulomb potential. Only DFT + U calculations with explicit exchange corrections produce a balanced picture of electronic, magnetic, and structural observables in agreement with experiment. To understand the reason, a rewriting of the functional form of the + U corrections is presented that leads to a more physical and transparent understanding of the effect of these correction terms. The approach highlights the importance of Hund's coupling (intraorbital exchange) in providing anisotropy across the occupation and energy eigenvalues of the Mn d states. This intraorbital exchange is the key to fully activating the Jahn-Teller distortion, reproducing the experimental band gap and stabilizing the correct magnetic ground state in LaMnO3. The best parameter values for LaMnO3 within the DFT (PBEsol) + U framework are determined to be U =8 eV and J =1.9 eV.

  5. 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. PMID:25375730

  6. Enhanced ferromagnetic properties in Ho and Ni co-doped BiFeO3 ceramics

    NASA Astrophysics Data System (ADS)

    Park, J. S.; Yoo, Y. J.; Hwang, J. S.; Kang, J.-H.; Lee, B. W.; Lee, Y. P.

    2014-01-01

    The magnetic properties of polycrystalline Bi1-xHoxFe1-yNiyO3 (x = 0, 0.1; y = 0, 0.03), which were prepared by the solid-state method, have been investigated. The powder X-ray diffraction reveals that all the samples are polycrystalline and show rhombohedral perovskite structure. The micro-Raman scattering studies confirm that Bi0.9Ho0.1Fe0.97Ni0.03O3 has a compressive lattice distortion induced by the simultaneous substitution of Ho and Ni ions at A and B-sites, respectively. From the magnetization dependences at room temperature, Bi0.9Ho0.1Fe0.97Ni0.03O3 has enhanced magnetization (0.2280 emu/g) and low coercive field (280 Oe). It was revealed that the Ni dopant plays an important role for the improved ferromagnetic properties and the Ho dopant favors the magnetic exchange interactions in the co-doped ceramic.

  7. 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.

  8. Blending Cr2O3 into a NiO-Ni electrocatalyst for sustained water splitting

    DOE PAGESBeta

    Gong, Ming; Zhou, Wu; Kenney, Michael James; Kapusta, Rich; Cowley, Sam; Wu, Yingpeng; Lu, Bingan; Lin, Meng -Chang; Wang, Di -Yan; Yang, Jiang; et al

    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

  9. Electro-optic and dielectric properties of photorefractive BaTiO3 and KNbO3

    NASA Astrophysics Data System (ADS)

    Zgonik, Marko; Nakagawa, Kiyoshi; Günter, Peter

    1995-08-01

    Recently determined complete sets of materials parameters describing the dielectric, elastic, piezoelectric, elasto-optic, and electro-optic properties of BaTiO3 and KNbO3 crystals at room temperature are used to calculate the effective electro-optic coefficients and dielectric constants required for describing photorefractive phenomena. We show a substantial deviation of the new values from the electro-optic coefficients for homogeneously applied electric fields that were used previously in describing the photorefractive effects. We derive angular dependences of the effective electro-optic coefficients and the effective dielectric constants relevant for grating recording in both crystals and verify them experimentally.

  10. Thermodynamic investigation of the magnetic phase transitions of CaMnO3 and SrRuO3

    NASA Astrophysics Data System (ADS)

    Neumeier, J. J.; Cornelius, A. L.; Andres, K.

    2001-11-01

    Measurements of the linear thermal expansion Δl/l and molar heat capacity CP at constant pressure are presented on antiferromagnetic CaMnO3 and ferromagnetic SrRuO3 in the neighborhood of their magnetic phase transitions. The jumps in the linear thermal-expansion coefficient α and CP are used to calculate the influence of pressure on the magnetic ordering temperatures Tc through the Ehrenfest relation. Good agreement is obtained with measured values of dTc/dP.

  11. 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.

  12. 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.

  13. Interface Structure of MoO3 on Organic Semiconductors.

    PubMed

    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

  14. Structural phase transitions in EuNbO3 perovskite

    NASA Astrophysics Data System (ADS)

    Kususe, Yoshiro; Yoshida, Suguru; Fujita, Koji; Akamatsu, Hirofumi; Fukuzumi, Masafumi; Murai, Shunsuke; Tanaka, Katsuhisa

    2016-07-01

    The crystal structures of europium niobate, EuNbO3, have been examined over a wide temperature range between 20 and 500 K using synchrotron X-ray diffraction. We have observed two successive structural phase transitions at 360 and 460 K. Below 350 K, EuNbO3 adopts an orthorhombic perovskite structure (space group Imma), which is characterized by NbO6 octahedral tilting about the pseudocubic two-fold axis. The result differs from previous reports in which EuNbO3 was assigned to a cubic aristotype (space group Pm 3 barm) of perovskite at room temperature. At around 360 K, EuNbO3 undergoes a first-order phase transition to a tetragonal symmetry (space group I4/mcm) with the NbO6 octahedral tilting about the pseudocubic four-fold axis. As the temperature is further increased, the I4/mcm tetragonal phase changes into the Pm 3 barm cubic aristotype at 460 K. The tetragonal-to-cubic transformation is characterized as a continuous phase transition.

  15. Single-domain multiferroic BiFeO3 films.

    PubMed

    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. Insulating room temperature ferromagnetic SrTiO3

    NASA Astrophysics Data System (ADS)

    Posadas, Agham; Mitra, Chandrima; Lin, Chungwei; Dhamdere, Ajit; Smith, David; Tsoi, Maxim; Demkov, Alex

    2013-03-01

    We report the epitaxial growth of ferromagnetic insulating material based on SrTiO3 using molecular beam epitaxy (MBE). SrTi1-xCoxO3-δ films (x = 0.1 to 0.5) were grown on Si(100) substrates via a buffer layer of four unit cells of undoped SrTiO3. The crystalline structure was characterized by reflection high energy electron diffraction, x-ray diffraction, and cross-section transmission electron microscopy. Robust room-temperature ferromagnetism is confirmed in samples with composition 30-40% Co. We also performed in situx-ray photoelectron spectroscopy of the Sr, Co, Ti, and O core levels to determine stoichiometry and cobalt oxidation state. In all single phase samples, an oxygen vacancy concentration of approximately equal to the amount of Co substitution was measured (compensated doping). In order to elucidate the origin of ferromagnetism, we also performed first-principles calculations of SrTiO3 simultaneously doped with Co and an oxygen vacancy. We find that such a configuration at concentrations of ~ 25% can result in a ferromagnetic insulating state with high spin Co2+. The ability to integrate an insulating ferromagnet on silicon in epitaxial form may potentially be useful for spin filtering and spin wave applications in the field of spintronics.

  17. Structural characterisation of Fe2O3 nanoparticles

    NASA Astrophysics Data System (ADS)

    Hagelstein, Michael; Vinga Szabó, Dorothée; Schlabach, Sabine; Masala, Paolo; Scavini, Marco; Coduri, Mauro; Ferrero, Claudio

    2016-05-01

    The structure of nano-crystalline Fe2O3 particles, synthesized using the microwave plasma technique, has been analysed using synchrotron based X-ray absorption spectroscopy and X-ray powder diffraction, as well as transmission electron microscopy. Furthermore, magnetic properties, the crystal structure, and the microstructures are compared and the potential model character of the samples for structure simulations is discussed.

  18. 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.

  19. Structures and energetics of Ga2O3 polymorphs

    NASA Astrophysics Data System (ADS)

    Yoshioka, S.; Hayashi, H.; Kuwabara, A.; Oba, F.; Matsunaga, K.; Tanaka, I.

    2007-08-01

    First-principles calculations are made for five Ga2O3 polymorphs. The structure of ɛ-Ga2O3 with the space group Pna 21 (No. 33, orthorhombic), which is sometimes called κ-Ga2O3 in the literature, is consistent with experimental reports. The structure of γ-Ga2O3 is optimized within 14 inequivalent configurations of defective spinel structures. Phonon dispersion curves of four polymorphs are obtained. The volume expansivity, bulk modulus, and specific heat at constant volume are computed as a function of temperature within the quasi-harmonic approximation. The Helmholtz free energies of the polymorphs are thus compared. The expansivity shows a relationship of β<ɛ<α<δ, while β<ɛ<δ<α for the bulk modulus. The formation free energies have the tendency β<ɛ<α<δ<γ at low temperatures. With the increase of temperature, the difference in free energy between the β-phase and the ɛ-phase becomes smaller. Eventually the ɛ phase becomes more stable at above 1600 K.

  20. 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.

  1. 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

  2. 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.

  3. 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

  4. 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...

  5. 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.

  6. Composition dependence of photoluminescence properties of poly(9,9-di-n-hexylfluorenyl-2,7-diyl) with perovskite-structured SrTiO3 nanocomposites

    NASA Astrophysics Data System (ADS)

    Din, U. K. N.; Salleh, M. M.; Aziz, T. H. T.; Umar, A. A.

    2016-05-01

    Nanocomposite thin films of poly(9,9-di-n-hexylfluorenyl-2,7-diyl) (PHF) with 10-50 wt% perovskite-structured SrTiO3 nanoparticles (designated as PHF:SrTiO3) were prepared by spin coating. The photoluminescence (PL) properties of the nanocomposites thin films were studied. The incorporation of SrTiO3 nanoparticles into the nanocomposite thin films enhanced the original PL intensities of the host PHF thin films. The intensities of the PL peak for the nanocomposite thin films were dependent on the amount of SrTiO3 nanoparticles in the films and the homogeneity of the nanoparticle distribution. The distribution of the SrTiO3 nanoparticles contributed to the overlapping molecular orbital sites in PHF:SrTiO3, which promoted the excited electrons from the conduction band of SrTiO3 transferred to the excited energy level of the PHF host material. In this case, the perovskite-structured SrTiO3 nanoparticles act as sensitizers.

  7. Facile Synthesis of Fe2O3 Nano-Dots@Nitrogen-Doped Graphene for Supercapacitor Electrode with Ultralong Cycle Life in KOH Electrolyte.

    PubMed

    Liu, Li; Lang, Junwei; Zhang, Peng; Hu, Bin; Yan, Xingbin

    2016-04-13

    Fe2O3 nanodots supported on nitrogen-doped graphene sheets (denoted as Fe2O3 NDs@NG) with different loading masses are prepared through a facile one-pot solvothermal method. The resulting Fe2O3 NDs@NG composites exhibit outstanding electrochemical properties in aqueous KOH electrolyte. Among them, with the optimal loading mass of Fe2O3 NDs, the corresponding Fe2O3 NDs@NG-0.75 sample is able to deliver a high specific capacitance of 274 F g(-1) at 1 A g(-1) and the capacitance is still as high as 140 F g(-1) even at a ultrahigh current density of 50 A g(-1), indicating excellent rate capability. More remarkably, it displays superior capacitance retention after 100 000 cycles (about 75.3% at 5 A g(-1)), providing the best reported long-term cycling stability for iron oxides in alkaline electrolytes to date. Such excellent electrochemical performance is attributed to the right combination of highly dispersed Fe2O3 NDs and appropriately nitrogen-doped graphene sheets, which enable the Fe2O3 NDs@NG-0.75 to offer plenty of accessible redox active sites, facilitate the electron transfer and electrolyte diffusion, as well as effectively alleviate the volume change of Fe2O3 NDs during the charge-discharge process. PMID:27007301

  8. The Perovskite to Post-Pero