Science.gov

Sample records for modulu sr-0 jaderneho

  1. Influence of electron beam irradiation on the structural, electrical and thermal properties of Gd0.5Sr0.5MnO3 and Dy0.5Sr0.5MnO3 manganites

    NASA Astrophysics Data System (ADS)

    Nagaraja, B. S.; Rao, Ashok; Babu, P. D.; Sanjeev, Ganesh; Okram, G. S.

    2016-01-01

    We present systematic studies on the effect of electron beam irradiation on structural, electrical and thermal properties of Gd0.5Sr0.5MnO3 and Dy0.5Sr0.5MnO3 manganites. The XRD patterns and Rietveld analysis show that the samples remain single phased even after they undergo electron beam irradiation. Both the series of the samples Gd0.5Sr0.5MnO3 and Dy0.5Sr0.5MnO3 show insulating trends in their temperature dependent electrical resistivity, ρ(T) behavior. The resistivity data for both the series of samples (pristine as well as irradiated) indicate that the small polaron hopping model is valid in high temperature region; on contrary, variable range hopping model governs the low temperature regime. Magnetic studies demonstrate that the Neel temperatures of pristine and irradiated samples of Gd0.5Sr0.5MnO3 and Dy0.5Sr0.5MnO3 do not change appreciably when they are subjected to irradiation. Thermo-electrical power is observed to increase with irradiation in Gd0.5Sr0.5MnO3 samples, whereas for Dy0.5Sr0.5MnO3 samples a decrease in thermo-electric power is seen when the samples are irradiated.

  2. Positive magnetoresistance of La0.7Sr0.3MnO3/C composites

    NASA Astrophysics Data System (ADS)

    Kabirov, Yu. V.; Gavrilyachenko, V. G.; Bogatin, A. S.

    2016-07-01

    The perovskite manganite La0.7Sr0.3MnO3 compound is used as a component in ceramic (1‑x)(La0.7Sr0.3MnO3)-xC composites at x = 0.15-0.85. It is found that every studied specimen is characterized by the linear dependence of the positive magnetoresistance (PMR) on the magnetic field strength at room temperature. The 0.6(La0.7Sr0.3MnO3)-0.4C composite has the largest magnetoresistance value (15%) at room temperature and intensity of magnetic field H=15kOe. A possible mechanism for the PMR of (1‑x)(La0.7Sr0.3MnO3)-xC composites is discussed.

  3. Ni-doped La0.5Sr0.5TiO3 nanofibers: Fabrication and intrinsic ferromagnetism

    NASA Astrophysics Data System (ADS)

    Ponhan, Wichaid; Amornkitbamrung, Vittaya; Maensiri, Santi

    2016-06-01

    We report room-temperature ferromagnetism in ˜104-133 nm nanofibers of La0.5Sr0.5Ti1- x Ni x O3 (0.02 ≤ x ≤ 0.05). As-spun nanofibers of La0.5Sr0.5Ti1- x Ni x O3 are fabricated by an electrospinning technique. Nanofibers of the as spun and calcined La0.5Sr0.5Ti1- x Ni x O3 samples are characterized using X-ray diffraction (XRD) analysis, transmission electron microscopy (TEM), X-ray photoelectron microscopy (XPS), X-ray absorption near edge structure (XANES) determination, and vibrating sample magnetometry (VSM). The results of XRD analysis and TEM together with selected electron diffraction (SEAD) analysis indicate that La0.5Sr0.5Ti1- x Ni x O3 nanofibers have a cubic perovskite structure with no secondary phase. The as-spun samples are paramagnetic, whereas the La0.5Sr0.5Ti1- x Ni x O3 samples are ferromagnetic having specific magnetizations of 0.098-0.484 emu/g at 10 kOe. The XPS spectra show that there are some oxygen vacancies in the nanofibers, which its may play an important role in inducing room-temperature ferromagnetism in La0.5Sr0.5Ti1- x Ni x O3 nanofibers. XANES spectra show that most of the Ni ions in La0.5Sr0.5Ti1- x Ni x O3 nanofibers are in the Ni2+ state mixed with some Ni metal. The finding of room temperature ferromagnetism in this nanofibrous structure of the La0.5Sr0.5Ti1- x Ni x O3 system is of interest in research on diluted magnetic oxides.

  4. Silica-Aerogel Composites Opacified with La(0.7)Sr(0.3)MnO3

    NASA Technical Reports Server (NTRS)

    Rhine, Wendell; Polli, Andrew; Deshpande, Kiranmayi

    2009-01-01

    As part of an effort to develop improved lightweight thermal-insulation tiles to withstand temperatures up to 1,000 C, silica aerogel/fused-quartz-fiber composite materials containing La0.7Sr0.3MnO3 particles as opacifiers have been investigated as potentially offering thermal conductivities lower than those of the otherwise equivalent silica-aerogel composite materials not containing La(0.7)Sr(0.3)MnO3 particles. The basic idea of incorporating opacifying particles into silica-aerogels composite to reduce infrared radiative contributions to thermal conductivities at high temperatures is not new: it has been reported in a number of previous NASA Tech Briefs articles. What is new here is the selection of La(0.7)Sr(0.3)MnO3 particles as candidate opacifiers that, in comparison with some prior opacifiers (carbon black and metal nanoparticles), are more thermally stable. The preparation of a composite material of the present type includes synthesis of the silica-aerogel component in a sol-gel process. The La(0.7)Sr(0.3)MnO3 particles, made previously in a separate process, are mixed into the sol, which is then cast onto fused-quartz-fiber batting. Then the aerogel-casting solution is poured into the mold, where it permeates the silica fiber felt. After the sol has gelled, the casting is aged and then subjected to supercritical drying to convert the gel to the final aerogel form. The separate process for making the La(0.7)Sr(0.3)MnO3 particles begins with the slow addition of corresponding proportions of La(CH3COOH)3, Mn(CH3COOH)3, and Sr(NO3)2 to a solution of H2O2 in H2O. The solution is then peptized by drop-wise addition of NH4OH to obtain a sol. Next, the sol is dried in an oven at a temperature of 120 C to obtain a glassy solid. The solid is calcined at 700 C to convert it to La(0.7)Sr(0.3)MnO3. Then La(0.7)Sr(0.3)MnO3 particles are made by ball-milling the calcined solid. The effectiveness of La(0.7)Sr(0.3)MnO3 particles as opacifiers and thermal

  5. Sol-Gel Synthesis of La(0.6)Sr(0.4)CoO(3-x) and Sm(0.5)Sr(0.5)CoO(3-x) Cathode Nanopowders for Solid Oxide Fuel Cells

    NASA Technical Reports Server (NTRS)

    Bansal, Narottam P.; Wise, Brent

    2011-01-01

    Nanopowders of La(0.6)Sr(0.4)CoO(3-x) (LSC) and Sm(0.5)Sr(0.5)CoO(3-x) (SSC) compositions, which are being investigated as cathode materials for intermediate temperature solid oxide fuel cells (IT-SOFC) with La(Sr)Ga(Mg)O(3-x) (LSGM) as the electrolyte, were synthesized by low-temperature sol-gel method using metal nitrates and citric acid. Thermal decomposition of the citrate gels was followed by simultaneous DSC/TGA methods. Development of phases in the gels, on heat treatments at various temperatures, was monitored by x-ray diffraction. Solgel powders calcined at 550 to 1000 C consisted of a number of phases. Single perovskite phase La(0.6)Sr(0.4)CoO(3-x) or Sm(0.5)Sr(0.5)CoO(3-x) powders were obtained at 1200 and 1300 C, respectively. Morphological analysis of the powders calcined at various temperatures was done by scanning electron microscopy. The average particle size of the powders was approx.15 nm after 700 C calcinations and slowly increased to 70 to 100 nm after heat treatments at 1300 to 1400 C.

  6. Synthesis and luminescence characterization of Sr(0.5)Ca(0.5)TiO3:Sm(3+) phosphor.

    PubMed

    Vidyadharan, Viji; Remya, Mohan P; Gopi, Subhash; Thomas, Sunil; Joseph, Cyriac; Unnikrishnan, N V; Biju, P R

    2015-11-01

    The spectroscopic properties of trivalent samarium doped Sr0.5Ca0.5TiO3 perovskite phosphor material (Sr0.5Ca0.5TiO3:xSm(3+), x=0.05, 0.1, 0.5, 1, 1.5) synthesized by the solid state method have been studied. The X-Ray Diffraction profile confirms the orthorhombic perovskite Sr0.5Ca0.5TiO3 structure of the prepared samples. The SEM study reveals the surface morphology. The Judd-Ofelt intensity parameters were calculated for 0.5 wt% Sm(3+) doped Sr0.5Ca0.5TiO3. Transition probabilities, branching ratios and radiative lifetime were evaluated by using Judd-Ofelt analysis. The emission spectra under 405 nm excitation shows five emission peaks at 564 nm, 599 nm, 645 nm, 707 nm and 776 nm corresponding to the transitions (4)G5/2→(6)Hj (j=5/2, 7/2, 9/2, 11/2 and 13/2) respectively. The higher values of branching ratio and stimulated emission cross-section for (4)G5/2→(6)H7/2 transition of Sr0.5Ca0.5TiO3:0.5 wt% Sm(3+) shows its suitability in the field of visible lasers and optical fiber amplifiers. The experimental lifetimes of Sm(3+) doped samples were estimated using the decay curves corresponding to (4)G5/2→(6)H7/2 transition upon 405 nm excitation. Concentration dependence on emission intensity and experimental lifetime were also studied. From the CIE diagram we can see that as the concentration of Sm(3+) ions increases from 0.05 wt% to 1.5 wt% the CIE color co-ordinates changes from greenish yellow to yellowish orange.

  7. Magnetic and magnetotransport characterization of La0.7Sr0.3MnO3/YBCO/La0.7Sr0.3MnO3/YBCO spin valve

    NASA Astrophysics Data System (ADS)

    Dybko, K.; Aleshkevych, P.; Sawicki, M.; Przyslupski, P.

    2015-01-01

    We present magnetoresistance measurements on La0.7Sr0.3MnO3/YBCO/La0.7Sr0.3MnO3/YBCO (L1/Y1/L2/Y) heterostructure. The Ll/Y1/L2/Y spin valve shows large magnetoresistance peaks in coercive field at temperatures below the onset of the superconducting transition. The rotation in parallel magnetic field demonstrates a change of magnetoresistance; simultaneously the transition temperature to superconducting state Tc0(H=450 Oe, β) exhibits nonmonotonic dependence due to change of noncolinearity of magnetic moments of LSMO layers. Nonmonotonic change of the transition temperature as a function of angle is interpreted as a signature of generation of the triplet component superconducting phase in the Ll/Y1/L2/Y heterostructure.

  8. Ba0.9Sr0.1TiO3-based optical microcavities fabricated by chemical solution deposition

    NASA Astrophysics Data System (ADS)

    Hong, X. K.; Hu, G. J.; Shang, J. L.; Bao, J.; Chu, J. H.; Dai, N.

    2007-06-01

    Single or coupled optical microcavities have been prepared by inserting one or two dense Ba0.9Sr0.1TiO3 layers, respectively, in the quasiperiodic Ba0.9Sr0.1TiO3 multilayers fabricated based on phase separation. The single microcavities exhibit well-defined resonant modes in the investigated wavelength range with a quality factor no less than 60. The resonant frequency of the mode can be tuned through varying the spinning rate during the spin-coating process to change the thickness of the inserted layer. The mode properties of the coupled microcavities strongly depend on the mismatch parameter of the inserted defect layers. The approach reported here offers a simple, inexpensive, and flexible route for fabricating high quality microcavities.

  9. Synthesis and characterization of PVDF-La0.7Sr0.3MnO3 nanocomposite films

    NASA Astrophysics Data System (ADS)

    Thirmal, Ch.; Murugavel, P.; Subramanian, V.

    2015-06-01

    The thick films of pure PVDF and PVDF-La0.7Sr0.3MnO3 nanocomposite on Aluminum substrates are synthesized by dip coating technique. The synthesized films are studied for their structural, thermal, morphological and dielectric properties along with the ac conductivity studies. The enhanced dielectric constant and ac conductivity are analyzed with respect to Maxwell-Wagner mechanism induced interfacial polarization.

  10. Structural transitions in the manganite Pr 0.5Sr 0.5MnO 3

    NASA Astrophysics Data System (ADS)

    Damay, F.; Martin, C.; Hervieu, M.; Maignan, A.; Raveau, B.; André, G.; Bourée, F.

    1998-04-01

    The structural transitions in the Pr 0.5Sr 0.5MnO 3 CMR perovskite have been studied, coupling neutron powder diffraction (NPD) and electron microscopy (EM) techniques. Both techniques show the existence of a Fmmm type structure at low temperature ( T<135 K) that corresponds to the antiferromagnetic insulating (AFMI) state. No evidence of charge ordering is observed. At 135 K a transition to a ferromagnetic I4/mcm structure is observed by NPD. Further increasing the temperature ( T⩾265 K), Pr 0.5Sr 0.5MnO 3 becomes paramagnetic but keeps its I4/mcm structure. By EM, the transition occurring around 135 K is also observed, but it corresponds to a change from the Fmmm to an Imam structure, with a simultaneous disappearance of the twinning domains present in the Fmmm structure. This effect is reversible. The EM study also evidences that at high temperature ( T˜430 K) another transition from the Imam to an I4/mcm structure occurs. The divergence between the NPD and EM observations is attributed to the fact that the structure of Pr 0.5Sr 0.5MnO 3 may be sensitive to the magnetic field that exists in the electron microscope (1 or 2 T).

  11. Resistance switching mechanism of La0.8Sr0.2MnO3-δ thin films

    NASA Astrophysics Data System (ADS)

    Luo, X. D.; Gao, R. L.; Fu, C. L.; Cai, W.; Chen, G.; Deng, X. L.; Zhang, H. R.; Sun, J. R.

    2016-02-01

    Effects of oxygen vacancies on the electrical transport properties of oxygen stoichiometric La0.8Sr0.2MnO3 and oxygen-deficient La0.8Sr0.2MnO3-δ films have been investigated. The result presents that the oxygen-deficient films annealed in vacuum show obvious increase of resistance and lattice parameter. With the sweeping voltage or temperature increasing, the resistance exhibits obvious bipolar switching effect, no forming process was needed. Oxygen deficiency in the annealed film leads to the formation of a structural disorder in the Mn-O-Mn conduction channel due to the accumulation of oxygen vacancies under high external electric field or temperatures and hence is believed to be responsible for the bipolar resistance switching effect and the enhanced resistivity compared with oxygen stoichiometric La0.8Sr0.2MnO3 film. These results may be important for practical applications in photoelectric or storage devices and point to a useful direction for other oxidizing materials.

  12. Sr0.95In0.05Li2Ti6O14: A high performance lithium host material

    NASA Astrophysics Data System (ADS)

    Qian, Shangshu; Yu, Haoxiang; Yan, Lei; Li, Peng; Lin, Xiaoting; Zhang, Yanyu; Long, Nengbing; Shui, Miao; Shu, Jie

    2016-08-01

    Via Sr-site substitution, a series of Sr0.95M0.05Li2Ti6O14 (Mz+ = Na+, Cu2+, In3+) are prepared as anode materials for lithium-ion batteries. It is found that the introduction of Na+, Cu2+ or In3+ into the crystal lattice can reduce the charge-transfer resistance and improve the lithium-ion diffusion coefficient of SrLi2Ti6O14. Especially for In3+-doping, it exhibits more obvious effect on these improvements. Furthermore, the substitution of Sr2+ by In3+ can also enhance the electronic conductivity via inducing a reduction of an equivalent number of Ti cations from Ti4+ to Ti3+. As a result, Sr0.95In0.05Li2Ti6O14 shows the best cycle and rate properties among all as-prepared samples. In addition, in-situ observation also proves that Sr0.95In0.05Li2Ti6O14 is a zero-strain lithium storage compound during charge/discharge process. As a result, it delivers a lithium storage capacity of 136.4 mAh g-1 at 200 mA g-1, 126.3 mAh g-1 at 400 mA g-1 and 121.0 mAh g-1 at 600 mA g-1. In contrast, SrLi2Ti6O14 only presents a charge capacity of 138.3 mAh g-1 at 200 mA g-1, 120.3 mAh g-1 at 400 mA g-1 and 111.3 mAh g-1 at 600 mA g-1. Therefore, In3+-doping is an effective method to enhance the electrochemical properties of SrLi2Ti6O14.

  13. Growth of Sr(0.61)Ba(0.39)Nb2O6 fibers - New results regarding orientation

    NASA Technical Reports Server (NTRS)

    Wilde, Jeffrey P.; Jundt, Dieter H.; Galambos, Ludwig; Hesselink, Lambertus

    1991-01-01

    The paper describes stable growth of Sr(0.61)Ba(0.39)Nb2O6 (SBN) single-crystal optical fibers (grown by the laser-heated pedestal growth method) along the 100-line and 110-line crystallographic axes. The orientation of SBN fibers was investigated using transmission holograms recorded by focusing two separate, but mutually coherent, optical wavefronts into one end of the fiber. Results showed that the crystal quality of 100-line and 110-line SBN fibers grown at a given pull velocity strongly depended on the fiber diameter; generally, the quality improves with decreasing diameter.

  14. Electron-phonon interactions in superconducting La1.84Sr0.16CuO4 films.

    PubMed

    Shim, Heejae; Chaudhari, P; Logvenov, Gennady; Bozovic, Ivan

    2008-12-12

    We have measured quasiparticle tunneling across a junction perpendicular to the superconducting copper oxide planes. The tunneling spectra show peaks in the density of states. There are 11 minima in the second derivative d2I/dV2, where I is the current and V the voltage, suggesting multiple boson-quasiparticle interactions. These minima match precisely with the published Raman scattering data, leading us to conclude that the relevant bosons in superconducting La1.84Sr0.16CuO4 films are phonons. PMID:19113657

  15. Combustion synthesis of Sm 0.5Sr 0.5CoO 3- x and La 0.6Sr 0.4CoO 3- x nanopowders for solid oxide fuel cell cathodes

    NASA Astrophysics Data System (ADS)

    Bansal, Narottam P.; Zhong, Zhimin

    Nanopowders of Sm 0.5Sr 0.5CoO 3- x (SSC) and La 0.6Sr 0.4CoO 3- x (LSC) compositions, which are being investigated as cathode materials for intermediate temperature solid oxide fuel cells (SOFC), were synthesized by a solution-combustion method using metal nitrates and glycine as fuel. Development of crystalline phases in the as-synthesized powders after heat treatments at various temperatures was monitored by X-ray diffraction (XRD). Perovskite phase in LSC formed more readily than in SSC. Single-phase perovskites were obtained after heat treatment of the combustion synthesized LSC and SSC powders at 1000 and 1200 °C, respectively. The as-synthesized powders had an average particle size of ∼12 nm as determined from X-ray line broadening analysis using the Scherrer equation. Average grain size of the powders increased with increase in calcination temperature. Morphological analysis of the powders calcined at various temperatures was done by scanning electron microscopy (SEM).

  16. Octonary resistance states in La0.7Sr0.3MnO3/BaTiO3/La0.7Sr0.3MnO3 multiferroic tunnel junctions

    DOE PAGES

    Yue -Wei Yin; Tao, Jing; Huang, Wei -Chuan; Liu, Yu -Kuai; Yang, Sheng -Wei; Dong, Si -Ning; Zhu, Yi -Mei; Li, Qi; Li, Xiao -Guang

    2015-10-06

    General drawbacks of current electronic/spintronic devices are high power consumption and low density storage. A multiferroic tunnel junction (MFTJ), employing a ferroelectric barrier layer sandwiched between two ferromagnetic layers, presents four resistance states in a single device and therefore provides an alternative way to achieve high density memories. Here, an MFTJ device with eight nonvolatile resistance states by further integrating the design of noncollinear magnetization alignments between the ferromagnetic layers is demonstrated. Through the angle-resolved tunneling magnetoresistance investigations on La0.7Sr0.3MnO3/BaTiO3/La0.7Sr0.3MnO3 junctions, it is found that, besides collinear parallel/antiparallel magnetic configurations, the MFTJ shows at least two other stable noncollinear (45°more » and 90°) magnetic configurations. As a result, combining the tunneling electroresistance effect caused by the ferroelectricity reversal of the BaTiO3 barrier, an octonary memory device is obtained, representing potential applications in high density nonvolatile storage in the future.« less

  17. Combustion Synthesis of Sm0.5Sr0.5CoO3-x and La0.6Sr0.4CoO3-x Nanopowders for Solid Oxide Fuel Cell Cathodes

    NASA Technical Reports Server (NTRS)

    Bansal, Narottam P.; Zhong, zhimin

    2005-01-01

    Nanopowders of Sm0.5Sr0.5CoO(3-x) (SSC) and La0.6Sr0.4CoO(3-x) (LSC) compositions, which are being investigated as cathode materials for intermediate temperature solid oxide fuel cells, were synthesized by a solution-combustion method using metal nitrates and glycine as fuel. Development of crystalline phases in the as-synthesized powders after heat treatments at various temperatures was monitored by x-ray diffraction. Perovskite phase in LSC formed more readily than in SSC. Single phase perovskites were obtained after heat treatment of the combustion synthesized LSC and SSC powders at 1000 and 1200 C, respectively. The as-synthesized powders had an average particle size of 12 nm as determined from x-ray line broadening analysis using the Scherrer equation. Average grain size of the powders increased with increase in calcination temperature. Morphological analysis of the powders calcined at various temperatures was done by scanning electron microscopy.

  18. Exchange coupling in (111)-oriented La0.7Sr0.3MnO3/ La0.7Sr0.3FeO3 superlattices

    NASA Astrophysics Data System (ADS)

    Jia, Yue; Chopdekar, Rajesh; Arenholz, Elke; Young, Anthony; Marcus, Matthew; Scholl, Andreas; Takamura, Yayoi

    2015-03-01

    Epitaxial La0.7Sr0.3MnO3(LSMO)/La0.7Sr0.3FeO3(LSFO) superlattices serve as ideal systems to explore the magnetic structure and exchange coupling in (111)-oriented perovskite oxides. The (111) orientation offers a buckled honeycomb structure resembling that of graphene with the stacking of highly polar layers. Furthermore, the bulk LSFO magnetic structure predicts that the (111) interface should have fully uncompensated antiferromagnetic (AF) moments leading to exchange bias interactions. Detailed soft x-ray magnetic spectroscopy and microscopy reveal that interfacial effects and the ultrathin nature of the sublayers of the superlattices can stabilize orientations of the LSFO AF spin axis which differ from that of LSFO films and LSMO/LSFO bilayers. A portion of the interfacial AF moments can be reoriented to an arbitrary direction by a moderate external magnetic field through spin-flop coupling with the ferromagnetic LSMO sublayers with low magnetocrystalline anisotropy in the (111) plane. The remaining decoupled moments are pinned by the crystalline anisotropy, displaying 3-fold symmetry consistent with the crystal symmetry of the (111) plane.

  19. Optical anisotropy and dielectric parameters of (Ba0.5Sr0.5)Nb2O6 films on a Pt(111)/Si(001) substrate

    NASA Astrophysics Data System (ADS)

    Kovtun, A. P.; Zinchenko, S. P.; Pavlenko, A. V.; Tolmachev, G. N.

    2016-06-01

    (Ba0.5Sr0.5)Nb2O6 films were synthesized on a Pt(111)/Si(001) substrate by RF gas-discharge sputtering in pure oxygen atmosphere. It was found that the films have a dominant crystallographic orientation in the [001] direction and natural unipolarity, which was revealed through analysis of dielectric and piezoelectric parameters. It was demonstrated that the optical parameters of film material in the Ba0.5Sr0.5, Nb2O6/Pt(111)/Si(001) heterostructure match those typical for a (Ba0.5Sr0.5)Nb2O6 single crystal.

  20. Superconductivity and abnormal pressure effect in Sr{}_{0.5}La{}_{0.5}FBiSe2 superconductor

    NASA Astrophysics Data System (ADS)

    Li, Lin; Xiang, Yongliang; Chen, Yihong; Jiao, Wenhe; Zhang, Chuhang; Zhang, Li; Dai, Jianhui; Li, Yuke

    2016-04-01

    Through the solid state reaction method, we synthesized a new BiSe2-based superconductor Sr{}0.5La{}0.5FBiSe2 with superconducting transition temperature T {}c ≈ \\quad 3.8 K. A strong diamagnetic signal below T c in susceptibility χ (T) is observed indicating the bulk nature of superconductivity. Different to most BiS2-based compounds where superconductivity develops from a semiconducting-like normal state, the present compound exhibits a metallic behavior down to T c . Under weak magnetic field or pressure, however, a remarkable crossover from metallic to insulating behaviors takes place around T min where the resistivity picks up a local minimum. With increasing pressure, T {}c decreases monotonously and T min shifts to high temperatures, while the absolute value of the normal state resistivity at low temperatures first decreases and then increases with pressure up to 2.5 GPa. These results imply that the electronic structure of Sr{}0.5La{}0.5FBiSe2 may be different to those in the other BiS2-based systems.

  1. Vortex pinning and dynamics in high performance Sr0.6K0.4Fe2As2 superconductor

    NASA Astrophysics Data System (ADS)

    Dong, Chiheng; Lin, He; Huang, He; Yao, Chao; Zhang, Xianping; Wang, Dongliang; Zhang, Qianjun; Ma, Yanwei; Awaji, Satoshi; Watanabe, Kazuo

    2016-04-01

    We have studied vortex pinning and dynamics in a Sr0.6K0.4Fe2As2 superconducting tape with critical current density Jc ˜ 0.1 MA/cm2 at 4.2 K and 10 T. It is found that grain boundary pinning is dominant in the vortex pinning mechanism. Furthermore, we observe large density of dislocations which can also serve as effective pinning centers. We find that the temperature dependence of critical current density is in agreement with the model of vortices pinned via spatial fluctuation of charge carrier mean free path. Magnetic relaxation measurement indicates that the magnetization depends on time in a logarithmic way. The relaxation rate in the low and intermediate temperature region is small, and it exhibits a weak temperature and field dependence. A crossover from elastic creep to plastic creep regime is observed. Finally, we conclude a vortex phase diagram for the high performance Sr0.6K0.4Fe2As2 superconducting tape.

  2. Specific Heat of Single Crystalline Nd0.5Sr0.5MnO3

    NASA Astrophysics Data System (ADS)

    Sanchez, Carlos; Aguilar, Victor; Bernal, Oscar; Zhao, Guo-Meng

    2014-03-01

    Substantial studies of magnetization and specific heat on Nd0.5Sr0.5MnO3 have demonstrated the existence of a charge ordering (CO), ferromagnetic (FM), antiferromagnetic (AFM) transitions. In this work, the specific heat of two single crystalline Nd0.5Sr0.5MnO3 samples, one containing 16O and the other highly concentrated 18O, was measured as a function of temperature, from 3K to 300K, at both zero and 50 kOe applied field. Measurements were done using a Quantum Design Physical Property Measurement System (PPMS) with Specific Heat option. The FM transition was found to depend on the isotope mass, which seems to agree with previous works. The CO transitions was observed as a sharp peak at the CO temperature (Tco), which seems to depend strongly on field, oxygen isotope mass, and thermal cycling history. Work Supported by NSF-DMR 1105380. CSU-LSAMP is supported by the National Science Foundation under Grant # HRD-1302873 and the CSU Office of the Chancellor.

  3. Thermally assisted interlayer magnetic coupling through Ba0.05Sr0.95TiO3 barriers

    NASA Astrophysics Data System (ADS)

    Carreira, Santiago J.; Avilés Félix, Luis; Sirena, Martín; Alejandro, Gabriela; Steren, Laura B.

    2016-08-01

    We report on the interlayer exchange coupling across insulating barriers observed on Ni80Fe20/Ba0.05Sr0.95TiO3/La0.66Sr0.33MnO3 (Py/BST0.05/LSMO) trilayers. The coupling mechanism has been analyzed in terms of the barrier thickness, samples' substrate, and temperature. We examined the effect of MgO (MGO) and SrTiO3 (STO) (001) single-crystalline substrates on the magnetic coupling and also on the magnetic anisotropies of the samples in order to get a deeper understanding of the magnetism of the structures. We measured a weak coupling mediated by spin-dependent tunneling phenomena whose sign and strength depend on barrier thickness and substrate. An antiferromagnetic (AF) exchange prevails for most of the samples and smoothly increases with the barrier thicknesses as a consequence of the screening effects of the BST0.05. The coupling monotonically increases with temperature in all the samples and this behavior is attributed to thermally assisted mechanisms. The magnetic anisotropy of both magnetic components has a cubic symmetry that in the case of permalloy is added to a small uniaxial component.

  4. Crystal structure and luminescence of Sr 0.99Eu 0.01AlSiN 3

    NASA Astrophysics Data System (ADS)

    Watanabe, Hiromu; Yamane, Hisanori; Kijima, Naoto

    2008-08-01

    Strontium europium aluminum silicon nitride, Sr 0.99Eu 0.01AlSiN 3, was synthesized by heating a mixture of binary nitrides at 2173 K and a N 2 gas pressure of 190 MPa. Single crystals of Sr 0.99Eu 0.01AlSiN 3 approximately 30 μm were obtained. The structure was confirmed to be an isotypic structure of CaAlSiN 3 in the orthorhombic space group Cmc2 1, analyzed by single-crystal X-ray diffraction. The lattice parameters are a=9.843(3), b=5.7603(16), c=5.177(2) Å, cell volume=293.53(17) Å 3. It shows an orange-red photoluminescence by 5 d→4 f transition of Eu 2+ at around 610 nm under excitation ranging from ultraviolet to 525 nm. The photoluminescence intensity, temperature characteristics, and oxidative stability were comparable or superior to those of CaAlSiN 3:Eu 2+ phosphor.

  5. Microstructure and dielectric tunable properties of Ba0.6Sr0.4TiO3-Mg2SiO4-MgO composite.

    PubMed

    He, Yanyan; Xu, Yebin; Liu, Ting; Zeng, Chunlian; Chen, Wanping

    2010-07-01

    Ba(0.6)Sr(0.4)TiO(3)-Mg(2)SiO(4)-MgO composite ceramics were prepared by a solid-state reaction method and their dielectric tunable characteristics were investigated for the potential application as microwave tunable materials. The addition of Mg(2)SiO(4)-MgO into Ba(0.6)Sr(0.4)TiO(3) forms ferroelectric (Ba(0.6)Sr(0.4)TiO(3))-dielectric (Mg(2)SiO(4)-MgO) composites and shifts the Curie temperature to a lower temperature. The dielectric constant and loss tangent of Ba(0.6)Sr(0.4)TiO(3)-Mg(2)Si(O4)- MgO composites have been decreased and the overall tunability is maintained at a sufficiently high level. The microwave dielectric properties of Ba(0.6)Sr(0.4)TiO(3)-Mg(2)Si(O4)-MgO composites were evaluated. Ba(0.6)Sr(0.4)TiO(3)-Mg(2)SiO(4)-MgO composites have tunability of 9.2 to 10.5% at 100 kHz under 2 kV/mm, indicating that it is a promising candidate material for tunable microwave applications requiring a low dielectric constant.

  6. Magnetic properties of (La0.56Ce0.14)Sr0.30MnO3 perovskite

    NASA Astrophysics Data System (ADS)

    Yahyaoui, Samia; Diep, H. T.

    2016-09-01

    We investigate in this paper magnetic properties of the perovskite compound (La0.56Ce0.14)Sr0.30MnO3. The method we use here is Monte Carlo simulation, in which we take into account different kinds of interactions between nearest and between next-nearest magnetic ions Mn3+ (S = 2), Mn4+ (S = 3 / 2) and Ce3+ (S = 1 / 2). Using a classical spin model, we have calculated the internal energy, the magnetization per ion type and their corresponding magnetic susceptibility, as well as the Edwards-Anderson order parameter for each ion kind. We also studied the applied-field effect on the system magnetization. Our results show a good agreement with experiments.

  7. Relaxor behavior of ferroelectric Ca0.22Sr0.12Ba0.66Nb2O6

    NASA Astrophysics Data System (ADS)

    Shekhar Pandey, Chandra; Schreuer, Jürgen; Burianek, Manfred; Mühlberg, Manfred

    2013-01-01

    The relaxor behavior of tetragonal tungsten bronze uniaxial relaxor ferroelectric calcium strontium barium niobate (Ca0.22Sr0.12Ba0.66Nb2O6 or CSBN-22) single crystal was studied by measuring elastic constants and thermal expansion with the aid of resonant ultrasound spectroscopy and dilatometry, respectively, in the temperature range 300 K-1503 K. Thermal expansion yields evidence of the Burns temperature TB and the intermediate characteristic temperature T*, which was also supported by the temperature evolutions of the elastic constants cij. CSBN-22 was found to be ˜2%-3% elastically stiffer than CBN-28. The presented results open the perspective to understand the relaxor behavior of CSBN.

  8. Pressure-induced superconductivity in Ba0.5Sr0.5Fe2As2

    NASA Astrophysics Data System (ADS)

    Tsoi, Georgiy M.; Malone, Walter; Uhoya, Walter; Mitchell, Jonathan E.; Vohra, Yogesh K.; Wenger, Lowell E.; Sefat, Athena S.; Weir, S. T.

    2012-12-01

    High-pressure electrical resistance measurements have been performed on single crystal Ba0.5Sr0.5Fe2As2 platelets to pressures of 16 GPa and temperatures down to 10 K using designer diamond anvils under quasi-hydrostatic conditions with an insulating steatite pressure medium. The resistance measurements show evidence of pressure-induced superconductivity with an onset transition temperature at ˜31 K and zero resistance at ˜22 K for a pressure of 3.3 GPa. The transition temperature decreases gradually with increasing pressure before completely disappearing for pressures above 12 GPa. The present results provide experimental evidence that a solid solution of two 122-type materials, i.e., Ba1-xSrxFe2As2 (0 < x < 1), can also exhibit superconductivity under high pressure.

  9. Microwave loss mechanisms in Ba0.25Sr0.75TiO3 thin film varactors

    NASA Astrophysics Data System (ADS)

    Vorobiev, A.; Rundqvist, P.; Khamchane, K.; Gevorgian, S.

    2004-10-01

    Parallel-plate Au(Pt )/Ba0.25Sr0.75TiO3/(Pt)Au thin film varactors were fabricated on high resistance Si substrates and characterized at dc, rf, and microwave frequencies. In the frequency range 10-45 GHz the varactors show relatively low losses, with loss tangent less than 0.025 at 45 GHz. Due to the thick and highly conductive Pt/Au electrodes the metal losses are less than 10%. However, the loss tangent of the ferroelectric film is still three to five times higher than that in Ba0.27Sr0.73TiO3 single crystal. The analysis of the dc field dependences of loss tangent and permittivity in a wide frequency range shows that these additional losses are mainly due to the charged defects. Extrapolation of measured low frequency (1 MHz) loss tangents to the microwave region using the power law ω1/3 is in good agreement with experiment. The dc current through the varactor is found to be controlled by Schottky emission and Poole-Frenkel mechanisms depending on the polarity. The Poole-Frenkel mode is associated with field enhanced thermal excitation of charge carriers from internal traps. The trap activation energy (about 0.15 eV) determined from the Poole-Frenkel mode agrees well with the energy level of the oxygen vacancy. We assume that the oxygen vacancies within the grain boundaries of the ferroelectric film act as charged defects and cause additional (extrinsic) microwave losses. The possible correlation between the film's internal strains and density of the oxygen vacancies are discussed. The knowledge of the extrinsic loss mechanism and corresponding microstructure defects is useful in optimization of the varactor design, deposition, annealing process, and further improvement of the varactor performance.

  10. Structure and redox properties of perovskite Y0.9Sr0.1Cr1-xFexO3-δ

    NASA Astrophysics Data System (ADS)

    Xu, Dandan; Bu, Yunfei; Tan, Wenyi; Zhong, Qin

    2013-03-01

    The aim of this paper is to examine the feasibility of Y0.9Sr0.1Cr1-xFexO3-δ for potential use as anode materials in solid oxide fuel cells (SOFCs) fed with fuel gas containing H2S, as well as other electrochemical devise. Y0.9Sr0.1Cr1-xFexO3-δ (x = 0.1, 0.3, 0.5) were synthesized by gel combustion method and had single-phase orthorhombic perovskite structure. These materials were all stable in reducing atmosphere (10%, v/v H2/N2) up to 800 °C. By the comparison of the O 1s peaks assigned to Y0.9Sr0.1Cr1-xFexO3-δ before and after reduction in H2/N2, lower content of lattice oxygen and higher content of adsorbed oxygen were observed for Y0.9Sr0.1Cr0.9Fe0.1O3-δ, while others appeared opposite results. This phenomenon suggested that reduced Y0.9Sr0.1Cr0.9Fe0.1O3-δ could capture oxygen when exposure to air, which is essential for anode materials. Moreover, Y0.9Sr0.1Cr0.9Fe0.1O3-δ maintained good chemical stability under H2S-containing atmosphere through XRD and FT-IR analysis. So Y0.9Sr0.1Cr0.9Fe0.1O3-δ was suggested as a promising anode material for SOFCs fed with fuel gas containing H2S.

  11. Insight into the structure and functional application of the Sr0.95Ce0.05CoO3-δ cathode for solid oxide fuel cells.

    PubMed

    Yang, Wei; Zhang, Huairuo; Sun, Chunwen; Liu, Lilu; Alonso, J A; Fernández-Díaz, M T; Chen, Liquan

    2015-04-01

    A new perovskite cathode, Sr0.95Ce0.05CoO3-δ, performs well for oxygen-reduction reactions in solid oxide fuel cells (SOFCs). We gain insight into the crystal structure of Sr1-xCexCoO3-δ (x = 0.05, 0.1) and temperature-dependent structural evolution of Sr0.95Ce0.05CoO3-δ by X-ray diffraction, neutron powder diffraction, and scanning transmission electron microscopy experiments. Sr0.9Ce0.1CoO3-δ shows a perfectly cubic structure (a = a0), with a large oxygen deficiency in a single oxygen site; however, Sr0.95Ce0.05CoO3-δ exhibits a tetragonal perovskite superstructure with a double c axis, defined in the P4/mmm space group, that contains two crystallographically different cobalt positions, with distinct oxygen environments. The structural evolution of Sr0.95Ce0.05CoO3-δ at high temperatures was further studied by in situ temperature-dependent NPD experiments. At 1100 K, the oxygen atoms in Sr0.95Ce0.05CoO3-δ show large and highly anisotropic displacement factors, suggesting a significant ionic mobility. The test cell with a La0.8Sr0.2Ga0.83Mg0.17O3-δ-electrolyte-supported (∼300 μm thickness) configuration yields peak power densities of 0.25 and 0.48 W cm(-2) at temperatures of 1023 and 1073 K, respectively, with pure H2 as the fuel and ambient air as the oxidant. The electrochemical impedance spectra evolution with time of the symmetric cathode fuel cell measured at 1073 K shows that the Sr0.95Ce0.05CoO3-δ cathode possesses superior ORR catalytic activity and long-term stability. Mixed ionic-electronic conduction properties of Sr0.95Ce0.05CoO3-δ account for its good performance as an oxygen-reduction catalyst. PMID:25756843

  12. Insight into the structure and functional application of the Sr0.95Ce0.05CoO3-δ cathode for solid oxide fuel cells.

    PubMed

    Yang, Wei; Zhang, Huairuo; Sun, Chunwen; Liu, Lilu; Alonso, J A; Fernández-Díaz, M T; Chen, Liquan

    2015-04-01

    A new perovskite cathode, Sr0.95Ce0.05CoO3-δ, performs well for oxygen-reduction reactions in solid oxide fuel cells (SOFCs). We gain insight into the crystal structure of Sr1-xCexCoO3-δ (x = 0.05, 0.1) and temperature-dependent structural evolution of Sr0.95Ce0.05CoO3-δ by X-ray diffraction, neutron powder diffraction, and scanning transmission electron microscopy experiments. Sr0.9Ce0.1CoO3-δ shows a perfectly cubic structure (a = a0), with a large oxygen deficiency in a single oxygen site; however, Sr0.95Ce0.05CoO3-δ exhibits a tetragonal perovskite superstructure with a double c axis, defined in the P4/mmm space group, that contains two crystallographically different cobalt positions, with distinct oxygen environments. The structural evolution of Sr0.95Ce0.05CoO3-δ at high temperatures was further studied by in situ temperature-dependent NPD experiments. At 1100 K, the oxygen atoms in Sr0.95Ce0.05CoO3-δ show large and highly anisotropic displacement factors, suggesting a significant ionic mobility. The test cell with a La0.8Sr0.2Ga0.83Mg0.17O3-δ-electrolyte-supported (∼300 μm thickness) configuration yields peak power densities of 0.25 and 0.48 W cm(-2) at temperatures of 1023 and 1073 K, respectively, with pure H2 as the fuel and ambient air as the oxidant. The electrochemical impedance spectra evolution with time of the symmetric cathode fuel cell measured at 1073 K shows that the Sr0.95Ce0.05CoO3-δ cathode possesses superior ORR catalytic activity and long-term stability. Mixed ionic-electronic conduction properties of Sr0.95Ce0.05CoO3-δ account for its good performance as an oxygen-reduction catalyst.

  13. PREPARATION AND ELECTRICAL PROPERTIES OF BiFeO3/La0.7Sr0.3MnO3 MULTILAYERS

    NASA Astrophysics Data System (ADS)

    Zhu, Huiwen; Wang, Shunli; Li, Xiaoyun

    2013-07-01

    (La0.7Sr0.3MnO3 12 nm/BiFeO3 12 nm)10 was grown on SrTiO3 (001) substrate using rf magnetron sputtering. The structure analysis indicated that BiFeO3/La0.7Sr0.3MnO3 multilayers were highly (001)-oriented. Compared with bottom La0.7Sr0.3MnO3 electrode, the top La0.7Sr0.3MnO3 electrode displayed a rougher surface. The electric transport characteristics of the sample were investigated mainly at low temperature, and it was found that the sample exhibited resistance-temperature curves similar to those of La0.7Sr0.3MnO3 with the exception of an upturn at lower temperature region. Furthermore, a nonlinear I-V curve, which is characteristic of a tunneling conduction mechanism, was observed at 50 K. At higher temperature, the I-V curves were found to be diode-like. When the temperature was further increased to 300 K, the sample showed a space charge limited conduction (SCLC) characteristic.

  14. Spectroscopic properties of UV active medium Ce3+:LiSr0.8Ca0.2AlF6

    NASA Astrophysics Data System (ADS)

    Nizamutdinov, A. S.; Shavelev, A. A.; Marisov, M. A.; Semashko, V. V.

    2016-02-01

    The aim of this work is phase composition and near UV spectroscopic studies of UV active media in fluoride crystals with colquiriite structure, such as Ce3+:LiSr0.8Ca0.2AlF6. Colquiriite structure mixed crystals show higher segregation coefficient of Ce3+ activator ions than common LiCaAlF6 hosts. An important result is based on the fact that this enhancement was achieved for two types of Ce3+ centers in a multisite Ce:LiSr0.8Ca0.2AlF6 system. Thus, it provides a higher gain coefficient for the 5d-4f transitions of Ce3+ ions and it spans a wider continuous wavelength tuning range between 280 and 320 nm for tunable Ce:LiSr0.8Ca0.2AlF6 laser systems.

  15. The Role of Iron in the Enhancement of Negative Magnetoresistance in La0.8Sr0.2FexCo1-xO3-z

    SciTech Connect

    Nemeth, Z.; Homonnay, Z.; Vertes, A.; Hakl, J.; Vad, K.; Meszaros, S.; Lackner, B.; Kellner, K.; Gritzner, G.; Greneche, J.M.; Lindbaum, A.

    2005-04-26

    The role of iron in enhancing the magnetoresistance in the compounds La0.8Sr0.2FexCo1-xO3-z was investigated by studying the electronic and magnetic structure of La0.8Sr0.2FexCo1-xO3-z as a function of temperature. For this purpose 57Fe transmission Moessbauer spectroscopy, magnetoresistance, as well as AC and DC magnetization measurements were applied. The detailed study of the temperature dependence of 57Fe Moessbauer parameters gave possibility to explore correlations between the local electronic and magnetic state of iron and the magnetic susceptibility as well as magnetoresistance in La0.8Sr0.2FexCo1-xO3-z. On the basis of the obtained results an attempt was made to explain the exotic magnetic and MR properties of these perovskites.

  16. Strongly enhanced current densities in Sr0.6K0.4Fe2As2 + Sn superconducting tapes

    PubMed Central

    Lin, He; Yao, Chao; Zhang, Xianping; Zhang, Haitao; Wang, Dongliang; Zhang, Qianjun; Ma, Yanwei; Awaji, Satoshi; Watanabe, Kazuo

    2014-01-01

    Improving transport current has been the primary topic for practical application of superconducting wires and tapes. However, the porous nature of powder-in-tube (PIT) processed iron-based tapes is one of the important reasons for low critical current density (Jc) values. In this work, the superconducting core density of ex-situ Sr0.6K0.4Fe2As2 + Sn tapes, prepared from optimized precursors, was significantly improved by employing a simple hot pressing as an alternative route for final sintering. The resulting samples exhibited optimal critical temperature (Tc), sharp resistive transition, small resistivity and high Vickers hardness (Hv) value. Consequently, the transport Jc reached excellent values of 5.1 × 104 A/cm2 in 10 T and 4.3 × 104 A/cm2 in 14 T at 4.2 K, respectively. Our tapes also exhibited high upper critical field Hc2 and almost field-independent Jc. These results clearly demonstrate that PIT pnictide wire conductors are very promising for high-field magnet applications. PMID:24663054

  17. Magnetic investigation of silver sheathed Sr0.6K0.4Fe2As2 superconductor

    NASA Astrophysics Data System (ADS)

    Brunner, Boris; Reissner, Michael; Kováč, Pavol; Yao, Chao; Zhang, Xianping; Ma, Yanwei

    Magnetic investigation of a silver sheathed Sr0.6K0.4Fe2As2 tape prepared by ex-situ powder-in-tube technique (PIT) is reported. A transition temperature of 34.2 K was achieved. Dc magnetic measurements were performed in fields up to 14 T between 4.2 K and Tc. From hysteresis loops magnetic critical current densities Jc were determined. The tape exhibits excellent Jc performance. In low fields, the observed steep decline of Jc in increasing field is comparable to that measured in MgB2, although at a significantly lower absolute value. A kink-like crossover to a much flatter dependence at higher fields allows for a much better high field performance than that of MgB2. Such kink is also visible in the field dependence of the mean activation energies U, which were determined from magnetic relaxation measurements. The obtained U values are similar (< 40 meV at 4.2 K and 1 T) to those of Bi2212 tapes, but an order of magnitude smaller in comparison with good MgB2 wires.

  18. Colossal elastoresistance, electroresistance and magnetoresistance in Pr0.5Sr0.5MnO3 thin films

    NASA Astrophysics Data System (ADS)

    Chen, Liping; Guo, Xuexiang; Gao, J.

    2016-05-01

    Pr0.5Sr0.5MnO3 thin films on substrates of (001)-oriented LaAlO3 were epitaxially grown by pulsed laser deposition. It was found that a substrate-induced strain of ~1.3% brings a great resistivity change of ~98% at 25 K. We studied the dependence of resistivity on the applied electric current and magnetic field. In the greatly strained films of 60 nm thickness the electroresistance ER=[ρ(I1 μA)-ρ(I1000 μA)]/ρ(I1 μA) reaches ~70% at T=25 K, much higher than ER~7% in the strain-relaxed films of 400 nm thickness, implying the strain effect on ER. Also the magnetoresistance of the film falls with strain-relaxation. Therefore the electric properties of the film could be efficiently modified by strain, electric current and magnetic field. All of them may be explained by the effect on the percolative phase separation and competition in the half-doped manganite material. The manganite films located at phase boundary are expected to be an ideal compound for providing practical colossal effects of elastoresistance, electroresistance and magnetoresistance due to the multiphase coexistence.

  19. Insulating phase at low temperature in ultrathin La0.8Sr0.2MnO3 films.

    PubMed

    Feng, Yaqing; Jin, Kui-juan; Gu, Lin; He, Xu; Ge, Chen; Zhang, Qing-hua; He, Min; Guo, Qin-lin; Wan, Qian; He, Meng; Lu, Hui-bin; Yang, Guozhen

    2016-03-01

    Metal-insulator transition is observed in the La0.8Sr0.2MnO3 thin films with thickness larger than 5 unit cells. Insulating phase at lower temperature appeared in the ultrathin films with thickness ranging from 6 unit cells to 10 unit cells and it is found that the Mott variable range hopping conduction dominates in this insulating phase at low temperature with a decrease of localization length in thinner films. A deficiency of oxygen content and a resulting decrease of the Mn valence have been observed in the ultrathin films with thickness smaller than or equal to 10 unit cells by studying the aberration-corrected scanning transmission electron microscopy and electron energy loss spectroscopy of the films. These results suggest that the existence of the oxygen vacancies in thinner films suppresses the double-exchange mechanism and contributes to the enhancement of disorder, leading to a decrease of the Curie temperature and the low temperature insulating phase in the ultrathin films. In addition, the suppression of the magnetic properties in thinner films indicates stronger disorder of magnetic moments, which is considered to be the reason for this decrease of the localization length.

  20. Colossal Piezoresistance in strained La0.67Sr0.33MnO3 thin films

    NASA Astrophysics Data System (ADS)

    Viitaniemi, Maria; Kwak, In Hae; Biswas, Amlan

    2015-03-01

    Piezoresistance is the change in electrical resistance as a function of strain. A known mechanism leading to piezoresistance is thermodynamic phase separation. It has been shown that the compound (La1-yPry)1-xCaxMnO3 (LPCMO) exhibits colossal piezoresistance (CPR) at low temperatures due to electronic phase separation. For use in many applications, such as sensors, materials must exhibit CPR near room temperature. A possible candidate compound is La0.67Sr0.33MnO3 (LSMO) which has a Curie temperature of approximately 350 K. However, bulk LSMO single crystals do not show CPR since such samples are uniformly ferromagnetic and metallic with no phase separation. In this study, we examine the piezoresistance of ultrathin LSMO films grown on SrTiO3 (STO) substrates using a three-point beam bending method to control the compressive and tensile strain. It has been suggested that the lattice mismatch strain due to the substrate induces phase separation in these thin films. We have observed CPR in such strained LSMO thin films even at room temperature. NSF DMR-1410237.

  1. Strain-relaxation and critical thickness of epitaxial La1.85Sr0.15CuO4 films

    DOE PAGES

    Meyer, Tricia L; Jiang, Lu; Park, Sungkyun; Egami, Takeshi; Lee, Ho Nyung

    2015-12-08

    We report the thickness-dependent strain-relaxation behavior and the associated impacts upon the superconductivity in epitaxial La1.85Sr0.15CuO4 films grown on different substrates, which provide a range of strain. We have found that the critical thickness for the onset of superconductivity in La1.85Sr0.15CuO4 films is associated with the finite thickness effect and epitaxial strain. In particular, thin films with tensile strain greater than ~0.25% revealed no superconductivity. We attribute this phenomenon to the inherent formation of oxygen vacancies that can be minimized via strain relaxation.

  2. Magnetism in La0.7Sr0.3Mn1-xCoxO3 (0 ≤ x ≤ 1)

    NASA Astrophysics Data System (ADS)

    Kumar, Ashutosh; Sharma, Himanshu; Tomy, C. V.; Thakur, Ajay D.

    2016-05-01

    We study the structural and magnetic properties of La0.7Sr0.3Mn1-xCoxO3 (0 ≤ x ≤ 1). Rietveld refinement of X-ray Diffraction (XRD) pattern suggests phase purity of the polycrystalline samples with R-3c space group. Interplay of Ferromagnetic (FM) and Antiferromagnetic (AFM) interaction upon Co substitution at Mn site in La0.7Sr0.3MnO3 is evident from magnetic measurements. There is an optimal cobalt substitution at which the coercive field is maximum.

  3. Metamaterials: A New Ba0.6 Sr0.4 TiO3 -Silicon Hybrid Metamaterial Device in Terahertz Regime (Small 19/2016).

    PubMed

    Wu, Liang; Du, Ting; Xu, Ningning; Ding, Chunfeng; Li, Hui; Sheng, Quan; Liu, Ming; Yao, Jianquan; Wang, Zhiyong; Lou, Xiaojie; Zhang, Weili

    2016-05-01

    A giant terahertz modulation based on a Ba0.6 Sr0.4 TiO3 -silicon hybrid metamaterial is reported by L. Wu, W. Zhang, and co-workers on page 2610. The proposed nanoscale Ba0.6 Sr0.4 TiO3 (BST) hybrid metamaterial, delivering a transmission contrast of up to ≈79% due to electrically enabled carrier transport between the ferroelectric thin film and silicon substrate, is promising in developing high-performance real world photonic devices for terahertz technology.

  4. Spectroscopic and photoluminescence characterization of Dy(3+) in Sr0.5Ca0.5TiO3 phosphor.

    PubMed

    Vidyadharan, Viji; Sreeja, E; Jose, Saritha K; Joseph, Cyriac; Unnikrishnan, N V; Biju, P R

    2016-02-01

    The spectroscopic and photoluminescence characteristics of trivalent dysprosium (Dy(3+))-doped Sr0.5Ca0.5TiO3 phosphor materials synthesized via solid-state reaction method were studied. The X-ray diffraction profile confirmed the orthorhombic perovskite structure of the prepared samples. Judd-Ofelt analysis was carried out to obtain the intensity parameters and predicted radiative properties of Sr0.5Ca0.5TiO3:2wt%Dy(3+). The photoluminescence spectrum of Dy(3+)-doped Sr0.5Ca0.5TiO3 showed three emission peaks at 481, 574 and 638 nm corresponding to (4)F9/2 →(6)H15/2, (4)F9/2 →(6)H13/2 and (4)F9/2 →(6)H11/2 transitions respectively. The variation of luminescence intensity with different excitation wavelengths and Dy(3+) concentrations is discussed. The decay profiles of (4)F9/2 excited levels of Dy(3+) ions show bi-exponential behaviour and also a decrease in average lifetime with increase in Dy(3+) concentration. Yellow to blue luminescence intensity ratio, CIE chromaticity co-ordinates and correlated color temperature were also calculated for different concentrations of Dy(3+)-doped Sr0.5Ca0.5TiO3 phosphor at different λex. PMID:26032295

  5. Spectroscopic and photoluminescence characterization of Dy(3+) in Sr0.5Ca0.5TiO3 phosphor.

    PubMed

    Vidyadharan, Viji; Sreeja, E; Jose, Saritha K; Joseph, Cyriac; Unnikrishnan, N V; Biju, P R

    2016-02-01

    The spectroscopic and photoluminescence characteristics of trivalent dysprosium (Dy(3+))-doped Sr0.5Ca0.5TiO3 phosphor materials synthesized via solid-state reaction method were studied. The X-ray diffraction profile confirmed the orthorhombic perovskite structure of the prepared samples. Judd-Ofelt analysis was carried out to obtain the intensity parameters and predicted radiative properties of Sr0.5Ca0.5TiO3:2wt%Dy(3+). The photoluminescence spectrum of Dy(3+)-doped Sr0.5Ca0.5TiO3 showed three emission peaks at 481, 574 and 638 nm corresponding to (4)F9/2 →(6)H15/2, (4)F9/2 →(6)H13/2 and (4)F9/2 →(6)H11/2 transitions respectively. The variation of luminescence intensity with different excitation wavelengths and Dy(3+) concentrations is discussed. The decay profiles of (4)F9/2 excited levels of Dy(3+) ions show bi-exponential behaviour and also a decrease in average lifetime with increase in Dy(3+) concentration. Yellow to blue luminescence intensity ratio, CIE chromaticity co-ordinates and correlated color temperature were also calculated for different concentrations of Dy(3+)-doped Sr0.5Ca0.5TiO3 phosphor at different λex.

  6. X-ray photoemission study of the infinite-layer cuprate superconductor Sr(0.9) La (0.1) CuO(2)

    NASA Technical Reports Server (NTRS)

    Vasquez, R. P.; Jung, C. U.; Kim, J. Y.; Kim, M. S.; Lee, S. Y.; Lee, S. I.

    2001-01-01

    The electron-doped infinite-layer superconductor Sr(0.9)La(0.1) CuO(2) is studied with x-ray photoemission spectroscopy (XPS). A nonaqueous chemical etchant is shown to effectively remove contaminants and to yield surfaces from which signals intrinsic to the superconductor dominate.

  7. Surface characterization, in vitro and in vivo biocompatibility of Mg-0.3Sr-0.3Ca for temporary cardiovascular implant.

    PubMed

    Bornapour, M; Mahjoubi, H; Vali, H; Shum-Tim, D; Cerruti, M; Pekguleryuz, M

    2016-10-01

    Magnesium-based alloys are attractive candidate materials for medical applications. Our earlier work showed that the ternary Mg-0.3Sr-0.3Ca alloy exhibits slower degradation rates than both binary Mg-Sr and Mg-Ca alloys. The ternary alloy immersed in simulated body fluid (SBF) forms a compact surface layer of corrosion products that we hypothesized to be a Sr-substituted hydroxyapatite (HA). The main objectives of the current work are to understand the bio-degradation mechanism of Mg-0.3Sr-0.3Ca, to identify the exact nature of its protective layer and to evaluate the in vitro and in vivo biocompatibility of the alloy for cardiovascular applications. To better simulate the physiological environment, the alloy was immersed in SBF which was daily refreshed. Raman spectroscopy and X-Ray photoelectron spectroscopy (XPS) confirmed the formation of a thin, Sr-substituted HA layer at the interface between the alloy and the corrosion products. In vitro biocompatibility evaluated via indirect cytotoxicity assays using HUVECs showed no toxicity effect and ions extracted from Mg-0.3Sr-0.3Ca in fact increased the viability of HUVECs after one week. In vivo tests were performed by implanting a tubular Mg-0.3Sr-0.3Ca stent along with a WE43 control stent into the right and left femoral artery of a dog. Post implantation and histological analyses showed no thrombosis in the artery with Mg-0.3Sr-0.3Ca stent after 5weeks of implantation while the artery implanted with WE43 stent was extensively occluded and thrombosed. Microscopic observation of the Mg-0.3Sr-0.3Ca implant-tissue interface confirmed the in situ formation of Sr-substituted HA on the surface during in vivo test. These results show that the interfacial layer protects the surface of the Mg-0.3Sr-0.3Ca alloy both in vitro and in vivo, and is the key factor in the bio-corrosion resistance of the alloy. PMID:27287101

  8. Enhanced microwave dielectric properties of Ba0.4Sr0.6TiO3 ceramics doping by metal Fe powders

    NASA Astrophysics Data System (ADS)

    Zhang, Qiwei; Zhai, Jiwei; Ben, Qianqian; Yu, Xian; Yao, Xi

    2012-11-01

    Ba0.4Sr0.6TiO3 ceramics by adding mental Fe powders have been fabricated via the solid-state reaction method. The microstructures and optical properties of samples are systematically studied in order to establish the effects of Fe powder additives on microwave dielectric properties of Ba0.4Sr0.6TiO3 ceramics by x-ray diffraction, x-ray photoelectron spectroscopy, and optical reflective spectrum. The results show the coexistence of Fe2+ and Fe3+ in Ba0.4Sr0.6TiO3 ceramics, the decrease of O vacancy concentrations, and their incorporation into the B-site (Ti) of the Ba0.4Sr0.6TiO3 host lattice give rise to excellent microwave dielectric properties. All samples have a higher Q value above 290 while maintaining relatively high tunability above 16.6%. In particular, the sample with the composition of x = 0.035 mol has the dielectric constant of 889, Q × f value of 826 (at 1.370 GHz), and tunability of 24%, which are very promising for high power tunable devices. In comparison, Fe2O3 oxide doped Ba0.4Sr0.6TiO3 ceramics with the same molar ratios of Fe exhibit inferior microwave properties. It indicates that additives of the metal Fe powders can more effectively improve dielectric properties of BaxSr1-xTiO3 system than Fe2O3 oxide.

  9. Study of magnetic transition and magnetic entropy changes of Pr0.6Sr0.4MnO3 and Pr0.6Sr0.4Mn0.9Fe0.1O3 compounds

    NASA Astrophysics Data System (ADS)

    Nasri, Abir.; Hlil, E. K.; Lehlooh, A.-F.; Ellouze, M.; Elhalouani, F.

    2016-04-01

    In the present work, we analyze the magnetic transition and magnetic entropy change \\vertΔ SM\\vert of Pr0.6Sr0.4Mn1- x Fe x O3 samples. Using Arrott plots, we report that the phase transition for Pr0.6Sr0.4MnO3 sample is of second order, while the Pr0.6Sr0.4Mn0.9Fe0.1O3 sample exhibits a first-order magnetic phase transition. From the magnetization measurements at temperature close to the Curie temperature, the magnetic entropy change, \\vertΔ SM\\vert and the Relative Cooling Power (RCP) have been estimated. The maximum of magnetic entropy change \\vertΔ S_M^{max}\\vert reaches, under an applied magnetic field of 5T, 3.58 and 3.66J/kg K for Pr0.6Sr0.4MnO3 and Pr0.6Sr0.4Mn0.9Fe0.1O3, respectively. The RCP values have been estimated to 159.37 and 223.52J/kg. For both samples, the \\vertΔ SM\\vert values evaluated using the Maxwell theory were found in accordance with those calculated by the Landau theory.

  10. Epitaxial La0.5Sr0.5CoO3 thin films: Structure, magnetism, and transport

    SciTech Connect

    Torija, Maria; Sharma, M; Fitzsimmons, M. R.; Varela, M; Leighton, chris

    2008-01-01

    La1 xSrxCoO3 has received considerable attention in bulk form. This is due to interest in the fundamental magnetic properties spin-state transitions and magnetic phase separation as well as potential applications in ferroelectric memory and solid-oxide fuel cells. The structure and properties in thin film form are not well understood, and the influence of dimensional confinement on effects such as magnetic phase separation is unknown. Here, we report a comprehensive investigation of structure, magnetism, and transport in strained epitaxial La0.5Sr0.5CoO3 001 films deposited on SrTiO3 001 substrates by reactive dc magnetron sputtering. The crystalline quality, phase purity, strain state, oxygen stoichiometry, morphology, and magnetic and electronic properties of the epilayers are all probed and are found to be particularly sensitive to the total sputtering gas pressure and the ratio of reactive to inert gas PO2 /PAr. The various structure-property relationships are discussed in detail, particularly with respect to the degree of oxygenation and oxygen-induced resputtering. The films are strained and tetragonally distorted due to the 1.9% lattice mismatch with SrTiO3. Significant strain relaxation occurs at thicknesses around 200 , resulting in a crossover from two-dimensional-like to three-dimensional growth. Polarized neutron reflectometry was combined with x-ray reflectometry to obtain chemical and magnetic depth profiles, which are compared with cross-sectional scanning transmission electron microscopy. The results indicate a thin 10 layer at the film/substrate interface with significantly different structural properties to the bulk of the film, as well as a strongly graded magnetic and chemical profile at the film surface due to the significant roughness. The Curie temperature was found to decrease very slowly as the thickness is reduced down to 50 , at which point a rapid decrease occurs, almost coincident with a sharp decrease in saturation magnetization. At

  11. Synthesis and electrochemical performance of La0.7Sr0.3Co1-xFexO3 catalysts for zinc air secondary batteries

    NASA Astrophysics Data System (ADS)

    Ahn, Seyoung; Kim, Ketack; Kim, Hyunsoo; Nam, Sangyong; Eom, Seungwook

    2010-05-01

    We prepared La0.7Sr0.3Co1-xFexO3 (x=0.1-0.4) catalysts for a zinc air battery by using the citrate method under controlled pH. The prepared precursor powder was heat treated at the calcination temperature of 700 °C and examined for the optimum structure of the cathode. The structure and performance of the catalysts were examined by x-ray diffraction and a scanning electron microscope. The air electrode was prepared by blending the catalyst, Vulcan XC-72R (carbon black), and (polytetrafluoroethylene PTFE) suspension. The oxygen reduction reaction and the oxygen evolution reaction were examined by linear sweep voltammetry. The results showed that La0.7Sr0.3Co0.7Fe0.3O3 (LSCF0.7) is an excellent catalyst for the zinc air secondary battery.

  12. Increase of dielectric constant in PVDF by incorporating La1.8Sr0.2NiO4 into its matrix

    NASA Astrophysics Data System (ADS)

    Kumar, Rajnish; Goswami, Ashwin M.; Kar, Manoranjan

    2016-05-01

    To obtain the material with high dielectric constant and high dielectric strength for the technological applications, nanocomposite of Lanthanum Strontium Nickelete (La1.8Sr0.2NiO4) as nanofiller and polyvinylidene fluoride (PVDF) as polymer matrix has been prepared. The different nanofiler weight concentration varies from 2-8 weight percent. X-ray diffraction technique confirms the phase formation of nanocomposite. Differential scanning calorimeter (DSC) has been employed to study the percentage of crystallinity and Impedance measurement has been carried out to study the dielectric constant. DSC analysis shows decreasing trend of crystallinity whereas impedance analysis gives increasing dielectric constant with increasing La1.8Sr0.2NiO4 concentration in the nanocomposite. Also, these materials can be used as insulator in the transformer as the strength and dielectric behavior of present composite meets the technological requirements.

  13. Structural properties and singular phase transitions of metallic Pr0.50Sr0.50CoO3 cobaltite.

    PubMed

    Padilla-Pantoja, Jessica; García-Muñoz, José Luis; Bozzo, Bernat; Jirák, Zdeněk; Herrero-Martín, Javier

    2014-12-01

    The Pr0.50Sr0.50CoO3 perovskite exhibits unique magnetostructural properties among the rest of the ferromagnetic/metallic Ln0.50Sr0.50CoO3 compounds. Existing reports are largely controversial. We have determined and described its structural evolution, which follows the Pm3̅m → R3̅c → Imma → I4/mcm transformations. The structural changes have been thoroughly described. The results are confronted with distinct nonconventional properties and spin-lattice coupling effects in another half-doped cobaltite based on praseodymium, Pr0.50Ca0.50CoO3. The Imma →  I4/mcm symmetry change is responsible for the unexpected second magnetic transition. PMID:25383644

  14. 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

  15. Methane oxidation over A-site ordered and disordered Sr(0.8)Gd(0.2)CoO(3-δ) perovskites.

    PubMed

    Vereshchagin, Sergei N; Solovyov, Leonid A; Rabchevskii, Evgenii V; Dudnikov, Vyacheslav A; Ovchinnikov, Sergey G; Anshits, Alexander G

    2014-06-11

    A tetragonal phase Sr0.8Gd0.2CoO3-δ with ordered Gd(3+)/Sr(2+) ions and oxygen vacancy sites is found to be about five times less active in the reaction of methane combustion than a quenched cubic perovskite phase with randomly distributed (disordered) Gd(3+)/Sr(2+) ions over the A-sites of the crystal lattice. PMID:24777361

  16. Performance Enhancement of the Dielectric Properties of Sn-Doped Ba0.8Sr0.2TiO3 Perovskite

    NASA Astrophysics Data System (ADS)

    Brahem, R.; Farhat, N.; Graça, M. P. F.; Costa, L. C.

    2016-06-01

    The aim of this paper is to study performance enhancement of the dielectric properties of polycrystalline {Ba}_{0.8} {Sr}_{0.2} {Ti}_{(1 - x)} {Sn}x {O}3 , with 0 ≤ x ≤ 0.2 . The material was characterized by x-ray diffraction, scanning electron microscopy (SEM), micro-Raman spectroscopy and impedance spectroscopy technique. The results have been analyzed by studying the effects of substituting Sn4+ for Ti4+. The observed diffraction peaks have been indexed to a cubic structure with space group Pm3m. The calculated lattice parameters increase from 3.9834 Å to 4.0091 Å with increasing Sn concentration. The SEM micrographs show that with increasing Sn an increase of the grain size from x = 0 up to x = 0.15 was observed. The dielectric measurements confirm the relaxor behavior of all the concentrations of {Ba}_{0.8} {Sr}_{0.2} {Ti}_{(1 - x)} {Sn}x {O}3 compounds. The {Ba}_{0.8} {Sr}_{0.2} {Ti}_{0.95} {Sn}_{0.05} {O}3 compound presents the most interesting properties, namely high dielectric constant value (&epsilon^'(T_{m} ) = 5017 ) and a Curie temperature slightly above room temperature (T_{c} = 317 {K}) . An important dielectric constant value persists for a wide range of temperatures around room temperature. This is considered as an advantage of the {Ba}_{0.8} {Sr}_{0.2} {Ti}_{0.95} {Sn}_{0.05} {O}3 relaxor ferroelectrics.

  17. Performance Enhancement of the Dielectric Properties of Sn-Doped Ba0.8Sr0.2TiO3 Perovskite

    NASA Astrophysics Data System (ADS)

    Brahem, R.; Farhat, N.; Graça, M. P. F.; Costa, L. C.

    2016-10-01

    The aim of this paper is to study performance enhancement of the dielectric properties of polycrystalline {Ba}_{0.8} {Sr}_{0.2} {Ti}_{(1 - x)} {Sn}x {O}3, with 0 ≤ x ≤ 0.2. The material was characterized by x-ray diffraction, scanning electron microscopy (SEM), micro-Raman spectroscopy and impedance spectroscopy technique. The results have been analyzed by studying the effects of substituting Sn4+ for Ti4+. The observed diffraction peaks have been indexed to a cubic structure with space group Pm3m. The calculated lattice parameters increase from 3.9834 Å to 4.0091 Å with increasing Sn concentration. The SEM micrographs show that with increasing Sn an increase of the grain size from x = 0 up to x = 0.15 was observed. The dielectric measurements confirm the relaxor behavior of all the concentrations of {Ba}_{0.8} {Sr}_{0.2} {Ti}_{(1 - x)} {Sn}x {O}3 compounds. The {Ba}_{0.8} {Sr}_{0.2} {Ti}_{0.95} {Sn}_{0.05} {O}3 compound presents the most interesting properties, namely high dielectric constant value (ɛ^'(T_{{m}} ) = 5017) and a Curie temperature slightly above room temperature (T_{{c}} = 317 K). An important dielectric constant value persists for a wide range of temperatures around room temperature. This is considered as an advantage of the {Ba}_{0.8} {Sr}_{0.2} {Ti}_{0.95} {Sn}_{0.05} {O}3 relaxor ferroelectrics.

  18. Dielectric response of Ba0.05Sr0.95TiO3(110) films to variations in temperature and electric field

    NASA Astrophysics Data System (ADS)

    Boikov, Yu. A.; Claeson, T.

    2015-05-01

    Three-layer epitaxial heterostructures, in which a 1000-nm-thick intermediate layer of Ba0.05Sr0.95TiO3 is integrated with strontium ruthenate conducting electrodes, have been grown by laser evaporation. Using photolithography and ion etching, film parallel-plate capacitors SrRuO3/Ba0.05Sr0.95TiO3/SrRuO3 are formed based on the grown heterostructures. A sharp maximum in the temperature dependence of the capacitor capacitance is observed at T ≈ 75 K. At T < 100 K, the capacitance decreases by 50-60% upon applying a bias voltage V b = ±2.5 V to the oxide electrodes. The estimate of the specific capacitance (~2.1 μF/cm2) of the Ba0.05Sr0.95TiO3(110)/SrRuO3(110) interface is obtained. For T > 250 K and the measuring signal frequency of 1 kHz, the dielectric loss tangent of the film capacitors increases exponentially with increasing temperature.

  19. Magnetocaloric effect in (La 0.47Gd 0.2)Sr 0.33MnO 3 polycrystalline nanoparticles

    NASA Astrophysics Data System (ADS)

    Juan, Zhao; Gui, Wang

    2009-01-01

    In this paper, nanosized particles of (La 0.47Gd 0.2)Sr 0.33MnO 3 perovskite-type oxides were successfully synthesized at a relatively low calcinated temperature at 800 °C for 10 h using amorphous molecular alloy as precursor. X-ray diffraction (XRD) and electron diffraction (ED) revealed that the resulting product is of pure single-phase rhombohedral structure. The Curie temperature TC and magnetic entropy change (MCE) in (La 0.47Gd 0.2)Sr 0.33MnO 3 polycrystalline nanoparticles are determined and compared to those of similar systems prepared by the conventional solid-state reaction method. The Curie temperature TC is shifted to 298 k, and a relatively large MCE with a broad peak around Curie temperature is observed in (La 0.47Gd 0.2)Sr 0.33MnO 3 polycrystalline particles. These results suggested that this material is a suitable candidate as working substance in magnetic refrigeration near room temperature.

  20. Suppression of magnetism and development of superconductivity within the collapsed tetragonal phase of Ca0.67Sr0.33Fe2As2 under pressure

    NASA Astrophysics Data System (ADS)

    Jeffries, J. R.; Butch, N. P.; Kirshenbaum, K.; Saha, S. R.; Samudrala, G.; Weir, S. T.; Vohra, Y. K.; Paglione, J.

    2012-05-01

    Structural and electronic characterizations of (Ca0.67Sr0.33)Fe2As2 have been performed as a function of pressure up to 12 GPa using conventional and designer diamond anvil cells. The compound (Ca0.67Sr0.33)Fe2As2 behaves intermediately between its end members, displaying a suppression of magnetism and the onset of superconductivity. Like other members of the AFe2As2 family, (Ca0.67Sr0.33)Fe2As2 undergoes a pressure-induced isostructural volume collapse, which we associate with the development of As-As bonding across the mirror plane of the structure. This collapsed tetragonal phase abruptly cuts off the magnetic state and supports superconductivity with a maximum Tc=22.2K. The maximum Tc of the superconducting phase is not strongly correlated with any structural parameter, but its proximity to the abrupt suppression of magnetism as well as the volume-collapse transition suggests that magnetic interactions and structural inhomogeneity may play a role in its development.

  1. Systematic study of (La1-xGdx)1.85Sr0.15CuO4 (0<=x<=1): Structure, superconductivity, resistivity, and magnetic properties

    NASA Astrophysics Data System (ADS)

    Xiao, Gang; Cieplak, Marta Z.; Chien, C. L.

    1989-09-01

    A room-temperature structural phase diagram has been determined in (La1-xGdx)1.85Sr0.15CuO4 system (0<=x<=1). There exist three stable phases (T, T* and T'), in which the local Cu-O unit is an octahedron, a pyramid, and a square, respectively. The Jahn-Teller distortion is reduced in the order of T, T*, and T'. For each phase, there is a solubility region. No magnetic ordering is found in the T and T* phase, both of which exhibit paramagnetism with a constant Gd magnetic moment consistent with that of Gd3+. In Gd2CuO4 and Gd1.85Sr0.15CuO4, the initial susceptibility indicates a Néel state in the Cu-O2 plane at TN=285 K and another magnetic transition at low temperature. TN is not sensitive to the Sr doping at all, indicating that extra holes cannot be doped onto the Cu-O2 plane. While the T* and T' phases are insulating, exhibiting a variable-range hopping behavior, the Gd-doped (La1-xGdx)1.85Sr0.15CuO4 (x<=0.1) is superconducting with Tc reducing with increasing Gd concentration. The suppression of Tc is not due to a variation of the electron-boson coupling strength which remains unchanged in the system, but correlates closely with the low-temperature resistivity anomaly. Such an anomaly can be best described by a logarithmic temperature dependence.

  2. More Cu, more problems: Decreased CO2 conversion ability by Cu-doped La0.75Sr0.25FeO3 perovskite oxides

    NASA Astrophysics Data System (ADS)

    Daza, Yolanda A.; Maiti, Debtanu; Hare, Bryan J.; Bhethanabotla, Venkat R.; Kuhn, John N.

    2016-06-01

    The effect of Cu doping on the conversion of CO2 to CO was investigated on H2-reduced La0.75Sr0.25FeO3 perovskite oxides. Six La0.75Sr0.25Fe1 -YCuYO3 perovskites, labeled Cu100*Y (with Y = 0, 0.10, 0.25, 0.50, 0.75, and 1) were synthesized and characterized through X-ray diffraction (XRD), temperature-programmed oxygen vacancy formation, and temperature-programmed reduction (TPR). The incorporation of Cu facilitates the formation of oxygen vacancies at lower temperatures but also increased the instability of the perovskite. DFT simulations suggested that the Cu10 sample is favored to produce oxygen vacancies compared to Cu0 and Cu25 samples, which was consistent with experimental oxygen vacancy formation results. For the Cu0, Cu10, and Cu25 samples, temperature-programmed CO2 conversion (TPO-CO2) after isothermal H2-reduction at 450 °C and post-reduction XRD were performed to evaluate the ability of the materials to convert CO2 at low temperatures and to identify the crystalline phases active in the reaction. The peak conversion of CO2 to CO was achieved 30 °C lower on the Cu10 sample versus the Cu0, but less CO was produced, due to a decreased re-oxidation activity of the Cu-doped samples. CO production was inhibited in the Cu25 sample, likely due to a combined effect of poor CO2 dissociative chemisorption energies on metallic Cu and increased thermodynamic stability of the oxygen vacant perovskites. Control experiments (Cu deposited onto La0.75Sr0.25FeO3) indicated the stability of the copper-containing perovskite oxides phases was the primary limiting factor preventing CO formation from CO2.

  3. Ethylene production by ODHE in catalytically modified Ba(0.5)Sr(0.5)Co(0.8)Fe(0.2)O(3-δ) membrane reactors.

    PubMed

    Lobera, M Pilar; Escolástico, Sonia; Garcia-Fayos, Julio; Serra, José M

    2012-08-01

    Process intensification by the integration of membranes and high-temperature reactors offers several advantages with regard to conventional process schemes, that is, energy saving, safe operation, reduced plant/unit size, and higher process performance, for example, higher productivity, catalytic activity, selectivity, or stability. We present the study of oxidative dehydrogenation of ethane at 850 °C on a catalytic membrane reactor based on a mixed ionic-electronic conducting membrane. The surface of the membrane made of Ba(0.5)Sr(0.5)Co(0.8)Fe(0.2)O(3-δ) has been activated by using different porous catalytic layers based on perovskites. The layer was deposited by screen printing, and the porosity and thickness was studied for the catalyst composition. The different catalyst formulations are based on partial substitution of A- and B-site atoms of doped strontium ferrite/cobaltites (A(0.6)Sr(0.4)Co(0.5)Fe(0.5)O(3-δ) and Ba(0.6)Sr(0.4)BO(3-δ)) and were synthesized by an ethylenediaminetetraacetic acid-citrate complexation route. The use of a disk-shaped membrane in the reactor enabled the direct contact of gaseous oxygen and hydrocarbons to be avoided, and thus, the ethylene content increased. High ethylene yields (up to ≈81 %) were obtained by using a catalytic coating based on Ba(0.5)Sr(0.5)Co(0.8)Fe(0.2)O(3-δ), which included macropores produced by the addition of graphite platelets into the screen-printing ink. The promising catalytic results obtained with this catalytically modified membrane reactor are attributed to the combination of 1) the high activity, as a result of the high temperature and oxygen species diffusing through the membrane; 2) the control of oxygen dosing and the low concentration of molecules in the gas phase; and 3) suitable fluid dynamics, which enables appropriate feed contact with the membrane and the rapid removal of products.

  4. Characterization of (Ba(0.5)Sr(0.5)) TiO3 Thin Films for Ku-Band Phase Shifters

    NASA Technical Reports Server (NTRS)

    Mueller, Carl H.; VanKeuls, Fredrick W.; Romanofsky, Robert R.; Miranda, Felix A.; Warner, Joseph D.; Canedy, Chadwick L.; Ramesh, Rammamoorthy

    1999-01-01

    The microstructural properties of (Ba(0.5)Sr(0.5)TiO3) (BSTO) thin films (300, 700, and 1400 nm thick) deposited on LaAlO3 (LAO) substrates were characterized using high-resolution x-ray diffractometry. Film crystallinity was the parameter that most directly influenced tunability, and we observed that a) the crystalline quality was highest in the thinnest film and progressively degraded with increasing film thickness; and b) strain at the film/substrate interface was completely relieved via dislocation formation. Paraelectric films such as BSTO offer an attractive means of incorporating low-cost phase shifter circuitry into beam-steerable reflectarray antennas.

  5. Perpendicular Exchange-Biased Magnetotransport at the Vertical Heterointerfaces in La(0.7)Sr(0.3)MnO3:NiO Nanocomposites.

    PubMed

    Zhang, Wenrui; Li, Leigang; Lu, Ping; Fan, Meng; Su, Qing; Khatkhatay, Fauzia; Chen, Aiping; Jia, Quanxi; Zhang, Xinghang; MacManus-Driscoll, Judith L; Wang, Haiyan

    2015-10-01

    Heterointerfaces in manganite-based heterostructures in either layered or vertical geometry control their magnetotransport properties. Instead of using spin-polarized tunneling across the interface, a unique approach based on the magnetic exchange coupling along the vertical interface to control the magnetotransport properties has been demonstrated. By coupling ferromagnetic La0.7Sr0.3MnO3 and antiferromagnetic NiO in an epitaxial vertically aligned nanocomposite (VAN) architecture, a dynamic and reversible switch of the resistivity between two distinct exchange biased states has been achieved. This study explores the use of vertical interfacial exchange coupling to tailor magnetotransport properties, and demonstrates their viability for spintronic applications.

  6. Mechanical behavior of La0.8Sr0.2Ga0.8Mg0.2O3 perovskites

    SciTech Connect

    Pathak, Siddhartha; Steinmetz, David; Kuebler, Jakob; Payzant, E Andrew; Orlovskaya, Nina

    2009-01-01

    Mechanical properties such as Young's modulus, fracture toughness and slow crack growth have been measured for phase pure and highly dense (<5% porosity) La0.8Sr0.2Ga0.8Mg0.2O3 perovskites. The Young's modulus was measured to be ~175 GPa, while strength and fracture toughness both exhibited low values confirming the poor mechanical properties of the material. LSGM was also proved to be highly susceptible to slow crack growth in humid air at room temperature where in order to survive a one year period the static stresses in the material should be as low as 50 MPa for a 50% failure probability.

  7. Investigation of conduction mechanism in Pr0.67Sr0.13Ag0.20MnO3 manganites

    NASA Astrophysics Data System (ADS)

    Modi, Anchit; Bhat, Masroor Ahamad; Gaur, N. K.

    2016-05-01

    We report the electronic conduction mechanism in Pr0.67Sr0.13Ag0.20MnO3 synthesized successfully by conventional solid state reaction method. The compound under investigation was subjected by X - Ray diffraction using Rietveld refinement which confirms the single phase nature of the sample. The resistivity behavior indicates the semiconducting behavior and reduction in resistivity on the application of magnetic fields. The electronic nature can further been evaluated by using variable range hopping (VRH) model and small polaron hopping model (SPH) showing that the double exchange interaction increases suppress the band gap and enhances carrier delocalization on the application of magnetic fields.

  8. Microscopic Examination of the Microwave Sintered (Pb0.6Sr0.4)TiO3 Positive-Temperature-Coefficient Resistor Materials

    NASA Astrophysics Data System (ADS)

    Chou, Chen-Chia; Chang, Hon-Yi; Lin, I-Nan; Shaw, Bin-Jen; Tan, Jian-Tao

    1998-09-01

    The (Pb0.6Sr0.4)TiO3 (PSrT) ceramics processed by the microwave sintering technique, exhibiting unique high-Tc behavior and low resistivity, were examined using a scanning electron microscope, scanning transmission electron microscope with energy dispersive spectroscopy, and electron diffraction in the present work. The results imply that different atomic species may interact differently with microwaves and produce a large strain field within materials, suggesting that domain mobility is restricted in the specimens due to lattice distortions. The Pb-species distribution and complicated domain arrangements induced by the strain field greatly influence the electrical properties of the materials.

  9. FABRICATION OF LATERAL ORGANIC SPIN VALVES BASED ON La0.7Sr0.3MnO3 ELECTRODES

    NASA Astrophysics Data System (ADS)

    Jiang, S. W.; Wang, P.; Jiang, S. C.; Chen, B. B.; Wang, M.; Jiang, Z. S.; Wu, D.

    2014-06-01

    We report the successful fabrication of lateral organic spin valves (OSVs) using polycrystalline pentacene as spacer and half-metallic La0.7Sr0.3MnO3 (LSMO) as two electrodes. The distance between two electrodes ranges from 30 nm to 100 nm. The current-voltage characteristics follow the power law relation, which are attributed to the space charge limited current behavior. The devices with a spacing of 30 nm exhibits clear spin-valve characteristics with a magnetoresistance (MR) ratio of 2% at 9 K. The MR effects disappear for electrode spacing about 100 nm, suggesting that the spin diffusion length is less than 100 nm.

  10. Interface ferromagnetism and orbital reconstruction in BiFeO3-La0.7Sr0.3MnO3 heterostructures

    SciTech Connect

    Yu, P; Lee, J.-S.; Okamoto, Satoshi; Rossell, M.D.; Huijben, M.; Yang, C.-H.; He, Q; Zhang, J.-X.; Yang, S.Y.; Lee, M.J.; Ramasse, Q.M.; Erni, R.; Chu, Y.-H.; Arena, D.A.; Kao, C.-C.; Martin, L.W.; Ramesh, R

    2010-01-01

    We report the formation of a novel ferromagnetic state in the antiferromagnet BiFeO3 at the interface with ferromagnet La0.7Sr0.3MnO3. Using x-ray magnetic circular dichroism at Mn and Fe L2,3 edges, we discovered that the development of this ferromagnetic spin structure is strongly associated with the onset of a significant exchange bias. Our results demonstrate that the magnetic state is directly related to an electronic orbital reconstruction at the interface, which is supported by the linearly polarized x-ray absorption measurement at the oxygen K edge.

  11. Ethylene production by ODHE in catalytically modified Ba(0.5)Sr(0.5)Co(0.8)Fe(0.2)O(3-δ) membrane reactors.

    PubMed

    Lobera, M Pilar; Escolástico, Sonia; Garcia-Fayos, Julio; Serra, José M

    2012-08-01

    Process intensification by the integration of membranes and high-temperature reactors offers several advantages with regard to conventional process schemes, that is, energy saving, safe operation, reduced plant/unit size, and higher process performance, for example, higher productivity, catalytic activity, selectivity, or stability. We present the study of oxidative dehydrogenation of ethane at 850 °C on a catalytic membrane reactor based on a mixed ionic-electronic conducting membrane. The surface of the membrane made of Ba(0.5)Sr(0.5)Co(0.8)Fe(0.2)O(3-δ) has been activated by using different porous catalytic layers based on perovskites. The layer was deposited by screen printing, and the porosity and thickness was studied for the catalyst composition. The different catalyst formulations are based on partial substitution of A- and B-site atoms of doped strontium ferrite/cobaltites (A(0.6)Sr(0.4)Co(0.5)Fe(0.5)O(3-δ) and Ba(0.6)Sr(0.4)BO(3-δ)) and were synthesized by an ethylenediaminetetraacetic acid-citrate complexation route. The use of a disk-shaped membrane in the reactor enabled the direct contact of gaseous oxygen and hydrocarbons to be avoided, and thus, the ethylene content increased. High ethylene yields (up to ≈81 %) were obtained by using a catalytic coating based on Ba(0.5)Sr(0.5)Co(0.8)Fe(0.2)O(3-δ), which included macropores produced by the addition of graphite platelets into the screen-printing ink. The promising catalytic results obtained with this catalytically modified membrane reactor are attributed to the combination of 1) the high activity, as a result of the high temperature and oxygen species diffusing through the membrane; 2) the control of oxygen dosing and the low concentration of molecules in the gas phase; and 3) suitable fluid dynamics, which enables appropriate feed contact with the membrane and the rapid removal of products. PMID:22791570

  12. Synthesis and characteristic of nanocrystalline La0.7Sr0.3MnO3 manganites by solid state reaction route

    NASA Astrophysics Data System (ADS)

    Astik, Nidhi; Patil, Swapnilkumar; Bhargava, Parag; Jha, Prafulla K.

    2016-05-01

    Nanocrystalline stoichiometric La0.7Sr0.3MnO3 (x=0.3) manganites have been synthesized through solid-state reaction by ball milling mechanical method at two different sintering temperatures 1250°C and 1350°C. The synthesized samples were characterized using X-ray diffraction (XRD) and found to have rhombohedral crystal structure (R-3c). The calcined samples exhibited a pure single phase perovskite, had a crystallite size of about 47-51 nm. The morphology of the prepared nanocrystalline manganites were recorded by the field emission gun-scanning electron microscope (FEG-SEM) and EDAX.

  13. Magnetic transition behavior of perovskite manganites Nd0.5Sr0.3Ca0.2MnO3 polycrystalline

    NASA Astrophysics Data System (ADS)

    Ru, Xing; Su-Lei, Wan; Wen-Qing, Wang; Lin, Zheng; Xiang, Jin; Min, Zhou; Yi, Lu; Jian-Jun, Zhao

    2016-04-01

    A polycrystalline sample Nd0.5Sr0.3Ca0.2MnO3 is prepared by the conventional solid state reaction method. The structure and magnetic properties are investigated with x-ray diffraction (XRD) patterns, a superconducting quantum interference device (SQUID), and electron spin resonance (ESR). The sample is in single phase with the space group Pbnm symmetry. With the decrease of temperature, Nd0.5Sr0.3Ca0.2MnO3 undergoes three magnetic transitions: ferromagnetic transition at T C ≈ 210 K, charge-ordering at T CO ≈ 175 K, and antiferromagnetic transition at T N = 155 K. In addition, the activation energy E a ≈ 52.78 meV can be extracted by curve fitting. Project supported by the National Natural Science Foundation of China (Grant Nos. 11164019, 51562032, and 61565013), the Inner Mongolia Natural Science Foundation, China (Grant Nos. 2015MS0109, NJZZ11166, and NJZY12202), and the Science and Technology in Baotou Production-Study-Research Cooperation Projects, China (Grant No. 2014X1014-01).

  14. Enhanced Microwave Absorption Properties of Intrinsically Core/shell Structured La(0.6)Sr(0.4)MnO(3) Nanoparticles.

    PubMed

    Cheng, Y L; Dai, J M; Zhu, X B; Wu, D J; Yang, Z R; Sun, Y P

    2009-06-17

    The intrinsically core/shell structured La(0.6)Sr(0.4)MnO(3) nanoparticles with amorphous shells and ferromagnetic cores have been prepared. The magnetic, dielectric and microwave absorption properties are investigated in the frequency range from 1 to 12 GHz. An optimal reflection loss of -41.1 dB is reached at 8.2 GHz with a matching thickness of 2.2 mm, the bandwidth with a reflection loss less than -10 dB is obtained in the 5.5-11.3 GHz range for absorber thicknesses of 1.5-2.5 mm. The excellent microwave absorption properties are a consequence of the better electromagnetic matching due to the existence of the protective amorphous shells, the ferromagnetic cores, as well as the particular core/shell microstructure. As a result, the La(0.6)Sr(0.4)MnO(3) nanoparticles with amorphous shells and ferromagnetic cores may become attractive candidates for the new types of electromagnetic wave absorption materials. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (doi:10.1007/s11671-009-9374-y) contains supplementary material, which is available to authorized users.

  15. Epitaxial Ferroelectric Ba(0.5)Sr(0.5)TiO3 Thin Films for Room-Temperature High-Frequency Tunable Element Applications

    NASA Technical Reports Server (NTRS)

    Chen, C. L.; Feng, H. H.; Zhang, Z.; Brazdeikis, A.; Miranda, F. A.; VanKeuls, F. W.; Romanofsky, R. R.; Huang, Z. J.; Liou, Y.; Chu, W. K.; Chu, C. W.

    1999-01-01

    Perovskite Ba(0.5)SR(0.5)TiO3 thin films have been synthesized on (001) LaAl03 substrates by pulsed laser ablation. Extensive X-ray diffraction, rocking curve, and pole-figure studies suggest that the films are c-axis oriented and exhibit good in-plane relationship of <100>(sub BSTO)//<100>(sub LAO). Rutherford Backscattering Spectrometry studies indicate that the epitaxial films have excellent crystalline quality with an ion beam minimum yield chi(sub min) Of only 2.6 %. The dielectric property measurements by the interdigital technique at 1 MHz show room temperature values of the relative dielectric constant, epsilon(sub r), and loss tangent, tan(sub delta), of 1430 and 0.007 with no bias, and 960 and 0.001 with 35 V bias, respectively. The obtained data suggest that the as-grown Ba(0.5)SR(0.5)TiO3 films can be used for development of room-temperature high-frequency tunable elements.

  16. Preparation and magnetocaloric effect of (La0.67-XGdX)Sr0.33MnO3 (X =0.1,0.15) nanoparticles

    NASA Astrophysics Data System (ADS)

    Wang, G.; Wang, Z.-D.; Zhang, L.-D.

    2005-05-01

    We report a new route to synthesize nanosized (La0.67-XGdX)Sr0.33MnO3 (X=0.1,0.15) perovskite crystalline complex oxides at calcination temperatures of 600-900 °C using amorphous molecular alloy as precursor. The precursor could completely decompose into oxide at temperatures below 500 °C according to thermogravimetric analysis and differential thermal analysis results. X-ray diffraction demonstrated that the decomposed species was composed of perovskite structure at a calcination temperature of 600 °C for 2 h. The size and topography of the oxides are dependent on the calcination temperature of the precursor. The resulting particle size is in the range of 40-120 nm as determined by a transmission electron microscope. This method is effective and can be easily quantitatively controlled to synthesize nanosized perovskite complex oxides. The Curie temperature TC and the magnetocaloric effect of (La0.67-XGdX)Sr0.33MnO3 (X=0.1,0.15) nanoparticles are discussed based on the measurement of the low-field magnetization curve and the isothermal magnetization curve.

  17. Impact of Ni doping on La0.7Sr0.3NixMn1-xO3 perovskite manganite materials

    NASA Astrophysics Data System (ADS)

    Thamilmaran, P.; Arunachalam, M.; Sankarrajan, S.; Sakthipandi, K.

    2015-12-01

    On-line ultrasonic measurements on La0.7Sr0.3Mn1-xNixO3 perovskite manganite material (x=0.01, 0.02 and 0.03) were performed on the samples synthesised by solid state reaction technique. The XRD studies on the samples confirm the crystalline nature with single phase rhombohedral structure having R3C space group. The average size of the particles determined using SEM images are 0.587, 0.412 and 0.356 μm for x=0.01, 0.02 and 0.03 respectively. The temperature dependent ultrasonic velocities and attenuation measurements on the samples were used to reveal the ferromagnetic to paramagnetic phase transition temperature (Curie temperature) 374, 358 and 342 K for the values of x=0.01, 0.02 and 0.03 respectively. In addition, ultrasonic measurements confirm that the increase in Ni doping concentration in La0.7Sr0.3Mn1-xNixO3 perovskites leads to a decrease in Curie temperature. The change in Mn3+/Mn4+ ratio with the phase transition temperature was explained on the basis of variation in amplitude of observed anomaly in ultrasonic measurements. The replacement of Mn4+ ion by Ni2+ ion leads to a change in the structural parameters and in the concentration of Mn3+ and Mn4+ ions.

  18. Electrical transport and magnetic behaviors of La0.67Sr0.33Mn1-xBxO3 (B = Cr, Ru)

    NASA Astrophysics Data System (ADS)

    Acharya, Deepshikha; Bhargav, Abhinav; Tank, Tejas M.; Sanyal, Sankar P.

    2016-05-01

    Polycrystalline samples of La0.67Sr0.33Mn1-xCrxO3 (with x=0, 0.05 and 0.1) and La0.67Sr0.33Mn1-xRuxO3 (with x = 0.05 and 0.1) were synthesized using the conventional solid state reaction route and found single phase in nature. Electrical resistivity measurements as a function of temperature in range 5 K-400 K and as a function of magnetic field up to 5 Tesla were performed using d.c. four-probe method. Magnetization data were acquired as a function of temperature in a range 10 K-400 K with an applied magnetic field of 500 Oe. When Mn is partially substituted by Cr and Ru the system displays dramatic changes in the electrical transport behavior and shows double-peaked feature in resistivity curve. Both Cr and Ru substitutions effectively reduce insulator-metal transition (TP) and paramagnetic-ferromagnetic transition (TC) temperatures implying that there might exist FM interaction between Mn+3 and Cr+3 as well Mn+3 and Ru+4. The largest low-temperature magnetoresistance (MR%) is attributed to grain boundary effects and difference in size disorder for Cr and Ru substituted compounds.

  19. Internal electrical and strain fields influence on the electrical tunability of epitaxial Ba0.7Sr0.3TiO3 thin films

    NASA Astrophysics Data System (ADS)

    Bagdzevicius, S.; Mackeviciute, R.; Ivanov, M.; Fraygola, B.; Sandu, C. S.; Setter, N.; Banys, J.

    2016-03-01

    Perpetual demand for higher transfer speed and ever increasing miniaturization of radio and microwave telecommunication devices demands new materials with high electrical tunability. We have investigated built in electrical and strain fields' influence on the electrical tunability in Ba0.7Sr0.3TiO3 thin film hetero-system grown by pulsed laser deposition technique. We observed the built in electrical field by local piezo-force microscopy (as deflected hysteresis loops) and macroscopic impedance analysis (as asymmetric tunability curves), with the calculated 88 kV/cm built in field at room temperature. Negative -1.4% misfit strain (due to clamping by the substrate) enhanced ferroelectric phase transition temperature in Ba0.7Sr0.3TiO3 thin film by more than 300 K. Built in fields do not deteriorate functional film properties—dielectric permittivity and tunability are comparable to the best to date values observed in Ba1-xSrxTiO3 thin films.

  20. Preparation of Ba0.09Sr0.91TiO3/YBa2Cu3O7-x bilayers and investigation of their dielectric properties

    NASA Astrophysics Data System (ADS)

    Jia, Jiqiang; Zhao, Gaoyang; Shi, Xiaoxue; Lei, Li

    2016-08-01

    YBa2Cu3O7-x (YBCO) films of 110 nm thickness were prepared on LaAlO3 (LAO) substrates via the sol-gel method. Subsequently, about 400 nm thick Ba0.09Sr0.91TiO3 (BST) films were epitaxially grown on the YBCO and LNO films surface; the BST films exhibited a strong c-axis orientation. The dielectric adjustability and relative dielectric constant was investigated in the range of 300-83 K. Results indicate that the tunability of the Ba0.09Sr0.91TiO3/YBa2Cu3O7-x (BST/YBCO) displayed an increase relative to c-axis-oriented BST on LaNiO3 (LNO). The tunability was further enhanced as the operating temperature decreased, yet the loss tangent (tanδ) decreased. The tunability and the tanδ at 100 kHz and 83 K were 58% and 0.029, respectively.

  1. Promoted CO2-poisoning resistance of La0.8Sr0.2MnO3-δ-coated Ba0.5Sr0.5Co0.8Fe0.2O3-δ cathode for intermediate temperature solid oxide fuel cells

    NASA Astrophysics Data System (ADS)

    Qiu, Peng; Wang, Ao; Li, Jin; Li, Zongbao; Jia, Lichao; Chi, Bo; Pu, Jian; Li, Jian

    2016-09-01

    The solution impregnation technology was used to prepare a novel core-shell structure cathode for intermediate temperature solid oxide fuel cells (IT-SOFCs). The core was composed of porous Ba0.5Sr0.5Co0.8Fe0.2O3-δ (BSCF) backbone with high oxygen conductivity, while the dense shell consisted of La0.8Sr0.2MnO3-δ (LSM) high catalytic activity and the excellent CO2-poisoning resistance. The presence of the dense LSM shell prevented the BSCF cathode from being poisoned by CO2, and improved its electrochemical performance. The best performance was achieved when the BSCF cathode was impregnated twice in the LSM precursor solution and coated by LSM shell.

  2. La0.8Sr0.2Fe0.8Cu0.2O3-δ as “cobalt-free” cathode for La0.8Sr0.2Ga0.8Mg0.2O3-δ electrolyte

    NASA Astrophysics Data System (ADS)

    Zurlo, Francesca; Di Bartolomeo, Elisabetta; D'Epifanio, Alessandra; Felice, Valeria; Natali Sora, Isabella; Tortora, Luca; Licoccia, Silvia

    2014-12-01

    A "cobalt-free" cathode material with stoichiometric composition La0.8Sr0.2Fe0.8Cu0.2O3-δ (LSFCu) was specifically developed for use with La0.8Sr0.2Ga0.8Mg0.2O3-δ (LSGM) electrolyte in intermediate temperature solid oxide fuel cell (IT-SOFC) systems. The chemical stability of LSFCu in contact with LSGM electrolyte was investigated by structural and morphological analysis. The electrochemical properties of LSFCu dense pellets were investigated in the temperature range 600-750 °C by electrochemical impedance spectroscopy (EIS). LSFCu|LSGM|LSFCu symmetrical cells were prepared and area specific resistance (ASR) values, directly depending on the rate limiting step of the oxygen reduction reaction, were evaluated. Fuel cells were prepared using LSFCu as cathode material on a LSGM pellet and electrochemical tests were performed in the 700-800 °C temperature range and compared to similar fuel cells prepared by using commercial La0.6Sr0.4Fe0.8Co0.2O3-δ (LSFCo) as a cathode. The maximum current density and power density recorded for LSFCu and LSFCo were similar. This fact demonstrates that Cu can be used as Co substitute in perovskite cathode materials.

  3. The ionic conductivity, thermal expansion behavior, and chemical compatibility of La 0.54Sr 0.44Co 0.2Fe 0.8O 3-δ as SOFC cathode material

    NASA Astrophysics Data System (ADS)

    Fan, Baoan; Yan, Jiabao; Yan, Xiaochao

    2011-10-01

    In this paper, the ionic conductivities of La 0.54Sr 0.44Co 0.2Fe 0.8O 3-δ and La 0.6Sr 0.4Co 0.2Fe 0.8O 3-δ were measured by electron-blocked alternating current impedance analysis technique. The results show that the oxygen ion conductivity of La 0.54Sr 0.44Co 0.2Fe 0.8O 3-δ is nearly five times higher than that of La 0.6Sr 0.4Co 0.2Fe 0.8O 3-δ, which makes La 0.54Sr 0.44Co 0.2Fe 0.8O 3-δ cathode more conductive than YSZ electrolyte. Consequently, the electrochemical reaction region is extended from the interface between the cathode and the electrolyte to the whole surface of the cathode grains, with a result of the cathode polarization overpotential being decreased and the cell electrical performance being improved. Besides, the XRD results show that both La 0.54Sr 0.44Co 0.2Fe 0.8O 3-δ and La 0.6Sr 0.4Co 0.2Fe 0.8O 3-δ begin to react with 8YSZ([Y 2O 3] 0.08·[ZrO 2] 0.92) at 850 °C, but La 0.54Sr 0.44Co 0.2Fe 0.8O 3-δ with a faster reaction rate. The thermal expansion experiments manifest that the two LSCFs have approximate thermal expansion coefficients, being about 14 × 10 -6-15 × 10 -6 K -1 from 500 °C to 700 °C, which is moderately higher than that of 8YSZ.

  4. Domain wall transformations and hopping in La(0.7)Sr(0.3)MnO(3) nanostructures imaged with high resolution x-ray magnetic microscopy.

    PubMed

    Finizio, S; Foerster, M; Krüger, B; Vaz, C A F; Miyawaki, T; Mawass, M A; Peña, L; Méchin, L; Hühn, S; Moshnyaga, V; Büttner, F; Bisig, A; Le Guyader, L; El Moussaoui, S; Valencia, S; Kronast, F; Eisebitt, S; Kläui, M

    2014-11-12

    We investigate the effect of electric current pulse injection on domain walls in La(0.7)Sr(0.3)MnO(3) (LSMO) half-ring nanostructures by high resolution x-ray magnetic microscopy at room temperature. Due to the easily accessible Curie temperature of LSMO, we can employ reasonable current densities to induce the Joule heating necessary to observe effects such as hopping of the domain walls between different pinning sites and nucleation/annihilation events. Such effects are the dominant features close to the Curie temperature, while spin torque is found to play a small role close to room temperature. We are also able to observe thermally activated domain wall transformations and we find that, for the analyzed geometries, the vortex domain wall configuration is energetically favored, in agreement with micromagnetic simulations. PMID:25336527

  5. Characterization of La(0.8)Sr(0.2)MnO(3 +/-delta) nanopowders synthesized by aerosol flame synthesis for SOFC cathode.

    PubMed

    Jung, Young-Geul; Choi, Jinyi; Yoon, Yongsub; Shin, Dongwook

    2011-08-01

    Lanthanum strontium manganite (La(0.8)Sr(0.2)MnO(3 +/- delta), LSM) powders with a high specific surface area (55.26 m2/g) were successfully synthesized by aerosol flame synthesis (AFS) technique. The crystallinity and morphology of the synthesized powders sintered at various temperatures were studied by XRD, TEM and BET. The synthesized powders exhibited spherical shape mostly in a few nanometer ranges with a relatively high crystallinity due to thermal plasma reactions in a high temperature of oxy-hydrogen flame. To analyze electrochemical performances of synthesized LSM powders, impedance spectroscopy (IS) was carried out with the symmetric cells prepared by slurry based electrostatic spray deposition (ESD) onto the YSZ electrolyte pellet. The interfacial polarization resistances were 3.04 ohms cm2 at 750 degrees C which is relatively lower than that of micro-porous film (7.24 ohms cm2) applying micro-sized powders deposited on same condition. PMID:22103223

  6. 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.

  7. Controllable-permittivity and high-tunability of Ba0.5Sr0.5TiO3/MgO based ceramics by composite configuration

    NASA Astrophysics Data System (ADS)

    Tang, Linjiang; Wang, Jinwen; Zhai, Jiwei; Bing Kong, Ling; Yao, Xi

    2013-04-01

    Ba0.5Sr0.5TiO3 (BST50)/MgO composites, with 2-2-type configurations, consisting of BST layers and MgO layers, were fabricated by using tape-casting and laminating technique. Microstructure, dielectric response, and tunable properties of the 2-2-type composites were investigated. An important feature of the 2-2 type composites is that DC fields can be effectively applied to the high-permittivity ferroelectric phase when the fields are applied in parallel direction to the inter-phase boundaries. As a result, with increasing volume fraction (q) of MgO, tunability of the composites remained almost unchanged, whereas their permittivity value could be reduced significantly. This behavior has not been observed in the conventional 3-0 type composites.

  8. Quench behavior of Sr0.6K0.4Fe2As2/Ag tapes with AC and DC transport currents at different temperature

    NASA Astrophysics Data System (ADS)

    Liu, Qi; Zhang, Guomin; Yang, Hua; Li, Zhenming; Liu, Wei; Jing, Liwei; Yu, Hui; Liu, Guole

    2016-09-01

    In applications, superconducting wires may carry AC or DC transport current. Thus, it is important to understand the behavior of normal zone propagation in conductors and magnets under different current conditions in order to develop an effective quench protection system. In this paper, quench behavior of Ag sheathed Sr0.6K0.4Fe2As2 (Sr-122 in the family of iron-based superconductor) tapes with AC and DC transport current is reported. The measurements are performed as a function of different temperature (20 K-30 K), varying transport current and operating frequency (50 Hz-250 Hz). The focus of the research is the minimum quench energy (MQE), the normal zone propagation velocity (NZPV) and the comparison of the related results with AC and DC transport current.

  9. Turning antiferromagnetic Sm(0.34)Sr(0.66)MnO3 into a 140 K ferromagnet using a nanocomposite strain tuning approach.

    PubMed

    Suwardi, Ady; Prasad, Bhagwati; Lee, Shinbuhm; Choi, Eun-Mi; Lu, Ping; Zhang, Wenrui; Li, Leigang; Blamire, Mark; Jia, Quanxi; Wang, Haiyan; Yao, Kui; MacManus-Driscoll, Judith L

    2016-04-21

    Ferromagnetic insulating thin films of Sm(0.34)Sr(0.66)MnO3 (SSMO) on (001) SrTiO3 substrates with a T(C) of 140 K were formed in self-assembled epitaxial nanocomposite thin films. High T(C) ferromagnetism was enabled through vertical epitaxy of the SSMO matrix with embedded, stiff, ∼40 nm Sm2O3 nanopillars giving a c/a ratio close to 1 in the SSMO. In contrast, bulk and single phase SSMO films of the same composition have much stronger tetragonal distortion, the bulk having c/a >1 and the films having c/a <1, both of which give rise to antiferromagnetic coupling. The work demonstrates a unique and simple route to creating ferromagnetic insulators for spintronics applications where currently available ferromagnetic insulators are either hard to grow and/or have very low T(C).

  10. Evolution of photoinduced effects in phase-separated Sm0.5Sr0.5Mn1‑yCryO3 thin films

    NASA Astrophysics Data System (ADS)

    Chai, Xiaojie; Xing, Hui; Jin, Kexin

    2016-03-01

    Systematic study on electrical transport properties has been performed in Sm0.5Sr0.5Mn1‑yCryO3 thin films illuminated by the light. An evolution of persistent and transient photoinduced effects induced by the impurity doping and temperature has been observed, which is closely related to the number of ferromagnetic clusters. The maximum persistent photoinduced effect is observed at y = 0.08 and the corresponding value is about 61.7% at the power density of 13.7 mW/mm2. The underlying mechanism can be understood by the coexistence and competition of the multiphases in phase-separated manganites induced by Cr-doping. These results would pave the way for practical applications in innovative photoelectric devices of all-oxides.

  11. Strong perpendicular exchange bias in epitaxial La0.7Sr0.3MnO3:LaFeO3 nanocomposite thin films

    NASA Astrophysics Data System (ADS)

    Fan, Meng; Zhang, Wenrui; Jian, Jie; Huang, Jijie; Wang, Haiyan

    2016-07-01

    Strong exchange bias (EB) in perpendicular direction has been demonstrated in vertically aligned nanocomposite (VAN) (La0.7Sr0.3MnO3)1-x : (LaFeO3)x (LSMO:LFO, x = 0.33, 0.5, 0.67) thin films deposited by pulsed laser deposition. Under a moderate magnetic field cooling, an EB field as high as ˜800 Oe is achieved in the VAN film with x = 0.33, suggesting a great potential for its applications in high density memory devices. Such enhanced EB effects in perpendicular direction can be attributed to the high quality epitaxial co-growth of vertically aligned ferromagnetic LSMO and antiferromagnetic LFO phases, and the vertical interface coupling associated with a disordered spin-glass state. The VAN design paves a powerful way for integrating perpendicular EB effect within thin films and provides a new dimension for advanced spintronic devices.

  12. Orbital Reconstruction Enhanced Exchange Bias in La0.6Sr0.4MnO3/Orthorhombic YMnO3 Heterostructures

    PubMed Central

    Zheng, Dongxing; Jin, Chao; Li, Peng; Wang, Liyan; Feng, Liefeng; Mi, Wenbo; Bai, Haili

    2016-01-01

    The exchange bias in ferromagnetic/multiferroic heterostructures is usually considered to originate from interfacial coupling. In this work, an orbital reconstruction enhanced exchange bias was discovered. As La0.6Sr0.4MnO3 (LSMO) grown on YMnO3 (YMO) suffers a tensile strain (a > c), the doubly degenerate eg orbital splits into high energy 3z2 − r2 and low energy x2 − y2 orbitals, which makes electrons occupy the localized x2 − y2 orbital and leads to the formation of antiferromagnetic phase in LSMO. The orbital reconstruction induced antiferromagnetic phase enhances the exchange bias in the LSMO/YMO heterostructures, lightening an effective way for electric-field modulated magnetic moments in multiferroic magnetoelectric devices. PMID:27090614

  13. Enhanced ferromagnetic and metal insulator transition in Sm0.55Sr0.45MnO3 thin films: Role of oxygen vacancy induced quenched disorder

    NASA Astrophysics Data System (ADS)

    Srivastava, M. K.; Siwach, P. K.; Kaur, A.; Singh, H. K.

    2010-11-01

    Effect of quenched disorder (QD) caused by oxygen vacancy (OV) and substrate induced inhomogeneous compressive strain, on the magnetic and transport properties of oriented polycrystalline Sm0.55Sr0.45MnO3 thin films is investigated. QD is related intimately to the ordering/disordering of the OVs and controls the paramagnetic-ferromagnetic/insulator-metal transition. OV ordered films show enhanced TC/TIM˜165 K, which is depressed by oxygen annealing. OV disordering realized by quenching reduces TC/TIM. The first order IM transition observed in SSMO single crystals is transformed into nonhysteretic and continuous one in the OV ordered films. QD appears to be diluted by OV disorder/annihilation and results in stronger carrier localization.

  14. Magnetoelectric coupling at the interface of BiFeO3/La0.7Sr0.3MnO3 multilayers

    SciTech Connect

    Calderon, M. J.; Liang, Shuhua; Yu, Rong; Salafranca, Juan; Scalapino, D. J.; Dong, Shuai; Yunoki, Seiji; Brey, L.; Moreo, Adriana; Dagotto, Elbio R

    2011-01-01

    Electric-field controlled exchange bias in a heterostructure composed of the ferromagnetic manganite La0.7Sr0.3MO3 and the ferroelectric antiferromagnetic BiFeO3 has recently been demonstrated experimentally. By means of a model Hamiltonian, we provide a possible explanation for the origin of this magnetoelectric coupling. We find, in agreement with experimental results, a net ferromagnetic moment at the BiFeO3 interface. The induced ferromagnetic moment is the result of the competition between the eg-electron double exchange and the t2g-spin antiferromagnetic superexchange that dominates in bulk BiFeO3. The balance of these simultaneous ferromagnetic and antiferromagnetic tendencies is strongly affected by the interfacial electronic charge density, which, in turn, can be controlled by the BiFeO3 ferroelectric polarization.

  15. Grain-boundary control and low-field magnetoresistance in La0.7Sr0.3MnO3

    NASA Astrophysics Data System (ADS)

    Patil, S. I.; Ogale, Anjali S.; Shinde, S. R.; Kundaliya, Darshan C.; Ogale, S. B.; Bhagat, S. M.; Venkatesan, T.

    2005-05-01

    Sintered La0.7Sr0.3MnO3 ceramics were prepared by standard solid-state reaction route. Some of these pellets were again heated to 850 °C and quenched to room temperature. These samples were then studied for low-field magnetoresistance (LFMR) effects. Remarkably, upon quenching from high temperature the polycrystalline as well as the crystalline samples are seen to exhibit a dramatic change in LFMR with the emergence of a large positive MR. In the quenched samples a positive LFMR as high as 48% was noted in a field of 200 Oe. This positive MR effect was found to show time-dependent relaxation.

  16. Induced Ti magnetization at La0.7Sr0.3MnO3 and BaTiO3 interfaces

    DOE PAGES

    Liu, Yaohua; Tornos, J.; te Velthuis, S. G. E.; Freeland, J. W.; Zhou, H.; Steadman, P.; Bencok, P.; Leon, C.; Santamaria, J.

    2016-04-01

    In artificial multiferroics hybrids consisting of ferromagnetic La0.7Sr0.3MnO3 (LSMO) and ferroelectric BaTiO3 epitaxial layers, net Ti moments are found from polarized resonant soft x-ray reflectivity and absorption. Moreover, the Ti dichroic reflectivity follows the Mn signal during the magnetization reversal, indicating exchange coupling between the Ti and Mn ions. But, the Ti dichroic reflectivity shows stronger temperature dependence than the Mn dichroic signal. Besides a reduced ferromagnetic exchange coupling in the interfacial LSMO layer, this may also be attributed to a weak Ti-Mn exchange coupling that is insufficient to overcome the thermal energy at elevated temperatures.

  17. Orbital Reconstruction Enhanced Exchange Bias in La0.6Sr0.4MnO3/Orthorhombic YMnO3 Heterostructures

    NASA Astrophysics Data System (ADS)

    Zheng, Dongxing; Jin, Chao; Li, Peng; Wang, Liyan; Feng, Liefeng; Mi, Wenbo; Bai, Haili

    2016-04-01

    The exchange bias in ferromagnetic/multiferroic heterostructures is usually considered to originate from interfacial coupling. In this work, an orbital reconstruction enhanced exchange bias was discovered. As La0.6Sr0.4MnO3 (LSMO) grown on YMnO3 (YMO) suffers a tensile strain (a > c), the doubly degenerate eg orbital splits into high energy 3z2 ‑ r2 and low energy x2 ‑ y2 orbitals, which makes electrons occupy the localized x2 ‑ y2 orbital and leads to the formation of antiferromagnetic phase in LSMO. The orbital reconstruction induced antiferromagnetic phase enhances the exchange bias in the LSMO/YMO heterostructures, lightening an effective way for electric-field modulated magnetic moments in multiferroic magnetoelectric devices.

  18. Study on structure, electrical and dielectric properties of Eu0.65Sr0.35Fe0.3Mn0.7O3

    NASA Astrophysics Data System (ADS)

    Abdel-Latif, I. A.

    2016-08-01

    Polycrystalline Eu0.65Sr0.35Fe0.3Mna7O3 was synthesized using a standard solid state reaction technique. The preliminary microstructure of this compound at room temperature was studied using a field emission scanning electron microscope (FESEM), and the crystal structure was investigated using X-ray diffraction (XRD). The considered compound was found to crystallize in a single-phase orthorhombic structure in the Pbnm space group (62). The Raman spectrum shows three Raman-active vibrational modes at approximately 208, 476 and 616cm-1. The temperature variation of the resistivity shows that these compounds have semiconductor behaviour with an activation energy 0.498 eV. The frequency dependence of the dielectric constant in these materials indicates that space charge polarization contributes significantly to their observed dielectric parameters.

  19. Turning antiferromagnetic Sm(0.34)Sr(0.66)MnO3 into a 140 K ferromagnet using a nanocomposite strain tuning approach.

    PubMed

    Suwardi, Ady; Prasad, Bhagwati; Lee, Shinbuhm; Choi, Eun-Mi; Lu, Ping; Zhang, Wenrui; Li, Leigang; Blamire, Mark; Jia, Quanxi; Wang, Haiyan; Yao, Kui; MacManus-Driscoll, Judith L

    2016-04-21

    Ferromagnetic insulating thin films of Sm(0.34)Sr(0.66)MnO3 (SSMO) on (001) SrTiO3 substrates with a T(C) of 140 K were formed in self-assembled epitaxial nanocomposite thin films. High T(C) ferromagnetism was enabled through vertical epitaxy of the SSMO matrix with embedded, stiff, ∼40 nm Sm2O3 nanopillars giving a c/a ratio close to 1 in the SSMO. In contrast, bulk and single phase SSMO films of the same composition have much stronger tetragonal distortion, the bulk having c/a >1 and the films having c/a <1, both of which give rise to antiferromagnetic coupling. The work demonstrates a unique and simple route to creating ferromagnetic insulators for spintronics applications where currently available ferromagnetic insulators are either hard to grow and/or have very low T(C). PMID:27020599

  20. Perpendicular Exchange-Biased Magnetotransport at the Vertical Heterointerfaces in La(0.7)Sr(0.3)MnO3:NiO Nanocomposites.

    PubMed

    Zhang, Wenrui; Li, Leigang; Lu, Ping; Fan, Meng; Su, Qing; Khatkhatay, Fauzia; Chen, Aiping; Jia, Quanxi; Zhang, Xinghang; MacManus-Driscoll, Judith L; Wang, Haiyan

    2015-10-01

    Heterointerfaces in manganite-based heterostructures in either layered or vertical geometry control their magnetotransport properties. Instead of using spin-polarized tunneling across the interface, a unique approach based on the magnetic exchange coupling along the vertical interface to control the magnetotransport properties has been demonstrated. By coupling ferromagnetic La0.7Sr0.3MnO3 and antiferromagnetic NiO in an epitaxial vertically aligned nanocomposite (VAN) architecture, a dynamic and reversible switch of the resistivity between two distinct exchange biased states has been achieved. This study explores the use of vertical interfacial exchange coupling to tailor magnetotransport properties, and demonstrates their viability for spintronic applications. PMID:26394548

  1. Annealing temperature dependence of local atomic and electronic structure of polycrystalline La0.5Sr0.5MnO3

    NASA Astrophysics Data System (ADS)

    Zhang, Hong-Guang; Li, Yong-Tao; Xie, Liang; Dong, Xue-Guang; Li, Qi

    2015-10-01

    The local atomic and electronic structure of La0.5Sr0.5MnO3 was investigated at different annealing temperatures (TA) by X-ray absorption spectroscopy (XAS) and photoemission spectroscopy (XPS). The extended X-ray absorption fine structure indicates that the MnO6 octahedral distortion is reduced by increasing TA. The chemical shift for the sample with TA = 1350°C measured by XPS of Mn 2p core level demonstrates the increasing of Mn3+ ions content. From the deconvolution of valence band photoemission spectra, the number of eg electron is also proved to increase with increasing TA. It is also demonstrated that there is a strongest hybridization between O 2p and surrounding atomic orbital states in sample with TA = 1350°C, which is consistent with valence band photoemission.

  2. A novel counter electrode material of La0.5Sr0.5CoO3 for dye-sensitized solar cells

    NASA Astrophysics Data System (ADS)

    Zhong, Yongfeng; Qin, Tianze; Yang, Bo; Zuo, Xueqin; Li, Guang; Wu, Mingzai; Ma, Yongqing; Jin, Shaowei; Zhu, Kerong

    2016-11-01

    In this work, La0.5Sr0.5CoO3 (LSCO) perovskite oxide with perfect crystallinity was successfully synthesized via a sol-gel method and then used as counter electrodes (CEs) for dye-sensitized solar cells (DSSCs). The DSSCs with LSCO CEs exhibited excellent electrocatalytic activity for the triiodide reduction and yielded a power conversion efficiency of 7.17%, which is greater than that of the Pt electrode (7.06%). Compared with the hydrothermal method and solvothermal method, sol-gel method is more suitable for large scale preparation. This work should open up a new class of CE materials for low-cost and high-efficiency DSSCs.

  3. Large magnetocaloric effect in La0.845Sr0.155Mn1-xMxO3 (M = Mn, Cu, Co) perovskites

    NASA Astrophysics Data System (ADS)

    Phan, Manh-Huong; Phan, The-Long; Yu, Seong-Cho; Tho, Nguyen Duc; Chau, Nguyen

    2004-06-01

    We present the results of an investigation on the magnetocaloric effect in the perovskites of La0.845Sr0.155Mn1-xMxO3 (M = Mn, Cu, Co). It is found that there was a large magnetic entropy change, i.e. a large magneto-caloric effect, in all these samples. Among them, the magnetic entropy change reaches a maximum value of 2.67 J/kg K at the applied field of 13.5 kOe for the Cu-doped sample, suggesting that this material would be a suitable candidate for the advanced magnetic refrigeration technology. The large magnetic entropy change produced by the abrupt reduction of magnetization is attributed to the strong coupling between spin and lattice that occurs in the vicinity of the ferromagnetic-paramagnetic transition temperature (TC) - which is experimentally verified by electron paramagnetic resonance study.

  4. Giant elastocaloric effect in ferroelectric Ba0.5Sr0.5TiO3 alloys from first-principles

    NASA Astrophysics Data System (ADS)

    Lisenkov, S.; Ponomareva, I.

    2012-09-01

    As the need for efficient energy converting devices has been rapidly increasing, the materials that exhibit large or even giant caloric responses have emerged as promising candidates for solid-state refrigeration, which is an energy-efficient and environmentally friendly alternative to the conventional refrigeration technology. However, despite recent ground breaking discoveries of giant caloric responses in some materials, they appear to remain one of nature's rarities. Here we predict the existence of giant elastocaloric effect in ferroelectric Ba0.5Sr0.5TiO3 alloys, which adds one more member to this exclusive collection. Moreover, this computational finding reveals the multicaloric nature of such alloys, which could lead to new paradigms for cooling devices.

  5. Magnetic field penetration depth of La(1.85)Sr(0.15)CuO4 measured by muon spin relaxation

    NASA Technical Reports Server (NTRS)

    Kossler, W. J.; Kempton, J. R.; Yu, X. H.; Schone, H. E.; Uemura, Y. J.

    1987-01-01

    Muon-spin-relaxation measurements have been performed on a high-Tc superconductor La(1.85)Sr(0.15)CuO4. In an external transverse magnetic field of 500 G, a magnetic field penetration depth of 2000 A at T = 10 K has been determined from the muon-spin-relaxation rate which increased with decreasing temperature below Tc. From this depth and the Pauli susceptibility, the superconducting carrier density is estimated at 3 x 10 to the 21st per cu cm. The zero-field relaxation rates above and below Tc were equal, which suggests that the superconducting state in this sample is not associated with detectable static magnetic ordering.

  6. Real-time observation of pulse reshaping using Sr0.61Ba0.39Nb2O6 single crystal fiber in a microwave cavity

    NASA Astrophysics Data System (ADS)

    Huang, Chuanyong; Guo, Ruyan; Bhalla, Amar S.

    2005-03-01

    Ferroelectric single crystal fiber Sr0.61Ba0.39Nb2O6 (SBN) is evaluated for optical pulse engineering in terms of wavelength shifting and pulse compression/expansion through nonlinear optical (Pockels) effect at microwave frequencies. The microwave-photonic interaction was investigated experimentally in a TE103 microwave cavity at 10GHz. It is shown that the frequency component of an optical pulse can be controlled effectively using the SBN single crystal in a microwave cavity without the need of contact electrodes or any interruption to the optical system. The technique may be utilized in several aspects of optical communications such as channel definition and security encoding of the signal, and shows potential for a range of optoelectronic applications.

  7. Evolution of photoinduced effects in phase-separated Sm0.5Sr0.5Mn1-yCryO3 thin films.

    PubMed

    Chai, Xiaojie; Xing, Hui; Jin, Kexin

    2016-01-01

    Systematic study on electrical transport properties has been performed in Sm0.5Sr0.5Mn1-yCryO3 thin films illuminated by the light. An evolution of persistent and transient photoinduced effects induced by the impurity doping and temperature has been observed, which is closely related to the number of ferromagnetic clusters. The maximum persistent photoinduced effect is observed at y = 0.08 and the corresponding value is about 61.7% at the power density of 13.7 mW/mm(2). The underlying mechanism can be understood by the coexistence and competition of the multiphases in phase-separated manganites induced by Cr-doping. These results would pave the way for practical applications in innovative photoelectric devices of all-oxides. PMID:27001006

  8. Microstructural and dielectric properties of Ba0.6Sr0.4Ti1-xZrxO3 based combinatorial thin film capacitors library

    NASA Astrophysics Data System (ADS)

    Liu, Guozhen; Wolfman, Jérôme; Autret-Lambert, Cécile; Sakai, Joe; Roger, Sylvain; Gervais, Monique; Gervais, François

    2010-12-01

    Epitaxial growth of Ba0.6Sr0.4Ti1-xZrxO3 (0≤x≤0.3) composition spread thin film library on SrRuO3/SrTiO3 layer by combinatorial pulsed laser deposition (PLD) is reported. X-ray diffraction and energy dispersive x-ray spectroscopy studies showed an accurate control of the film phase and composition by combinatorial PLD. A complex evolution of the microstructure and morphology with composition of the library is described, resulting from the interplay between epitaxial stress, increased chemical pressure, and reduced elastic energy upon Zr doping. Statistical and temperature-related capacitive measurements across the library showed unexpected variations in the dielectric properties. Doping windows with enhanced permittivity and tunability are identified, and correlated to microstructural properties.

  9. Formation of nanodomain ensembles during polarization reversal in Sr0.61Ba0.39Nb2O6: Ce single crystals

    NASA Astrophysics Data System (ADS)

    Shur, V. Ya.; Shikhova, V. A.; Pelegov, D. V.; Ievlev, A. V.; Ivleva, L. I.

    2011-11-01

    The results of the study of nano- and microdomain structure evolution in single crystals of relaxor ferroelectric strontium barium niobate Sr0.61Ba0.39Nb2O6 doped by cerium are presented. It was shown that the initial nanodomain structure represents a self-similar three-dimensional maze. The fractal dimension and average period were revealed. It was demonstrated that application of series of alternating electric field pulses makes it possible to produce a single-domain state in the surface layer. The features of the growth and "merging," as well as the shape of ensembles of isolated nanodomains formed during switching from the single-domain state, were investigated. The formation of the nanodomain ensembles was considered as a result of the self-organized discrete switching controlled by determined nucleation.

  10. Magnetism, superconductivity, and the volume collapse transition in (Ca0.67Sr0.33)Fe2As2 under pressure

    NASA Astrophysics Data System (ADS)

    Jeffries, Jason; Butch, N. P.; Saha, S. R.; Kirshenbaum, K.; Weir, S. T.; Vohra, Y. K.; Paglione, J.

    2012-02-01

    The alkaline earth site of CaFe2As2 can be chemically substituted with Sr, forming a homogeneous solid solution series ending with SrFe2As2. It is found that (Ca0.67Sr0.33)Fe2As2 exhibits a pressure-temperature phase diagram intermediate between the two end members of the series, shifting the phase lines for the suppression of magnetism, the development of superconductivity, and the occurrence of a volume collapse transition to higher pressures. The overall shift in the pressure-temperature phase diagram permits the study of each phase field, yielding valuable information about the correlations between local atomic structure, magnetism, superconductivity, and the volume collapse transition. Lawrence Livermore National Laboratory is operated by Lawrence Livermore National Security, LLC, for the U.S. Department of Energy, National Nuclear Security Administration under Contract DE-AC52-07NA27344.

  11. Surface functionalized Ba0.6Sr0.4TiO3 /poly(vinylidene fluoride) nanocomposites with significantly enhanced dielectric properties

    NASA Astrophysics Data System (ADS)

    Li, Kecheng; Wang, Hong; Xiang, Feng; Liu, Weihong; Yang, Haibo

    2009-11-01

    A nanocomposite was prepared by embedding Ba0.6Sr0.4TiO3 (BST)/silver core/shell nanoparticles (BST@Ag) into polyvinylidene-fluoride (PVDF). Through functionalizing the surface of BST nanoparticles by silver coating, the relative permittivity of composites was significantly increased to 153 at 100 Hz which is 73% higher than that of the composite making of untreated BST nanoparticals. The loss tangent was still low (less than 0.2) when the filler content of BST@Ag was 0.55. Increasing the conductivity of the interlayer between BST and PVDF by silver enhances the space charge polarization and forms a nanocapacitance network through the interparticle junctions connecting the electrodes of sample.

  12. Non-uniform oxygen diffusion in epitaxial La0.7Sr0.3MnO3-δ film on SrTiO3 substrate

    NASA Astrophysics Data System (ADS)

    Nikolaenko, Yu M.; Artemov, A. N.; Medvedev, Yu V.; Efros, N. B.; Zhikharev, I. V.; Reshidova, I. Yu; Tikhii, A. A.; Kara-Murza, S. V.

    2016-09-01

    The diffusion mechanism of oxygen transport in the epitaxial La0.7Sr0.3MnO3-δ films was examined for different practically significant conditions of annealing. An indirect method based on the interrelation between the phase transition temperature and the oxygen index was used for stepwise monitoring of the oxygen content in the film. Using a serial procedure of film annealing at different temperatures, we have revealed the abnormal behavior of diffusion transport of oxygen. The analysis of experimental data using numerical simulations demonstrates non-uniformity of the diffusion coefficient across the film thickness. The nature of the spatial dependence of the diffusion coefficient is associated with the lattice distortions of the film material.

  13. Defect-induced spin deterioration of La0.64Sr0.36MnO3 : Ab initio study

    NASA Astrophysics Data System (ADS)

    Wang, Kunpeng; Ma, Yuchen; Betzler, Klaus

    2007-10-01

    We present an ab initio study of the effect of various point defects with different concentrations on the magnetic properties of La0.64Sr0.36MnO3 (LSMO). We find that the 100% spin polarization is destroyed by oxygen vacancies with a concentration of 11.1% and by O substituting for La ( Lav+Oi pair) with a concentration of 12.5%. Interstitial oxygen defects make no contribution to the spin deterioration of LSMO at the Fermi level despite the theoretical half-metallic gap is decreased. When the La/Sr vacancy concentration increases up to 25.0%, the majority spin at the Fermi level is decreased dramatically. The results elucidate the underlying mechanism for the deterioration of the spin polarization of LSMO.

  14. Effect of laser fluence on electrical properties of (Sr0.75,La0.25)TiO3 thin films grown by pulsed-laser-deposition.

    PubMed

    Eom, Kitae; Kim, Taemin; Seo, Jiwon; Choi, Jaedu; Lee, Jaichan

    2014-11-01

    We have grown Sr0.75La0.25TiO3 (SLTO) thin films using pulsed laser deposition (PLD) with various laser energy fluences. We investigated the effect of energy fluence on the compositions of SLTO films. The stoichiometry of SLTO films was controlled by adjusting the laser energy density. At low energy densities below 1.0 J/cm2, SLTO films become non-stoichiometric with Ti deficiency. The Ti deficiency increases with decreasing the laser energy fluence. We have also investigated the effect of laser energy fluence on the electrical properties of the thin films. The electrical resistivity and carrier density intimately depend on the laser energy fluence as a result of the non-stoichiometry. After eliminating the effect of oxygen vacancies by post-annealing, the electrical properties are dependent on the cation stoichiometry in the oxide films.

  15. Application of on-wafer TRL calibration on the measurement of microwave properties of Ba0.5Sr0.5TiO3 thin films.

    PubMed

    Lue, H T; Tseng, T Y

    2001-11-01

    A series of Al/Ba0.5Sr0.5TiO3(BST)/sapphire multi-layered coplanar waveguide (CPW) transmission lines of different geometries and thin-film configurations was fabricated. We employed an accurate on-wafer Through-Line-Reflect (TRL) calibration technique and quasi-TEM analysis to measure the dielectric constant, loss tangent, and tunability of BST thin films using this CPW structure. Experimental results show that the overall insertion loss is less than 3 dB/cm even at frequencies as high as 20 GHz, which is the lowest obtained to date for metal/BST CPW devices. This result indicates that, with optimized impedance matching, normal conductors are also possibly suitable for fabricating low-loss tunable phase-shifter devices.

  16. High-frequency ultrasonic studies of the structural phase transition in an La0.875Sr0.125MnO3 single crystal

    NASA Astrophysics Data System (ADS)

    Bogdanova, Kh. G.; Bulatov, A. R.; Golenishchev-Kutuzov, V. A.; Mamin, R. F.; Potapov, A. A.

    2007-03-01

    The specific features of a phase transition from a disordered orbital state to an ordered orbital state in an La0.875Sr0.125MnO3 single crystal are investigated using acoustic methods at a frequency f = 500 MHz. The phase transition is accompanied by a distortion of MnO6 octahedra due to the cooperative Jahn-Teller effect and is a first-order phase transition, as judged from the sharp change observed in the damping of acoustic pulses, the acoustic wave velocity, and the temperature hysteresis. It is revealed that the parameters of the acoustic waves change significantly throughout the temperature range of existence of the cooperatively distorted structure. In an external magnetic field, the structural phase transition is shifted toward lower temperatures.

  17. Griffiths phase and colossal magnetoresistance in Nd0.5Sr0.5MnO3 oxygen-deficient thin films

    NASA Astrophysics Data System (ADS)

    Solin, N. I.; Korolyov, A. V.; Medvedev, Yu. V.; Nikolaenko, Yu. M.; Khokhlov, V. A.; Prokhorov, A. Yu.; Levchenko, G. G.

    2013-05-01

    This work is devoted to study the influence of the Griffiths phase in colossal magnetoresistance manganites. Griffiths-phase-like behavior of the paramagnetic susceptibility χ0 is observed in Nd0.5Sr0.5MnO3 oxygen-deficient thin films fabricated by magnetron sputtering deposition. In Nd0.5Sr0.5MnO3-δ films with oxygen deficiency for ТG≈260-280 K>T>TC=138 K (ТG and ТС—Griffiths and Curie temperatures, respectively), paramagnetic matrix consists of a magnetic phase with short-range order (˜1-1.5 nm) (which is responsible for the colossal magnetoresistance (CMR) above ТС), and is embedded in this matrix region with long-range ferromagnetic order (≫10 nm), responsible for the Griffiths phase-like behavior of the paramagnetic susceptibility. Electrical resistivity is caused by carrier tunneling between the localized states and obeys the Efros-Shklovskii law. Magnetic resistivity is caused by change of the localized state sizes under the magnetic field. The temperature and magnetic field dependencies of size of the phase inhomogeneity inclusions, found from measurements of magneto-transport properties, can be satisfactorily described by the model of thermodynamic phase separation into metallic droplets of small radius in a paramagnetic matrix. Intrinsic nanoscale inhomogeneities caused by thermodynamic phase separation, rather than the Griffiths phase, determine the electrical resistivity and colossal magnetoresistance of the films. In half-doped manganites, the nature of long-range ordered magnetic phases may be related, besides the chemical heterogeneity, to proximity to a ferromagnetic-antiferromagnetic boundary at the phase diagram as well. The results are in good agreement with the model of existence of an analog of Griffiths phase temperature in half-doped manganites.

  18. Glassy low-energy spin fluctuations and anisotropy gap in La1.88Sr0.12CuO4

    NASA Astrophysics Data System (ADS)

    Rømer, A. T.; Chang, J.; Christensen, N. B.; Andersen, B. M.; Lefmann, K.; Mähler, L.; Gavilano, J.; Gilardi, R.; Niedermayer, Ch.; Rønnow, H. M.; Schneidewind, A.; Link, P.; Oda, M.; Ido, M.; Momono, N.; Mesot, J.

    2013-04-01

    We present high-resolution triple-axis neutron scattering studies of the high-temperature superconductor La1.88Sr0.12CuO4 (Tc=27 K). The temperature dependence of the low-energy incommensurate magnetic fluctuations reveals distinctly glassy features. The glassiness is confirmed by the difference between the ordering temperature TN≃Tc inferred from elastic neutron scattering and the freezing temperature Tf≃11 K obtained from muon spin rotation studies. The magnetic field independence of the observed excitation spectrum as well as the observation of a partial suppression of magnetic spectral weight below 0.75 meV for temperatures smaller than Tf, indicate that the stripe frozen state is capable of supporting a spin anisotropy gap, of a magnitude similar to that observed in the spin and charge stripe-ordered ground state of La1.875Ba0.125CuO4. The difference between TN and Tf implies that the significant enhancement in a magnetic field of nominally elastic incommensurate scattering is caused by strictly inelastic scattering—at least in the temperature range between Tf and Tc—which is not resolved in the present experiment. Combining the results obtained from our study of La1.88Sr0.12CuO4 with a critical reappraisal of published neutron scattering work on samples with chemical composition close to p=0.12, where local probes indicate a sharp maximum in Tf(p), we arrive at the view that the low-energy fluctuations are strongly dependent on composition in this regime, with anisotropy gaps dominating only sufficiently close to p=0.12 and superconducting spin gaps dominating elsewhere.

  19. Magnetocaloric effect in pristine and Bi-doped Pr0.6Sr0.4MnO3 manganite

    NASA Astrophysics Data System (ADS)

    Daivajna, Mamatha D.; Rao, Ashok

    2016-11-01

    Near room temperature, magnetocaloric effect in pristine and Bi-doped Pr0.6Sr0.4MnO3 manganites has been studied using in-field heat capacity measurements. The Debye temperature (θD) for the pristine sample was estimated to be 522 K and its value increases to 530 K for the Bi-doped sample with x=0.05. The entropy associated with paramagnetic (PM) to ferromagnetic (FM) transition is found to be 2.4 J/mol K and 2.3 J/mol K for x=0 and 0.05 compositions respectively. The estimated values of adiabatic temperature ∆Tad for the samples with x=0 and x=0.05 are respectively 2.2 K and 1.9 K for 0-6 Tesla. The maximum isothermal change in entropy, ∆SM for the sample Pr0.6Sr0.4MnO3 with transition temperature 306 K is found to be 2.7 J/kg-K with application of external magnetic field of 2 T and for Bi-doped sample (with x=0.05) the isothermal change in entropy reduces to 2.0 J/kg-K. The calculated maximum values of the isothermal entropy changes, ∆SM for the pristine sample, vary in the range 1.7-3.9 J/kg-K for a magnetic field change of 1-6 T. The present results suggest that these compounds can be possible candidates as magnetic refrigerants. This results in a large relative cooling power (RCP) around 93.5 J kg-1 K for the pristine sample under an application of magnetic field of 2 T. On contrary, with Bi-doping, RCP decreases to 56 J kg-1 K at external field of 2 T.

  20. Assessing electron beam sensitivity for SrTiO3 and La0.7Sr0.3MnO3 using electron energy loss spectroscopy.

    PubMed

    Nord, Magnus; Vullum, Per Erik; Hallsteinsen, Ingrid; Tybell, Thomas; Holmestad, Randi

    2016-10-01

    Thresholds for beam damage have been assessed for La0.7Sr0.3MnO3 and SrTiO3 as a function of electron probe current and exposure time at 80 and 200kV acceleration voltage. The materials were exposed to an intense electron probe by aberration corrected scanning transmission electron microscopy (STEM) with simultaneous acquisition of electron energy loss spectroscopy (EELS) data. Electron beam damage was identified by changes of the core loss fine structure after quantification by a refined and improved model based approach. At 200kV acceleration voltage, damage in SrTiO3 was identified by changes both in the EEL fine structure and by contrast changes in the STEM images. However, the changes in the STEM image contrast as introduced by minor damage can be difficult to detect under several common experimental conditions. No damage was observed in SrTiO3 at 80kV acceleration voltage, independent of probe current and exposure time. In La0.7Sr0.3MnO3, beam damage was observed at both 80 and 200kV acceleration voltages. This damage was observed by large changes in the EEL fine structure, but not by any detectable changes in the STEM images. The typical method to validate if damage has been introduced during acquisitions is to compare STEM images prior to and after spectroscopy. Quantifications in this work show that this method possibly can result in misinterpretation of beam damage as changes of material properties. PMID:27454005

  1. Assessing electron beam sensitivity for SrTiO3 and La0.7Sr0.3MnO3 using electron energy loss spectroscopy.

    PubMed

    Nord, Magnus; Vullum, Per Erik; Hallsteinsen, Ingrid; Tybell, Thomas; Holmestad, Randi

    2016-10-01

    Thresholds for beam damage have been assessed for La0.7Sr0.3MnO3 and SrTiO3 as a function of electron probe current and exposure time at 80 and 200kV acceleration voltage. The materials were exposed to an intense electron probe by aberration corrected scanning transmission electron microscopy (STEM) with simultaneous acquisition of electron energy loss spectroscopy (EELS) data. Electron beam damage was identified by changes of the core loss fine structure after quantification by a refined and improved model based approach. At 200kV acceleration voltage, damage in SrTiO3 was identified by changes both in the EEL fine structure and by contrast changes in the STEM images. However, the changes in the STEM image contrast as introduced by minor damage can be difficult to detect under several common experimental conditions. No damage was observed in SrTiO3 at 80kV acceleration voltage, independent of probe current and exposure time. In La0.7Sr0.3MnO3, beam damage was observed at both 80 and 200kV acceleration voltages. This damage was observed by large changes in the EEL fine structure, but not by any detectable changes in the STEM images. The typical method to validate if damage has been introduced during acquisitions is to compare STEM images prior to and after spectroscopy. Quantifications in this work show that this method possibly can result in misinterpretation of beam damage as changes of material properties.

  2. Performance assessment of Bi0.3Sr0.7Co0.3Fe0.7O3-δ-LSCF composite as cathode for intermediate-temperature solid oxide fuel cells with La0.8Sr0.2Ga0.8Mg0.2O3-δ electrolyte

    NASA Astrophysics Data System (ADS)

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

    2015-12-01

    Perovskite-type Bi0.3Sr0.7Co0.3Fe0.7O3-δ (BiSCF3737) oxide with perfectly cubic structure based on the Pm-3m space group has been developed and investigated as cathode for intermediate-temperature solid oxide fuel cells (IT-SOFCs). BiSCF3737 is incorporated into (La0.6Sr0.4)0.9Co0.2Fe0.8O3±δ (LSCF) to form a composite cathode called LSCF-BiSCF. X-ray diffraction (XRD) results demonstrate that BiSCF3737 has an extremely desirable chemical compatibility with LSCF as well as with La0.8Sr0.2Ga0.8Mg0.2O3-δ (LSGM) electrolyte. The cells with LSGM electrolyte (0.5 mm thickness) and symmetrical electrodes are fabricated for electrocatalaytic activity test. Compared with the pure constituent (LSCF or BiSCF3737), the composite with optimum composition, i.e., LSCF50-BiSCF50, exhibits better electrochemical activity for oxygen reduction. The LSGM electrolyte-supported (∼300 μm thickness) cell with LSCF50-BiSCF50 composite cathode exhibits higher power densities of 0.617 and 0.802 W cm-2 at 650 and 700 °C, respectively, with humidified H2 (∼3% H2O) as the fuel and ambient air as the oxidant. Over 78 h stability test at 600 °C indicates that a little performance decrease occurs but no interfacial damage happens, suggesting that LSCF50-BiSCF50 is a potential material for IT-SOFCs.

  3. Structure refinement of Ba0.5Sr0.5Co0.8Fe0.2O3-d as cathode materials for intermediate temperature solid oxide fuel cells (IT-SOFC)

    NASA Astrophysics Data System (ADS)

    Zakaria, Nurhamidah; Osman, Rozana A. M.; Idris, Mohd Sobri

    2016-07-01

    Ba0.5Sr0.5Co0.8Fe0.2O3-δ was successfully prepared using modified solid-state synthesis routes. The lowest temperature to obtained single phase of Ba0.5Sr0.5Co0.8Fe0.2O3-δ is about 900°C for 15 hours. Longer period of time are required compared to only 5 hours at 950°C as established in literatures. The X-ray Diffraction (XRD) data confirmed that Ba0.5Sr0.5Co0.8Fe0.2O3-δ is formed a cubic perovskite with the space group of Pm-3m. The lattice parameters of Ba0.5Sr0.5Co0.8Fe0.2O3-δ are a = 3.990 (1) Å and unit cell volume is V = 63.5 (1) Å3. The Rietveld refinement of XRD data revealed that the crystal structure of Ba0.5Sr0.5Co0.8Fe0.2O3-δ slightly changes as a function of temperature.

  4. Magnetic anisotropy of epitaxially (100)- and (111)-oriented Sr0.8Ho0.2CoO3-δ thin films on SrTiO3 substrates

    NASA Astrophysics Data System (ADS)

    Ahn, Yoonho; Seo, Jeongdae; Son, Jong Yeog

    2016-06-01

    We investigated magnetic properties of epitaxial Sr0.8Ho0.2CoO3-δ thin films grown on single crystal SrTiO3 substrates deposited by pulsed laser deposition method. On the single crystal (100) and (111) SrTiO3 substrates, the (100)- and (111)-oriented Sr0.8Ho0.2CoO3-δ thin films were obtained, respectively. The (100)- and (111)-oriented Sr0.8Ho0.2CoO3-δ thin films exhibited rough surface with grains and smooth surface with a step and terrace structure, respectively. This result suggests they grow in an island and layer-by-layer growth mode, respectively. The (111)-oriented Sr0.8Ho0.2CoO3-δ thin film exhibited ferromagnetic hysteresis with remnant magnetization of 0.15 μB / Co . In contrast, superparamagnetic hysteresis was observed in the (100)-oriented Sr0.8Ho0.2CoO3-δ thin film.

  5. Competing Interfacial Reconstruction Mechanisms in La0.7Sr0.3MnO3/SrTiO3 Heterostructures.

    PubMed

    Li, Zhipeng; Song, Dongsheng; Yu, Rong; Ge, Binghui; Liao, Zhenyu; Li, Yueliang; Dong, Shuai; Zhu, Jing

    2016-09-14

    Interface coupling between complex oxides offers unique possibilities to tailor materials properties and stabilize novel ground states. Understanding the structural reconstruction of the corner-shared octahedral framework and the charge redistribution are crucial for controlling interfacial properties in oxide electronics. Here, we study the interfacial oxygen octahedral behavior in La0.7Sr0.3MnO3/SrTiO3 heterostructure, by directly imaging the oxygen octahedra at the atomic scale and extracting the structural parameters. We combine these experimental results with electronic structure calculations to elucidate the effect of reconstructed MnO6 octahedral geometry on increased interfacial magnetization and conductivity. The Mn valence profiles near the interface are quantitatively analyzed and compared at variant temperatures, revealing the insulating nature of interfacial manganite with reduced Mn valence. This study suggests a pathway to manipulate the interfacial properties and creation of new ground states in complex oxide heterostructures by tuning competing structural and electronic parameters. PMID:27551951

  6. Microstructures of La 1.85Sr 0.15CuO 4 doped with Ni at high doping level

    NASA Astrophysics Data System (ADS)

    Wu, X. S.; Jiang, S. S.; Pan, F. M.; Lin, J.; Xu, N.; Mao Zhiqiang; Xu Gaoji; Zhang Yuheng

    1996-02-01

    Ceramic superconductors of La 1.85Sr 0.15Cu 1- yNi yO 4 with 0.00 ≤ y ≤ 0.50 were synthesized. There is no impurity phase detected in the entire Ni doped region. The structure of these Ni-doped samples was characterized by X-ray diffraction studies. The atomic structural parameters were obtained by Rietveld refinements for the Ni-doped samples with y ≤ 0.50. Some meaningful bond distances were determined according to the refined results. According to the variations of some bond distances with y, the whole doping range could be divided into two regions: low doping level (LDL) and high doping level (HDL). The bond length between the two apical oxygen atoms in the CuO 6 octahedra for the Ni-doped samples increased with increasing content of Ni in the LDL, and decreased in the HDL. The average bond distance of LaO was not changed in the whole doping region. The metal-insulator transition was also observed in this Ni-doped system.

  7. Thickness dependent structural, magnetic and magneto-transport properties of epitaxial Nd0.50Sr0.50MnO3 thin films

    NASA Astrophysics Data System (ADS)

    Kumar, Pawan; Singh, Hari Krishna

    2016-05-01

    We report the thickness-dependent structural, magnetic and magneto-transport properties in epitaxial Nd0.50Sr0.50MnO3 thin films (10 to 300nm) prepared by DC magnetron sputtering technique on single crystalline (001) oriented substrate LaAlO3. X-ray diffraction pattern reveals the epitaxial growth of all the films and the out-of-plane lattice parameter of films were found to increase with thickness. As thickness of the film increases the paramagnetic insulator (PMI) to ferromagnetic metal (FMM) transition temperature (TC), charge ordered transition temperature (TCO) and magnetic moment were found to increase with a strong bifurcation in ZFC-FC magnetization. The asymmetry in the coercivity seen in field dependent magnetization loops (M-H loops) suggests the presence of exchange bias (EB) effect. While temperature dependent resistivity of films show the semiconducting nature for thickness 10-200nm in temperature range from 5-300K, the film of thickness 300nm shows the insulator to metal transition with transition temperature (TIM) at 175K. Temperature dependent low field magnetoresistance (LFMR) measured at 4kOe found to decrease with thickness and for high field magnetoresistance (HFMR) at 40kOe and 60kOe also show similar dependence and a crossover at intermediate temperature range in the magnitude of MR between 10nm and 200nm films at constant field. Colossal increase in magnetoresistance observed for 10nm film at low temperature.

  8. Electric-field-induced strain effects on the magnetization of a Pr0.67Sr0.33MnO3 film

    DOE PAGES

    Zhang, B.; Sun, C. -J.; Lu, W.; Venkatesan, T.; Han, M. -G.; Zhu, Y.; Chen, J.; Chow, G. M.

    2015-05-26

    The electric-field control of magnetic properties of Pr0.67Sr0.33MnO3 (PSMO) film on piezoelectric Pb(Mg1/3Nb2/3)O3-PbTiO3 (PMNT) substrate was investigated. The piezoelectric response of the PMNT substrate to the electric field produced strain that was coupled to the PSMO film. The in-plane compressive (tensile) strain increased (decreased) the magnetization. The change of magnetic moment was associated with the Mn ions. First principle simulations showed that the strain-induced electronic redistribution of the two eg orbitals (3dz2 and 3dx2-y2) of Mn ions was responsible for the change of magnetic moment. This work demonstrates that the magnetoelectric effect in manganite/piezoelectric hetero-structures originates from the change inmore » eg orbital occupancy of Mn ions induced by strain rather than the interfacial effect.« less

  9. Comparative Study of Magnetic Ordering and Electrical Transport in Bulk and Nano-Grained Nd0.67Sr0.33MnO3 Manganites

    NASA Astrophysics Data System (ADS)

    Arun, B.; Suneesh, M. V.; Vasundhara, M.

    2016-11-01

    We have prepared bulk and nano-sized Nd0.67Sr0.33MnO3 manganites by solid state and low-temperature mild solgel methods respectively. Both the compounds crystallized into an orthorhombic structure with Pbnm space group confirmed from Rietveld refinement of X-ray powder diffraction patterns. Nano-grained compound shows an average particle size of 22 nm with broad grain size distribution revealed from the Transmission electron micrographs. It appeared that the long range ferromagnetic order becomes unstable upon the reduction of the samples dimension down to nano meter scale. DC magnetization and AC susceptibility results showed frustration of spins in nano-grained compound and thereby it could lead to a cluster glass-like behaviour. Temperature dependence of electrical resistivity under different magnetic fields shows the broad maxima at higher temperatures and a low temperature upturn in both the compounds, however, the latter is more prominent in the nano grained compound. Combination of Kondo effect with electron and phonon interactions govern the low temperature resistivity and a small polaron hopping mechanism dominates at high temperatures for both the compounds. The magnetoresistance is understood by the effect of spin polarized tunneling through the grain boundary. The experimental results revealed that the reduction in particle size influences severely on the magnetic, electrical and magneto transport properties.

  10. Photoinduced transient thermoelectric effect in a perovskite manganite Pr0.67Sr0.33MnO3 film

    NASA Astrophysics Data System (ADS)

    Sasaki, M.; Wu, G. R.; Gao, W. X.; Negishi, H.; Inoue, M.; Xiong, G. C.

    1999-05-01

    Pulsed laser-induced transient thermoelectric effect (TTE) for perovskite manganite Pr0.67Sr0.33MnO3 thin films has been measured under dc electric and magnetic fields. Without any external fields, a photoinduced TTE voltage is small (~0.5 mV). When an electric field is applied, its magnitude enhances appreciably and decays exponentially with two relaxation times, but its sign is changed by varying temperature. The TTE voltage and its sign are also varied by applying magnetic field, from which the Curie temperature is determined. Based on the available band model of this material, we have discussed a possible mechanism for the observed TTE signals. The TTE phenomenon is primarily due to the formation of a bipolar state of photogenerated electrons and holes, which reflect strongly on the characteristic band structure in the paramagnetic and ferromagnetic phases. Its decay process is a recombination of the electron-hole pairs through some recombination centers, in which the Jahn-Teller or polaron effect is found to be appreciable near the Curie temperature.

  11. Investigations of atomic structure and bonding at domain boundaries in bulk La0.5Eu0.2Sr0.3MnO3

    NASA Astrophysics Data System (ADS)

    Sun, B. Z.; He, L. L.; Luo, F.; Yan, C. H.

    2005-08-01

    The article [1] featured on the cover of this issue investigates the formation of the orthorhombic phase and 120° large-angle orientation domains in bulk La0.7Sr0.3MnO3 compound doped with Eu. The cover picture is a transmission electron microscopy image of the domain boundaries of this phase. Insets show the composite [012] zone electron diffraction pattern (bottom right) and diffraction patterns from the single domains. The 120° rotational symmetry originates from the three-fold axis of the high-temperature pseudo-cubic phase.The first author is a Ph. D. candidate in the Institute of Metal Research of the Chinese Academy of Sciences, working on microstructural characterization on the atomic scale for colossal magnetoresistance materials.This issue does also contain an important Rapid Research Letter contribution by Cai and Sandhage [2] on the shape-preserving reactive conversion of biosilica shell surfaces of diatoms, a topic at the interface of materials and biological sciences.

  12. Thermoelectric properties of Sr0.61Ba0.39Nb2O6-δ ceramics in different oxygen-reduction conditions

    NASA Astrophysics Data System (ADS)

    Li, Yi; Liu, Jian; Wang, Chun-Lei; Su, Wen-Bin; Zhu, Yuan-Hu; Li, Ji-Chao; Mei, Liang-Mo

    2015-04-01

    The thermoelectric properties of Sr0.61Ba0.39Nb2O6-δ ceramics, reduced in different conditions, are investigated in the temperature range from 323 K to 1073 K. The electrical transport behaviors of the samples are dominated by the thermal-activated polaron hopping in the low temperature range, the Fermi glass behavior in the middle temperature range, and the Anderson localized behavior in the high temperature range. The thermal conductivity presents a plateau at high-temperatures, indicating a glass-like thermal conduction behavior. Both the thermoelectric power factor and the thermal conductivity increase with the increase of the degree of oxygen-reduction. Taking these two factors into account, the oxygen-reduction can still contribute to promoting the thermoelectric figure of merit. The highest ZT value is obtained to be ˜0.19 at 1073 K in the heaviest oxygen reduced sample. Project supported by the National Basic Research Program of China (Grant No. 2013CB632506) and the National Natural Science Foundation of China (Grant Nos. 51202132 and 51002087).

  13. Structural and magnetic characterization of La0.8Sr0.2MnO3 nanoparticles prepared via a facile microwave-assisted method

    NASA Astrophysics Data System (ADS)

    Moradi, J.; Ghazi, M. E.; Ehsani, M. H.; Kameli, P.

    2014-07-01

    Nanoparticles of La0.8Sr0.2MnO3 (LSMO) with different particle sizes are synthesized by a very fast, inexpensive, reproducible, and environmentally friendly method: the microwave irradiation of the corresponding mixture of nitrates. The structural and magnetic properties of the samples are investigated by the X-Ray diffraction (XRD), Fourier transform infra-red (FT-IR) spectroscopy, field-emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), and magnetic (DC magnetization and AC susceptibility) measurements. The XRD study coupled with the Rietveld refinement show that all samples crystallize in a rhombohedral structure with the space group of R-3C. The FT-IR spectroscopy and FE-SEM images indicate formation of the perovskite structure of LSMO. The DC magnetization measurements confirm the decrease in the particle size effects on the magnetic properties, e.g. reduction in the ferromagnetic (FM) moment and increase in the surface spin disorder. Magnetic dynamics of the samples studied by AC magnetic susceptibility shows that the magnetic behavior of the nanometer-sized samples is well-described by the Vogel-Fulcher and critical slowing down laws. Strong interaction between magnetic nanoparticles of LSMO was detected by fitting the experimental data with the mentioned models.

  14. Ac magnetotransport in La 0.7Sr 0.3Mn 0.95Fe 0.05O 3 at low dc magnetic fields

    NASA Astrophysics Data System (ADS)

    Barik, S. K.; Mahendiran, R.

    2011-12-01

    We report the ac electrical response of La 0.7Sr 0.3Mn 1- xFe xO 3(x=0.05) as a function of temperature, magnetic field (H) and frequency of radio frequency ( rf) current ( f=0.1-20 MHz). The ac impedance (Z) was measured while rf current directly passes through the sample as well as in a coil surrounding the sample. It is found that with increasing frequency of the rf current, Z(T) shows an abrupt increase accompanied by a peak at the ferromagnetic Curie temperature. The peak decreases in magnitude and shifts down with increasing value of H. We find a magnetoimpedance of ΔZ/Z=-21% for ΔH=500 Oe at f=1 MHz around room temperature when the rf current flows directly through the sample and ΔZ/Z=-65.9% when the rf current flows through a coil surrounding the sample. It is suggested that the magnetoimpedance observed is a consequence of suppression of transverse permeability which enhances skin depth for current flow. Our results indicate that the magnetic field control of high frequency impedance of manganites is more useful than direct current magnetoresistance for low-field applications.

  15. Magnetic field effect on the electrochemical performance of La0.7Sr0.3MnO3-δ cathodes

    NASA Astrophysics Data System (ADS)

    Greiner, Yoan; Mascot, Manuel; Naa, Christian Freddy; Fasquelle, Didier

    2016-10-01

    La 0.7 Sr 0.3 MnO 3 - δ (LSM) magnetic properties are exploited through the application of a magnetic field, resulting in a significant decrease of the cathode polarization resistance, a crucial component of high temperature solid oxide fuel cells. The magnetic field is applied during the drying process after the deposition of LSM cathodes by screen-printing on a Gd 0.1 Ce 0.9 O 1.95 (GDC) electrolyte. This specific process aims to decrease the cathode polarization resistance of solid oxide fuel cells. X-ray diffraction patterns show a structural modification triggered by the magnetic field. LSM cathode performance is investigated over a temperature range of 700-800 °C by impedance spectroscopy. The measured electrode area specific resistance (ASR) of a LSM/GDC/LSM symmetric half-cell without and with magnetic field was 0.30 Ω cm2 and 0.20 Ω cm2, respectively, at 800 °C. The ASR value was therefore decreased by 33% with the magnetic field effect. This behaviour may be attributed to LSM grain reorientation, microstructure change, and tortuosity modification of LSM cathodes.

  16. Electrochemical stability of Sm(0.5)Sr(0.5)CoO(3-δ)-infiltrated YSZ for solid oxide fuel cells/electrolysis cells.

    PubMed

    Fan, Hui; Han, Minfang

    2015-01-01

    Composite SSC (Sm(0.5)Sr(0.5)CoO(3-δ))-YSZ (yttria stabilized zirconia) oxygen electrodes were prepared by an infiltration process. X-ray diffraction (XRD) analysis and scanning electron microscopy (SEM) of the composite electrodes showed the formation of SSC perovskite and a well-connected network of SSC particles in the porous YSZ backbone, respectively. The electrochemical performance of the cell was investigated under both fuel cell and steam electrolysis modes using polarization curves and electrochemical impedance spectroscopy (EIS). The cell experienced a large degradation rate at 700 °C with a constant voltage of 0.7 V for over 100 h under power generation operation. The subsequent post-cell SEM micrograph revealed that agglomeration of the infiltrated SSC particles was possibly the cause for the performance deterioration. Furthermore, the long-term stability of the cell was examined at 700 °C with a constant voltage of 1.3 V under steam electrolysis mode. SEM associated with energy dispersive X-ray spectroscopy (EDS) was employed to characterize the post-test cell after the long-term electrolysis operation and it indicated that besides the agglomeration of SSC particles, the delamination of the SSC-YSZ oxygen electrode from the YSZ electrolyte, as well as segregation of cobalt-enriched particles (particularly cobalt oxides) at the interface, was probably responsible for the cell degradation under the steam electrolysis mode.

  17. Size-induced Griffiths phase-like in ferromagnetic metallic La0.67Sr0.33MnO3 nanoparticles

    NASA Astrophysics Data System (ADS)

    Baaziz, H.; Tozri, A.; Dhahri, E.; Hlil, E. K.

    2016-04-01

    The La0.67Sr0.33MnO3 (LSMO) compound was prepared by the citrate-gel method and annealed at different temperatures (600 °C (L6), 800 °C (L8), 1000 °C (L10) and 1200 °C (L12)). X-ray diffraction (XRD), transmission electron microscopy (TEM) and magnetic measurements were used to investigate the particle size effects on the physical properties. All samples were found to be single phase crystallizing in rhombohedral symmetry with R 3 bar c space group. It was also found that the reduction of grain size intensively affects the magnetic properties of these compounds. The variation in the magnetic properties as a function of the particle size may be explained in terms of core-shell model. For the L6, L8 and L10 samples, the weaker effective magnetic moments and the deviation of the inverse susceptibility from the Curie-Weiss law were observed, indicating the possible existence of a Griffiths-like cluster phase. However, the latter was found to disappear for L12. The reduction of Griffiths phase may be related to the weaker FM interactions which were weakened by the size reduction, possibly due to the surface spin disorders. Otherwise, the competition between paramagnetic and ferromagnetic phases may strongly affect the magnetic properties that may result in the disappearance of the Griffiths phase.

  18. Gate control of ferromagnetic insulating phase in lightly-doped La0.875Sr0.125MnO3-δ film

    NASA Astrophysics Data System (ADS)

    Kuang, H.; Wang, J.; Hu, F. X.; Zhao, Y. Y.; Liu, Y.; Wu, R. R.; Sun, J. R.; Shen, B. G.

    2016-02-01

    The electric field effect on the lightly doped La0.875Sr0.125MnO3-δ (LSMO) thin film in electric double-layer transistors was investigated by measuring transport properties of the film under various gate voltages. It was found that the positive gate bias leads to an increase of the charge-orbital ordering (COO) transition temperature and a decrease of the Curie temperature TC, indicating the suppression of ferromagnetic metal (FMM) phases and preference of COO/ferromagnetic insulator (FMI) with the hole depletion by gate bias. Such different electric field effects can be ascribed to the weakening of the ferromagnetic interaction and enhancement of Jahn-Teller (JT) distortion caused by the transformation of JT inactive Mn4+-ions to JT active Mn3+-ions. Moreover, a step-like increase in the high temperature region of the ρ-T curve, which is related to the transition of cooperative JT distortion, was found to develop with increasing the positive bias, indicating that the cooperative JT distorted phase is stabilized by the depletion of holes in LSMO film. These results demonstrate that the modulation of holes via electric field strongly affects the balance between energy gains of different interactions and thus produce different effects on the competing FMI, FMM, and cooperative JT distorted phases in LSMO film.

  19. Parallel charge sheets of electron liquid and gas in La0.5Sr0.5TiO3/SrTiO3 heterostructures.

    PubMed

    Renshaw Wang, X; Sun, L; Huang, Z; Lü, W M; Motapothula, M; Annadi, A; Liu, Z Q; Zeng, S W; Venkatesan, T; Ariando

    2015-01-01

    We show here a new phenomenon in La0.5Sr0.5TiO3/SrTiO3 (LSTO/STO) heterostructures; that is a coexistence of three-dimensional electron liquid (3DEL) and 2D electron gas (2DEG), separated by an intervening insulating LSTO layer. The two types of carriers were revealed through multi-channel analysis of the evolution of nonlinear Hall effect as a function of film thickness, temperature and back gate voltage. We demonstrate that the 3D electron originates from La doping in LSTO film and the 2D electron at the surface of STO is due to the polar field in the intervening insulating layer. As the film thickness is reduced below a critical thickness of 6 unit cells (uc), an abrupt metal-to-insulator transition (MIT) occurs without an intermediate semiconducting state. The properties of the LSTO layer grown on different substrates suggest that the insulating phase of the intervening layer is a result of interface strain induced by the lattice mismatch between the film and substrate. Further, by fitting the magnetoresistance (MR) curves, the 6 unit cell thick LSTO is shown to exhibit spin-orbital coupling. These observations point to new functionalities, in addition to magnetism and superconductivity in STO-based systems, which could be exploited in a multifunctional context. PMID:26669575

  20. Raman Scattering in La0.2Sr0.8FeO3-δ thin film: annealing-induced reduction and phase transformation

    NASA Astrophysics Data System (ADS)

    Islam, Mohammad; Xie, Yujun; Scafetta, Mark; May, Steven; Spanier, Jonathan

    2015-03-01

    Raman scattering in thin film La0.2Sr0.8FeO3-δ on MgO(001) collected at 300 K following different stages of annealing at selected temperatures (300 K

  1. Protein and polymer immobilized La0.7Sr0.3MnO3 nanoparticles for possible biomedical applications

    NASA Astrophysics Data System (ADS)

    Bhayani, K. R.; Kale, S. N.; Arora, Sumit; Rajagopal, Rajashree; Mamgain, H.; Kaul-Ghanekar, R.; Kundaliya, Darshan C.; Kulkarni, S. D.; Pasricha, Renu; Dhole, S. D.; Ogale, S. B.; Paknikar, K. M.

    2007-08-01

    La0.7Sr0.3MnO3 (LSMO) is a mixed-valent room temperature ferromagnet with properties that are attractive for their applicability in biomedicine. We report, for the first time, immobilization of commonly used biocompatible molecules on LSMO nanoparticles, namely bovine serum albumin and dextran. The former was conjugated to LSMO using 1-ethyl-3-(3-dimethyl aminopropyl)-carbodiimide (CDI) as a coupling agent while the latter was used without any coupler. These bioconjugated nanoparticles exhibit several properties that suggest their applicability in the field of biomedicine, namely (a) no changes in the Curie temperature at ~360 K after conjugation with biomolecules, (b) rapid attainment of the desired temperature (48 °C) at low concentration (e.g. fluidized dextran-coated system at 80 µg ml-1) upon exposure to 20 MHz radio-frequency, (c) extremely low cytotoxicity in skin carcinoma, human fibrosarcoma and neuroblastoma cell lines and (d) high stability of the LSMO system with negligible leaching of ionic manganese into the delivery medium, indicating their safety in possible human applications.

  2. Evidence of weak localization in quantum interference effects observed in epitaxial La0.7Sr0.3MnO3 ultrathin films

    PubMed Central

    Niu, Wei; Gao, Ming; Wang, Xuefeng; Song, Fengqi; Du, Jun; Wang, Xinran; Xu, Yongbing; Zhang, Rong

    2016-01-01

    Quantum interference effects (QIEs) dominate the appearance of low-temperature resistivity minimum in colossal magnetoresistance manganites. The T1/2 dependent resistivity under high magnetic field has been evidenced as electron-electron (e-e) interaction. However, the evidence of the other source of QIEs, weak localization (WL), still remains insufficient in manganites. Here we report on the direct experimental evidence of WL in QIEs observed in the single-crystal La0.7Sr0.3MnO3 (LSMO) ultrathin films deposited by laser molecular beam epitaxy. The sharp cusps around zero magnetic field in magnetoresistance measurements is unambiguously observed, which corresponds to the WL effect. This convincingly leads to the solid conclusion that the resistivity minima at low temperatures in single-crystal manganites are attributed to both the e-e interaction and the WL effect. Moreover, the temperature-dependent phase-coherence length corroborates the WL effect of LSMO ultrathin films is within a two-dimensional localization theory. PMID:27181882

  3. The low temperature magnetostructural transition in Pr0.50Sr0.50CoO3: Bulk versus thin film behavior

    NASA Astrophysics Data System (ADS)

    Padilla-Pantoja, J.; Herrero-Martín, J.; Torrelles, X.; Bozzo, B.; Blasco, J.; Ritter, C.; García-Muñoz, J. L.

    2014-05-01

    We present a comparative study of the magnetic transitions in metallic Pr0.50Sr0.50CoO3 (PSCO) perovskites prepared in polycrystalline and thin film forms. As the bulk system, the strained epitaxial PSCO (010) film grown on LAO (100) is metallic in all the temperature range, with a ferromagnetic transition at 225 K, close to Tc ˜ 235 K in the ceramic PSCO specimen. Unlike the bulk system, the PSCO film does not show the second magnetic transition on cooling. In the ceramic sample, the second magnetic transition is coupled to an orthorhombic-to-monoclinic symmetry change. There is a contraction of the average ⟨Pr-O⟩ bond distance in the monoclinic phase below Ta, but the ⟨Co-O⟩ bond length is not modified across the transition. The orthorhombic to monoclinic structural transition stabilizes four short Pr-O2 bonds to basal oxygens in CoO6 octahedra. A strong hybridization of Pr 4f and O 2p orbitals in these bonds can be activated at Ta and probably assist the magnetostructural transition.

  4. Interfacial dislocations in (111) oriented (Ba0.7Sr0.3)TiO3 films on SrTiO3 single crystal

    NASA Astrophysics Data System (ADS)

    Shen, Xuan; Yamada, Tomoaki; Lin, Ruoqian; Kamo, Takafumi; Funakubo, Hiroshi; Wu, Di; Xin, Huolin L.; Su, Dong

    2015-10-01

    We have investigated the interfacial structure of epitaxial (Ba,Sr)TiO3 films grown on (111)-oriented SrTiO3 single-crystal substrates using transmission electron microscopy (TEM) techniques. Compared with the (100) epitaxial perovskite films, we observe dominant dislocation half-loop with Burgers vectors of a⟨110⟩ comprised of a misfit dislocation along ⟨112⟩, and threading dislocations along ⟨110⟩ or ⟨100⟩. The misfit dislocation with Burgers vector of a⟨110⟩ can dissociate into two ½a⟨110⟩ partial dislocations and one stacking fault. We found the dislocation reactions occur not only between misfit dislocations, but also between threading dislocations. Via three-dimensional electron tomography, we retrieved the configurations of the threading dislocation reactions. The reactions between threading dislocations lead to a more efficient strain relaxation than do the misfit dislocations alone in the near-interface region of the (111)-oriented (Ba0.7Sr0.3)TiO3 films.

  5. Pulse and quasi-static remagnetization peculiarities and relaxation properties of Nd0.5Sr0.5MnO3 single crystal

    NASA Astrophysics Data System (ADS)

    Dovgii, V. T.; Linnik, A. I.; Kamenev, V. I.; Tarenkov, V. Yu.; Sidorov, S. L.; Todris, B. M.; Mikhailov, V. I.; Davideiko, N. V.; Linnik, T. A.; Popov, Ju. F.; Balbashov, A. M.

    2016-06-01

    Hysteresis features of magnetization and resistance of Nd0.5Sr0.5MnO3 single crystal in quasi-static (up to 9 T) and pulse (up to 14 T) magnetic fields are studied. The relaxation processes of magnetization and resistance after the action of a magnetic field of 9 T are also studied. It is shown that relaxation curves are approximated by two exponents with different time constants. These two constants relate to relaxation of the metastable ferromagnetic phase towards two different crystal structures (Imma and p21/m). Mechanism of phase transitions: antiferromagnetic insulator↔ferromagnetic metal (AFM/I↔FM/M) and existence of a high-conductive state of a sample after removal of magnetizing field in the temperature range below 150 K is proposed. The mechanism is connected with structural transition induced by magnetic field (due to magnetostriction) and slow relaxation of the FM-phase (larger volume) to the equilibrium AFM-phase (smaller volume) after field removal. It is shown that during pulse magnetization at the temperature 18 K time required for the AFM/I→FM/M phase transition is by six-seven orders of magnitude less than for realization of the FM/M→AFM/I phase transition.

  6. Room temperature magnetocaloric effect and refrigerant capacitance in La0.7Sr0.3MnO3 nanotube arrays

    NASA Astrophysics Data System (ADS)

    Kumaresavanji, M.; Sousa, C. T.; Pires, A.; Pereira, A. M.; Lopes, A. M. L.; Araujo, J. P.

    2014-08-01

    High aspect ratio La0.7Sr0.3MnO3 nanotube (NT) arrays have been synthesized using nitrates based sol-gel precursor by nanoporous anodized aluminum oxide template assisted method. Their phase purity and microstructures were analyzed by X-ray diffraction, scanning electron microscopy, and energy-dispersive x-ray spectroscopy. Magnetocaloric effect (MCE) of as prepared NTs was investigated by means of field dependence magnetization measurements. Significant magnetic entropy change, -△SM = 1.6 J/kg K, and the refrigerant capacitance, RC = 69 J/kg, were achieved near the transition temperature at 315 K for 5 T. For comparison, a bulk sample was also prepared using the same precursor solution which gives a value of -△SM = 4.2 J/kg K and a RC = 165 J/kg. Though the bulk sample exhibits higher △SM value, the NTs present an expanded temperature dependence of -△SM curves that spread over a broad temperature range and assured to be appropriate for active magnetic refrigeration. The diminutive MCE observed in manganite NTs is explained by the increased influence of surface sites of nanograins which affect the structural phase transition occurred by external magnetic field due to the coupling between magnetism and the lattice in manganese perovskites. Our report paves the way for further investigation in 1D manganite nanostructured materials towards applications in such magnetic refrigeration technology or even on hyperthermia/drug delivery.

  7. Conduction mechanism in Eu0.5Sr0.5Mn0.9Cr0.1O3 perovskite

    NASA Astrophysics Data System (ADS)

    Modi, Anchit; Bhat, Masroor Ahmad; Pandey, Devendra K.; Gaur, N. K.

    2016-05-01

    A systematic study of polycrystalline sample with composition Eu0.5Sr0.5Mn0.9Cr0.1O3 has been undertaken and synthesized by conventional solid state reaction techniques. The room temperature XRD study reveals the single phase formation of the reported compound with orthorhombic structure having Pbnm space group. The temperature dependent resistivity study indicates the highly resistive nature of the compound especially in the low temperature region exhibits a semiconductor behavior and favored the variable range hopping conduction model. The obtained experimental data in the temperature range of our study can be described by the equation ρ(T) = ρ0exp[(T*/T)1/4]. The fitting results are used for the calculation of the temperature scale T* ˜ 9.05×106 K and finally the density of state at Fermi level N(EF) is calculated to be ˜ 61.63 × 1018 eV-1 cm-3.

  8. Hot pressing to enhance the transport Jc of Sr0.6K0.4Fe2As2 superconducting tapes

    PubMed Central

    Lin, He; Yao, Chao; Zhang, Xianping; Dong, Chiheng; Zhang, Haitao; Wang, Dongliang; Zhang, Qianjun; Ma, Yanwei; Awaji, Satoshi; Watanabe, Kazuo; Tian, Huanfang; Li, Jianqi

    2014-01-01

    High-performance Sr0.6K0.4Fe2As2 (Sr-122) tapes have been successfully fabricated using hot pressing (HP) process. The effect of HP temperatures (850–925°C) on the c-axis texture, resistivity, Vickers micro-hardness, microstructure and critical current properties has been systematically studied. Taking advantage of high degree of c-axis texture, well grain connectivity and large concentration of strong-pinning defects, we are able to obtain an excellent Jc of 1.2 × 105 A/cm2 at 4.2 K and 10 T for Sr-122 tapes. More importantly, the field dependence of Jc turns out to be very weak, such that in 14 T the Jc still remains ~ 1.0 × 105 A/cm2. These Jc values are the highest ever reported so far for iron-pnictide wires and tapes, achieving the level desired for practical applications. Our results clearly strengthen the position of iron-pnictide conductors as a competitor to the conventional and MgB2 superconductors for high field applications. PMID:25374068

  9. Potentiometric NO2 Sensors Based on Thin Stabilized Zirconia Electrolytes and Asymmetric (La0.8Sr0.2)0.95MnO3 Electrodes

    PubMed Central

    Zou, Jie; Zheng, Yangong; Li, Junliang; Zhan, Zhongliang; Jian, Jiawen

    2015-01-01

    Here we report on a new architecture for potentiometric NO2 sensors that features thin 8YSZ electrolytes sandwiched between two porous (La0.8Sr0.2)0.95MnO3 (LSM95) layers—one thick and the other thin—fabricated by the tape casting and co-firing techniques. Measurements of their sensing characteristics show that reducing the porosity of the supporting LSM95 reference electrodes can increase the response voltages. In the meanwhile, thin LSM95 layers perform better than Pt as the sensing electrode since the former can provide higher response voltages and better linear relationship between the sensitivities and the NO2 concentrations over 40–1000 ppm. The best linear coefficient can be as high as 0.99 with a sensitivity value of 52 mV/decade as obtained at 500 °C. Analysis of the sensing mechanism suggests that the gas phase reactions within the porous LSM95 layers are critically important in determining the response voltages. PMID:26205270

  10. Apparent Oxygen Uphill Diffusion in La0.8Sr0.2MnO3 Thin Films upon Cathodic Polarization

    PubMed Central

    Huber, Tobias M.; Navickas, Edvinas; Friedbacher, Gernot; Hutter, Herbert

    2015-01-01

    Abstract The impact of cathodic bias on oxygen transport in La0.8Sr0.2MnO3 (LSM) thin films was investigated. Columnar‐grown LSM thin films with different microstructures were deposited by pulsed laser deposition. 18O tracer experiments were performed on thin film microelectrodes with an applied cathodic bias of −300 or −450 mV, and the microelectrodes were subsequently analyzed by time‐of‐flight secondary ion mass spectrometry. The 18O concentration in the cathodically polarized LSM microelectrodes was strongly increased relative to that in the thermally annealed film (without bias). Most remarkable, however, was the appearance of a pronounced 18O fraction maximum in the center of the films. This strongly depended on the applied bias and on the microstructure of the LSM thin layers. The unusual shape of the 18O depth profiles was caused by a combination of Wagner–Hebb‐type stoichiometry polarization of the LSM bulk, fast grain boundary transport and voltage‐induced modification of the oxygen incorporation kinetics, PMID:27525207

  11. Surface modification of La(0.8)Sr(0.2)CrO(3-δ)-YSZ dual-phase membranes for syngas production.

    PubMed

    Yu, Anthony S; Oh, Tae-Sik; Zhu, Ran; Gallegos, Alexa; Gorte, Raymond J; Vohs, John M

    2015-01-01

    Oxygen permeation fluxes were studied in Mixed Ionic and Electronic Conducting (MIEC) membranes based on composites of 40 vol% La(0.8)Sr(0.2)CrO3 (LSCr) and 60 vol% yttria-stabilized zirconia (YSZ), using ambient air and flowing CO to establish a P(O2) gradient. The ambipolar conductivity of the dense LSCr-YSZ composite was determined for membranes with dense layers that were 115 μm and 650 μm thick. Other parts of the investigation focused on how modifications to the surface on the CO side affected the fluxes. Using a porous LSCr-YSZ composite on the surface as the base case, oxygen fluxes were shown to increase dramatically upon addition of 5 wt% CeO2 as a catalyst and an additional increase was observed with 1 wt% Pt. Changes in the structure of the porous composite LSCr-YSZ surface to improve connectivity of the YSZ phase also led to large increases in the oxygen fluxes.

  12. Linear and nonlinear optical properties of rare earth doped of Ba0.7Sr0.3TiO3 thin films

    NASA Astrophysics Data System (ADS)

    Reshmi, R.; Sreeja, R.; Jayaraj, M. K.; James, J.; Sebastian, M. T.

    2009-08-01

    Ba0.7Sr0.3TiO3:Eu ferroelectric films were deposited on quartz substrates by pulsed laser deposition. The linear absorption coefficient and the linear refractive index calculated from the transmission spectrum at 532 nm were found to be 1.67×104 cm-1 and 1.82 respectively. The room temperature photoluminescence shows the characteristic emission of Eu3+ ions. The nonlinear optical properties of the film were investigated by a single beam Z-scan setup. The negative nonlinear refractive index and two photon absorption coefficient was found to be -1.508×10-6 m2/GW and 240 m/GW respectively. The real and imaginary part of the third order susceptibility of the thin films is 2.58×10-17 m2/V2 and 1.16×10-16 m2/V2 respectively. The BST:Eu thin films show good optical limiting property.

  13. Characterization of atmospheric plasma-sprayed La 0.8Sr 0.2Ga 0.8Mg 0.2O 3 electrolyte

    NASA Astrophysics Data System (ADS)

    Li, Cheng-Xin; Xie, Ying-Xin; Li, Chang-Jiu; Yang, Guan-Jun

    La 0.8Sr 0.2Ga 0.8Mg 0.2O 3 (LSGM) deposit in free standing planar shape was prepared by atmospheric plasma spraying (APS) to examine the coating microstructure and electrical conductivity to aim at applying APS LSGM to solid oxide fuel cells (SOFCs). The electrical conductivity of the plasma-sprayed LSGM coating was investigated. The coating microstructure was characterized by X-ray diffraction and scanning electron microscopy. The result showed that a fraction amorphous phase was present in the as-sprayed LSGM deposit, which starts to recrystallize at the temperature of 785 °C. The electrical conductivities of the LSGM with recrystallization treatment are 0.04 and 0.09 S cm -1 at 1000 °C at the directions perpendicular and parallel to the coating surfaces, respectively. The electrical conductivity at perpendicular direction is about one-tenth that of sintered bulk at 1000 °C. This result is due to the lamellar structure feature with the limited interface bonding which dominates the electrical conductivity of APS coatings. The activation energy for ion conduction within APS-deposited LSGM deposit depends on temperature range. The change of activation energy indicates that the ion transportation dominant changes with temperature.

  14. Downscaling at submicrometer scale of the gap width of interdigitated Ba0.5Sr0.5TiO3 capacitors.

    PubMed

    Khalfallaoui, Abderrazek; Burgnies, Ludovic; Blary, Karine; Velu, Gabriel; Lippens, Didier; Carru, Jean-Claude

    2015-02-01

    The goal of this work was to study the influence of shrinking the gap width between the fingers of interdigitated tunable capacitors (IDCs). Voltage control of the capacitance was achieved with a 500-nm-thick Ba0.5Sr0.5TiO3 film which is in paraelectric state at room temperature. Eight devices with finger spacing ranging from 3 μm down to 0.25 μm were fabricated by the sol-gel deposition technique, electron beam patterning, and gold evaporation. The equivalent capacitance, quality factor, and tunability of the devices were measured subsequently by vector network analysis from 40 MHz to 40 GHz and for a dc bias voltage varying from -30 V to +30 V. This experimental study mainly shows that a decrease of the gap below 1 μm 1) introduces a frequency dependence of the capacitance caused by resonance effects with the finger inductance; 2) degrades the quality factor above 20 GHz, and 3) optimizes the tunability of the devices by enhancing the local electric field values. As a consequence, some trade-offs are pointed out related to the goal of ultra-thin ferroelectric film which can be voltage controlled by means of finger-shaped electrodes with deep submicrometer spacing.

  15. Positive exchange-bias and giant vertical hysteretic shift in La0.3Sr0.7FeO3/SrRuO3 bilayers

    PubMed Central

    Rana, Rakesh; Pandey, Parul; Singh, R. P.; Rana, D. S.

    2014-01-01

    The exchange-bias effects in the mosaic epitaxial bilayers of the itinerant ferromagnet (FM) SrRuO3 and the antiferromagnetic (AFM) charge-ordered La0.3Sr0.7FeO3 were investigated. An uncharacteristic low-field positive exchange bias, a cooling-field driven reversal of positive to negative exchange-bias and a layer thickness optimised unusual vertical magnetization shift were all novel facets of exchange bias realized for the first time in magnetic oxides. The successive magnetic training induces a transition from positive to negative exchange bias regime with changes in domain configurations. These observations are well corroborated by the hysteretic loop asymmetries which display the modifications in the AFM spin correlations. These exotic features emphasize the key role of i) mosaic disorder induced subtle interplay of competing AFM-superexchange and FM double exchange at the exchange biased interface and, ii) training induced irrecoverable alterations in the AFM spin structure. PMID:24569516

  16. Thermodynamic conditions during growth determine the magnetic anisotropy in epitaxial thin-films of La0.7Sr0.3MnO3

    NASA Astrophysics Data System (ADS)

    Vila-Fungueiriño, J. M.; Tinh Bui, Cong; Rivas-Murias, B.; Winkler, E.; Milano, J.; Santiso, J.; Rivadulla, F.

    2016-08-01

    The suitability of a particular material for use in magnetic devices is determined by the process of magnetization reversal/relaxation, which in turn depends on the magnetic anisotropy. Therefore, designing new ways to control magnetic anisotropy in technologically important materials is highly desirable. Here we show that magnetic anisotropy of epitaxial thin-films of half-metallic ferromagnet La0.7Sr0.3MnO3 (LSMO) is determined by the proximity to thermodynamic equilibrium conditions during growth. We performed a series of x-ray diffraction and ferromagnetic resonance (FMR) experiments in two different sets of samples: the first corresponds to LSMO thin-films deposited under tensile strain on (0 0 1) SrTiO3 by pulsed laser deposition (PLD; far from thermodynamic equilibrium); the second were deposited by a slow chemical solution deposition (CSD) method, under quasi-equilibrium conditions. Thin films prepared by PLD show fourfold in-plane magnetic anisotropy, with an overimposed uniaxial term. However, the uniaxial anisotropy is completely suppressed in the CSD films. This change is due to a different rotation pattern of MnO6 octahedra to accommodate epitaxial strain, which depends not only on the amplitude of tensile stress imposed by the STO substrate, but also on the growth conditions. Our results demonstrate that the nature and magnitude of the magnetic anisotropy in LSMO can be tuned by the thermodynamic parameters during thin-film deposition.

  17. Giant radio-frequency magnetoabsorption effect in the cobaltite ceramic La0.5Sr0.5CoO3

    NASA Astrophysics Data System (ADS)

    Belevtsev, B. I.; Kirichenko, A. Ya.; Cherpak, N. T.; Golubnichaya, G. V.; Maximchuk, I. G.; Beznosov, A. B.; Krasovitsky, V. B.; Pal-Val, P. P.; Chukanova, I. N.

    2003-08-01

    The DC transport properties of and the radio-frequency (RF) wave absorption (at 1.33 MHz) in a ceramic sample of La0.5Sr0.5CoO3-δ are measured. The Curie temperature Tc of the sample is about 250 K. A giant negative magnetoabsorption effect is found. In the vicinity of Tc, the absolute value of the magnetoabsorption is about 38% in the rather low magnetic field 2.1 kOe. This differs drastically from the measured DC magnetoresistance (MR) δ(H)=[R(0)-R(H)]/R(0) which is a mere 0.26% near Tc in the same field and increases to about 2.15% in H=20 kOe. The phenomenon can be understood taking into account that the magnetoabsorption is determined by influence of magnetic field on the conductivity and the magnetic permeability, while the MR is determined solely by the former. The magnetoabsorption effect can be used to develop RF devices controlled by magnetic field and temperature.

  18. Electric-field influence on the neutron diffuse scattering near the ferroelectric transition of Sr0.61Ba0.39Nb2O6

    NASA Astrophysics Data System (ADS)

    Ondrejkovic, Petr; Kempa, Martin; Savinov, Maxim; Bednyakov, Petr; Kulda, Jiri; Bourges, Philippe; Dec, Jan; Hlinka, Jirka

    2016-08-01

    Uniaxial relaxor ferroelectric Sr0.61Ba0.39Nb2O6 single crystal has been investigated in the vicinity of its phase transition using neutron scattering and dielectric spectroscopy. A global-type thermal hysteresis is evidenced by both techniques in the ferroelectric phase and up to about 15 K above Tc. In addition, a part of the transverse neutron diffuse scattering in the 001 Brillouin zone, presumably related to static nanodomain structure, can be suppressed by prior poling the crystal in electric field of 3 kV/cm. The remaining part of the transverse neutron diffuse scattering and the real part of permittivity show a similar temperature dependence. The temperature position of the maximal scattering intensity Tmax depends significantly on the scattering wave vector. Tmax shifts monotonically to higher temperature with the increasing wave vector in all investigated cooling and heating regimes. It is concluded that the critical fluctuations have space correlations which depend on frequency and wave vector.

  19. Effects of synthesis conditions on Curie temperature of La0.75Sr0.25MnO3 fine particles formed by ultrasonic spray pyrolysis

    NASA Astrophysics Data System (ADS)

    Kinoshita, Takuya; Furuyabu, Takamitsu; Adachi, Motoaki

    2014-10-01

    Manganese perovskite La0.75Sr0.25MnO3 (LSM) fine particles were synthesized by an ultrasonic spray pyrolysis method at various synthesis temperatures (Ts), reaction times (tr), and source solution concentrations (Ctotal) to clarify the effects of these synthesis conditions on their Curie temperature Tc and maximum particle temperature attained by magnetic heating at Thmax. At constant Ctotal, the Tc of synthesized LSM particles was increased from 288.6 to 363.5 K (15.6 to 90.5 °C) by increasing Ts from 1073 to 1627 K (800 to 1400 °C), and was increased from 281.8 to 339 K (8.89 to 66 °C) by increasing tr from 2.4 to 19 s. When the AC magnetic field was applied, the particles generated heat, and the particle temperature Th increased with time for t < about 2 min, and then attained constant Thmax near Tc. Thmax increased with increasing Tc. The LSM particles produced at Ts = 1213 K, Ctotal = 0.5 mol L-1, and tr = 9.4 s had Thmax = 316.6 K (43.6 °C), which is within the temperature range of 316-318 K (43-45 °C) for hyperthermia therapy for cancer.

  20. Preferential polarization and its reversal in polycrystalline BiFeO3/La0.5Sr0.5CoO3 heterostructures

    NASA Astrophysics Data System (ADS)

    Roy Choudhury, Palash; Parui, Jayanta; Chiniwar, Santosh; Krupanidhi, S. B.

    2015-04-01

    Polycrystalline BiFeO3 thin films were grown on La0.5Sr0.5CoO3 buffered Pt (200)/TiO2/SiO2/Si substrates under different oxygen partial pressures (10, 25, 50 and 100 mTorr) by pulsed laser ablation. Piezoresponse Force Microscopy and Piezo-Force Spectroscopy have shown that all the films are ferroelectric in nature with locally switchable domains. It has also revealed a preferential downward domain orientation in as-grown films grown under lower oxygen partial pressure (10 and 25 mTorr) with a reversal of preferential domain orientation as the oxygen partial pressure is increased to 100 mTorr during laser ablation. Such phenomena are atypical of multi-grained polycrystalline ferroelectric films and have been discussed on the basis of defect formation with changing growth conditions. For the 50 mTorr grown film, asymmetric domain stability and retention during write-read studies has been observed which is attributed to grain-size-related defect concentration, affecting pinning centres that inhibit domain wall motion.

  1. Enhanced colloidal stability of polymer coated La0.7Sr0.3MnO3 nanoparticles in physiological media for hyperthermia application.

    PubMed

    Thorat, N D; Otari, S V; Patil, R M; Khot, V M; Prasad, A I; Ningthoujam, R S; Pawar, S H

    2013-11-01

    Surface of La(0.7)Sr(0.3)MnO3 (LSMO) magnetic nanoparticles (MNPs) is functionalized with polymer (dextran) and their colloidal stability in various mediums is carried out. The influence of the surface functionalization of LSMO MNPs on their colloidal stability in physiological media is studied and correlated with their hyperthermia properties. Many studies have concerned the colloidal stability of MNPs coated with polymer, but their long-term stability when such complexes are exposed to physiological media is still not well understood. After zeta potential study, it is found that the dextran coating on MNPs improves the colloidal stability in water as well as in physiological media like PBS. The specific absorption rates (SAR) of these MNPs are found to be in 50-85 W/g in different concentrations of glucose and NaCl; and there values are suitable for hyperthermia treatment of cancer cells under AC magnetic field. After incorporation of MNPs up to 0.2-1mg/mL in 2 × 10(5)cells/mL (L929), the apoptosis and necrosis studies are carried out by acridine orange and ethidium bromide (AO and EB) staining and followed by visualization of microstructures under a fluorescence microscope. It is found that there are no morphological changes (i.e. no signs of cell rounding, bubble formation on the membrane and nuclear fragmentation) suggesting biocompatibility of dextran coated LSMO nanoparticles up to these concentrations.

  2. Temperature evolution of the luminescence decay of Sr0.33Ba0.67Nb2O6 : Pr3+.

    PubMed

    Mahlik, S; Lazarowska, A; Speghini, A; Bettinelli, M; Grinberg, M

    2014-04-23

    This article presents a spectroscopic investigation of Sr(0.33)Ba(0.67)(NbO2)3, doped with 1 mol% of Pr(3+). Photoluminescence and luminescence kinetics were measured at different temperatures at ambient (ferroelectric phase) and 76 kbar pressures (paraelectric phase). The photoluminescence spectrum is dominated by (1)D2 → (3)H4 transition of Pr(3+) in both phases. At ambient pressure when the system is excited with UV radiation, the intensity of dominant (1)D2 → (3)H4 emission evidently increases in the 200-293 K temperature range. This effect is attributed to enhancement of the excitation of the (1)D2 state through the praseodymium trapped exciton state, which at higher temperatures does not populate the higher lying (3)P0 state. Additionally, under UV radiation the material exhibits afterglow luminescence activated by temperature that can also have an impact on the increase of the (1)D2 emission. We propose that the afterglow luminescence is related to the existence of electron traps. At a pressure of 76 kbar the depth of the electron traps decreases in comparison to the ones observed at ambient pressure. However, the phase transition does not change the number of electron traps. PMID:24695003

  3. Ultra high energy density nanocomposite capacitors with fast discharge using Ba0.2Sr0.8TiO3 nanowires.

    PubMed

    Tang, Haixiong; Sodano, Henry A

    2013-04-10

    Nanocomposites combining a high breakdown strength polymer and high dielectric permittivity ceramic filler have shown great potential for pulsed power applications. However, while current nanocomposites improve the dielectric permittivity of the capacitor, the gains come at the expense of the breakdown strength, which limits the ultimate performance of the capacitor. Here, we develop a new synthesis method for the growth of barium strontium titanate nanowires and demonstrate their use in ultra high energy density nanocomposites. This new synthesis process provides a facile approach to the growth of high aspect ratio nanowires with high yield and control over the stoichiometry of the solid solution. The nanowires are grown in the cubic phase with a Ba0.2Sr0.8TiO3 composition and have not been demonstrated prior to this report. The poly(vinylidene fluoride) nanocomposites resulting from this approach have high breakdown strength and high dielectric permittivity which results from the use of high aspect ratio fillers rather than equiaxial particles. The nanocomposites are shown to have an ultra high energy density of 14.86 J/cc at 450 MV/m and provide microsecond discharge time quicker than commercial biaxial oriented polypropylene capacitors. The energy density of our nanocomposites exceeds those reported in the literature for ceramic/polymer composites and is 1138% greater than the reported commercial capacitor with energy density of 1.2 J/cc at 640 MV/m for the current state of the art biaxial oriented polypropylene.

  4. Interfacial dislocations in (111) oriented (Ba0.7Sr0.3)TiO3 films on SrTiO3 single crystal

    DOE PAGES

    Shen, Xuan; Yamada, Tomoaki; Lin, Ruoqian; Kamo, Takafumi; Funakubo, Hiroshi; Wu, Di; Xin, Huolin L.; Su, Dong

    2015-10-08

    In this study, we have investigated the interfacial structure of epitaxial (Ba,Sr)TiO3 films grown on (111)-oriented SrTiO3 single-crystal substrates using transmission electron microscopy (TEM) techniques. Compared with the (100) epitaxial perovskite films, we observe dominant dislocation half-loop with Burgers vectors of a<110> comprised of a misfit dislocation along <112>, and threading dislocations along <110> or <100>. The misfit dislocation with Burgers vector of a <110> can dissociate into two ½ a <110> partial dislocations and one stacking fault. We found the dislocation reactions occur not only between misfit dislocations, but also between threading dislocations. Via three-dimensional electron tomography, we retrievedmore » the configurations of the threading dislocation reactions. The reactions between threading dislocations lead to a more efficient strain relaxation than do the misfit dislocations alone in the near-interface region of the (111)-oriented (Ba0.7Sr0.3)TiO3 films.« less

  5. Neutron scattering study of spin ordering and stripe pinning in superconducting La1.93Sr0.07CuO4

    DOE PAGES

    Jacobsen, H.; Zaliznyak, I. A.; Savici, A. T.; Winn, B. L.; Chang, S.; Hücker, M.; Gu, G. D.; Tranquada, J. M.

    2015-11-20

    Tmore » he relationships among charge order, spin fluctuations, and superconductivity in underdoped cuprates remain controversial. We use neutron scattering techniques to study these phenomena in La1.93Sr0.07CuO4 a superconductor with a transition temperature of c = 20 K. At << c, we find incommensurate spin fluctuations with a quasielastic energy spectrum and no sign of a gap within the energy range from 0.2 to 15 meV. A weak elastic magnetic component grows below ~ 10 K, consistent with results from local probes. Regarding the atomic lattice, we have discovered unexpectedly strong fluctuations of the CuO6 octahedra about Cu-O bonds, which are associated with inequivalent O sites within the CuO2 planes. Moreover, we observed a weak elastic (3 ⁻30) superlattice peak that implies a reduced lattice symmetry. he presence of inequivalent O sites rationalizes various pieces of evidence for charge stripe order in underdoped La2-xSrxCuO4. he coexistence of superconductivity with quasi-static spin-stripe order suggests the presence of intertwined orders; however, the rotation of the stripe orientation away from the Cu-O bonds might be connected with evidence for a finite gap at the nodal points of the superconducting gap function.« less

  6. Magnetic field dependence of high- Tc interface superconductivity in La1.55Sr0.45CuO4/La2CuO4 heterostructures

    DOE PAGES

    Gasparov, V. A.; Drigo, L.; Audouard, A.; He, Xi; Božović, I.

    2016-07-11

    Heterostructures made of a layer of a cuprate insulator La2CuO4 on the top of a layer of a nonsuperconducting cuprate metal La1.55Sr0.45CuO4 show high-Tc interface superconductivity confined within a single CuO2 plane. Given this extreme quasi-two-dimensional quantum confinement, it is of interest to find out how interface superconductivity behaves when exposed to an external magnetic field. With this motivation, we have performed contactless tunnel-diode-oscillator-based measurements in pulsed magnetic fields up to 56 T as well as measurements of the complex mutual inductance between a spiral coil and the film in static fields up to 3 T. Remarkably, we observe thatmore » interface superconductivity survives up to very high perpendicular fields, in excess of 40 T. Additionally, the critical magnetic field Hm(T) reveals an upward divergence with decreasing temperature, in line with vortex melting as in bulk superconducting cuprates.« less

  7. Selective electrochemical decomposition of outgrowths and nanopatterning in La0.7Sr0.3MnO3 perovskite thin films

    PubMed Central

    Cavallini, Massimiliano; Graziosi, Patrizio; Calbucci, Marco; Gentili, Denis; Cecchini, Raimondo; Barbalinardo, Marianna; Bergenti, Ilaria; Riminucci, Alberto; Dediu, Valentin

    2014-01-01

    The outgrowth formation in inorganic thin films is a dramatic problem that has limited the technological impact of many techniques and materials. Outgrowths are often themselves part of the films, but are detrimental for vertical junctions since they cause short-circuits or work as defects, compromising the reproducibility and in some cases the operation of the corresponding devices. The problem of outgrowth is particularly relevant in ablation-based methods and in some complex oxides, but is present in a large variety of systems and techniques. Here we propose an efficient local electrochemical method to selectively decompose the outgrowths of conductive oxide thin films by electrochemical decomposition, without altering the properties of the background film. The process is carried out using the same set-up as for local oxidation nanolithography, except for the sign of the voltage bias and it works at the nanoscale both as serial method using a scanning probe and as parallel method using conductive stamps. We demonstrated our process using La0.7Sr0.3MnO3 perovskite as a representative material but in principle it can be extended to many other conductive systems. PMID:25491921

  8. Magnetic and magnetocaloric properties of the first-order phase transition in Sm0.5+ x Sr0.5- x MnO3 compounds

    NASA Astrophysics Data System (ADS)

    Thanh, Tran Dang; Linh, Dinh Chi; Manh, Tien Van; Nan, Wen-Zhe; Yu, Seong-Cho; Piao, Hong-Guang; Pan, Liqing

    2016-08-01

    In this work, we present a detailed study on the magnetic and the magnetocaloric properties of Sm0.5+ x Sr0.5- x MnO3 compounds with x = 0 - 0.1, which were prepared by using a solid-state reaction method. The x-dependent magnetic, as well as magnetocaloric, properties, including the magnetic phase transition, have been studied. The increase in Sm/Sr ratio plays an important role in controlling the Curie temperature ( T C ). We point out that all the samples undergo a first-order phase transition and exhibit a giant magnetocaloric effect. The magnetic entropy change (Δ S m ) of samples was calculated based on isothermal M( H, T) data. The maximum value of Δ S m (denoted as |Δ S max|) at around T C is found to be 2.6 - 8.9 J·kg -1·K -1 for Δ H = 30 kOe and depends on the value of x. We have also used the universal master curve method for the temperature dependences of Δ S m curves measured at different Δ H values, Δ S m ( T,Δ H), to distinguish the magnetic order in the samples. Interestingly, none of the Δ S m ( T,Δ H) curves for the samples follow the universal master curve, Δ S m ( T,Δ H)/Δ S max versus θ = ( T -T C )/( T r - T C ). As a consequence, a breakdown in the universal behavior of Δ S m ( T,Δ H)/Δ S max versus θ curve is another feature confirming a first-order phase-transition nature.

  9. Electrostatic versus Electrochemical Doping and Control of Ferromagnetism in Ion-Gel-Gated Ultrathin La0.5Sr0.5CoO3-δ.

    PubMed

    Walter, Jeff; Wang, Helin; Luo, Bing; Frisbie, C Daniel; Leighton, Chris

    2016-08-23

    Recently, electrolyte gating techniques employing ionic liquids/gels in electric double layer transistors have proven remarkably effective in tuning charge carrier density in a variety of materials. The ability to control surface carrier densities at levels above 10(14) cm(-2) has led to widespread use in the study of superconductivity, insulator-metal transitions, etc. In many cases, controversy remains over the doping mechanism, however (i.e., electrostatic vs electrochemical (e.g., redox-based)), and the technique has been less applied to magnetic materials. Here, we discuss ion gel gating of nanoscale 8-unit-cell-thick hole-doped La0.5Sr0.5CoO3-δ (LSCO) films, probing in detail the critical bias windows and doping mechanisms. The LSCO films, which are under compressive stress on LaAlO3(001) substrates, are metallic and ferromagnetic (Curie temperature, TC ∼ 170 K), with strong anomalous Hall effect and perpendicular magnetic anisotropy. Transport measurements reveal that negative gate biases lead to reversible hole accumulation (i.e., predominantly electrostatic operation) up to some threshold, whereas positive bias immediately induces irreversibility. Experiments in inert/O2 atmospheres directly implicate oxygen vacancies in this irreversibility, supported by atomic force microscopy and X-ray photoelectron spectroscopy. The results are thus of general importance, suggesting that hole- and electron-doped oxides may respond very differently to electrolyte gating. Reversible voltage control of electronic/magnetic properties is then demonstrated under hole accumulation, including resistivity, magnetoresistance, and TC. The sizable anomalous Hall coefficient and perpendicular anisotropy in LSCO provide a particularly powerful probe of magnetism, enabling direct extraction of the voltage-dependent order parameter and TC shift. The latter amounts to ∼7%, with potential for much stronger modulation at lower Sr doping. PMID:27479878

  10. Effect of praseodymium doping on the structural, magnetic and magnetocaloric properties of Sm0.55Sr0.45MnO3 manganite

    NASA Astrophysics Data System (ADS)

    Mleiki, A.; Othmani, S.; Cheikhrouhou-Koubaa, W.; Koubaa, M.; Cheikhrouhou, A.; Hlil, E. K.

    2015-12-01

    The effect of praseodymium doping on the microstructure, magnetic and magnetocaloric effects in Sm0.55-xPrxSr0.45MnO3 (x=0.0 and x=0.1) has been investigated. Our compounds have been elaborated using the conventional solid-state reaction at high temperature. X-Ray diffraction study reveals that our samples crystallize in the distorted orthorhombic system with Pbnm space group. Magnetization measurements M (T) at H=0.05 T were performed and show a paramagnetic (PM) to ferromagnetic (FM) transition with decreasing temperature. Praseodymium doping leads to an increase of the Curie temperature TC from 95 K (x=0.0) to 132 K (x=0.1). Moreover, we observe a small anomaly in the M (T) behavior around 30 K. It has been shown that x=0.1 sample exhibit first order FM-PM phase transition under low magnetic field accompanied by a thermal hysteresis in the field cooled cooling and warming protocols. However, the phase transition from PM to FM is modified from first order to second order above a critical field HC. A metamagnetic behavior has been observed in the M (H) curves around 110 K for x=0.0 and 160 K for x=0.1. The maximum of the magnetic entropy change (- ΔSMmax) was calculated using the isothermal magnetization curves M (H) under magnetic field change of 5 T and is found to be 6.56 J kg-1 K-1 for x=0.0 and 7.14 J kg-1 K-1 for x=0.1. The relative cooling power (RCP) is found to be 222.6 J/Kg and 258.8 J/Kg for x=0.0 and x=0.1, respectively. This suggests that these compounds may be suitable candidates for magnetic refrigeration.

  11. Crystal structure, phase transitions, and magnetic properties of titanium doped La0.5Sr0.5MnO3 perovskites

    NASA Astrophysics Data System (ADS)

    Hazzez, M.; Ihzaz, N.; Boudard, M.; Oumezzine, M.

    2016-04-01

    The current paper investigates the effect of titanium substitution on the structure as well as the magnetic properties of La0.5Sr0.5Mn1-xTixO3 (0≤x≤0.5) polycrystalline powder. The samples studied crystallize in a distorted perovskite structures of tetragonal (space group I4/mcm) symmetry with octahedral tilting scheme (a0a0c-), leading to the absence of octahedral tilting all along two perovskite main directions and to an out-of-phase along the third direction, or rhombohedral (space group R 3 bar c) symmetry with octahedral tilting scheme (a-a-a-) yielding to out-of-phase along the three perovskite main directions. As the Ti content increases, a better matching of the (Mn/Ti)-O distances and (Mn/Ti)-O-(Mn/Ti) bond angle occurs. This phenomenon is created by an elongation of the (Mn/Ti)-O distance, as Mn4+ is substituted by the larger ion Ti4+. In the whole compositional range, the symmetry-adapted to atomic displacements, responsible for the out-of-phase tilting of the (Mn/Ti)O6 octahedra, stays active, anticipating tetragonal-to-rhombohedral phase transition. Taking in to account what has been explained above, measurements of magnetic properties show a decrease of magnetic ordering temperature when Ti content increases, which in turn leads to the diminution of the exchange interaction caused by reducing the FM coupling and the replacement of neighboring manganese Mn3+-O-Mn4+ by Mn3+-O-Ti4+ bonds. This phenomenon results in broadening of the paramagnetic to ferromagnetic phase transition range. Further changes in magnetic properties with the increase in Ti concentration are studied.

  12. Preparation Process and Dielectric Properties of Ba(0.5)Sr(0.5)TiO3-P(VDF-CTFE) Nanocomposites

    NASA Technical Reports Server (NTRS)

    Zhang, Lin; Wu, Peixuang; Li, Yongtang; Cheng, Z. -Y.; Brewer, Jeffrey C.

    2014-01-01

    Ceramic-polymer 0-3 nanocomposites, in which nanosized Ba(0.5)Sr(0.5)TiO3 (BST) powders were used as ceramic filler and P(VDF-CTFE) 88/12 mol% [poly(vinylidene fluoridechlorotrifluoroethylene)] copolymer was used as matrix, were studied over a concentration range from 0 to 50 vol.% of BST powders. It is found that the solution cast composites are porous and a hot-press process can eliminate the porosity, which results in a dense composite film. Two different configurations used in the hot-press process are studied. Although there is no clear difference in the uniformity and microstructure of the composites prepared using these two configurations, the composite prepared using one configuration exhibit a higher dielectric constant with a lower loss. For the composite with 40 vol. BST, a dielectric constant of 70 with a loss of 0.07 at 1 kHz is obtained at room temperature. The composites exhibit a lower dielectric loss than the polymer matrix at high frequency. However, at low frequency, the composites exhibit a higher loss than the polymer matrix due to a low frequency relaxation process that appears in the composites. It is believed that this relaxation process is related to the interfacial layer formed between BST particle and the polymer matrix. The temperature dependence of the dielectric property of the composites was studied. It is found that the dielectric constant of these composites is almost independent of the temperature over a temperature range from 20 to 120 C. Key words: A. Polymer-matrix composites (PMCs); B. Electrical Properties; E. Casting; E. Heat treatment; Dielectric properties.

  13. Tuning the optical, electrical and magnetic properties of Ba(0.5)Sr(0.5)Ti(x)M(1-x)O3 (BST) nanopowders.

    PubMed

    Turky, Ali Omar; Rashad, Mohamed Mohamed; Kandil, Abd El-Hakim Taha; Bechelany, Mikhael

    2015-05-21

    Metal doped barium strontium titanate (BST; Ba0.5Sr0.5TixM1-xO3) nanopowders have been successfully synthesized through the oxalate precursor route based on low cost starting materials. The effect of metal ion substitution, namely Fe(3+), Mn(2+), Co(2+) and Y(3+), on the crystal structure, microstructure and optical, electrical, dielectric and magnetic properties of BST was studied. The results revealed that a crystalline single cubic BST phase was formed for pure and Mn(2+), Co(2+) and Y(3+) ion-substituted BST samples, whereas a tetragonal BST structure was obtained for the Fe(3+) substituted BST sample at an annealing temperature of 1000 °C for 2 h. Furthermore, addition of the metal ions was found to decrease the crystallite size and unit cell volume of the produced BST phase. The microstructure of the produced pure BST phase was metal ion dependent. Most BST particles appeared as a cubic like structure. The transparency of BST was found to increase with metal substitution. Meanwhile, the band gap energy was increased from 3.4 eV for pure BST to 3.8, 4.1, 4.2 and 4.3 eV as the result of substitution by Fe(3+), Mn(2+) and Co(2+) and Y(3+) ions, respectively. The DC resistivity was metal ion dependent. The highest DC resistivity (ρ = 66.60 × 10(5) Ω cm) was accomplished with the Mn(2+) ion. Moreover, the addition of metal ions decreased the dielectric properties of the expected Mn(2+) ion and increased the magnetic properties.

  14. Improved electrochemical stability at the surface of La(0.8)Sr(0.2)CoO3 achieved by surface chemical modification.

    PubMed

    Tsvetkov, Nikolai; Lu, Qiyang; Yildiz, Bilge

    2015-01-01

    The degradation of the surface chemistry on perovskite (ABO3) oxides is a critical issue for their performance in energy conversion systems such as solid oxide fuel/electrolysis cells and in splitting of H2O and CO2 to produce fuels. This degradation is typically in the form of segregation and phase separation of dopant cations from the A-site, driven by elastic and electrostatic energy minimization and kinetic demixing. In this study, deposition of Ti at the surface was found to hinder the dopant segregation and the corresponding electrochemical degradation on a promising SOFC cathode material, La(0.8)Sr(0.2)CoO3 (LSC). The surface of the LSC films was modified by Ti (denoted as LSC-T) deposited from a TiCl4 solution. The LSC and LSC-T thin films were investigated by electrochemical impedance spectroscopy, nano-probe Auger electron spectroscopy, and X-ray photoelectron spectroscopy (XPS), upon annealing at 420-530 °C in air up to about 90 hours. The oxygen exchange coefficient, k(q), on LSC-T cathodes was found to be up to 8 times higher than that on LSC cathodes at 530 °C and retained its stability. Sr-rich insulating particles formed at the surface of the annealed LSC and LSC-T films, but with significantly less coverage of such particles on the LSC-T. From this result, it appears that modification of the LSC surface with Ti reduces the segregation of the blocking Sr-rich particles at the surface, and a larger area on LSC surface (with a higher Sr doping level in the lattice) is available for the oxygen reduction reaction. The stabilization of the LSC surface through Ti-deposition can open a new route for designing surface modifications on perovskite oxide electrodes for high temperature electro- and thermo-chemical applications. PMID:26227310

  15. Structure, magnetic and electrical transport properties of the perovskites La0.67-xEuxSr0.33MnO3

    NASA Astrophysics Data System (ADS)

    Dhahri, Neila; Dhahri, Abdessalem; Dhahri, Jemai; Hlil, El-kebir; Dhahri, Essebti

    2013-01-01

    In this paper we report the structural, magnetic and electrical properties of a series of nanocrystalline La0.67-xEuxSr0.33MnO3 (0≤x≤0.3) materials which were prepared by the solid-state reaction method in air. The X-ray powder diffraction has shown that all our synthesized samples are a single phase and have crystallized in the hexagonal symmetry with R3barC space group. The scanning electron microscopy has shown smooth and densified structures, clean and pure images. Electric and magnetic measurements show that all our samples had exhibited a ferromagnetic to paramagnetic transition and a metallic to semiconductor one when temperature increases. The substitution of La3+ by Eu3+ leads to a continuously simultaneous decrease of the Curie temperature TC (from 350 K for x=0.0-258 K for x=0.3) and the metal-semi-conductor transition temperature Tp (from 310 K for x=0.0-224 K for x=0.3). The electrical resistivity data were analyzed using different theoretical models and it has been concluded that at low temperatures (ferromagnetic metallic region) the resistivity may originate from grain/domain boundary, electron-electron scattering and two-magnon scattering effects. While in the paramagnetic insulating regime, the variation of resistivity with temperature may be explained by adiabatic small polaron Hopping mechanism and variable-range hopping mechanisms. The values of activation energies were found decreasing, while the density of states at the Fermi-level, N (EF) was increasing with decreasing . A suitable explanation for the observed behavior is given.

  16. Novel microstructural strategies to enhance the electrochemical performance of La0.8Sr0.2MnO3-δ cathodes.

    PubMed

    Dos Santos-Gómez, L; Losilla, E R; Martín, F; Ramos-Barrado, J R; Marrero-López, D

    2015-04-01

    Novel strategies based on spray-pyrolysis deposition are proposed to increase the triple-phase boundary (TPB) of La0.8Sr0.2MnO3-δ (LSM) cathodes in contact with yttria-stabilized zirconia (YSZ) electrolyte: (i) nanocrystalline LSM films deposited on as-prepared YSZ surface; (ii) the addition of poly(methyl methacrylate) microspheres as pore formers to further increase the porosity of the film cathodes; and (iii) the deposition of LSM by spray pyrolysis on backbones of Zr0.84Y0.16O1.92 (YSZ), Ce0.9Gd0.1O1.95 (CGO), and Bi1.5Y0.5O3-δ (BYO) previously fixed onto the YSZ. This last method is an alternative to the classical infiltration process with several advantages for large-scale manufacturing of planar solid oxide fuel cells (SOFCs), including easier industrial implementation, shorter preparation time, and low cost. The morphology and electrochemical performance of the electrodes are investigated by scanning electron microscopy and impedance spectroscopy. Very low values of area specific resistance are obtained, ranging from 1.4 Ω·cm(2) for LSM films deposited on as-prepared YSZ surface to 0.06 Ω-cm(2) for LSM deposited onto BYO backbone at a measured temperature of 650 °C. These electrodes exhibit high performance even after annealing at 950 °C, making them potentially suitable for applications in SOFCs at intermediate temperatures.

  17. Novel microstructural strategies to enhance the electrochemical performance of La0.8Sr0.2MnO3-δ cathodes.

    PubMed

    Dos Santos-Gómez, L; Losilla, E R; Martín, F; Ramos-Barrado, J R; Marrero-López, D

    2015-04-01

    Novel strategies based on spray-pyrolysis deposition are proposed to increase the triple-phase boundary (TPB) of La0.8Sr0.2MnO3-δ (LSM) cathodes in contact with yttria-stabilized zirconia (YSZ) electrolyte: (i) nanocrystalline LSM films deposited on as-prepared YSZ surface; (ii) the addition of poly(methyl methacrylate) microspheres as pore formers to further increase the porosity of the film cathodes; and (iii) the deposition of LSM by spray pyrolysis on backbones of Zr0.84Y0.16O1.92 (YSZ), Ce0.9Gd0.1O1.95 (CGO), and Bi1.5Y0.5O3-δ (BYO) previously fixed onto the YSZ. This last method is an alternative to the classical infiltration process with several advantages for large-scale manufacturing of planar solid oxide fuel cells (SOFCs), including easier industrial implementation, shorter preparation time, and low cost. The morphology and electrochemical performance of the electrodes are investigated by scanning electron microscopy and impedance spectroscopy. Very low values of area specific resistance are obtained, ranging from 1.4 Ω·cm(2) for LSM films deposited on as-prepared YSZ surface to 0.06 Ω-cm(2) for LSM deposited onto BYO backbone at a measured temperature of 650 °C. These electrodes exhibit high performance even after annealing at 950 °C, making them potentially suitable for applications in SOFCs at intermediate temperatures. PMID:25793738

  18. Dual-templating synthesis of three-dimensionally ordered macroporous La(0.6)Sr(0.4)MnO3-supported Ag nanoparticles: controllable alignments and super performance for the catalytic combustion of methane.

    PubMed

    Arandiyan, Hamidreza; Dai, Hongxing; Deng, Jiguang; Wang, Yuan; Xie, Shaohua; Li, Junhua

    2013-11-25

    Highly dispersed Ag nanoparticles supported on high-surface-area 3DOM La0.6Sr0.4MnO3 were successfully generated via the dimethoxytetraethylene glycol-assisted gas bubbling reduction route. The macroporous materials showed super catalytic performance for methane combustion.

  19. Catalytic properties of La0.8Sr0.2Co0.5M0.5O3 (M Co, Ni, Cu) in methane combustion1

    NASA Astrophysics Data System (ADS)

    Yue-Hui, Wu; Lai-Tao, Luo; Wei, Liu

    2010-03-01

    A set of perovskite-type catalysts of general formula La0.8Sr0.2Co0.5M0.5O3 (M = Co, Ni, Cu) were prepared by alanine solution combustion method and used successfully for the methane combustion. The property of these materials were characterized by XRD, and TPR measurements. The effects of transition-metal ions on site B on structure and performance of the catalysts were studied. The result indicated that the structure and catalytic activities of the catalysts can remarkably affect by transition-metal ions on site B, the decrease of the electrons filled in d orbitals in the atom on site B is propitious to increase the catalytic activity for methane combustion, and the sequences of catalysts activities are La0.8Sr0.2CoO3 τ; Ce0.8Sr0.2CoO3 τ; Nd0.8Sr0.2CoO3.

  20. Effect of La0.1Sr0.9Co0.5Mn0.5O3-δ protective coating layer on the performance of La0.6Sr0.4Co0.8Fe0.2O3-δ solid oxide fuel cell cathode

    NASA Astrophysics Data System (ADS)

    Chou, Ping-Yi; Ciou, Chun-Jing; Lee, Yu-Chen; Hung, I.-Ming

    2012-01-01

    This study investigates the interface reactivity between La0.1Sr0.9Co0.5Mn0.5O3-δ (LSCM) protective coating layer and Crofer22H interconnects. Additionally, we report the mechanism of Cr poisoning of the La0.6Sr0.4Co0.8Fe0.2O3-δ (LSCF) cathode's electrochemical properties. The phase, chemical composition, and element distribution of compounds formed at the LSCM-Crofer22H interface are analyzed by X-ray diffraction (XRD) and electron dispersive microscopy (EDS). After heat treatment at 800 °C for 100 h, the LSCM/Crofer22H sample contains SrCrO3, a compound with good conductivity; the area specific resistance (ASR) for the LSCM/Crofer22H interconnect is approximately 17-40 mΩ cm2. We found that the amount of (Mn0.98Fe0.02)(Mn0.02Fe0.48Cr1.5)O4, Cr3O4, and (Fe,Cr)2O3 oxides form in LSCF/LSCM/Crofer22H is significantly less than that in LSCF/Crofer22H. LSCF conductivity after heating at 800 °C for 100 h, is notably higher when in contact with LSCM/Crofer22H than it is when in contact with Crofer22H. These results demonstrate that the LSCM protective coating prevents LSCF cathode poisoning by Cr evaporated from the Corfer22H interconnects.

  1. In-plane strain modulated magnetization and magnetoelectric effect in La0.7Sr0.3MnO3-BaTiO3 and La0.7Sr0.3MnO3-BaTiO3-BiFeO3 multilayer's

    NASA Astrophysics Data System (ADS)

    Kumar, Virendra; Gaur, Anurag; Chaudhury, Ram Janay; Kumar, Dileep

    2016-10-01

    La0.7Sr0.3MnO3-BaTiO3(LSMO/BTO) and La0.7Sr0.3MnO3-BaTiO3-BiFeO3 (LSMO/BTO/BFO) multilayer thin films are deposited on STO (100) substrate by pulsed laser deposition. In-plane lattice mismatch induced strain is thoroughly investigated with the conclusion, that upper BTO layer of bilayer resides in high strained state, while upper BFO layer of trilayer remains under partially relaxed state. Significantly higher value (∼20) of dielectric constant is observed for LSMO/BTO bilayer in compliance with its higher (12.28 μC/cm2) in-plane strain induced interfacial polarization, which exceeds (2.06 μC/cm2), the observed value of polarization for LSMO/BTO/BFO trilayer. In LSMO/BTO bilayer, antiferromagnetic LSMO phase coexists due to the existence of strong tensile strain between the interfaces, which causes the reduction in value of saturation magnetization up to 50.76 emu/cm3 in comparison to 145.01 emu/cm3 for LSMO/BTO/BFO trilayer. The maximum value of linear magnetoelectric coefficient (α31) observed for LSMO/BTO bilayer is 24.77 mV/cm-Oe, which is higher in comparison to 19.54 mV/cm-Oe for LSMO/BTO/BFO trilayer, where the upper layer undergoes less strain in comparison to the bilayer.

  2. Enhanced Magnetocaloric Effect Driven by Interfacial Magnetic Coupling in Self-Assembled Mn3O4-La(0.7)Sr(0.3)MnO3 Nanocomposites.

    PubMed

    Vandrangi, Suresh K; Yang, Jan-Chi; Zhu, Yuan-Min; Chin, Yi-Ying; Lin, Hong-Ji; Chen, Chien-Te; Zhan, Qian; He, Qing; Chen, Yi-Chun; Chu, Ying-Hao

    2015-12-01

    Magnetic refrigeration, resulting from the magnetocaloric effect of a material around the magnetic phase-transition temperature, is a topic of great interest as it is considered to be an alternate energy solution to conventional vapor-compression refrigeration. The viability of a magnetic refrigeration system for magnetic cooling can be tested by exploiting materials in various forms, from bulk to nanostrucutres. In this study, magnetocaloric properties of self-assembled Mn3O4-La(0.7)Sr(0.3)MnO3 nanocomposites, with varying doping concentrations of Mn3O4 in the form of nanocrystals embedded in the La(0.7)Sr(0.3)MnO3 matrix, are investigated. The temperatures corresponding to the paramagnetic-to-ferromagnetic transitions are higher, and the values of change in magnetic entropy under a magnetic field of 2 T show an enhancement (highest being ∼130%) for the nanocomposites with low doping concentrations of Mn3O4, compared to that of pure La(0.7)Sr(0.3)MnO3 thin films. Relative cooling power remain close to those of La(0.7)Sr(0.3)MnO3. The enhanced magnetic phase-transition temperature and magnetocaloric effect are interpreted and evidenced in the framework of interfacial coupling between Mn3O4 and La(0.7)Sr(0.3)MnO3. This work demonstrates the potentiality of self-assembled nanostructures for magnetic cooling near room temperature under low magnetic fields. PMID:26574919

  3. Structure, Crystallographic Sites, and Tunable Luminescence Properties of Eu(2+) and Ce(3+)/Li(+)-Activated Ca1.65Sr0.35SiO4 Phosphors.

    PubMed

    Xia, Zhiguo; Miao, Shihai; Chen, Mingyue; Molokeev, Maxim S; Liu, Quanlin

    2015-08-17

    Eu(2+) and Ce(3+)/Li(+) singly doped and Eu(2+)/Ce(3+)/Li(+)-codoped Ca1.65Sr0.35SiO4 phosphors have been synthesized by a solid-state reaction method. The crystal structure was determined by Rietveld refinement to verify the formation of the αL′-Ca2SiO4 phase with the Sr addition into Ca2SiO4, and the preferred crystallographic positions of the Eu(2+) and Ce(3+)/Li(+) ions in Ca1.65Sr0.35SiO4 were analyzed based on a comparison of the unit-cell volumes and the designed chemical compositions of undoped isostructural compounds Ca(2–x)Sr(x)SiO4 (x = 0.25, 0.35, 0.45, 0.55 and 0.65). Ce(3+)/Li(+) singly activated Ca1.65Sr0.35SiO4 phosphors exhibit strong absorption in the range of 250–450 nm and a blue emission peak centered at about 465 nm. When Eu(2+) ions are codoped, the emission colors of Ca1.65Sr0.35SiO4:Ce(3+)/Li(+),Eu(2+) phosphors under the irradiation of 365 nm can be finely tuned from blue to green through the energy transfer from Ce(3+) to Eu(2+). The involved energy-transfer process between Ce(3+) and Eu(2+) and the corresponding mechanism are discussed in detail. The reported Ca1.65Sr0.35SiO4:Ce(3+)/Li(+),Eu(2+) phosphor might be a candidate for color-tunable blue-green components in the fabrication of near-ultraviolet-pumped white-light-emitting diodes (WLEDs). PMID:26062769

  4. In situ formation of oxygen vacancy in perovskite Sr(0.95)Ti(0.8)Nb(0.1)M(0.1)O3 (M = Mn, Cr) toward efficient carbon dioxide electrolysis.

    PubMed

    Zhang, Jun; Xie, Kui; Wei, Haoshan; Qin, Qingqing; Qi, Wentao; Yang, Liming; Ruan, Cong; Wu, Yucheng

    2014-11-18

    In this work, redox-active Mn or Cr is introduced to the B site of redox stable perovskite Sr(0.95)Ti(0.9)Nb(0.1)O3.00 to create oxygen vacancies in situ after reduction for high-temperature CO2 electrolysis. Combined analysis using X-ray diffraction, X-ray photoelectron spectroscopy, transmission electron microscopy and thermogravimetric analysis confirms the change of the chemical formula from oxidized Sr(0.95)Ti(0.9)Nb(0.1)O3.00 to reduced Sr(0.95)Ti(0.9)Nb(0.1)O2.90 for the bare sample. By contrast, a significant concentration of oxygen vacancy is additionally formed in situ for Mn- or Cr-doped samples by reducing the oxidized Sr(0.95)Ti(0.8)Nb(0.1)M(0.1)O3.00 (M = Mn, Cr) to Sr(0.95)Ti(0.8)Nb(0.1)M0.1O2.85. The ionic conductivities of the Mn- and Cr-doped titanate improve by approximately 2 times higher than bare titanate in an oxidizing atmosphere and 3-6 times higher in a reducing atmosphere at intermediate temperatures. A remarkable chemical accommodation of CO2 molecules is achieved on the surface of the reduced and doped titanate, and the chemical desorption temperature reaches a common carbonate decomposition temperature. The electrical properties of the cathode materials are investigated and correlated with the electrochemical performance of the composite electrodes. Direct CO2 electrolysis at composite cathodes is investigated in solid-oxide electrolyzers. The electrode polarizations and current efficiencies are observed to be significantly improved with the Mn- or Cr-doped titanate cathodes.

  5. Dielectric properties of Ba0.6Sr0.4TiO3-Sr(Ga0.5Ta0.5)O3 solid solutions.

    PubMed

    Xu, Yebin; Liu, Ting; He, Yanyan; Yuan, Xiao

    2008-11-01

    Ba(0.6)Sr(0.4)TiO(3)-Sr(Ga(0.5)Ta(0.5))O(3) solid solutions are prepared by a solid-state reaction method, and their dielectric and tunable characteristics are investigated. The solid solutions with cubic perovskite structures are obtained for compositions of 10-50 mol% Sr(Ga(0.5)Ta(0.5))O(3). It is observed that the addition of Sr(Ga(0.5)Ta(0.5))O(3) into Ba(0.6)Sr(0.4)TiO(3) causes a shift in the phase transition peak to a lower temperature. Ba(0.6)Sr(0.4)TiO(3)-Sr(Ga(0.5)Ta(0.5))O(3) solid solutions exhibit depressed and broadened phase transition peaks, resulting in decreased dielectric constants and dielectric losses at room temperature. With the increase of Sr(Ga(0.5)Ta(0.5))O(3) content, the dielectric constant, loss tangent, and tunability are decreased. 0.9Ba(0.6)Sr(0.4)TiO(3)-0.1Sr(Ga(0.5)Ta(0.5))O(3) has a dielectric constant epsilon = 534 and a tunability of 16% at 100 kHz under 2.63 kV/mm. The dielectric characteristics of Ba(0.6)Sr(0.4)TiO(3)-Sr(Ga(0.5)Ta(0.5))O(3) ceramics at microwave frequencies are also evaluated.

  6. Spin dynamics in the La1.85Sr0.15Cu1-xFexO4 system probed by ESR

    NASA Astrophysics Data System (ADS)

    Cieplak, Marta Z.; Sienkiewicz, A.; Mila, F.; Guha, S.; Xiao, Gang; Xiao, J. Q.; Chien, C. L.

    1993-08-01

    We study the magnetic properties of the La1.85Sr0.15Cu1-xFexO4 system (x=0-0.1) in the vicinity of the metal-insulator (MI) transition using static-susceptibility measurements and the electron-spin resonance (ESR) of the Fe ions. Spin-glass (SG) freezing is present for all nonsuperconducting specimens. The iron ESR line broadens on approaching the freezing temperature, similarly to the effect observed in canonical spin glasses. This broadening can be attributed to the influence of the slowing down of spin fluctuations on the spin-spin relaxation rate. It depends differently on x on the two different sides of the MI transition suggesting the existence of two different SG phases: insulating (ISG) where the Fe spins couple to the Cu-spin array by superexchange interactions, and metallic (MSG), where there exists, in addition, Ruderman-Kittel-Kasuya-Yosida-like coupling mediated by the free carriers. The proximity of the MI transition suppresses this coulping, giving rise to the observed dependence of the paramagnet -SG phase boundary on x. In the MSG phase, at high temperatures, the spin-lattice relaxation mechanism is also mediated by the free carriers. It differs from the analogous process observed in conventional metals in that the ESR linewidth increases with increasing T faster than linearly. We explain this behavior by assuming that the effective magnetic field felt by the Fe moments originates mainly from the spins of holes located on the nearest-neighbor oxygen ions. The linewidth divided by T which probes the dynamical susceptibility at the Fe site varies as a+bT. Here a goes to zero as the MI transition is approached and so plays the role of the Pauli susceptibility of the free carriers, whereas b is independent of x in the vicinity of the MI transition but decreases for small Fe dopings away from the MI transition and may be identified as originating from the antiferromagnetic spin fluctuations in the system.

  7. Synthesis and characterization of La0.75Sr0.25Mn0.5Cr0.2Ti0.3O3 Anodes for SOFCs

    NASA Astrophysics Data System (ADS)

    Karim, A. H.; Afif, A.; Begum, F.; Petra, P. I.; Azad, A. K.

    2016-03-01

    La0.75Sr0.25Mn0.5Cr0.2Ti0.3O3 has been synthesized in solid state reaction method and tested as a potential anode material for solid oxide fuel cells. Rietveld refinement of X-ray powder diffraction data of the composition using Fullprof software shows that the materials crystallize in the rhombohedral symmetry in the R-3C space group. The cell parameters are: a = b = 5.5143 (4) Å, c = 13.452(1) Å, α = β = 90°, δ = 120°. Addition of titanium to the B-site of La0.75Sr0.25Mn0.5Cr0.2Ti0.3O3-δ yields a total conductivity of 1.96 Scm-1 in air at 800 °C with activation energy of 1.02 eV.

  8. Microwave dielectric properties of BaTiO3 and Ba0.5Sr0.5TiO3 thin films on (001) MgO

    NASA Astrophysics Data System (ADS)

    Alldredge, L. M. B.; Chang, Wontae; Kirchoefer, Steven W.; Pond, Jeffrey M.

    2009-11-01

    The microwave properties of BaTiO3 and Ba0.5Sr0.5TiO3 films were characterized as a function of in-plane film strain, crystallographic direction, film distortion, and dc bias. The strain dependence of BaTiO3 and Ba0.5Sr0.5TiO3 films showed an opposite pattern at room temperature, going from compression to tension, or vice versa. At zero bias, the dielectric constant and dielectric loss showed little dependence on direction ([100] and [110]). However, the tunability was consistently smaller along the [110] direction than along [100]. These observations agreed well with our previous work on how polarizations (both ionic and spontaneous) form and contribute to the nonlinear dielectric behavior.

  9. Nanostructured Gd 0.8Sr 0.2Fe 0.8M 0.2O 3 (M=Cr, Ga) materials for solid oxide fuel cell cathodes

    NASA Astrophysics Data System (ADS)

    Ruiz de Larramendi, I.; Pinedo, R.; Ortiz-Vitoriano, N.; Ruiz de Larramendi, J. I.; Arriortua, M. I.; Rojo, T.

    Polycrystalline samples of Gd0.8Sr0.2Fe0.8M0.2O3 (M=Cr, Ga) are prepared by combustion route and pore wetting technique in order to compare the influence of the morphology in the performance of two cathodes for Solid Oxide Fuel Cells. When polycarbonate membranes are used as templates nanowire arrays with a diameter of 50-70 nm are obtained. Comparing the results obtained by Electrochemical Impedance Spectroscopy (EIS) measurements, it is clearly observed that the cathodic resistance considerably decreases when optimized synthesis parameters are used, obtaining a better performance for the Gd0.8Sr0.2Fe0.8Ga0.2O3 nanowires with an area specific resistance (ASR) value at 850 ∘C of 0.195 Ω cm2.

  10. Effect of YBa2Cu3O7-δ film thickness on the dielectric properties of Ba0.1Sr0.9TiO3 in Ag /Ba0.1Sr0.9TiO3/YBa2Cu3O7-δ/LaAlO3 multilayer structures

    NASA Astrophysics Data System (ADS)

    Zhu, Xiaohong; Peng, Wei; Li, Jie; Chen, Yingfei; Tian, Haiyan; Xu, Xiaoping; Zheng, Dongning

    2005-01-01

    Ferroelectric and superconductor bilayers of Ba0.1Sr0.9TiO3 (BSTO)/YBa2Cu3O7-δ (YBCO), with different YBCO film thicknesses, have been fabricated in situ by pulsed-laser deposition on 1.2° vicinal LaAlO3 substrates. The dielectric properties of BSTO thin films were measured with a parallel-plate capacitor configuration in the temperature range of 77-300K. We observed a strong dependence of the dielectric properties of BSTO thin films on the thickness of the YBCO layer. As the YBCO-film thickness increases, the temperature of the dielectric permittivity maximum of BSTO thin films shifts to higher values, and the leakage current and dielectric loss increase drastically, while the dielectric constant and dielectric tunability decrease remarkably. The results are explained in terms of the transformation in the growth mode of the YBCO layer from two-dimensional step flow to three-dimensional island that leads to significant deterioration in the dielectric properties of BSTO thin films. We propose that improved dielectric properties could be obtained by reasonably manipulating the growth mode of the YBCO layer in the multilayer structures.

  11. Signatures of a two-dimensional ferromagnetic electron gas at the La0.7Sr0.3MnO3/SrTiO3 interface arising from orbital reconstruction.

    PubMed

    Nemes, Norbert Marcel; Calderón, María José; Beltrán, Juan Ignacio; Bruno, Flavio Yair; García-Barriocanal, Javier; Sefrioui, Zouhair; León, Carlos; García-Hernández, Mar; Muñoz, María Carmen; Brey, Luis; Santamaría, Jacobo

    2014-11-26

    The magnetoresistance of La0.7Sr0.3MnO3/SrTiO3 superlattices with magnetic field rotating out-of-plane shows unexpected peaks for in-plane fields. Resistivity calculations with spin-orbit coupling reveal that orbital reconstruction at the manganite interface leads to a 2D ferromagnetic electron gas coupled antiparallel to the manganite "bulk". These orbital and magnetic reconstructions are supported by X-ray linear dichroism and ab initio calculations.

  12. Density functional theory + U analysis of the electronic structure and defect chemistry of LSCF (La0.5Sr0.5Co0.25Fe0.75O3-δ).

    PubMed

    Ritzmann, Andrew M; Dieterich, Johannes M; Carter, Emily A

    2016-04-28

    Reducing operating temperatures is a key step in making solid oxide fuel cell (SOFC) technology viable. A promising strategy for accomplishing this goal is employing mixed ion-electron conducting (MIEC) cathodes. La1-xSrxCo1-yFeyO3-δ (LSCF) is the most widely employed MIEC cathode material; however, rational optimization of the composition of LSCF requires fundamental insight linking its electronic structure to its defect chemistry. To provide the necessary insight, density functional theory plus U (DFT+U) calculations are used to investigate the electronic structure of LSCF (xSr = 0.50, yCo = 0.25). The DFT+U calculations show that LSCF has a significantly different electronic structure than La1-xSrxFeO3 because of the addition of cobalt, but that minimal electronic structure differences exist between La0.5Sr0.5Co0.25Fe0.75O3 and La0.5Sr0.5Co0.5Fe0.5O3. The oxygen vacancy formation energy (ΔEf,vac) is calculated for residing in different local environments within La0.5Sr0.5Co0.25Fe0.75O3. These results show that configurations have the highest ΔEf,vac, while have the lowest ΔEf,vac and may act as traps for . We conclude that compositions with more Fe than Co are preferred because the additional sites would lead to higher overall ΔEf,vac (and lower concentrations), while the trapping strength of the sites is relatively weak (∼0.3 eV).

  13. Phase diagram and high density two-dimensional electron gas at the LaAlO3/ La0.5Sr0.5TiO3/SrTiO3 heterostructures

    NASA Astrophysics Data System (ADS)

    Ma, Haijiao; Huang, Zhen; Zeng, Shengwei; Annadi, Anil; Venkatesan, Thirumalai Venky; Ariando, Ariando

    2015-03-01

    We report a two dimensional electron gas with a high carrier density at the LaAlO3/La0.5Sr0.5TiO3/SrTiO3 heterostructures, reaching a value of about five times higher than that observed at the LaAlO3/SrTiO3 interface. The La0.5Sr0.5TiO3 polar layer is introduced to preserve the degeneracy of the Ti t2g orbitals and minimize the disorder at the La0.5Sr0.5TiO3/SrTiO3 interface. Various thickness combinations of La0.5Sr0.5TiO3and LaAlO3 layers are used for tuning the total internal potential of the polar layer responsible for the charge transfer. Experimental data showed that the carrier density increases by raising the total internal potential, and this is in a good agreement with a simple electrostatic model. A complete metal-insulator phase diagram is obtained, which shows that at least 3.15 eV polar potential is needed to form the metallic interface at the SrTiO3, providing an estimate for the critical thickness needed for the metallic phase. Nonlinear Hall effect was observed below 60 K which can be understood by multiple filling of the degenerated orbitals responsible for multiple band electronic conductions. Ariando Research Group is part of Department of Physics and of NUSNNI-NanoCore, the inter-faculty and multidisciplinary Nano-Institute at the National University of Singapore.

  14. Modification of energy band alignment and electric properties of Pt/Ba0.6Sr0.4TiO3/Pt thin-film ferroelectric varactors by Ag impurities at interfaces

    NASA Astrophysics Data System (ADS)

    Hirsch, S.; Komissinskiy, P.; Flege, S.; Li, S.; Rachut, K.; Klein, A.; Alff, L.

    2014-06-01

    We report on the effects of Ag impurities at interfaces of parallel-plate Pt/Ba0.6Sr0.4TiO3/Pt thin film ferroelectric varactors. Ag impurities occur at the interfaces due to diffusion of Ag from colloidal silver paint used to attach the varactor samples with their back side to the plate heated at 600-750 °C during deposition of Ba0.6Sr0.4TiO3. X-ray photoelectron spectroscopy and secondary ion mass spectrometry suggest that amount and distribution of Ag adsorbed at the interfaces depend strongly on the adsorbent surface layer. In particular, Ag preferentially accumulates on top of the Pt bottom electrode. The presence of Ag significantly reduces the barrier height between Pt and Ba0.6Sr0.4TiO3 leading to an increased leakage current density and, thus, to a severe degradation of the varactor performance.

  15. Influence of Cr deficiency on sintering, thermal expansion and electrical properties of La0.75Sr0.25Cr1-xO3-δ as a SOFC interconnect material

    NASA Astrophysics Data System (ADS)

    Ren, Yi; Ma, Wen; Li, Xiaoying; Wang, Jun; Bai, Yu; Dong, Hongying

    2016-04-01

    The SOFC interconnect materials La0.75Sr0.25Cr1-xO3-δ (x = 0-0.04) were prepared using an auto-ignition process. The influences of Cr deficiency on their sintering, thermal expansion and electrical properties were investigated. All the samples were pure perovskite phase after sintering at 1400∘C for 4 h. The cell volume of La0.75Sr0.25Cr1-xO3-δ decreased with increasing Cr deficient content. The relative density of the sintered bulk samples increased from 93.2% (x = 0) to a maximum value of 94.7% (x = 0.02) and then decreased to 87.7% (x = 0.04). The thermal expansion coefficients of the sintered bulk samples were in the range of 10.60-10.98 × 10-6K-1 (30-1000∘C), which are compatible with that of YSZ. Among the investigated samples, the sample with 0.02 Cr deficiency had a maximum conductivity of 40.4 Scm-1 and the lowest Seebeck coefficient of 154.8 μVK-1 at 850∘C in pure He. The experimental results indicate that La0.75Sr0.25Cr0.98O3-δ has the best properties and is much suitable for SOFC interconnect material application.

  16. Microstructure and Microwave Dielectric Properties of (1- x)MgAl2O4- x(Ca0.8Sr0.2)TiO3 Ceramics

    NASA Astrophysics Data System (ADS)

    Huang, Yafei; Yu, Jun; Shen, Chunying; Tang, Mingliang

    2016-10-01

    The microwave dielectric properties of the (1- x)MgAl2O4- x(Ca0.8Sr0.2)TiO3 ( x = 0.02 to 0.10) ceramic system synthesized by the traditional solid-state reaction method have been investigated. Spinel-structured MgAl2O4 was present together with perovskite-structured (Ca0.8Sr0.2)TiO3, and this multiphase system was verified by x-ray diffraction (XRD) and energy spectrum analyses throughout the whole compositional range. With increasing x, the temperature coefficient of resonant frequency ( τ f) and permittivity ( ɛ r) gradually increased. Consequently, near-zero τ f could be obtained for samples with x = 0.08. Excellent microwave dielectric properties with relative permittivity ( ɛ r) of 10.92, quality factor ( Q × f) of 52,563 GHz (at 12.9 GHz), and temperature coefficient of resonant frequency ( τ f) of -5.6 ppm/°C were obtained for 0.92MgAl2O4-0.08(Ca0.8Sr0.2)TiO3 composite sintered at 1440°C for 3 h, making this material a promising candidate for use in global communication satellites and radar detectors.

  17. Cobalt-free Ba0.5Sr0.5Fe0.8Cu0.1Ti0.1O3-δ as a bi-functional electrode material for solid oxide fuel cells

    NASA Astrophysics Data System (ADS)

    Yang, Guangming; Shen, Jian; Chen, Yubo; Tadé, Moses O.; Shao, Zongping

    2015-12-01

    In this study, we investigate a cobalt-free titanium-doped perovskite oxide with the nominal composition of Ba0.5Sr0.5Fe0.8Cu0.1Ti0.1O3-δ (BSFCuTi) as a potential electrode material for intermediate temperature solid oxide fuel cells (IT-SOFCs). In comparison to Ba0.5Sr0.5Fe0.9Cu0.1O3-δ, BSFCuTi exhibits improved phase stability and a reduced thermal expansion coefficient even though the electrical conductivity decreases. A low area specific resistance of 0.088 Ω cm2 is achieved at 600 °C based on a symmetrical cell test, which is comparable to the result for the benchmark Ba0.5Sr0.5Co0.8Fe0.2O3-δ cobalt-based perovskite electrocatalyst. Stable operation for a period of 200 h is also demonstrated. The I-V test shows a very high power output of 1.16 W cm-2 for a single cell using a BSFCuTi cathode at 600 °C. In addition, the BSFCuTi can be partially reduced under a reducing atmosphere to prepare a suitable anode material. A cell with BSFCuTi as the material for both electrodes and a thick Gd0.2Ce0.8O1.9 electrolyte (300 μm) delivers an attractive power density of 480 mW cm-2 at 800 °C. The high activity, favorable stability and bi-functionality make BSFCuTi a promising electrode material for IT-SOFCs.

  18. Effect of Mg-DOPING on Magnetic and Transport Behaviour of Nd0.7Sr0.3Mn1-yMgyO3 (0 ≤ y ≤ 0.3)

    NASA Astrophysics Data System (ADS)

    van Khiem, Nguyen; Hoai Nam, Dao Nguyen; Phuc, Nguyen Xuan

    2001-04-01

    The ferromagnetic-paramagnetic phase transition temperature, TC, of Nd0.7Sr0.3Mn1-yMgyO3 monotonically decreases from -235 K to -180 K with increasing Mg-doping concentration y from 0 to 0.1. Transport measurements show that Mg-doping does not significantly influence the resistivity in the paramagnetic phase in contrast to that in the ferromagnetic phase below TC. Interestingly, the magnetoresistance ratio near TC, in applied fields up to 5 T, increases from 180% for y = 0 to 480% for.y = 0.1. The compounds become spin-glass-like insulators with y ≥ 0.2.

  19. Studies of superspin glass state and AC-losses in La0.7Sr0.3MnO3 nanoparticles obtained by high-energy ball-milling

    NASA Astrophysics Data System (ADS)

    Phong, P. T.; Manh, D. H.; Nguyen, L. H.; Tung, D. K.; Phuc, N. X.; Lee, I.-J.

    2014-11-01

    Single-phase perovskite compound La0.7Sr0.3MnO3 was synthesized by a high-energy ball milling method. Nanoparticle nature of this manganite with the average particle diameter of 11 nm was revealed from structure and morphology characterizations. The results of ac magnetic susceptibility measurements show that the system can be described as an ensemble of interacting magnetic nanoparticles, which indicates that the dipole-dipole interactions are strong enough to create superspin glass state in the sample. Furthermore, the specific loss power which is exhausted on the irradiation of an ensemble of particles with a magnetic field has been calculated and measured experimentally.

  20. Investigation of a new lead-free Bi0.5(Na0.40K0.10)TiO3-(Ba0.7Sr0.3)TiO3 piezoelectric ceramic

    PubMed Central

    2012-01-01

    Lead-free piezoelectric compositions of the (1-x)Bi0.5(Na0.40K0.10)TiO3-x(Ba0.7Sr0.3)TiO3 system (when x = 0, 0.05, 0.10, 0.15, and 0.20) were fabricated using a solid-state mixed oxide method and sintered between 1,050°C and 1,175°C for 2 h. The effect of (Ba0.7Sr0.3)TiO3 [BST] content on phase, microstructure, and electrical properties was investigated. The optimum sintering temperature was 1,125°C at which all compositions had densities of at least 98% of their theoretical values. X-ray diffraction patterns that showed tetragonality were increased with the increasing BST. Scanning electron micrographs showed a slight reduction of grain size when BST was added. The addition of BST was also found to improve the dielectric and piezoelectric properties of the BNKT ceramic. A large room-temperature dielectric constant, εr (1,609), and piezoelectric coefficient, d33 (214 pC/N), were obtained at an optimal composition of x = 0.10. PMID:22221833

  1. Observation of superconductivity ( Tc = 50 K) in a new tetragonal alkaline-earth cuprate Sr 0.8Ba 1.2CuO 3+δ, synthesised at ambient pressure

    NASA Astrophysics Data System (ADS)

    Hodges, J. P.; Slater, P. R.; Edwards, P. P.; Greaves, C.; Slaski, M.; Van Tendeloo, G.; Amelinckx, S.

    1996-02-01

    The ambient-pressure synthesis of a new tetragonal alkaline-earth superconducting cuprate, Sr 0.8Ba 1.2CuO 3+δ, from a cupro-oxycarbonate is reported. Magnetic-susceptibility measurements show the presence of a superconducting transition ˜50 K in a post-annealed sample. The crystal structure, refined from time-of-flight powder neutron-diffraction data was found to have an oxygen-deficient La 2CuO 4-type tetragonal T structure ( a = 3.8988(3) Å and c = 12.815(3) Å) with oxygen vacancies located within the CuO 2 planes. Ordering of these oxygen vacancies is responsible for the observation of a superlattice in both neutron- and electron-diffraction measurements. An interpretation of the electron-diffraction patterns suggests that the superlattice in Sr 0.8Ba 1.2CuO 3+δ and also in the isostructural superconductor Sr 2CuO 3+δ are of an identical nature.

  2. Stainless steel-supported solid oxide fuel cell with La0.2Sr0.8Ti0.9Ni0.1O3-δ/yttria-stabilized zirconia composite anode

    NASA Astrophysics Data System (ADS)

    Dayaghi, Amir Masoud; Kim, Kun Joong; Kim, Sunwoong; Park, Juahn; Kim, Sun Jae; Park, Byung Hyun; Choi, Gyeong Man

    2016-08-01

    A metal-supported solid oxide fuel cell (MS-SOFC) is fabricated by co-firing stainless steel (STS) support with a new reduction-resistant oxide-anode and yttria-stabilized zirconia electrolyte. La and Ni co-doped SrTiO3 (La0.2Sr0.8Ti0.9Ni0.1O3-δ, LSTN) which shows Ni exsolution capability is composited with Y0.16Zr0.84O2-δ (YSZ) electrolyte to form a new LSTN-YSZ anode. A cermet layer composed of STS and YSZ (STS-YSZ) is inserted between a porous STS support and a new LSTN-YSZ composite anode for stable contact. With La0.6Sr0.4Co0.2Fe0.8O3-δ (LSCF) cathode and Ce0.8Gd0.2O2-δ (GDC) interlayer coated on top of co-fired half-cell, YSZ/LSTN-YSZ/STS-YSZ/STS, a newly designed and fabricated cell achieved maximum power density of 185 mW cm-2 at 650 °C. This power density is an improvement over many conventional co-fired MS-SOFCs that use a Ni-cermet anode.

  3. Chemically stable perovskites as cathode materials for solid oxide fuel cells: La-doped Ba0.5Sr0.5Co0.8Fe0.2O(3-δ).

    PubMed

    Kim, Junyoung; Choi, Sihyuk; Jun, Areum; Jeong, Hu Young; Shin, Jeeyoung; Kim, Guntae

    2014-06-01

    Ba0.5Sr0.5Co0.8Fe0.2O(3-δ) (BSCF) has won tremendous attention as a cathode material for intermediate-temperature solid-oxide fuel cells (IT-SOFC) on the basis of its fast oxygen-ion transport properties. Nevertheless, wide application of BSCF is impeded by its phase instabilities at intermediate temperature. Here we report on a chemically stable SOFC cathode material, La0.5Ba0.25Sr0.25Co0.8Fe0.2O(3-δ) (LBSCF), prepared by strategic approaches using the Goldschmidt tolerance factor. The tolerance factors of LBSCF and BSCF indicate that the structure of the former has a smaller deformation of cubic symmetry than that of the latter. The electrical property and electrochemical performance of LBSCF are improved compared with those of BSCF. LBSCF also shows excellent chemical stability under air, a CO2-containg atmosphere, and low oxygen partial pressure while BSCF decomposed under the same conditions. Together with this excellent stability, LBSCF shows a power density of 0.81 W cm(-2) after 100 h, whereas 25 % degradation for BSCF is observed after 100 h.

  4. Stainless steel-supported solid oxide fuel cell with La0.2Sr0.8Ti0.9Ni0.1O3-δ/yttria-stabilized zirconia composite anode

    NASA Astrophysics Data System (ADS)

    Dayaghi, Amir Masoud; Kim, Kun Joong; Kim, Sunwoong; Park, Juahn; Kim, Sun Jae; Park, Byung Hyun; Choi, Gyeong Man

    2016-08-01

    A metal-supported solid oxide fuel cell (MS-SOFC) is fabricated by co-firing stainless steel (STS) support with a new reduction-resistant oxide-anode and yttria-stabilized zirconia electrolyte. La and Ni co-doped SrTiO3 (La0.2Sr0.8Ti0.9Ni0.1O3-δ, LSTN) which shows Ni exsolution capability is composited with Y0.16Zr0.84O2-δ (YSZ) electrolyte to form a new LSTN-YSZ anode. A cermet layer composed of STS and YSZ (STS-YSZ) is inserted between a porous STS support and a new LSTN-YSZ composite anode for stable contact. With La0.6Sr0.4Co0.2Fe0.8O3-δ (LSCF) cathode and Ce0.8Gd0.2O2-δ (GDC) interlayer coated on top of co-fired half-cell, YSZ/LSTN-YSZ/STS-YSZ/STS, a newly designed and fabricated cell achieved maximum power density of 185 mW cm-2 at 650 °C. This power density is an improvement over many conventional co-fired MS-SOFCs that use a Ni-cermet anode.

  5. Composite cathode La0.4Sr0.4TiO3-δ-Ce0.8Sm0.2O2-δ impregnated with Ni for high-temperature steam electrolysis

    NASA Astrophysics Data System (ADS)

    Gan, Yun; Qin, Qingqing; Chen, Shigang; Wang, Yan; Dong, Dehua; Xie, Kui; Wu, Yucheng

    2014-01-01

    Composite Ni-SDC (Samaria doped Ceria) cathodes are able to operate in strong reducing atmospheres for steam electrolysis, and composite cathodes based on redox-stable La0.4Sr0.4TiO3 (LSTO) have demonstrated promising performances without the reducing gas flow. However, the electro-catalytic activity of cathodes based on LSTO is insufficient for the efficient electrochemical reduction of steam or carbon oxide. In this work, catalytic-active Ni nanoparticles were loaded on a La0.4Sr0.4TiO3-δ-Ce0.8Sm0.2O2-δ cathode (Ni-loaded LSTO-SDC) via an impregnation method to improve the electrode performances for direct steam electrolysis. The synergetic effect of catalytically-active Ni nanoparticles and the redox-stable LSTO-SDC skeleton contributed to the improved performances and the excellent stability of the cathode for direct steam electrolysis. The current efficiency with a Ni-loaded cathode was enhanced by 3% and 17% compared to the values with a bare LSTO-SDC cathode under 2.0 V of applied voltage at 800 °C with a flow of 3% H2O/5% H2/Ar and 3% H2O/Ar to cathodes, respectively.

  6. Robust NdBa0.5Sr0.5Co1.5Fe0.5O5+δ cathode material and its degradation prevention operating logic for intermediate temperature-solid oxide fuel cells

    NASA Astrophysics Data System (ADS)

    Lee, Tae-Hee; Park, Ka-Young; Kim, Nam-In; Song, Sun-Ju; Hong, Ki-Ha; Ahn, Docheon; Azad, Abul K.; Hwang, Junyeon; Bhattacharjee, Satadeep; Lee, Seung-Cheol; Lim, Hyung-Tae; Park, Jun-Young

    2016-11-01

    We report solutions (durable material and degradation prevention method) to minimize the performance degradation of cell components occurring in the solid oxide fuel cell (SOFC) operation. Reliability testing is carried out with the Nisbnd Nd0.1Ce0.9O2-δ (NDC) anode-supported intermediate temperature-SOFCs. For the cathode materials, single perovskite structured Ba0.5Sr0.5Co0.8Fe0.2O3-δ (BSCF) and double perovskite structured NdBa0.5Sr0.5Co1.5Fe0.5O5+δ (NBSCF) are prepared and evaluated under harsh SOFC operating conditions. The double perovskite NBSCF cathode shows excellent stability in harsh SOFC environments of high humidity and low flow rate of air. Furthermore, we propose the concurrent fuel and air starvation mode, in which the cell potential is temporarily reduced due to the formation of both fuel-starvation (in the anode) and air-depletion (in the cathode) concurrently under a constant load. This is carried out in order to minimize the performance decay of the stable NBSCF-cell through the periodic and extra reduction of aH2 O (and aO2) in the anode. The operating-induced degradation of SOFCs, which are ordinarily assumed to be unrecoverable, can be completely circumvented by the proposed periodical operation logic to prevent performance degradation (concurrent fuel-starvation and air-depletion mode).

  7. Effect of ionic-size change of the rare earth ion on the electrical properties of the hole doped double perovskite Gd0.95Sr0.05BaCo2O5.5

    NASA Astrophysics Data System (ADS)

    Janaki, J.; Rajaji, V.; Kumary, T. Geetha; Kalavathi, S.; Bharathi, A.

    2013-02-01

    We report the effect of co-doping Y on the electrical properties of the hole doped double perovskite Gd0.95Sr0.05BaCo2O5.5. New compositions Gd0.95-xYxSr0.05BaCo2O5.5 have been successfully synthesized and characterized. A contraction in all three lattice parameters of the orthorhombic unit cell has been observed on Y doping. A reduction in the insulator to metal-like transition temperature (TIM) has been observed upon Y doping from 348K for x=0 to 331K for x=0.2. These observed shifts have been interpreted in terms of the possible mechanisms of the insulator-metal transition. The low temperature electrical resistivity data in the range 300-77K has been fitted to different conduction models. They fit best to a variable range hopping (VRH) model at low temperature below 120K followed by small polaron hopping model (SPH) at intermediate temperature (120-200K). The presence of magnetic polarons in the cobaltite systems has been envisaged recently and this provides further evidence for the same.

  8. Ergodic Relaxor State with High Energy Storage Performance Induced by Doping Sr0.85Bi0.1TiO3 in Bi0.5Na0.5TiO3 Ceramics

    NASA Astrophysics Data System (ADS)

    Li, Qing-Ning; Zhou, Chong-Rong; Xu, Ji-Wen; Yang, Ling; Zhang, Xin; Zeng, Wei-Dong; Yuan, Chang-Lai; Chen, Guo-Hua; Rao, Guang-Hui

    2016-10-01

    The large maximum polarization P max and low remnant polarization P r in relaxor ferroelectrics are key features for the energy storage density ( W) and energy-storage efficiency ( η) in materials selection. In this study, the ergodic relaxor (ER) state with high energy storage performance associated with low P r and large P max, induced by Sr0.85Bi0.1TiO3(SBT) addition in (1 - x)Bi0.5Na0.5TiO3- xSr0.85Bi0.1TiO3 (BNT-SBT x with x = 0.25-0.45, Bi0.5Na0.5TiO3 abbreviated as BNT) ceramics has been observed. In particular, significantly increased energy storage density ( W = 1.5 J/cm3) and energy-storage efficiency ( η = 73%) are obtained for BNT-SBT ergodic relaxor ceramics. These results suggest a new means of designing lead-free energy-storage materials.

  9. Evidence of a pseudogap driven by competing orders of multi-band origin in the ferromagnetic superconductor Sr0.5Ce0.5FBiS2

    NASA Astrophysics Data System (ADS)

    Aslam, Mohammad; Paul, Arpita; Thakur, Gohil S.; Gayen, Sirshendu; Kumar, Ritesh; Singh, Avtar; Das, Shekhar; Ganguli, Ashok K.; Waghmare, Umesh V.; Sheet, Goutam

    2016-05-01

    From temperature and magnetic field dependent point-contact spectroscopy on the ferromagnetic superconductor Sr0.5Ce0.5FBiS2 (bulk superconducting {{T}\\text{c}}=2.5 K) we observe (a) a pseudogap in the normal state that sustains to a remarkably high temperature of 40 K and (b) two-fold enhancement of T c upto 5 K in the point-contact geometry. In addition, Andreev reflection spectroscopy reveals a superconducting gap of 6 meV for certain point-contacts suggesting that the mean field T c of this system could be approximately 40 K, the onset temperature of pseudo-gap. Our results suggest that quantum fluctuations originating from other competing orders in Sr0.5Ce0.5FBiS2 forbid a global phase coherence at high temperatures thereby suppressing T c. Apart from the known ordering to a ferromagnetic state, our first-principles calculations reveal nesting of a multi-band Fermi surface and a significant electron-phonon coupling that could result in charge density wave-like instabilities.

  10. Rh promoted La0.75Sr0.25(Fe0.8Co0.2)1-xGaxO3-δ perovskite catalysts: Characterization and catalytic performance for methane partial oxidation to synthesis gas

    NASA Astrophysics Data System (ADS)

    Palcheva, R.; Olsbye, U.; Palcut, M.; Rauwel, P.; Tyuliev, G.; Velinov, N.; Fjellvåg, H. H.

    2015-12-01

    Synthesis gas production via selective oxidation of methane at 600 °C in a pulse reaction over La0.75Sr0.25(Fe0.8Co0.2)1-xGaxO3-δ (x = 0.1, 0.25, 0.4) perovskite-supported rhodium catalysts, was investigated. The perovskite oxides were prepared by sol-gel citrate method and characterized by X-ray Diffraction (XRD), Moessbauer Spectroscopy (MS), Temperature Programmed Reduction (TPR-H2), X-ray Photoelectron Spectroscopy (XPS) and High Resolution Transmission Electron Microscopy (HRTEM). According to XRD analysis, the synthesized samples were a single perovskite phase. The perovskite structure of Ga substituted samples remained stable after TPR-H2, as confirmed by XRD. Data of MS identified Fe3+ ions in two distinctive coordination environments, and Fe4+ ions. The Rh2O3 thin overlayer was detected by the HRTEM for the Rh impregnated perovskite oxides. During the interaction of methane with oxidized perovskite-supported Rh (0.5 wt.%) catalysts, besides CO, H2, and surface carbon, CO2 and H2O were formed. The Rh perovskite catalyst with x = 0.25 gallium exhibits the highest catalytic activity of 83% at 600 °C. The CO selectivity was affected by the reducibility of La0.75Sr0.25(Fe0.8Co0.2)1-xGaxO3-δ perovskite materials.

  11. Synthesis, crystal structure and photoluminescence of a new Eu-doped Sr containing sialon (Sr0.94Eu0.06)(Al0.3Si0.7)4(N0.8O0.2)6

    NASA Astrophysics Data System (ADS)

    Yamane, Hisanori; Shimooka, Satoshi; Uheda, Kyota

    2012-06-01

    Colorless transparent platelet single crystals of a novel Eu2+-doped strontium silicon aluminum oxynitride, (Sr0.94Eu0.06)(Al0.3Si0.7)4(N0.8O0.2)6, were prepared at 1800 °C and 0.92 MPa of N2. Fundamental reflections of electron and X-ray diffraction of the crystals were indexed with a face-centered orthorhombic unit cell (a=5.8061(5) Å, b=37.762(3) Å, c=9.5936(9) Å). Diffuse streaks elongated in the b-axis direction were observed around the fundamental reflections hkl with h=2n+1 of the electron and X-ray diffraction, indicating stacking faults of (0 1 0)[1 0 0]/2. A crystal structure model without the stacking faults was obtained using the X-ray diffraction data of the fundamental reflections with the space group Fdd2. A SiN4-tetrahedron double layer of [SiN2]2 and a Sr/Eu double layer of [(Sr0.94Eu0.06)Al1.2Si0.8N0.8 O1.2]2 are stacked alternately along the b-axis direction. The title compound showed an emission with a peak wavelength of 490 nm under 334 nm excitation at room temperature.

  12. Theoretical investigation of the magnetocaloric effect on La0.7(Ba, Sr)0.3Mn0.9Ga0.1O3 compound at room temperature

    NASA Astrophysics Data System (ADS)

    Tlili, R.; Hammouda, R.; Bejar, M.; Dhahri, E.

    2015-07-01

    Based on a phenomenological model, the magnetic and magnetocaloric properties of La0.7(Ba, Sr)0.3Mn0.9Ga0.1O3 oxide have been studied. Indeed, the magnetic measurements have demonstrated that the sample exhibits a ferromagnetic-paramagnetic transition at room temperature. The value of the magnetocaloric effect such as magnetic entropy change, full width at half-maximum, relative cooling power and magnetic specific heat change has been determined from the calculation of magnetization as a function of temperature under different external magnetic fields. The maximum magnetic entropy change (- ΔSMmax) and the relative cooling power (RCP) are, respectively, 0.57 J kg-1 K-1 and 28.68 J kg-1 for a 10 kOe field change at 300 K, which are the characteristics of a good magnetocaloric material. Hence, the La0.7(Ba, Sr)0.3Mn0.9Ga0.1O3 compound can be considered as a promising material in magnetic refrigeration technology. According to the master curve behavior for the temperature dependence of ΔSM predicted for different maximum fields, this work has confirmed that the paramagnetic-ferromagnetic phase transition observed for our sample is of a second order.

  13. Y0.08Sr0.88TiO3-CeO2 composite as a diffusion barrier layer for stainless-steel supported solid oxide fuel cell

    NASA Astrophysics Data System (ADS)

    Kim, Kun Joong; Kim, Sun Jae; Choi, Gyeong Man

    2016-03-01

    A new diffusion barrier layer (DBL) is proposed for solid oxide fuel cells (SOFCs) supported on stainless-steel where DBL prevents inter-diffusion of atoms between anode and stainless steel (STS) support during fabrication and operation of STS-supported SOFCs. Half cells consisting of dense yttria-stabilized zirconia (YSZ) electrolyte, porous Ni-YSZ anode layer, and ferritic STS support, with or without Y0.08Sr0.88TiO3-CeO2 (YST-CeO2) composite DBL, are prepared by tape casting and co-firing at 1250 and 1350 °C, respectively, in reducing (H2) atmosphere. The porous YST-CeO2 layer (t ∼ 60 μm) blocks inter-diffusion of Fe and Ni, and captures the evaporated Cr during cell fabrication (1350 °C). The cell with DBL and La0.6Sr0.4Co0.2Fe0.8O3-δ (LSCF) cathode achieved a maximum power density of ∼220 mW cm-2 which is stable at 700 °C. In order to further improve the power performance, Ni coarsening in anode during co-firing must be prevented or alternative anode which is resistive to coarsening is suggested. This study demonstrates that the new YST-CeO2 layer is a promising as a DBL for stainless-steel-supported SOFCs fabricated with co-firing process.

  14. High Curie temperature for La(0.7)Sr(0.3)MnO(3) thin films deposited on CeO(2) /YSZ-based buffered silicon substrates.

    PubMed

    Perna, P; Méchin, L; Chauvat, M P; Ruterana, P; Simon, Ch; Scotti di Uccio, U

    2009-07-29

    Two kinds of epitaxial structures were grown by standard pulsed laser deposition on (001) Si, namely La(0.7)Sr(0.3)MnO(3)/Bi(4)Ti(3)O(12)/CeO(2) /YSZ/Si (BTO-based), and La(0.7)Sr(0.3)MnO(3)/SrTiO(3)/CeO(2) /YSZ/Si (STO-based) multilayers. The samples were investigated by means of x-ray diffraction, transmission electron microscopy, magnetic and transport measurements. The Curie temperature T(C) of the BTO-based samples was found to be higher (360 K) than for the typical reference epitaxial LSMO film grown on (001) SrTiO(3) single crystal (345 K), due to high compressive in-plane strain. The STO-based samples show high structural quality, low roughness and high T(C) (350 K), making them interesting candidates for use in innovative LSMO-based bolometers or spintronic devices operating at room temperature.

  15. Preparation and properties of highly c-axis-oriented Sr0.6Ba0.4Nb2O6 thin films by the sol-gel process

    NASA Astrophysics Data System (ADS)

    Shen, Zhiru; Ye, Hui; Zou, Tong; Guo, Bing

    2005-01-01

    Highly oriented ferroelectric strontium barium niobate (Sr0.6Ba0.4Nb2O6) thin films were prepared on P-type Si(100) substrate by the Sol-Gel process. The XRD patterns of the SBN films show that SBN film prepared by using NbCl5, KOH as raw materials performed a highly c-axis preferred orientation perpendicular to the Si substrate, better than films that was prepared using Nb(OC2H5)5 as starting agents. It may be duo to the existence of the potassium ion that not be filtered out completely during the preparation of the niobium alkoxide. The characteristics of D-F and C-V curves were obtained for SBN/Si film. The film exhibits high dielectric constant. In order to investigate ferroelectric characteristics further, the P-E loops of the SBN/Pt/Si were also measured. The films show better optical properties, transmittance of Sr0.6Ba0.4Nb2O6 films on MgO(001) and SiO2 substrates was more than 60% at the range from 450 to 850nm, refractive index was measured to be 2.14 and 2.12 on the MgO and SiO2 substrate at 633nm respectively.

  16. Ethanol reforming using Ba0.5Sr0.5Cu0.2Fe0.8O3-δ/Ag composites as oxygen transport membranes

    NASA Astrophysics Data System (ADS)

    Park, C. Y.; Lee, T. H.; Dorris, S. E.; Park, J.-H.; Balachandran, U.

    2012-09-01

    Cobalt-free oxygen transport membranes (OTMs), Ba0.5Sr0.5Cu0.2Fe0.8O3-δ (BSCF) and its composites, Ba0.5Sr0.5Cu0.2Fe0.8O3-δ/Ag (BSCF/Ag), were fabricated by conventional solid state synthesis, and their oxygen transport properties were evaluated. The metal (Ag) content in the composite was 10-40 vol.%. Based on oxygen-permeation results, BSCF/40 vol.% Ag with Rh catalyst was selected for testing its ability to supply high-purity oxygen (from air) for ethanol reforming. It was found that the composite played an important role in producing hydrogen from ethanol reforming at 600 °C. The composite with catalyst shifted ethanol conversion toward production of hydrogen and away from production of other products, i.e., using a catalyst increased the selectivity for hydrogen in the reformate. The crystal structure, thermal expansion, coke formation, and the microstructural behavior of the OTMs are discussed.

  17. 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.

  18. Modeling tunable bulk acoustic resonators based on induced piezoelectric effect in BaTiO3 and Ba0.25Sr0.75TiO3 films

    NASA Astrophysics Data System (ADS)

    Vendik, Irina B.; Turalchuk, Pavel A.; Vendik, Orest G.; Berge, John

    2008-01-01

    A model for tunable thin film bulk acoustic resonators (TFBARs) based on ferroelectric films is proposed. The model is based on electromechanical equations taking into account piezoelectric effect and electrostriction effect induced by the dc electric field. The dc field induced shift of the resonant frequency is explained by the high-order nonlinear effects in the ferroelectric material. The main contribution to the tunability of the resonant frequency under dc electric field can be attributed to electrostriction, which is nonlinear with respect to the mechanical deformation. It is shown that the upward or downward shift in the resonant frequency is given by the sign of the nonlinear component of the electrostriction tensor M. The model is verified by comparing the results with the measured microwave input impedance of BaTiO3 and Ba0.25Sr0.75TiO3 based TFBARs. For a positive sign of the nonlinear coefficient of electrostriction M, the model predicts an upward shift of the resonant frequencies (resonance and antiresonance) under dc biasing in case of the TFBAR based on BaTiO3, whereas a negative sign of the nonlinear coefficient of electrostriction M predicts downward shift of the resonant frequencies for TFBAR based on Ba0.25Sr0.75TiO3 films.

  19. Magneto-transport properties of La0.75Ca0.15Sr0.1MnO3 with YBa2Cu3O7-δ addition

    NASA Astrophysics Data System (ADS)

    Zghal, E.; Koubaa, M.; Berthet, P.; Sicard, L.; Cheikhrouhou-Koubaa, W.; Decorse-Pascanut, C.; Cheikhrouhou, A.; Ammar-Merah, S.

    2016-09-01

    We report the structural, magnetic, electrical and magentoresistance properties of (La0.75Ca0.15Sr0.1MnO3)1-x(YBa2Cu3O7-δ)x (with x=0, 0.025, 0.05, 0.075, 0.1, 0.2, and 0.3) composites synthesized through sol-gel method. The powder X-ray diffraction patterns indicate no evidence of reaction between La0.75Ca0.15Sr0.1MnO3 (LCSMO) and YBa2Cu3O7-δ (YBCO). The addition of YBCO induces a reduction of the total magnetization while the Curie temperature remains almost constant (∼312 K). The behavior of the electrical resistivity evolves differently depending on the doping level. Above the paramagnetic-insulating transition temperature the resistivity data were best-fitted by using the adiabatic small polaron and variable range hopping models. Ferromagnetic-metallic regime in the composites seems to emanate from the electron-phonon or/and electron-magnon scattering processes. With increasing the YBCO doping content (until x=0.1), the positive magnetoresistance (MR) of YBCO phase dominates the negative MR of LCSMO one, which gives rise to the decreasing of MR of the composites.

  20. Evidence of a pseudogap driven by competing orders of multi-band origin in the ferromagnetic superconductor Sr0.5Ce0.5FBiS2.

    PubMed

    Aslam, Mohammad; Paul, Arpita; Thakur, Gohil S; Gayen, Sirshendu; Kumar, Ritesh; Singh, Avtar; Das, Shekhar; Ganguli, Ashok K; Waghmare, Umesh V; Sheet, Goutam

    2016-05-18

    From temperature and magnetic field dependent point-contact spectroscopy on the ferromagnetic superconductor Sr0.5Ce0.5FBiS2 (bulk superconducting [Formula: see text] K) we observe (a) a pseudogap in the normal state that sustains to a remarkably high temperature of 40 K and (b) two-fold enhancement of T c upto 5 K in the point-contact geometry. In addition, Andreev reflection spectroscopy reveals a superconducting gap of 6 meV for certain point-contacts suggesting that the mean field T c of this system could be approximately 40 K, the onset temperature of pseudo-gap. Our results suggest that quantum fluctuations originating from other competing orders in Sr0.5Ce0.5FBiS2 forbid a global phase coherence at high temperatures thereby suppressing T c. Apart from the known ordering to a ferromagnetic state, our first-principles calculations reveal nesting of a multi-band Fermi surface and a significant electron-phonon coupling that could result in charge density wave-like instabilities.

  1. Structural and dielectric behavior of pulsed laser ablated Sr 0.6Ca 0.4TiO 3 thin film and asymmetric multilayer of SrTiO 3 and CaTiO 3

    NASA Astrophysics Data System (ADS)

    Chakraborty, Pradip; Choudhury, Palash Roy; Krupanidhi, S. B.

    2011-12-01

    Homogeneous thin films of Sr 0.6Ca 0.4TiO 3 (SCT40) and asymmetric multilayer of SrTiO 3 (STO) and CaTiO 3 (CTO) were fabricated on Pt/Ti/SiO 2/Si substrates by using pulsed laser deposition technique. The electrical behavior of films was observed within a temperature range of 153 K-373 K. A feeble dielectric peak of SCT40 thin film at 273 K is justified as paraelectric to antiferroelectric phase transition. Moreover, the Curie-Weiss temperature, determined from the ɛ'( T) data above the transition temperature is found to be negative. Using Landau theory, the negative Curie-Weiss temperature is interpreted in terms of an antiferroelectric transition. The asymmetric multilayer exhibits a broad dielectric peak at 273 K, and is attributed to interdiffusion at several interfaces of multilayer. The average dielectric constants for homogeneous Sr 0.6Ca 0.4TiO 3 films (˜650) and asymmetric multilayered films (˜350) at room temperature are recognized as a consequence of grain size effect. Small frequency dispersion in the real part of the dielectric constants and relatively low dielectric losses for both cases ensure high quality of the films applicable for next generation integrated devices.

  2. Distorted weak anti-localization effects in Bi2Se3/La0.70Sr0.30MnO3 (TI/FM) heterostructures grown by pulsed laser deposition

    NASA Astrophysics Data System (ADS)

    Hunte, Frank; Kumar, Raj; Lee, Yi-Fang; Punugupati, Sandhyarani; Schwartz, Justin; Narayan, Jay

    Topological insulator/ferromagnet (TI/FM) heterostructures with broken time reversal symmetry by interface-induced magnetism are the potential platforms for the observation of novel quantum transport phenomena, magnetic monopoles and exotic quantum magneto-electric effects. TI/FM heterostructures with low Curie temperature ferromagnets i. e. GdN, EuS have been fabricated and studied. One of the challenges encountered with these heterostructures is their low Curie temperatures which limits their potential for applications in spintronic devices at room temperature. To address this issue, we have grown Bi2Se3/La0.70Sr0.30MnO3 (TI/FM) heterostructures by the method of pulsed laser deposition. La0.70Sr0.30MnO3(LSMO) is a strong ferromagnetic material with Tc ~350 K and Bi2Se3 is the most studied topological insulator. XRD and phi scan results show that epitaxial thin films of Bi2Se3 are grown on the LSMO template. Strong in-plane magnetization is confirmed by magnetometry measurements of the Bi2Se3/LSMO heterostructure. Magneto-transport measurements show a distorted weak anti-localization effect with hysteretic behavior due to interface induced ferromagnetism in the Bi2Se3 TI films. This work was supported, in part, by National Science Foundation ECCS-1306400.

  3. A study on the extent of exchange coupling between (Ba0.5Sr0.5Fe12O19)1-x(CoFe2O4)x magnetic nanocomposites synthesized by solgel combustion method

    NASA Astrophysics Data System (ADS)

    Harikrishnan, V.; Ezhil Vizhi, R.

    2016-11-01

    One step citrate gel combustion method followed by high temperature annealing was employed for preparing (Ba0.5Sr0.5Fe12O19)1-x(CoFe2O4)x (x=0.1, 0.2, and 0.3) composite ferrite powders. The powders were subjected to annealing at 800 °C in order to decisively study the phase evolution of the combined hard and soft ferrites. Thermogravitry (TGA)/differential scanning calorimetry (DSC) analysis exhibited three stages of decomposition in the precursor gels combined with an exothermic peak at 210 °C. X-ray diffraction (XRD) analysis confirmed that the diffraction peaks were perfectly indexed to the hexagonal magnetoplumbite structure of Ba0.5Sr0.5Fe12O19 and the cubic spinel structure of CoFe2O4. Fourier transform infrared spectroscopy (FT-IR) analysis for the samples showed a Co-O stretching vibration accompanied with Co-O-Co or Fe-O-Fe bands at 1220 cm-1. The morphology of the samples were examined by field emission scanning electron microscope (FE-SEM) and transmission electron microscope (TEM). The crystallinity of a selected sample was evaluated by using the high resolution transmission electron microscope (HR-TEM) and selected area electron diffraction (SAED) pattern. It confirmed the presence of planes comprising the hard and soft phases in the synthesized nanocomposites. The magnetic parameters like saturation magnetization MS, remanent magnetization MR, squareness ratio SR, coercivity HC and magnetic moment μB were evaluated using hysteresis by employing vibrating sample magnetometer (VSM). Maximum HC of 4.7 kOe and MS of 60.4 emu/g were obtained for (Ba0.5Sr0.5Fe12O19)0.9(CoFe2O4)0.1. Switching field distribution curves were analysed by using the demagnetization curve. The exchange coupling between the hard and soft phases were analysed by the dM/dH plots and it indicated the exchange coupling first increased with the increase in the concentration of spinels and then decreased. The possible comparison of exchange coupling between the hard and soft phases

  4. Judd-Ofelt analysis of Pr3+ ions in Sr1.5Ca0.5SiO4 and Sr0.5Ca0.5TiO3 host matrices

    NASA Astrophysics Data System (ADS)

    Vidyadharan, Viji; Gopi, Subash; Remya, Mohan P.; Thomas, Vinoy; Joseph, Cyriac; Unnikrishnan, N. V.; Biju, P. R.

    2016-01-01

    The spectroscopic properties of Pr3+ doped Sr1.5Ca0.5SiO4 and Sr0.5Ca0.5TiO3 host matrices have been investigated using optical absorption and emission spectra. The oscillator strengths of observed bands of Pr3+ ions and Judd-Ofelt intensity parameters were calculated by including and excluding the hypersensitive 3H4 → 3P2 transition using standard and modified Judd-Ofelt (JO) theory. In both the host matrices the JO parameters follow the same trend as Ω6 > Ω2 > Ω4. The JO intensity parameters obtained by using the Modified JO theory was used to compute the radiative properties such as radiative transition probability (AR), branching ratio (βR) and radiative lifetime (τR) for the observed fluorescence bands. The photoluminescence spectrum of Pr3+ doped Sr1.5Ca0.5SiO4 upon 444 nm excitation shows three emission peaks at 489, 608 and 733 nm corresponding to the transitions 3P0 → 3H4, 3H6 and 3F4 respectively. But in the case of Sr0.5Ca0.5TiO3 host matrix we observed an emission peak at 611 nm corresponding to the 1D2 → 3H4 transition at λex = 336 nm. The experimental branching ratio (βexp) obtained from the fluorescence spectra was compared with the calculated values. The non radiative relaxation rate was calculated from the experimental (τexp) and predicted (τR) lifetimes. Stimulated emission cross section (σe), gain bandwidth (σe × Δλeff) and optical gain (σe × τR) for 0.5 wt% Pr3+ doped Sr1.5Ca0.5SiO4 and Sr0.5Ca0.5TiO3 phosphor samples were also calculated and their high value suggests its candidature as a good optical material.

  5. Carrier tuning the metal-insulator transition of epitaxial La0.67Sr0.33MnO3 thin film on Nb doped SrTiO3 substrate

    NASA Astrophysics Data System (ADS)

    Zhan, J. M.; Li, P. G.; Liu, H.; Tao, S. L.; Ma, H.; Shen, J. Q.; Pan, M. J.; Zhang, Z. J.; Wang, S. L.; Yuan, G. L.

    2016-04-01

    La0.67Sr0.33MnO3 (LSMO) thin films were deposited on (001)SrTiO3(STO) and n-type doped Nb:SrTiO3(NSTO) single crystal substrates respectively. The metal to insulator transition temperature(TMI) of LSMO film on NSTO is lower than that on STO, and the TMI of LSMO can be tuned by changing the applied current in the LSMO/NSTO p-n junction. Such behaviors were considered to be related to the carrier concentration redistribution in LSMO film caused by the change of depletion layer thickness in p-n junction which depends greatly on the applied electric field. The phenomenon could be used to configure artificial devices and exploring the underlying physics.

  6. Magnetoelectric Coupling Characteristics of the La0.67Sr0.33MnO3/PbZr0.2Ti0.8O3(001) Interface

    NASA Astrophysics Data System (ADS)

    Hammouri, Mahmoud; Karpov, Dmitry; Fohtung, Edwin; Vasiliev, Igor

    Multiferroic heterostructures composed of thin layers of ferromagnetic and ferroelectric perovskites have attracted considerable attention in recent years. We apply ab initio computational methods based on density functional theory to study the characteristics of the magnetoelectric coupling at the (001) interface between La0.67Sr0.33MnO3 (LSMO) and PbZr0.2Ti0.8O3(PZT). The calculations are carried out using the Quantum ESPRESSO electronic structure code combined with Vanderbilt ultrasoft pseudopotentials. Our study shows that the interfacial interaction between LSMO and PZT and the polarization of PZT have a strong influence on the distribution of magnetization within the LSMO layer. A significant change in the magnetization of the LSMO layer adjacent to PZT is observed after reversal of the direction of polarization of PZT. Supported by NMSU GREG award. EF is funded by the DoD-AFOSR under Award No FA9550-14-1-0363.

  7. Fabrication of (111)-oriented Ca0.5Sr0.5IrO3/SrTiO3 superlattices—A designed playground for honeycomb physics

    NASA Astrophysics Data System (ADS)

    Hirai, Daigorou; Matsuno, Jobu; Takagi, Hidenori

    2015-04-01

    We report the fabrication of (111)-oriented superlattice structures with alternating 2m-layers (m = 1, 2, and 3) of Ca0.5Sr0.5IrO3 perovskite and two layers of SrTiO3 perovskite on SrTiO3(111) substrates. In the case of m = 1 bilayer films, the Ir sub-lattice is a buckled honeycomb, where a topological state may be anticipated. The successful growth of superlattice structures on an atomic level along the [111] direction was clearly demonstrated by superlattice reflections in x-ray diffraction patterns and by atomically resolved transmission electron microscope images. The ground states of the superlattice films were found to be magnetic insulators, which may suggest the importance of electron correlations in Ir perovskites in addition to the much discussed topological effects.

  8. Conductivity of perovskites La0.9Sr0.1Sc1- x Fe x O3-α ( x = 0.003-0.47) in oxidizing and reducing atmospheres

    NASA Astrophysics Data System (ADS)

    Stroeva, A. Yu.; Gorelov, V. P.; Kuz'min, A. V.

    2016-08-01

    The conductivity of single-phase ceramic materials based on proton-conducting perovskite La0.9Sr0.1ScO3-α containing from 0.3 to 47 at % Fe in the scandium sublattice has been studied. Synthesis has been performed by burning with ethylene glycol. Measurements have been carried out by the four-probe (500-900°C) and impedance (100-500°C) methods in oxidizing and reducing atmospheres, as well as at different pressures {p_{{O_2}}} (2.1 × 104-10‒15 Pa) and {p_{{H_2}O}} (0.04-2.5 kPa). Substitution of scandium with iron significantly decreases the proton conductivity.

  9. Effect of Mn and Ti substitution on the reflection loss characteristic of Ba0.6Sr0.4Fe11-zMnTizO19 (z = 0, 1, 2 and 3)

    NASA Astrophysics Data System (ADS)

    Gunanto, Y. E.; Cahyadi, L.; Adi, W. Ari

    2016-04-01

    The synthesis and characterization of composition Ba0.6Sr0.4Fe11-zMnTizO19 (z = 0; 1; 2 and 3) compound by solid state reaction using mechanical milling have been performed. The raw materials were BaCO3, SrCO3, Fe2O3, MnCO3, and TiO2. The mixed powder was compacted and sintered at 1000°C for 5 hours. X-ray diffraction studies indicate expansion of hexagonal unit cell and compression of atomic density with substitution of Mn2+ and Ti4+ ions. Effect of substitution upon magnetic properties revealed that total magnetization, remanence, and coercivity changed with substitution due to preferential site occupancy of substituted Mn2+ and Ti4+ ions. Since the coercivity and total magnetization may be controlled by substitution while maintaining resistive properties, this material is useful for microwave absorber.

  10. Highly efficient and robust cathode materials for low-temperature solid oxide fuel cells: PrBa0.5Sr0.5Co(2-x)Fe(x)O(5+δ).

    PubMed

    Choi, Sihyuk; Yoo, Seonyoung; Kim, Jiyoun; Park, Seonhye; Jun, Areum; Sengodan, Sivaprakash; Kim, Junyoung; Shin, Jeeyoung; Jeong, Hu Young; Choi, YongMan; Kim, Guntae; Liu, Meilin

    2013-01-01

    Solid oxide fuel cells (SOFC) are the cleanest, most efficient, and cost-effective option for direct conversion to electricity of a wide variety of fuels. While significant progress has been made in anode materials with enhanced tolerance to coking and contaminant poisoning, cathodic polarization still contributes considerably to energy loss, more so at lower operating temperatures. Here we report a synergistic effect of co-doping in a cation-ordered double-perovskite material, PrBa0.5Sr0.5Co(2-x)Fe(x)O(5+δ), which has created pore channels that dramatically enhance oxygen ion diffusion and surface oxygen exchange while maintaining excellent compatibility and stability under operating conditions. Test cells based on these cathode materials demonstrate peak power densities ~2.2 W cm(-2) at 600°C, representing an important step toward commercially viable SOFC technologies.

  11. Electric-field modulation of photoinduced effect in phase-separated Pr0.65 (Ca0.75Sr0.25)0.35MnO3/PMN-PT heterostructure

    NASA Astrophysics Data System (ADS)

    Li, W.; Dong, X. L.; Wang, S. H.; Jin, K. X.

    2016-08-01

    In this letter, we report the photoinduced effect modulated by different electric fields in the Pr0.65 (Ca0.75Sr0.25)0.35MnO3/0.7PbMg1/3Nb2/3O3-0.3PbTiO3 heterostructure. The film exhibits a decrease in the resistance up to five orders of magnitude by enhancing applied electric fields, combined with an electric-field-induced insulator-to-metal transition. More interestingly, a reversible bistability arises in the photoinduced change in resistance at T < 80 K as the voltages are increased. The results can be attributed to the phase separation in manganites, which provides a prototype of photoelectric conversion for electric-field modulation of all-oxide heterostructures.

  12. Strong perpendicular exchange bias in epitaxial La(0.7)Sr(0.3)MnO3:BiFeO3 nanocomposite films through vertical interfacial coupling.

    PubMed

    Zhang, Wenrui; Chen, Aiping; Jian, Jie; Zhu, Yuanyuan; Chen, Li; Lu, Ping; Jia, Quanxi; MacManus-Driscoll, Judith L; Zhang, Xinghang; Wang, Haiyan

    2015-09-01

    An exchange bias effect with perpendicular anisotropy is of great interest owing to potential applications such as read heads in magnetic storage devices with high thermal stability and reduced dimensions. Here we report a novel approach for achieving perpendicular exchange bias by orienting the ferromagnetic/antiferromagnetic coupling in the vertical geometry through a unique vertically aligned nanocomposite (VAN) design. Our results demonstrate robust perpendicular exchange bias phenomena in micrometer-thick films employing a prototype material system of antiferromagnetic BiFeO3 and ferromagnetic La0.7Sr0.3MnO3. The unique response of exchange bias to a perpendicular magnetic field reveals the existence of exchange coupling along their vertical heterointerfaces, which exhibits a strong dependence on their strain states. This VAN approach enables a large selection of material systems for achieving perpendicular exchange bias, which could lead to advanced spintronic devices.

  13. Positive to negative zero-field cooled exchange bias in La0.5Sr0.5Mn0.8Co0.2O3 ceramics

    PubMed Central

    Shang, Cui; Guo, Shaopu; Wang, Ruilong; Sun, Zhigang; Xiao, Haibo; Xu, Lingfang; Yang, Changping; Xia, Zhengcai

    2016-01-01

    Exchange bias effect obtained after zero-field cooling from unmagnetized state usually exhibits a shift of hysteresis loop negative to the direction of the initial magnetic field, known as negative zero-field cooled exchange bias. Here, positive zero-field cooled exchange bias is reported in La0.5Sr0.5Mn0.8Co0.2O3 ceramics. In addition, a transition from positive to negative exchange bias has been observed with increasing initial magnetization field and measurement temperature. Based on a simple spin bidomain model with variable interface, two type of interfacial spin configuration formed during the initial magnetization process are proposed to interpret the observed phenomenon. PMID:27168382

  14. Interfacial charge-mediated non-volatile magnetoelectric coupling in Co0.3Fe0.7/Ba0.6Sr0.4TiO3/Nb:SrTiO3 multiferroic heterostructures

    PubMed Central

    Zhou, Ziyao; Howe, Brandon M.; Liu, Ming; Nan, Tianxiang; Chen, Xing; Mahalingam, Krishnamurthy; Sun, Nian X.; Brown, Gail J.

    2015-01-01

    The central challenge in realizing non-volatile, E-field manipulation of magnetism lies in finding an energy efficient means to switch between the distinct magnetic states in a stable and reversible manner. In this work, we demonstrate using electrical polarization-induced charge screening to change the ground state of magnetic ordering in order to non-volatilely tune magnetic properties in ultra-thin Co0.3Fe0.7/Ba0.6Sr0.4TiO3/Nb:SrTiO3 (001) multiferroic heterostructures. A robust, voltage-induced, non-volatile manipulation of out-of-plane magnetic anisotropy up to 40 Oe is demonstrated and confirmed by ferromagnetic resonance measurements. This discovery provides a framework for realizing charge-sensitive order parameter tuning in ultra-thin multiferroic heterostructures, demonstrating great potential for delivering compact, lightweight, reconfigurable, and energy-efficient electronic devices. PMID:25582090

  15. Microstructural and thermal properties of pure BaFe12O19 and Sr doped barium ferrite (Ba0.9Sr0.1Fe12O19) synthesized by auto combustion method

    NASA Astrophysics Data System (ADS)

    Taufeeq, Saba; Parveen, Azra; Agrawal, Shraddha; Azam, Ameer

    2016-05-01

    Nanoparticles (NPs) of Pure BaFe12O19 and Strontium doped Barium Ferrite (Ba0.9Sr0.1Fe12O19) have been successfully synthesized by Auto combustion method using citric acid as a chelating agent and calcined at 450°C for 3 hrs and 850°C for 4 hrs. Microstructural studies were carried by XRD and SEM techniques. Structural studies suggest that the crystal system remains hexagonal even with the doping of Strontium. The XRD analysis confirms the formation of the structures in the nanometer regime and the peaks are the evidence of the crystalline phase. The SEM images shows the morphology of surface of the samples. The thermal property studied by TGA shows the weight loss which is with varying the temperature and weight loss also varies with Sr doping. The TGA analysis exhibits the loss of weight at different temperatures.

  16. Positive to negative zero-field cooled exchange bias in La0.5Sr0.5Mn0.8Co0.2O3 ceramics.

    PubMed

    Shang, Cui; Guo, Shaopu; Wang, Ruilong; Sun, Zhigang; Xiao, Haibo; Xu, Lingfang; Yang, Changping; Xia, Zhengcai

    2016-01-01

    Exchange bias effect obtained after zero-field cooling from unmagnetized state usually exhibits a shift of hysteresis loop negative to the direction of the initial magnetic field, known as negative zero-field cooled exchange bias. Here, positive zero-field cooled exchange bias is reported in La0.5Sr0.5Mn0.8Co0.2O3 ceramics. In addition, a transition from positive to negative exchange bias has been observed with increasing initial magnetization field and measurement temperature. Based on a simple spin bidomain model with variable interface, two type of interfacial spin configuration formed during the initial magnetization process are proposed to interpret the observed phenomenon. PMID:27168382

  17. Room temperature ferromagnetic properties of epitaxial (111) Y0.225Sr0.775CoO3-δ thin film grown on single crystalline (111) MgO substrate

    NASA Astrophysics Data System (ADS)

    Seo, Jeongdae; Ahn, Yoonho; Yeog Son, Jong

    2015-08-01

    Epitaxial (111) Y0.225Sr0.775CoO3-δ (YSCO) thin films were deposited on single crystalline (111) MgO substrates by a pulsed laser deposition method. The YSCO thin film exhibited room temperature ferromagnetism with a remanent magnetization of 1.5×10-5 emu. The magnetic force microscopy (MFM) study revealed that the YSCO thin film had a mosaic MFM domain structure. The comparison of domain wall energy for the YSCO and PZT indicates that the large domain wall energy induce the large domain size, though the large magnetization value reduce the magnetic domain size in the case of Co. According to the optical conductivity analysis by spectroscopic ellipsometry, it is inferred that the transition from the intermediate spin state to the high spin state of the YSCO thin film is attributed to the ferromagnetism of the Co4+ ion.

  18. Proton uptake in the H(+)-SOFC cathode material Ba(0.5)Sr(0.5)Fe(0.8)Zn(0.2)O(3-δ): transition from hydration to hydrogenation with increasing oxygen partial pressure.

    PubMed

    Poetzsch, Daniel; Merkle, Rotraut; Maier, Joachim

    2015-01-01

    Thermogravimetric investigations on the perovskite Ba(0.5)Sr(0.5)Fe(0.8)Zn(0.2)O(3-δ) (BSFZ, with mixed hole, oxygen vacancy and proton conductivity) from water vapor can occur by acid-base reaction (hydration) or redox reaction (hydrogen uptake), depending on the oxygen partial pressure, i.e. on the material's defect concentrations. In parallel, the effective diffusion coefficient of the stoichiometry relaxation kinetics also changes. These striking observations can be rationalized in terms of a defect chemical model and transport equations for materials with three mobile carriers. Implications for the search of cathode materials with mixed electronic and protonic conductivity for application on proton conducting oxide electrolytes are discussed.

  19. Synthesis of the Pb-based superconductor of the Pb3201 phase (Pb 2Cu)Sr 0.9La 1.1CuO 6+δ by the modified polymerized complex method

    NASA Astrophysics Data System (ADS)

    Kato, Masatsune; Sakuma, Atsushi; Noji, Takashi; Koike, Yoji

    1996-02-01

    We have succeeded in obtaining single-phase samples of the Pb3201 phase (Pb 2Cu)Sr 0.9La 1.1CuO 6+δ by the modified polymerized complex method. At the first step of the synthesis, a transparent gel is found to be obtained by increasing the molar ratio of citric acid to total metal ions up to 5 without controlling the pH of the solution and without ethylene glycol. Secondly, the precursor is prepared by calcining the transparent gel. Finally, highly homogeneous samples with the onset temperature of the superconducting transition, ∼ 37 K, are obtained by sintering the precursor and subsequently annealing it. Moreover, the Pb3201 phase is found to be stable only for x = 1.1 in (Pb 2Cu)Sr 2- xLa xCuO 6+δ.

  20. Interface-mediated ferroelectric patterning and Mn valency in nano-structured PbTiO3/La0.7Sr0.3MnO3

    NASA Astrophysics Data System (ADS)

    Krug, Ingo P.; Doganay, Hatice; Nickel, Florian; Gottlob, Daniel M.; Schneider, Claus M.; Morelli, Alessio; Preziosi, Daniele; Lindfors-Vrejoiu, Ionela; Laskowski, Robert; Barrett, Nick

    2016-09-01

    We employed a multitechnique approach using piezo-force response microscopy and photoemission microscopy to investigate a self-organizing polarization domain pattern in PbTiO3/La0.7Sr0.3MnO3 (PTO/LSMO) nanostructures. The polarization is correlated with the nanostructure morphology as well as with the thickness and Mn valence of the LSMO template layer. On the LSMO dots, the PTO is upwards polarized, whereas outside the nanodots, the polarization appears both strain and interface roughness dependent. The results suggest that the electronic structure and strain of the PTO/LSMO interface contribute to determining the internal bias of the ferroelectric layer.

  1. Structure and properties of epitaxial perovskite Pb(Zr0.52Ti0.48)O3/La0.7Sr0.3MnO3 heterostructures

    NASA Astrophysics Data System (ADS)

    Zou, Cheng; Chen, Yuan-Fu; Li, Ping-Jian; Fan, Rui; Peng, Bing; Zhang, Wen-Xu; Wang, Ze-Gao; Hao, Xin; Liu, Jing-Bo; Zhang, Wan-Li; Li, Yan-Rong; Li, Run-Wei

    2012-04-01

    The morphology, crystalline structure of epitaxial heterostructures of Pb(Zr0.52Ti0.48)O3/La0.7Sr0.3MnO3 (PZT/LSMO) grown on single crystalline SrTiO3 substrates by pulse laser deposition (PLD), have been investigated. The morphology results show that the LSMO layers and PZT layers are smooth and homogenous. The crystalline structure measurements indicate that good epitaxial relationships between LSMO and PZT and STO were obtained. The effects of applied electric and magnetic fields on the physical properties of epitaxial perovskite ferroelectric/ferromagnetic heterostructures were investigated. The results show that the polarized electric field has a very significant influence on the transport properties of LSMO layers while has little influence on the magnetization, and the magnetic field has an obvious influence on the ferroelectric behavior of the PZT layer.

  2. Field-dependent magnetization of BiFeO3 in ultrathin La0.7Sr0.3MnO3/BiFeO3 superlattice

    DOE PAGES

    Fitzsimmons, Michael R.; Jia, Quanxi X.; Singh, Surendra; Chen, A. P.; Xiong, J.

    2015-12-02

    We report the observation of field-induced magnetization of BiFeO3 (BFO) in an ultrathin La0.7Sr0.3MnO3 (LSMO)/BFO superlattice using polarized neutron reflectivity (PNR). The depth dependent structure and magnetic characterization of subnano layer thick (thickness ~ 0.7 nm each) LSMO/BFO hetrostructure is carried out using X-ray reflectivity and PNR techniques. Our PNR results indicate parallel alignment of magnetization as well as enhancement in magnetic moment across LSMO/BFO interfaces. The study showed an increase in average magnetization on increasing applied magnetic field at 10K. As a result, we observed a saturation magnetization of 110 ± 15 kA/m (~0.8 μB/Fe) for ultrathin BFO layermore » (~2 unit cell) sandwiched between ultrathin LSMO layers (~ 2 unit cell).« less

  3. Influence of lattice strain on charge/orbital ordering and phase separation in Pr0.7(Ca0.6Sr0.4)0.3MnO3 thin films

    NASA Astrophysics Data System (ADS)

    Zhao, Y. Y.; Wang, J.; Hu, F. X.; Kuang, H.; Wu, R. R.; Zheng, X. Q.; Sun, J. R.; Shen, B. G.

    2014-05-01

    The static and dynamic lattice strain effects on the competition between ferromagnetic and charge/orbital ordering (COO) phase, phase separation (PS) and transport properties were studied in Pr0.7(Ca0.6Sr0.4)0.3MnO3 (PCSMO) films. It is found that the tensile strained films show pronounced percolative transport behaviors with increased hysteresis, indicating that the stability of the long-range COO is enhanced by the tensile strain. On the other hand, a nearly reversible insulator-metal transition was observed in the compressive strained films, suggesting a strong suppression of the long-range COO. The experiment of dynamic strain effect induced by the bias electric field further verifies the conclusion. Moreover, coactions of the ferroelectric polarization of the substrate and the dynamic strain effect on the PS were found in present PCSMO/PMN-PT film.

  4. Highly efficient and robust cathode materials for low-temperature solid oxide fuel cells: PrBa0.5Sr0.5Co2-xFexO5+δ

    NASA Astrophysics Data System (ADS)

    Choi, Sihyuk; Yoo, Seonyoung; Kim, Jiyoun; Park, Seonhye; Jun, Areum; Sengodan, Sivaprakash; Kim, Junyoung; Shin, Jeeyoung; Jeong, Hu Young; Choi, Yongman; Kim, Guntae; Liu, Meilin

    2013-08-01

    Solid oxide fuel cells (SOFC) are the cleanest, most efficient, and cost-effective option for direct conversion to electricity of a wide variety of fuels. While significant progress has been made in anode materials with enhanced tolerance to coking and contaminant poisoning, cathodic polarization still contributes considerably to energy loss, more so at lower operating temperatures. Here we report a synergistic effect of co-doping in a cation-ordered double-perovskite material, PrBa0.5Sr0.5Co2-xFexO5+δ, which has created pore channels that dramatically enhance oxygen ion diffusion and surface oxygen exchange while maintaining excellent compatibility and stability under operating conditions. Test cells based on these cathode materials demonstrate peak power densities ~2.2 W cm-2 at 600°C, representing an important step toward commercially viable SOFC technologies.

  5. An investigation on the microstructures and magnetic properties of the Sr0.35-xBaxCa0.30La0.35Fe11.71Co0.29O19 hexaferrites

    NASA Astrophysics Data System (ADS)

    Yang, Yujie; Liu, Xiansong

    2014-11-01

    M-type hexaferrite Sr0.35-xBaxCa0.30La0.35Fe11.71Co0.29O19 (0≤x≤0.35) magnetic powders and magnets were prepared by the solid-state reaction. The phase compositions of the magnetic powders were investigated by X-ray diffraction. X-ray diffraction patterns show that the hexagonal single phase is obtained in all samples. The micrographs of the magnets were observed by a field emission scanning electron microscopy. All magnets have formed hexagonal structures and the particles are distributed evenly. Magnetic properties of the magnets were measured by a magnetic properties test instrument. The remanence, intrinsic coercivity, magnetic induction coercivity and maximum energy product of the magnets continuously decrease with increasing barium content (x).

  6. Non-uniform oxygen diffusion in epitaxial La0.7Sr0.3MnO3‑δ film on SrTiO3 substrate

    NASA Astrophysics Data System (ADS)

    Nikolaenko, Yu M.; Artemov, A. N.; Medvedev, Yu V.; Efros, N. B.; Zhikharev, I. V.; Reshidova, I. Yu; Tikhii, A. A.; Kara-Murza, S. V.

    2016-09-01

    The diffusion mechanism of oxygen transport in the epitaxial La0.7Sr0.3MnO3‑δ films was examined for different practically significant conditions of annealing. An indirect method based on the interrelation between the phase transition temperature and the oxygen index was used for stepwise monitoring of the oxygen content in the film. Using a serial procedure of film annealing at different temperatures, we have revealed the abnormal behavior of diffusion transport of oxygen. The analysis of experimental data using numerical simulations demonstrates non-uniformity of the diffusion coefficient across the film thickness. The nature of the spatial dependence of the diffusion coefficient is associated with the lattice distortions of the film material.

  7. A bottom-up building process of nanostructured La0.75Sr0.25Cr0.5Mn0.5O3-δ electrodes for symmetrical-solid oxide fuel cell: Synthesis, characterization and electrocatalytic testing

    NASA Astrophysics Data System (ADS)

    Chanquía, Corina M.; Montenegro-Hernández, Alejandra; Troiani, Horacio E.; Caneiro, Alberto

    2014-01-01

    Pure-phase La0.75Sr0.25Cr0.5Mn0.5O3-δ (LSCM) nanocrystallites have been successfully synthesized by the combustion method, employing glycine as fuel and complexing agent, and ammonium nitrate as combustion trigger. A detailed morphological and structural characterization is performed, by using of X-ray diffraction, N2 physisorption and electron microscopy. The LSCM material consists in interconnected nanocrystallites (∼30 nm) forming a sponge-like structure with meso and macropores, being its specific surface area around 10 m2 g-1. Crystalline structural analyses show that the LSCM nanopowder has trigonal/rhombohedral symmetry in the R-3c space group. By employing the spin coating technique and quick-stuck thermal treatments of the ink-electrolyte, electrodes with different crystallite size (95, 160 and 325 nm) are built onto both sides of the La0.8Sr0.2Ga0.8Mg0.2O3-δ-disk electrolyte. To test the influence of the electrode crystallite size on the electrocatalytic behavior of the symmetrical cells, electrochemical impedance spectroscopy measurements at 800 °C were performed. When the electrode crystallite size becomes smaller, the area specific resistance decreases from 3.6 to 1.31 Ω cm2 under 0.2O2-0.8Ar atmosphere, possibly due to the enlarging of the triple-phase boundary, while this value increases from 7.04 to 13.78 Ω cm2 under 0.17H2-0.03H2O-0.8Ar atmosphere, probably due to thermodynamic instability of the LSCM nanocrystallites.

  8. Highly active La0.4Sr0.6Co0.8Fe0.2O3-δ nanocatalyst for oxygen reduction in intermediate temperature-solid oxide fuel cells

    NASA Astrophysics Data System (ADS)

    Chanquía, Corina M.; Mogni, Liliana; Troiani, Horacio E.; Caneiro, Alberto

    2014-12-01

    Pure-phase La0.4Sr0.6Co0.8Fe0.2O3-δ (LSCF) nanocrystallites were successfully synthesized by the combustion method, by employing glycine as fuel and complexing agent, and ammonium nitrate as combustion trigger. The morphological and structural characterization of the LSCF nanopowders was performed by using X-ray diffraction, N2 physisorption and electron microscopy. The LSCF nanopowder consists of interconnected nanocrystallites (∼45 nm) forming a sponge-like structure with meso and macropores, being its specific surface area around 10 m2 g-1. Crystalline structural analyses show that the LSCF nanopowder presents cubic symmetry in the Pm-3m space group. By employing the spin coating technique and different thermal treatments, symmetrical cells with different electrode crystallite size (45 and 685 nm) were built, by using La0.8Sr0.2Ga0.8Mg0.2O3-δ as electrolyte. Electrochemical impedance spectroscopy measurements were performed varying temperature and pO2. The area specific resistance of the nanostructured sample (45 nm) decreases by two orders of magnitude with respect to the submicrostructured sample (685 nm), reaching values as low as 0.8 Ω cm2 at 450 °C. This improvement is attributed to the cathode morphology optimization in the nanoscale, i.e., enlargement of the exposed surface area and shortening of the oxygen diffusion paths, which reduce the polarization resistance associated to the surface exchange and O-ion bulk diffusion process.

  9. 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).

  10. Electrochemically influenced cation inter-diffusion and Co3O4 formation on La0.6Sr0.4CoO3 infiltrated into SOFC cathodes

    DOE PAGES

    Song, Xueyan; Lee, Shiwoo; Chen, Yun; Gerdes, Kirk

    2015-06-18

    Nanosized LSC electrocatalyst was infiltrated into a porous scaffold cathode composed of Sm2O3-doped CeO2 (SDC) and La0.6Sr0.4Co0.2Fe0.8O3-δ (LSCF) in a commercial button solid oxide fuel cell (SOFC). To understand the stability of cathodes infiltrated with LSC, the infiltrated composite cells were subjected to both electrochemical operating and thermal aging states at 750 °C for 1500 h. Nanostructure and local chemistry evolution of La0.6Sr0.4CoO3 (LSC) infiltrated cathodes upon operation and aging were investigated by transmission electron microscopy. After operation, the LSC remained a cubic perovskite, and the crystal grains exhibit comparable size to as-infiltrated LSC grains. Inter-diffusion of Fe from themore » LSCF to a Fe-incorporated LSC layer developed on the LSCF backbone. However, only sharp interfaces were observed between LSC and SDC backbone in the as-infiltrated cathode and such interfaces remain after operation. The infiltrated LSC on the SDC backbone also retains granular particle morphology. Furthermore, newly grown Co3O4 nanocrystals were found in the operated cathode. After thermal aging, on the other hand, cation inter-diffusion across the interfaces of the infiltrate particles and the cathode backbones is less than that from the operated cells. Lastly, the following hypothesis is proposed: Co3O4 forms on LSC arising from local charge balancing between cobalt and oxygen vacancies.« less

  11. Precursor solution additives improve desiccated La0.6Sr0.4Co0.8Fe0.2O3-x infiltrated solid oxide fuel cell cathode performance

    NASA Astrophysics Data System (ADS)

    Burye, Theodore E.; Nicholas, Jason D.

    2016-01-01

    Here, the addition of the surfactant Triton X-100 or the chelating agent citric acid to Solid Oxide Fuel Cell (SOFC) La0.6Sr0.4Co0.8Fe0.2O3-x (LSCF) precursor nitrate solutions is shown via scanning electron microscopy (SEM) and X-ray diffraction (XRD) to reduce average infiltrate nano-particle size and improve infiltrate phase purity. In addition, the desiccation of LSCF precursor solutions containing the aforementioned organic solution additives further reduces the average LSCF infiltrate nano-particle size and improves the low-temperature infiltrate phase purity. In particular, CaCl2-desiccation reduces the average size of Triton X-100 derived (TXD) LSCF particles fired at 700 °C from 48 to 22 nm, and reduces the average size of citric acid derived LSCF particles fired at 700 °C from 50 to 41 nm. Modeling and electrochemical impedance spectroscopy (EIS) tests indicate that particle size reductions alone are responsible for desiccation-induced cathode performance improvements such as CaCl2-desiccated TXD La0.6Sr0.4Co0.8Fe0.2O3-x - Ce0.9Gd0.1O1.95 (LSCF-GDC) cathodes reaching a polarization resistance of 0.17 Ωcm2 at 540 °C, compared to 600 °C for undesiccated TXD LSCF-GDC cathodes. This excellent low-temperature performance, combined with a low open-circuit 540 °C degradation rate, suggests that the desiccation of organic-additive-containing infiltrate precursor solutions may be useful for the development of durable, high-power, low-temperature SOFCs.

  12. Rietveld refinement, impedance spectroscopy and magnetic properties of Bi0.8Sr0.2FeO3 substituted Na0.5Bi0.5TiO3 ceramics

    NASA Astrophysics Data System (ADS)

    Kumari, Rekha; Ahlawat, Neetu; Agarwal, Ashish; Sanghi, Sujata; Sindhu, Monica; Ahlawat, Navneet

    2016-09-01

    We herein presented the investigation on the structural, electrical and magnetic properties of (1-x)(Na0.5Bi0.5TiO3)-x(Bi0.8Sr0.2FeO3) polycrystalline ceramic samples, with x=0.1, 0.3, 0.5 and 0.7. These samples were prepared by conventional solid state reaction method and the crystalline phase of prepared ceramics was identified with the help of X-ray diffraction pattern. Rietveld analysis of the obtained XRD data confirmed that all the synthesized samples adopt the rhombohedral crystal structure with R3c space group. Impedance spectroscopic measurements were performed on all the compositions in the frequency range 10 Hz-5 MHz to probe the electrical microstructure of polycrystalline (1-x)(Na0.5Bi0.5TiO3)-x(Bi0.8Sr0.2FeO3) ceramics, which changes significantly as a function of x (content of BSFO). A significant increase in dielectric constant has been observed with increase in BSFO concentration, which was attributed to enhancement of oxygen vacancies. Detailed study of impedance complex plane plots revealed the presence of non-Debye type relaxation for all the prepared systems and enabled us to separate the contribution from grains and grain boundaries. Equivalent circuit model (RgCPEg)(RgbCPEgb)(ReCPEe) was employed to explain the impedance data for all the prepared samples. The activation energies obtained from electric modulus as well as dc conductivity increase with increase in BSFO content, which approaches the value 1 eV and indicates an Arrehenius type thermally activated process. Remnant magnetization (Mr) and coercive field (Hc) are found to be increase with BSFO concentration.

  13. Nanoblast synthesis and consolidation of (La0.8Sr0.2)(Ga0.9Mg0.1)O(3-delta) under Spark plasma sintering conditions.

    PubMed

    Vasylkiv, Oleg; Borodianska, Hanna; Badica, Petre; Zhen, Yongda; Tok, Alfred

    2009-01-01

    Four-cation nanograined strontium and magnesium doped lanthanum gallate (La0.8Sr0.2) (Ga0.9Mg0.1)O(3-delta) (LSGM) and its composite with 2 wt% of ceria (LSGM-Ce) were prepared. Morphologically homogeneous nanoreactors, i.e., complex intermediate metastable aggregates of desired composition were assembled by spray atomization technique, and subsequently loaded with nanoparticles of highly energetic C3H6N6O6. Rapid nanoblast calcination technique was applied and the final composition was synthesized within the preliminary localized volumes of each single nanoreactor on the first step of spark plasma treatment. Subsequent SPS consolidations of nanostructured extremely active LSGM and LSGM-Ce powders were achieved by rapid treatment under pressures of 90-110 MPa. This technique provided the heredity of the final structure of nanosize multimetal oxide, allowed the prevention of the uncontrolled agglomeration during multicomponent aggregates assembling, subsequent nanoblast calcination, and final ultra-rapid low-temperature SPS consolidation of nanostructured ceramics. LaSrGaMgCeO(3-delta) nanocrystalline powder consisting of approximately 11 nm crystallites was consolidated to LSGM-Ce nanoceramic with average grain size of approximately 14 nm by low-temperature SPS at 1250 degrees C. Our preliminary results indicate that nanostructured samples of (La0.8Sr0.2)(Ga0.9Mg0.1)O(3-delta) with 2 wt% of ceria composed of approximataley 14 nm grains can exhibit giant magnetoresistive effect in contrast to the usual paramagnetic properties measured on the samples with larger grain size.

  14. Anisotropic modulation of magnetic properties and the memory effect in a wide-band (011)-Pr0.7Sr0.3MnO3/PMN-PT heterostructure.

    PubMed

    Zhao, Ying-Ying; Wang, Jing; Kuang, Hao; Hu, Feng-Xia; Liu, Yao; Wu, Rong-Rong; Zhang, Xi-Xiang; Sun, Ji-Rong; Shen, Bao-Gen

    2015-01-01

    Memory effect of electric-field control on magnetic behavior in magnetoelectric composite heterostructures has been a topic of interest for a long time. Although the piezostrain and its transfer across the interface of ferroelectric/ferromagnetic films are known to be important in realizing magnetoelectric coupling, the underlying mechanism for nonvolatile modulation of magnetic behaviors remains a challenge. Here, we report on the electric-field control of magnetic properties in wide-band (011)-Pr0.7Sr0.3MnO3/0.7Pb(Mg1/3Nb2/3)O3-0.3PbTiO3 heterostructures. By introducing an electric-field-induced in-plane anisotropic strain field during the cooling process from room temperature, we observe an in-plane anisotropic, nonvolatile modulation of magnetic properties in a wide-band Pr0.7Sr0.3MnO3 film at low temperatures. We attribute this anisotropic memory effect to the preferential seeding and growth of ferromagnetic (FM) domains under the anisotropic strain field. In addition, we find that the anisotropic, nonvolatile modulation of magnetic properties gradually diminishes as the temperature approaches FM transition, indicating that the nonvolatile memory effect is temperature dependent. By taking into account the competition between thermal energy and the potential barrier of the metastable magnetic state induced by the anisotropic strain field, this distinct memory effect is well explained, which provides a promising approach for designing novel electric-writing magnetic memories. PMID:25909177

  15. Anisotropic modulation of magnetic properties and the memory effect in a wide-band (011)-Pr0.7Sr0.3MnO3/PMN-PT heterostructure

    NASA Astrophysics Data System (ADS)

    Zhao, Ying-Ying; Wang, Jing; Kuang, Hao; Hu, Feng-Xia; Liu, Yao; Wu, Rong-Rong; Zhang, Xi-Xiang; Sun, Ji-Rong; Shen, Bao-Gen

    2015-04-01

    Memory effect of electric-field control on magnetic behavior in magnetoelectric composite heterostructures has been a topic of interest for a long time. Although the piezostrain and its transfer across the interface of ferroelectric/ferromagnetic films are known to be important in realizing magnetoelectric coupling, the underlying mechanism for nonvolatile modulation of magnetic behaviors remains a challenge. Here, we report on the electric-field control of magnetic properties in wide-band (011)-Pr0.7Sr0.3MnO3/0.7Pb(Mg1/3Nb2/3)O3-0.3PbTiO3 heterostructures. By introducing an electric-field-induced in-plane anisotropic strain field during the cooling process from room temperature, we observe an in-plane anisotropic, nonvolatile modulation of magnetic properties in a wide-band Pr0.7Sr0.3MnO3 film at low temperatures. We attribute this anisotropic memory effect to the preferential seeding and growth of ferromagnetic (FM) domains under the anisotropic strain field. In addition, we find that the anisotropic, nonvolatile modulation of magnetic properties gradually diminishes as the temperature approaches FM transition, indicating that the nonvolatile memory effect is temperature dependent. By taking into account the competition between thermal energy and the potential barrier of the metastable magnetic state induced by the anisotropic strain field, this distinct memory effect is well explained, which provides a promising approach for designing novel electric-writing magnetic memories.

  16. Examination of the mechanism for the reversible aging behavior at open circuit when changing the operating temperature of (La0.8Sr0.2)0.95 MnO3 electrodes

    DOE PAGES

    Abernathy, Harry; Finklea, Harry O.; Mebane, David S.; Song, Xueyan; Chen, Yun; Gerdes, Kirk

    2015-02-17

    The aging behavior of symmetrical cells, consisting of either (La0.8Sr0.2)0.95 MnO3 (LSM) or La0.6Sr0.4Co0.2Fe0.8O3 (LSCF) electrodes screen printed on either 8 mol% yttria-stabilized zirconia (YSZ) or Ce0.8Gd0.2O2 (GDC) electrolyte substrates, is reported as the symmetrical cell is thermally cycled between 700 °C and 800 °C. For LSM, between 700 °C and 850 °C, the polarization resistance exhibits slow increases or decreases with time (on the order of days) after a quick change in temperature. When increasing the temperature, the polarization resistance decreases with time, and when decreasing the temperature, the polarization resistance slowly increases with time. In a previous work,more » the authors had explained these results with LSM by connecting the testing conditions to literature reports of surface analysis of LSM thin films which demonstrated a change in the amount of surface cation segregation as a function of temperature. In this work, TEM/EDS/XPS analysis of dense LSM pellets thermally cycled under the same conditions as the symmetrical cells does not indicate any significant reversible change in the surface composition of the LSM pellet between 700 °C and 800 °C. An alternative hypothesis is proposed to explain the relationship between polarization resistance and the LSM cation/anion vacancy concentrations controlled by the Schottky reaction. The timescale of aging behavior is related to the time necessary for the cations to move to or from the LSM surface to adjust to the new equilibrium at each temperature. Furthermore, the relevance in understanding the mechanism behind the aging behavior is emphasized with respect to fuel cell sample/stack modeling as well as to proper testing procedures for reaching reliable conclusions when comparing different electrode samples.« less

  17. Degradation of (La0.6Sr0.4)0.95(Co0.2Fe0.8)O3-δ Solid Oxide Fuel Cell Cathodes at the Nanometer Scale and below.

    PubMed

    Ni, Na; Cooper, Samuel J; Williams, Robert; Kemen, Nils; McComb, David W; Skinner, Stephen J

    2016-07-13

    The degradation of intermediate temperature solid oxide fuel cell (ITSOFC) cathodes has been identified as a major issue limiting the development of ITSOFCs as high efficiency energy conversion devices. In this work, the effect of Cr poisoning on (La0.6Sr0.4)0.95(Co0.2Fe0.8)O3-δ (LSCF6428), a particularly promising ITSOFC cathode material, was investigated on symmetrical cells using electrochemical impedance spectroscopy and multiscale structural/chemical analysis by advanced electron and ion microscopy. The systematic combination of bulk and high-resolution analysis on the same cells allows, for the first time, direct correlation of Cr induced performance degradation with subtle and localized structural/chemical changes of the cathode down to the atomic scale. Up to 2 orders of magnitude reduction in conductivity, oxygen surface exchange rate, and diffusivity were observed in Cr poisoned LSCF6428 samples. These effects are associated with the formation of nanometer size SrCrO4; grain boundary segregation of Cr; enhanced B-site element exsolution (both Fe and Co); and reduction in the Fe valence, the latter two being related to Cr substitution in LSCF. The finding that significant degradation of the cathode happens before obvious microscale change points to new critical SOFC degradation mechanisms effective at the nanometer scale and below. PMID:27336290

  18. Unravelling the effect of SrTiO3 antiferrodistortive phase transition on the magnetic properties of La0.7Sr0.3MnO3 thin films

    NASA Astrophysics Data System (ADS)

    Mota, D. A.; Romaguera Barcelay, Y.; Senos, A. M. R.; Fernandes, C. M.; Tavares, P. B.; Gomes, I. T.; Sá, P.; Fernandes, L.; Almeida, B. G.; Figueiras, F.; Mirzadeh Vaghefi, P.; Amaral, V. S.; Almeida, A.; Pérez de la Cruz, J.; Agostinho Moreira, J.

    2014-10-01

    Epitaxial La0.7Sr0.3MnO3 (LSMO) thin films, with different thicknesses ranging from 20 to 330 nm, were deposited on (1 0 0)-oriented strontium titanate (STO) substrates by pulsed laser deposition, with their structure and morphology characterized at room temperature. The magnetic and electric transport properties of the as-processed thin films reveal an abnormal behaviour in the temperature dependent magnetization M(T) below the antiferrodistortive STO phase transition (TSTO), and also an anomaly in the magnetoresistance and electrical resistivity close to the same temperature. Films with thickness ≤100 nm show an in-excess magnetization and pronounced changes in the coercivity due to the interface-mediated magnetoelastic coupling with antiferrodistortive domain wall movement occurring below TSTO. However, in thicker LSMO thin films, an in-defect magnetization is observed. This reversed behaviour can be understood with the emergence in the upper layer of the film, of a columnar structure needed to relax the elastic energy stored in the film, which leads to randomly oriented magnetic domain reconstructions. For enough high-applied magnetic fields, as thermodynamic equilibrium is reached, a full suppression of the anomalous magnetization occurs, wherein the temperature dependence of the magnetization starts to follow the expected Brillouin behaviour.

  19. Modeling the magnetic isotherms of (La0.56Ce0.14)Sr0.30MnO3 by a mean-field scaling method and estimation of magnetic entropy change

    NASA Astrophysics Data System (ADS)

    Yahyaoui, S.; Khalfaoui, M.; Kallel, S.; Kallel, N.; Amaral, J. S.; Ben Lamine, A.

    2015-11-01

    We report a study on the magnetic properties of the (La0.56Ce0.14)Sr0.30MnO3 perovskite, by a mean-field method. By scaling of the experimental magnetization data, the mean-field exchange parameter λ and the BS function of the equation of state BS [ (H +Hexch) / T ] are directly determined, as well as the order of the phase transition. The spin quantum number of the manganite has been also determined. The mean-field scaling has been used to estimate magnetic entropy change (- ΔSM) within the thermodynamics of the model and without using the usual numerical integration of a Maxwell relation. The maxima of the positive absolute value of (- ΔSM) upon variation of the applied magnetic field at 1 and 5 T are about 1.68 and 5.04 J kg-1 K-1, respectively. Satisfactory agreement between the mean-field model and experimental behavior has been found.

  20. Application of high velocity oxygen fuel flame (HVOF) spraying to fabrication of La0.8Sr0.2Ga0.8Mg0.2O3 electrolyte for solid oxide fuel cells

    NASA Astrophysics Data System (ADS)

    Zhang, Shan-Lin; Li, Cheng-Xin; Li, Chang-Jiu; Yang, Guan-Jun; Liu, Meilin

    2016-01-01

    La0.8Sr0.2Ga0.8Mg0.2O3 (LSGM) is considered a promising electrolyte for intermediate-temperature solid oxide fuel cells (IT-SOFCs) due to its high ionic conductivity and stability under fuel cell operating conditions. Here we report our findings in investigating the feasibility of using a high velocity oxygen fuel flame (HVOF) spraying process for cost-effective fabrication of dense LSGM electrolyte membranes. The flame and in-flight particle behavior were simulated numerically to optimize the microstructure and phase compositions of the LSGM deposits. The measured gas leakage rate of an LSGM deposit is ∼7 × 10-7 cm4gf-1 s-1. The single cell assembled with 50-55 μm HVOF-sprayed LSGM electrolyte shows open circuit voltage (OCV) of 1.08 V at 800 °C, suggesting that the as-sprayed LSGM deposit is dense enough for direct application as SOFC electrolyte. At 800 °C, the ionic conductivity of the sprayed LSGM deposit is ∼0.04 S cm-1, indicating that the HVOF spraying is a promising process for low-temperature fabrication of dense LSGM electrolyte membranes for IT-SOFCs.

  1. Operando and in situ X-ray spectroscopies of degradation in La0.6Sr0.4Co0.2Fe0.8O(3-δ) thin film cathodes in fuel cells.

    PubMed

    Lai, Samson Y; Ding, Dong; Liu, Mingfei; Liu, Meilin; Alamgir, Faisal M

    2014-11-01

    Information from ex situ characterization can fall short in describing complex materials systems simultaneously exposed to multiple external stimuli. Operando X-ray absorption spectroscopy (XAS) was used to probe the local atomistic and electronic structure of specific elements in a La0.6Sr0.4Co0.2Fe0.8O(3-δ) (LSCF) thin film cathode exposed to air contaminated with H2O and CO2 under operating conditions. While impedance spectroscopy showed that the polarization resistance of the LSCF cathode increased upon exposure to both contaminants at 750 °C, XAS near-edge and extended fine structure showed that the degree of oxidation for Fe and Co decreases with increasing temperature. Synchrotron-based X-ray photoelectron spectroscopy tracked the formation and removal of a carbonate species, a Co phase, and different oxygen moieties as functions of temperature and gas. The combined information provides insight into the fundamental mechanism by which H2O and CO2 cause degradation in the cathode of solid oxide fuel cells. PMID:25205041

  2. Tuning of cu doping on phase transition and high-field phase diagram of Nd0.5Sr0.5Mn1-xCuxO3

    NASA Astrophysics Data System (ADS)

    Shang, C.; Xia, Z. C.; Wei, M.; Jin, Z.; Chen, B. R.; Shi, L. R.; Ouyang, Z. W.; Huang, S.; Xiao, G. L.

    2016-10-01

    Pulsed high magnetic fields up to 52 T have been used in the systematic investigation of the magnetic properties of manganites Nd0.5Sr0.5Mn1-xCuxO3 (0≤x≤0.15). The Cu-doping dependent first-order metamagnetic transitions are observed below the charge ordering temperature, which is ascribed to both Cu-doping and field-induced collapse of the charge ordering with antiferromagnetic phase. Based on the magnetization and electrical transport measurements, a three-dimensional phase diagram with coordinate axis of temperature, magnetic field, and doping level has been obtained, in which the critical fields of the metamagnetic transitions increase with the increase in Cu content and decrease with increasing temperature. The experimental results confirm that Mn-site substitution with Cu destroys the Mn3+-O2--Mn4+ bridges and weakens the double exchange interaction between Mn3+ and Mn4+ ions, which shows an obvious tuning effect on the metamagnetic transition under the external magnetic field.

  3. Magnetic properties of perovskites La0.7Sr0.3 Mn0.73+ Mn0.3-x4+ TixO3: Monte Carlo simulation versus experiments

    NASA Astrophysics Data System (ADS)

    Yahyaoui, Samia; Kallel, Sami; Diep, H. T.

    2016-10-01

    This work presents a Monte Carlo study of the phase transition in the perovskites La0.7Sr0.3Mn0.73+Mn0.3-x4+ TixO3 (x=0.1, 0.2, and 0.25). We take into account nearest-neighbor (NN) interactions between magnetic ions Mn3+(S=2) and Mn4+(S = 3 / 2) using a spin model describing a strong anisotropy on the z-axis. We have calculated the uniform and staggered magnetizations as well as the Edwards-Anderson order parameter as functions of temperature, with and without an applied magnetic field. Fitting the experimental Curie temperature at x=0, we estimated values of various exchange interactions in the system. The dominant one is that between Mn3+ and Mn4+ which is at the origin of the ferromagnetic ordering. Effects of the very small interaction J2 between NN Mn3+ is analyzed: we show that it can cause an antiferromagnetic phase above Tc which disappears at smaller J2 or at Mn3+ concentrations smaller than 0.55. Our results show a good agreement with experiments on the magnetizations for substitution concentration x=0.1, 0.2 and 0.3. We also studied the applied-field effect on the magnetization and our obtained results are compared with experiments performed at x = 10 %.

  4. NiCo2O4@La0.8Sr0.2MnO3 core-shell structured nanorods as efficient electrocatalyst for Lisbnd O2 battery with enhanced performances

    NASA Astrophysics Data System (ADS)

    Luo, Yong; Lu, Fanliang; Jin, Chao; Wang, Yarong; Yang, Ruizhi; Yang, Chenghao

    2016-07-01

    La1-xSrxMnO3 perovskite oxides are promising electrocatalysts for Lisbnd O2 batteries because of their excellent intrinsic catalytic activity for oxygen reduction reaction (ORR). However, the relatively inert catalytic activity for oxygen evolution reaction (OER) suppresses their practical applications in Lisbnd O2 battery. Here, nanoscale NiCo2O4 (NCO) layer with high OER catalytic activity has been homogenously incorporated into the surface of La0.8Sr0.2MnO3 (LSM) nanorods to form a core-shell structure. In this typical structure, the ORR mainly occurred on the LSM core, while the OER mainly occurred on the nanoscale NCO shell, and structure damage of catalysts coming from gas evolution can be greatly avoided. The synergy of high catalytic activity and core-shell structure results in the Lisbnd O2 battery with good rate capability and excellent cycle stability, which sustains 80 cycles without capacity attenuation at a high current density of 200 mA g-1.

  5. Remarkable charge-trapping performance based in Zr0.5Hf0.5O2 with nanocrystal Ba0.6Sr0.4TiO3 blocking layer for nonvolatile memory device

    NASA Astrophysics Data System (ADS)

    Yan, X. B.; Jia, X. L.; Yang, T.; Zhao, J. H.; Li, Y. C.; Zhou, Z. Y.; Zhang, Y. Y.

    2016-10-01

    Two kinds of charge trapping memory device with Au/Zr0.5Hf0.5O2(ZHO)/SiO2/p-Si and Au/Ba0.6Sr0.4TiO3(BST)/Zr0.5Hf0.5O2/SiO2/p-Si structure were fabricated and investigated. The double BST/ZHO films exhibit a larger memory window of 7.36 V under ±14 V sweeping voltages in its C-V curve and the device has good charge retention properties with only small charge loss of ∼ 5% after more than 104 s. The good characteristics are attributed to the inter-diffusion between BST and ZHO where more deep defect sites were created after RTA treatment, which provides high potential barriers for the trapped charges to tunnel back to the silicon substrate. Furthermore, the nanocrystal in the BST layer increases the tunneling barrier of tunneling current into the gate and effectively restrains the leakage of storage charge from blocking layer, which improves the charge retention characteristic.

  6. In situ examination of oxygen non-stoichiometry in La0.80Sr0.20CoO3 thin films at intermediate and low temperatures by X-ray diffraction

    SciTech Connect

    Biegalski, Michael D; Crumlin, Ethan; Belianinov, Alex; Mutoro, Eva; Shao-Horn, Yang; Kalinin, Sergei

    2014-01-01

    Structural evolution of epitaxial La0.80Sr0.20CoO3 thin films under chemical and voltage stimuli were examined in situ using X-ray diffraction. The changes in lattice parameter (chemical expansivity) were used to quantify oxygen reduction reaction processes and vacancy concentration changes in LSCO. At 550 C the observed lattice parameter reduction at an applied bias of 0.6 V was equivalent to that from the reducing condition of a two percent carbon monoxide atmosphere with an oxygen non-stoichiometry of 0.24. At lower temperatures (200 C) the application of bias reduced the sample much more effectively than a carbon monoxide atmosphere and induced an oxygen non-stoichiometry of 0.47. Despite these large changes in oxygen concentration, the epitaxial thin film was completely re-oxidized and no signs of crystallinity loss or film amorphization were observed. This work demonstrates that the effects of oxygen evolution and reduction can be examined with applied bias at low temperatures, extending the ability to probe these processes with in-situ analytical techniques.

  7. Cationic Intermixing and Reactivity at the La2 Mo2 O9 /La0.8 Sr0.2 MnO3-δ Solid Oxide Fuel Cell Electrolyte-Cathode Interface.

    PubMed

    Ravella, Uday K; Liu, Jingjing; Corbel, Gwenaël; Skinner, Stephen J; Lacorre, Philippe

    2016-08-23

    Among standard high-temperature cathode materials for solid oxide fuel cells, La0.8 Sr0.2 MnO3-δ (LSM) displays the least reactivity with the oxide-ion conductor La2 Mo2 O9 (LMO), yet a reaction is observed at high processing temperatures, identified by using XRD and focused ion beam secondary-ion mass spectrometry (FIB-SIMS) after annealing at 1050 and 1150 °C. Additionally, Sr and Mn solutions were deposited and annealed on LMO pellets, as well as a Mo solution on a LSM pellet. From these studies several reaction products were identified by using XRD and located by using FIB-SIMS on the surface of pelletised samples. We used depth profiling to show that the reactivity extended up to ∼10 μm from the surface region. If Sr was present, a SrMoO4 -type scheelite phase was always observed as a reaction product, and if Mn was present, LaMnO3+δ single crystals were observed on the surface of the LMO pellets. Additional phases such as La2 MoO6 and La6 MoO12 were also detected depending on the configuration and annealing temperature. Reaction mechanisms and detailed reaction formulae are proposed to explain these observations. The strongest driving force for cationic diffusion appears to originate from Mo(6+) and Mn(3+) cations, rather than from Sr(2+) .

  8. Degradation of (La0.6Sr0.4)0.95(Co0.2Fe0.8)O3-δ Solid Oxide Fuel Cell Cathodes at the Nanometer Scale and below.

    PubMed

    Ni, Na; Cooper, Samuel J; Williams, Robert; Kemen, Nils; McComb, David W; Skinner, Stephen J

    2016-07-13

    The degradation of intermediate temperature solid oxide fuel cell (ITSOFC) cathodes has been identified as a major issue limiting the development of ITSOFCs as high efficiency energy conversion devices. In this work, the effect of Cr poisoning on (La0.6Sr0.4)0.95(Co0.2Fe0.8)O3-δ (LSCF6428), a particularly promising ITSOFC cathode material, was investigated on symmetrical cells using electrochemical impedance spectroscopy and multiscale structural/chemical analysis by advanced electron and ion microscopy. The systematic combination of bulk and high-resolution analysis on the same cells allows, for the first time, direct correlation of Cr induced performance degradation with subtle and localized structural/chemical changes of the cathode down to the atomic scale. Up to 2 orders of magnitude reduction in conductivity, oxygen surface exchange rate, and diffusivity were observed in Cr poisoned LSCF6428 samples. These effects are associated with the formation of nanometer size SrCrO4; grain boundary segregation of Cr; enhanced B-site element exsolution (both Fe and Co); and reduction in the Fe valence, the latter two being related to Cr substitution in LSCF. The finding that significant degradation of the cathode happens before obvious microscale change points to new critical SOFC degradation mechanisms effective at the nanometer scale and below.

  9. Performance enhancement of solution impregnated nanostructured La0.8Sr0.2Co0.8Ni0.2O3-δ oxygen electrode for intermediate temperature solid oxide electrolysis cells

    NASA Astrophysics Data System (ADS)

    Tan, Yuan; Duan, Nanqi; Wang, Ao; Yan, Dong; Chi, Bo; Wang, Ning; Pu, Jian; Li, Jian

    2016-02-01

    Nanostructured La0.8Sr0.2Co0.8Ni0.2O3-δ (LSCN) based Gd2O3-doped CeO2 (GDC) oxygen electrodes are prepared by impregnation method for intermediate temperature solid oxide electrolysis cell (SOEC) for efficient hydrogen production. The microstructure features and the electrochemical performance of the impregnated LSCN-GDC oxygen electrodes with various LSCN loadings are evaluated and investigated. Electrochemical tests show that the impregnated LSCN-GDC oxygen electrodes present great enhancement of oxygen evolution performance, due to the good nanoparticle LSCN dispersion on the GDC scaffold surface to maximize the active reaction sites. The cell with 30 wt% LSCN loaded LSCN-GDC as the oxygen electrode presents a polarization resistance of 0.072 Ω cm2 at 800 °C with 60 vol% absolute humidity (AH), only about half of that for the screen-printed LSCN electrode. The hydrogen production rate is 484 mL cm-2 h-1 at 750 °C at 1.5 V with 60 vol%AH. For stability test in galvanostatic SOEC operation up to 100 h, the solution impregnated cell shows a very stable performance without obvious degradation.

  10. Enhanced electrochemical performance of solution impregnated La 0.8Sr 0.2Co 0.8Ni 0.2O 3- δ cathode for intermediate temperature solid oxide fuel cells

    NASA Astrophysics Data System (ADS)

    Xu, Xiang; Wang, Fangzhong; Liu, Yihui; Pu, Jian; Chi, Bo; Jian, Li

    Solution impregnated La 0.8Sr 0.2Co 0.8Ni 0.2O 3 + Gd-doped CeO 2 (LSCN + GDC) cathodes for intermediate temperature solid oxide fuel cells (IT-SOFC) are prepared and their electrochemical properties are evaluated and compared with the conventional LSCN cathodes. The results indicate that the cathode performance can be enhanced by the presence of the nanosized microstructure produced with the solution impregnation method. It is determined that the amount of LSCN loading in the LSCN + GDC composite cathode needs to be higher than 35 wt% in order to achieve a performance superior to that of the conventional LSCN cathode. The optimum amount of LSCN loading is in the range of 45-55 wt% with an activation energy near 1.32 eV for oxygen reduction. At temperatures between 600 and 750 °C, the polarization resistance of the 55 wt% LSCN loaded LSCN + GDC cathode is in the range of 1.07 and 0.08 Ω cm 2, which is only about one half of that for the conventional cathode.

  11. Fabrication and performance of membrane solid oxide fuel cells with La 0.75Sr 0.25Cr 0.5Mn 0.5O 3- δ impregnated anodes

    NASA Astrophysics Data System (ADS)

    Zhu, Xingbao; Lü, Zhe; Wei, Bo; Chen, Kongfa; Liu, Mingliang; Huang, Xiqiang; Su, Wenhui

    La 0.75Sr 0.25Cr 0.5Mn 0.5O 3- δ (LSCrM)-impregnated anodes have been fabricated by infiltrating 70% porous yttria-stabilized zirconia (YSZ) matrixes with an LSCrM solution. In these anodes, LSCrM is a primary electronic conducive phase while the well-sintered YSZ provides an ionic-conducting pathway throughout the electrode. The maximum power densities of a single cell with YSZ + 35 wt.% LSCrM composite anode reach 567 and 561 mW cm -2 at 850 °C in dry H 2 and CH 4, respectively. Further, Ag and Ni are added via nitrate impregnating method for improving electronic conductivity and catalytic activity. With the addition of 6 wt.% Ni and 2 wt.% Ag to the YSZ + 32 wt.% LSCrM composite anode, the maximum power densities at 850 °C increase to 1302 mW cm -2 in dry H 2 and 769 mW cm -2 in dry CH 4. No carbon deposition is detected in the tested anodes, even with the presence of Ni.

  12. Studies of electrical conductivity and complex initial permeability of multiferroic xBa0.95Sr0.05TiO3-(1-x)BiFe0.90Gd0.10O3 ceramics

    NASA Astrophysics Data System (ADS)

    Miah, Mohammad J.; Khan, M. N. I.; Hossain, A. K. M. Akther

    2016-07-01

    Multiferroic xBa0.95Sr0.05TiO3-(1-x)BiFe0.90Gd0.10O3 [xBST-(1-x)BFGO] (x = 0.00, 0.10 and 0.20) ceramics were prepared by the standard solid-state reaction technique. Crystal structure of the ceramics was determined by X-ray diffraction pattern. All the compositions exhibited rhombohedral crystal structure. The tolerance factor `t' varied from 0.847 to 0.864. The AC conductivity spectrum followed the Jonscher's power law. The Nyquist plots indicated that only grains have the contribution to the resistance in this material and the values of grain resistance (Rg) increased with BST content. The real part of complex initial permeability decreased with the increase in frequency and increased with increasing BST content. Magnetoelectric coefficient was determined for all compositions. The maximum value of magnetoelectric coefficient was found to be 1.467 mV.cm-1.Oe-1 for x = 0.20.

  13. Palladium and ceria infiltrated La 0.8Sr 0.2Co 0.5Fe 0.5O 3- δ cathodes of solid oxide fuel cells

    NASA Astrophysics Data System (ADS)

    Chen, Jing; Liang, Fengli; Chi, Bo; Pu, Jian; Jiang, San Ping; Jian, Li

    La 0.8Sr 0.2Co 0.5Fe 0.5O 3- δ (LSCF) cathodes infiltrated with electrocatalytically active Pd and (Gd,Ce)O 2 (GDC) nanoparticles are investigated as high performance cathodes for the O 2 reduction reaction in intermediate temperature solid oxide fuel cells (IT-SOFCs). Incorporation of nano-sized Pd and GDC particles significantly reduces the electrode area specific resistance (ASR) as compared to the pure LSCF cathode; ASR is 0.1 Ω cm 2 for the reaction on a LSCF cathode infiltrated with 1.2 mg cm -2 Pd and 0.06 Ω cm 2 on a LSCF cathode infiltrated with 1.5 mg cm -2 GDC at 750 °C, which are all significantly smaller than 0.22 Ω cm 2 obtained for the reaction on a conventional LSCF cathode. The activation energy of GDC- and Pd-impregnated LSCF cathodes is 157 and 176 kJ mol -1, respectively. The GDC-infiltrated LSCF cathode has a lower activation energy and higher electrocatalytic activity for the O 2 reduction reaction, showing promising potential for applications in IT-SOFCs.

  14. Visualization by neutron diffraction of 2D oxygen diffusion in the Sr(0.7)Ho(0.3)CoO(3-δ) cathode for solid-oxide fuel cells.

    PubMed

    Cascos, V; Martínez-Coronado, R; Alonso, J A; Fernández-Díaz, M T

    2014-06-25

    Sr0.7Ho0.3CoO3-δ oxide has been recently described as an excellent cathode material (1274 mW cm(-2) at 850 °C with pure H2 as fuel1) for solid oxide fuel cells (SOFCs) with LSGM as electrolyte. In this work, we describe a detailed study of its crystal structure conducted to find out the correlation between the excellent performance as a cathode and the structural features. The tetragonal crystal structure (e.g., I4/mmm) basically contains layers of octahedrally coordinated Co2O6 units alternated with layers of Co1O4 tetrahedra sharing corners. An "in situ" neutron power diffraction (NPD) experiment, between 25 and 800 °C, reveals the presence of a high oxygen deficiency affecting O4 oxygen atoms, with large displacement factors that suggest a large lability and mobility. Difference Fourier maps allow the visualization at high temperatures of the 2D diffusion pathways within the tetrahedral layers, where O3 and O4 oxygens participate. The measured thermal expansion coefficient is 16.61 × 10(-6) K(-1) between 300 and 850 °C, exhibiting an excellent chemical compatibility with the electrolyte. PMID:24873238

  15. Preparation of La 0.8Sr 0.2Ga 0.83Mg 0.17O 2.815 powders by microwave-induced poly(vinyl alcohol) solution polymerization

    NASA Astrophysics Data System (ADS)

    Zhai, Yuling; Ye, Chang; Xia, Feng; Xiao, Jianzhong; Dai, Lei; Yang, Yifan; Wang, Yongqian

    A new and simple chemical route, named microwave-induced poly(vinyl alcohol) (PVA) solution polymerization, has been used to prepare fine, homogeneous and high-density pellets of purer La 0.8Sr 0.2Ga 0.83Mg 0.17O 2.815 (denoted as LS 0.2GM 0.17). The effect of different contents of PVA as the polymeric carrier, was studied and we obtained an optimal amount of PVA (1.65:1 ratio of positively charged valences of the cations (Me n+) to negatively charged hydroxyl (-OH -) groups of the organics), which could ensure homogenous distribution of the metal ions in the polymeric network structure and inhibit segregation. The behavior of the powder after calcination at different temperatures was studied. The PVA solution process consumed less organic material compared with the Pechini process, and consequently PVA was a more effective carrier in the preparation of LSGM. Higher heating rate and a more homogenous heating manner without thermal gradients in the microwave oven resulted in fewer secondary phases in the LS 0.2GM 0.17 powder after calcination at 1400 °C for 9 h and a smaller pellet grain size (2-3 μm) without segregation. The density of LS 0.2GM 0.17 pellet sintered at 1400 °C for 9 h was 6.19 g cm -3.

  16. Effects of strain relaxation in Pr0.67Sr0.33MnO3 films probed by polarization dependent X-ray absorption near edge structure

    DOE PAGES

    zhang, Bangmin; Chen, Jingsheng; Venkatesan, T.; Sun, Cheng -Jun; Heald, Steve M.; Chow, Gan Moog; Yang, Ping; Chi, Xiao; Lin, Weinan

    2016-01-28

    In this study, the Mn K edge X-ray absorption near edge structure (XANES) of Pr0.67Sr0.33MnO3 films with different thicknesses on (001) LaAlO3 substrate were measured, and the effects of strain relaxation on film properties were investigated. The films experienced in-plane compressive strain and out-of-plane tensile strain. Strain relaxation evolved with the film thickness. In the polarization dependent XANES measurements, the in-plane (parallel) and out-of-plane (perpendicular) XANES spectrocopies were anisotropic with different absorption energy Er. The resonance energy Er along two directions shifted towards each other with increasing film thickness. Based on the X-ray diffraction results, it was suggested that themore » strain relaxation weakened the difference of the local environment and probability of electronic charge transfer (between Mn 3d and O 2p orbitals) along the in-plane and out-of-plane directions, which was responsible for the change of Er. XANES is a useful tool to probe the electronic structures, of which the effects on magnetic properties with the strain relaxation was also been studied.« less

  17. Modification of electrical properties of Au/n-type InP Schottky diode with a high-k Ba0.6Sr0.4TiO3 interlayer

    NASA Astrophysics Data System (ADS)

    Thapaswini, P. Prabhu; Padma, R.; Balaram, N.; Bindu, B.; Rajagopal Reddy, V.

    2016-05-01

    Au/Ba0.6Sr0.4TiO3 (BST)/n-InP metal/insulator/semiconductor (MIS) Schottky diodes have been analyzed by current-voltage (I-V) and capacitance-voltage (C-V) measurements. The surface morphology of the BST films on InP is fairly smooth. The Au/BST/n-InP MIS Schottky diode shows better rectification ratio and low leakage current compared to the conventional Au/n-InP metal-semiconductor (MS) Schottky diode. Higher barrier height is achieved for the MIS Schottky diode compared to the MS Schottky diode. The Norde and Cheung's methods are employed to determine the barrier height, ideality factor and series resistance. The interface state density (NSS) is determined from the forward bias I-V data for both the MS and MIS Schottky diodes. Results reveal that the NSS of the MIS Schottky diode is lower than that of the MS Schottky diode. The Poole-Frenkel emission is found dominating the reverse current in both Au/n-InP MS and Au/BST/n-InP MIS Schottky diodes, indicating the presence of structural defects and trap levels in the dielectric film.

  18. Electrical, magnetic and magnetocaloric properties of polycrystalline Pr0.63A0.07Sr0.3MnO3 (A=Pr, Sm and Bi)

    NASA Astrophysics Data System (ADS)

    Elghoul, A.; Krichene, A.; Boujelben, W.

    2016-11-01

    We studied the effects of the partial substitution (10%) of praseodymium by samarium and bismuth, on the structural, magnetic, magnetocaloric and electrical properties of the Pr0.63A0.07Sr0.3MnO3 (A=Pr, Sm and Bi) manganites prepared using the solid state reaction. Refinement of the X-ray diffraction patterns shows that all our samples are single phase and crystallize in the orthorhombic structure with Pnma space group. Magnetic studies indicate that all the samples exhibit a ferromagnetic-paramagnetic transition with increasing temperature. Curie temperature TC decreases by substitution. M(H) curves indicate the presence of some antiferromagnetic domains in the substituted samples testifying the phase-separated nature of these samples. The magnetic entropy curves -ΔS(T) show a maximum in vicinity of TC. Important values of maximum of -ΔS are recorded for our compounds. For the parent compound, we found 4.59 J/kg K for an applied magnetic field of 2 T at TC=266 K which raises the possibility of using this compound as a magnetic refrigerant. The temperature dependence of the electrical resistivity ρ(T) indicates that all compounds exhibit a metal-insulator transition with increasing temperature. Electrical study suggests the presence of a correlation between electrical and magnetic properties.

  19. The role of structural and magnetic inhomogeneities in the formation of magneto-transport properties of the La0.6-xSmxSr0.3Mn1.1O3-δ ceramics

    NASA Astrophysics Data System (ADS)

    Pashchenko, A. V.; Pashchenko, V. P.; Prokopenko, V. K.; Revenko, Yu. F.; Mazur, A. S.; Burchovetskii, V. V.; Turchenko, V. A.; Liedienov, N. A.; Pitsyuga, V. G.; Levchenko, G. G.; Dyakonov, V. P.; Szymczak, H.

    2016-10-01

    X-ray diffraction, magnetic, transport and SEM measurements were used to investigate the role of structural and magnetic inhomogeneities in the formation of magneto-transport properties of the La0.6-xSmxSr0.3Mn1.1O3-δ (x=0-0.6) ceramics. Reduction of the a parameter of perovskite structure and change of its symmetry are shown to be due to both replacement of La3+ by Sm3+ and an increase concentration of anion and cation vacancies. Broad asymmetric 55Mn NMR spectra are indicative of the high frequency electron double exchange Mn3+↔Mn4+ and demonstrate the heterogeneity of magnetic and valence Mn-states. An excess manganese is dissolved in perovskite structure statistically without formation of planar antiferromagnetic clusters of Mn2+ ions in the deformed A positions. Constructing phase diagram of "composition-structure-properties" describes a strong correlation between structural, resistive and magnetic properties as well as reflects a special role of structural defects in the formation of magneto-transport properties of the rare-earth manganites.

  20. Comparative study on multifunctional behavior of La0.7Ca0.24Sr0.06MnO3 and La0.88Ca0.12MnO3 single crystals

    NASA Astrophysics Data System (ADS)

    Tank, Tejas M.; Mukovskii, Ya. M.; Sanyal, Sankar P.

    2016-05-01

    We have investigated electrical-transport, magneto-transport, magnetic and thermal properties of the hole doped La0.7Ca0.24Sr0.06MnO3 (LCSMO) and La0.88Ca0.12MnO3 (LCMO) single crystals, prepared using floating zone technique. The crystallographic direction dependence of metal to insulator transition (TP) occurs at 290 K along c-axis and TP = 280 K along ab-plane for LCSMO single crystal, while no electronic transition was observed over the whole temperature range under the magnetic field at 8 T for LCMO single crystal. Resistivity study shows that the TP is higher along the c-axis as compared to that in the ab-plane, so signifying more favorable hoping of electrons is along the c-axis in LCSMO. The ac-susceptibility study confirms that these crystals, revealing ferromagnetic to paramagnetic transition temperature (TC) at 277 K for LCSMO and TC = 118 K for LCMO single crystals, which is close to the sharp peak around TC in heat capacity data. For magneto-electric device application point of view, these crystals show the maximum MR of 80% and 65% for LCSMO and LCMO single crystals at 8 T applied magnetic field respectively.

  1. Microstructure and dielectric properties of (Ba 0.6Sr 0.4)TiO 3 thin films grown on super smooth glazed-Al 2O 3 ceramics substrate

    NASA Astrophysics Data System (ADS)

    Chen, Hongwei; Yang, Chuanren; Zheng, Shanxue; Zhang, Jihua; Zhang, Qiaozhen; Lei, Guanhuan; Lou, Feizhi; Yang, Lijun

    2011-12-01

    Modified substrates with nanometer scale smooth surface were obtained via coating a layer of CaO-Al2O3-SiO2 (CaAlSi) high temperature glaze with proper additives on the rough-95% Al2O3 ceramics substrates. (Ba0.6Sr0.4)TiO3 (BST) thin films were deposited on modified Al2O3 substrates by radio-frequency magnetron sputtering. The microstructure, dielectric, and insulating properties of BST thin films grown on glazed-Al2O3 substrates were investigated by X-ray diffraction (XRD), atomic force microscope (AFM), and dielectric properties measurement. These results showed that microstructure and dielectric properties of BST thin films grown on glazed-Al2O3 substrates were almost consistent with that of BST thin films grown on LaAlO3 (1 0 0) single-crystal substrates. Thus, the expensive single-crystal substrates may be substituted by extremely cheap glazed-Al2O3 substrates.

  2. Hierarchical Mesoporous/Macroporous Perovskite La0.5Sr0.5CoO3-x Nanotubes: A Bifunctional Catalyst with Enhanced Activity and Cycle Stability for Rechargeable Lithium Oxygen Batteries.

    PubMed

    Liu, Guoxue; Chen, Hongbin; Xia, Lu; Wang, Suqing; Ding, Liang-Xin; Li, Dongdong; Xiao, Kang; Dai, Sheng; Wang, Haihui

    2015-10-14

    Perovskites show excellent specific catalytic activity toward both oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) in alkaline solutions; however, small surface areas of the perovskites synthesized by traditional sol-gel methods lead to low utilization of catalytic sites, which gives rise to poor Li-O2 batteries performance and restricts their application. Herein, a hierarchical mesporous/macroporous perovskite La0.5Sr0.5CoO3-x (HPN-LSC) nanotube is developed to promote its application in Li-O2 batteries. The HPN-LSC nanotubes were synthesized via electrospinning technique followed by postannealing. The as-prepared HPN-LSC catalyst exhibits outstanding intrinsic ORR and OER catalytic activity. The HPN-LSC/KB electrode displays excellent performance toward both discharge and charge processes for Li-O2 batteries, which enhances the reversibility, the round-trip efficiency, and the capacity of resultant batteries. The synergy of high catalytic activity and hierarchical mesoporous/macroporous nanotubular structure results in the Li-O2 batteries with good rate capability and excellent cycle stability of sustaining 50 cycles at a current density of 0.1 mA cm(-2) with an upper-limit capacity of 500 mAh g(-1). The results will benefit for the future development of high-performance Li-O2 batteries using hierarchical mesoporous/macroporous nanostructured perovskite-type catalysts. PMID:26418118

  3. Effects of Chrome Contamination on the Performance of La0.6Sr0.4Co0.2Fe0.8O­3 Cathode Used in Solid Oxide Fuel Cells

    SciTech Connect

    Kim, Jin Yong Y.; Sprenkle, Vince L.; Canfield, Nathan L.; Meinhardt, Kerry D.; Chick, Lawrence A.

    2006-04-01

    Chrome poisoning effects of various Cr-containing metal sources on the electrochemical performance of the La0.6Sr0.4Co0.2Fe0.8O­3 (LSCF6428) cathode have been investigated. It was found that chromia-forming metals caused significant fade in power density due to the chrome poisoning, while alumina-forming alloys exhibited no influence on the cell degradation. This degradation caused by the chrome poisoning was accelerated at higher operating temperatures. Microstructural analysis conducted on the cells tested with chromia-formers exhibited the formation of a strontium chromate phase in the entire cathode, leading to the homogeneous distribution of Cr in the cathode. Although the Mn-containing chromia former such as Crofer22 formed a continuous layer of the Cr-Mn oxide scale on the mesh surface, it was not effective enough to prevent Cr poisoning of the cathode. In contrast, alumina-formers such as Haynes214 and Kanthal formed a continuous layer of the alumina scale, resulting in no Cr contamination in the LSCF cathode.

  4. Effect of the symmetric cell preparation temperature on the activity of Ba0.5Sr0.5Fe0.8Cu0.2O3-δ as cathode for intermediate temperature Solid Oxide Fuel Cells

    NASA Astrophysics Data System (ADS)

    Vázquez, Santiago; Basbus, Juan; Soldati, Analía L.; Napolitano, Federico; Serquis, Adriana; Suescun, Leopoldo

    2015-01-01

    In this work we studied the electrochemical performance of Ba0.5Sr0.5Fe0.8Cu0.2O3-δ (BSFCu) as cathode for Intermediate Temperature Solid Oxide Fuel Cells (IT-SOFC) with Ce0.9Gd0.1O1.95 (CGO) electrolyte and the effect of the symmetric cell preparation temperature on the oxygen reduction reaction (ORR) activity. Symmetrical cells with the configuration BSFCu/CGO/BSFCu were prepared at 900 °C, 950 °C and 1000 °C to perform the electrochemical characterization in the 500-700 °C temperature range. The resultant area specific resistance (ASR) of the cells with different preparation temperatures followed the tendency: ASR900°C < ASR950°C < ASR1000°C. The symmetric cell constructed at 900 °C showed ASR values of 0.18, 0.078 and 0.035 Ω cm2 at 600, 650 and 700 °C respectively, which demonstrated superior electrochemical activities than previous reports. Additional, X-ray diffraction (XRD), scanning and transmission electron microscopies (SEM and TEM) techniques were used to characterize the microstructure of the original and fired BSFCu materials and correlate it with the cell preparation temperature.

  5. Electric and Magnetic Characterization of patterned La0.6Sr0.4MnO3/SrTiO3/Si junctions using strained SrTiO3 as a Ferroelectric Barrier

    NASA Astrophysics Data System (ADS)

    Jalili Shafighi, Parisa; Cottier, Ryan; Currie, Daniel. A.; Koehne, Barry. D.; Johnson, Andrew; Veazey, Joshua. P.; Theodoropoulou, Nikoleta; Texas State University, San Marcos, TX Team; Hope College, Holland, MI Team

    Controlling a magnetic device via electrical means is a sought-after goal for technological devices and can be achieved through magnetoelectric coupling between ferroelectric and ferromagnetic materials. We investigate such as possibility through a by epitaxially growing a magnetic oxide, La0.6Sr0.4MnO3 (LSMO) as an active magnetic electrode on a ferroelectric oxide, strained SrTiO3(STO) on Si. STO thin films grown on Si are compressively strained (1.7 %) and can be ferroelectric at T =300 K when less than 5nm thick. LSMO is ferromagnetic up to 340 K (in bulk), has an in-plane crystal constant of a = 0.3870 nm, and is closely lattice matched to STO (a = 0.3905 nm) with a 0.9% in-plane tensile strain. Since STO is compressively strained in Si, an even smaller lattice mismatch is expected between LSMO and STO/Si. We investigate the epitaxial growth of LSMO/STO/Si and electrical characteristics in a capacitor type structure fabricated using photolithography as a function of Temperature and Magnetic Field. Acknowledgements: Support by the NSF-Career grant, DMR-1255629, Hope College Frissel Research Fund, NSF-MRI Grant, CHE-1126462 is gratefully acknowledged.

  6. Development and understanding of La0.85Sr0.15Cr1-xNixO3-δ anodes for La5.6WO11.4-δ-based Proton Conducting Solid Oxide Fuel Cells

    NASA Astrophysics Data System (ADS)

    Solís, Cecilia; Navarrete, Laura; Balaguer, María; Serra, José M.

    2014-07-01

    Porous electrodes based on the system La0.85Sr0.15Cr1-xNixO3-δ (x = 0.1 and 0.2) have been investigated as anodes for proton conducting solid oxide fuel cells based on the La5.6WO11.4-δ (LWO) electrolyte material. The microstructure of the anodes was optimized by varying both the starting powder morphology and the final anode sintering temperature. Two different electrode thicknesses were studied, i.e. 15 and 30 μm. The importance of the catalytic role of Ni was also studied by using different concentrations of Ni (10% and 20%) in the chromite and by tuning the Ni particle sizes through the control of the reduction temperature. Additionally, a ceramic-ceramic (cer-cer) composite electrode comprising a physical mixture of the optimized chromite and LWO phase was also considered. Finally, a kinetics study and modeling based on Langmuir-Hinshelwood mechanism was carried out in order to quantitatively describe the rate of dissociative adsorption of H2 on the Ni particles spread on the chromite surface.

  7. Large enhancement of magnetic anisotropy and laser induced resistive switching effect in La0.7Sr0.3MnO3 films due to strain from BaTiO3 substrates

    NASA Astrophysics Data System (ADS)

    Kalappattil, V.; Das, R.; Srikanth, H.; Phan, M. H.; Moya, X.

    Multifunctional oxide materials are interesting for their fundamental physical properties and technological applications. Epitaxial films of La0.7Sr0.3MnO3 (LSMO) on BaTiO3 (BTO) show intriguing properties such as a giant magnetoelectric effect due to strain from BTO substrate. The LSMO film shows sharp jumps in magnetization M(T) and resistance R(T) at first-order structural phase transitions of BTO (TR-O 200K and TO-T 270 K) due to strain coupling from BTO. A temperature evolution of effective in-plane anisotropy field (HK) measured using the radio-frequency transverse susceptibility (TS) shows a sharp increase in HK around TR-O, which vanishes around TO-T.The in-plane magnetic anisotropy plays an important role in changing the magnetic and resistive states around TO-T. A switchable laser-induced resistive change of up to 300 %, which is about 10 times greater than those of conventional oxide systems, has been achieved in LSMO films using a 0.5 W violet laser just below the TO-T.The repeatability and stability of the laser-induced resistive switching effect reveal potential applications of LSMO/BTO heterostructures in developing new type of temperature sensors and memory devices. Work at USF supported by ARO Grant No. W911NF-15-1-0626.

  8. Optimization of the electrochemical performance of a Ni/Ce0.9Gd0.1O2-δ-impregnated La0.57Sr0.15TiO3 anode in hydrogen

    NASA Astrophysics Data System (ADS)

    Xia, Tian; Brüll, Annelise; Grimaud, Alexis; Fourcade, Sébastien; Mauvy, Fabrice; Zhao, Hui; Grenier, Jean-Claude; Bassat, Jean-Marc

    2014-09-01

    A-site deficient perovskite La0.57Sr0.15TiO3 (LSTO) materials are synthesized by a modified polyacrylamide gel route. X-ray diffraction pattern of LSTO indicates an orthorhombic structure. The thermal expansion coefficient of LSTO is 10.0 × 10-6 K-1 at 600 °C in 5%H2/Ar. LSTO shows an electrical conductivity of 2 S cm-1 at 600 °C in 3%H2O/H2. A new composite material, containing the porous LSTO backbone impregnated with small amounts of Ce0.9Gd0.1O2-δ (CGO) (3.4-8.3 wt.%) and Ni/Cu (2.0-6.3 wt.%), is investigated as an alternative anode for solid oxide fuel cells (SOFCs). Because of the substantial electro-catalytic activity of the fine and well-dispersed Ni particles on the surface of the ceramic framework, the polarization resistance of 6.3%Ni-8.3%CGO-LSTO anode reaches 0.73 Ω cm2 at 800 °C in 3%H2O/H2. In order to further improve the anodic performance, corn starch and carbon black are used as pore-formers to optimize the microstructure of anodes.

  9. Fe substitution for Mn in PrSrCaMnO - The electrical and dielectrical properties of Pr0.6Sr0.3Ca0.1Mn1-xFexO3 perovskite

    NASA Astrophysics Data System (ADS)

    Cherif, B.; Jemai, R.; Rahmouni, H.; Baazaoui, M.; Khirouni, K.

    2016-09-01

    We have performed admittance spectroscopy measurements on a series of Pr_{0.6}Sr_{0.3}Ca_{0.1}Mn_{1-x}FexO3 (PSCMO) compounds with x=0, 0.025, 0.050 and 0.075. The results show that all samples exhibit a metal-insulator transition at a temperature which decreases with the iron content. The conduction mechanism is described by thermally activated hopping of small polaron. Activation energy changes at specific temperature T s, probably due to the contribution of the polarization effect to the conductivity. The dielectric permittivity increases with the temperature until a temperature T d near the specific temperature T s and then begins to decrease. This is explained by the fact that at a certain temperature, the free carriers acquire sufficient energy to overcome potential barriers, and so they enhance the conductivity and decrease the polarization. The dielectric permittivity measurements are well described by a modified Curie-Weiss law.

  10. Electrical transport and magnetic properties of epitaxial Nd0.7 Sr0.3 MnO3 thin films on (001)-oriented LaAlO3 substrate

    NASA Astrophysics Data System (ADS)

    Gopalarao, T. R.; Ravi, S.; Pamu, D.

    2016-07-01

    Nd0.7 Sr0.3 MnO3 thin films were deposited using RF-magnetron sputtering on (001) oriented LaAlO3 substrate by varying thickness in the range of 12-200 nm. X-ray diffraction patterns of both air annealed and oxygen annealed films show epitaxial growth along (00l) orientation with decrease in lattice strain with increase in film thickness. Raman spectra show the presence of strong peaks corresponding to rotational and stretching modes of MnO6 octahedra and their intensity is found to decrease with increase in film thickness. Both air and oxygen annealed films except for 12 nm thickness exhibit ferromagnetic transition with a maximum TC of 200 K. The magnetic anisotropic constant was estimated from the analysis of M-H curve and its value is found to decrease with increase in film thickness. Metal-insulator transitions have been observed in all films including the 12 nm thick film. The electrical resistivity data in the metallic region, i.e. close to TMI, were analysed by considering electron-magnon scattering mechanism and in the low temperature region far below TMI; the analysis was carried out by considering the combination of electron-electron scattering and charge localisation effect. The resistivity data in the insulating region (T >TMI) were analysed by considering Mott-variable range hopping model.

  11. Ferromagnetic and multiferroic interfaces in granular perovskite composite xLa0.5Sr0.5CoO3-(1-x)BiFeO3

    NASA Astrophysics Data System (ADS)

    Lohr, Javier H.; López, Carlos A.; Saleta, Martín E.; Sánchez, Rodolfo D.

    2016-08-01

    Nanopowder of ferromagnetic La0.5Sr0.5CoO3 (LSCO) and multiferroic BiFeO3 (BFO) were synthesized by spray pyrolysis method. Different compositions of multiferroic xLSCO-(1-x)BFO composites were synthesized at 800 °C for 2 h. Scanning electron microscopy and energy dispersive spectroscopy elemental mapping were performed to study the morphology of composites. Ferri/ferromagnetic responses above TC (LSCO) are observed, which are associated with the interfaces LSCO/BFO. This interface presents a different behavior compared to the original perovskites, and the magnitude of the magnetization depends on x. Electrical DC conductivity as a function of temperature for LSCO nanopowder (x = 1) presents a different behavior than that reported in bulk material. For x = 1 and 0.9, the model by Glazman and Matveev [Zh. Eksp. Teor. Fiz. 94, 332 (1988)] is proposed to describe the electrical conductivity. On the other hand, x = 0, 0.1, and 0.5 present a variable range hopping behavior. Complex impedance spectroscopy as a function of frequency indicates a pure resistive behavior for x ≥ 0.5 compositions, while a complex resistive-capacitive behavior is observed for low x values (0, 0.1). In these samples, low values of magnetoelectric coupling were measured with an AC lock-in technique.

  12. Influence of electrospraying parameters on the microstructure of La 0.6Sr 0.4Co 0.2F 0.8O 3-δ films for SOFCs

    NASA Astrophysics Data System (ADS)

    Marinha, Daniel; Rossignol, Cécile; Djurado, Elisabeth

    2009-07-01

    Ceramics can play a remarkable role in the engineering of intermediate temperature solid oxide fuel cells (IT-SOFCs) capable of meeting the ambitious targets of reduced cost and improved lifetime. While mixed ionic-electronic conductors such as La xSr 1-xCo yFe 1-yO 3-δ are being used as volumic cathodes to increase the catalytic performance of these components, adequate microstructures are also an important requirement for optimal performance, particularly at lower operating temperatures. This work is devoted to the fabrication of La 0.6Sr 0.4Co 0.2Fe 0.8O 3-δ films on Ce 0.9Gd 0.1O 2-δ substrates by electrostatic spray deposition (ESD) and to the characterization of the microstructural dependence on the deposition conditions. A wide variety of microstructures ranging from dense to porous, with particular features such as reticulation and micro-porosity, were obtained by varying the ESD deposition parameters: nozzle-to-substrate distance (15, 30, 43, 45, and 58 mm), solution flow rate (0.34 and 1.5 mL/h), and substrate temperature (300, 350, 400 and 450 °C). The correlation between deposition parameters and resulting microstructures was systematically studied and put into evidence.

  13. Solution-processed perfect uniaxial orientation of perovskite titanate (Ca0.65Sr0.35)0.997Pr0.002TiO3 phosphor thin films

    NASA Astrophysics Data System (ADS)

    Nakajima, Tomohiko; Shinoda, Kentaro; Tsuchiya, Tetsuo

    2014-01-01

    We report the preparation of perfect uniaxially-oriented (Ca0.65Sr0.35)0.997Pr0.002TiO3 phosphor thin films on glass substrates with an oriented Dion-Jacobson perovskite RbLaNb2O7 seed layer prepared using an excimer-laser-assisted metal organic deposition process. The obtained phosphor thin films on the seed layer exhibited perfect uniaxial (010)-orientation below 40 mJ/cm2. At 40 mJ/cm2, the film showed intense red luminescence at 612 nm. The luminance was evaluated to be 14.5 cd/m2 under 300 nm excitation light at 3.5 mW/cm2, and this value was 26% higher than that of unoriented film. Above 45 mJ/cm2, the phosphor thin films had a mud-crack pattern. Thus, the crystal orientation quality and luminescence intensity was lowered. The precise control of preparation conditions is necessary for preparation of heterostructures with good orientation quality.

  14. EFFECTS OF ELECTRODE RESISTANCE ON THE DIELECTRIC BEHAVIORS OF Au/BaxSr1-xTiO3/La1.1Sr0.9NiO4 CAPACITORS

    NASA Astrophysics Data System (ADS)

    Qiu, Jie; Liu, Guozhen; Wolfman, Jérôme

    2016-05-01

    BaxSr1-xTiO3 (0.1≤x≤0.5) (BST) thin films were prepared on La1.1Sr0.9NiO4 (LSNO)/SrTiO3 (STO) structure by combinatorial pulsed laser deposition (comb-PLD). The capacitances of the Au/BST/LSNO capacitors exhibited strong frequency dependence especially when the applied frequency was higher than 10kHz. On the basis of an equivalent circuit model, we presented a theoretical simulation of the relationships between capacitance and frequency for the capacitors with different electrode serial resistances. Based on the fitting results, the observed strong frequency dependence of the measured capacitance at high frequency in our study could be ascribed to the large serial resistance of 750 Ω for oxide electrode LSNO. Further simulation studies found that large serial resistance (1000 Ω) could result in an apparent deviation from the intrinsic dielectric properties especially at high frequencies (>100kHz) for capacitors with capacitances above 1nF. Our results provide useful information for the design of all-oxide electronic devices.

  15. Interfacial charge-mediated non-volatile magnetoelectric coupling in Co0.3Fe0.7/Ba0.6Sr0.4TiO3/Nb:SrTiO3 multiferroic heterostructures

    DOE PAGES

    Zhou, Ziyao; Howe, Brandon M.; Liu, Ming; Nan, Tianxiang; Chen, Xing; Mahalingam, Krishnamurthy; Sun, Nian X.; Brown, Gail J.

    2015-01-13

    The central challenge in realizing non-volatile, E-field manipulation of magnetism lies in finding an energy efficient means to switch between the distinct magnetic states in a stable and reversible manner. In this work, we demonstrate using electrical polarization-induced charge screening to change the ground state of magnetic ordering in order to non-volatilely tune magnetic properties in ultra-thin Co0.3Fe0.7/Ba0.6Sr0.4TiO3/Nb:SrTiO3 (001) multiferroic heterostructures. A robust, voltage-induced, non-volatile manipulation of out-of-plane magnetic anisotropy up to 40 Oe is demonstrated and confirmed by ferromagnetic resonance measurements. This discovery provides a framework for realizing charge-sensitive order parameter tuning in ultra-thin multiferroic heterostructures, demonstrating great potentialmore » for delivering compact, lightweight, reconfigurable, and energy-efficient electronic devices.« less

  16. Structural and physical properties of Ba0.6Sr0.4TiO3 film prepared by pulsed laser deposition in a mixture of argon and oxygen

    NASA Astrophysics Data System (ADS)

    Lou, J. Z.; Fang, X. Y.; Wang, S. J.; Dai, X. H.; Jia, C. J.; Zhang, L.; Jia, Y. L.; Wang, Y. L.; Ma, L. X.; Liu, B. T.

    2015-06-01

    In order to investigate the effect of argon introduction on the structural and physical properties of Ba0.6Sr0.4TiO3 (BST) films, epitaxial BST films have been grown by pulsed laser deposition (PLD) on (001) oriented Nb-SrTiO3 (STON) substrates in the ambient gas of pure oxygen and the mixture of argon and oxygen, respectively. The atomic force microscopy (AFM) reveals that the sample deposited in the mixture of argon and oxygen has a bigger grain size than that deposited in pure oxygen. The dielectric properties of two BST films have been investigated using the Pt/BST/STON parallel plate capacitors. The tunability and the figure of merit (FOM) of the BST film deposited in the mixture gas are about 41% and 7.07 at a DC bias voltage of 8 V at room temperature, which are better than 32% and 4.51, for BST film deposited in pure oxygen. On account of the introduction of argon, the leakage current density of the BST film deposited in the mixture gas has fallen by almost five times, and the leakage current mechanism is both in accordance with ohmic conductive mechanism.

  17. Irradiation effects on the surface morphology and on the magnetic microstructure of giant magnetoresistance La 0.7Sr 0.3MnO 3 thin films studied by magnetic force microscopy

    NASA Astrophysics Data System (ADS)

    Desfeux, R.; Elard, F.; Da Costa, A.; Mathieu, Ch.; Wolfman, J.; Hamet, J. F.; Simon, Ch.

    1999-05-01

    Giant magnetoresistance La 0.7Sr 0.3MnO 3 thin films have been grown by pulsed laser ablation on SrTiO 3 (0 0 1) oriented substrates. SQUID measurements have evidenced that these films are ferromagnetic at room temperature. Some of these films have been irradiated using 6 GeV Pb ions. Atomic force microscopy study performed at the micron scale in air and at room temperature reveals that the topographic images are similar for the two kinds of films. The magnetic force microscopy (MFM) images of the non-irradiated sample shown an uniform surface, indicating that different types of magnetic domains could not be evidenced. On the other hand, the MFM images of the irradiated sample show the existence of numerous walls, indicating the existence of magnetic domains with different magnetization direction. We conclude that irradiation plays an important role on the magnetic order and that the columnar defects created in the films by the irradiation are possible pinning centers for the magnetic domain walls.

  18. Cationic Intermixing and Reactivity at the La2 Mo2 O9 /La0.8 Sr0.2 MnO3-δ Solid Oxide Fuel Cell Electrolyte-Cathode Interface.

    PubMed

    Ravella, Uday K; Liu, Jingjing; Corbel, Gwenaël; Skinner, Stephen J; Lacorre, Philippe

    2016-08-23

    Among standard high-temperature cathode materials for solid oxide fuel cells, La0.8 Sr0.2 MnO3-δ (LSM) displays the least reactivity with the oxide-ion conductor La2 Mo2 O9 (LMO), yet a reaction is observed at high processing temperatures, identified by using XRD and focused ion beam secondary-ion mass spectrometry (FIB-SIMS) after annealing at 1050 and 1150 °C. Additionally, Sr and Mn solutions were deposited and annealed on LMO pellets, as well as a Mo solution on a LSM pellet. From these studies several reaction products were identified by using XRD and located by using FIB-SIMS on the surface of pelletised samples. We used depth profiling to show that the reactivity extended up to ∼10 μm from the surface region. If Sr was present, a SrMoO4 -type scheelite phase was always observed as a reaction product, and if Mn was present, LaMnO3+δ single crystals were observed on the surface of the LMO pellets. Additional phases such as La2 MoO6 and La6 MoO12 were also detected depending on the configuration and annealing temperature. Reaction mechanisms and detailed reaction formulae are proposed to explain these observations. The strongest driving force for cationic diffusion appears to originate from Mo(6+) and Mn(3+) cations, rather than from Sr(2+) . PMID:27478975

  19. Investigation of Sm 0.5Sr 0.5CoO 3- δ/Co 3O 4 composite cathode for intermediate-temperature solid oxide fuel cells

    NASA Astrophysics Data System (ADS)

    Zhang, Haizhou; Liu, Huanying; Cong, You; Yang, Weishen

    The electrochemical properties of an Sm 0.5Sr 0.5CoO 3- δ/Co 3O 4 (SSC/Co 3O 4) composite cathode were investigated as a function of the cathode-firing temperature, SSC/Co 3O 4 composition, oxygen partial pressure and CO 2 treatment. The results showed that the composite cathodes had an optimal microstructure at a firing temperature of about 1100 °C, while the optimum Co 3O 4 content in the composite cathode was about 40 wt.%. A single cell with this optimized C 40-1100 cathode exhibited a very low polarization resistance of 0.058 Ω cm 2, and yielded a maximum power density of 1092 mW cm -2 with humidified hydrogen fuel and air oxidant at 600 °C. The maximum power density reached 1452 mW cm -2 when pure oxygen was used as the oxidant for a cell with a C 30-1100 cathode operating at 600 °C due to the enhanced open-circuit voltage and accelerated oxygen surface-exchange rate. X-ray diffraction and thermogravimetric analyses, as well as the electrochemical properties of a CO 2-treated cathode, also implied promising applications of such highly efficient SSC/Co 3O 4 composite cathodes in single-chamber fuel cells with direct hydrocarbon fuels operating at temperatures below 500 °C.

  20. Electronic structure, electron field emission and magnetic behaviors of carbon nanotubes fabricated on La0.66Sr0.33MnO3 (LSMO) for spintronics application.

    PubMed

    Ray, Sekhar Chandra; Tsai, Huang-Ming; Chen, Huang-Chin; Wu, Shang-Lun; Ling, Dah-Chin; Lin, I-Nan; Pong, Way-Faung

    2011-12-01

    This work elucidates the electronic structure, electron field emission and magnetic anisotropic behaviors of single wall carbon nanotubes (SWCNTs) for the spin-electronics device application grown on the La0.66Sr0.33MnO3 (LSMO)/SrTiO3 (STO) substrate. Micro-Raman spectroscopy, X-ray absorption near-edge structure (XANES) and valence-band photoemission spectroscopy (VBPES) were used for the study of electronics structure. The field emission characteristics were studied from the electron field emission current density (J) versus applied electric field (E(A)) from which the turn-on electric field (E(TOE)) was evaluated. The magnetization behaviors are also presented by the M-H hysteresis loop and were obtained by applying the magnetic field in the parallel and perpendicular direction of the CNTs at 305 K and 5 K temperatures. A magnetic measurement shows that the coercivity of the CNTs/LSMO/STO is higher and has hig anisotropic-nature than the composite LSMO/STO that could be the good material for the future possible spin-electronics device applications.

  1. Magnetic and structural properties of Sr0.75La0.25FexCu0.20O19 (10.40≤x≤11.80) hexagonal ferrites prepared by the solid-state reaction

    NASA Astrophysics Data System (ADS)

    Yang, Yujie; Shao, Juxiang; Wang, Fanhou; Liu, Xiansong; Feng, Shuangjiu; Huang, Duohui; Yang, Junsheng; Jin, Chengguo

    2016-05-01

    In this study, the hexaferrite magnetic powders and magnets according to the formula Sr0.75La0.25FexCu0.20O19, where x ranging from 10.40 to 11.80 with a step of 0.2 were prepared by the solid-state reaction. X-ray diffraction was performed to investigate the microstructures of the magnetic powders. The results show that a single magnetoplumbite phase is obtained for the magnetic powders with Fe content (10.60≤x≤11.60). For the magnetic powders with Fe content (x) of 10.40 or 11.80, magnetic impurities appear in the structure. A field emission scanning electron microscopy was hired to explore the micrographs of the magnets. The hexaferrite magnets are formed of hexagonal-shaped crystals. A magnetic properties test instrument was used in order to study the magnetic properties of the magnets. The remanence and maximum energy product first increase with Fe content (x) from 10.40 to 11.00 and then begin to decrease when Fe content (x) continues to increase. While the intrinsic coercivity and magnetic induction coercivity first increase with Fe content (x) from 10.40 to 11.20 and then decrease when Fe content (x)>11.20.

  2. Influence of strontium-rich pore-filling phase on the performance of La0.6Sr0.4CoO3-δ thin-film cathodes

    NASA Astrophysics Data System (ADS)

    Pecho, Omar; Holzer, Lorenz; Yáng, Zhèn; Martynczuk, Julia; Hocker, Thomas; Flatt, Robert J.; Prestat, Michel

    2015-01-01

    Nanoporous 1-μm thin La0.6Sr0.4CoO3-δ (LSC) layers are deposited by spray pyrolysis and subsequently sintered at 600 °C, 800 °C, and 1000 °C. A strontium- and oxygen-rich phase can be found within the pore network, which appears at low sintering temperatures. This so-called "secondary phase" occupies up to 20.7 vol.% of the LSC films for the 600 °C annealing process. It does not hinder the electrochemical activity towards oxygen reduction of such layers that exhibit an area-specific resistance (ASR) as low as 0.13 Ω cm2 at 600 °C in air. This result makes the spray pyrolysed LSC thin films promising candidates as intermediate-temperature solid oxide fuel cell cathodes. For higher sintering temperatures the secondary phase progressively disappears. A correlation between the inverse of the ASR and the whole LSC surface area (regardless of the presence of the secondary phase or not) is also evidenced. The increase of ASR with increasing sintering temperature is found to be primarily related to the exchange neutral flux density of the Sr-deficient LSC.

  3. Synthesis and characterization of La0.6Sr0.4Fe0.8Cu0.2O3-δ oxide as cathode for Intermediate Temperature Solid Oxide Fuel Cells

    NASA Astrophysics Data System (ADS)

    Vázquez, Santiago; Davyt, Sebastián; Basbus, Juan F.; Soldati, Analía L.; Amaya, Alejandro; Serquis, Adriana; Faccio, Ricardo; Suescun, Leopoldo

    2015-08-01

    Nanocrystalline La0.6Sr0.4Fe0.8Cu0.2O3-δ (LSFCu) material was synthetized by combustion method using EDTA as fuel/chelating agent and NH4NO3 as combustion promoter. Structural characterization using thermodiffraction data allowed to determine a reversible phase transition at 425 °C from a low temperature R-3c phase to a high temperature Pm-3m phase and to calculate the thermal expansion coefficient (TEC) of both phases. Important characteristics for cathode application as electronic conductivity and chemical compatibility with Ce0.9Gd0.1O2-δ (CGO) electrolyte were evaluated. LSFCu presented a p-type conductor behavior with maximum conductivity of 135 S cm-1 at 275 °C and showed a good stability with CGO electrolyte at high temperatures. This work confirmed that as prepared LSFCu has excellent microstructural characteristics and an electrical conductivity between 100 and 60 S cm-1 in the 500-700 °C range which is sufficiently high to work as intermediate temperature Solid Oxide Fuel Cells (IT-SOFCs) cathode. However a change in the thermal expansion coefficient consistent with a small oxygen loss process may affect the electrode-electrolyte interface during fabrication and operation of a SOFC.

  4. Enhanced magnetoelectric effect in La0.67Sr0.33MnO3/PbZr0.52Ti0.48O3 multiferroic nanocomposite films with a SrRuO3 buffer layer

    NASA Astrophysics Data System (ADS)

    Tang, Z. H.; Tang, M. H.; Lv, X. S.; Cai, H. Q.; Xiao, Y. G.; Cheng, C. P.; Zhou, Y. C.; He, J.

    2013-04-01

    Epitaxial thin films of La0.67Sr0.33MnO3/PbZr0.52Ti0.48O3 (LSMO/PZT) were deposited on SrTiO3 substrates with a SrRuO3 buffer layer by employing the pulsed laser deposition method. Its crystal structure, surface morphology, and polarization switching were investigated by using X-ray diffraction, scanning electron microscopy, and piezo-force microscopy measurements, respectively. Ferroelectric behavior along with a remnant polarization (2Pr) of 62 μC/cm2, a saturated magnetization of ˜76 emu/cm3, and a magnetoelectric effect voltage coefficient αME around 202 mV/cm Oe and 300 mV/cm Oe at 1 kHz were obtained successfully for the LSMO/PZT bilayers at room temperature. The result indicated that the coupling effects of electric and magnetic fields exist in the fabricated composite thin films.

  5. Improving La0.6Sr0.4Co0.8Fe0.2O3-δ infiltrated solid oxide fuel cell cathode performance through precursor solution desiccation

    NASA Astrophysics Data System (ADS)

    Burye, Theodore E.; Nicholas, Jason D.

    2015-02-01

    Here, for the first time, the average size of solid oxide fuel cell (SOFC) electrode nano-particles was reduced through the chemical desiccation of infiltrated precursor nitrate solutions. Specifically, after firing at 700 °C, CaCl2-desiccated La0.6Sr0.4Co0.8Fe0.2O3-δ (LSCF) - Ce0.9Gd0.1O1.95 (GDC) cathodes contained LSCF infiltrate particles with an average size of 22 nm. This is in contrast to comparable, undesiccated LSCF-GDC cathodes which contained LSCF infiltrate particles with an average size of 48 nm. X-ray diffraction, scanning electron microscopy, and controlled atmosphere electrochemical impedance spectroscopy revealed that desiccation reduced the average infiltrate particle size without altering the infiltrate phase purity, the cathode concentration polarization resistance, or the cathode electronic resistance. Compared to undesiccated LSCF-GDC cathodes achieving polarization resistances of 0.10 Ωcm2 at 640 °C, comparable CaCl2-dessicated LSCF-GDC cathodes achieved 0.10 Ωcm2 at 575 °C. Mathematical modeling suggested that these performance improvements resulted solely from average infiltrate particle size reductions.

  6. Stability of La0.6Sr0.4Co0.2Fe0.8O3/Ce0.9Gd0.1O2 cathodes during sintering and solid oxide fuel cell operation

    NASA Astrophysics Data System (ADS)

    Kiebach, Ragnar; Zhang, Wei-Wei; Zhang, Wei; Chen, Ming; Norrman, Kion; Wang, Hsiang-Jen; Bowen, Jacob R.; Barfod, Rasmus; Hendriksen, Peter Vang

    2015-06-01

    Degradation phenomena of La0.58Sr0.4Co0.2Fe0.8O3/Ce0.9Gd0.1O2 (LSCF/CGO) cathodes were investigated via post-mortem analyses of an experimental solid oxide fuel cell (SOFC) stack tested at 700 °C for 2000 h using advanced electron microscopy (SEM-EDS, HR-TEM-EDS) and time-of-flight secondary ion mass spectrometry (TOF-SIMS). Similar studies were carried out on non-tested reference cells for comparison. The analysis focused on the LSCF/CGO cathode and the CGO barrier layer, as the cathode degradation can be a major contributor to the overall degradation in this type of SOFC. SEM-EDS and TOF-SIMS were used to investigate inter-diffusion across the barrier layer-electrolyte interface and the barrier layer-cathode interface. In addition, TOF-SIMS data were employed to investigate impurity distribution before and after testing. HR-TEM-EDS was used to investigate possible phase segregation in the LSCF and to look for reaction between the phases. The results show that phase separation and inter-diffusion across the cathode-barrier layer interface and the barrier layer-electrolyte interface happened mainly during sintering and cathode firing, and to a very little degree during the test period.

  7. Kinetic arrest of first-order transition between charge-ordered and ferromagnetic phases in Gd0.5Sr0.5MnO3 single crystals: magnetization relaxation studies

    NASA Astrophysics Data System (ADS)

    Wagh, Aditya A.; Kumar, P. S. Anil; Elizabeth, Suja

    2016-10-01

    We have studied the span and nature of first-order phase transition (FOPT) between charge-ordered insulating and ferromagnetic metallic phases in oriented single crystals of Gd0.5Sr0.5MnO3. Magnetic field—temperature phase diagram was formulated from magnetization data for different crystallographic axes and non-monotonic variation of supercooling limit was observed at low temperature. A peculiar nature of magnetization was observed as irreversible open hysteresis loops during thermal cycling. We perceive that the nature of metastable states responsible for open hysteresis loops is different from that of supercooled ones. Further, thermal cycling magnetization data reveal that magnetic phases formed at 8 K after zero-field or field-cooled protocols (89 kOe) are not in equilibrium. Relaxation time constant is found to increase below 30 K in magnetization relaxation measurements made across the FOPT. The non-monotonic variation of relaxation time constant is a manifestation of kinetic arrest of the FOPT. We propose that the non-equilibrium, glass-like magnetic phase (at 8 K and 89 kOe) is a consequence of kinetic arrest.

  8. Porous YSZ impregnated with La0.4Sr0.5Ba0.1TiO3 as a possible composite anode for SOFCs fueled with sour feeds

    NASA Astrophysics Data System (ADS)

    Vincent, Adrien L.; Hanifi, Amir R.; Luo, Jing-Li; Chuang, Karl T.; Sanger, Alan R.; Etsell, Thomas H.; Sarkar, Partha

    2012-10-01

    The system LSBT/YSZ (LSBT is La0.4Sr0.5Ba0.1TiO3) is a promising combination as an anode material for full ceramic SOFCs. An anode comprising a porous layer of YSZ impregnated with LSBT shows good performance for conversion of high sulfur content fuels. The microstructures within the composite matrix were determined and correlated with the parameters of the production process. The anodes were characterized electrochemically using impedance spectroscopy (EIS) and potentiodynamic tests performed at 850 °C with various fuels to determine the effect of H2S in the feeds: H2, H2/H2S (5000 ppm), CH4, CH4/H2S (5000 ppm). The highest power densities (200 mW cm-2 in H2/H2S) were obtained for LSBT/YSZ composites after impregnation six times with LSBT, corresponding to 12.6 wt% LSBT; further impregnations dramatically decreased performance as a result of restricted access of fuel to active sites.

  9. Abnormal percolative transport and colossal electroresistance induced by anisotropic strain in (011)-Pr0.7(Ca0.6Sr0.4)0.3MnO3/PMN-PT heterostructure

    NASA Astrophysics Data System (ADS)

    Zhao, Ying-Ying; Wang, Jing; Kuang, Hao; Hu, Feng-Xia; Zhang, Hong-Rui; Liu, Yao; Zhang, Ying; Wang, Shuan-Hu; Wu, Rong-Rong; Zhang, Ming; Bao, Li-Fu; Sun, Ji-Rong; Shen, Bao-Gen

    2014-11-01

    Abnormal percolative transport in inhomogeneous systems has drawn increasing interests due to its deviation from the conventional percolation picture. However, its nature is still ambiguous partly due to the difficulty in obtaining controllable abnormal percolative transport behaviors. Here, we report the first observation of electric-field-controlled abnormal percolative transport in (011)-Pr0.7(Ca0.6Sr0.4)0.3MnO3/0.7Pb(Mg1/3Nb2/3)O3-0.3PbTiO3 heterostructure. By introducing an electric-field-induced in-plane anisotropic strain-field in a phase separated PCSMO film, we stimulate a significant inverse thermal hysteresis (~ -17.5 K) and positive colossal electroresistance (~11460%), which is found to be crucially orientation-dependent and completely inconsistent with the well accepted conventional percolation picture. Further investigations reveal that such abnormal inverse hysteresis is strongly related to the preferential formation of ferromagnetic metallic domains caused by in-plane anisotropic strain-field. Meanwhile, it is found that the positive colossal electroresistance should be ascribed to the coactions between the anisotropic strain and the polarization effect from the poling of the substrate which leads to orientation and bias-polarity dependencies for the colossal electroresistance. This work unambiguously evidences the indispensable role of the anisotropic strain-field in driving the abnormal percolative transport and provides a new perspective for well understanding the percolation mechanism in inhomogeneous systems.

  10. The impact of Co/La ratios on microstructure and magnetic properties of the Sr0.75-xCa0.25LaxFe12-yCoyO19 hexaferrites

    NASA Astrophysics Data System (ADS)

    Yang, Yujie; Wang, Fanhou; Shao, Juxiang; Huang, Duohui; Liu, Xiansong; Feng, Shuangjiu; Wen, Cuie

    2015-06-01

    Hexagonal ferrite Sr0.75-xCa0.25LaxFe12-yCoyO19 magnetic powder and magnets were synthesized according to a ceramic process. The phase compositions of the magnetic powder samples were determined by X-ray diffraction. There is a single magnetoplumbite phase in the samples with y/x from 0.3 to 0.6, and when y/x>0.6, the CoFe2O4 phase is observed. The micrographs of the sintered magnets were observed by a field emission scanning electron microscopy. The magnets have formed the hexagonal structures and the particles are distributed inhomogeneously. The impact of Co/La ratios on magnetic properties of the magnets was studied systematically. The remanence, magnetic induction coercivity and maximum energy product of the magnets first increase with y/x from 0.3 to 0.6, and then decrease when y/x>0.6. However, the intrinsic coercivity of the magnets first increases with y/x from 0.3 to 0.9, and decreases when y/x>0.9. The rectangularity of the demagnetizing curves for the magnets decreases with increasing y/x.

  11. Influence of heat treatment temperatures on structural and magnetic properties of Sr0.50Ca0.20La0.30Fe11.15Co0.25O19 hexagonal ferrites

    NASA Astrophysics Data System (ADS)

    Yang, Yujie; Liu, Xiansong; Jin, Dali

    2014-09-01

    M-type ferrite Sr0.50Ca0.20La0.30Fe11.15Co0.25O19 magnetic powders and magnets were prepared by a ceramic process. The phase identification of magnetic powders was performed by X-ray diffraction. At calcination temperatures ranging from 1170 to 1270 °C, the phase compositions of the magnetic powders consist of M-type hexaferrites together with small amount of impurity phases such as α-Fe2O3, LaFeO3 and CoFe2O4. At calcination temperatures above 1270 °C, single-phase M-type hexaferrites can be obtained. The microstructures of the magnets were investigated by field emission scanning electron microscopy. The particles appear in hexagonal plate-like shape and the particles are distributed homogeneously. The radial shrinkage of the magnets increases with the increase of calcination or sintering temperature. The magnetic properties of the magnets and magnetic powders were measured by a permanent magnetic measure equipment and a vibrating sample magnetometer, respectively. For high remanence, intrinsic coercivity, magnetic induction coercivity and maximum energy product, the optimized calcination and sintering temperatures are 1250 °C and 1190 °C, respectively.

  12. Dielectric properties of (Na0.5Bi0.5)TiO3-Ba0.7Sr0.3Sn0.02Ti0.98O3 composite ceramics

    NASA Astrophysics Data System (ADS)

    Wang, Jing; Rong, Guijuan; Liu, Lei; Cheng, Haiyan; Jiang, Qi; Li, Chuangchuang; Wang, Mengmeng

    2016-05-01

    Lead-free x(Na0.5Bi0.5)TiO3-(1 - x)Ba0.7Sr0.3Sn0.02Ti0.98O3 (NBT-BSST) ceramics are prepared by a wet solid-phase reaction method. The effect of NBT/BSST ratio on phase structure, microstructure and dielectric properties has been investigated in detail. The X-ray diffraction (XRD) analysis illustrates that the composites are composed of tetragonal perovskite. With increasing NBT content, the ceramic capacitors display stronger temperature stability in its dielectric behavior. A great enhance of dielectric properties and other electric parameters is obtained in this system by properly modulating the compositions. For example, the composite ceramics with 30% NBT content possess a large dielectric constant (𝜀r) of 3200 and a low dielectric loss (tan δ) of 0.09. The temperature coefficient of capacitance of NBT-BSST varies from -50% to 20% while the NBT content is 30% at the whole range of measured temperature. The results show that NBT-BSST ceramics are a good candidate of lead-free dielectric materials.

  13. XPS study of surface state of novel perovskite system Dy0.5Sr0.5Co0.8Fe0.2O3-δ as cathode for solid oxide fuel cells

    NASA Astrophysics Data System (ADS)

    Kautkar, Pranay R.; Acharya, Smita A.; Tumram, Priya V.; Deshpande, U. P.

    2016-05-01

    In the present attempt,novel perovskite oxide Dy0.5Sr0.5Co0.8Fe0.2O3-δ (DSCF) as cathode material has been synthesized by an Ethylene glycol-citrate combined sol-gel combustion route. Orthorhombic symmetry structure is confirmed by X-ray diffraction (XRD) and data is well fitted using Rietveld refinement by Full-Prof software suite. Chemical natureof surface of DSCF has been analyzed by using X-ray photoelectron spectroscopy (XPS). XPS result shows that Dy ions are in +3 oxidation state and Sr in +2 states. However Co2p and Fe2p spectra indicates partial change in oxidation state from Co3+/Fe3+ to Co4+/Fe4+. These attribute to develop active sites on the surface for oxygen ions. O1s XPS spectra shows two oxygen peaks relatedto lattice oxygen in perovskite and absorbed oxygen in oxygen vacancy are detected. O1s spectra demonstrate the existence of adsorbed oxygen species on the surface of DSCF oxide which is quite beneficial for intermediate temperature of Solid Oxide Fuel Cell.

  14. Study of barrier layer capacitance effect in lead free Ba0.95Sr0.05(Fe0.5Nb0.5)O3-BaZr0.1Ti0.9O3 ceramics

    NASA Astrophysics Data System (ADS)

    Kumar Patel, Piyush; Yadav, K. L.

    2014-11-01

    Lead-free Ba0.95Sr0.05(Fe0.5Nb0.5)O3-BaZr0.1Ti0.9O3 (50/50) ceramic, a material with potential applications for energy storage, are investigated. X-ray diffraction patterns show a single phase perovskite structure in all the samples. Sintering temperature affects the microstructural and dielectric properties of the ceramics. Microstructural analysis showed the uniformly distributed and highly packed grains in all the samples. We obtained high dielectric constant with low dielectric loss due to the controlled sintering. Giant dielectric constant (~19496) with low dielectric loss (~0.32) was obtained for 1250 °C sintered sample at room temperature and 1 kHz frequency. Complex impedance analysis confirms that the grain boundary effect (barrier layer formation) is responsible for such a high value of dielectric constant. Another interesting feature of this ceramic is the appearance of room temperature magnetodielectric response (1.9%, 8 kOe) at 100 Hz frequency.

  15. Methane partial oxidation using FeO(x)@La(0.8)Sr(0.2)FeO(3-δ) core-shell catalyst--transient pulse studies.

    PubMed

    Shafiefarhood, Arya; Hamill, Joseph Clay; Neal, Luke Michael; Li, Fanxing

    2015-12-14

    The chemical looping reforming (CLR) process, which utilizes a transition metal oxide based redox catalyst to partially oxidize methane to syngas, represents a potentially efficient approach for methane valorization. The CLR process inherently avoids costly cryogenic air separation by replacing gaseous oxygen with regenerable ionic oxygen (O(2-)) from the catalyst lattice. Our recent studies show that an Fe2O3@La0.8Sr0.2FeO3-δ core-shell redox catalyst is effective for CLR, as it combines the selectivity of an LSF shell with the oxygen capacity of an iron oxide core. The reaction between methane and the catalyst is also found to be highly dynamic, resulting from changes in lattice oxygen availability and surface properties. In this study, a transient pulse injection approach is used to investigate the mechanisms of methane partial oxidation over the Fe2O3@LSF redox catalyst. As confirmed by isotope exchange, the catalyst undergoes transitions between reaction "regions" with markedly different mechanisms. While oxygen evolution maintains a modified Mars-van Krevelen mechanism throughout the reaction with O(2-) conduction being the rate limiting step, the mechanism of methane conversion changes from an Eley-Rideal type in the first reaction region to a Langmuir-Hinshelwood-like mechanism in the third region. Availability of surface oxygen controls the reduction scheme of the catalyst and the underlying reaction mechanism.

  16. Thickness dependence of La0.7Sr0.3MnO3/PbZr0.2Ti0.8O3 magnetoelectric interfaces

    NASA Astrophysics Data System (ADS)

    Zhou, Jinling; Tra, Vu Thanh; Dong, Shuai; Trappen, Robbyn; Marcus, Matthew A.; Jenkins, Catherine; Frye, Charles; Wolfe, Evan; White, Ryan; Polisetty, Srinivas; Lin, Jiunn-Yuan; LeBeau, James M.; Chu, Ying-Hao; Holcomb, Mikel Barry

    2015-10-01

    Magnetoelectric materials have great potential to revolutionize electronic devices due to the coupling of their electric and magnetic properties. Thickness varying La0.7Sr0.3MnO3 (LSMO)/PbZr0.2Ti0.8O3 (PZT) heterostructures were built and measured in this article by valence sensitive x-ray absorption spectroscopy. The sizing effects of the heterostructures on the LSMO/PZT magnetoelectric interfaces were investigated through the behavior of Mn valence, a property associated with the LSMO magnetization. We found that Mn valence increases with both LSMO and PZT thickness. Piezoresponse force microscopy revealed a transition from monodomain to polydomain structure along the PZT thickness gradient. The ferroelectric surface charge may change with domain structure and its effects on Mn valence were simulated using a two-orbital double-exchange model. The screening of ferroelectric surface charge increases the electron charges in the interface region, and greatly changes the interfacial Mn valence, which likely plays a leading role in the interfacial magnetoelectric coupling. The LSMO thickness dependence was examined through the combination of two detection modes with drastically different attenuation depths. The different length scales of these techniques' sensitivity to the atomic valence were used to estimate the depth dependence Mn valence. A smaller interfacial Mn valence than the bulk was found by globally fitting the experimental results.

  17. Hierarchical Mesoporous/Macroporous Perovskite La0.5Sr0.5CoO3-x Nanotubes: A Bifunctional Catalyst with Enhanced Activity and Cycle Stability for Rechargeable Lithium Oxygen Batteries.

    PubMed

    Liu, Guoxue; Chen, Hongbin; Xia, Lu; Wang, Suqing; Ding, Liang-Xin; Li, Dongdong; Xiao, Kang; Dai, Sheng; Wang, Haihui

    2015-10-14

    Perovskites show excellent specific catalytic activity toward both oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) in alkaline solutions; however, small surface areas of the perovskites synthesized by traditional sol-gel methods lead to low utilization of catalytic sites, which gives rise to poor Li-O2 batteries performance and restricts their application. Herein, a hierarchical mesporous/macroporous perovskite La0.5Sr0.5CoO3-x (HPN-LSC) nanotube is developed to promote its application in Li-O2 batteries. The HPN-LSC nanotubes were synthesized via electrospinning technique followed by postannealing. The as-prepared HPN-LSC catalyst exhibits outstanding intrinsic ORR and OER catalytic activity. The HPN-LSC/KB electrode displays excellent performance toward both discharge and charge processes for Li-O2 batteries, which enhances the reversibility, the round-trip efficiency, and the capacity of resultant batteries. The synergy of high catalytic activity and hierarchical mesoporous/macroporous nanotubular structure results in the Li-O2 batteries with good rate capability and excellent cycle stability of sustaining 50 cycles at a current density of 0.1 mA cm(-2) with an upper-limit capacity of 500 mAh g(-1). The results will benefit for the future development of high-performance Li-O2 batteries using hierarchical mesoporous/macroporous nanostructured perovskite-type catalysts.

  18. Self-Arranged Misfit Dislocation Network Formation upon Strain Release in La0.7Sr0.3MnO3/LaAlO3(100) Epitaxial Films under Compressive Strain.

    PubMed

    Santiso, José; Roqueta, Jaume; Bagués, Núria; Frontera, Carlos; Konstantinovic, Zorica; Lu, Qiyang; Yildiz, Bilge; Martínez, Benjamín; Pomar, Alberto; Balcells, Lluis; Sandiumenge, Felip

    2016-07-01

    Lattice-mismatched epitaxial films of La0.7Sr0.3MnO3 (LSMO) on LaAlO3 (001) substrates develop a crossed pattern of misfit dislocations above a critical thickness of 2.5 nm. Upon film thickness increases, the dislocation density progressively increases, and the dislocation spacing distribution becomes narrower. At a film thickness of 7.0 nm, the misfit dislocation density is close to the saturation for full relaxation. The misfit dislocation arrangement produces a 2D lateral periodic structure modulation (Λ ≈ 16 nm) alternating two differentiated phases: one phase fully coherent with the substrate and a fully relaxed phase. This modulation is confined to the interface region between film and substrate. This phase separation is clearly identified by X-ray diffraction and further proven in the macroscopic resistivity measurements as a combination of two transition temperatures (with low and high Tc). Films thicker than 7.0 nm show progressive relaxation, and their macroscopic resistivity becomes similar than that of the bulk material. Therefore, this study identifies the growth conditions and thickness ranges that facilitate the formation of laterally modulated nanocomposites with functional properties notably different from those of fully coherent or fully relaxed material.

  19. Structural, thermal and electrical conductivity characteristics of Ln0.5Sr0.5Ti0.5Mn0.5O3±d (Ln: La, Nd and Sm) complex perovskites as anode materials for solid oxide fuel cell

    NASA Astrophysics Data System (ADS)

    Jeong, Jihoon; Azad, Abul K.; Schlegl, Harald; Kim, Byungjun; Baek, Seung-Wook; Kim, Keunsoo; Kang, Hyunil; Kim, Jung Hyun

    2015-03-01

    The Ti and Mn replaced complex perovskites, Ln0.5Sr0.5Ti0.5Mn0.5O3±d (Ln: La, Nd and Sm), were reported as potential anode materials for high temperature-operating solid oxide fuel cells (HT-SOFCs). For the present research study, synthesis, crystallographic, thermal and electrical conductivity properties of Ln0.5Sr0.5Ti0.5Mn0.5O3±d complex perovskites were investigated using X-ray diffraction (XRD), Rietveld method, thermogravimetric analysis (TGA) and electrical conductivity to apply these oxide materials for the HT-SOFC anode materials. XRD results showed that Ln0.5Sr0.5Ti0.5Mn0.5O3±d oxide systems synthesized as single phases did not react with 8 mol% yttria stabilized zirconia (8YSZ) and 10 mol% Gd-doped cerium oxide (CGO91) up to 1500 °C and did not decompose under dry 3.9% hydrogen at 850 °C. The crystal structures of La0.5Sr0.5Ti0.5Mn0.5O3±d (LSTM), Nd0.5Sr0.5Ti0.5Mn0.5O3±d (NSTM) and Sm0.5Sr0.5Ti0.5Mn0.5O3±d (SSTM) showed orthorhombic symmetry with the space group Pbnm and SSTM showed a more distorted structure. Thermogravimetric analysis (TGA) proved weight gains in these three sample occurred under oxidizing conditions and weight loss under reducing conditions. Electrical conductivity values of NSTM were higher than those of LSTM and SSTM under oxidizing and reducing conditions.

  20. Fabrication and characterization of Sm0.2Ce0.8O2-δ-Sm0.5Sr0.5CoO3-δ composite cathode for anode supported solid oxide fuel cell

    NASA Astrophysics Data System (ADS)

    Chang, Jen-Chen; Lee, Maw-Chwain; Yang, Rung-Je; Chang, Yang-Chuang; Lin, Tai-Nan; Wang, Chun-Hsiu; Kao, Wei-Xin; Lee, Lin-Song

    2011-03-01

    The Sm0.5Sr0.5CoO3-δ (SSC) with perovskite structure is synthesized by the glycine nitrate process (GNP). The phase evolution of SSC powder with different calcination temperatures is investigated by X-ray diffraction and thermogravimetric analyses. The XRD results show that the single perovskite phase of the SSC is completely formed above 1100 °C. The anode-supported single cell is constructed with a porous Ni-yttria-stabilized zirconia (YSZ) anode substrate, an airtight YSZ electrolyte, a Sm0.2Ce0.8O2-δ (SDC) barrier layer, and a screen-printed SSC-SDC composite cathode. The SEM results show that the dense YSZ electrolyte layer exhibits the good interfacial contact with both the Ni-YSZ and the SDC barrier layer. The porous SSC-SDC cathode shows an excellent adhesion with the SDC barrier layer. For the performance test, the maximum power densities are 464, 351 and 243 mW cm-2 at 800, 750 and 700 °C, respectively. According to the results of the electrochemical impedance spectroscopy (EIS), the charge-transfer resistances of the electrodes are 0.49 and 1.24 Ω cm2, and the non charge-transfer resistances are 0.48 and 0.51 Ω cm2 at 800 and 700 °C, respectively. The cathode material of SSC is compatible with the YSZ electrolyte via a delicate scheme employed in the fabrication process of unit cell.

  1. Magnetocaloric effect and critical behavior in Pr0.5Sr0.5MnO3: an analysis of the validity of the Maxwell relation and the nature of the phase transitions.

    PubMed

    Caballero-Flores, R; Bingham, N S; Phan, M H; Torija, M A; Leighton, C; Franco, V; Conde, A; Phan, T L; Yu, S C; Srikanth, H

    2014-07-16

    The Maxwell relation, the Clausius-Clapeyron equation, and a non-iterative method to obtain the critical exponents have been used to characterize the magnetocaloric effect (MCE) and the nature of the phase transitions in Pr0.5Sr0.5MnO3, which undergoes a second-order paramagnetic to ferromagnetic (PM-FM) transition at TC ~ 247 K, and a first-order ferromagnetic to antiferromagnetic (FM-AFM) transition at TN ~ 165 K. We find that around the second-order PM-FM transition, the MCE (as represented by the magnetic entropy change, ΔSM) can be precisely determined from magnetization measurements using the Maxwell relation. However, around the first-order FM-AFM transition, values of ΔSM calculated with the Maxwell relation deviate significantly from those calculated by the Clausius-Clapeyron equation at the magnetic field and temperature ranges where a conversion between the AFM and FM phases occurs. A detailed analysis of the critical exponents of the second-order PM-FM transition allows us to correlate the short-range type magnetic interactions with the MCE. Using the Arrott-Noakes equation of state with the appropriate values of the critical exponents, the field- and temperature-dependent magnetization [Formula: see text] curves, and hence the [Formula: see text] curves, have been simulated and compared with experimental data. A good agreement between the experimental and simulated data has been found in the vicinity of the Curie temperature TC, but a noticeable discrepancy is present for [Formula: see text]. This discrepancy arises mainly from the coexistence of AFM and FM phases and the presence of ferromagnetic clusters in the AFM matrix. PMID:24945593

  2. Copper oxide as a synergistic catalyst for the oxygen reduction reaction on La0.6Sr0.4Co0.2Fe0.8O3-δ perovskite structured electrocatalyst

    NASA Astrophysics Data System (ADS)

    Hong, Tao; Brinkman, Kyle; Xia, Changrong

    2016-10-01

    This work presents the effect of dispersed copper oxide (CuO) nanoparticles on the oxygen reduction reaction (ORR) on a typical solid oxide fuel cell (SOFC) electrocatalyst, La0.6Sr0.4Co0.2Fe0.8O3-δ (LSCF). The ORR kinetics were enhanced by a factor up to 4 at 750 °C as demonstrated by electrical conductivity relaxation measurements used to determine the chemical surface exchange coefficient, kchem. The value of kchem increased from 2.6 × 10-5 cm s-1 to 9.3 × 10-5 cm s-1 at 750 °C when the LSCF surface was coated with submicron CuO particles. The enhanced kchem was attributed to additional reactions that occur on the CuO surface and at the LSCF-CuO-gas three-phase boundaries (3PBs) as suggested by the kchem dependence on CuO coverage and 3PB length. This enhancement was further demonstrated by the introduction of CuO nanoparticles into LSCF electrodes. CuO infiltrated electrodes reduced the interfacial polarization resistance from 2.27 Ω cm2 to 1.5 Ω cm2 at 600 °C and increased the peak power density from 0.54 W cm-2 to 0.72 W cm-2 at 650 °C. Electrochemical impedance spectroscopy indicated that the reduced resistance was due to the shrinkage of the low frequency arc, which is associated with the electrochemical surface exchange reaction.

  3. Exsolution of Fe and SrO Nanorods and Nanoparticles from Lanthanum Strontium Ferrite La0.6Sr0.4FeO3−δ Materials by Hydrogen Reduction

    PubMed Central

    2015-01-01

    Formation of uniform Fe and SrO rods as well as nanoparticles following controlled reduction of La0.6Sr0.4FeO3−δ (LSF) and Ni-LSF samples in dry and moist hydrogen is studied by aberration-corrected electron microscopy. Metallic Fe and SrO precipitate from the perovskite lattice as rods of several tenths of nm and thicknesses up to 20 nm. Based on a model of Fe whisker growth following reduction of pure iron oxides, Fe rod exsolution from LSF proceeds via rate-limiting lattice oxygen removal. This favors the formation of single iron metal nuclei at the perovskite surface, subsequently growing as isolated rods. The latter is only possible upon efficient removal of reduction-induced water and, subsequently, reduction of Fe +III/+IV to Fe(0). If water remains in the system, no reduction or rod formation occurs. In contrast, formation of SrO rods following reduction in dry hydrogen is a catalytic process aided by Ni particles. It bears significant resemblance to surface diffusion-controlled carbon whisker growth on Ni, leading to similar extrusion rods and filaments. In addition to SrO rod growth, the exsolution of Fe nanoparticles and, subsequently, Ni–Fe alloy particles is observed. The latter have also been observed under static hydrogen reduction. Under strict control of the experimental parameters, the presented data therefore open an attractive chemically driven pathway to metal nanoarchitectures beyond the formation of “simple” nanoparticles. PMID:26435764

  4. Enhanced performance of solid oxide fuel cells with Ni/CeO 2 modified La 0.75Sr 0.25Cr 0.5Mn 0.5O 3- δ anodes

    NASA Astrophysics Data System (ADS)

    Zhu, Xingbao; Lü, Zhe; Wei, Bo; Chen, Kongfa; Liu, Mingliang; Huang, Xiqiang; Su, Wenhui

    The optimization of electrodes for solid oxide fuel cells (SOFCs) has been achieved via a wet impregnation method. Pure La 0.75Sr 0.25Cr 0.5Mn 0.5O 3- δ (LSCrM) anodes are modified using Ni(NO 3) 2 and/or Ce(NO 3) 3/(Sm,Ce)(NO 3) x solution. Several yttria-stabilized zirconia (YSZ) electrolyte-supported fuel cells are tested to clarify the contribution of Ni and/or CeO 2 to the cell performance. For the cell using pure-LSCrM anodes, the maximum power density (P max) at 850 °C is 198 mW cm -2 when dry H 2 and air are used as the fuel and oxidant, respectively. When H 2 is changed to CH 4, the value of P max is 32 mW cm -2. After 8.9 wt.% Ni and 5.8 wt.% CeO 2 are introduced into the LSCrM anode, the cell exhibits increased values of P max 432, 681, 948 and 1135 mW cm -2 at 700, 750, 800 and 850 °C, respectively, with dry H 2 as fuel and air as oxidant. When O 2 at 50 mL min -1 is used as the oxidant, the value of P max increases to 1450 mW cm -2 at 850 °C. When dry CH 4 is used as fuel and air as oxidant, the values of P max reach 95, 197, 421 and 645 mW cm -2 at 750, 800, 850 and 900 °C, respectively. The introduction of Ni greatly improves the performance of the LSCrM anode but does not cause any carbon deposit.

  5. Enhanced microwave dielectric tunability of Ba0.5Sr0.5TiO3 thin films grown with reduced strain on DyScO3 substrates by three-step technique

    NASA Astrophysics Data System (ADS)

    Liu, Hongrui; Avrutin, Vitaliy; Zhu, Congyong; Özgür, Ümit; Yang, Juan; Lu, Changzhi; Morkoç, Hadis

    2013-01-01

    Tunable dielectric properties of epitaxial ferroelectric Ba0.5Sr0.5TiO3 (BST) thin films deposited on nearly lattice-matched DyScO3 substrates by radio frequency magnetron sputtering have been investigated at microwave frequencies and correlated with residual compressive strain. To reduce the residual strain of the BST films caused by substrate clamping and improve their microwave properties, a three-step deposition method was devised and employed. A high-temperature deposition at 1068 K of the nucleation layer was followed by a relatively low-temperature deposition (varied in the range of 673-873 K) of the BST interlayer and a high-temperature deposition at 1068 K of the top layer. Upon post-growth thermal treatment at 1298 K the films grown by the three-step method with the optimized interlayer deposition temperature of 873 K exhibited lower compressive strain compared to the control layer (-0.002 vs. -0.006). At 10 GHz, a high dielectric tunability of 47.9% at an applied electric field of 60 kV/cm was achieved for the optimized films. A large differential phase shift of 145°/cm and a figure of merit of 23°/dB were obtained using a simple coplanar waveguide phase shifter at 10 GHz. The low residual strain and improved dielectric properties of the films fabricated using the three-step deposition technique were attributed to reduced clamping of the BST films by the nearly lattice-matched substrate.

  6. Interface properties of magnetic tunnel junction La0.7Sr0.3MnO3/SrTiO3 superlattices studied by standing-wave excited photoemission spectroscopy

    NASA Astrophysics Data System (ADS)

    Gray, A. X.; Papp, C.; Balke, B.; Yang, S.-H.; Huijben, M.; Rotenberg, E.; Bostwick, A.; Ueda, S.; Yamashita, Y.; Kobayashi, K.; Gullikson, E. M.; Kortright, J. B.; de Groot, F. M. F.; Rijnders, G.; Blank, D. H. A.; Ramesh, R.; Fadley, C. S.

    2010-11-01

    The chemical and electronic-structure profiles of magnetic tunnel junction (MTJ) La0.7Sr0.3MnO3/SrTiO3 (LSMO/STO) superlattices have been quantitatively determined via soft and hard x-ray standing-wave excited photoemission, x-ray absorption and x-ray reflectivity, in conjunction with x-ray optical and core-hole multiplet theoretical modeling. Epitaxial superlattice samples consisting of 48 and 120 bilayers of LSMO and STO, each nominally four unit cells thick, and still exhibiting LSMO ferromagnetism, were studied. By varying the incidence angle around the superlattice Bragg condition, the standing wave was moved vertically through the interfaces. By comparing experiment to x-ray optical calculations, the detailed chemical profile of the superlattice and its interfaces was quantitatively derived with angstrom precision. The multilayers were found to have a small ˜6% change in periodicity from top to bottom. Interface compositional mixing or roughness over ˜6Å was also found, as well as a significant change in the soft x-ray optical coefficients of LSMO near the interface. The soft x-ray photoemission data exhibit a shift in the position of the Mn3p peak near the interface, which is not observed for Mn3s . Combined with core-hole multiplet theory incorporating Jahn-Teller distortion, these results indicate a change in the Mn bonding state near the LSMO/STO interface. Our results thus further clarify the reduced (MTJ) performance of LSMO/STO compared to ideal theoretical expectations.

  7. Performance of Y0.9Sr0.1Cr0.9Fe0.1O3-δ as a sulfur-tolerant anode material for intermediate temperate solid oxide fuel cells

    NASA Astrophysics Data System (ADS)

    Bu, Yun-Fei; Zhong, Qin; Xu, Dan-Dan; Zhao, Xiao-Lu; Tan, Wen-Yi

    2014-03-01

    Perovskite-type Y0.9Sr0.1Cr0.9Fe0.1O3-δ maintained good chemical stability under a H2S-containing atmosphere based on results from X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FT-IR) in our previous study. In this research, the YSCF-based anode was studied using H2 and H2S-containing fuels. The activity of an electrode is closely related to its material composition, lattice structure, physic-chemical properties, and morphologic structure. Therefore, the characteristics of the YSCF powders and the cell were analyzed by XRD, Brunauer-Emmett-Teller (BET) surface area analysis, and scanning electron microscopy (SEM). The conductivities of YSCF were evaluated by four-probe method in 10% H2-N2, 1% H2S-N2 and air, respectively. Thermodynamic calculations and X-ray photoelectron spectroscopy (XPS) analysis have been used to investigate the stability of the elements in YSCF upon exposure to hydrogen sulfide (H2S) in hydrogen (H2) over a range of partial pressures of sulfur (pS2) and oxygen (pO2) that are representative of fuel cell operating conditions. In addition, the performance of the complete cell (YSCF-SDC|SDC|Ag) under H2S and H2 fuel mixtures was also evaluated by electrochemical impedance spectra (EIS) and I-V and I-P curves. The emergence of FeSO4 in the sulfur treatment should play an important role in preventing further sulfur-poisoning.

  8. Performance and sulfur poisoning of Ni/CeO2 impregnated La0.75Sr0.25Cr0.5Mn0.5O3-δ anode in solid oxide fuel cells

    NASA Astrophysics Data System (ADS)

    Li, Yiqian; Zhang, Yaohui; Zhu, Xingbao; Wang, Zhihong; Lü, Zhe; Huang, Xiqiang; Zhou, Yongjun; Zhu, Lin; Jiang, Wei

    2015-07-01

    In this study, comparison experiments are conducted based on yttria-stabilized zirconia (YSZ) electrolyte supported single solid oxide fuel cells (SOFCs) with pure La0.75Sr0.25Cr0.5Mn0.5O3-δ (LSCrM) or Ni/CeO2 impregnated LSCrM anodes. The single cells are tested in dry H2 and H2/H2S (50 ppm) mixture, respectively. Compared with the pure LSCrM anode, the cell with Ni/CeO2 impregnated LSCrM presents a significant performance improvement when the pure H2 is fueled to the anode, and shows a good stability during a constant-current discharge testing (398 mA cm-2). When the fuel is switched to H2/H2S mixture, the cell with Ni/CeO2 impregnated LSCrM anode still shows a remarkable constant-current discharge (120 mA cm-2) performance compared with pure LSCrM anode. The Ni/CeO2 impregnation can improve the electrochemical performance of the LSCrM anode without any sacrifice of sulfur tolerance ability. The Ni/CeO2 impregnated LSCrM might be a potential anode material for solid oxide fuel cell operating in sulfur-containing fuels. The XRD and XPS results demonstrate that the anode poisoning product is composed of adsorbed sulfur, metal sulfides and sulfate radical. The mass spectrum result confirms that the poisoning mechanism involves the reaction of sulfur with anode rather than the direct reaction between H2S gas and anode.

  9. Magnetocaloric effect and critical behavior in Pr0.5Sr0.5MnO3: an analysis of the validity of the Maxwell relation and the nature of the phase transitions.

    PubMed

    Caballero-Flores, R; Bingham, N S; Phan, M H; Torija, M A; Leighton, C; Franco, V; Conde, A; Phan, T L; Yu, S C; Srikanth, H

    2014-07-16

    The Maxwell relation, the Clausius-Clapeyron equation, and a non-iterative method to obtain the critical exponents have been used to characterize the magnetocaloric effect (MCE) and the nature of the phase transitions in Pr0.5Sr0.5MnO3, which undergoes a second-order paramagnetic to ferromagnetic (PM-FM) transition at TC ~ 247 K, and a first-order ferromagnetic to antiferromagnetic (FM-AFM) transition at TN ~ 165 K. We find that around the second-order PM-FM transition, the MCE (as represented by the magnetic entropy change, ΔSM) can be precisely determined from magnetization measurements using the Maxwell relation. However, around the first-order FM-AFM transition, values of ΔSM calculated with the Maxwell relation deviate significantly from those calculated by the Clausius-Clapeyron equation at the magnetic field and temperature ranges where a conversion between the AFM and FM phases occurs. A detailed analysis of the critical exponents of the second-order PM-FM transition allows us to correlate the short-range type magnetic interactions with the MCE. Using the Arrott-Noakes equation of state with the appropriate values of the critical exponents, the field- and temperature-dependent magnetization [Formula: see text] curves, and hence the [Formula: see text] curves, have been simulated and compared with experimental data. A good agreement between the experimental and simulated data has been found in the vicinity of the Curie temperature TC, but a noticeable discrepancy is present for [Formula: see text]. This discrepancy arises mainly from the coexistence of AFM and FM phases and the presence of ferromagnetic clusters in the AFM matrix.

  10. Temperature-dependent and time-dependent effects of hyperthermia mediated by dextran-coated La0.7Sr0.3MnO3: in vitro studies

    PubMed Central

    Haghniaz, Reihaneh; Umrani, Rinku D; Paknikar, Kishore M

    2015-01-01

    Background The purpose of this study was to investigate the therapeutic efficacy of dextran-coated (Dex) La0.7Sr0.3MnO3 (LSMO) nanoparticles-mediated hyperthermia at different temperatures (43°C, 45°C, and 47°C) based on cell killing potential and induction of heat shock proteins in a murine melanoma cell (B16F1) line. Methods LSMO nanoparticles were synthesized by a citrate-gel method and coated with dextran. B16F1 cells were exposed to the Dex-LSMO nanoparticles and heated using a radiofrequency generator. After heating, the morphology and topology of the cells were investigated by optical microscopy and atomic force microscopy. At 0 hours and 24 hours post heating, cells were harvested and viability was analyzed by the Trypan blue dye exclusion method. Apoptosis and DNA fragmentation were assessed by terminal deoxynucleotidyl transferase-dUTP nick end labeling (TUNEL) assay and agarose gel electrophoresis, respectively. An enzyme-linked immunosorbent assay was used to quantify heat shock protein levels. Results Our data indicate that cell death and induction of heat shock proteins in melanoma cells increased in a time-dependent and temperature-dependent manner, particularly at temperatures higher than 43°C. The mode of cell death was found to be apoptotic, as evident by DNA fragmentation and TUNEL signal. A minimum temperature of 45°C was required to irreversibly alter cell morphology, significantly reduce cell viability, and result in 98% apoptosis. Repeated cycles of hyperthermia could induce higher levels of heat shock proteins (more favorable for antitumor activity) when compared with a single cycle. Conclusion Our findings indicate a potential use for Dex-LSMO-mediated hyperthermia in the treatment of melanoma and other types of cancer. PMID:25759583

  11. Nano-ceria pre-infiltration improves La0.6Sr0.4Co0.8Fe0.2O3-x infiltrated Solid Oxide Fuel Cell cathode performance

    NASA Astrophysics Data System (ADS)

    Burye, Theodore E.; Nicholas, Jason D.

    2015-12-01

    Here, scanning electron microscopy, X-ray diffraction, and thermo-gravimetric analysis experiments show that the pre-infiltration of Ce0.9Gd0.1O1.95 (GDC) nano-particles reduces the average size of La0.6Sr0.4Co0.8Fe0.2O3-x (LSCF) produced from the subsequent infiltration of precursor nitrate solutions containing the surfactant Triton X-100 or the chelating agent citric acid. In contrast, GDC pre-infiltration has no effect on the average size of LSCF particles produced from precursor solutions containing only lanthanum, strontium, cobalt, and iron nitrate. Consistent with the observed particle size trends, electrochemical impedance spectroscopy measurements show that GDC pre-infiltration improves the performance of Triton X-100 Derived (TXD) LSCF-GDC cathodes and Citric Acid Derived (CAD) LSCF-GDC cathodes, but has no effect on the performance of Pure Nitrate Derived (PND) LSCF-GDC cathodes. In particular, TXD LSCF-GDC cathodes with more than ∼5 vol% of GDC pre-infiltration display average LSCF particle sizes of 21 nm and open-circuit polarization resistance values of 0.10 Ωcm2 at 540 °C, compared to 48 nm and 640 °C without GDC pre-infiltration. Results suggest that this 100 °C reduction in cathode operating temperature is caused solely by LSCF particle size reductions. 7.4 vol% GDC pre-infiltrated TXD LSCF-GDC cathodes also display lower 540 °C degradation rates than conventionally infiltrated PND LSCF-GDC cathodes.

  12. Direct-current transport properties of and microwave absorption in a bulk ceramic sample and a film of La0.5Sr0.5CoO3- δ: magnetic inhomogeneity effects

    NASA Astrophysics Data System (ADS)

    Belevtsev, B. I.; Cherpak, N. T.; Chukanova, I. N.; Gubin, A. I.; Krasovitsky, V. B.; Lavrinovich, A. A.

    2002-03-01

    The DC transport properties of and microwave absorption (at 41 GHz) in a bulk ceramic sample and a film (220 nm thick) of La0.5Sr0.5CoO3-δ are measured. The bulk sample was cut from a target from which the film was also produced, by pulsed-laser deposition. It is found that the temperature behaviours of the DC resistivity and magnetoresistance (MR) of the bulk sample are quite different from those of the film. This is attributed to oxygen depletion of the film as compared with the target. Below the Curie temperature TC, the film behaves like a highly inhomogeneous system of weakly connected ferromagnetic grains (or clusters). The microwave study provides further data on the inhomogeneity of the samples. It is found that the surface layer of the bulk sample has very low conductivity compared with the bulk. This can be explained by the oxygen depletion of the surface layer. The most important feature of doped cobaltates revealed in this study is the following: the microwave conductivity, which should be related mainly to the conductivity within the poorly connected grains, increases by an order of magnitude at the transition to the ferromagnetic state. The increase is much greater than that found in the reported DC measurements on doped cobaltates of the highest crystal perfection. The microwave effect found is attributed to an inherent magnetically inhomogeneous state of the doped cobaltates. On the basis of the results obtained, it can be suggested that the rather low MR in the doped cobaltates as compared with that of the manganites is attributable to their more inhomogeneous magnetic state.

  13. Abnormal percolative transport and colossal electroresistance induced by anisotropic strain in (011)-Pr(0.7)(Ca(0.6)Sr(0.4))(0.3)MnO₃/PMN-PT heterostructure.

    PubMed

    Zhao, Ying-Ying; Wang, Jing; Kuang, Hao; Hu, Feng-Xia; Zhang, Hong-Rui; Liu, Yao; Zhang, Ying; Wang, Shuan-Hu; Wu, Rong-Rong; Zhang, Ming; Bao, Li-Fu; Sun, Ji-Rong; Shen, Bao-Gen

    2014-01-01

    Abnormal percolative transport in inhomogeneous systems has drawn increasing interests due to its deviation from the conventional percolation picture. However, its nature is still ambiguous partly due to the difficulty in obtaining controllable abnormal percolative transport behaviors. Here, we report the first observation of electric-field-controlled abnormal percolative transport in (011)-Pr(0.7)(Ca(0.6)Sr(0.4))(0.3)MnO3/0.7Pb(Mg(1/3)Nb(2/3))O3-0.3PbTiO3 heterostructure. By introducing an electric-field-induced in-plane anisotropic strain-field in a phase separated PCSMO film, we stimulate a significant inverse thermal hysteresis (~ -17.5 K) and positive colossal electroresistance (~11460%), which is found to be crucially orientation-dependent and completely inconsistent with the well accepted conventional percolation picture. Further investigations reveal that such abnormal inverse hysteresis is strongly related to the preferential formation of ferromagnetic metallic domains caused by in-plane anisotropic strain-field. Meanwhile, it is found that the positive colossal electroresistance should be ascribed to the coactions between the anisotropic strain and the polarization effect from the poling of the substrate which leads to orientation and bias-polarity dependencies for the colossal electroresistance. This work unambiguously evidences the indispensable role of the anisotropic strain-field in driving the abnormal percolative transport and provides a new perspective for well understanding the percolation mechanism in inhomogeneous systems. PMID:25399635

  14. Abnormal percolative transport and colossal electroresistance induced by anisotropic strain in (011)-Pr0.7(Ca0.6Sr0.4)0.3MnO3/PMN-PT heterostructure

    PubMed Central

    Zhao, Ying-Ying; Wang, Jing; Kuang, Hao; Hu, Feng-Xia; Zhang, Hong-Rui; Liu, Yao; Zhang, Ying; Wang, Shuan-Hu; Wu, Rong-Rong; Zhang, Ming; Bao, Li-Fu; Sun, Ji-Rong; Shen, Bao-Gen

    2014-01-01

    Abnormal percolative transport in inhomogeneous systems has drawn increasing interests due to its deviation from the conventional percolation picture. However, its nature is still ambiguous partly due to the difficulty in obtaining controllable abnormal percolative transport behaviors. Here, we report the first observation of electric-field-controlled abnormal percolative transport in (011)-Pr0.7(Ca0.6Sr0.4)0.3MnO3/0.7Pb(Mg1/3Nb2/3)O3-0.3PbTiO3 heterostructure. By introducing an electric-field-induced in-plane anisotropic strain-field in a phase separated PCSMO film, we stimulate a significant inverse thermal hysteresis (~ -17.5 K) and positive colossal electroresistance (~11460%), which is found to be crucially orientation-dependent and completely inconsistent with the well accepted conventional percolation picture. Further investigations reveal that such abnormal inverse hysteresis is strongly related to the preferential formation of ferromagnetic metallic domains caused by in-plane anisotropic strain-field. Meanwhile, it is found that the positive colossal electroresistance should be ascribed to the coactions between the anisotropic strain and the polarization effect from the poling of the substrate which leads to orientation and bias-polarity dependencies for the colossal electroresistance. This work unambiguously evidences the indispensable role of the anisotropic strain-field in driving the abnormal percolative transport and provides a new perspective for well understanding the percolation mechanism in inhomogeneous systems. PMID:25399635

  15. Effects of pre-oxidation on the microstructural and electrical properties of La0.67Sr0.33MnO3-δ coated ferritic stainless steels

    NASA Astrophysics Data System (ADS)

    Yang, Peng; Liu, Chien-Kuo; Wu, Jin-Yu; Shong, Wei-Ja; Lee, Ruey-Yi; Sung, Chia-Chi

    2012-09-01

    LaxSr1-xMnO3 (LSM) is commonly used as a protective layer on the metallic interconnects of solid oxide fuel cells (SOFCs) to prevent surface oxidation and chromium poisoning. However, the volume shrinkage at elevated temperatures causes the LSM coatings to crack, resulting in chromium diffusion. Therefore, this paper investigates the effects of pre-oxidation on the microstructure and electrical properties of ferritic stainless steels coated with La0.67Sr0.33MnO3 (LSM). Four ferritic stainless steels were selected for use as interconnect substrates: Crofer22APU, Crofer22H, ss441, and ZMG232L. The candidate materials were pre-oxidised at 850 °C for 25 and 50 h, respectively. After the pre-oxidation process, the LSM films with a thickness of 3-4 μm were deposited on the surface of samples by using Pulsed DC magnetron sputtering. After aging the coated specimens at elevated temperatures, the morphologies and crystalline structures were examined using SEM/EDX and XRD, respectively. The results indicated that the pre-oxidised layer, (Mn, Cr)3O4, could significantly suppress chromium penetration from the interior to the surface of the specimens. Moreover, the area specific resistance (ASR) values for the 25-h pre-oxidised specimens were 2.24, 12.21, 2.30, and 6.77 mΩ cm2 for Crofer22APU, Crofer22H, ss441, and ZMG232L, respectively, at 800 °C for 500 h in an air atmosphere.

  16. Oxidative CO2 reforming of methane in La0.6Sr0.4Co0.8Ga0.2O3-δ (LSCG) hollow fiber membrane reactor.

    PubMed

    Kathiraser, Yasotha; Wang, Zhigang; Kawi, Sibudjing

    2013-12-17

    CO2 utilization in catalytic membrane reactors for syngas production is an environmentally benign solution to counter the escalating global CO2 concerns. In this study, integration of a La0.6Sr0.4Co0.8Ga0.2O3-δ (LSCG) hollow fiber membrane reactor with Ni/LaAlO3-Al2O3 catalyst for the oxidative CO2 reforming of methane (OCRM) reaction was successfully tested for 160 h of reaction. High CH4 and CO2 conversions of ca. 94% and 73% were obtained with O2 flux ca. 1 mL·min(-1)·cm(-2) at 725 °C for the 160-h stability test. Surface temperature programmed desorption studies of the membrane were conducted with H2, CO, and CO2 as probe gases to facilitate understanding on the effect of H2 and CO product gases as well as CO2 reactant gases on the membrane surface. Scanning electron microscopy-energy dispersive X-ray (SEM-EDX), X-ray photoelectron spectroscopy (XPS), and Fourier transform infrared (FTIR) analysis of the postreacted membrane after 160-h stability tests suggests Sr-enriched phases with the presence of adsorbed carbonate and hydrogenated carbon. This shows the subsequent reactant spillover on the membrane surface from the catalyst bed took place due to the reaction occurring on the catalyst. However, XRD analysis of the bulk structure does not show any phase impurities, thus confirming the structural integrity of the LSCG hollow fiber membrane.

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

    NASA Astrophysics Data System (ADS)

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

    2014-06-01

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

  18. Calcioferrite with composition (Ca3.94Sr0.06)Mg1.01(Fe2.93Al1.07)(PO4)6(OH)4·12H2O

    PubMed Central

    Lafuente, Barbara; Downs, Robert T.; Yang, Hexiong; Jenkins, Robert A.

    2014-01-01

    Calcioferrite, ideally Ca4MgFe3+ 4(PO4)6(OH)4·12H2O (tetra­calcium magnesium tetrairon(III) hexakis-phosphate tetra­hydroxide dodeca­hydrate), is a member of the calcioferrite group of hydrated calcium phosphate minerals with the general formula Ca4 AB 4(PO4)6(OH)4·12H2O, where A = Mg, Fe2+, Mn2+ and B = Al, Fe3+. Calcioferrite and the other three known members of the group, montgomeryite (A = Mg, B = Al), kingsmountite (A = Fe2+, B = Al), and zodacite (A = Mn2+, B = Fe3+), usually occur as very small crystals, making their structure refinements by conventional single-crystal X-ray diffraction challenging. This study presents the first structure determination of calcioferrite with composition (Ca3.94Sr0.06)Mg1.01(Fe2.93Al1.07)(PO4)6(OH)4·12H2O based on single-crystal X-ray diffraction data collected from a natural sample from the Moculta quarry in Angaston, Australia. Calcioferrite is isostructural with montgomeryite, the only member of the group with a reported structure. The calcioferrite structure is characterized by (Fe/Al)O6 octa­hedra (site symmetries 2 and -1) sharing corners (OH) to form chains running parallel to [101]. These chains are linked together by PO4 tetra­hedra (site symmetries 2 and 1), forming [(Fe/Al)3(PO4)3(OH)2] layers stacking along [010], which are connected by (Ca/Sr)2+ cations (site symmetry 2) and Mg2+ cations (site symmetry 2; half-occupation). Hydrogen-bonding inter­actions involving the water mol­ecules (one of which is equally disordered over two positions) and OH function are also present between these layers. The relatively weaker bonds between the layers account for the cleavage of the mineral parallel to (010). PMID:24764934

  19. The effect of group IIIA metal ion dopants on the photocatalytic activities of nanocrystalline Sr0.25H1.5Ta2O6·H2O.

    PubMed

    Liang, Shijing; Zhu, Shuying; Zhu, Jia; Chen, Yan; Zhang, Yongfan; Wu, Ling

    2012-01-21

    A series of group IIIA metal ion electron acceptors doped into Sr(0.25)H(1.5)Ta(2)O(6)·H(2)O (HST) samples have been prepared by an impregnation and calcination method for the first time. The samples are characterized by XRD, TEM, DRS and XPS. The variations in the electronic structure and photoelectric response after metal ion doping are investigated by theoretical calculations and photocurrent experiments, respectively. Results show that the metal ions can be efficiently incorporated into the HST crystal structure, which is reflected in the lattice contraction. Meanwhile, the photoabsorption edges of the metal-doped HST samples are red shifted to a longer wavelength. Taking into account the ionic radii and electronegativities of the dopants, as well as the XRD and XPS results, it is concluded that Ta(5+) ions may be partially substituted by the Al(3+) and Ga(3+) ions in the framework, while In(3+) ions are the favourable substitutes for Sr(2+) sites in the cavity. The first-principles DFT calculations confirm that the variation of the band structure is sensitive to the type of group IIIA metal ion. Introducing the dopant only at the Ta site induces an obvious variation in the band structure and the band gap becomes narrow. Meanwhile, an ''extra step'' appeared in the band gap, which can trap photogenerated electrons from the valance band (VB) and could enhance the charge mobility and the photocurrent. For the photocatalytic degradation of methyl orange in an aqueous solution and in benzene in the gas phase, the doped samples show superior photocatalytic activities compared with both undoped samples and TiO(2). The enhanced photocatalytic activities can be well explained by their electronic structure, photoabsorption performance, photoelectric response, and the concentration of the active species. Due to the fact that Ga ion doping can create an acceptor impurity level and change the electronic band, efficiently narrowing the band gap, the Ga-doped sample shows

  20. High-Performance Microchanneled Asymmetric Gd(0.1)Ce(0.9)O(1.95-δ)-La(0.6)Sr(0.4)FeO(3-δ)-Based Membranes for Oxygen Separation.

    PubMed

    Cheng, Shiyang; Huang, Hua; Ovtar, Simona; Simonsen, Søren B; Chen, Ming; Zhang, Wei; Søgaard, Martin; Kaiser, Andreas; Hendriksen, Peter Vang; Chen, Chusheng

    2016-02-01

    A microchanneled asymmetric dual phase composite membrane of 70 vol % Gd(0.1)Ce(0.9)O(1.95-δ)-30 vol % La(0.6)Sr(0.4)FeO(3-δ) (CGO-LSF) was fabricated by a "one step" phase-inversion tape casting. The sample consists of a thin dense membrane (100 μm) and a porous substrate including "finger-like" microchannels. The oxygen permeation flux through the membrane with and without catalytic surface layers was investigated under a variety of oxygen partial pressure gradients. At 900 °C, the oxygen permeation flux of the bare membrane was 1.6 (STP) ml cm(-2) min(-1) for the air/He-case and 10.10 (STP) ml cm(-2) min(-1) for the air/CO-case. Oxygen flux measurements as well as electrical conductivity relaxation show that the oxygen flux through the bare membrane without catalyst is limited by the oxygen surface exchange. The surface exchange can be enhanced by introduction of catalyst on the membrane surface. An increase of the oxygen flux of ∼1.49 (STP) mL cm(-2) min(-1) at 900 °C was observed when catalyst is added for the air/He-case. Mass transfer polarization through the finger-like support was confirmed to be negligible, which benefits the overall performance. A stable flux of 7.00 (STP) ml cm(-2) min(-1) was observed between air/CO/CO2 over 200 h at 850 °C. Partial surface decomposition was observed on the permeate side exposed to CO, in line with predictions from thermodynamic calculations. In a mixture of CO, CO2, H2, and H2O at similar oxygen activity the material will according to the calculation not decompose. The microchanneled asymmetric CGO-LSF membranes show high oxygen permeability and chemical stability under a range of technologically relevant oxygen potential gradients. PMID:26829707

  1. Systematic evaluation of cobalt-free Ln0.5Sr0·5Fe0·8Cu0·2O3-δ (Ln = La, Pr, and Nd) as cathode materials for intermediate-temperature solid oxide fuel cells

    NASA Astrophysics Data System (ADS)

    Pang, Shengli; Wang, Wenzhi; Chen, Tao; Shen, Xiangqian; Wang, Yonggang; Xu, Kaijie; Xi, Xiaoming

    2016-09-01

    Cobalt-free perovskites, Ln0.5Sr0·5Fe0·8Cu0·2O3-δ (Ln = La, Pr, and Nd), are systematically evaluated as the cathode materials for intermediate-temperature solid oxide fuel cells (IT-SOFCs) using Gd0.1Ce0·9O1.95 as the electrolyte. The samples exhibit an orthorhombic perovskite structures, and their cell volumes decrease as the ionic radius of Ln decreases. Both the oxygen vacancy content and the magnitude of lattice oxygen release per formula unit increase in the temperature range from 370 °C to 850 °C as the ionic radius of Ln decreases. Ln0.5Sr0.5Fe0.8Cu0.2O3-δ is chemically and thermally compatible with the Gd0.1Ce0·9O1.95 electrolyte. In the temperature range of 600 °C-750 °C, Nd0.5Sr0·5Fe0·8Cu0·2O3-δ possesses the highest catalytic activity for the oxygen reduction reaction with area specific resistance values of 0.071 Ω cm2 and 0.141 Ω cm2 at 750 °C and 700 °C, respectively. The maximum power densities of the anode-supported single cells at 800 °C and 700 °C are 1003.7 mW cm-2 and 516.7 mW cm-2 for Pr0.5Sr0·5Fe0·8Cu0·2O3-δ and 944.5 mW cm-2 and 530.2 mW cm-2 for Nd0.5Sr0·5Fe0·8Cu0·2O3-δ, respectively. Ln0.5Sr0.5Fe0.8Cu0.2O3-δ is shown to be a promising cathode material for IT-SOFCs.

  2. Random existence of charge ordered stripes and its influence on the magnetotransport properties of La0.6Sr0.4MnO3 perovskite substituted with diamagnetic ions at Mn sublattice

    NASA Astrophysics Data System (ADS)

    Vijayanandhini, K.; Kutty, T. R. N.

    2008-05-01

    Phase-singular solid solutions of La0.6Sr0.4Mn1-yMeyO3 (0⩽y⩽0.3) [Me =Li1+, Mg2+, Al3+, Ti4+, Nb5+, Mo6+ or W6+] [LSMey] perovskite of rhombohedral symmetry (space group: R3¯c) have been prepared wherein the valence of the diamagnetic substituent at Mn site ranged from 1 to 6. With increasing y-content in LSMey, the metal-insulator (TM-I) transition in resistivity-temperature ρ(T ) curves shifted to low temperatures. The magnetization studies M(H ) as well as the M(T ) indicated two groups for LSMey. (1) Group A with Me =Mg, Al, Ti, or Nb which are paramagnetic insulators (PIs) at room temperature with low values of M (<0.5μB/Mn); the magnetic transition [ferromagnetic insulator (FMI)-PI] temperature (TC) shifts to low temperatures and nearly coincides with that of TM-I and the maximum magnetoresistance (MR) of ˜50% prevails near TC (≈TM-I). (2) Group-B samples with Me =Li, Mo, or W which are FMIs with Ms=3.3-3.58μB/Mn and marginal reduction in TC˜350K as compared to the undoped LSMO (TC˜378K). The latter samples show large temperature differences ΔT =Tc-TM-I, reaching up to ˜288K. The maximum MR (˜60%) prevails at low temperatures corresponding to the M-I transition TM-I rather than around TC. High resolution lattice images as well as microscopy analysis revealed the prevalence of inhomogeneous phase mixtures of randomly distributed charge ordered-insulating (COI) bistripes (˜3-5nm width) within FMI charge-disordered regions, yet maintaining crystallographically single phase with no secondary precipitate formation. The averaged ionic radius ⟨rB⟩, valency, or charge/radius ratio ⟨CRR⟩ cannot be correlated with that of large ΔT; hence cannot be used to parametrize the discrepancy between TC and TM-I. The M-I transition is controlled by the charge conduction within the electronically heterogeneous mixtures (COI bistripes+FMI charge disordered); large MR at TM-I suggests that the spin-ordered FM-insulating regions assist the charge transport

  3. 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.

  4. Effect of (Ca0.8Sr0.2)0.6La0.267TiO3 on Phase, Microstructure, and Microwave Dielectric Properties of Mg0.95Zn0.05TiO3 Synthesized by Polymeric Precursor Method

    NASA Astrophysics Data System (ADS)

    Naeem, Abdul; Ullah, Asad; Mahmood, Tahira; Iqbal, Yaseen; Mahmood, Asad; Hamayun, Muhammad

    2016-08-01

    A number of compounds in the (1 - x)Mg0.95Zn0.05TiO3- x(Ca0.8Sr0.2)0.6 La0.267TiO3 ( x = 0 to 0.25) composition series have been obtained via a polymeric precursor route to investigate the effect of increasing (Ca0.8Sr0.2)0.6La0.267TiO3 proportion on the phase, microstructure, and microwave dielectric properties of the sintered ceramics. Composite powders having nanometric particles were obtained by calcining the precursors at 700°C. Refinement results revealed that these samples comprised a mixture of Mg0.95Zn0.05TiO3 and (Ca0.8Sr0.2)0.6La0.267TiO3 ceramics. A combination of optimum microwave dielectric properties, i.e., dielectric constant of 25.17, quality factor of 58,754 GHz, and temperature coefficient of resonant frequency of -5.8 ppm/°C, was achieved for the x = 0.2 composition sintered at 1200°C.

  5. Effect of Zr4+ Content on the Grain Growth, Dielectric Relaxation Behavior, and Ferroelectric Properties of Ba0.4Sr0.6Ti1- x Zr x O3 Nano-Ceramics Prepared by Different Methods Assisted by Fast Microwave Sintering

    NASA Astrophysics Data System (ADS)

    Zixiong, Sun; Yongping, Pu; Yuwen, Liu

    2014-05-01

    The effect of Zr4+ content on the grain growth, dielectric relaxation, and piezoelectric properties of Ba0.4Sr0.6Ti1- x Zr x O3 (BSTZ; x = 0, 0.02, 0.04, 0.06) ceramics prepared by solid-state (SS) and sol-gel modified hydrothermal (SH) methods assisted by fast microwave sintering was investigated in this study. A combination of x-ray diffraction (XRD), scanning electron microscopy (SEM), impedance analysis, and ferroelectric analysis was used. All the ceramics had pure perovskite structures at room temperature, as seen from XRD patterns, indicating that Zr4+ was incorporated into Ba0.4Sr0.6TiO3 lattices to form a solid solution. In the SEM micrographs, SH samples had higher densities and smaller and more homogeneous grain size than SS samples, which was in agreement with density measurements. Nano-ceramics were obtained by this method. When the temperature dependence of dielectric constant and dielectric loss was studied, SH samples had higher permittivity, better thermally activated relaxation, and lower dielectric loss at high temperature. Ferroelectric characteristics can still be detected in Ba0.4Sr0.6Ti1- x Zr x O3 ceramics and residual polarization ( P r) decreased with increasing Zr4+ content.

  6. THERMAL AND ELECTRICAL PROPERTIES OF Ba0.5Sr0.5CoxFe1-x-yNiyO3-δ (x = 0.4, 0 ≤ y ≤ 0.25) AS CATHODE MATERIAL FOR IT-SOFCs

    NASA Astrophysics Data System (ADS)

    Burnwal, Suman Kumar; Kistaiah, P.

    2015-03-01

    Ba0.5Sr0.5CoxFe1-x-yNiyO3-δ (BSCFNi; x = 0.4, 0 ≤ y ≤ 0.25) were studied in relation to their potential use as intermediate temperature solid oxide fuel cell (IT-SOFC) cathode. An emphasis is made on the effect of Ni-doping on crystal structure, thermal expansion coefficient (TEC) and dc electrical conductivity. A cubic perovskite structure was observed in the X-ray diffraction (XRD) measurement. The TEC of BSCFNi obtained for 0 ≤ y ≤ 0.25, varies in the range of (12.38-18.81) × 10-6 K-1, measured in the temperature range of 30°C to 800°C. The electrical conductivity which is a major defect of Ba0.5Sr0.5CoxFe1-xO3-δ (BSCF) was improved by Ni-doping. The compound with y = 0.20 and 0.25 demonstrated a conductivity of σ = 62.59 S-cm-1 and 72.64 S-cm-1 at 400°C and 77.01 S-cm-1 and 89.68 S-cm-1 at 500°C.

  7. Rietveld fitting of x-ray diffraction spectra for the double phase composites La0.7-xSr0.3Mn1-yO3-1.5(x+y)/(Mn3O4)y/3

    NASA Astrophysics Data System (ADS)

    Liu, S. P.; Tang, G. D.; Hao, P.; Xu, L. Q.; Zhang, Y. G.; Qi, W. H.; Zhao, X.; Hou, D. L.; Chen, W.

    2009-01-01

    The effects of lanthanum deficiency on the structural and magnetic properties of manganites with normal composition La0.7-xSr0.3MnO3 prepared by the sol-gel method with the highest heat treatment temperature at 800 °C have been investigated. X-ray diffraction (XRD) spectra indicate that the materials possess a single phase with the R3¯c perovskite structure for x ≤0.05, and that they possess two phases with the R3¯c perovskite being the dominant phase and Mn3O4 being the second phase for x ≥0.10. Using XRD analysis, these materials can be expressed as La0.7-xSr0.3Mn1-yO3-1.5(x+y)/(Mn3O4)y/3. On the basis of the thermal equilibrium theory of crystal defects, the ion ratios at the A, B, and O sites in the ABO3 perovskite phase were calculated. Those ion ratios were used in Rietveld fitting of the XRD spectra. It was found that the dependence of the Curie temperature TC on the content ratio RM4 of Mn4+ ions at B site is similar to that of the typical perovskite La1-xSrxMnO3.

  8. Frequency-dependent impedance spectroscopy on the 0.925(Bi0.5Na0.40K0.10)TiO3-0.075(Ba0.70Sr0.30)TiO3 ceramic

    NASA Astrophysics Data System (ADS)

    Ullah, Amir; Rahman, Muneeb-ur; Iqbal, Muhammad Javid; Ahn, Chang Won; Kim, Ill Won; Ullah, Aman

    2016-06-01

    The electrical properties of the 0.925(Bi0.5(Na0.40K0.10)TiO3-0.075(Ba0.70Sr0.30)TiO3 (0.925BNKT-0.075BST) ceramic were investigated by using AC impedance spectroscopy over a wide range of frequencies (10 -2 ~ 105 Hz). The X-ray diffraction patterns confirmed the formation of a single-phase compound. A single semicircular arc in the impedance spectrum indicates that the main contribution of the bulk resistance ( R b ) were due to grain effects, with Rb decreasing with increasing temperature. The conductivity of the ceramics increased with increasing temperature, and the activation energy resulting from the DC conductivity was 0.86 eV. The ceramic displayed a typical negative temperature coefficient of resistance (NTCR) behavior, like that of a semiconductor.

  9. Instability and growth of nanoscale Ce0.8Gd0.2O1.9/NiO infiltrate in Sr0.94Ti0.9Nb0.1O3-Zr0.84Y0.16O1.92 anodes for solid oxide fuel cells

    NASA Astrophysics Data System (ADS)

    Zhang, Wei; Theil Kuhn, Luise; Stanley Jørgensen, Peter; Reddy Sudireddy, Bhaskar; Jonna Bentzen, Janet; Bernuy-Lopez, Carlos; Veltzé, Sune; Ramos, Tânia

    2014-07-01

    Microstructural evolution of Ce0.8Gd0.2O1.9/NiO (CGO/NiO) co-infiltrated nanoparticles in Sr0.94Ti0.9Nb0.1O3-Zr0.84Y0.16O1.92 (STN94-YSZ) anodes for solid oxide fuel cells (SOFCs) is investigated during electrochemical testing in a symmetric cell setup. The CGO/NiO infiltrated symmetric cells were subjected to varying atmospheres of H2O/H2 between 650 and 850 °C and characterized by electrochemical impedance spectroscopy. Analytical high resolution transmission electron microscopy showed that the CGO/NiO infiltrate was found to coalesce and grow from an indistinguishable CGO/NiO fluorite structure of an average diameter of 5 nm to individual well-connected, but phase-separated, CGO and Ni particles of 50 nm in average. This study confirms that instability and growth of CGO/NiO infiltrates in STN-based SOFC electrodes affect the morphology and can potentially be linked to reported losses in electrochemical performance.

  10. Fabrication of novel electrolyte-layer free fuel cell with semi-ionic conductor (Ba0.5Sr0.5Co0.8Fe0.2O3-δ- Sm0.2Ce0.8O1.9) and Schottky barrier

    NASA Astrophysics Data System (ADS)

    Afzal, Muhammad; Saleemi, Mohsin; Wang, Baoyuan; Xia, Chen; Zhang, Wei; He, Yunjuan; Jayasuriya, Jeevan; Zhu, Bin

    2016-10-01

    Perovskite Ba0.5Sr0.5Co0.8Fe0.2O3-δ (BSCF) is synthesized via a chemical co-precipitation technique for a low temperature solid oxide fuel cell (LTSOFC) (300-600 °C) and electrolyte-layer free fuel cell (EFFC) in a comprehensive study. The EFFC with a homogeneous mixture of samarium doped ceria (SDC): BSCF (60%:40% by weight) which is rather similar to the cathode (SDC: BSCF in 50%:50% by weight) used for a three layer SOFC demonstrates peak power densities up to 655 mW/cm2, while a three layer (anode/electrolyte/cathode) SOFC has reached only 425 mW/cm2 at 550 °C. Chemical phase, crystal structure and morphology of the as-prepared sample are characterized by X-ray diffraction and field emission scanning electron microscopy coupled with energy dispersive spectroscopy. The electrochemical performances of 3-layer SOFC and EFFC are studied by electrochemical impedance spectroscopy (EIS). As-prepared BSCF has exhibited a maximum conductivity above 300 S/cm at 550 °C. High performance of the EFFC device corresponds to a balanced combination between ionic and electronic (holes) conduction characteristic. The Schottky barrier prevents the EFFC from the electronic short circuiting problem which also enhances power output. The results provide a new way to produce highly effective cathode materials for LTSOFC and semiconductor designs for EFFC functions using a semiconducting-ionic material.

  11. Liquid plasma sprayed nano-network La0.4Sr0.6Co0.2Fe0.8O3/Ce0.8Gd0.2O2 composite as a high-performance cathode for intermediate-temperature solid oxide fuel cells

    NASA Astrophysics Data System (ADS)

    Zhang, Shan-Lin; Li, Chang-Jiu; Li, Cheng-Xin; Yang, Guan-Jun; Huang, Kevin; Liu, Meilin

    2016-09-01

    Here, we investigate the feasibility of using a liquid plasma spray process as a novel method for the cost-effective fabrication of a nanonetwork of La0.4Sr0.6Co0.2Fe0.8O3-δ (LSCF) and Ce0.8Gd0.2O2-δ (GDC) composite as a high-performance cathode for intermediate-temperature solid oxide fuel cells. A suspension containing well-dispersed nanosized GDC particles in an LSCF precursor solution is designed as the feedstock. The effects of GDC concentration in the suspension on the phase composition, microstructure, and electrochemical performance of the resulting cathode are studied. When the GDC concentration increases to 15 g L-1, the nanosized GDC particles distribute uniformly and continuously on the LSCF backbone to form a porous network structure. The electrochemical studies further indicate that the cathode polarization decreased with the increase in GDC concentration from 0 g L-1 to 15 g L-1, whereas a further increase in the GDC concentration increases the cathode polarization instead. At 600 and 750 °C, the cathode prepared using 15 g L-1 GDC concentration exhibits an impressive area-specific polarization resistance (Rp) of 0.1 Ω cm2 and 0.009 Ω cm2, respectively. Finally, the Rp of the optimal cathode almost does not change after the isothermal dwelling at 650 °C for 350 h.

  12. High-performance solid oxide fuel cells based on a thin La0.8Sr0.2Ga0.8Mg0.2O3-δ electrolyte membrane supported by a nickel-based anode of unique architecture

    NASA Astrophysics Data System (ADS)

    Sun, Haibin; Chen, Yu; Chen, Fanglin; Zhang, Yujun; Liu, Meilin

    2016-01-01

    Solid oxide fuel cells (SOFCs) based on a thin La0.8Sr0.2Ga0.8Mg0.2O3-δ (LSGM) electrolyte membrane supported by a nickel-based anode often suffers from undesirable reaction/diffusion between the Ni anode and the LSGM during high-temperature co-firing. In this study, a high performance intermediate-temperature SOFC is fabricated by depositing thin LSGM electrolyte membranes on a LSGM backbone of unique architecture coated with nano-sized Ni and Gd0.1Ce0.9O2-δ (GDC) particles via a combination of freeze-drying tape-casting, slurry drop-coating, and solution infiltration. The thickness of the dense LSGM electrolyte membranes is ∼30 μm while the undesirable reaction/diffusion between Ni and LSGM are effectively hindered because of the relatively low firing temperature, as confirmed by XRD analysis. Single cells show peak power densities of 1.61 W cm-2 at 700 °C and 0.52 W cm-2 at 600 °C using 3 vol% humidified H2 as fuel and ambient air as oxidant. The cell performance is very stable for 115 h at a constant current density of 0.303 A cm-2 at 600 °C.

  13. Anode-supported single-chamber solid oxide fuel cell based on cobalt-free composite cathode of Nd0.5Sr0.5Fe0.8Cu0.2O3-δ-Sm0.2Ce0.8O1.9 at intermediate temperatures

    NASA Astrophysics Data System (ADS)

    Yin, Jie-Wei; Zhang, Chunming; Yin, Yi-Mei; Shi, Huangang; Lin, Ye; Lu, Jun; Ma, Zi-Feng

    2015-07-01

    As a candidate of cathode material of single-chamber solid oxide fuel cell (SC-SOFC), cobalt-free mixed ionic electronic conductor (MIEC) Nd0.5Sr0.5Fe0.8Cu0.2O3-δ (NSFCu) is synthesized by sol-gel method with ethylene diamine tetraacetic acid and citric acid as co-complexing agents. The XRD shows NSFCu is stable after CO2 treatment and chemical compatible with SDC at high temperatures. CO2-TPD (CO2-temperature programmed desorption) demonstrates both CO2 adsorption and desorption phenomenon on NSFCu surface. However, the polarization resistances (Rp) of NSFCu and SDC (10:4 in weight) composite electrodes showed no decay in 5% CO2. Single cell using N2-O2-CH4 mixed gas (CH4 to O2 ratio = 1.5) as fuel shows maximum power density of 635 mW cm-2 at 700 °C. These results suggest that NSFCu-SDC is a promising composite cathode material for application in single-chamber solid oxide fuel cell.

  14. Studies on the percolation limit of Ce0.9Gd0.1O1.95 in La0.6Sr0.4Co0.2Fe0.8O3-δ-Ce0.9Gd0.1O1.95 nanocomposites for solid oxide fuel cells application

    NASA Astrophysics Data System (ADS)

    Jamale, Atul P.; Jadhav, S. T.; Dubal, S. U.; Bhosale, C. H.; Jadhav, L. D.

    2015-10-01

    A large difference in thermal expansion coefficient of electrode and electrolyte leads to imperfect electrode/electrolyte interface and hence significant polarization losses in solid oxide fuel cells. To overcome the difficulties associated with electrode and electrode/electrolyte interface, there is need to fabricate the composite cathode. Thus the present paper deals with study of La0.6Sr0.4Co0.2Fe0.8O3-δ(LSCF)-Ce0.9Gd0.1O1.95(GDC) nanocomposite with different fractions of GDC obtained by physical mixing of combustion synthesized nanopowders. No secondary phases were observed upon sintering at 1100 °C for 2 h affirming the chemical compatibility between LSCF and GDC. The composites with relatively high GDC% have higher density as a consequence of rapid grain growth and less conductivity. The nanocomposite with 50% of GDC showed electric conductivity of 30 Scm-1 at 500 °C and low area specific resistance of 106 Ω cm2 with 10 μs relaxation time at 200 °C.

  15. Compositionally continuously graded cathode layers of (Ba0.5Sr0.5)(Fe0.91Al0.09)O3-δ-Gd0.1Ce0.9O2 by wet powder spraying technique for solid oxide fuel cells

    NASA Astrophysics Data System (ADS)

    Jiang, Taizhi; Wang, Zhenhua; Ren, Baiyu; Qiao, Jinshuo; Sun, Wang; Sun, Kening

    2014-02-01

    Compositionally continuously graded cathode layers (CGCLs) of (Ba0.5Sr0.5)(Fe0.91Al0.09)O3-δ-Gd0.1Ce0.9O2 (BSFA-GDC) have been constructed by a handy and effective technique called wet powder spraying (WPS). CGCLs exhibit similar thermal expansion coefficient (TEC) value between adjacent thin layers. The continuously graded structure and the well-distributed components of BSFA-GDC cathode are confirmed by morphological characterization with scanning electron microscopy (SEM), and by compositional analysis with energy dispersion X-ray spectrometer (EDS), respectively. The polarization resistance (Rp) of CGCLs with three different thicknesses is investigated by electrochemical impedance spectra (EIS). The EIS results show that CGCLs with a moderate thickness of 20 μm achieve the lowest Rp of 0.301 Ω cm2 at 800 °C. In addition, anode-supported single cells with the configuration of NiO-YSZ/YSZ/GDC/BSFA-GDC have been fabricated and tested. The cell with the CGCLs thickness of 20 μm reaches the highest output power density of 848 mW cm-2 at 800 °C.

  16. Decrease in electrical resistance of surface oxide of iron-chromium-aluminium alloy by La0.6Sr0.4Co0.2Fe0.8O3 coating and heat treatment for the application of metal-supported solid oxide fuel cells

    NASA Astrophysics Data System (ADS)

    Pham, Hung-Cuong; Taniguchi, Shunsuke; Inoue, Yuko; Chou, Jyh-Tyng; Izumi, Toru; Matsuoka, Koji; Sasaki, Kazunari

    2015-11-01

    We have investigated the property of a Fe-Cr-Al-type stainless steel as a porous alloy substrate for metal-supported solid oxide fuel cells (SOFCs) especially on the cathode side. We found that the microstructure and electrical resistance of the surface oxide layer of the alloy changes depending on the heat-treatment conditions. A relatively low electrical resistance was obtained when the porous alloy substrate was coated with La0.6Sr0.4Co0.2Fe0.8O3 (LSCF) and heat treated at 700-800 °C in air. The morphology of the surface oxide layer observed by high-resolution transmission electron microscopy was a columnar structure of γ-Al2O3 polycrystal and Sr3Al2O6 growing outward in the same direction. In contrast, the surface oxide layer of the alloy showed a high electrical resistance when the uncoated porous alloy substrate was heat treated. The morphology of the surface oxide layer in that case was a columnar structure consisting of only γ-Al2O3 growing outward in various directions.

  17. Magnetic field, frequency and temperature dependence of complex conductance of ultrathin La1.65Sr0.45CuO4/La2CuO4 films and the organic superconductors κ-(BEDT-TTF)2Cu[N(CN)2]Br

    DOE PAGES

    V. A. Gasparov; Bozovic, I.; He, Xi; Dubuis, G.; Pavuna, D.; Kushch, N. D.; Yagubskii, E. B.; Schlueter, J. A.

    2015-09-01

    In this study, we used atomic-layer molecular beam epitaxy (ALL-MBE) to synthesize bilayer films of a cuprate metal (La1.65Sr0.45CuO4) and a cuprate insulator (La2CuO4), in which interface superconductivity occurs in a layer that is just one-half unit cell thick. We have studied the magnetic field and temperature dependence of the complex sheet conductance, σ(ω), of these films, and compared them to κκ-(BEDT-TTF)2Cu[N(CN)2]Br single crystals. The magnetic field H was applied both parallel and perpendicular to the 2D conducting layers. Experiments have been carried out at frequencies between 23 kHz and 50 MHz using either two-coil mutual inductance technique, or themore » LC resonators with spiral or rectangular coils. The real and the imaginary parts of the mutual-inductance M(T,ω) between the coil and the sample were measured and converted to complex conductivity. For H perpendicular to the conducting layers, we observed almost identical behavior in both films and κ-Br single crystals: (i) the transition onset in the inductive response, Lk–1(T) occurs at a temperature lower by 2 K than in Re σ(T), (ii) this shift is almost constant with magnetic field up to 8 T; (iii) the vortex diffusion constant D(T) is exponential due to pinning of vortex cores. These results can be described by the extended dynamic theory of the Berezinski–Kosterlitz–Thouless (BKT) transition and dynamics of bound vortex–antivortex pairs with short separation lengths.« less

  18. Control of VO•• ˜ TiT i ' dipole pairs as well as M gTi ″ defects on dielectric properties of Mg doped (Pb0.35Sr0.65)TiO3 thin film

    NASA Astrophysics Data System (ADS)

    Hu, Tao; Wang, Zongrong; Ma, Ning; Du, Piyi

    2016-01-01

    Mg doped (Pb0.35Sr0.65)TiO3 (PST) thin films were fabricated on indium tin oxide /glass substrates by the sol-gel technique. The formation of the PST phase and control of the magnesium doping on the microstructure, defect states, and dielectric properties of the thin film were investigated by means of XRD, SEM, AFM, XPS, and impedance analysis. Results showed that the oxygen vacancies and the associated Ti3+ ions formed as VO•• ˜ TiT i ' dipole pairs, and the dipole pairs were aligned opposite to the direction of the intrinsic dipole moments in the PST thin film. The amount of dipole pairs was strongly affected by the formed M gTi ″ in the thin film. The minimum amount of the dipole pairs appeared in the PST thin film with Mg doping content of 6% in molar ratio. The thin film with Mg doping content of 6% showed high permittivity due to low offset from VO•• ˜ TiT i ' dipole pairs and low dielectric loss due to low defect electrons generated in the thin film simultaneously. The formed M gTi ″ in the oxygen octahedral contributed lower response of the dipole moments to external electric field and resulted in lower tunability of the PST thin film with increasing Mg doping content. Controlled by the substitution of Mg2+ ions for Ti4+ ions and the induced VO•• ˜ TiT i ' dipole pairs, the optimal figure of merit was obtained in the PST thin film with Mg doping content of 6% with which the thin film possessed the smallest dielectric loss and still high tunability simultaneously.

  19. Magnetic field, frequency and temperature dependence of complex conductance of ultrathin La1.65Sr0.45CuO4/La2CuO4 films and the organic superconductors κ-(BEDT-TTF)2Cu[N(CN)2]Br

    NASA Astrophysics Data System (ADS)

    Gasparov, V. A.; He, Xi; Dubuis, G.; Pavuna, D.; Kushch, N. D.; Yagubskii, E. B.; Schlueter, J. A.; Bozovic, I.

    2015-09-01

    We used atomic-layer molecular beam epitaxy (ALL-MBE) to synthesize bilayer films of a cuprate metal (La1.65Sr0.45CuO4, LSCO) and a cuprate insulator (La2CuO4, LCO), in which interface superconductivity occurs in a layer that is just one-half unit cell thick. We have studied the magnetic field and temperature dependence of the complex sheet conductance, σ(ω), of these films, and compared them to κ-(BEDT-TTF)2Cu[N(CN)2]Br single crystals. The magnetic field H was applied both parallel and perpendicular to the 2D conducting layers. Experiments have been carried out at frequencies between 23 kHz and 50 MHz using either two-coil mutual inductance technique, or the LC resonators with spiral or rectangular coils. The real and the imaginary parts of the mutual-inductance M(T,ω) between the coil and the sample were measured and converted to complex conductivity. For H perpendicular to the conducting layers, we observed almost identical behavior in both films and κ-Br single crystals: (i) the transition onset in the inductive response, Lk-1(T) occurs at a temperature lower by 2 K than in Reσ(T), (ii) this shift is almost constant with magnetic field up to 8 T; (iii) the vortex diffusion constant D(T) is exponential due to pinning of vortex cores. These results can be described by the extended dynamic theory of the Berezinski-Kosterlitz-Thouless (BKT) transition and dynamics of bound vortex-antivortex pairs with short separation lengths.

  20. Intermediate-to-low temperature protonic ceramic membrane fuel cells with Ba 0.5Sr 0.5Co 0.8Fe 0.2O 3-δ-BaZr 0.1Ce 0.7Y 0.2O 3-δ composite cathode

    NASA Astrophysics Data System (ADS)

    Lin, Bin; Ding, Hanping; Dong, Yingchao; Wang, Songlin; Zhang, Xiaozhen; Fang, Daru; Meng, Guangyao

    The perovskite-type Ba 0.5Sr 0.5Co 0.8Fe 0.2O 3-δ-BaZr 0.1Ce 0.7Y 0.2O 3-δ (BSCF-BZCY) composite oxides were synthesized by a modified Pechini method and examined as a novel composite cathode for intermediate-to-low temperature protonic ceramic membrane fuel cells (ILT-PCMFCs). Thin proton-conducting BaZr 0.1Ce 0.7Y 0.2O 3-δ (BZCY) electrolyte and NiO-BaZr 0.1Ce 0.7Y 0.2O 3-δ (NiO-BZCY) anode functional layer were prepared over porous anode substrates composed of NiO-BaZr 0.1Ce 0.7Y 0.2O 3-δ by a one-step dry-pressing/co-firing process. A laboratory-sized quad-layer cell of NiO-BZCY/NiO-BZCY(∼50 μm)/BZCY(∼20 μm)/BSCF-BZCY(∼50 μm) was operated from 550 to 700 °C with humidified hydrogen (∼3% H 2O) as fuel and the static air as oxidant. A high open-circuit potential of 1.009 V, a maximum power density of 418 mW cm -2, and a low polarization resistance of the electrodes of 0.10 Ω cm 2 was achieved at 700 °C. These investigations have indicated that proton-conducting BZCY electrolyte with BSCF perovskite cathode is a promising material system for the next generation solid oxide fuel cells (SOFCs).

  1. Promoted electrochemical performance of intermediate temperature solid oxide fuel cells with Pd0.95Mn0.05O-infiltrated (La0.8Sr0.2)0.95MnO3-δ-Y0.16Zr0.84O2 composite cathodes

    NASA Astrophysics Data System (ADS)

    Wang, Ao; Pu, Jian; Yan, Dong; Duan, Nan-Qi; Tan, Yuan; Jia, Lichao; Chi, Bo; Li, Jian

    2016-01-01

    Pd0.95Mn0.05O-infiltrated (La0.8Sr0.2)0.95MnO3-δ-8 mol.% Y2O3 stabilized ZrO2 (LSM-YSZ) cathode is used to large size (11 × 11 × 0.1 cm) Ni-YSZ anode-supported planar cells for the first time and electrochemically evaluated in the intermediate temperature range from 650 to 800 °C with H2 as the fuel and air as the oxidant. The initial open circuit voltage (OCV) of the cell is 1.15 V, and the achieved maximum power density increases from 328 to 734 mW cm-2 with the increase of testing temperatures from 600 to 800 °C, which is almost 2.6 times higher than that of the cell with conventional LSM-YSZ cathode. After each thermal cycle between 750 and 300 °C, the OCV remains almost unchanged and the cell voltage decreases less than 0.007 V, indicating that the cell is capable of thermal cycling. The cell voltage at 310 mA cm-2 and 750 °C declines linearly with testing time at a rate of 2.6 × 10-4 V h-1 for the growth of the infiltrated Pd0.95Mn0.05O size, resulting in reduction of the total surface area of the particles. The mechanism of performance degradation of the cell with Pd0.95Mn0.05O-infiltrated LSM-YSZ composites cathode is discussed in detail.

  2. Microstructural properties, electrical behavior and low field magnetoresistance of (1-x)La0.67Sr0.33MnO3 (LSMO)+(x)Ni0.5Zn0.5Fe2O4 (NZFO) composites

    NASA Astrophysics Data System (ADS)

    Dar, Mashkoor Ahmad; Varshney, Dinesh

    2015-12-01

    The composites with composition of (1-x)La0.67Sr0.33MnO3 (LSMO)+(x)Ni0.5Zn0.5Fe2O4 (NZFO) with x=0.0 (S1), 0.04 (S2), 0.07 (S3), 0.10 (S4), 0.30 (S5) and 1.0 (S6) were synthesized by solid-state reaction route. Structural study using Rietveld refinement of X-ray diffraction (XRD) pattern indicates a rhombohedrally-distorted structure (space group R3c) for LSMO phase while to that NZFO compound crystallizes in cubic structure (space group Fd3m). XRD patterns and microstructural analysis show that LSMO and NZFO phase exists independently in Ni0.5Zn0.5Fe2O4 doped composites. The transport properties of the compositions x=0.0, x=0.04, and x=0.07 showed that NZFO phase improves the resistivity and shifts the metal-insulator transition temperature TMI towards lower temperature. The magnetoresistance (MR) of composite samples with x=0.04 and x=0.07 decreases monotonously from 200 to 300 K in a magnetic field of 8 T. At lower temperatures (~5 K), a sharp drop of negative MR at low fields (H<1 T) has been observed followed by a slower varying MR at a comparatively high-field regime (H>1 T) where MR is almost linear with applied magnetic field. Temperature dependence of resistivity for composites samples with x=0.04 and x=0.07 has been best fitted by small Polaron hopping (SPH) and variable range hopping models (VRH).

  3. Structural, magnetic, and superconducting properties of pulsed-laser-deposition-grown La1.85 Sr0.15 CuO4 / La2/3 Ca1/3 MnO3 superlattices on (001)-oriented LaSrAlO4 substrates

    DOE PAGES

    Das, S.; Sen, K.; Marozau, I.; Uribe-Laverde, M. A.; Biskup, N.; Varela, M.; Khaydukov, Y.; Soltwedel, O.; Keller, T.; Döbeli, M.; et al

    2014-03-12

    Epimore » taxial La1.85 Sr0.15 CuO4 / La2/3 Ca1/3 MnO3 (LSCO/LCMO) superlattices (SL) on (001)- oriented LaSrAlO4 substrates have been grown with pulsed laser deposition (PLD) technique. Their structural, magnetic and superconducting properties have been determined with in-situ reflection high energy electron diffraction (RHEED), x-ray diffraction, specular neutron reflectometry, scanning transmission electron microscopy (STEM), electric transport, and magnetization measurements. We find that despite the large mismatch between the in-plane lattice parameters of LSCO (a = 0.3779 nm) and LCMO (a = 0.387 nm) these superlattices can be grown epitaxially and with a high crystalline quality. While the first LSCO layer remains clamped to the LSAO substrate, a sizeable strain relaxation occurs already in the first LCMO layer. The following LSCO and LCMO layers adopt a nearly balanced state in which the tensile and compressive strain effects yield alternating in-plane lattice parameters with an almost constant average value. No major defects are observed in the LSCO layers, while a significant number of vertical antiphase boundaries are found in the LCMO layers. The LSCO layers remain superconducting with a relatively high superconducting onset temperature of Tconset ≈ 36 K. The macroscopic superconducting response is also evident in the magnetization data due to a weak diamagnetic signal below 10 K for H ∥ ab and a sizeable paramagnetic shift for H ∥ c that can be explained in terms of a vortex-pinning-induced flux compression. The LCMO layers maintain a strongly ferromagnetic state with a Curie temperature of TCurie ≈ 190 K and a large low-temperature saturation moment of about 3.5 (1) μB. These results suggest that the LSCO/LCMO superlattices can be used to study the interaction between the antagonistic ferromagnetic and superconducting orders and, in combination with previous studies on YBCO/LCMO superlattices, may allow one to identify the relevant

  4. Temperature-dependent emissivity property in La0.7Sr0.3MnO3 films

    NASA Astrophysics Data System (ADS)

    Fan, Desong; Li, Qiang; Dai, Ping

    2016-04-01

    Thermochromic films have been deposited by magnetron sputtering technique on different substrates. The crystallinity and surface morphology of the films have been characterized. Characterization result shows that the films are of perovskite structure. Composition analysis is performed and the result indicated that the element composition of the film can be close to its stoichiometric ratio. Temperature-dependent reflectivity and emissivity are studied. Reflectivity spectra show a downward trend with increasing temperature. Emissivity of the film is large at high temperature and it decreases sharply upon cooling. The emissivity increment at 123-373 K can approach 0.43 at 1.4 Pa sputtering pressure environment, which is attractive for thermal control application in spacecraft.

  5. Raman Spectroscopy of the Thermoelectric Sr0.61Ba0.39Nb2O6

    NASA Astrophysics Data System (ADS)

    Primrose, Michael; Toulouse, Jean; Bock, Jonathan; Randall, Clive

    2015-03-01

    Strontium Barium Niobate (SBN) has recently been shown by Lee et al. to exhibit high thermoelectric power factors at temperatures above 500 K when it has been highly reduced. To determine the effects of reduction on the phonons, the Raman spectra of unreduced and reduced SBN have been measured at room temperature along the axis of polarization (c-axis) and perpendicular to it (a-axis). The Raman features of the unreduced crystal are found to be very broad and overlapping. In particular, a strong Lorentzian central (quasi-elastic) peak extending out to 400cm-1 is observed for light polarized along the a axis. By contrast and unexpectedly in the reduced crystal, thought to be more disordered, well resolved Raman peaks are observed, particularly at low frequencies. Also in the reduced crystal, the central peak is much suppressed and narrower, but a new peak appears at 1000cm-1 for both c and a polarizations. In addition, the high frequency peaks (>200 cm-1) appear to broaden and to shift toward higher frequencies. High temperatures results may be available at the time of the conference.

  6. Single crystalline monoclinic La0.7Sr0.3MnO3 nanowires with high temperature ferromagnetism

    SciTech Connect

    Carretero-Genevrier, Adrian; Gazquez Alabart, Jaume; Idrobo Tapia, Juan C; Oro, Judith; Arbiol, Jordi; Varela del Arco, Maria; Ferain, Etienne; Rodriguez-Carvajal, Juan; Puig, Teresa; Mestres, Narcis; Obradors, Xavier

    2011-01-01

    Porous mixed-valent manganese oxides are a group of multifunctional materials that can be used as molecular sieves, catalysts, battery materials, and gas sensors. However, material properties and thus activity can vary significantly with different synthesis methods or process conditions, such as temperature and time. Here, we report on a new synthesis route for MnO{sub 2} and LaSr-doped molecular sieve single crystalline nanowires based on a solution chemistry methodology combined with the use of nanoporous polymer templates supported on top of single crystalline substrates. Because of the confined nucleation in high aspect ratio nanopores and of the high temperatures attained, new structures with novel physical properties have been produced. During the calcination process, the nucleation and crystallization of {var_epsilon}-MnO{sub 2} nanoparticles with a new hexagonal structure is promoted. These nanoparticles generated up to 30 {mu}m long and flexible hexagonal nanowires at mild growth temperatures (T{sub g} = 700 C) as a consequence of the large crystallographic anisotropy of {var_epsilon}-MnO{sub 2}. The nanocrystallites of MnO{sub 2} formed at low temperatures serve as seeds for the growth of La{sub 0.7}Sr{sub 0.3}MnO{sub 3} nanowires at growth temperatures above 800 C, through the diffusion of La and Sr into the empty 1D-channels of {var_epsilon}-MnO{sub 2}. Our particular growth method has allowed the synthesis of single crystalline molecular sieve (LaSr-2 x 4) monoclinic nanowires with composition La{sub 0.7}Sr{sub 0.3}MnO{sub 3} and with ordered arrangement of La{sup 3+} and Sr{sup 2+} cations inside the 1D-channels. These nanowires exhibit ferromagnetic ordering with strongly enhanced Curie temperature (T{sub c} > 500 K) that probably results from the new crystallographic order and from the mixed valence of manganese.

  7. Preparation of the Second Shipment of Spent Nuclear Fuel from the Ustav Jaderneho Vyzkumu Rez (UJV Rez), a.s., Czech Republic to the Russian Federation for Reprocessing - 13478

    SciTech Connect

    Trtilek, Radek; Podlaha, Josef

    2013-07-01

    After more than 50 years of operation of the LVR-15 research reactor operated by the UJV Rez, a. s. (formerly Nuclear Research Institute - NRI), a large amount of the spent nuclear fuel (SNF) of Russian origin has been accumulated. In 2005 UJV Rez, a. s. jointed the Russian Research Reactor Fuel Return (RRRFR) program under the United States (US) - Russian Global Threat Reduction Initiative (GTRI) and started the process of SNF shipment from the LVR-15 research reactor back to the Russian Federation (RF). In 2007 the first shipment of SNF was realized. In 2011, preparation of the second shipment of spent fuel from the Czech Republic started. The experience obtained from the first shipment will be widely used, but some differences must be taken into the account. The second shipment will be realized in 2013 and will conclude the return transport of all, both fresh and spent, high-enriched nuclear fuel from the Czech Republic to the Russian Federation. After the shipment is completed, there will be only low-enriched nuclear fuel on the territory of the Czech Republic, containing maximum of 20% of U-235, which is the conventionally recognized limit between the low- and high-enriched nuclear materials. The experience (technical, organizational, administrative, logistic) obtained from the each SNF shipment as from the Czech Republic as from other countries using the Russian type research reactors are evaluated and projected onto preparation of next shipment of high enriched nuclear fuel back to the Russian Federation. The results shown all shipments provided by the UJV Rez, a. s. in the frame of the GTRI Program have been performed successfully and safely. It is expected the experience and results will be applied to preparation and completing of the Chinese Miniature Neutron Source Reactors (MNSR) Spent Nuclear Fuel Repatriation in the near future. (authors)

  8. Surface Tuning of La0.5Sr0.5CoO3 Perovskite Catalysts by Acetic Acid for NOx Storage and Reduction.

    PubMed

    Peng, Yue; Si, Wenzhe; Luo, Jinming; Su, Wenkang; Chang, Huazhen; Li, Junhua; Hao, Jiming; Crittenden, John

    2016-06-21

    Selective dissolution of perovskite A site (A of ABO3 structure) was performed on the La1 - xSrxCoO3 catalysts for the NOx storage and reduction (NSR) reaction. The surface area of the catalysts were enhanced using dilute HNO3 impregnation to dissolve Sr. Inactive SrCO3 was removed effectively within 6 h, and the catalyst preserved the perovskite framework after 24 h of treatment. The tuned catalysts exhibited higher NSR performance (both NOx storage and NO-to-NO2 oxidation) under lean-burn and fuel-rich cycles at 250 °C. Large amounts of NOx adsorption were due to the increase of nitrate/nitrite species bonding to the A site and the growth of newly formed monodentate nitrate species. Nitrate species were stored stably on the partial exposed Sr(2+) cations. These exposed Sr(2+) cations played an important role on the NOx reduction by C3H6. High NO-to-NO2 oxidation ability was due to the generation of oxygen defects and Co(2+)-Co(3+) redox couples, which resulted from B-site exsolution induced by A-site dissolution. Hence, our method is facile to modify the surface structures of perovskite catalysts and provides a new strategy to obtain highly active catalysts for the NSR reaction.

  9. Superconductivity in La1.56Sr0.44CuO4/La2CuO4 Superlattices

    SciTech Connect

    Bozovic I.; Suter, A.; Morenzoni, E.; Prokscha, T.; Luetkens, H.; Wojek, B.M.; Logvenov, G.; Gozar, A.

    2011-12-01

    Superlattices of the repeated structure La{sub 1.56}Sr{sub 0.44}CuO{sub 4}/La{sub 2}CuO{sub 4} (LSCO-LCO), where none of the constituents is superconducting, show a superconducting transition of T{prime}{sub c} 25 K. In order to elucidate the nature of the superconducting state we have performed a low-energy {mu}SR study. By applying a magnetic field parallel (Meissner state) and perpendicular (vortex state) to the film planes, we could show that superconductivity is sheet like, resulting in a very anisotropic superconducting state. This result is consistent with a simple charge-transfer model, which takes into account the layered structure and the difference in the chemical potential between LCO and LSCO, as well as Sr interdiffusion. Using a pancake-vortex model we could estimate a strict upper limit of the London penetration depth to 380 nm in these superlattices. The temperature dependence of the muon depolarization rate in field cooling experiments is very similar to what is observed in intercalated BSCCO and suggests that vortex-vortex interaction is dominated by electromagnetic coupling but negligible Josephson interaction.

  10. Improved microstructure, dielectric and ferroelectric properties of microwave-sintered Sr 0.5Ba 0.5Nb 2O 6

    NASA Astrophysics Data System (ADS)

    Patro, P. K.; Kulkarni, A. R.; Gupta, S. M.; Harendranath, C. S.

    2007-11-01

    Ferroelectric strontium barium niobate (SBN) powder was synthesized by solid-state route. The green compacts were sintered in the temperature range 1250-1350 °C in a microwave furnace. The microstructural study, using SEM, revealed the grain size in the range 2-20 μm without microcracks, depending on the sintering temperature. This is in contrast to that obtained conventionally for sintered SBN powder synthesized by solid-state route, which resulted in duplex microstructure with microcracks [N.S. VanDamme, A.E. Sutherland, L. Jones, K. Bridger, S.R. Winzer, J. Am. Ceram. Soc. 74 (1991) 1785; P.K. Patro, A.R. Kulkarni, C.S. Harendranath, Ceram. Int. 30 (2004) 1405; P.K. Patro, Trans. Ind. Inst. Metals 59 (2006) 229]. Impedance analyzer and ferroelectric hysteresis loop tracer were used for the dielectric, ferroelectric, I- V and electric fatigue measurements. Microwave sintering also resulted in a dielectric maxima εmax 2590 at 1 kHz (compared to 1103 for conventional sintering [P.K. Patro, A.R. Kulkarni, C.S. Harendranath, Ceram. Int. 30 (2004) 1405]) for the sintering temperature of 1350 °C. Similar improvement in microwave-sintered SBN was observed depending on their sintering condition. The origin of this difference is attributed to microstructural differences arising from difference in heating method. In this paper the observed dielectric and ferroelectric behavior have been correlated with different sintering conditions and consequent microstructure due to microwave sintering.

  11. Strain engineering to control the magnetic and magnetotransport properties of La0.67Sr0.33MnO3 thin films

    SciTech Connect

    Yang, F.; Kemik, N.; Biegalski, M.D.; Christen, H.M.; Arenholz, E.; Takamura, Y.

    2010-06-15

    This work studies the control of the magnetic and magnetotransport properties of La{sub 0.67}Sr{sub 0.33}MnO{sub 3} thin films through strain engineering. The strain state is characterized by the tetragonal distortion (c/a ratio), which can be varied continuously between a compressive strain of 1.005 to a tensile strain of 0.952 by changing the type of substrate, the growth rate, and the presence of an underlying La{sub 0.67}Sr{sub 0.33}FeO{sub 3} buffer layer. Increasing tensile tetragonal distortion of the La{sub 0.67}Sr{sub 0.33}MnO{sub 3} thin film decreases the saturation magnetization, changes the temperature dependence of the resistivity and magnetoresistance, and increases the resistivity by several orders of magnitude.

  12. Effect of Terraces at the Interface on the Structural and Physical Properties of La0.8Sr0.2MnO3 Thin Films

    NASA Astrophysics Data System (ADS)

    Ya-Qing, Feng; Kui-Juan, Jin; Chen, Ge; Xu, He; Lin, Gu; Zhen-Zhong, Yang; Hai-Zhong, Guo; Qian, Wan; Meng, He; Hui-Bin, Lu; Guo-Zhen, Yang

    2016-07-01

    Not Available Supported by the Strategic Priority Research Program (B) of Chinese Academy of Sciences under Grant No XDB07030200, the National High-Technology Research and Development Program of China under Grant No 2014AA032607, and the National Natural Science Foundation of China under Grant No 11404380.

  13. Neutron Diffraction Study of Parasitic Nd-Moment Order in the Checkerboard-Type Phase Nd1.3Sr0.7NiO4

    DOE PAGES

    Kobayashi, Riki; Yoshizawa, Hideki; Matsuda, Masaaki; Kajimoto, Ryoichi; Ishizaka, Kyoko; Tokura, Yoshinori

    2015-05-25

    In this paper, the Nd-moment order in the layered nickelate Nd2-xSrxNiO4 (x = 0.7) has been investigated by performing a neutron diffraction experiment using a single crystal sample. First, the checkerboard (CB)-type charge order was confirmed by observing the temperature dependence of the nuclear superlattice peak at Q=(5,0,0) between 1.9 and 300 K, which indicates that the transition temperature of the CB-type charge order is above 300 K. Magnetic superlattice peaks with the propagation vector k=(1-ε,0,1) appear below 67 K, and the value of ε was determined to be 0.455 in good agreement with previous studies. The intensity of themore » magnetic superlattice peaks appearing below 67 K shows a sharp increase below ≈20 K. This behavior indicates that the Nd moments freeze under the influence of the Ni ordering. The CB-type antiferromagnetic (AFM) Ni order in the NiO2 layers is stacked antiferromagnetically in the c-axis direction, while the Nd moments in the Nd/SrO2 layers are coupled antiferromagnetically with the Ni moments. Finally, the Nd moments are parallel to the c-axis, while the Ni moments are canted towards the c-axis direction from the basal ab-plane at low temperatures where the Nd moments are well ordered.« less

  14. Hyperthermia mediated by dextran-coated La0.7Sr0.3MnO3 nanoparticles: in vivo studies

    PubMed Central

    Haghniaz, Reihaneh; Umrani, Rinku D; Paknikar, Kishore M

    2016-01-01

    Purpose The aim of this study was to evaluate radiofrequency-induced dextran-coated lanthanum strontium manganese oxide nanoparticles-mediated hyperthermia to be used for tumor regression in mice. Materials and methods Nanoparticles were injected intra-tumorally in melanoma-bearing C57BL/6J mice and were subjected to radiofrequency treatment. Results Hyperthermia treatment significantly inhibited tumor growth (~84%), increased survival (~50%), and reduced tumor proliferation in mice. Histopathological examination demonstrated immense cell death in treated tumors. DNA fragmentation, increased terminal deoxynucleotidyl transferase-dUTP nick end labeling signal, and elevated levels of caspase-3 and caspase-6 suggested apoptotic cell death. Enhanced catalase activity suggested reactive oxygen species-mediated cell death. Enhanced expression of heat shock proteins 70 and 90 in treated tumors suggested the possible development of “antitumor immunity”. Conclusion The dextran-coated lanthanum strontium manganese oxide-mediated hyperthermia can be used for the treatment of cancer. PMID:27175076

  15. Improved Dielectric Properties of Heterostructured Ba2.5Sr0.5TiO3 Thin Film Composites for Microwave Dielectric Devices

    NASA Technical Reports Server (NTRS)

    Jain, M.; Majumder, S. B.; Katiyar, R. S.; Bhalla, A. S.; Agrawal, D. C.; Kulkarni, V. N.; VanKeuls, F. W.; Miranda, F. A.; Romanofsky, R. R.; Mueller, C. H.; Fernandez, F.

    2002-01-01

    In the present work we have deposited MgO and Ba(sub 0.5)Sr(sub 0.5)TiO(sub 3)(BST50) thin layers in different sequences to make MgO:BST50 hetero-structured thin films. These films were characterized by X-ray diffraction and Rutherford backscattering technique and found to be highly (100) textured. The figure of merit {(C(sub0)-C(sub v)/(C(sub0-tandelta)} of the hetero-structured films was found to be higher as compared to pure BST50 films measured at 1 MHz frequency with electric field of 25.3 kV/cm. These films were used to make eight element coupled micro-strip phase shifter and characterized in a frequency range of 13-15 GHz. The high frequency figure of merit (kappa factor, defined as the ratio of degree of phase shift per dB loss) measured at around 14 GHz with electric field of 333 kV/cm has been markedly improved (around 64.28 deg/dB for hetero-structured film as compared to 24.65 deg /dB for pure film). Improvement in dielectric properties in a wide frequency range in the MgO:BST are believed to be due to the higher densification of the hetero-structured films.

  16. Surface Tuning of La0.5Sr0.5CoO3 Perovskite Catalysts by Acetic Acid for NOx Storage and Reduction.

    PubMed

    Peng, Yue; Si, Wenzhe; Luo, Jinming; Su, Wenkang; Chang, Huazhen; Li, Junhua; Hao, Jiming; Crittenden, John

    2016-06-21

    Selective dissolution of perovskite A site (A of ABO3 structure) was performed on the La1 - xSrxCoO3 catalysts for the NOx storage and reduction (NSR) reaction. The surface area of the catalysts were enhanced using dilute HNO3 impregnation to dissolve Sr. Inactive SrCO3 was removed effectively within 6 h, and the catalyst preserved the perovskite framework after 24 h of treatment. The tuned catalysts exhibited higher NSR performance (both NOx storage and NO-to-NO2 oxidation) under lean-burn and fuel-rich cycles at 250 °C. Large amounts of NOx adsorption were due to the increase of nitrate/nitrite species bonding to the A site and the growth of newly formed monodentate nitrate species. Nitrate species were stored stably on the partial exposed Sr(2+) cations. These exposed Sr(2+) cations played an important role on the NOx reduction by C3H6. High NO-to-NO2 oxidation ability was due to the generation of oxygen defects and Co(2+)-Co(3+) redox couples, which resulted from B-site exsolution induced by A-site dissolution. Hence, our method is facile to modify the surface structures of perovskite catalysts and provides a new strategy to obtain highly active catalysts for the NSR reaction. PMID:27233105

  17. Large transport Jc in Cu-sheathed Sr0.6K0.4Fe2As2 superconducting tape conductors

    PubMed Central

    Lin, He; Yao, Chao; Zhang, Haitao; Zhang, Xianping; Zhang, Qianjun; Dong, Chiheng; Wang, Dongliang; Ma, Yanwei

    2015-01-01

    Copper sheath is the first choice for manufacturing high-Tc superconducting wires and tapes because of its high electrical and thermal conductivities, low-cost and good mechanical properties. However, Cu can easily react with superconducting cores, such as BSCCO, MgB2 and pnictides, and therefore drastically decrease the transport Jc. Here, we report the fabrication of Cu-sheathed Sr1−xKxFe2As2 tapes with superior Jc performance using a simple hot pressing method that is capable of eliminating the lengthy high-temperature sintering. We obtained high-quality Sr1−xKxFe2As2 tapes with processing at 800 oC for 30 minutes and measured high Tc and sharp transition. By this rapid fabrication, Cu sheath does not give rise to apparent reaction layer, and only slightly diffuses into Sr-122 core. As a consequence, we achieved high transport Jc of 3.1 × 104 A/cm2 in 10 T and 2.7 × 104 A/cm2 in 14 T at 4.2 K. The in-field Jc performance is by far the highest reported for Cu-sheathed high-Tc conductors. More importantly, Cu-sheathed Sr-122 tapes also showed a high Je value of 1.0 × 104 A/cm2 in 10 T at 4.2 K, which has reached the widely accepted practical level for applications. These results demonstrate that Cu is a very promising sheath for the practical application of pnictide conductors. PMID:26122741

  18. Epitaxial Strain-Induced Chemical Ordering in La0.5Sr0.5CoO3-delta Films on SrTiO3

    SciTech Connect

    W Donner; C Chen; M Liu; A Jacobson; Y Lee; M Gadre; D Morgan

    2011-12-31

    Fast ion conductors are at the foundation of a number of important technologies, ranging from fuel cells to batteries to gas separators. Recent results suggest that strained interfaces and thin films may offer new mechanisms for achieving enhanced ionic transport. In this work, we investigate strained 40-nm films of perovskite La{sub 0.5}Sr{sub 0.5}CoO{sub 3-{delta}}, which is an important material for solid oxide fuel cell cathodes and oxygen separation membranes. We demonstrate that a strained thin film of La{sub 0.5}Sr{sub 0.5}CoO{sub 3-{delta}} on SrTiO{sub 3} can have dramatically different anion and cation thermodynamics and kinetics than bulk La{sub 0.5}Sr{sub 0.5}CaO{sub 3-{delta}}. We use synchrotron X-ray diffraction to show that La{sub 0.5}Sr{sub 0.5}CoO{sub 3-{delta}} thin films form an ordered phase at 650 K. The ordered phase consists of La and Sr cations in planes parallel to the surface and is associated with coherent expansion in the c-direction of {approx}5%. This chemical ordering is not observed in the bulk material and is ascribed to the interplay between the epitaxial strain imposed by the substrate, changes in oxygen vacancy content and cation mobility, and the ordering of oxygen vacancies.

  19. Large transport Jc in Cu-sheathed Sr0.6K0.4Fe2As2 superconducting tape conductors

    NASA Astrophysics Data System (ADS)

    Lin, He; Yao, Chao; Zhang, Haitao; Zhang, Xianping; Zhang, Qianjun; Dong, Chiheng; Wang, Dongliang; Ma, Yanwei

    2015-06-01

    Copper sheath is the first choice for manufacturing high-Tc superconducting wires and tapes because of its high electrical and thermal conductivities, low-cost and good mechanical properties. However, Cu can easily react with superconducting cores, such as BSCCO, MgB2 and pnictides, and therefore drastically decrease the transport Jc. Here, we report the fabrication of Cu-sheathed Sr1-xKxFe2As2 tapes with superior Jc performance using a simple hot pressing method that is capable of eliminating the lengthy high-temperature sintering. We obtained high-quality Sr1-xKxFe2As2 tapes with processing at 800 oC for 30 minutes and measured high Tc and sharp transition. By this rapid fabrication, Cu sheath does not give rise to apparent reaction layer, and only slightly diffuses into Sr-122 core. As a consequence, we achieved high transport Jc of 3.1 × 104 A/cm2 in 10 T and 2.7 × 104 A/cm2 in 14 T at 4.2 K. The in-field Jc performance is by far the highest reported for Cu-sheathed high-Tc conductors. More importantly, Cu-sheathed Sr-122 tapes also showed a high Je value of 1.0 × 104 A/cm2 in 10 T at 4.2 K, which has reached the widely accepted practical level for applications. These results demonstrate that Cu is a very promising sheath for the practical application of pnictide conductors.

  20. Laser-Ablated Ba(0.50)Sr(0.50)TiO3/LaAlO3 Films Analyzed Statistically for Microwave Applications

    NASA Technical Reports Server (NTRS)

    Romanofsky, Robert R.

    2003-01-01

    Scanning phased-array antennas represent a highly desirable solution for futuristic near-Earth and deep space communication scenarios requiring vibration-free, rapid beam steering and enhanced reliability. The current state-of-practice in scanning phased arrays is represented by gallium arsenide (GaAs) monolithic microwave integrated circuit (MMIC) technology or ferrite phase shifters. Cost and weight are significant impediments to space applications. Moreover, conventional manifold-fed arrays suffer from beam-forming loss that places considerable burden on MMIC amplifiers. The inefficiency can result in severe thermal management problems.

  1. A K-Band Linear Phased Array Antenna Based on Ba(0.60)Sr(0.40)TiO3 Thin Film Phase Shifters

    NASA Technical Reports Server (NTRS)

    Romanofsky, R.; Bernhard, J.; Washington, G.; VanKeuls, F.; Miranda, F.; Cannedy, C.

    2000-01-01

    This paper summarizes the development of a 23.675 GHz linear 16-element scanning phased array antenna based on thin ferroelectric film coupled microstripline phase shifters and microstrip patch radiators.

  2. DIELECTRIC PROPERTIES OF BA(0.6)SR(0.4)TiO(3) THIN FILMS WITH VARIOUS STRAIN STATES

    SciTech Connect

    B. PARK; E. PETERSON; ET AL

    2001-04-01

    We could systematically control the strain states of a Ba{sub 0.6}Sr{sub 0.4}TiO{sub 3} film by depositing a very thin Ba{sub 1{minus}x}Sr{sub x}TiO{sub 3} interlayer between the main layer of the Ba{sub 0.6}Sr{sub 0.4}TiO{sub 3} and a MgO(001) substrate. Ba{sub 0.6}Sr{sub 0.4}TiO{sub 3} films showed very strong dependence of dielectric properties on the strain states. The strain induced by the MgO substrate was relaxed faster than that induced by an interlayer.

  3. Low-energy dispersion of dynamic charge stripes in La1.75Sr0.25NiO4 observed with inelastic neutron scattering

    NASA Astrophysics Data System (ADS)

    Zhong, Ruidan; Tranquada, John; Gu, Genda; Reznik, Dmitry; Winn, Barry

    The dynamic stripe correlations have been the subject of intense research, owing to the possible links with high-Tc superconductivity. In light of a recently published, direct observation of charge-stripe fluctuations in La2-xSrxNiO4 using inelastic neutron scattering, we did a follow-up neutron experiment on a x=0.25 sample to characterize the low-energy dispersion of these dynamic charge stripes using the HYSPEC instrument at the Spallation Neutron Source. The scattering signals are collected in the vicinity of a charge-order peak with a large wave vector (4.4, 3, 0), where dynamic spin-stripe correlations are negligible. Mapping the low-energy charge-stripe fluctuations in a wide temperature range, we observe a finite dispersion along the stripe-modulation direction at T >=160K where the charge stripes become disordered, while the steep dispersion in the orthogonal direction is not resolved. Work at BNL supported by Office of Basic Energy Sciences, US DOE, under Contract No. DE-SC00112704.

  4. Layed Perovskite PRBA0.5SR0.5CO205 as High Performance Cathode for Solid Oxide Fuels Using Photon Conducting Electrolyte

    SciTech Connect

    Brinkman, K.

    2010-05-05

    The layered perovskite PrBa{sub 0.5}Sr{sub 0.5}Co{sub 2}O{sub 5+{delta}} (PBSC) was investigated as a cathode material for a solid oxide fuel cell using a proton-conducting electrolyte based on BaCe{sub 0.7}Y{sub 0.2}Zr{sub 0.1}O{sub 3-{delta}} (BCYZ). The sintering conditions for the PBSC-BCYZ composite cathode were optimized resulting in the lowest area-specific resistance and apparent activation energy obtained with the cathode sintered at 1200 C for 2h. The maximum power densities of the PBSC-BCYZ/BZCY/NiO-BCYZ cell were 0.179, 0.274, 0.395, and 0.522 Wcm{sup -2} at 550, 600, 650, and 700 C, respectively with a 15{micro}m thick electrolyte. A relatively low cell interfacial polarization resistance of 0.132 {Omega}cm{sup 2} at 700 C indicated that the PBSC-BCYZ could be a good cathode candidate for intermediate temperature SOFCs with proton-conducting electrolyte.

  5. Preparation and characterization of Sr0.5Ba0.5Nb2O6 glass-ceramic on piezoelectric properties

    NASA Astrophysics Data System (ADS)

    Shan, Jiang; Xuan-Ming, Wang; Jia-Yu, Li; Yong, Zhang; Tao, Zheng; Jing-Wen, Lv

    2016-03-01

    We studied the influence of heat treatment time on the optical, thermal, electrical, and mechanical properties of strontium barium niobate (Sr1-xBaxNb2O6 hereafter SBN) piezoelectric glass-ceramics with tungsten bronze-type structure, which have good piezoelectric properties and are important lead-free piezoelectric materials. We found that the best heat treatment time is 4 h. The properties of the prepared materials are better than that of SBN ceramics and the glass-ceramic growth is faster than the SBN crystal when the heat treatment time of the SBN piezoelectric glass-ceramic is controlled, reducing the preparation costs greatly.

  6. Exchange current model for (La0.8Sr0.2)0.95MnO3 (LSM) porous cathode for solid oxide fuel cells

    NASA Astrophysics Data System (ADS)

    Miyoshi, Kota; Miyamae, Takuma; Iwai, Hiroshi; Saito, Motohiro; Kishimoto, Masashi; Yoshida, Hideo

    2016-05-01

    In this paper, we propose an empirical formula for i0,TPB, the exchange current density per unit triple-phase boundary (TPB) length, for porous lanthanum strontium manganite (LSM) cathodes of solid oxide fuel cells (SOFCs); the evaluation of i0,TPB is of crucial importance in numerical simulations of electrodes based on reconstructed microstructures obtained by a dual beam focused ion beam scanning electron microscopy (FIB-SEM) and tomography techniques. To derive a widely applicable empirical formula for i0,TPB, electrochemical measurements of porous LSM cathodes are conducted under various oxygen partial pressures (0.05-0.25 atm) and temperatures (800-950 °C). By comparing the derived formula with that derived from a thin and dense patterned LSM electrode used in previous studies, it is found that at an air temperature of 800 °C, i0,TPB derived from a porous LSM cathode is approximately 40% smaller than that for the patterned electrode. This can be attributed to the fact that the electrochemical reaction in thin and dense electrodes can occur not only at the TPBs but also at the LSM surface owing to the non-negligible ionic conductivity of LSM. The derived formula is also applied to a three-dimensional numerical simulation to confirm its validity.

  7. Synthesis and frequency-dependent dielectric properties of epitaxial La1.875Sr0.125NiO4 thin films

    SciTech Connect

    Podpirka, Adrian; Tselev, Alexander; Ramanathan, Shriram

    2012-01-01

    Epitaxial thin films of La{sub 1.875}Sr{sub 0.125}NiO{sub 4} (lanthanum strontium nickelate, LSNO) have been synthesized by sputtering onto single crystal oxide substrates and their structural and dielectric properties are reported. High dielectric constants on the order of 10{sup 7} have been measured up to 1 MHz in interdigitated capacitors with a frequency dependence that correlates with substrate imposed strain and texture. The observation of a high dielectric constant albeit with moderate loss tangent at high frequencies motivates further explorations of charge ordering phenomena in such complex oxides and serves to examine size effects on dielectric response by comparison with studies on bulk single crystal LSNO.

  8. Effect of ozone treatment on the electrical properties of (Ba0.7Sr0.3)TiO3 thin films

    NASA Astrophysics Data System (ADS)

    Halder, Sandip; Schneller, Theodor; Meyer, Rene; Waser, Rainer

    2005-06-01

    Thin films of (BaxSr1-x)TiO3 were deposited on Pt-coated Si substrates by chemical solution deposition. The films were postannealed under ozone atmosphere at various temperatures. Although there was no change observed in the microstructure after the anneal in ozone, the dielectric dispersion and the loss tangents were reduced for the films. It was also noticed that the leakage current reduced by almost two orders of magnitude after treatment with ozone. The ozone treatment was done at various temperatures between 250 and 450°C to find an optimum temperature with regard to the electrical properties. Films postannealed in ozone at 350°C for 30min showed a leakage reduction by almost three orders of magnitude. The leakage dependence on ozone postannealing is discussed on the basis of an interface-dominated (Schottky injection) and a bulk-dominated (point defect approach) charge transport process as the two limiting conduction mechanisms across thin films.

  9. Persistent Fe moments in the normal-state collapsed-tetragonal phase of the pressure-induced superconductor Ca0.67Sr0.33Fe2As2

    NASA Astrophysics Data System (ADS)

    Jeffries, J. R.; Butch, N. P.; Lipp, M. J.; Bradley, J. A.; Kirshenbaum, K.; Saha, S. R.; Paglione, J.; Kenney-Benson, C.; Xiao, Y.; Chow, P.; Evans, W. J.

    2014-10-01

    Using nonresonant Fe Kβ x-ray emission spectroscopy, we reveal that Sr substitution into CaFe2As2 decouples the Fe moment from the volume collapse transition, yielding a collapsed-tetragonal, paramagnetic normal state out of which superconductivity develops. X-ray diffraction measurements implicate the c-axis lattice parameter as the controlling criterion for the Fe moment, promoting a generic description for the appearance of pressure-induced superconductivity in the alkaline-earth-based 122 ferropnictides (AFe2As2). The evolution of Tc with pressure lends support to theories for superconductivity involving unconventional pairing mediated by magnetic fluctuations.

  10. Uniaxial pressure effect of Metal-Insulator Transition (TMI) in oriented Sm0.55(Sr0.5Ca0.5)0.45MnO3

    NASA Astrophysics Data System (ADS)

    Arumugam, Sonachalam; Mohan Radheep, D.; Sarkar, P.; Mandal, P.; Arumugam Team; Prabhat Mandal Collaboration

    2013-06-01

    Perovskite type manganites R1 - xAxMnO3 (R: rare earth ions, A: alkaline earth ions) exhibit various fundamental phenomena like colossal magnetoresistance (CMR), phase separation, and first-order ferromagnetic (FM) to paramagnetic (PM) phase transition etc. Similar to CMR, piezoresistance (PR), the change in electrical resistance in response to external pressure, can also be important parameter for various technological applications. Several studies shows that the order of phase transition can be changed either by applying external perturbations like magnetic field, pressure (P) , etc. or internally like doping etc. SSCMO single crystal was grown using floating zone technique and the quality was carefully checked and aligned along the c axis as well as ab-plane. We have investigated the effect of uniaxial pressure (P) on electrical resistivity along the ab-plane and c - axis in a single crystal of SSCMO. A huge PR ~107 % at P = 90 MPa and a remarkable increase (~79 K/GPa) of TMI have been observed with the application of P || c - axis, while TMI decreases at the rate of ~77 K/GPa for P⊥ c axis. These values of PR and dTMI /dP are much larger than those observed in other perovskite and bilayer manganites. Hence, these materials may be used for various technological applications. The authors SA and DMR wishes to thank DST, UGC and CSIR-SRF scheme (India) for the financial support to carry out the research work.

  11. Electrochemical performance of Ba 0.5Sr 0.5Co xFe 1- xO 3- δ (x = 0.2-0.8) cathode on a ScSZ electrolyte for intermediate temperature SOFCs

    NASA Astrophysics Data System (ADS)

    Lim, Yong Ho; Lee, Jun; Yoon, Jong Seol; Kim, Chul Eui; Hwang, Hae Jin

    Intermediate temperature solid oxide fuel cell cathode materials (Ba, Sr)Co xFe 1- xO 3- δ [ x = 0.2-0.8] (BSCF), were synthesized by a glycine-nitrate process (GNP) using Ba(NO 3) 2, Sr(NO 3) 2, Co(NO 3) 2·6H 2O, and Fe(NO 3) 3·9H 2O as starting materials and glycine as an oxidizer and fuel. Electrolyte-supported symmetric BSCF/GDC/ScSZ/GDC/BSCF cells consisting of porous BSCF electrodes, a GDC buffer layer, and a ScSZ electrolyte were fabricated by a screen printing technique, and the electrochemical performance of the BSCF cathode was investigated at intermediate temperatures (500-700 °C) using AC impedance spectroscopy. Crystallization behavior was found to depend on the pH value of the precursor solution. A highly acidic precursor solution increased the single phase perovskite formation temperature. In the case of using a precursor solution with pH 2, a single perovskite phase was obtained at 1000 °C. The thermal expansion coefficient of BSCF was gradually increased from 24 × 10 -6 K -1 for BSCF (x = 0.2) to 31 × 10 -6 K -1 (400-1000 °C) for BSCF (x = 0.8), which resulted in peeling-off of the cathode from the GDC/ScSZ electrolyte. Only the BSCF (x = 0.2) cathode showed good adhesion to the GDC/ScSZ electrolyte and low polarization resistance. The area specific resistance (ASR) of the BSCF (x = 0.2) cathode was 0.183 Ω cm 2 at 600 °C. The ASR of other BSCF (x = 0.4, 0.6, and 0.8) cathodes, however, was much higher than that of BSCF (x = 0.2).

  12. Enhancement of Thermoelectric Performance of Sr0.9Ba0.1Ti0.8Nb0.2O3 Ceramics by A-Site Cation Nonstoichiometry

    NASA Astrophysics Data System (ADS)

    Zhang, Xin; Liu, Jian; Li, Yi; Su, Wen-Bin; Li, Ji-Chao; Zhu, Yuan-Hu; Li, Mao-Kui; Wang, Chun-Ming; Wang, Chun-Lei

    2015-03-01

    Not Available Supported by the National Basic Research Program of China under Grant No 2013CB632506, the National Natural Science Foundation of China under Grant Nos 51202132, 51002087 and 11374186, and the Independent Innovation Foundation of Shandong University under Grant No IIFSDU 2012TS028.

  13. Suspension plasma spraying of La0.6Sr0.4Co0.2Fe0.8O3-δ cathodes: Influence of carbon black pore former on performance and degradation

    NASA Astrophysics Data System (ADS)

    Fan, E. S. C.; Kuhn, J.; Kesler, O.

    2016-06-01

    Suspension plasma spray deposition is utilized to fabricate solid oxide fuel cell cathodes with minimal material decomposition. Adding carbon black as a pore former to the feedstock suspension results in smoother and more porous coatings, but over the range of carbon black concentrations studied, has little impact on the overall symmetrical cell performance. The cathode made with a suspension containing 25 wt% carbon has the highest deposition efficiency and a polarization resistance of 0.062 Ωcm2 at 744 °C. This cathode is tested for 500 h, and it is observed that adding an SDC interlayer between the YSZ electrolyte and the cathode(s) and/or coating the metal substrate with lanthanum chromite decrease the rate of performance degradation.

  14. Growth temperature control of the epitaxy, magnetism, and transport in SrTiO3(001) / La0.5Sr0.5CoO3 thin films

    SciTech Connect

    Sharma, M; Gazquez Alabart, Jaume; Varela del Arco, Maria; Schmitt, J.; Leighton, chris

    2011-01-01

    The authors report a detailed study of the influence of deposition temperature on the microstructure, phase purity, nanoscale chemical homogeneity, stoichiometry, and magnetic and electronic properties of epitaxial La{sub 0.5}Sr{sub 0.5}CoO{sub 3} thin films grown on SrTiO{sub 3}(001) substrates via reactive dc magnetron sputtering. The results are interpreted in terms of the temperature-dependent interplay between crystallization, strain relaxation, and cation mobility (which improve with increasing deposition temperature), and oxygenation (which deteriorates at the highest deposition temperatures). In addition to the established approach to epitaxial sputter deposition based on high temperature deposition combined with subsequent ex situ annealing in O{sub 2}, our results also identify a narrow deposition temperature window {approx}600-625 C, where single phase, highly crystalline, low surface roughness epitaxial films can be obtained with close to ideal stoichiometry without postdeposition annealing. Electronic and magnetic properties similar to bulk single crystals can be obtained in this region.

  15. Ab initio study of magnetoelectric coupling in La0.66Sr0.33MnO3 / PbZr0.2Ti0.8O3 multiferroic heterostructures

    NASA Astrophysics Data System (ADS)

    Hammouri, Mahmoud; Fohtung, Edwin; Vasiliev, Igor

    2016-10-01

    Multiferroic heterostructures composed of thin layers of ferromagnetic and ferroelectric perovskites have attracted considerable attention in recent years. We apply ab initio computational methods based on density functional theory to study the magnetoelectric coupling at the (0 0 1) interface between \\text{L}{{\\text{a}}0.66}\\text{S}{{\\text{r}}0.33}\\text{Mn}{{\\text{O}}3} (LSMO) and \\text{PbZ}{{\\text{r}}0.2}\\text{T}{{\\text{i}}0.8}{{\\text{O}}3} (PZT). Our study demonstrates that the ferroelectric polarization of PZT has a strong influence on the distribution of magnetization in LSMO. The presence of polarized PZT changes the balance between the ferromagnetic and antiferromagnetic states of LSMO. The observed interfacial magnetoelectric effect can be explained by the variation of the charge density across the LSMO/PZT interface and by the change of the magnetic order in the LSMO layer adjacent to PZT.

  16. Superconducting transition at 38 K in insulating-overdoped La2CuO4-La1.64Sr0.36CuO4 superlattices: evidence for interface electronic redistribution from resonant soft X-ray scattering.

    PubMed

    Smadici, S; Lee, J C T; Wang, S; Abbamonte, P; Logvenov, G; Gozar, A; Cavellin, C Deville; Bozovic, I

    2009-03-13

    We use resonant soft x-ray scattering (RSXS) to quantify the hole distribution in a superlattice of insulating La2CuO4 (LCO) and overdoped La2-xSrxCuO4 (LSCO). Despite its nonsuperconducting constituents, this structure is superconducting with T_{c}=38 K. We found that the conducting holes redistribute electronically from LSCO to the LCO layers. The LCO layers were found to be optimally doped, suggesting they are the main drivers of superconductivity. Our results demonstrate the utility of RSXS for separating electronic from structural effects at oxide interfaces. PMID:19392148

  17. Low loss composition of BaxSryCa1-x-yTiO3: Ba0.12-0.25Sr0.35-0.47Ca0.32-0.53TiO3

    DOEpatents

    Xiang, Xiao-Dong; Chang, Hauyee; Takeuchi, Ichiro

    2001-01-01

    A dielectric thin-film material for microwave applications, including use as a capacitor, the thin-film comprising a composition of barium strontium calcium and titanium of perovskite type (Ba.sub.x Sr.sub.y Ca.sub.1-x-y)TiO.sub.3. Also provided is a method for making a dielectric thin film of that formula over a wide compositional range through a single deposition process.

  18. Synchrotron diffraction topography of SrxBa1-xNb2O6 (SBN), CaxBa1-xNb2O6 (CBN) and mixed (Ca0.28Ba0.72)y(Sr0.61Ba0.39)1-yNb2O6 (CSBN) crystals

    NASA Astrophysics Data System (ADS)

    Wieteska, K.; Wierzchowski, W.; Malinowska, A.; Lefeld-Sosnowska, M.; Świrkowicz, M.; Łukasiewicz, T.; Paulmann, C.

    2013-12-01

    We present the results of synchrotron diffraction topographic investigations of SBN and CBN, as well as mixed strontium-calcium niobate CSBN crystals grown by means of the Czochralski method. The methods of characterisation included different complementary methods of conventional and synchrotron X-ray diffraction topography. Typical elements of the defect structure revealed in SBN and CBN crystals were some facetted regions, particularly the core present in the middle region and some linear or stripe-like contrasts, absent in the studied mixed CSBN crystals. The section and monochromatic beam topographs indicate a certain lattice misorientation between the regions separated by linear contrast. It indicates that the linear or stripe contrasts observed in the topographs are caused by small-angle grain boundaries formed by glide bands. Most of the investigated crystals contained ferroelectric domains of micron or submicron dimensions revealed using selective etching method. The domains cannot be directly resolved by the diffraction topography, but probably contribute to the contrast in some reflections.

  19. Measurement of three-dimensional stress field of RP model having a notch by using digital holography

    NASA Astrophysics Data System (ADS)

    Tanak, Y.; Murata, S.

    2010-06-01

    We measure three-dimensional stress field of RP model having a V-notch. RP model (Elastic modulues E = 3317 MPa, 9.3 × 7.7 × 50 mm3 having a V-notch) is made of acrylic transparent resin and tracer particle (averaged diameter: 60μm) are dispersed. The model is subjected to the static load (100 N) at the middle. Firstly, three-dimensional deflection is measured by using digital holographic PTV (Particle Tracking Velocimetry). Finally, three-dimensional stress field of RP model is visualized as a differential value of the deflection field.

  20. Large magnetic-entropy change above 300 K in CMR materials

    NASA Astrophysics Data System (ADS)

    Phan, M. H.; Tian, S. B.; Hoang, D. Q.; Yu, S. C.; Nguyen, C.; Ulyanov, A. N.

    2003-03-01

    A large magnetic-entropy change Δ SM associated with the ferromagnetic-paramagnetic transition in CMR materials (La 0.65Sr 0.35MnO 3, La 0.6Sr 0.2Ca 0.2MnO 3, La 0.6Sr 0.2Ba 0.2MnO 3 and La 0.7Ca 0.06Ba 0.24MnO 3) has been observed. It is shown that the Δ SM reaches a maximum value of 2.26 J/kg/K for La 0.6Sr 0.2Ba 0.2MnO 3 composition at Curie temperature of 354 K, upon 10 kOe applied field variation. Due to the large Δ SM and high Curie temperature, these CMR materials are suggested to use as active magnetic refrigerants for magnetic refrigeration technology above room temperature.

  1. Nickel and titanium doubly doped lanthanum strontium chromite for high temperature electrochemical devices

    NASA Astrophysics Data System (ADS)

    Gupta, Sapna; Singh, Prabhakar

    2016-02-01

    Lanthanum chromite based materials are promising candidate for use as electrochemical components in high temperature electrochemical devices. In this study, nickel and titanium doubly doped lanthanum strontium chromites are developed and the effects of nickel and titanium co-doping of the chromite perovskite La0.85Sr0.15Cr1-2yNiyTiyO3-δ (0.05 ≤ y ≤ 0.3) on the electrical conductivity, chemical stability, microstructure, density, thermal expansion and electrochemical performance are measured. Density and the electrical conductivity increases with nickel concentration whereas Sr-segregation on the surface of La0.85Sr0.15Cr1-2yNiyTiyO3-δ has been observed for y ≥ 0.2 and is associated with reduction in the electrical conductivity. For y = 0.1, La0.85Sr0.15Cr1-2yNiyTiyO3-δ shows the highest electrical conductivity in air and reducing atmosphere (PO2 ∼10-24 atm). The conductivity of La0.85Sr0.15Cr1-2yNiyTiyO3-δ (y = 0.1) in reducing atmosphere (3.58 S cm-1 at 950 °C) also remains higher than the most widely investigated compositions such as (La0.75Sr0.25)0.95Cr0.5Mn0.5O3-δ (2.81 S cm-1) and (La0.75Sr0.25)0.95Cr0.7Fe0.3O3-δ (1.41 S cm-1). Smaller deviation in the oxygen stoichiometry is similarly observed for La0.85Sr0.15Cr0.8Ni0.1Ti0.1O3-δ (δ = 0.011) when compared to La0.75Sr0.25CrO3-δ (δ = 0.091), La0.75Sr0.25Cr0.5Mn0.5O3-δ (δ = 0.175) and La0.75Sr0.25Cr0.5Fe0.5O3-δ (δ = 0.148) at 1000 °C and ∼10-24 atm. Highest electrochemical performance and structural/interfacial stability is obtained for new composition La0.85Sr0.15Cr0.8Ni0.1Ti0.1O3-δ (LSCNT0.1) when mixed with 8YSZ in both oxidizing and reducing atmosphere.

  2. FABRICATION AND CHARACTERIZATION OF La2-xSrxCuO4/Nb-SrTiO3 HETEROJUNCTIONS IN DIFFERENT DOPED REGIMES

    NASA Astrophysics Data System (ADS)

    Zhang, Y.; Wang, G. F.; Li, W. L.; Shen, J. Q.; Li, P. G.; Lei, M.; Tang, W. H.

    2013-01-01

    Two types of p-n junction were fabricated by depositing underdoped La1.9Sr0.1CuO4 film and overdoped La1.8Sr0.2CuO4 film on n-type 0.5 wt.% Nb-doped SrTiO3 (NSTO) substrates using pulsed laser deposition technique (PLD), respectively. Current-voltage (I-V) characteristics of the La2-xSrxCuO4/NSTO heterojunction were measured in the temperature range from 5 K to 300 K. All I-V curves show a fine rectifying property and a visible reduction of the diffusion potential (Vd) is observed, but the behaviors of Vd are vastly different for the underdoped and overdoped regimes at temperatures below Tc. Analysis results show that the characteristics of the heterojunction are possibly affected not only by the superconducting gap of LSCO at Tc, but also by the depletion layer in the interface of LSCO/NSTO junction. The variation of the depletion layer is possibly different under the same applied bias voltages for the underdoped La1.9Sr0.1CuO4/NSTO junction and overdoped La1.8Sr0.2CuO4/NSTO junction due to the difference of carrier density at La1.9Sr0.1CuO4 and La1.8Sr0.2CuO4.

  3. The influences of mole composition of strontium (x) on properties of barium strontium titanate (Ba1-xSrxTiO3) prepared by solid state reaction method

    NASA Astrophysics Data System (ADS)

    Sandi, Dianisa Khoirum; Supriyanto, Agus; Jamaluddin, Anif; Iriani, Yofentina

    2016-02-01

    Barium Strontium Titanate (Ba1-xSrxTiO3) or BST was prepared by solid state reaction method. Raw materials are BaCO3, SrCO3, and TiO2. Those materials are mixed for 8 h, pressed, and sintered at temperature 1200°C for 2 h. Mole composition of Sr (x) was varied to study its influences on structural, morphological, and electrical properties of BST. Variation of (x) are x = 0; x = 0.1; and x = 0.5. XRD patterns showed a single phase of BST, which mean that mixture of raw materials was homogenous. Crystal structure was influenced by x. BaTiO3 and Ba0.9Ti0.1TiO3 have tetragonal crystal structure, while Ba0.5Sr0.5TiO3 is cubic. The diffraction angle shifted to right side (angle larger) as the increases of x. Crystalline size of BaTiO3, Ba0.9Sr0.1TiO3, and Ba0.5Sr0.5TiO3 are 38.13 nm; 38.62 nm; and 37.13 nm, respectively. SEM images showed that there are still of pores which were influenced by x. Ba0.9Sr0.1TiO3 has densest surface (pores are few and small in size). Sawyer Tower circuit showed that BaTiO3 and Ba0.9Sr0.1 TiO3 is ferroelectric, while Ba0.5Sr0.5TiO3 is paraelectric. The dielectric constants of BaTiO3, Ba0.9Sr0.1TiO3 and Ba0.5Sr0.5TiO3 at frequency of 1 KHz are 156; 196; and 83, respectively. Ba0.9Sr0.1TiO3 has relatively highest dielectric constant. It is considered that Ba0.9Sr0.1TiO3 has densest surface.

  4. Crystal structure and physicochemical properties of doped lanthanum manganites

    NASA Astrophysics Data System (ADS)

    Aksenova, T. V.; Gavrilova, L. Ya.; Cherepanov, V. A.

    2012-12-01

    Substituted lanthanum-strontium manganites La0.7Sr0.3Mn0.9Me0.1O3 ± δ (Me = Ti, Cr, Fe, and Cu) are obtained by standard ceramic and glycerin-nitrate techniques. High-temperature powder X-ray diffraction is employed to study the crystal structure of La0.7Sr0.3Mn0.9Me0.1O3 ± δ oxides. It is shown that in the range 298-1023 K in air, La0.7Sr0.3Mn0.9Me0.103 ± δ manganites crystallized in an orthorhombic cell (space group R-3c). The isobaric temperature dependences of unit cell parameters are determined. Thermal expansion coefficients are calculated for La0.7Sr0.3Mn0.9Me0.103 ± δ oxides. The conductivity of La0.7Sr0.3Mn0.9Me0.103 ± δ is studied as a function of temperature in the range 500 K ≤ T ≤ 1200 K in air. It is shown that substituting 3 d metal for manganese considerably lowers the conductivity of basic La0.7Sr0.3Mn0.9O3 ± δ. The chemical stability of iron-substituted manganite La0.7Sr0.3Mn0.9Fe0.1O3 ± δ is studied with respect to the electrolyte material.

  5. Synthesis of novel perovskite crystal structure phase of strontium doped rare earth manganites using sol gel method

    NASA Astrophysics Data System (ADS)

    Abdel-Latif, I. A.; Ismail, Adel A.; Bouzid, Houcine; Al-Hajry, A.

    2015-11-01

    In the present work, polycrystalline perovskites of R0.6Sr0.4MnO3 nanocomposites (R=La, Nd, or Sm) were synthesized using the sol-gel method in the presence of citric acid and polyethylene glycol as chelating and structure directing agents respectively. The synthesized gel was calcined at 800 °C for 5 h. The XRD revealed that the obtained nanocrystalline R0.6Sr0.4MnO3 is monoclinic crystal structure of space group (I2/a). TEM images showed that the prepared perovskites are homogeneous and uniform with particle sizes in a range 20-40 nm and the HR-TEM images and lattice fringes displayed the monoclinic structure. IV measurements showed that Nd0.6Sr0.4MnO3 has semiconducting properties at room temperature. With applying low magnetic field, a transition from semiconductor behavior to Ohmic resistivity was observed. The static resistance of Nd0.6Sr0.4MnO3 was calculated to be ~2.985 TΩ for semiconductor phase and the resistance increased 1000 times that gives rise to negative magnetoresistance (MR). The value of MR of Nd0.6Sr0.4MnO3 equals to 99.84%, which leads to the use of these materials in fabrication of magnetic devices in the industrial scale.

  6. Chemical compatibility study of melilite-type gallate solid electrolyte with different cathode materials

    NASA Astrophysics Data System (ADS)

    Mancini, Alessandro; Felice, Valeria; Natali Sora, Isabella; Malavasi, Lorenzo; Tealdi, Cristina

    2014-05-01

    Chemical reactivity between cathodes and electrolytes is a crucial issue for long term SOFCs stability and performances. In this study, chemical reactivity between selected cathodic materials and the ionic conducting melilite La1.50Sr0.50Ga3O7.25 has been extensively investigated by X-ray powder diffraction in a wide temperature range (up to 1573 K). Perovskite-type La0.8Sr0.2MnO3-d and La0.8Sr0.2Fe0.8Cu0.2O3-d and K2NiF4-type La2NiO4+d were selected as cathode materials. The results of this study allow identifying the most suitable electrode material to be used in combination with the melilite-type gallate electrolyte and set the basis for future work on this novel system.

  7. Effects of standardized Ginkgo biloba extract on the acquisition, retrieval and extinction of conditioned suppression: Evidence that short-term memory and long-term memory are differentially modulated.

    PubMed

    Zamberlam, C R; Vendrasco, N C; Oliveira, D R; Gaiardo, R B; Cerutti, S M

    2016-10-15

    Studies in our laboratory have characterized the putative neuromodulatory effects of a standardized extract of the green leaves of Ginkgo biloba (EGb), which comprises a formulation of 24% ginkgo-flavoglycosides and 6% ginkgo-terpenoid lactones, on conditioned suppression. This model comprises a suitable animal model for investigating the behavioral changes and pharmacological mechanisms that underlie fear memory and anxiety. The characterization of the effects on distinct stages of fear memory or fear extinction will help illustrate both the beneficial and harmful effects. Three hundred adult male Wistar rats were randomly assigned to 30 groups according to the treatment as follows: i-ii) control groups (CS-US and CSno-US); iii) vehicle group (12% Tween®80); and iv-vi) EGb groups (250, 500 and 1000mgkg(-1)); or experimental procedures designed to assess the effects of EGb treatment prior to the acquisition (n=20 per group) and retrieval of conditioned fear (n=10 per group) or prior to the extinction training (n=10 per group) and extinction retention test (n=10 per group). Furthermore, to better understand the effects of acute EGb treatment on fear memory, we conducted two additional analyses: the acquisition of within- and between-session extinction of fear memory (short- and long-term memory, respectively). No difference was identified between the control and treatment groups during the retention test (P>0.05), with the exception of the CSno-US group in relation to all groups (P<0.05). A between-session analysis indicated that EGb at 250mgkg(-1) facilitated the acquisition of extinction fear memory, which was verified by the suppression ration in the first trial of extinction training (SR=0.39) and the extinction retention test session (SR=0.53, P<0.05), without impairments in fear memory acquisition, which were evaluated during the retention test (SR=0.79). Moreover, EGb administered at 1000mgkg(-1) prior to conditioning did not enhance the long-term extinction

  8. Application of strontium isotopes for tracing landfill leachate plumes in groundwater.

    PubMed

    Vilomet, J D; Angeletti, B; Moustier, S; Ambrosi, J P; Wiesner, M; Bottero, J Y; Chatelet-Snidaro, L

    2001-12-01

    We are evaluating strontium isotopes as alternative tracers of landfill leachate in groundwater. The municipal landfill studied here is located in southeastern France. This landfill has no bottom liner, and wastes are placed directly on the ground. Based on the evaluation of chloride concentration, the plume extends a maximum of 4,600 m. Strontium isotopic composition characterizes two sources: natural groundwater (87Sr/86Sr = 0.708175) and landfill leachate contamination (87Sr/86Sr = 0.708457). The evolution of mixing ratios obtained with strontium reveals a second source of groundwater contamination: fertilizers (87Sr/ 86Sr = 0.707859). These results suggestthat isotopic signatures can be used to provide useful information on sources of groundwater contamination where conventional water quality parameters may yield ambiguous results.

  9. THE EFFECT OF A-SITE STOICHIOMETRY ON LSCF CATHODE PERFORMANCE AND STABILITY

    SciTech Connect

    Templeton, Jared W.; Hardy, John S.; Lu, Zigui; Stevenson, Jeffry W.

    2011-11-01

    Anode-supported solid oxide fuel cells (SOFCs) were prepared and tested identically except for variations in the A-site stoichiometry of the LSCF cathode. A commercial supplier provided lanthanum strontium cobalt ferrite (LSCF) powders that were stoichiometric [La0.6Sr0.4Co0.2Fe0.8O3-δ], A-site deficient [(La0.6Sr0.4)1-xCo0.2Fe0.8O3-δ], and Sr-deficient [La0.6Sr0.4-xCo0.2Fe0.8O3-δ], in which the imposed deficiency (x) was 0.02, 0.05, and 0.1 in the non-stoichiometric cases. Multiple 1,000 hour tests were run using each LSCF cathode composition. The performance and stability of the cells will be discussed.

  10. Effects of standardized Ginkgo biloba extract on the acquisition, retrieval and extinction of conditioned suppression: Evidence that short-term memory and long-term memory are differentially modulated.

    PubMed

    Zamberlam, C R; Vendrasco, N C; Oliveira, D R; Gaiardo, R B; Cerutti, S M

    2016-10-15

    Studies in our laboratory have characterized the putative neuromodulatory effects of a standardized extract of the green leaves of Ginkgo biloba (EGb), which comprises a formulation of 24% ginkgo-flavoglycosides and 6% ginkgo-terpenoid lactones, on conditioned suppression. This model comprises a suitable animal model for investigating the behavioral changes and pharmacological mechanisms that underlie fear memory and anxiety. The characterization of the effects on distinct stages of fear memory or fear extinction will help illustrate both the beneficial and harmful effects. Three hundred adult male Wistar rats were randomly assigned to 30 groups according to the treatment as follows: i-ii) control groups (CS-US and CSno-US); iii) vehicle group (12% Tween®80); and iv-vi) EGb groups (250, 500 and 1000mgkg(-1)); or experimental procedures designed to assess the effects of EGb treatment prior to the acquisition (n=20 per group) and retrieval of conditioned fear (n=10 per group) or prior to the extinction training (n=10 per group) and extinction retention test (n=10 per group). Furthermore, to better understand the effects of acute EGb treatment on fear memory, we conducted two additional analyses: the acquisition of within- and between-session extinction of fear memory (short- and long-term memory, respectively). No difference was identified between the control and treatment groups during the retention test (P>0.05), with the exception of the CSno-US group in relation to all groups (P<0.05). A between-session analysis indicated that EGb at 250mgkg(-1) facilitated the acquisition of extinction fear memory, which was verified by the suppression ration in the first trial of extinction training (SR=0.39) and the extinction retention test session (SR=0.53, P<0.05), without impairments in fear memory acquisition, which were evaluated during the retention test (SR=0.79). Moreover, EGb administered at 1000mgkg(-1) prior to conditioning did not enhance the long-term extinction

  11. Sol-gel preparation and luminescent properties of red-emitting phosphor Sr-Ba-Mo-W-O-(Eu(3+),Sm(3+)).

    PubMed

    Li, Fei; Xie, Huidong; Xi, Haihong; Wang, Xiaochang

    2016-02-01

    Two series of red-emitting phosphors Sr-Ba-Mo-W-O:Eu,Sm and Sr-Ba-Mo-W-O:Eu have been synthesized by a sol-gel method. The effects of the chemical composition, concentrations of Sm(3+) and Eu(3+), the Sr(2+)/Ba(2+) ratio, and the W(6+)/Mo(6+) ratio on the luminescent properties were investigated. The as-prepared phosphors were characterized by X-ray diffraction and Raman spectra. Results showed that single phases of the two series were prepared. The compositions of Sr0.6 Ba0.13Mo0.8 W0.2O4:Eu0.10Sm0.08 and Sr0.75Ba0.1Mo0.8 W0.2O4:Eu0.10 had the strongest luminescent intensity. The excitation spectra of Sm(3+), Eu(3+) co-doped phosphors were broader and the strongest peak moved to 404 nm when compared with that of Eu(3+) single-doped phosphors. The luminescent intensity of the Sr0.6Ba0.13Mo0.8W0.2O4:Eu0.10 Sm0.08 at 618 nm were 2.8 times greater than that of Sr0.75Ba0.1Mo0.8 W0.2O4:Eu0.10. The luminescent intensity of Sr0.6Ba0.13Mo0.8 W0.2 O4:Eu0.10Sm0.08 and Sr0.75Ba0.1Mo0.8W0.2O4:Eu0.10 at 150 °C decreased to 56.8% and 50.3% of the initial value at room temperature, respectively.

  12. Multiband electronic transport in α-Yb1-x Sr x AlB4 [x  =  0, 0.19(3)] single crystals.

    PubMed

    Ryu, Hyejin; Abeykoon, Milinda; Bozin, Emil; Matsumoto, Yosuke; Nakatsuji, S; Petrovic, C

    2016-10-26

    We report on the evidence for the multiband electronic transport in α-YbAlB4 and α-Yb0.81(2)Sr0.19(3)AlB4. Multiband transport reveals itself below 10 K in both compounds via Hall effect measurements, whereas anisotropic magnetic ground state sets in below 3 K in α-Yb0.81(2)Sr0.19(3)AlB4. Our results show that Sr(2+) substitution enhances conductivity, but does not change the quasiparticle mass of bands induced by heavy fermion hybridization. PMID:27541840

  13. Lanthanoid-free perovskite oxide catalyst for dehydrogenation of ethylbenzene working with redox mechanism.

    PubMed

    Watanabe, Ryo; Ikushima, Maiko; Mukawa, Kei; Sumomozawa, Fumitaka; Ogo, Shuhei; Sekine, Yasushi

    2013-01-01

    For the development of highly active and robust catalysts for dehydrogenation of ethylbenzene (EBDH) to produce styrene; an important monomer for polystyrene production, perovskite-type oxides were applied to the reaction. Controlling the mobility of lattice oxygen by changing the structure of Ba1 - x SrxFe y Mn1 - y O3 - δ (0 ≤ x ≤ 1, 0.2 ≤ y ≤ 0.8), perovskite catalyst showed higher activity and stability on EBDH. The optimized Ba/Sr and Fe/Mn molar ratios were 0.4/0.6 and 0.6/0.4, respectively. Comparison of the dehydrogenation activity of Ba0.4Sr0.6Fe0.6Mn0.4O3 - δ catalyst with that of an industrial potassium promoted iron (Fe-K) catalyst revealed that the Ba0.4Sr0.6Fe0.6Mn0.4O3 - δ catalyst showed higher initial activity than the industrial Fe-K oxide catalyst. Additionally, the Ba0.4Sr0.6Fe0.6Mn0.4O3 - δ catalyst showed high activity and stability under severe conditions, even at temperatures as low as 783 K, or at the low steam/EB ratio of 2, while, the Fe-K catalyst showed low activity in such conditions. Comparing reduction profiles of the Ba0.4Sr0.6Fe0.6Mn0.4O3 - δ and the Fe-K catalysts in a H2O/H2 atmosphere, reduction was suppressed by the presence of H2O over the Ba0.4Sr0.6Fe0.6Mn0.4O3 - δ catalyst while the Fe-K catalyst was reduced. In other words, Ba0.4Sr0.6Fe0.6Mn0.4O3 - δ catalyst had higher potential for activating the steam than the Fe-K catalyst. The lattice oxygen in perovskite-structure was consumed by H2, subsequently the consumed lattice oxygen was regenerated by H2O. So the catalytic performance of Ba0.4Sr0.6Fe0.6Mn0.4O3 - δ was superior to that of Fe-K catalyst thanks to the high redox property of the Ba0.4Sr0.6Fe0.6Mn0.4O3 - δ perovskite oxide.

  14. Lanthanoid-free perovskite oxide catalyst for dehydrogenation of ethylbenzene working with redox mechanism

    NASA Astrophysics Data System (ADS)

    Watanabe, Ryo; Ikushima, Maiko; Mukawa, Kei; Sumomozawa, Fumitaka; Ogo, Shuhei; Sekine, Yasushi

    2013-10-01

    For the development of highly active and robust catalysts for dehydrogenation of ethylbenzene (EBDH) to produce styrene; an important monomer for polystyrene production, perovskite-type oxides were applied to the reaction. Controlling the mobility of lattice oxygen by changing the structure of Ba1-xSrxFeyMn1-yO3-d(0 ≤ x≤ 1, 0.2 ≤ y≤ 0.8), perovskite catalyst showed higher activity and stability on EBDH. The optimized Ba/Sr and Fe/Mn molar ratios were 0.4/0.6 and 0.6/0.4, respectively. Comparison of the dehydrogenation activity of Ba0.4Sr0.6Fe0.6Mn0.4O3-d catalyst with that of an industrial potassium promoted iron (Fe-K) catalyst revealed that the Ba0.4Sr0.6Fe0.6Mn0.4O3-d catalyst showed higher initial activity than the industrial Fe-K oxide catalyst. Additionally, the Ba0.4Sr0.6Fe0.6Mn0.4O3-d catalyst showed high activity and stability under severe conditions, even at temperatures as low as 783 K, or at the low steam/EB ratio of 2, while, the Fe-K catalyst showed low activity in such conditions. Comparing reduction profiles of the Ba0.4Sr0.6Fe0.6Mn0.4O3-d and the Fe-K catalysts in aH2O/H2 atmosphere, reduction was suppressed by the presence of H2O over the Ba0.4Sr0.6Fe0.6Mn0.4O3-d catalyst while the Fe-K catalyst was reduced. In other words, Ba0.4Sr0.6Fe0.6Mn0.4O3-d catalyst had higher potential for activating the steam than the Fe-K catalyst. The lattice oxygen in perovskite-structure was consumed by H2, subsequently the consumed lattice oxygen was regenerated by H2O. So the catalytic performance of Ba0.4Sr0.6Fe0.6Mn0.4O3-d was superior to that of Fe-K catalyst thanks to the high redox property of the Ba0.4Sr0.6Fe0.6Mn0.4O3-d perovskite oxide.

  15. Controlling the switching field in nanomagnets by means of domain-engineered antiferromagnets

    DOE PAGES

    Folven, Eric; Linder, J.; Gomonay, O. V.; Scholl, Andreas; Doran, A.; Young, A. T.; Retterer, Scott T.; Malik, V. K.; Tybell, Thomas; Takamura, Yayoi; et al

    2015-09-14

    Using soft x-ray spectromicroscopy, we investigate the magnetic domain structure in embedded nanomagnets defined in La0.7Sr0.3MnO3 thin films and LaFeO3/La0.7Sr0.3MnO3 bilayers. We find that shape-controlled antiferromagnetic domain states give rise to a significant reduction of the switching field of the rectangular nanomagnets. This is discussed within the framework of competition between an intrinsic spin-flop coupling and shape anisotropy. In conclusion, the data demonstrates that shape effects in antiferromagnets may be used to control the magnetic properties in nanomagnets.

  16. Multiband electronic transport in α-Yb1-x Sr x AlB4 [x  =  0, 0.19(3)] single crystals

    NASA Astrophysics Data System (ADS)

    Ryu, Hyejin; Abeykoon, Milinda; Bozin, Emil; Matsumoto, Yosuke; Nakatsuji, S.; Petrovic, C.

    2016-10-01

    We report on the evidence for the multiband electronic transport in α-YbAlB4 and α-Yb0.81(2)Sr0.19(3)AlB4. Multiband transport reveals itself below 10 K in both compounds via Hall effect measurements, whereas anisotropic magnetic ground state sets in below 3 K in α-Yb0.81(2)Sr0.19(3)AlB4. Our results show that Sr2+ substitution enhances conductivity, but does not change the quasiparticle mass of bands induced by heavy fermion hybridization.

  17. Lanthanoid-free perovskite oxide catalyst for dehydrogenation of ethylbenzene working with redox mechanism

    PubMed Central

    Watanabe, Ryo; Ikushima, Maiko; Mukawa, Kei; Sumomozawa, Fumitaka; Ogo, Shuhei; Sekine, Yasushi

    2013-01-01

    For the development of highly active and robust catalysts for dehydrogenation of ethylbenzene (EBDH) to produce styrene; an important monomer for polystyrene production, perovskite-type oxides were applied to the reaction. Controlling the mobility of lattice oxygen by changing the structure of Ba1 − xSrxFeyMn1 − yO3 − δ (0 ≤ x ≤ 1, 0.2 ≤ y ≤ 0.8), perovskite catalyst showed higher activity and stability on EBDH. The optimized Ba/Sr and Fe/Mn molar ratios were 0.4/0.6 and 0.6/0.4, respectively. Comparison of the dehydrogenation activity of Ba0.4Sr0.6Fe0.6Mn0.4O3 − δ catalyst with that of an industrial potassium promoted iron (Fe–K) catalyst revealed that the Ba0.4Sr0.6Fe0.6Mn0.4O3 − δ catalyst showed higher initial activity than the industrial Fe–K oxide catalyst. Additionally, the Ba0.4Sr0.6Fe0.6Mn0.4O3 − δ catalyst showed high activity and stability under severe conditions, even at temperatures as low as 783 K, or at the low steam/EB ratio of 2, while, the Fe–K catalyst showed low activity in such conditions. Comparing reduction profiles of the Ba0.4Sr0.6Fe0.6Mn0.4O3 − δ and the Fe–K catalysts in a H2O/H2 atmosphere, reduction was suppressed by the presence of H2O over the Ba0.4Sr0.6Fe0.6Mn0.4O3 − δ catalyst while the Fe–K catalyst was reduced. In other words, Ba0.4Sr0.6Fe0.6Mn0.4O3 − δ catalyst had higher potential for activating the steam than the Fe–K catalyst. The lattice oxygen in perovskite-structure was consumed by H2, subsequently the consumed lattice oxygen was regenerated by H2O. So the catalytic performance of Ba0.4Sr0.6Fe0.6Mn0.4O3 − δ was superior to that of Fe–K catalyst thanks to the high redox property of the Ba0.4Sr0.6Fe0.6Mn0.4O3 − δ perovskite oxide. PMID:24790949

  18. Significant enhancement of photovoltage in artificially designed perovskite oxide structures

    NASA Astrophysics Data System (ADS)

    Zhou, Wen-jia; Jin, Kui-juan; Guo, Hai-zhong; He, Xu; He, Meng; Xu, Xiu-lai; Lu, Hui-bin; Yang, Guo-zhen

    2015-03-01

    La0.9Sr0.1MnO3/insulator/SrNb0.007Ti0.993O3 multilayer and La0.9Sr0.1MnO3/SrNb0.007Ti0.993O3/In2O3:SnO2(ITO)/La0.9Sr0.1MnO3/SrNb0.007Ti0.993O3 multilayer structures were designed to enhance the photovoltage. The photovoltages of these two structures under an illumination of 308 nm laser are 410 and 600 mV, respectively. The latter is 20 times larger than that (30 mV) observed in La0.9Sr0.1MnO3/SrNb0.007Ti0.993O3 single junction. The origin of such significant enhancement of photovoltage is discussed in this letter. These results suggest that the photoelectric property of perovskite oxides could be much improved by artificial structure designing. The enhanced photovoltaic effects have potential applications in the ultraviolet photodetection and solar cells.

  19. The effect of parental and maternal-fetal histocompatibility at MHC on sex ratio in offspring.

    PubMed

    Astolfi, P; Martinetti, M; Gigli-Berzolari, F; Cuccia, M

    1990-04-01

    The secondary sex ratio (male births of total births) variation was investigated as a function of MHC antigens. Previous studies have indicated that at conception male zygotes are more frequent than female ones and abortions of male fetuses prevail. The present investigation addresses the question whether the histocompatibility relationships either between parents or between mother and offsprings may favor or hinder the outcome of pregnancy: particular combinations may cause distortions in the sex ratio. The results of the analysis of a sample of fertile families, demonstrate that, in first parities, female births are favored when parents share antigens at both HLA-A and -B loci (S.R. = 0.389), and mothers and fetuses share antigens at the HLA-B locus (S.R. = 0.222). The lack of antigens shared by parents at the three loci HLA-A, -B and -DR increases first male births (S.R. = 0.696). In the case of fetal maternal histocompatibility at DR locus only a slight, non-significant, increase in male first births (S.R. = 0.667) was observed. The effect of histocompatibility at HLA-B locus alone requires further investigation in order to assess the possible selective effect against male histocompatible embryos.

  20. 14 CFR 25.233 - Directional stability and control.

    Code of Federal Regulations, 2011 CFR

    2011-01-01

    ... tendency in 90° cross winds, up to a wind velocity of 20 knots or 0.2 V SR 0, whichever is greater, except that the wind velocity need not exceed 25 knots at any speed at which the airplane may be expected to... velocity required by § 25.237. (b) Landplanes must be satisfactorily controllable, without...

  1. 14 CFR 25.233 - Directional stability and control.

    Code of Federal Regulations, 2010 CFR

    2010-01-01

    ... tendency in 90° cross winds, up to a wind velocity of 20 knots or 0.2 V SR 0, whichever is greater, except that the wind velocity need not exceed 25 knots at any speed at which the airplane may be expected to... velocity required by § 25.237. (b) Landplanes must be satisfactorily controllable, without...

  2. 14 CFR 25.233 - Directional stability and control.

    Code of Federal Regulations, 2014 CFR

    2014-01-01

    ... tendency in 90° cross winds, up to a wind velocity of 20 knots or 0.2 V SR 0, whichever is greater, except that the wind velocity need not exceed 25 knots at any speed at which the airplane may be expected to... velocity required by § 25.237. (b) Landplanes must be satisfactorily controllable, without...

  3. 14 CFR 25.233 - Directional stability and control.

    Code of Federal Regulations, 2012 CFR

    2012-01-01

    ... tendency in 90° cross winds, up to a wind velocity of 20 knots or 0.2 V SR 0, whichever is greater, except that the wind velocity need not exceed 25 knots at any speed at which the airplane may be expected to... velocity required by § 25.237. (b) Landplanes must be satisfactorily controllable, without...

  4. 14 CFR 25.233 - Directional stability and control.

    Code of Federal Regulations, 2013 CFR

    2013-01-01

    ... tendency in 90° cross winds, up to a wind velocity of 20 knots or 0.2 V SR 0, whichever is greater, except that the wind velocity need not exceed 25 knots at any speed at which the airplane may be expected to... velocity required by § 25.237. (b) Landplanes must be satisfactorily controllable, without...

  5. 14 CFR 25.1323 - Airspeed indicating system.

    Code of Federal Regulations, 2014 CFR

    2014-01-01

    ..., considering the approved ranges of altitude and weight; and (2) With the flaps and power settings... greater, throughout the speed range, from— (1) V MO to 1.23 V SR 1, with flaps retracted; and (2) 1.23 V SR 0 to V FE with flaps in the landing position. (d) From 1.23 VSR to the speed at which...

  6. 14 CFR 25.1323 - Airspeed indicating system.

    Code of Federal Regulations, 2012 CFR

    2012-01-01

    ..., considering the approved ranges of altitude and weight; and (2) With the flaps and power settings... greater, throughout the speed range, from— (1) V MO to 1.23 V SR 1, with flaps retracted; and (2) 1.23 V SR 0 to V FE with flaps in the landing position. (d) From 1.23 VSR to the speed at which...

  7. Indirect and direct determination of the casein content of milk by Kjeldahl nitrogen analysis: collaborative study.

    PubMed

    Lynch, J M; Barbano, D M; Fleming, J R

    1998-01-01

    The classic method for determination of milk casein is based on precipitation of casein at pH 4.6. Precipitated milk casein is removed by filtration and the nitrogen content of either the precipitate (direct casein method) or filtrate (noncasein nitrogen; NCN) is determined by Kjeldahl analysis. For the indirect casein method, milk total nitrogen (TN; Method 991.20) is also determined and casein is calculated as TN minus NCN. Ten laboratories tested 9 pairs of blind duplicate raw milk materials with a casein range of 2.42-3.05% by both the direct and indirect casein methods. Statistical performance expressed in protein equivalents (nitrogen x 6.38) with invalid and outlier data removed was as follows: NCN method (wt%), mean = 0.762, sr = 0.010, sR = 0.016, repeatability relative standard deviation (RSDr) = 1.287%, reproducibility relative standard deviation (RSDr) = 2.146%; indirect casein method (wt%), mean = 2.585, repeatability = 0.015, reproducibility = 0.022, RSDr = 0.560%, RSDR = 0.841; direct casein method (wt%), mean = 2.575, sr = 0.015, sR = 0.025, RSDr = 0.597%, RSDR = 0.988%. Method performance was acceptable and comparable to similar Kjeldahl methods for determining nitrogen content of milk (Methods 991.20, 991.21, 991.22, 991.23). The direct casein, indirect casein, and noncasein nitrogen methods have been adopted by AOAC INTERNATIONAL.

  8. Suppression of structural phase transition by Sr substitution in the improper ferroelectric BaAl2O4

    NASA Astrophysics Data System (ADS)

    Mori, Shigeo; Ishii, Yui; Tanaka, Eri; Tsukasaki, Hirofumi; Kawaguchi, Shogo

    2015-10-01

    To clarify lattice fluctuations and precursor phenomena accompanied by structural phase transition in stuffed tridymite compounds, changes in diffuse scattering as a function of temperature in Ba0.6Sr0.4Al2O4 have been carefully investigated by powder X-ray diffraction using synchrotron radiation, electron diffraction and transmission electron microscopy (TEM) experiments. In situ electron diffraction experiments revealed that Ba0.6Sr0.4Al2O4 exhibits lattice fluctuation manifested as a unique honeycomb-shaped diffuse scattering in the wide temperature range between 298 and 100 K. Unlike in the case of BaAl2O4, Ba0.6Sr0.4Al2O4 shows no structural phase transition to the ferroelectric structure with the hexagonal P63 space group in the temperature range. In contrast, it is revealed that the electron beam irradiation to the Ba0.6Sr0.4Al2O4 sample inside the transmission electron microscope induced structural change from the hexagonal P6322 structure to the modulated structure with double periodicity in the three equivalent <110> directions in the low-temperature region. This implies that the total energy difference between these two structures is small. The hexagonal P6322 structure transforms into the modulated one with short correlation length owing to some small external perturbations.

  9. Effets Seebeck et Nernst dans les cuprates: Etude de la reconstruction de la surface de Fermi sous champ magnetique intense

    NASA Astrophysics Data System (ADS)

    Laliberte, Francis

    2010-06-01

    Ce memoire presente des mesures de transport thermoelectrique, les effets Seebeck et Nernst, dans une serie d'echantillons de supraconducteurs a haute temperature critique. Des resultats obtenus recemment au Laboratoire National des Champs Magnetiques Intenses a Grenoble sur La1.7Eu0.2Sr0.1 CuO4, La1.675Eu0.2Sr0.125CuO 4, La1.64Eu0.2Sr0.16CuO4, La1.74Eu0.1Sr0.16CuO4 et La 1.4Nd0.4Sr0.2CuO4 sont analyses. Une attention particuliere est accordee aux equations de la theorie semi-classique du transport et leur validite est verifiee. La procedure experimentale et les materiaux utilises pour concevoir les montages de mesures sont expliques en detail. Enfin, un chapitre est dedie a l'explication et l'interpretation des resultats de transport thermoelectrique sur YBa2Cu3O6+delta publies au cours de l'hiver 2010 dans les revues Nature et Physical Review Letters. Les donnees d'effet Seebeck dans les echantillons de La 1.8-x,Eu0.2SrxCuO 4, ou un changement de signe est observe, permettent de conclure a la presence d'une poche d'electrons dans la surface de Fermi qui domine le transport a basse temperature dans la region sous-dopee du diagramme de phase. Cette conclusion est similaire a celle obtenue par des mesures d'effet Hall dans YBa 2Cu3O6+delta et elle cadre bien dans un scenario de reconstruction de la surface de Fermi. Les donnees d'effet Nernst recueillies indiquent que la contribution des fluctuations supraconductrices est limitee a un modeste intervalle de temperature au-dessus de la temperature critique.

  10. Structural phase transitions and photoluminescence properties of oxonitridosilicate phosphors under high hydrostatic pressure

    PubMed Central

    Lazarowska, Agata; Mahlik, Sebastian; Grinberg, Marek; Li, Guogang; Liu, Ru-Shi

    2016-01-01

    Spectroscopic properties of a series of (Sr0.98-xBaxEu0.02)Si2O2N2 (0 ≤ x ≤ 0.98) compounds has been studied under high hydrostatic pressure applied in a diamond anvil cell up to 200 kbar. At ambient pressure the crystal structures of (Sr0.98-xBaxEu0.02)Si2O2N2 (0 ≤ x ≤ 0.98) are related to the ratio of strontium to barium and three different phases exists: orthorhombic Pbcn(0.78 ≤ x ≤ 0.98), triclinic P1 (0 < x ≤ 0.65) and triclinic P1 (0.65 < x < 0.78). It was found that Eu2+ luminescence reveals abrupt changes under pressure (decay time, energy and shape) which indicate the variation of the local symmetry and crystal field strength in Eu2+ sites. These changes are attributed to the reversible pressure-induced structural phase transitions of triclinic (Sr0.98-xBaxEu0.02)Si2O2N2 into orthorhombic structure. Pressure in which phase transition occurs decreases linearly with increasing of Ba composition in (Sr0.98-xBaxEu0.02)Si2O2N2 series. Additionally, very different pressure shifts of the Eu2+ luminescence in different phases of (Sr0.98-xBaxEu0.02)Si2O2N2:Eu from −40 cm−1/kbar to 0 cm−1/kbar have been observed. This effect is explained by different interaction of the Eu2+ 5d electron with the second coordination sphere around the impurity cations. PMID:27734847

  11. Structural phase transitions and photoluminescence properties of oxonitridosilicate phosphors under high hydrostatic pressure

    NASA Astrophysics Data System (ADS)

    Lazarowska, Agata; Mahlik, Sebastian; Grinberg, Marek; Li, Guogang; Liu, Ru-Shi

    2016-10-01

    Spectroscopic properties of a series of (Sr0.98-xBaxEu0.02)Si2O2N2 (0 ≤ x ≤ 0.98) compounds has been studied under high hydrostatic pressure applied in a diamond anvil cell up to 200 kbar. At ambient pressure the crystal structures of (Sr0.98-xBaxEu0.02)Si2O2N2 (0 ≤ x ≤ 0.98) are related to the ratio of strontium to barium and three different phases exists: orthorhombic Pbcn(0.78 ≤ x ≤ 0.98), triclinic P1 (0 < x ≤ 0.65) and triclinic P1 (0.65 < x < 0.78). It was found that Eu2+ luminescence reveals abrupt changes under pressure (decay time, energy and shape) which indicate the variation of the local symmetry and crystal field strength in Eu2+ sites. These changes are attributed to the reversible pressure-induced structural phase transitions of triclinic (Sr0.98-xBaxEu0.02)Si2O2N2 into orthorhombic structure. Pressure in which phase transition occurs decreases linearly with increasing of Ba composition in (Sr0.98-xBaxEu0.02)Si2O2N2 series. Additionally, very different pressure shifts of the Eu2+ luminescence in different phases of (Sr0.98-xBaxEu0.02)Si2O2N2:Eu from ‑40 cm‑1/kbar to 0 cm‑1/kbar have been observed. This effect is explained by different interaction of the Eu2+ 5d electron with the second coordination sphere around the impurity cations.

  12. S- and Sr-isotopic compositions in barite-silica chimney from the Franklin Seamount, Woodlark Basin, Papua New Guinea: constraints on genesis and temporal variability of hydrothermal fluid

    NASA Astrophysics Data System (ADS)

    Ray, Durbar; Banerjee, Ranadip; Balakrishnan, S.; Paropkari, Anil L.; Mukhopadhyay, Subir

    2016-08-01

    Isotopic ratios of strontium and sulfur in six layers across a horizontal section of a hydrothermal barite-silica chimney from Franklin Seamount of western Woodlark Basin have been investigated. Sr-isotopic ratios in barite samples (87Sr/86Sr = 0.70478-0.70493) are less radiogenic than seawater (87Sr/86Sr = 0.70917) indicating that substantial leaching of sub-seafloor magma was involved in the genesis of hydrothermal fluid. The SO2 of magma likely contributed a considerable amount of lighter S-isotope in fluid and responsible for the formation of barite, which is isotopically lighter (δ34S = 19.4-20.5 ‰) than modern seawater (δ34S ~ 21 ‰). The systematic changes in isotopic compositions across the chimney wall suggest temporal changes in the mode of mineral formation during the growth of the chimney. Enrichment of heavy S- and Sr-isotopes (δ34S = 20.58 ‰; 87Sr/86Sr = 0.70493) in the outermost periphery of the chimney indicates that, at the initial stage of chimney development, there was a significant contribution of seawater sulfate during barite mineralization. Thereafter, thickening of chimney wall occurred due to precipitation of fluid carrying more magmatic components relative to seawater. This led to a gradual enrichment of lighter isotopes (δ34S = 20.42-19.48 ‰; 87Sr/86Sr = 0.70491-0.704787) toward the inner portion of the chimney wall. In contrast, the innermost layer surrounding the fluid conduit is characterized by heavier and more radiogenic isotopes (δ34S = 20.3 ‰; 87Sr/86Sr = 0.7049). This suggests there was increasing influence of percolating seawater on the mineral paragenesis at the waning phase of the chimney development.

  13. Investigation of thermoluminescence characteristics of CaSrS: Ce nanophosphors

    NASA Astrophysics Data System (ADS)

    Sharma, Geeta; Lochab, S. P.; Singh, Nafa

    2010-11-01

    Thermoluminescence characteristics of Ca 0.75Sr 0.25S: Ce nanophosphors exposed to UV radiations have been investigated. Solid state diffusion method was employed to synthesize the nanophosphors. The confirmation for the formation of the mixed lattice was done by XRD. The particles formed were found to have 45 nm size as calculated by the Debye Scherrer formula. TEM results were in close agreement with the XRD as the nanoparticles formed possess capsule like structure with an average diameter of 50 nm. TL glow curves for the low doses (110-1680 mJ/cm 2) of UV show a main peak around 381 K and another peak of very low intensity around 570 K. The TL intensity increases up to 450 mJ/cm 2 of UV exposure. At higher doses (3.5-80 J/cm 2) the peak position varies slightly but the high temperature peak becomes more intense. Thermoluminescence characteristics of UV irradiated Ca 1- xSr xS: Ce as a function of x (0.25, 0.50, and 0.75) have also been investigated. TL glow curves of Ca 1- xSr xS: Ce (0.25, 0.50, and 0.75) recorded after 450 mJ/cm 2 of exposure of UV radiations show almost similar structure except slight variation in the peak position. Ca 0.25Sr 0.75S: Ce and Ca 0.50Sr 0.50S: Ce have single peak at 373 and 367 K, respectively, while Ca 0.75Sr 0.25S: Ce has a main peak at 381 K and a less intense peak at 570 K. Ca 0.75Sr 0.25S: Ce shows the most intense TL peak. The trap parameters namely, activation energy ( E), order of kinetics ( b), and frequency factor ( s) of Ca 0.75Sr 0.25S: Ce have been determined using Chen’s peak shape method and GCD function suggested by Kitis for second order kinetics.

  14. Carrier generation/recombination processes and polaron effect in perovskite manganite thin films

    NASA Astrophysics Data System (ADS)

    Wu, Guang-Ri; Inoue, Masasi; Sasaki, Minoru; Negishi, Hiroshi; Xiong, Guang-Cheng

    2000-07-01

    Pulsed-laser-induced transient thermoelectric effect (TTE) for perovskite manganite films, La 0.6Ca 0.4MnO 3 (LCMO), Pr 0.67Sr 0.33MnO 3 (PSMO), La 0.7Sr 0.3MnO 3 (LSMO), has been measured under DC electric and magnetic fields. The photoinduced TTE voltage and its sign are strongly dependent on both temperature and magnetic field, which is due to the formation of a bipolar state of photogenerated electrons and holes. It is found that Jahn-Teller and polaron effects are appreciable near the Curie temperature for the carrier recombination, in particular, for LCMO with small ionic radius of Ca 2+ ions.

  15. Low-temperature sintering of lanthanum strontium manganite-based contact pastes for SOFCs

    NASA Astrophysics Data System (ADS)

    McCarthy, B. P.; Pederson, L. R.; Chou, Y. S.; Zhou, X.-D.; Surdoval, W. A.; Wilson, L. C.

    Electrical contact pastes of composition (La 0.90Sr 0.10) 0.98MnO 3 + δ (LSM-10) formed strong bonds (∼3 MPa) to (Co,Mn) 3O 4 spinel-coated Crofer 22 APU ferritic steel coupons when exposed to alternating flows of air and nitrogen (10 ppm O 2) at 900 °C for 2 h or longer. When held at 900 °C in air only, bond strengths were negligible. Substantial bonds could also be created between LSM-10 contact paste and (La 0.80Sr 0.20) 0.98MnO 3 + δ (LSM-20) porous cathodes by processing in alternating air and nitrogen, without simultaneous densification of the cathode. Enhanced sintering of LSM-10 is attributed to transients in the defect structure induced by oxygen partial pressure changes.

  16. Effects of Oxide Additives to (Ba,Sr)TiO3 Ceramics Fired under Reduced Atmosphere

    NASA Astrophysics Data System (ADS)

    Sakai, Y.; Futakuchi, T.; Adachi, M.

    2011-10-01

    Ba0.6Sr0.4TiO3 doped with MgO, CaO, SrO, or BaO thick films with Ni electrodes were prepared by screen printing. The prepared thick films showed a perovskite single phase. TC was changed corresponding to the kinds of doping oxides. The tunability and tanδ value of thick films doping with 2 mol% of BaO or CaO at an electric field of 10 V/μm were approximately 85% and 0.3%, respectively. The leakage current of Ba0.6Sr0.4TiO3 thick films doped with 2 mol% of BaO thick films at 10 V/μm was less than 10-6 A/cm2 and the value was less than that of thick films doped with 2 mol% of CaO.

  17. New data on genesis of the crust in the eastern segment of the Middle Urals: Sr-Nd isotopic constraints

    NASA Astrophysics Data System (ADS)

    Smirnov, V. N.; Ronkin, Yu. L.; Puchkov, V. N.; Soloshenko, N. G.; Streletskaya, M. V.

    2016-04-01

    The analysis of the Sr and Nd isotopic composition in different granitoids of the Verkhisetsk, Shartash, Krasnopolsk, Petrokamensk, and Shabry massifs, which were successively formed in the island arc, continental marginal, and collisional geodynamic settings during the period from the Middle Devonian to the early Permian, revealed that 87Sr/86Sr0 values in them vary from 0.70331 to 0.70431 and ɛNd( t), from +1.9 to +6.2. The two-stage model Nd age of granitoids (938-629 Ma) indicates that their magma originates from material at least Neoproterozoic in age, not younger. The observed variations in the Nd model ages of granitoids and 87Sr/86Sr0 values provide grounds for assuming the primary heterogeneity of the source of granitoid melts.

  18. Impact of microstructure on oxygen semi-permeation performance of perovskite membranes: Understanding of oxygen transport mechanisms

    NASA Astrophysics Data System (ADS)

    Reichmann, M.; Geffroy, P.-M.; Richet, N.; Chartier, T.

    2016-08-01

    The influence of dense membrane microstructures on semi permeation performance is still not well understood, and no consensus or explanation can be established from the literature. The apparent discrepancy is likely due to a poor understanding of the oxygen transport mechanisms through the membrane and, specifically, to the impact of the microstructure on the oxygen surface exchange kinetics. The aim of this paper is to provide a better understanding of the impact of microstructures on oxygen transport mechanisms through the membrane. Two reference materials, Ba0.5Sr0.5Fe0.7Co0.3O3 (BSFCo) and La0.5Sr0.5Fe0.7Ga0.3O3 (LSFG) perovskites, are considered to explain the discrepancies observed in the literature.

  19. Effect of electrode materials on the scaling behavior of energy density in Pb(Zr0.96Ti0.03)Nb0.01O3 antiferroelectric films

    NASA Astrophysics Data System (ADS)

    Ge, Jun; Pan, Gang; Remiens, Denis; Chen, Ying; Cao, Fei; Dong, Xianlin; Wang, Genshui

    2012-09-01

    Antiferroelectric Pb(Zr, Nb, Ti)O3 (PZNT) films were deposited via a sol-gel process on Pt(111)/Ti/SiO2/Si, LaNiO3- and La0.5Sr0.5CoO3-buffered Si substrate. The scaling behavior of the energy density W of antiferroelectric films was investigated. The scaling behavior of W against frequency f of PZNT on LaNiO3-buffered Si takes the form of W ∝ f0.08, which differs significantly from that form of W ∝ f-0.14 of PZNT on La0.5Sr0.5CoO3-buffered Si. This indicates that the scaling relations of W vary substantially as bottom electrodes change and might be closely related to the variation of nonuniform strain field and depolarization field within the AFE films.

  20. A Perovskite Electrocatalyst for Efficient Hydrogen Evolution Reaction.

    PubMed

    Xu, Xiaomin; Chen, Yubo; Zhou, Wei; Zhu, Zhonghua; Su, Chao; Liu, Meilin; Shao, Zongping

    2016-08-01

    Perovskite oxides are demonstrated for the first time as efficient electrocatalysts for the hydrogen evolution reaction (HER) in alkaline solutions. A-site praseodymium-doped Pr0.5 (Ba0.5 Sr0.5 )0.5 Co0.8 Fe0.2 O3- δ (Pr0.5BSCF) exhibits dramatically enhanced HER activity and stability compared to Ba0.5 Sr0.5 Co0.8 Fe0.2 O3- δ (BSCF), superior to many well-developed bulk/nanosized nonprecious electrocatalysts. The improved HER performance originates from the modified surface electronic structures and properties of Pr0.5BSCF induced by the Pr-doping. PMID:27185219

  1. Resistive switching and voltage induced modulation of tunneling magnetoresistance in nanosized perpendicular organic spin valves

    NASA Astrophysics Data System (ADS)

    Göckeritz, Robert; Homonnay, Nico; Müller, Alexander; Fuhrmann, Bodo; Schmidt, Georg

    2016-04-01

    Nanoscale multifunctional perpendicular organic spin valves have been fabricated. The devices based on an La0.7Sr0.3MnO3/Alq3/Co trilayer show resistive switching of up to 4-5 orders of magnitude and magnetoresistance as high as -70% the latter even changing sign when voltage pulses are applied. This combination of phenomena is typically observed in multiferroic tunnel junctions where it is attributed to magnetoelectric coupling between a ferromagnet and a ferroelectric material. Modeling indicates that here the switching originates from a modification of the La0.7Sr0.3MnO3 surface. This modification influences the tunneling of charge carriers and thus both the electrical resistance and the tunneling magnetoresistance which occurs at pinholes in the organic layer.

  2. Emergence of superconductivity in topological insulator Bi2Se3 by Sr intercalation

    NASA Astrophysics Data System (ADS)

    Shruti, Maurya, V. K.; Srivastava, P.; Patnaik, S.

    2016-05-01

    Recently superconductivity wasreported by Sr intercalation in topological insulator Bi2Se3. In this report we extensively study anisotropic superconductingproperties of Sr0.1Bi2Se3 with transition at ~2.9 through resistivity and DC magnetization measurement. We also discuss synthesis methodology for growth of single crystal Sr-Bi2Se3. The anisotropic properties of Sr0.1Bi2Se3 single crystals were studied using transport measurements. Using Ginzburg Landau formulas the upper critical field Hc2(0) comes out to be 2.1 T and 1.4 T for magnetic field applied along the ab-plane and c-axis of the single crystalsand corresponding Ginzburg - Landau coherence lengths are ξab = 15.3 nm and ξc = 10.2 nm. The sample shows weak electronic anisotropy Γ = 1.5. Hall resistivity is linear with field at 10 K.

  3. Oxygen surface exchange kinetics and stability of (La,Sr)2 CoO4±δ/La 1-xSrxMO3-δ (M = Co and Fe) hetero-interfaces at intermediate temperatures

    DOE PAGES

    Lee, Dongkyu; Lee, Yueh-Lin; Hong, Wesley T.; Biegalski, Michael D.; Morgan, Dane; Shao-Horn, Yang

    2015-01-01

    Heterostructured oxide interfaces created by decorating Ruddlesden-Popper phases (A2BO4) or perovskites on perovskites have shown not only pronounced cation segregation at the interface and in the A2BO4 structure but also much enhanced kinetics for oxygen electrocatalysis at elevated temperatures. In this study, we report and compare the time-dependent surface exchange kinetics and stability of (La0.5Sr0.5)2CoO4 -decorated (LSC214) La0.6Sr0.4Co0.2Fe0.8O3-δ (LSCF113) and La0.8Sr0.2CoO3-δ (LSC113) thin films. While LSC214 decoration on LSC113 greatly reduced the degradation in the surface exchange kinetics as a function of time relative to LSC113, LSCF113 with LSC214 coverage showed comparable surface exchange kinetics and stability to LSCF113. Thismore » difference can be explained by greater surface stability of LSCF113 than LSC113 under testing conditions, and that LSC214 decoration on LSC113 reduced the decomposition of LSC113 to form secondary phases that impedes oxygen exchange kinetics, and thus resulted in enhanced stability. This hypothesis is supported by the observations that annealing at 550 °C led to the formation of Sr-rich secondary particles on LSC113 while no such particles were observed on LSCF113. Density functional theory (DFT) computation provides further support, which revealed greater capacity of surface Sr segregation for LSCF113 having SrO termination than LSC113 having (La0.25Sr0.75)O termination for the experimental conditions, and lower energy gain to move Sr from LSCF113 into LSC214 relative to the LSC214-LSC113 system.« less

  4. Nain geochemistry reviewed: anorthosite parent liquids and contamination problems

    SciTech Connect

    Morse, S.A.

    1985-01-01

    Sr-An relations of PLAG and candidate natural LIQ (dikes, chills) agree with partition coefficients derived from Kiglapait in predicting parent LIQuids like rift basalts (Servilleta) and flood basalt (Keweenaw, Parana). All LIQ are richer in Sr than consistent with proposed lower crust or MORB. Many diverse parent LIQS had 275-675 ppm Sr, with mean 430 ppm Sr, 8 ppm Rb. Referred to 1.4 Gry, Archean crust (ARCH) at Lost Channel has I(Sr) = 0.717, R = Rb/Sr = 0.4. Minimum melt granites (GR) 2.3-1.3 Gyr old average Sr = 190, Rb = 160 ppm at I(Sr) = 0.753. By contrast, Nain feldspars have R from 0.001 to 0.01, implying liquids 0.003 - 0.02. Neither GR nor ARCH can contaminate normal mantle-derived magmas (I= 0.7028) to achieve the I(Sr) 0.703-0.708 observed, without adding 15-50 ppm Rb, not observed. Therefore, the I(Sr) signature is either from an old, enriched mantle source later depleted, or form assimilation of Rb-poor supracrustals (marble.) with huge I(Sr), ppm Sr values. The latter are not yet demonstrated to exist. Proximal contaminants should show up in local Sr-isotopic heterogeneity (as at Rhum). Local isotopic uniformity could arise for mold deeper-seated, multi-cycle or conceivably lower mantle source component, brought up in a rift setting and degassed with exit of LIL as per Galer and O'Nions (J. Petrol., submitted). Rb-rich GR of all ages show the regional persistence of undepleted crust available for melting. Either ANORTH plumbing was very restricted or new crustal slices of GR source were delivered to the hot spot on a regular basis to yield new GR melts.

  5. Nanoparticles of spinel and perovskite ferromagnets and prospects for their application in medicine

    NASA Astrophysics Data System (ADS)

    Belous, A. G.; Solopan, S. O.; Yelenich, O. V.; Tovstolytkin, A. I.; Kolodiazhnyi, T. V.; Osinsky, S. P.; Bubnovskaya, L. N.

    2014-11-01

    In this work, nanoparticles of La0.75Sr0.25MnO3 compounds with perovskite structure and AFe2O4 (A = Mn, Fe, Co, Ni, Zn) with spinel structure have been synthesized by precipitation from diethylene glycol and microemulsion using Triton X-100 surfactant. Comparative X-ray diffraction and magnetic studies of the synthesized nanoparticles have been carried out. Magnetic fluids prepared from synthesized nanopowders have been characterized by calorimetric measurements of specific loss power (SLP).

  6. Control of functional responses via reversible oxygen loss in La₁-xSrxFeO₃-δ films.

    PubMed

    Xie, Yujun; Scafetta, Mark D; Sichel-Tissot, Rebecca J; Moon, Eun Ju; Devlin, Robert C; Wu, Hanqi; Krick, Alex L; May, Steven J

    2014-03-01

    La0.3 Sr0.7 FeO3-δ films undergo dramatic changes in electronic and optical properties due to reversible oxygen loss induced by low-temperature heating. This mechanism to control the functional properties may serve as a platform for new devices or sensors in which external stimuli are used to dynamically control the composition of complex oxide heterostructures. PMID:24734299

  7. Metalloporphyrin-modified perovskite-type oxide for the electroreduction of oxygen

    NASA Astrophysics Data System (ADS)

    Nagai, Tsukasa; Yamazaki, Shin-ichi; Asahi, Masafumi; Siroma, Zyun; Fujiwara, Naoko; Ioroi, Tsutomu

    2015-10-01

    Perovskite-type oxide-carbon (Vulcan XC72) mixture (La0.6Sr0.4Mn0.6Fe0.4O3/C) was modified by a metalloporphyrin (cobalt octaethylporphyrin: Co-OEP) having two-electron O2 reduction activity, and its electrochemical reduction activity for O2 (ORR) was investigated in an alkaline solution by rotating ring disk electrode (RRDE) voltammetry. The Co-OEP/La0.6Sr0.4Mn0.6Fe0.4O3/C catalyst showed improved ORR activity, with a positive shift of the onset potential. In addition, a decreased ring current compared to Co-OEP/C suggested that the quasi-four-electron reduction of O2 was also enhanced. Further experiments showed that ORR activity was also enhanced by Co-OEP-modification of other types of carbon (Ketjenblack EC600JD, Denka Black) or perovskite-type oxide (La0.6Ca0.4Mn0.6Fe0.4O3, La0.8Sr0.2Co0.6Fe0.4O3). In the case of the addition of other porphyrin complexes (cobalt tetraphenylporphyrin (Co-TPP), iron octaethylporphyrin (Fe-OEP)) to a La0.6Sr0.4Mn0.6Fe0.4O3/C catalyst, the onset potential did not shift to the positive side due to the lower activity compared to Co-OEP.

  8. Evaluation of lanthanum tungstates as electrolytes for proton conductors Solid Oxide Fuel Cells

    NASA Astrophysics Data System (ADS)

    Zayas-Rey, M. J.; dos Santos-Gómez, L.; Porras-Vázquez, J. M.; Losilla, E. R.; Marrero-López, D.

    2015-10-01

    La27W4NbO55-δ (LWNO) has been tested as electrolyte for proton conductor Solid Oxide Fuel Cells (PC-SOFCs). For this purpose, different electrodes and composite electrodes are considered, including: La0.8Sr0.2MnO3-δ, La0.6Sr0.4Co1-xFexO3-δ, La0.75Sr0.25Cr0.5Mn0.5O3-δ, SrFe0.75Nb0.25O3-δ and NiO. Chemical compatibility between the cell components is investigated by X-ray powder diffraction (XRPD) and energy dispersive spectroscopy (EDS). Furthermore, area specific resistance (ASR) for the different electrodes is determined in symmetrical cells by impedance spectroscopy. XRPD and EDS analysis does not reveal significant bulk reactivity between most of these electrodes and LWNO electrolyte in the typical operating temperature range of an SOFC (600-900 °C). However, minor interdiffusion of elements at the electrolyte/electrode interface has negative effects on both the ohmic losses and electrode polarization of the cells. ASR values are significantly improved by using a porous buffer layer of Ce0.8Gd0.2O1.9 (CGO), deposited between the electrolyte and electrode materials, to prevent reactivity. A single cell with a 350 μm-thick electrolyte, NiO-CGO and La0.6Sr0.4Co0.8Fe0.2O3-δ-CGO composite as anode and cathode, respectively, generates maximum power densities of 140 and 18 mWcm-2 at 900 and 650 °C, respectively.

  9. Interfacial Coupling-Induced Ferromagnetic Insulator Phase in Manganite Film.

    PubMed

    Zhang, Bangmin; Wu, Lijun; Yin, Wei-Guo; Sun, Cheng-Jun; Yang, Ping; Venkatesan, T; Chen, Jingsheng; Zhu, Yimei; Chow, Gan Moog

    2016-07-13

    Interfaces with subtle differences in atomic and electronic structures in perovskite ABO3 heterostructures often yield intriguingly different properties, yet their exact roles remain elusive. Here, we report an integrated study of unusual transport, magnetic, and structural properties of Pr0.67Sr0.33MnO3 film on SrTiO3 substrate. The variations in the out-of-plane lattice constant and BO6 octahedral rotation across the Pr0.67Sr0.33MnO3/SrTiO3 interface strongly depend on the thickness of the Pr0.67Sr0.33MnO3 film. In the 12 nm film, a new interface-sensitive ferromagnetic polaronic insulator (FI') phase is formed during the cubic-to-tetragonal phase transition of SrTiO3, apparently due to the enhanced electron-phonon interaction and atomic disorder in the film. The transport properties of the FI' phase in the 30 nm film are masked because of the reduced interfacial coupling and smaller interface-to-volume ratio. This work demonstrates how thickness-dependent interfacial coupling leads to the formation of a theoretically predicted ferromagnetic-polaronic insulator, as illustrated in a new phase diagram, that is otherwise ferromagnetic metal (FM) in bulk form. PMID:27276032

  10. New SrAl 2B 2O 7:Eu 2+, Mn 2+ phosphors for white light-emitting diodes

    NASA Astrophysics Data System (ADS)

    Zhou, Liya; Yi, Linghong; Feng, Xiaoming

    2011-12-01

    A series of Eu 2+ and Mn 2+ co-doped SrAl 2B 2O 7 phosphors were prepared by solid-state reaction method. X-ray powder diffraction (XRD) and photoluminescence excitation and emission were employed to characterize the phosphors. The results show that energy transfers between Eu 2+and Mn 2+ ions. As the content of Ca 2+ ions in Ca xSr 0.92- xAl 2B 2O 7:Eu 2+0.06, Mn 2+0.02 phosphors increased, the CIE coordinates decreased and close to the white color standard mandated by the National Television Standard Committee (NTSC). Meanwhile, a white LED (light-emitting diode) was fabricated by combining the Ca 0.5Sr 0.42Al 2B 2O 7:Eu 2+0.06, Mn 2+0.02 phosphors with a 370 nm InGaN chip. The color coordinate of the fabricated white LED was also close to the white color standard, indicating that the Ca 0.5Sr 0.42Al 2B 2O 7:Eu 2+0.06, Mn 2+0.02 phosphor is a promising single-host phosphor that can be used in white LEDs.

  11. New SrAl2B2O7:Eu2+, Mn2+ phosphors for white light-emitting diodes.

    PubMed

    Zhou, Liya; Yi, Linghong; Feng, Xiaoming

    2011-12-01

    A series of Eu(2+) and Mn(2+) co-doped SrAl(2)B(2)O(7) phosphors were prepared by solid-state reaction method. X-ray powder diffraction (XRD) and photoluminescence excitation and emission were employed to characterize the phosphors. The results show that energy transfers between Eu(2+)and Mn(2+) ions. As the content of Ca(2+) ions in Ca(x)Sr(0.92-x)Al(2)B(2)O(7):Eu(2+)(0.06), Mn(2+)(0.02) phosphors increased, the CIE coordinates decreased and close to the white color standard mandated by the National Television Standard Committee (NTSC). Meanwhile, a white LED (light-emitting diode) was fabricated by combining the Ca(0.5)Sr(0.42)Al(2)B(2)O(7):Eu(2+)(0.06), Mn(2+)(0.02) phosphors with a 370 nm InGaN chip. The color coordinate of the fabricated white LED was also close to the white color standard, indicating that the Ca(0.5)Sr(0.42)Al(2)B(2)O(7):Eu(2+)(0.06), Mn(2+)(0.02) phosphor is a promising single-host phosphor that can be used in white LEDs. PMID:21920803

  12. Modeling the paraelectric aging effect in the acceptor doped perovskite ferroelectrics: role of oxygen vacancy.

    PubMed

    Zhou, Yumei; Xue, Dezhen; Ding, Xiangdong; Zhang, Lixue; Sun, Jun; Ren, Xiaobing

    2013-10-30

    The time dependence of physical properties in the paraelectric phase was probed recently in a Mn(3+) doped (Ba0.8Sr0.2)TiO3 ceramic, providing a simple situation (without spontaneous polarization or domain walls) to quantify the role of the oxygen vacancy during aging. In the present study, we propose a quantitative model for paraelectric aging to understand how the distribution of the oxygen vacancy evolves with time and consequently influences the dielectric response of the paraelectric phase. First, by comparing dielectric behavior of paraelectric aging in a Mn(3+) doped (Ba0.75Sr0.25)TiO3 ceramic and the dielectric tunable effect, an internal bias field E(in) related to the oxygen vacancy is shown to exist in the paraelectric phase. Second, by introducing such a time dependent E(in) in a Landau-type model, we reproduce the dielectric response of Mn(3+) doped (Ba0.8Sr0.2)TiO3 ceramic during paraelectric aging. It is suggested that the increase of dielectric permittivity can be ascribed to the decrease of E(in) with time. The investigation of paraelectric aging is helpful for understanding the role of the oxygen vacancy in influencing the physical properties of ferroelectric materials.

  13. Interfacial Coupling-Induced Ferromagnetic Insulator Phase in Manganite Film.

    PubMed

    Zhang, Bangmin; Wu, Lijun; Yin, Wei-Guo; Sun, Cheng-Jun; Yang, Ping; Venkatesan, T; Chen, Jingsheng; Zhu, Yimei; Chow, Gan Moog

    2016-07-13

    Interfaces with subtle differences in atomic and electronic structures in perovskite ABO3 heterostructures often yield intriguingly different properties, yet their exact roles remain elusive. Here, we report an integrated study of unusual transport, magnetic, and structural properties of Pr0.67Sr0.33MnO3 film on SrTiO3 substrate. The variations in the out-of-plane lattice constant and BO6 octahedral rotation across the Pr0.67Sr0.33MnO3/SrTiO3 interface strongly depend on the thickness of the Pr0.67Sr0.33MnO3 film. In the 12 nm film, a new interface-sensitive ferromagnetic polaronic insulator (FI') phase is formed during the cubic-to-tetragonal phase transition of SrTiO3, apparently due to the enhanced electron-phonon interaction and atomic disorder in the film. The transport properties of the FI' phase in the 30 nm film are masked because of the reduced interfacial coupling and smaller interface-to-volume ratio. This work demonstrates how thickness-dependent interfacial coupling leads to the formation of a theoretically predicted ferromagnetic-polaronic insulator, as illustrated in a new phase diagram, that is otherwise ferromagnetic metal (FM) in bulk form.

  14. Systematic investigation of the strontium zirconium phosphate ceramic form for nuclear waste immobilization

    NASA Astrophysics Data System (ADS)

    Pet'kov, Vladimir; Asabina, Elena; Loshkarev, Vladimir; Sukhanov, Maksim

    2016-04-01

    We have summarized our data and literature ones on the thermophysical properties and hydrolytic stability of Sr0.5Zr2(PO4)3 compound as a host NaZr2(PO4)3-type (NZP) structure for immobilization of 90Sr-containing radioactive waste. Absence of any polymorphic transformations on the temperature dependence of its heat capacity between 7 and 665 K is caused by the stability of crystalline Sr0.5Zr2(PO4)3. Calculated values of thermal conductivity coefficients at zero porosity in the range 298-673 K were 1.86-2.40 W·m-1 K-1. The compound may be classified as low thermal expanding material due to its average linear thermal expansion coefficient. Study of the hydrolytic stability in acid and alkaline media has shown that the relative mass fraction of Sr2+ ions, released into aggressive leaching media, didn't exceed 1% of the mass of sample. Soxhlet leaching studies have shown substantial resistance towards the release of Sr2+ ions into distilled water. Feeble sinterability constrains practical applications of NZP substances, that is why known in literature methods of Sr0.5Zr2(PO4)3 dense ceramics obtaining have been reviewed.

  15. High pressure low temperature studies on 1-2-2 iron-based superconductors using designer diamond cells

    DOE PAGES

    Uhoya, Walter O.; Tsoi, Georgiy M.; Vohra, Yogesh K.; Mitchell, Jonathan, E.; Safa-Sefat, Athena; Weir, Samuel

    2013-01-01

    In this study, high pressure low temperature electrical resistance measurements were carried out on a series of 122 iron-based superconductors using a designer diamond anvil cell. These studies were complemented by image plate x-ray diffraction measurements under high pressures and low temperatures at beamline 16-BM-D, HPCAT, Advanced Photon Source. A common feature of the 1-2-2 iron-based materials is the observation of anomalous compressibility effects under pressure and a Tetragonal (T) to Collapsed Tetragonal (CT) phase transition under high pressures. Specific studies on antiferromagnetic spin-density-wave Ba0.5Sr0.5Fe2As2 and Ba(Fe0.9Ru0.1)2As2 samples are presented to 10 K and 41 GPa. The collapsed tetragonal phasemore » was observed at a pressure of 14 GPa in Ba0.5Sr0.5Fe2As2 at ambient temperature. The highest superconducting transition temperature in Ba0.5Sr0.5Fe2As2 was observed to be at 32 K at a pressure of 4.7 GPa. The superconductivity was observed to be suppressed on transformation to the CT phase in 122 materials.« less

  16. Perovskite Sr₁-xCexCoO₃-δ (0.05 ≤ x ≤ 0.15) as superior cathodes for intermediate temperature solid oxide fuel cells.

    PubMed

    Yang, Wei; Hong, Tao; Li, Shuai; Ma, Zhaohui; Sun, Chunwen; Xia, Changrong; Chen, Liquan

    2013-02-01

    Perovskite Sr(1-x)Ce(x)CoO(3-δ) (0.05 ≤ x ≤ 0.15) have been prepared by a sol-gel method and studied as cathodes for intermediate temperature solid oxide fuel cells. As SOFC cathodes, Sr(1-x)Ce(x)CoO(3-δ) materials have sufficiently high electronic conductivities and excellent chemical compatibility with SDC electrolyte. The peak power density of cells with Sr(0.95)Ce(0.05)CoO(3-δ) is 0.625 W cm(-2) at 700 °C. By forming a composite cathode with an oxygen ion conductor SDC, the peak power density of the cell with Sr(0.95)Ce(0.05)CoO(3-δ)-30 wt %SDC composite cathode, reaches 1.01 W cm(-2) at 700 °C, better than that of Sm(0.5)Sr(0.5)CoO(3)-based cathode. All these results demonstrates that Sr(1-x)Ce(x)CoO(3-δ) (0.05 ≤ x ≤ 0.15)-based materials are promising cathodes for an IT-SOFC. PMID:23336216

  17. Eu doping-induced enhancement of magnetocaloric effect in manganite La1.4Ca1.6Mn2O7

    NASA Astrophysics Data System (ADS)

    Ma, Y.; Dong, Q. Y.; Ke, Y. J.; Wu, Y. D.; Zhang, X. Q.; Wang, L. C.; Shen, B. G.; Sun, J. R.; Cheng, Z. H.

    2015-04-01

    The structure, magnetic properties and magnetocaloric effects of perovskite manganese oxides La1.4Ca1.6Mn2O7 and La1.3Eu0.1Sr0.05Ca1.55Mn2O7 have been investigated. They undergo a first-order ferromagnetic-paramagnetic phase transition around their respective Curie temperatures (235 K and 215 K, respectively). The doping of Eu and Sr atoms enhances greatly the value of magnetization, which leads to the large magnetocaloric effect. For a field change of 0-5 T, the maximum value of magnetic entropy change is only 4.5 J/kg K for La1.4Ca1.6Mn2O7 compound. However, it increases to 7.1 J/kg K for La1.3Eu0.1Sr0.05Ca1.55Mn2O7 compound. Meanwhile, a large refrigerant capacity of 240.4 J/kg is also achieved. Large reversible magnetocaloric effect and refrigerant capacity indicate the potentiality of La1.3Eu0.1Sr0.05Ca1.55Mn2O7 compound as a candidate for magnetic refrigerant.

  18. Geochemistry of some deep gold mine waters from the western portion of the Witwatersrand Basin, South Africa

    NASA Astrophysics Data System (ADS)

    Duane, M. J.; Pigozzi, G.; Harris, C.

    1997-02-01

    A suite of 12 mine water samples within the Witwatersrand Basin (South Africa) were analysed for trace element concentrations, strontium isotopic composition and stable isotopes (O and H). Chemical profiles for four Au mines (Western Deep Levels, Vaal Reefs, Freddies and President Steyn) are used to infer origin, chemical and isotopic evolution of the brines and for comparison with basement brines from other Precambrian areas. Systematic relationships are observed between {87Sr}/{86Sr} and {1}/{Sr} : two major mixing trends are required to explain the range of very radiogenic end-members. Possible end-members for the two components could be (1) {87Sr}/{86Sr} = 0.7251 , Sr concentration = 0.12 mg l -1 from a Vaal Reefs compartment and {87Sr}/{86Sr} = 0.7694 , Sr = 39.3 mg l -1 from a Freddies compartment. (2) {87Sr}/{86Sr} = 0.7251 , Sr = 0.12 mg l -1 (as above) with a {87Sr}/{86Sr} = 0.7404 , Sr = 745 mg l -1 from Western Deep Levels. Strontium isotope ratios range above those expected for present-day seawater and are even higher than some locally-derived low Rb minerals from the Precambrian basement. The brines acquired radiogenic 87Sr through interaction with granitic basement (Kaapvaal Craton), shales of the Central Rand Group (in particular Ventersdorp Contact Reef), siliclastics within the West Rand Group and particularly with dolomites from the overlying Transvaal Supergroup. In order to obtain their multielement and radiogenic isotope signatures the meteoric waters descended through fractured rocks between the main dykes and faults (example: Oberholzer and Bank Dyke at Western Deep Levels). They slowly interacted with Au bearing conglomerates and quartzites of the West Rand Group. The inverse relationship between Sr isotope composition and precious/heavy metal concentration suggests fluid/rock interaction within the shales and volcanics of the Ventersdsorp Contact Reef (high in Au and total organic carbon [TOC], less radiogenic strontium composition by

  19. A Limiting Current Oxygen Sensor Based on LSGM as a Solid Electrolyte and LSGMN ( N = Fe, Co) as a Dense Diffusion Barrier

    NASA Astrophysics Data System (ADS)

    Liu, Tao; Gao, Xiang; He, Bei-Gang; Yu, Jing-Kun

    2016-07-01

    The La0.8Sr0.2(Ga1- x Co x )0.8Mg0.2O3- δ (LSGMC x = 0.05, 0.1, 0.15, 0.2, 0.25) and La0.8Sr0.2(Ga1- x Fe x )0.8Mg0.2O3- δ (LSGMF x = 0.1, 0.2, 0.3) samples were prepared by solid-state reaction. The structure, conductivity, thermal expansion behavior, and chemical compatibility were studied by XRD, dilatometry, and four-terminal method. A limiting current oxygen sensor was prepared with La0.8Sr0.2Ga0.83Mg0.17O2.815 as a solid electrolyte and La0.8Sr0.2(Ga0.75Co0.25)0.8Mg0.2O3- δ as a dense diffusion barrier. The oxygen-sensitive characteristic was measured at different oxygen concentrations. The results show that the phase structure of samples is cubic, except La0.8Sr0.2(Ga0.75Co0.25)0.8Mg0.2O3- δ , which has a hexagonal structure. The change in activation energy for electrical conductivity and the increase in thermal expansion coefficient are confirmed to correlate with an increasing concentration of oxygen vacancies. The limiting current oxygen sensor exhibits a good limiting current platform and the limiting current depends linearly on the oxygen concentration: I L(mA) = 12.8519 + 2.2667 x_{{{O}_{{2}} }} (mol%, 0 < x_{{{{O}}_{ 2} }} < 3.31) at 750 °C, I L(mA) = 14.3222 + 3.5180 x_{{{O}_{{2}} }} (mol%, 0 < x_{{{{O}}_{ 2} }} < 4.16) at 800 °C, and I L(mA) = 15.2872 + 5.0269x_{{{O}_{{2}} }}(mol%, 0 < x_{{{{O}}_{ 2} }} < 4.12) at 850 °C. The sensor has the best sensitivity at 850 °C. As the oxygen concentration increases, the interface resistance of the sensor decreases at 850 °C.

  20. Anode materials for sour natural gas solid oxide fuel cells

    NASA Astrophysics Data System (ADS)

    Danilovic, Nemanja

    Novel anode catalysts have been developed for sour natural gas solid oxide fuel cell (SOFC) applications. Sour natural gas comprises light hydrocarbons, and typically also contains H2S. An alternative fuel SOFC that operates directly on sour natural gas would reduce the overall cost of plant construction and operation for fuel cell power generation. The anode for such a fuel cell must have good catalytic and electrocatalytic activity for hydrocarbon conversion, sulfur-tolerance, resistance to coking, and good electronic and ionic conductivity. The catalytic activity and stability of ABO3 (A= La, Ce and/or Sr, B=Cr and one or more of Ti, V, Cr, Fe, Mn, or Co) perovskites as SOFC anode materials depends on both A and B, and are modified by substituents. The materials have been prepared by both solid state and wet-chemical methods. The physical and chemical characteristics of the materials have been fully characterized using electron microscopy, XRD, calorimetry, dilatometry, particle size and area, using XPS and TGA-DSC-MS. Electrochemical performance was determined using potentiodynamic and potentiostatic cell testing, electrochemical impedance analysis, and conductivity measurements. Neither Ce0.9Sr0.1VO3 nor Ce0.9 Sr0.1Cr0.5V0.5O3 was an active anode for oxidation of H2 and CH4 fuels. However, active catalysts comprising Ce0:9Sr0:1V(O,S)3 and Ce0.9Sr 0.1Cr0.5V0.5(O,S)3 were formed when small concentrations of H2S were present in the fuels. The oxysulfides formed in-situ were very active for conversion of H2S. The maximum performance improved from 50 mW cm-2 to 85 mW cm -2 in 0.5% H2S/CH4 at 850°C with partial substitution of V by Cr in Ce0.9Sr0.1V(O,S)3. Selective conversion of H2S offers potential for sweetening of sour gas without affecting the hydrocarbons. Perovskites La0.75Sr0.25Cr0.5X 0.5O3--delta, (henceforth referred to as LSCX, X=Ti, Mn, Fe, Co) are active for conversion of H2, CH4 and 0.5% H2S/CH4. The order of activity in the different fuels depends on

  1. Structure and high-temperature properties of the (Sr,Ca,Y)(Co, Mn)O3-y perovskites — perspective cathode materials for IT-SOFC

    NASA Astrophysics Data System (ADS)

    Napolsky, Ph. S.; Drozhzhin, O. A.; Istomin, S. Ya.; Kazakov, S. M.; Antipov, E. V.; Galeeva, A. V.; Gippius, A. A.; Svensson, G.; Abakumov, A. M.; Van Tendeloo, G.

    2012-08-01

    Oxygen deficient perovskites Sr0.75Y0.25Co1-xMnxO3-y, x=0.5 and 0.75, were prepared by using the citrate route at 1373-1573 K for 48 h. The cubic Pm-3m perovskite structure for x=0.5 was confirmed by electron diffraction study and refined using neutron powder diffraction (NPD) data. For x=0.75, the superstructure corresponding to a=√{2}×aper, b=2×aper, c=√{2}×aper (a0b-b- tilt system, space group Imma) was revealed by electron diffraction. The solid solution Sr0.75-xCaxY0.25Co0.25Mn0.75O3-y, 0.1≤x≤0.6 and compound Ca0.75Y0.25Mn0.85Co0.15O2.92 were prepared in air at 1573 K for 48 h. The crystal structure of Ca0.75Y0.25Mn0.85Co0.15O2.92 was refined using NPD data (S.G. Pnma, a=5.36595(4), b=7.5091(6), c=5.2992(4) Å, Rp=0.057, Rwp=0.056, χ2=4.26). High-temperature thermal expansion properties of the prepared compounds were studied in air using both dilatometry and high-temperature X-ray powder diffraction data (HTXRPD). They expanding non-linearly at 298-1073 K due to the loss of oxygen at high temperatures. Calculated average thermal expansion coefficients (TECs) for Sr0.75Y0.25Co1-xMnxO3-y, x=0.5, 0.75 and Ca0.75Y0.25Mn0.85Co0.15O2.92(1) are 15.5, 15.1, and 13.8 ppm K-1, respectively. Anisotropy of the thermal expansion along different unit cell axes was observed for Sr0.15Ca0.6Y0.25Co0.25Mn0.75O3-y and Ca0.75Y0.25Mn0.85Co0.15O2.92. Conductivity of Sr0.75Y0.25Co1-xMnxO3-y, x=0.5 and 0.75 increases with the temperature reaching 110 S/cm for x=0.5 and 44 S/cm for x=0.75 at 1173 K. Samples of Sr0.75-xCaxY0.25Co0.25Mn0.75O3-y, 0.1≤y≤0.6 were found to be n-type conductors at room temperature with the similar temperature dependence of the conductivity and demonstrated the increase of the σ value from ˜1 to ˜50 S/cm as the temperature increases from 300 to 1173 K. Their conductivity is described in terms of the small polaron charge transport with the activation energy (Ep) increasing from 340 to 430 meV with an increase of the calcium content from x=0

  2. Promotion of Oxygen Reduction by Exsolved Silver Nanoparticles on a Perovskite Scaffold for Low-Temperature Solid Oxide Fuel Cells.

    PubMed

    Zhu, Yinlong; Zhou, Wei; Ran, Ran; Chen, Yubo; Shao, Zongping; Liu, Meilin

    2016-01-13

    Solid oxide fuel cells (SOFCs) have potential to be the cleanest and most efficient electrochemical energy conversion devices with excellent fuel flexibility. To make SOFC systems more durable and economically competitive, however, the operation temperature must be significantly reduced, which depends sensitively on the development of highly active electrocatalysts for oxygen reduction reaction (ORR) at low temperatures. Here we report a novel silver nanoparticle-decorated perovskite oxide, prepared via a facile exsolution process from a Sr0.95Ag0.05Nb0.1Co0.9O3-δ (SANC) perovskite precursor, as a highly active and robust ORR electrocatalyst for low-temperature SOFCs. The exsolved Sr0.95Ag0.05Nb0.1Co0.9O3-δ (denoted as e-SANC) electrode is very active for ORR, achieving a very low area specific resistance (∼0.214 Ω cm(2) at 500 °C). An anode-supported cell with the new heterostructured cathode demonstrates very high peak power density (1116 mW cm(-2) at 500 °C) and stable operation for 140 h at a current density of 625 mA cm(-2). The superior ORR activity and stability are attributed to the fast oxygen surface exchange kinetics and the firm adhesion of the Ag nanoparticles to the Sr0.95Nb0.1Co0.9O3-δ (SNC0.95) support. Moreover, the e-SANC cathode displays improved tolerance to CO2. These unique features make the new heterostructured material a highly promising cathode for low-temperature SOFCs.

  3. Electrochemical study of lithiated transition metal oxide composite for single layer fuel cell

    NASA Astrophysics Data System (ADS)

    Hu, Huiqing; Lin, Qizhao; Muhammad, Afzal; Zhu, Bin

    2015-07-01

    This study analyzed the effect of various semiconductors of transition metal oxides in modified lithiated NiO on the electrochemical performance of a single layer fuel cell (SLFC). A typical ionic conductor Ce0.8Sm0.2O2-δ (SDC) and three types of semiconductors Li0.3Ni0.6Cu0.07Sr0.03O2-δ (LNCuS), Li0.3Ni0.6Mn0.07Sr0.03O2-δ (LNMnS) and Li0.3Ni0.6Co0.07Sr0.03O2-δ (LNCoS), were the fundamental components of the SLFCs. The components were characterized by using X-ray diffraction (XRD), a scanning electron microscope (SEM), and an energy-dispersive X-ray spectrometer (EDS). The stability of the synthesized materials was evaluated using thermal gravity analysis (TGA). The ohmic resistances at 500 °C were 0.36, 0.48 and 0.58 Ω cm2 for 6SDC-4LNMnS, 6SDC-4LNCoS and 6SDC-4LNCuS, respectively. Among the three SLFCs, the single cell with 6SDC-4LNMnS achieves the highest power density (422 mW cm-2) but the lowest temperature stability, while the single cell with 6SDC-4LNCuS achieved the lowest power density (331 mW cm-2) but the highest temperature stability during the operation temperature.

  4. Temperature-independent sensors based on perovskite-type oxides

    NASA Astrophysics Data System (ADS)

    Zaza, F.; Frangini, S.; Leoncini, J.; Luisetto, I.; Masci, A.; Pasquali, M.; Tuti, S.

    2014-06-01

    The need of energy security and environment sustainability drives toward the development of energy technology in order to enhance the performance of internal combustion engines. Gas sensors play a key role for controlling the fuel oxygen ratio and monitoring the pollution emissions. The perovskite-type oxides can be synthesized for an extremely wide variety of combinations of chemical elements, allowing to design materials with suitable properties for sensing application. Lanthanum strontium ferrites, such as La0.7Sr0.3FeO3, are suitable oxygen sensing materials with temperature-independence conductivity, but they have low chemical stability under reducing conditions. The addition of aluminum into the perovskite structure improves the material properties in order to develop suitable oxygen sensing probes for lean burn engine control systems. Perovskite-type oxides with formula (La0.7Sr0.3)(AlxFe1-x)O3 was synthesized by the citrate-nitrate combustion synthesis method. XRD analyses, show that it was synthesized a phase-pure powder belonging to the perovskite structure. Aluminum affects both the unit cell parameters, by shrinking the unit cell, and the powder morphology, by promoting the synthesis of particles with small crystallite size and large specific surface area. The partial substitution of iron with aluminum improves the chemical stability under reducing gas conditions and modulates the oxygen sensitivity by affecting the relative amount of Fe4+ and Fe3+, as confirmed from TPR profiles. In the same time, the addition of aluminum does not affects the temperature-independent properties of lanthanum strontium ferrites. Indeed, the electrical measurements show that (La0.7Sr0.3)(AlxFe1-x)O3 perovskites have temperature-independence conductivity from 900 K.

  5. Palladium local structure of La(1-x)Sr(x)Co(1-y)Fe(y-0.03)Pd(0.03)O(3-δ) perovskites synthesized using a one pot citrate method.

    PubMed

    Puleo, Fabrizio; Liotta, Leonarda F; La Parola, Valeria; Banerjee, Dipanjan; Martorana, Antonino; Longo, Alessandro

    2014-11-01

    Nanostructured La1-xSrxCo1-yFey-0.03Pd0.03O3-δ (LSCF-Pd) perovskites with fixed La-Sr composition (x = 0.4) and two different Fe contents (y = 0.2 and 0.8) were successfully synthesized using a one pot citrate method starting from nitrates of the metal cations. Pd-free La1-xSrxCo1-yFeyO3-δ (LSCF) systems were prepared for comparison. LSCF powders were calcined at 1300 °C and characterized by XRD and Rietveld refinement, EXAFS, XPS, TPR analyses. Promotion of La0.6Sr0.4Co0.8Fe0.2O3-δ and of La0.6Sr0.4Co0.2Fe0.8O3-δ by incorporation of palladium was evidenced by solving the local environment of Pd using EXAFS spectroscopy. XPS analyses, in agreement with TPR measurements, demonstrated an increase of superficial oxygen vacancies, the variation being much more pronounced in the La0.6Sr0.4Co0.8Fe0.17Pd0.03O3-δ sample. It is argued that this increase is associated with the introduction of Pd in the B site of LSCF. Moreover, ionic Pd(4+) was detected as the only palladium species on the perovskite surface, whereas Pd metal clusters of about 2 nm, not detectable in the surface, are embedded in the matrix and strongly interact with the bulk. This result has strong consequences in the synthesis and in the design of new perovskite materials that can be used as cathodes in fuel cell application at intermediate operating temperatures.

  6. La-Sr-Ni-Co-O based perovskite-type solid solutions as catalyst precursors in the CO 2 reforming of methane

    NASA Astrophysics Data System (ADS)

    Valderrama, Gustavo; Kiennemann, Alain; Goldwasser, Mireya R.

    La 1- xSr xNi 0.4Co 0.6O 3 and La 0.8Sr 0.2Ni 1- yCo yO 3 solid solutions with perovskite-type structure were synthesized by the sol-gel resin method and used as catalytic precursors in the dry reforming of methane with CO 2 to syngas, between 873 and 1073 K at atmospheric pressure under continuous flow of reactant gases with CH 4/CO 2 = 1 ratio. These quaternary oxides were characterized by X-ray diffraction (XRD), BET specific surface area and temperature-programmed reduction (TPR) techniques. XRD analyses of the more intense diffraction peaks and cell parameter measurements showed formation of La-Sr-Ni-Co-O solid solutions with La 0.9Sr 0.1CoO 3 and/or La 0.9Sr 0.1NiO 3 as the main crystallographic phases present on the solids depending on the degree of substitution. TPR analyses showed that Sr doping decreases the temperature of reduction via formation of intermediary species producing Ni 0, Co 0 with particle sizes in the range of nanometers over the SrO and La 2O 3 phases. These metallic nano particles highly dispersed in the solid matrix are responsible for the high activity shown during the reaction and avoid carbon formation. The presence of Sr in doping quantities also promotes the secondary reactions of carbon formation and water-gas shift in a very small extension during the dry reforming reaction.

  7. Thermochemistry of perovskites in the lanthanum-strontium-manganese-iron oxide system

    NASA Astrophysics Data System (ADS)

    Marinescu, Cornelia; Vradman, Leonid; Tanasescu, Speranta; Navrotsky, Alexandra

    2015-10-01

    The enthalpies of formation from binary oxides of perovskites (ABO3) based on lanthanum strontium manganite La(Sr)MnO3 (LSM) and lanthanum strontium ferrite La(Sr)FeO3 (LSF) and mixed lanthanum strontium manganite ferrite La(Sr)Mn(Fe)O3 (LSMF) were measured by high temperature oxide melt solution calorimetry. Using iodometric titration, the oxygen content was derived. The perovskites with A-site cation deficiency have greater oxygen deficiency than the corresponding A-site stoichiometric series. Stability of LSMF decreases with increasing iron content. Increasing oxygen deficiency clearly destabilizes the perovskites. The results suggest an enthalpy of oxygen incorporation that is approximately independent of composition. 0.35La2O3 (xl, 25 °C)+Mn2O3 (xl, 25 °C)+0.3SrO (xl, 25 °C)+Fe2O3 (xl, 25 °C)+O2 (g, 25 °C)→La0.7Sr0.3Mn1-yFeyO3-δ (xl, 25 °C). (b) ∆ Hf,ox* (La0.7Sr0.3Mn1-yFeyO3-δ) .0.35 La2O3 (xl, 25 ººC) + (0.7-y+ 2δ)/2 Mn2O3 (xl, 25 ºC) + 0.3 SrO (xl, 25 ºC) + y/2Fe2O3 (xl, 25 ºC) + (0.3-2δ) MnO2 (xl, 25 ºC)→La0.7Sr0.3Mn1-yFeyO3-δ (xl, 25 ºC).

  8. Postcollisional granites in the South Tien Shan Variscan Collisional Belt, Kyrgyzstan

    NASA Astrophysics Data System (ADS)

    Solomovich, L. I.; Trifonov, B. A.

    2002-11-01

    Two major types of the potassium-rich postcollisional granites of Permian age were studied in the South Tien Shan Variscan Collisional Belt. The first type, metaluminous granites of the Jangart complex, are located along the southeastern boundary of this belt with the Precambrian Tarim Block. The plagioclase rims on K-feldspar megacrysts (rapakivi texture), extremely high FeO t/(FeO t+MgO) ratio, indications of the low H 2O and O 2 fugacities, high concentrations of the incompatible elements especially light rare earth elements (LREE), Ba, Nb along with heightened contents of the compatible elements especially Ni, Cr and moderately initial 87Sr/ 86Sr ratio (Sr 0=0.7075) make those granites similar to other rapakivi granites. The second type, peraluminous granites of the Inylchek complex, is located along the northwestern boundary of the belt with the Caledonian Kazakh Microcontinent. Those granites are rich in F, B, Li, Rb, Cs, Sn, Ta and heavy rare earth elements (HREE), but are poor in Ba, Sr, Ni and Cr and are characterized by the relatively high initial 87Sr/ 86Sr ratio (Sr 0=0.7098). Li-mica granites are distributed widely among them. The granites of a transitional type (Uchkoshkon complex) occupy an intermediate geographic position between major granite types. The initial Sr isotopic composition of the transitional granites varies widely (Sr 0 from 0.7080 to 0.7256). The variation in chemical composition of the coeval postcollisional granites across the Collisional belt, together with the variability of initial Sr isotopic ratios of the transitional granites, are thought to indicate basement heterogeneity. This heterogeneity, in turn, is probably related to thrusting of the Tarim Block under South Tien Shan during the collision.

  9. Atomic-Scale Chemical Imaging of Composition and Bonding at Perovskite Oxide Interfaces

    NASA Astrophysics Data System (ADS)

    Fitting Kourkoutis, L.

    2010-03-01

    Scanning transmission electron microscopy (STEM) in combination with electron energy loss spectroscopy (EELS) has proven to be a powerful technique to study buried perovskite oxide heterointerfaces. With the recent addition of 3^rd order and now 5^th order aberration correction, which provides a factor of 100x increase in signal over an uncorrected system, we are now able to record 2D maps of composition and bonding of oxide interfaces at atomic resolution [1]. Here, we present studies of the microscopic structure of oxide/oxide multilayers and heterostructures by STEM in combination with EELS and its effect on the properties of the film. Using atomic-resolution spectroscopic imaging we show that the degradation of the magnetic and transport properties of La0.7Sr0.3MnO3/SrTiO3 multilayers correlates with atomic intermixing at the interfaces and the presence of extended defects in the La0.7Sr0.3MnO3 layers. When these defects are eliminated, metallic ferromagnetism at room temperature can be stabilized in 5 unit cell thick manganite layers, almost 40% thinner than the previously reported critical thickness of 3-5 nm for sustaining metallic ferromagnetism below Tc in La0.7Sr0.3MnO3 thin films grown on SrTiO3.[4pt] [1] D.A. Muller, L. Fitting Kourkoutis, M. Murfitt, J.H. Song, H.Y. Hwang, J. Silcox, N. Dellby, O.L. Krivanek, Science 319, 1073-1076 (2008).

  10. Evidence for stable Sr isotope fractionation by silicate weathering in a small sedimentary watershed in southwestern Taiwan

    NASA Astrophysics Data System (ADS)

    Chao, Hung-Chun; You, Chen-Feng; Liu, Hou-Chun; Chung, Chuan-Hsiung

    2015-09-01

    Radiogenic Sr isotopes (87Sr/86Sr) are robust for provenance identification in hydrology, affected mainly by the age of background lithologies and the degree of chemical weathering. However, there is limited knowledge concerning the fractionation mechanism of stable Sr isotopes (88Sr/86Sr) in rivers. In this study, river water was collected on a weekly to monthly basis throughout dry and wet seasons. Furthermore, to study the variations of radiogenic and stable Sr isotopes during intense weathering, a major flooding event (2000 mm precipitation in three days, Typhoon Morakot), water was captured within a small drainage catchment system (161 km2) along the Hou-ku River in southwestern Taiwan. For a better constraint on the end member compositions, bedload sediments, suspended particles, and several host rocks were sampled for a systematic investigation. The carbonate and silicate phases of these solids were chemically separated. Dissolved major elements indicate that the watersheds were predominated by silicate weathering. Stable Sr isotopes show no significant variation (δ88Sr = 0.24-0.31‰) temporally and spatially with an average of 0.28‰. Additionally, all solids showed lower δ88Sr values than the river water while the host rocks had higher δ88Sr values (δ88Sr = 0.20-0.26‰) than the residual weathering products (δ88Sr = 0.08-0.22‰), indicating preferential leaching of heavy Sr into the hydrosphere and leaving light Sr in the residual solids. Results of laboratory acid leaching experiments reveal that dissolution of high δ88Sr value minerals occurred at an early stage of weathering. The variation of weathering intensity does not alter stable Sr isotopes in silicate weathering dominated river water, which contains higher stable Sr isotopes than the associated sediments. The silicatic sedimentary rocks preferentially released higher stable Sr isotopes into the hydrosphere during chemical weathering, thus leaving lower stable Sr isotopes in the residual

  11. Characterization of Hybrid Ferroelectric/HTS Thin Films for Tunable Microwave Components

    NASA Technical Reports Server (NTRS)

    Winters, M. D.; Mueller, C. H.; Bhasin, K. B.; Miranda, F. A.

    1996-01-01

    Since the discovery of High-Temperature-Superconductors (HTS) in 1986, a diversity of HTS-based microwave components has been demonstrated. Because of their low conductor losses, HTS-based components are very attractive for integration into microwave circuits for space communication systems. Recent advancements have made deposition of ferroelectric thin films onto HTS thin films possible. Due to the sensitivity of the ferroelectric's dielectric constant (epsilon(sub r)) to an externally applied electric field (E), ferroelectric/superconducting structures could be used in the fabrication of low loss, tunable microwave components. In this paper, we report on our study of Ba(0.5)Sr(0.5)TiO3/YBa2Cu3O(7-delta) and Ba(0.08)Sr(0.92)TiO3/YBa2Cu3O(7-delta) ferroelectric/superconducting thin films on lanthanum aluminate (LaAlO3) substrates. For the (Ba:Sr, 0.50:0.50) epitaxial sample, a epsilon(sub r) of 425 and a loss tangent (tan delta) of 0.040 were measured at 298 K, 1.0 MHz, and zero applied E. For the same sample, a epsilon(sub r) of 360 and tan delta of 0.036 were obtained at 77 K, 1.0 MHz, and zero applied E. Variations in epsilon(sub r) from 180 to 360 were observed over an applied E range of 0V/cm less than or equal to E less than or equal to 5.62 x 10(exp 4) V/cm with little change in tan delta. However, the range of epsilon(sub r) variation for the polycrystalline (Ba:Sr, 0.08:0.92) sample over 0V/cm less than or equal to E less than or equal to 4.00 x 10(exp 4) V/cm was only 3.6 percent while tan delta increased markedly. These results indicate that a lack of epitaxy between the ferroelectric and superconducting layers decreases tuning and increases microwave losses.

  12. Influence of the interfacing with an electrically inhomogeneous bottom electrode on the ferroelectric properties of epitaxial PbTiO3

    SciTech Connect

    Kim, Yunseok; Jesse, Stephen; Morelli, Alessio; Kalinin, Sergei V; Vrejoiu, Ionela

    2013-01-01

    The influence of an electrically inhomogeneous epitaxial bottom layer on the ferroelectric and electrical properties has been explored in epitaxial PbTiO3 (PTO)/La0.7Sr0.3MnO3 (LSMO) submicron structures using atomic force microscopy. The submicron LSMO-dot structures underneath the ferroelectric PTO film allow exploring gradual changes in material properties. The LSMO interfacial layer influences significantly both electrical and ferroelectric properties of the upper PTO layer. The obtained results show that the as-grown polarization state of an epitaxial ferroelectric layer is strongly influenced by the properties of the layer on top of which it is deposited.

  13. Bulk channel-type reconfigurable light-induced waveguides recorded by crossed lateral illumination

    NASA Astrophysics Data System (ADS)

    Gorram, M.; Coda, V.; Thévenin, P.; Montemezzani, G.

    2009-06-01

    Photoinduced channel waveguides are created in the bulk of biased electro-optic Sr0.61Ba0.39Nb2O6 crystals by a proper combination of crossed lateral illumination waves. The measured nearly-circular steady-state guided wave profiles agree well with theoretically expected mode profiles. The buried waveguides obtained by this technique can be easily tailored and are dynamically reconfigurable. The dynamics of formation is found to be anisotropic, with a faster effect for the confinement of the guided wave in the direction parallel to the applied electric field.

  14. Climatic and tectonic controls on chemical weathering in the New Zealand Southern Alps

    NASA Astrophysics Data System (ADS)

    Jacobson, Andrew D.; Blum, Joel D.; Chamberlain, C. Page; Craw, Dave; Koons, Peter O.

    2003-01-01

    Climatic and tectonic controls on the relative abundance of solutes in streams draining the New Zealand Southern Alps were investigated by analyzing the elemental and Sr isotope geochemistry of stream waters, bedload sediment, and hydrothermal calcite veins. The average relative molar abundance of major cations and Si in all stream waters follows the order Ca 2+ (50%) > Si (22%) > Na + (17%) > Mg 2+ (6%) > K + (5%). For major anions, the relative molar abundance is HCO 3- (89%) > SO 42- (7%) > Cl - (4%). Weathering reactions involving plagioclase and volumetrically small amounts of hydrothermal calcite define the ionic chemistry of stream waters, but nearly all streams have a carbonate-dominated Ca 2+ and HCO 3- mass-balance. Stream water Ca/Sr and 87Sr/ 86Sr ratios vary from 0.173 to 0.439 μmol/nmol and from 0.7078 to 0.7114, respectively. Consistent with the ionic budget, these ratios lie solely within the range of values measured for bedload carbonate (Ca/Sr = 0.178 to 0.886 μmol/nmol; 87Sr/ 86Sr = 0.7081 to 0.7118) and hydrothermal calcite veins (Ca/Sr = 0.491 to 3.33 μmol/nmol; 87Sr/ 86Sr = 0.7076 to 0.7097). Streams draining regions in the Southern Alps with high rates of physical erosion induced by rapid tectonic uplift and an extremely wet climate contain ˜10% more Ca 2+ and ˜30% more Sr 2+ from carbonate weathering compared to streams draining regions in drier, more stable landscapes. Similarly, streams draining glaciated watersheds contain ˜25% more Sr 2+ from carbonate weathering compared to streams draining non-glaciated watersheds. The highest abundance of carbonate-derived solutes in the most physically active regions of the Southern Alps is attributed to the tectonic exhumation and mechanical denudation of metamorphic bedrock, which contains trace amounts of calcite estimated to weather ˜350 times faster than plagioclase in this environment. In contrast, regions in the Southern Alps experiencing lower rates of uplift and erosion have a greater

  15. Long Spin Diffusion Length in Few-Layer Graphene Flakes

    NASA Astrophysics Data System (ADS)

    Yan, W.; Phillips, L. C.; Barbone, M.; Hämäläinen, S. J.; Lombardo, A.; Ghidini, M.; Moya, X.; Maccherozzi, F.; van Dijken, S.; Dhesi, S. S.; Ferrari, A. C.; Mathur, N. D.

    2016-09-01

    We report a spin valve with a few-layer graphene flake bridging highly spin-polarized La0.67Sr0.33MnO3 electrodes, whose surfaces are kept clean during lithographic definition. Sharp magnetic switching is verified using photoemission electron microscopy with x-ray magnetic circular dichroism contrast. A naturally occurring high interfacial resistance ˜12 M Ω facilitates spin injection, and a large resistive switching (0.8 M Ω at 10 K) implies a 70 - 130 μ m spin diffusion length that exceeds previous values obtained with sharp-switching electrodes.

  16. Large magnetic entropy change in Cu-doped manganites

    NASA Astrophysics Data System (ADS)

    Phan, Manh-Huong; Peng, Hua-Xin; Yu, Seong-Cho; Duc Tho, Nguyen; Chau, Nguyen

    2005-01-01

    Magnetic entropy change above 300 K, which is larger than that of gadolinium (Phys. Rev. B 57 (1998) 3478), has been observed in a Cu-doped manganites of La0.7Sr0.3Mn1-xCuxO3 (x = 0.05 , 0.1). The large magnetic entropy change originated from a sharp magnetization jump is associated with a first-order crystallographic phase transition of the sample near the Curie temperature. These results suggest that the present Cu-doped manganites are suitable candidate materials for magnetic refrigerants in the room temperature magnetic-refrigeration technology.

  17. Twin-Foucault imaging method

    NASA Astrophysics Data System (ADS)

    Harada, Ken

    2012-02-01

    A method of Lorentz electron microscopy, which enables observation two Foucault images simultaneously by using an electron biprism instead of an objective aperture, was developed. The electron biprism is installed between two electron beams deflected by 180° magnetic domains. Potential applied to the biprism deflects the two electron beams further, and two Foucault images with reversed contrast are then obtained in one visual field. The twin Foucault images are able to extract the magnetic domain structures and to reconstruct an ordinary electron micrograph. The developed Foucault method was demonstrated with a 180° domain structure of manganite La0.825Sr0.175MnO3.

  18. Preparation and Mixed Conductivity of Mn-DOPED Bi-Sr-Fe-BASED Perovskite Type Oxides

    NASA Astrophysics Data System (ADS)

    Baek, Doohyun; Takamura, Hitoshi

    2013-07-01

    Bi0.7Sr0.3FeO3-δ (BSF) with perovskite structure and Mn-doped BSFs were prepared by solid-state reaction and their mixed conductivities were discussed based on results of electrical conductivity and oxygen permeation measurement through membranes of those compounds. BSF showed only 2 S/cm at 800 °C suggesting that its charge unbalance is likely to be compensated by generation of oxygen vacancies. However, Mn-doping caused the increase of electrical conductivity and the decrease of oxygen permeation rate, that is, the extent of charge compensation by electron holes increased through Mn-doping.

  19. Effect of growth mechanisms on the deformation of a unit cell and polarization reversal in barium-strontium titanate heterostructures on magnesium oxide

    NASA Astrophysics Data System (ADS)

    Mukhortov, V. M.; Golovko, Yu. I.; Biryukov, S. V.; Anokhin, A.; Yuzyuk, Yu. I.

    2016-01-01

    The effect of a growth mechanism on the unit cell strain and the related change in the properties of single-crystal Ba0.8Sr0.2TiO3 films grown on MgO substrates according to the Frank-van der Merwe and Volmer-Weber growth mechanisms is studied. The unit cell strain is shown to depend substantially on the film thickness and the growth mechanism. It is found that the same film-substrate pair can be used to vary stresses in the film from two-dimensional tensile to compressive stresses due to a change in the growth mechanism and the film thickness.

  20. Spectral properties and highly efficient continuous-wave laser operation in Nd-doped Sr(1-x)Y(x)F(2+x) crystals.

    PubMed

    Ma, F K; Jiang, D P; Su, L B; Wang, J Y; Cai, W; Liu, J; Zheng, J G; Zheng, W G; Xu, J; Liu, Y

    2016-02-01

    Spectral properties of Nd:Sr(1-x)Y(x)F(2+x) crystals were investigated. Compared with Nd:SrF2, the spectral parameters of Nd:Sr(1-x)Y(x)F(2+x) (x=0.05,0.1) were altered in a large scale. LD-pumped true CW laser has been demonstrated in the crystals. The slope efficiency up to 43.5% in 0.43% Nd:Sr0.95Y0.05F2.05 was achieved. The system is a promising candidate for highly efficient lasers.

  1. Sr-Nd isotopes constrain on the deposit history of the basins in the Gulf of Mexico

    NASA Astrophysics Data System (ADS)

    Li, Y.; Jiang, S.

    2015-12-01

    The Brazos-Trinity Basin IV and Ursa Basin are situated on the northern slope of the Gulf of Mexico. The Ursa basin lies in the center of late Pleistocene Mississippi River deposition, received the sediment deposition during Marine Isotope Stage (MIS) 2- 4. The Brazos-Trinity Basin IV belongs to a part of the Brazos-Trinity fan, it recorded the turbidite deposition and hemiplegic deposition during MIS1- 5. The Sr and Nd isotopic composition of the detrital composition of the sediment in both basins indicates the change of the sediment provenance during the basin-filled process. In the Ursa basin, The difference of 87Sr/86Sr ratio and ɛNd of the detrital component between MIS1,2 (87Sr/86Sr ~ 0.7219 - 0.7321, ɛNd ~ -12 - -13.4) and MIS3,4(87Sr/86Sr ~ 0.7310 - 0.7354, ɛNd ~ -16 - -17.9) is suggested to be related with the provenance change of the detrital particles since LGM. The addition of detrital particle from Appalachians with less radiogenic 87Sr/86Sr and positive ɛNd altered the character of the sediment of the Mississippi River during the last glaciation and deglaciation. In the Brazos-Trinity Basin IV, the narrow range of 87Sr/86Sr and ɛNd indicate that the sediment source of Brazos-Trinity Basin IV had not changed obviously during MIS5e to MIS2, mostly from coastal rivers such as Brazos River, Trinity River and Sabine River. The pre-fan with 87Sr/86Sr ~0.735 and ɛNd ~ -14.5 to -16.9, which is very similar to the deep sediment in the Ursa Basin with 87Sr/86Sr ~0.733 to 0.735 and ɛNd ~ -16 to -18. It is suggested that sediments of the pre-fan of the Brazos-Trinity Basin IV were supplied from the ancestral Mississippi River Delta during the low sea level (MIS 6). During the MIS5, the discharge of Mississippi River is thought switched to its present course, ~300 km to the east.

  2. Switchable and tunable film bulk acoustic resonator fabricated using barium strontium titanate active layer and Ta2O5/SiO2 acoustic reflector

    NASA Astrophysics Data System (ADS)

    Sbrockey, N. M.; Kalkur, T. S.; Mansour, A.; Khassaf, H.; Yu, H.; Aindow, M.; Alpay, S. P.; Tompa, G. S.

    2016-08-01

    A solidly mounted acoustic resonator was fabricated using a Ba0.60Sr0.40TiO3 (BST) film deposited by metal organic chemical vapor deposition. The device was acoustically isolated from the substrate using a Bragg reflector consisting of three pairs of Ta2O5/SiO2 layers deposited by chemical solution deposition. Transmission electron microscopy verified that the Bragg reflector was not affected by the high temperatures and oxidizing conditions necessary to process high quality BST films. Electrical characterization of the resonator demonstrated a quality factor (Q) of 320 and an electromechanical coupling coefficient (Kt2) of 7.0% at 11 V.

  3. Site location and crystal field of Nd3+ ions in congruent strontium barium niobate

    NASA Astrophysics Data System (ADS)

    Molina, P.; Loro, H.; Álvarez-García, S.; Bausá, L. E.; Rodriguez, E. Martín; Guillot-Noël, O.; Goldner, Ph.; Bettinelli, M.; Ghigna, P.; Solé, J. García

    2009-08-01

    The site location of Nd3+ ions in congruent strontium barium niobate (Sr0.6Ba0.4Nb2O6) has been systematically investigated by means of low-temperature optical and electron paramagnetic resonance spectroscopies. The experimental results obtained by these complementary techniques clearly indicate that Nd3+ ions are mainly located in only one of the four available cationic sites, the A2 sites, and preserving the Cs local symmetry of these host cation sites. The energy levels and g -factor value experimentally obtained by both techniques have been used to calculate the crystal field parameters for the Nd3+ ions in this A2 cationic site.

  4. 87Sr/86Sr ratios in some eugeosynclinal sedimentary rocks and their bearing on the origin of granitic magma in orogenic belts

    USGS Publications Warehouse

    Peterman, Z.E.; Hedge, C.E.; Coleman, R.G.; Snavely, P.D.

    1967-01-01

    Rb and Sr contents and 87Sr/86Sr values were determined for samples of eugeosynclinal sedimentary rocks, mostly graywackes, from Oregon and California. These data are compatible with the theory of anataxis of eugeosynclinal sedimentary rocks in orogenic belts to produce granitic magmas provided that the melting occurs within several hundreds of m.y. after sedimentation. The low (87Sr/86Sr)0 values of the eugeosynclinal sedimentary rocks are related to the significant amounts of volcanogenic detritus present which probably were originally derived from the mantle. ?? 1967.

  5. Effects of Tb(3+) dopants in the La1-x Sr x MnO3 bulk and nanoparticle ferromagnets.

    PubMed

    Kaman, Ondřej; Hejtmánek, Jiří; Jirák, Zdeněk; Knížek, Karel; Maryško, Miroslav; Novák, Pavel; Vratislav, Stanislav

    2016-05-25

    Three forms of La,Sr-manganites are synthesized and the role of Tb doping is investigated. First two systems are sol-gel nanoparticles and sintered ceramics of the composition La0.56Tb0.07Sr0.37MnO3, whereas the third system is formed by comparable nanoparticles La0.51Tb0.06Sr0.43MnO3 synthesized in molten salt. The samples show pseudocubic perovskite structure with only small tilts of MnO6 that point to Ibmm symmetry in the bulk and [Formula: see text] symmetry in nanoparticles. SQUID magnetometry and neutron diffraction reveal a complete FM order of Mn spins in bulk, a reduced order in nanoparticles, and non-zero moments at A sites. Detailed analysis suggests that the dodecahedral coordination of A sites adapts to small terbium size, and the resulting crystal field splitting of Tb(3+) yields a singlet ground state. The response to exchange and external fields is characterized as a giant Van Vleck paramagnetism in contrast to the Curie-type behaviour of Tb-based orthoaluminates and orthocobaltites with the quasi-doublet ground state. PMID:27111093

  6. A composite cathode based on scandium doped titanate with enhanced electrocatalytic activity towards direct carbon dioxide electrolysis.

    PubMed

    Yang, Liming; Xie, Kui; Wu, Lan; Qin, Qingqing; Zhang, Jun; Zhang, Yong; Xie, Ting; Wu, Yucheng

    2014-10-21

    A composite cathode based on redox-stable La0.2Sr0.8TiO(3+δ) (LSTO) can perform direct carbon dioxide electrolysis; however, the insufficient electro-catalytic activity limits the electrode performances and current efficiencies. In this work, catalytically active scandium is doped into LSTO to enhance the electro-catalytic activity for CO2 electrolysis. The structures, electronic conductivities and ionic conductivities of La0.2Sr0.8Ti(1-x)Sc(x)O (LSTS(x)O) (x = 0, 0.05, 0.1, 0.15 and 0.2) are systematically studied and further correlated with electrode performances. The ionic conductivities of single-phase LSTS(x)O (x = 0, 0.05, 0.1 and 0.15) remarkably improve versus the scandium doping contents though the electrical conductivities gradually change in an adverse trend. Electrochemical measurements demonstrate promising electrode polarisation of LSTS(x)O electrodes and increasing scandium doping contents accordingly improve electrode performances. The Faradic efficiencies of carbon dioxide electrolysis are enhanced by 20% with LSTS0.15O in contrast to bare LSTO electrodes in a solid oxide electrolyser at 800 °C.

  7. Rb-Sr whole-rock and mineral ages, K-Ar, 40Ar/39Ar, and U-Pb mineral ages, and strontium, lead, neodymium, and oxygen isotopic compositions for granitic rocks from the Salinian Composite Terrane, California:

    USGS Publications Warehouse

    Kistler, R.W.; Champion, D.E.

    2001-01-01

    This report summarizes new and published age and isotopic data for whole-rocks and minerals from granitic rocks in the Salinian composite terrane, California. Rubidium-strontium whole-rock ages of plutons are in two groups, Early Cretaceous (122 to 100 Ma) and Late Cretaceous (95 to 82 Ma). Early Cretaceous plutons occur in all granitic rock exposures from Bodega Head in the north to those from the Santa Lucia and Gabilan Ranges in the central part of the terrane. Late Cretaceous plutons have been identified in the Point Reyes Peninsula, the Santa Lucia and the Gabilan Ranges, and in the La Panza Range in the southern part of the terrane. Ranges of initial values of isotopic compositions are 87Sr/86Sr, 0.7046-0.7147, δ18O, +8.5 to +12.5 per mil, 206Pb/204Pb, 18.901-19.860, 207Pb/204Pb, 15.618-15.814, 208Pb/204Pb, 38.569- 39.493, and εNd, +0.9 to -8.6. The initial 87Sr/86Sr=0.706 isopleth is identified in the northern Gabilan Range and in the Ben Lomond area of the Santa Cruz Mountains, in Montara Mountain, in Bodega Head, and to the west of the Farallon Islands on the Cordell Bank. This isotopic boundary is offset about 95 miles (160km) by right-lateral displacements along the San Gregorio-Hosgri and San Andreas fault systems.

  8. Long-range magnetic coupling across a polar insulating layer

    PubMed Central

    Lü, W. M.; Saha, Surajit; Wang, X. Renshaw; Liu, Z. Q.; Gopinadhan, K.; Annadi, A.; Zeng, S. W.; Huang, Z.; Bao, B. C.; Cong, C. X.; Venkatesan, M.; Yu, T.; Coey, J. M. D.; Ariando; Venkatesan, T.

    2016-01-01

    Magnetic interactions in solids are normally mediated by short-range exchange or weak dipole fields. Here we report a magnetic interaction that can propagate over long distances (∼10 nm) across a polar insulating oxide spacer. Evidence includes oscillations of magnetization, coercivity and field-cooled loop shift with the thickness of LaAlO3 in La0.67Sr0.33MnO3/LaAlO3/SrTiO3 heterostructures. Similar modifications of the hysteresis loop appear when two coupled films of La0.67Sr0.33MnO3 are separated by LaAlO3, or another polar insulator, but they are absent when the oxide spacer layer is nonpolar. The loop shift is attributed to strong spin–orbit coupling and Dzyaloshinskii–Moriya interaction at the interfaces. There is evidence from inelastic light scattering that the polar spacer mediates long-range transmission of orbital magnetization. This coupling mechanism is expected to apply for any conducting ferromagnetic oxide with mixed valence; in view of electron hopping frequency involved, it raises the prospect of terahertz tunability of magnetic coupling. PMID:26980456

  9. Charge superstructures in Zn-doped La2-xSrxCuO4

    NASA Astrophysics Data System (ADS)

    Lee, J. C.; Rusydi, A.; Smadici, S.; Wang, S.; Abbamonte, P.; Enoki, M.; Fujita, M.; Ruebhausen, M.; Yamada, K.

    2008-03-01

    We have observed valence band charge order in both twinned and untwinned samples of La1.95Sr0.05Cu0.95Zn0.05O4 with resonant soft x-ray scattering. In the untwinned sample the order was observed to be mainly electronic and centered at the (0,0.084,2)o position in reciprocal space, indicating diagonal charge order with period 12 ao, where ao is the orthorhombic lattice parameter. This order has approximately half the wavelength of the magnetic order previsouly observed with neutron scattering* in this system, suggesting a stripe interpretation. Preliminary measurements on a twinned sample revealed four satellites at (0,K,2)o, where K takes on integer multiples of the value 0.011. Relationships between these effects and the crystal structure of La1.95Sr0.05Cu0.95Zn0.05O4 will be discussed. *M. Matsuda, et. al., Phys. Rev. B 73, 140503(R) (2006)

  10. Luminescent properties and energy transfer of double-emitting Na2SrMgP2O8:Eu2+, Mn2+ phosphor

    NASA Astrophysics Data System (ADS)

    Wanjun, Tang; Shanshan, Hu; Fen, Zhang

    2013-10-01

    Olgite-type Na2SrMgP2O8 doped with Eu2+ and Mn2+ solely or doubly were prepared by a combustion-assisted synthesis method. The phase formation was confirmed by X-ray powder diffraction measurement. Upon excitation of 352 nm ultraviolet (UV) light, two intense broad bands have clearly been observed due to the allowed 5d-4f transition of Eu2+ and the forbidden 4T1-6A1 transition of Mn2+, respectively. On the basis of the luminescence spectra and fluorescence decay curves, we confirm that the energy transfer process from the Eu2+ to Mn2+ ions occur in the codoped Na2SrMgP2O8:Eu2+, Mn2+ phosphor. The composition-optimized Na2Sr0.99MgP2O8:0.01Eu2+ and Na2Sr0.99Mg0.9P2O8: 0.01Eu2+, 0.1Mn2+ phosphors exhibits superior external quantum efficiency (87.2% and 69.3%, respectively). Based on the principle of energy transfer, the relative intensities of blue and red emission could be tuned by adjusting the contents of Eu2+ and Mn2+.

  11. Structural and Luminescent Properties of Eu2+-doped Aluminates Prepared by the Sol-gel Method.

    PubMed

    Celan-Korošin, Nataša; Meden, Anton; Bukovec, Nataša

    2012-12-01

    Alkaline earth aluminates with the overall nominal compositions Mg0.5Sr0.5Al2O4 (MSA), Ca0.5Sr0.5Al2O4 (CSA) and Ca0.5Mg0.5Al2O4 (CMA) doped with 0.5 or 1 mol% of Eu2+ ions were obtained by a modified aqueous sol-gel method and annealed in a reductive atmosphere at 900, 1000, 1100 and 1300 °C. The sample compositions and their structures were studied by XRD employing the Rietveld method. Solid solubility was confirmed in CSA only, due to the similar ionic radii of Ca2+ and Sr2+. UV excited luminescence was observed in the blue region (λ = 440 nm) in samples of CSA and CMA containing the monoclinic phase of CaAl2O4 and in the green region (λ = 512 nm) in samples of MSA containing hexagonal or monoclinic phases of SrAl2O4. PMID:24061375

  12. Charge and Strain Control of Interface Magnetism

    NASA Astrophysics Data System (ADS)

    Fitzsimmons, M. R.; Dumesnil, K.; Jaouen, N.; Maroutian, T.; Agnus, G.; Tonnerre, J.-M.; Kirby, B.; Fohtung, E.; Holladay, B.; Fullerton, E. E.; Shpyrko, O.; Sinha, S. K.; Wang, Q.; Chen, A.; Jia, Q. X.

    2015-03-01

    We studied the influence of an electric field applied to an La0.67Sr0.33MnO3 (LSMO) layer in a LSMO/Pb(Zr0.2Ti0.8) O3 (PZT)/Nb-doped SrTiO3 (STO) heterostructure by measuring its magnetization depth profile using resonant x-ray magnetic reflectivity. The saturation magnetization of the ferromagnetically-ordered LSMO was not affected by the direction of the polarization of the PZT. However, the ferromagnetic thickness and magnetization of the LSMO film at remanence were reduced for hole-charge accumulation at the LSMO/PZT interface. To understand the independent roles of strain and hole-doping, we performed neutron scattering experiments of La0.8Sr0.2MnO3 films grown on Nb-doped STO in which bending strain (via 4-point bending jig) or electric field (via parallel plate capacitor) was applied to the films. We observed that bending strain affects the saturation magnetization of the LSMO film, whereas electric field affects the remanent magnetization of the film. These observations suggest strain may be a more effective means to control magnetism than charge. This work has benefited from use of CINT(LANL), NIST Center for Neutron Research and the Synchrotron SOLEIL and funding from LANL/LDRD program, DOE-BES (UCSD) and DOD (NMSU).

  13. Electronic structure and relaxation dynamics in a superconducting topological material.

    PubMed

    Neupane, Madhab; Ishida, Yukiaki; Sankar, Raman; Zhu, Jian-Xin; Sanchez, Daniel S; Belopolski, Ilya; Xu, Su-Yang; Alidoust, Nasser; Hosen, M Mofazzel; Shin, Shik; Chou, Fangcheng; Hasan, M Zahid; Durakiewicz, Tomasz

    2016-01-01

    Topological superconductors host new states of quantum matter which show a pairing gap in the bulk and gapless surface states providing a platform to realize Majorana fermions. Recently, alkaline-earth metal Sr intercalated Bi2Se3 has been reported to show superconductivity with a Tc ~ 3 K and a large shielding fraction. Here we report systematic normal state electronic structure studies of Sr0.06Bi2Se3 (Tc ~ 2.5 K) by performing photoemission spectroscopy. Using angle-resolved photoemission spectroscopy (ARPES), we observe a quantum well confined two-dimensional (2D) state coexisting with a topological surface state in Sr0.06Bi2Se3. Furthermore, our time-resolved ARPES reveals the relaxation dynamics showing different decay mechanism between the excited topological surface states and the two-dimensional states. Our experimental observation is understood by considering the intra-band scattering for topological surface states and an additional electron phonon scattering for the 2D states, which is responsible for the superconductivity. Our first-principles calculations agree with the more effective scattering and a shorter lifetime of the 2D states. Our results will be helpful in understanding low temperature superconducting states of these topological materials. PMID:26936229

  14. Spatial Control Of Functional Properties Via Octahedral Modulations In Complex Oxide Superlattices

    SciTech Connect

    Moon, E. J.; Colby, Robert J.; Wang, Q.; Karapetrova, E.; Schleputz, C. M.; Fitzsimmons, M. R.; May, Steven J.

    2014-12-15

    The design of distortions and rotations of the corner-connected BO6 octahedra across interfaces has emerged as an exciting platform to control electronic or ferroic behavior in ABO3 perovskite heterostructures. Here, we investigate isovalent manganite superlattices, [(La0.7Sr0.3MnO3)n/(Eu0.7Sr0.3MnO3)n]×m, as a route to spatial control over electronic bandwidth and ferromagnetism through the creation of octahedral superstructures. Electron energy loss spectroscopy confirms a uniform Mn valence state throughout the superlattices. In contrast, the presence of modulations of the MnO6 octahedral rotations along the growth direction commensurate with the superlattice period is revealed by scanning transmission electron microscopy and x-ray diffraction. We show that the Curie temperatures of the constituent materials can be systematically engineered via the octahedral superstructures leading to a modulated magnetization in samples where the superlattice period is larger than the interfacial octahedral coupling length scale, while a single magnetic transition is observed in the short period superlattices.

  15. Effects of Tb3+ dopants in the La1-x Sr x MnO3 bulk and nanoparticle ferromagnets

    NASA Astrophysics Data System (ADS)

    Kaman, Ondřej; Hejtmánek, Jiří; Jirák, Zdeněk; Knížek, Karel; Maryško, Miroslav; Novák, Pavel; Vratislav, Stanislav

    2016-05-01

    Three forms of La,Sr-manganites are synthesized and the role of Tb doping is investigated. First two systems are sol-gel nanoparticles and sintered ceramics of the composition La0.56Tb0.07Sr0.37MnO3, whereas the third system is formed by comparable nanoparticles La0.51Tb0.06Sr0.43MnO3 synthesized in molten salt. The samples show pseudocubic perovskite structure with only small tilts of MnO6 that point to Ibmm symmetry in the bulk and R\\bar{3}c symmetry in nanoparticles. SQUID magnetometry and neutron diffraction reveal a complete FM order of Mn spins in bulk, a reduced order in nanoparticles, and non-zero moments at A sites. Detailed analysis suggests that the dodecahedral coordination of A sites adapts to small terbium size, and the resulting crystal field splitting of Tb3+ yields a singlet ground state. The response to exchange and external fields is characterized as a giant Van Vleck paramagnetism in contrast to the Curie-type behaviour of Tb-based orthoaluminates and orthocobaltites with the quasi-doublet ground state.

  16. Thermoelectric properties of n-type double substituted SrTiO3 bulk materials.

    PubMed

    Cui, Yanjie; He, Jian; Amow, Gisele; Kleinke, Holger

    2010-01-28

    A series of La, Ta double substituted Sr(1-x)La(x)Ti(1-x)Ta(x)O(3), with x = 0.01, 0.05 and 0.10, and La, Nb double substituted Sr(0.90)La(0.10)Ti(0.90)Nb(0.10)O(3) for comparison were investigated in this project. Rietveld refinements were performed to check for purity and symmetry reduction. Electronic structure calculations indicate n-type conduction with steep and flat bands in the vicinity of the Fermi level for x = 0.125. Seebeck coefficient, electrical conductivity, and thermal conductivity measurements on hot-pressed and spark-plasma-sintered samples were performed over a wide range of temperatures. Best results were obtained by spark-plasma-sintering of double substituted Sr(0.99)La(0.01)Ti(0.99)Ta(0.01)O(3) with a thermoelectric figure-of-merit of 0.13 at 660 K.

  17. Ferroelectromagnetic solid solutions on the base piezoelectric ceramic materials for components of micromechatronics

    NASA Astrophysics Data System (ADS)

    Bochenek, Dariusz; Zachariasz, Radosław; Niemiec, Przemysław; Ilczuk, Jan; Bartkowska, Joanna; Brzezińska, Dagmara

    2016-10-01

    In the presented work, a ferroelectromagnetic solid solutions based on PZT and ferrite powders have been obtained. The main aim of combination of ferroelectric and magnetic powders was to obtain material showing both electric and magnetic properties. Ferroelectric ceramic powder (in amount of 90%) was based on the doped PZT type solid solution while magnetic component was nickel-zinc ferrite Ni1-xZnxFe2O4 (in amount of 10%). The synthesis of components of ferroelectromagnetic solid solutions was performed using the solid phase sintering. Final densification of synthesized powder has been done using free sintering. The aim of the work was to obtain and examine in the first multicomponent PZT type ceramics admixed with chromium with the following chemical composition Pb0.94Sr0.06(Zr0.46Ti0.54)O3+0.25 at% Cr2O3 and next ferroelectromagnetic solid solution based on a PZT type ferroelectric powder (Pb0.94Sr0.06(Zr0.46Ti0.54)O3+0.25 at% Cr2O3) and nickel-zinc ferrite (Ni0.64Zn0.36Fe2O4), from the point of view of their mechanical and electric properties, such as: electric permittivity, ε; dielectric loss, tanδ; mechanical losses, Q-1; and Young modulus, E.

  18. An easy and innovative method based on spray-pyrolysis deposition to obtain high efficiency cathodes for Solid Oxide Fuel Cells

    NASA Astrophysics Data System (ADS)

    dos Santos-Gómez, L.; Porras-Vázquez, J. M.; Martín, F.; Ramos-Barrado, J. R.; Losilla, E. R.; Marrero-López, D.

    2016-07-01

    A novel electrode preparation method based on the spray-pyrolysis deposition of metal nitrate solutions onto a porous electrolyte scaffold is proposed. This method has been proved with different cathode materials, usually used in Solid Oxide Fuel Cells, such as La0.8Sr0.2MnO3-δ and La0.6Sr0.4Co1-xFexO3-δ (x = 0, 0.2, 0.8 and 1). The electrode microstructure is composed by two layers; the inner layer is a porous electrolyte scaffold homogeneously coated by cathode nanoparticles, providing an increased number of triple phase boundary sites for oxygen reduction, whereas, the top layer is formed by only cathode nanoparticles and acts mainly as a current collector. Polarization resistance values as low as 0.07 and 1.0 Ω cm2 at 600 and 450 °C, respectively, are obtained at open circuit voltage. This alternative approach has several advantages with respect to the traditional wet infiltration method for large area electrode fabrication, such as higher reproducibility, shorter preparation time in a single thermal deposition step, and easy implementation at industrial scale as a continuous process.

  19. CoxFe1-x oxide coatings on metallic interconnects for solid oxide fuel cells

    NASA Astrophysics Data System (ADS)

    Shen, Fengyu; Lu, Kathy

    2016-10-01

    In order to improve the performance of Cr-containing steel as an interconnect material for solid oxide fuel cells, CoFe alloy coatings with Co:Fe ratios of 9:1, 8:2, 7:3, 6:4, and 5:5 are deposited by electrodeposition and then oxidized to CoxFe1-x oxide coatings with a thickness of ∼6 μm as protective layers on the interconnect. The area specific resistance of the coated interconnect increases with the Fe content. Higher Co content oxide coatings are more effective in limiting the growth of the chromia scale while all coatings are effective in inhibiting Cr diffusion and evaporation. With the Co0.8Fe0.2 oxide coated interconnect, the electrochemical performance of the Sm0.5Sr0.5Co0.2Fe0.8O3 cathode is improved. Only 1.54 atomic percentage of Cr is detected on the surface of the Sm0.5Sr0.5Co0.2Fe0.8O3 cathode while no Cr is detected 0.66 μm or more into the cathode. CoxFe1-x oxide coatings are promising candidates for solid oxide fuel cell interconnects with the advantage of using existing cathode species for compatibility and performance enhancement.

  20. Performance of Solid Oxide Fuel Cell With La and Cr Co-doped SrTiO3 as Anode.

    PubMed

    Yi, Fenyun; Chen, Hongyu; Li, He

    2014-06-01

    The La0.3Sr0.55Ti0.9Cr0.1O3-δ (LSTC10) anode material was synthesized by citric acid-nitrate process. The yttria-stabilized zirconia (YSZ) electrolyte-supported cell was fabricated by screen printing method using LSTC10 as anode and (La0.75Sr0.25)0.95MnO3-δ (LSM) as cathode. The electrochemical performance of cell was tested by using dry hydrogen as fuel and air as oxidant in the temperature range of 800-900 °C. At 900 °C, the open circuit voltage (OCV) and the maximum power density of cell are 1.08 V and 13.0 mW·cm(-2), respectively. The microstructures of cell after performance testing were investigated by scanning electron microscope (SEM). The results show that the anode and cathode films are porous and closely attached to the YSZ electrolyte. LSTC10 is believed to be a kind of potential solid oxide fuel cell (SOFC) anode material.