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Sample records for modulu sr-0 jaderneho

  1. Crystal structure of nonsuperconducting Pb 2(Sr 0.94Nd 0.06) 2(Nd 0.76Sr 0.24)Cu 3O 8

    NASA Astrophysics Data System (ADS)

    Hayri, Eric A.; Kvick, Åke

    1990-01-01

    The crystal structure of Pb 2(Sr 0.94Nd 0.06) 2(Nd 0.76Sr 0.24)Cu 3O 8 was determined by single crystal X-ray diffraction. The compound was found to be orthorhombic ( Cmmm) with a = 5.437(3), b = 5.472(2), c = 15.797(7)Å and Z = 2. In the structure double layers of CuO square pyramids are separated by (Nd, Sr) oxygen deficient layers which are stacked between (PbO)Cu(PbO) slabs. The oxygen in the Pb planes is shifted toward a pair of Pb atoms resulting in an orthorhombic distortion of the tetragonal unit cell. The possibilities for modulations and superlattices are discussed as is the role of the PbO planes in superconductivity.

  2. Magnetic anisotropy of La0.7Sr0.3MnO3 nanopowders

    NASA Astrophysics Data System (ADS)

    Radelytskyi, I.; Dłużewski, P.; Dyakonov, V.; Aleshkevych, P.; Kowalski, W.; Jarocki, P.; Szymczak, H.

    2013-06-01

    The magnetic anisotropy of La0.7Sr0.3MnO3 nanopowders was measured as a function of temperature by the modified singular point detection technique. In this method singularities indicating the anisotropy field were determined analyzing ac susceptibility data. The observed relationship between temperature dependence of anisotropy constant and temperature dependence of magnetization was used to deduce the origin of magnetic anisotropy in the nanopowders. It was shown that magnetic anisotropy of La0.7Sr0.3MnO3 nanopowder is determined by the two-ion (dipolar or pseudodipolar) and single-ion mechanisms.

  3. Exchange bias in Ba0.4Sr0.6TiO3/La0.7Sr0.3MnO3 heterostructures

    NASA Astrophysics Data System (ADS)

    Singamaneni, Srinivasa Rao; Prater, John T.; Narayan, Jagdish

    2017-05-01

    This work relates to the integration of the two-layer stack of the proposed multiferroic structure onto silicon substrates. Ba1-xSrxTiO3 is an excellent material for room-temperature voltage-tunable dielectric applications due to its high (ɛ=6000) dielectric constant. In this study we choose a composition of Ba0.4Sr0.6TiO3 (BST), which is cubic and paraelectric at 300K, and transforms to a ferroelectric tetragonal phase upon cooling through the Curie temperature (TC) at 200K. The main focus of the present work is to study what happens when BST is placed in contact with a room temperature ferromagnetic layer such as La0.7Sr0.3MnO3 (LSMO). In this study, the magnetic properties of a BST (200nm)/LSMO (63nm) heterostructure was compared to that of a single LSMO layer (63nm). Both films were deposited onto MgO/TiN buffered Si (100) using pulsed laser deposition (PLD) and a domain matching epitaxy (DME) paradigm. X-ray diffraction (XRD) measurements showed that these films were of single phase and epitaxial in nature, with an unrelaxed lattice strain of ˜0.2% that was predominately composed of thermal and defect-induced strain. The magnetic measurements showed that the Curie temperature (TC) of LSMO remained unchanged at 350K when the BST was in contact with the LSMO layer. Interestingly, at 4K both the coercive field (Hc) and the exchange bias (HEB) of the BST/LSMO heterostructure as compared to the lone LSMO film increased significantly from 400 to 800 Oe and from 155 to 305 Oe, respectively. These differences were found to disappear above 200 K, the ferroelectric TC of the BST over-layer. This strongly suggests that the observed changes in the magnetic behavior of the heterostructure was the result of stress and/or charge redistributions that resulted when the BST layer transformed from the cubic (paraelectric) to tetragonal (ferroelectric) phase at low temperature.

  4. Stripe conductivity in La1.775Sr0.225NiO4

    PubMed

    Pashkevich; Blinkin; Gnezdilov; Tsapenko; Eremenko; Lemmens; Fischer; Grove; Guntherodt; Degiorgi; Wachter; Tranquada; Buttrey

    2000-04-24

    We report Raman light-scattering and optical conductivity measurements on a single crystal of La1.775Sr0.225NiO4 which exhibits incommensurate charge-stripe order. The extra phonon peaks induced by stripe order can be understood in terms of the energies of phonons that occur at the charge-order wave vector Q(c). A strong Fano antiresonance for a Ni-O bond-stretching mode provides clear evidence for finite dynamical conductivity within the charge stripes.

  5. Stripe Conductivity in La1.775Sr0.225NiO4

    NASA Astrophysics Data System (ADS)

    Pashkevich, Yu. G.; Blinkin, V. A.; Gnezdilov, V. P.; Tsapenko, V. V.; Eremenko, V. V.; Lemmens, P.; Fischer, M.; Grove, M.; Güntherodt, G.; Degiorgi, L.; Wachter, P.; Tranquada, J. M.; Buttrey, D. J.

    2000-04-01

    We report Raman light-scattering and optical conductivity measurements on a single crystal of La1.775Sr0.225NiO4 which exhibits incommensurate charge-stripe order. The extra phonon peaks induced by stripe order can be understood in terms of the energies of phonons that occur at the charge-order wave vector Qc. A strong Fano antiresonance for a Ni-O bond-stretching mode provides clear evidence for finite dynamical conductivity within the charge stripes.

  6. 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.

  7. 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.

  8. Unidirectional Order and 3D Stacking of Stripes in Orthorhombic Pr1.67Sr0.33NiO4 and Nd1.67Sr0.33NiO4.

    NASA Astrophysics Data System (ADS)

    Hücker, Markus; Tranquada, John M.; Gu, Gen D.; Zimmermann, Martin V.; Büchner, Bernd K.

    2006-03-01

    The crystal structure and charge stripe order in Pr1. 67Sr0.33NiO4 and Nd1. 67Sr0.33NiO4 was studied by means of single crystal x-ray diffraction in zero and high electric fields. In contrast to tetragonal La1.67Sr0.33NiO4, these crystals are orthorhombic at room temperature. We find that the distortion of the NiO2 planes associated with the orthorhombic strain dictates the direction of the charge stripes. The critical temperature for charge stripe order is the same as in La1.67Sr0.33NiO4 (TCO˜245 K), i.e., it does not depend on the crystal symmetry. A second structural transition observed only in Nd1.67Sr0.33NiO4 at temperatures T˜100 K has no noticeable influence on the stripe order. In crystals with a hole content very close to 1/3 we observe a tripling of the charge stripe unit cell along the c-axis for temperatures T < 225 K, which indicates a strong tendency towards a well defined three dimensional order. A high electric field applied to Nd1.67Sr0.33NiO4 had no noticeable impact on the charge stripe order, i.e., a sliding of stripes was not observed. The work at Brookhaven was supported by the Office of Science, U.S. Department of Energy under Contract No. DE-AC02-98CH10886.

  9. 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

  10. 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.

  11. Improvement of La0.65Sr0.3MnO3-gamma-YSZ cathodes by infiltrating nanoSm0.6Sr0.4CoO3-gamma particles

    SciTech Connect

    Lu, Chun; Sholklapper, Tal; Chen, Xuan; Zhang, Xiaofeng; Jacobson, Craig P.; Visco, Steven J.; DeJonghe, Lutgard C.

    2004-05-01

    La0.65Sr0.3MnO3-delta-YSZ cathodes are infiltrated with Sm0.6Sr0.4CoO3-delta (SSC) at 800 C using a precipitation method. The effect of SSC infiltration has been characterized for symmetric cells and single cells at reduced temperatures. With SSC addition the cathode polarization resistance, determined from symmetric-cell measurements, significantly decreases: from approx. 19.8 to 8.5 Omega cdot cm2 at 600 C, and from 7.7 to 3.3 Omega cdot cm2 at 650 C. Consequently, the single-cell performance with 97 percentH2+3 percentH2O fuel is dramatically improved, which may be attributed to the superior electrocatalytic activity of SSC in the cathodes.

  12. Disorder enhanced intrinsic electroresistance in Sm0.60Sr0.40Mn1-xFexO3

    NASA Astrophysics Data System (ADS)

    Mahmud, S. T.; Saber, M. M.; Alagoz, H. S.; Biggart, K.; Bouveyron, R.; Khan, Mahmud; Jung, J.; Chow, K. H.

    2012-06-01

    The intrinsic electroresistance (ER) of polycrystalline Sm0.60Sr0.40Mn1-xFexO3 (0 ≤ x ≤ 0.02) have been investigated by magnetotransport measurements. It is found that the ER increases with x while it is suppressed by a magnetic field. These observations imply that the ER increases dramatically with the inhomogeneity in the samples. The possible mechanisms responsible for the observed behavior are discussed.

  13. Magnetocaloric effect in La0.65-xEuxSr0.35MnO3

    NASA Astrophysics Data System (ADS)

    Hamad, Mahmoud A.

    2014-05-01

    The magnetocaloric properties for the Eu-doped La0.65-xEuxSr0.35MnO3 samples with x = 0.05, 0.15, 0.20, and 0.30 upon 0.05T magnetic field have been investigated. It is found that the Eu doping in this system decreases the magnetocaloric properties lightly. Moreover, the results of Eu doping clearly indicate that the magnetocaloric effect in this system is tunable, which is beneficial for manipulating magnetocaloric refrigeration that occurs in various temperature ranges. This makes the La0.65-xEuxSr0.35MnO3 samples potential candidates for practical applications. A complete characterization of the magnetic properties of this material aids to the understanding required for the technological exploitation of such materials, and it suggests La0.65-xEuxSr0.35MnO3 perovskite as the promising magnetic refrigerant.

  14. 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.

  15. Preparation and characterization of a new graphite superconductor: Ca0.5Sr0.5C6.

    PubMed

    Nishiyama, Saki; Fujita, Hidenori; Hoshi, Masatoshi; Miao, Xiao; Terao, Takahiro; Yang, Xiaofan; Miyazaki, Takafumi; Goto, Hidenori; Kagayama, Tomoko; Shimizu, Katsuya; Yamaoka, Hitoshi; Ishii, Hirofumi; Liao, Yen-Fa; Kubozono, Yoshihiro

    2017-08-07

    We have produced a superconducting binary-elements intercalated graphite, CaxSr1-xCy, with the intercalation of Sr and Ca in highly-oriented pyrolytic graphite; the superconducting transition temperature, T c, was ~3 K. The superconducting CaxSr1-xCy sample was fabricated with the nominal x value of 0.8, i.e., Ca0.8Sr0.2Cy. Energy dispersive X-ray (EDX) spectroscopy provided the stoichiometry of Ca0.5(2)Sr0.5(2)Cy for this sample, and the X-ray powder diffraction (XRD) pattern showed that Ca0.5(2)Sr0.5(2)Cy took the SrC6-type hexagonal-structure rather than CaC6-type rhombohedral-structure. Consequently, the chemical formula of CaxSr1-xCy sample could be expressed as 'Ca0.5(2)Sr0.5(2)C6'. The XRD pattern of Ca0.5(2)Sr0.5(2)C6 was measured at 0-31 GPa, showing that the lattice shrank monotonically with increasing pressure up to 8.6 GPa, with the structural phase transition occurring above 8.6 GPa. The pressure dependence of T c was determined from the DC magnetic susceptibility and resistance up to 15 GPa, which exhibited a positive pressure dependence of T c up to 8.3 GPa, as in YbC6, SrC6, KC8, CaC6 and Ca0.6K0.4C8. The further application of pressure caused the rapid decrease of T c. In this study, the fabrication and superconducting properties of new binary-elements intercalated graphite, CaxSr1-xCy, are fully investigated, and suitable combinations of elements are suggested for binary-elements intercalated graphite.

  16. Unidirectional diagonal order and three-dimensional stacking of charge stripes in orthorhombic Pr1.67Sr0.33NiO4 and Nd1.67Sr0.33NiO4

    NASA Astrophysics Data System (ADS)

    Hücker, M.; Zimmermann, M. V.; Klingeler, R.; Kiele, S.; Geck, J.; Bakehe, S. N.; Zhang, J. Z.; Hill, J. P.; Revcolevschi, A.; Buttrey, D. J.; Büchner, B.; Tranquada, J. M.

    2006-08-01

    The interplay between crystal symmetry and charge stripe order in Pr1.67Sr0.33NiO4 and Nd1.67Sr0.33NiO4 has been studied by means of single crystal x-ray diffraction. In contrast to tetragonal La1.67Sr0.33NiO4 , these crystals are orthorhombic. The corresponding distortion of the NiO2 planes is found to dictate the direction of the charge stripes, similar to the case of diagonal spin stripes in the insulating phase of La2-xSrxCuO4 . In particular, diagonal stripes seem to always run along the short a axis, which is the direction of the octahedral tilt axis. In contrast, no influence of the crystal symmetry on the charge stripe ordering temperature itself was observed, with TCO˜240K for La, Pr, and Nd. The coupling between lattice and stripe degrees of freedom allows one to produce macroscopic samples with unidirectional stripe order. In samples with stoichiometric oxygen content and a hole concentration of exactly 1/3 , charge stripes exhibit a staggered stacking order with a period of three NiO2 layers, previously only observed with electron microscopy in domains of mesoscopic dimensions. Remarkably, this stacking order starts to melt about 40K below TCO . The melting process can be described by mixing the ground state, which has a three-layer stacking period, with an increasing volume fraction with a two-layer stacking period.

  17. 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.

  18. Investigation of magnetic properties of Sm0.55Sr0.45MnO3

    NASA Astrophysics Data System (ADS)

    Bhat, Masroor Ahmad; Choithrani, Renu; Gaur, N. K.

    2015-08-01

    In this paper, we report the enhancement of metal - insulator transition temperature (TMI) induced by magnetic field confirms the MR phenomenon. The polycrystalline Sm0.55Sr0.45MnO3 were synthesized using solid state reaction route. The XRD patterns using Full Prof Rietveld analysis shows that the sample has single phase nature without any detectable impurity. The SEM micrograph carried to observe the grain morphology and four probe resistivity measurements using with superconducting magnet to investigate the electrical behaviour. The sharp value of temperature coefficient of resistance (TCR) of 11% is used for infrared bolometric sensors.

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

    DOE PAGES

    Yue -Wei Yin; Tao, Jing; Huang, Wei -Chuan; ...

    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

  20. 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.

  1. Possible spin-triplet superconducting phase in the La0.7Sr0.3MnO3/YBa2Cu3O7/La0.7Sr0.3MnO3 trilayer

    NASA Astrophysics Data System (ADS)

    Dybko, K.; Werner-Malento, K.; Aleshkevych, P.; Wojcik, M.; Sawicki, M.; Przyslupski, P.

    2009-10-01

    We report on results of conductance spectroscopy measurements in the current-in-plane (CIP) and current-perpendicular-to-plane (CPP) geometries ([001] and [100] directions respectively) of La0.7Sr0.3MnO3/YBa2Cu3O7/La0.7Sr0.3MnO3 (LSMO/YBCO/LSMO) nonsymmetric trilayer structures in order to search for signature of the formation of spin-triplet phase. This trilayer shows an enhancement of the superconducting transition temperature in magnetic field parallel to the plane. We argue that this enhancement is a result of the formation of spin-triplet phase. The differential conductance (dI/dV) spectra show fully developed zero-bias conductance peaks (ZBCP). The ZBCP measured in CIP geometry demonstrates a sharp shape. This could be attributed to a spin-triplet state arising from the proximity effect at the interface of the half-metal with the d -wave superconductor, similar as was predicted theoretically for the p -wave superconductor and observed experimentally in p -wave Sr2RuO4 superconductor. The measurements of the dI/dV in CPP geometry reveal a V shape similar as was experimentally observed in YBCO superconductor and predicted theoretically for superconductor with a dx2-y2 pairing symmetry of the order parameter.

  2. Negative Thermal Expansion in Ba0.5Sr0.5Zn2SiGeO7

    PubMed Central

    Thieme, Christian; Rüssel, Christian

    2016-01-01

    Solid solutions with the composition Ba0.5Sr0.5Zn2Si2-xGexO7 and BaZn2Si2-xGexO7 were prepared with different values of x using a conventional mixed oxide route. Both compounds exhibit very different thermal expansion, which is due to the different crystal structures. Ba0.5Sr0.5Zn2Si2-xGexO7 solid solutions exhibit the structure of high-temperature BaZn2Si2O7 and show negative thermal expansion, which was proven via high-temperature X-ray diffraction. Up to around x = 1, the crystal structure remains the same. Above this value, the low-temperature phase becomes stable. The Sr-free solid solutions have the crystal structure of low-temperature BaZn2Si2O7 and show also a limited solubility of Ge. These Sr-free compositions show transitions of low- to high-temperature phases, which are shifted to higher temperatures with increasing Ge-concentration. PMID:28773746

  3. Magnetic properties of rare-earth-doped La0.7Sr0.3MnO3

    NASA Astrophysics Data System (ADS)

    Veverka, Pavel; Kaman, Ondřej; Knížek, Karel; Novák, Pavel; Maryško, Miroslav; Jirák, Zdeněk

    2017-01-01

    Rare-earth-doped ferromagnetic manganites La0.63RE0.07Sr0.30MnO3 (RE  =  Gd, Tb, Dy, and Ho) are synthesized in the form of sintered ceramics and nanocrystalline phases with the mean size of crystallites  ≈30 nm. The electronic states of the dopants are investigated by SQUID magnetometry and theoretically interpreted based on the calculations of the crystal field splitting of rare-earth energy levels. The samples show the orthorhombic perovskite structure of Ibmm symmetry, with a complete FM order of Mn spins in bulk and reduced order in nanoparticles. Non-zero moments are also detected at the perovskite A sites, which can be attributed to magnetic polarization of the rare-earth dopants. The measurements in external field up to 70 kOe show a standard Curie-type contribution of the spin-only moments of Gd3+ ions, whereas Kramers ions Dy3+ and non-Kramers ions Ho3+ contribute by Ising moments due to their doublet ground states. The behaviour of non-Kramers ions Tb3+ is anomalous, pointing to singlet ground state with giant Van Vleck paramagnetism. The Tb3+ doping leads also to a notably increased coercivity compared to other La0.63RE0.07Sr0.30MnO3 systems.

  4. Low temperature transport anomaly in Cr substituted (La0.67Sr0.33)MnO3 manganites

    NASA Astrophysics Data System (ADS)

    Tank, Tejas M.; Shelke, Vilas; Das, Sarmistha; Rana, D. S.; Thaker, C. M.; Samatham, S. S.; Ganesan, V.; Sanyal, S. P.

    2017-06-01

    The structural, electrical, and magnetic properties of La0.67Sr0.33Mn1-xCrxO3 (0 ≤ x ≤ 0.10) manganites have been studied by substitution of antiferromagnetic trivalent Cr ion at Mn-site. Systematic efforts have been carried out to understand the electrical resistivity behavior in the ferromagnetic metallic and paramagnetic semi-conducting phases of Cr substituted La0.67Sr0.33Mn1-xCrxO3 manganites. Polycrystalline samples show a resistivity minimum at a temperature (Tmin) of <40 K in the ferromagnetic metallic phase. Tmin shifts to higher temperatures on application of magnetic fields. The appearance of this resistivity minimum was analyzed by fittings the data according to the model that considers e-e scattering caused by enhanced Coulombic interactions. The electrical resistivity data has been best fitted in the metallic and semiconducting regime using various models. Present results suggest that intrinsic magnetic inhomogeneity like Cr3+ ions in these strongly electron-correlated manganite systems is originating due to the existence of the ferromagnetic interactions.

  5. Phonon Raman study in La 1.475Nd 0.4Sr 0.125CuO 4

    NASA Astrophysics Data System (ADS)

    Nimori, S.; Hata, H.; Ogita, N.; Nakamura, F.; Sakita, S.; Kikugawa, N.; Fujita, T.; Udagawa, M.

    1999-03-01

    The totally symmetric phonons in La 1.475Nd 0.4Sr 0.125CuO 4 single crystal have been investigated by Raman scattering in the temperature range between 6 and 445 K. Five phonon modes were observed in the OMT phase. Among them, the energies of three modes at 226 cm -1, 273 cm -1 and 430 cm -1 at 106 K, increase slightly by about 2 cm -1 in the OLT and TLT phases. However, two modes at 120 and 155 cm -1 at 111 K show the remarkable changes in TLT phase. The energy of the former decreases by about 10 cm -1 and the latter splits into two peaks. From the normal mode analysis, this anomaly is understood by the existence of two different interactions of La-Cu and Nd-Cu for the TLT phase. The asymmetric line shape of the apical oxygen vibration has been observed and its line shape is well explained by the interference effect between the sharp phonon peak and broad electron response. Our result concludes the existence of the electron-phonon interaction in La 1.475Nd 0.4Sr 0.125CuO 4.

  6. Negative Thermal Expansion in Ba0.5Sr0.5Zn₂SiGeO₇.

    PubMed

    Thieme, Christian; Rüssel, Christian

    2016-07-27

    Solid solutions with the composition Ba0.5Sr0.5Zn₂Si2-xGexO₇ and BaZn₂Si2-xGexO₇ were prepared with different values of x using a conventional mixed oxide route. Both compounds exhibit very different thermal expansion, which is due to the different crystal structures. Ba0.5Sr0.5Zn₂Si2-xGexO₇ solid solutions exhibit the structure of high-temperature BaZn₂Si₂O₇ and show negative thermal expansion, which was proven via high-temperature X-ray diffraction. Up to around x = 1, the crystal structure remains the same. Above this value, the low-temperature phase becomes stable. The Sr-free solid solutions have the crystal structure of low-temperature BaZn₂Si₂O₇ and show also a limited solubility of Ge. These Sr-free compositions show transitions of low- to high-temperature phases, which are shifted to higher temperatures with increasing Ge-concentration.

  7. Nanostructural and electrical properties of LA0.5SR0.5CoO3

    NASA Astrophysics Data System (ADS)

    Bahari, A.; Ramzannezhad, A.; Shajari, D.; Najafi, H.

    2017-02-01

    A group of ABO3 perovskite-type oxides is currently under intensive studies for their potential as chemical sensing, ferroelectric memories, gas separation and computer devices. This group includes LaxSr1-xCoO3 (LSCO). In the present work, we have synthesized LSCO samples by using the sol-gel method and studied their nano structural and electrical properties with using the scanning electron microscopy (SEM), energy dispersive X-ray (EDX), Current density-voltage (J-V) and Fourier transform infrared spectroscopy (FTIR) techniques. We synthesized nanoparticles with diameters between 50 and 100 nm by calcination of the pulverized gel powders, and then studied its structure. The band gap characteristics of the La0.5Sr0.5CoO3 structure were also analyzed. The obtained results show that La0.5Sr0.5CoO3 with favorable carrier mobility ( ˜ 1.7 × 10-2 cm2v-2s-1) and dielectric constant (16) exhibits a variety of interesting physical properties which include ferroelectric, dielectric, pyroelectric and piezoelectric behavior.

  8. Magnetic properties of rare-earth-doped La0.7Sr0.3MnO3.

    PubMed

    Veverka, Pavel; Kaman, Ondřej; Knížek, Karel; Novák, Pavel; Maryško, Miroslav; Jirák, Zdeněk

    2017-01-25

    Rare-earth-doped ferromagnetic manganites La0.63RE0.07Sr0.30MnO3 (RE  =  Gd, Tb, Dy, and Ho) are synthesized in the form of sintered ceramics and nanocrystalline phases with the mean size of crystallites  ≈30 nm. The electronic states of the dopants are investigated by SQUID magnetometry and theoretically interpreted based on the calculations of the crystal field splitting of rare-earth energy levels. The samples show the orthorhombic perovskite structure of Ibmm symmetry, with a complete FM order of Mn spins in bulk and reduced order in nanoparticles. Non-zero moments are also detected at the perovskite A sites, which can be attributed to magnetic polarization of the rare-earth dopants. The measurements in external field up to 70 kOe show a standard Curie-type contribution of the spin-only moments of Gd(3+) ions, whereas Kramers ions Dy(3+) and non-Kramers ions Ho(3+) contribute by Ising moments due to their doublet ground states. The behaviour of non-Kramers ions Tb(3+) is anomalous, pointing to singlet ground state with giant Van Vleck paramagnetism. The Tb(3+) doping leads also to a notably increased coercivity compared to other La0.63RE0.07Sr0.30MnO3 systems.

  9. Investigation of the origin of glassiness in La0.5Sr0.5CoO3

    NASA Astrophysics Data System (ADS)

    Manna, Kaustuv; Elizabeth, Suja; Anil Kumar, P. S.

    2013-05-01

    A comprehensive magnetic study has been carried out on the two sets of La0.5Sr0.5CoO3 samples with a view to understand the origin of low temperature glassiness in the ferromagnetic state. The samples prepared by the conventional solid-state synthesis method show a low temperature shoulder in both dc magnetization as well as in the ac susceptibility measurements, which exhibit characteristics of glassiness such as the frequency dependence and memory effect. These observations suggest the existence of a distinct low temperature cluster-glass like phase within dominant ferromagnetic phase. But, once the same sample is properly homogenized by repeated grinding and annealing process, the low temperature glassy phase disappears, and it shows a pure ferromagnetic behavior. Our comparative study clearly reveals that the reentrant spin-glass like nature is not intrinsic to La0.5Sr0.5CoO3 system, in fact this is an outcome of the compositional inhomogeneity.

  10. Critical behavior and spontaneous magnetization estimation in La0.5Sr0.5MnO3 compound

    NASA Astrophysics Data System (ADS)

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

    2015-07-01

    We report the critical behavior in La0.5Sr0.5MnO3 perovskite oxide manganite using methods including modified Arrott plot, Kouvel-Fisher plot, and critical isotherm analysis. By means of the above techniques around the ferromagnetic-paramagnetic (FM-PM) transition, the magnetic data analyzed shows the sample attending the second-order magnetic phase transition with the critical parameters β = 0.553±0.020 with TC=352.02±0.63 K (from the spontaneous magnetization MS(T) below TC) and γ =1.169±0.058 with TC=352.49±0.85 K (from the inverse initial susceptibility χ 0 - 1 (T) above TC). The exponent δ =3,216 independently obtained from the critical magnetization isotherm satisfies the Widom scaling relation δ = 1 + β / γ . Moreover, the critical exponents are in the theoretically expected values for mean-field interaction model rather than the other universal theory and also follow the single scaling equation of M (H , ε)ε-β =f± (H /ε β + γ) . Furthermore, to estimate the spontaneous magnetization of La0.5Sr0.5MnO3 perovskite, we used the magnetic entropy change (-ΔSM), obtained from isothermal magnetization. The results of this approach are compared to results obtained from classical analysis using Arrott curves.

  11. 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.

  12. Interface-induced spontaneous positive and conventional negative exchange bias effects in bilayer La0.7Sr0.3MnO3/Eu0.45Sr0.55MnO3 heterostructures.

    PubMed

    Murthy, J Krishna; Kumar, P S Anil

    2017-07-31

    We report zero-field-cooled spontaneous-positive and field-cooled conventional-negative exchange bias effects in epitaxial bilayer composed of La0.7Sr0.3MnO3 (LSMO) with ferromagnetic (FM) and Eu0.45Sr0.55MnO3 (ESMO) with A-type antiferromagnetic (AF) heterostructures respectively. A temperature dependent magnetization study of LSMO/ESMO bilayers grown on SrTiO3 (001) manifest FM ordering (TC) of LSMO at ~320 K, charge/orbital ordering of ESMO at ~194 K and AF ordering (TN) of ESMO at ~150 K. The random field Ising model has demonstrated an interesting observation of inverse dependence of exchange bias effect on AF layer thickness due to the competition between FM-AF interface coupling and AF domain wall energy. The isothermally field induced unidirectional exchange anisotropy formed at the interface of FM-LSMO layer and the kinetically phase-arrested magnetic phase obtained from the metamagnetic AF-ESMO layer could be responsible for the spontaneous exchange bias effect. Importantly, no magnetic poling is needed, as necessary for the applications. The FM-AF interface exchange interaction has been ascribed to the AF coupling with [Formula: see text] ([Formula: see text], coupling constant between AF spins) for the spontaneous positive hysteresis loop shift, and the field-cooled conventional exchange bias has been attributed to the ferromagnetically exchanged interface with [Formula: see text] (coupling constant between FM spins).

  13. Elastic anomalies in Sr 0.9NbO 3 detected by a vibrating reed technique

    NASA Astrophysics Data System (ADS)

    Sugiyama, J.; Isawa, K.; Yamauchi, H.

    1995-07-01

    Both the Young's modulus sound velocity ( VE) and the internal friction ( Q-1) have been measured for a polycrystalline sample of Sr 0.9NbO 3 in the temperature range between 30 and 350 K. As temperature lowers from 350 K, VE increases monotonically, then decreases at 230 K (= T1) and exhibits a minimum at 80 K (= T2). The overall softening of the velocity between T1 and T2 is about 22.0 %. Furthermore, in the Q-1-vs.- T curve, three peaks are clearly observed around 315 K, 195 K and 55 K, respectively. The observed elastic anomalies suggest that structural phase transitions occurred successively around 230 K and 80 K.

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

    PubMed

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

    2012-12-12

    High-pressure electrical resistance measurements have been performed on single crystal Ba(0.5)Sr(0.5)Fe(2)As(2) 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., Ba(1-x)Sr(x)Fe(2)As(2) (0 < x < 1), can also exhibit superconductivity under high pressure.

  15. Anomalies of magnetostriction and thermal expansion in La 0.7Sr 0.3MnO 3 perovskite

    NASA Astrophysics Data System (ADS)

    Demin, R. V.; Koroleva, L. I.; Balbashov, A. M.

    1998-01-01

    It has been found that an anisotropic contribution to the magnetostriction λ t of a La 0.7Sr 0.3MnO 3 single crystal is essential at low temperatures ( λ t ˜ 10 -4 at 90 K). In the region of the Curie temperature T c the value of λ t decreases sharply with T. The bulk magnetostriction ω is negative in the T c region and the | ω|( T) curve has a maximum at T c. The temperature dependence of the thermal expansion Δ l/l at T > T c is stronger than linear. The anomalies of ω and Δ l/l are explained by magnetic phase separation.

  16. Fabrication and transport properties of Sr0.6K0.4Fe2As2 multifilamentary superconducting wires

    NASA Astrophysics Data System (ADS)

    Yao, Chao; Ma, Yanwei; Zhang, Xianping; Wang, Dongliang; Wang, Chunlei; Lin, He; Zhang, Qianjun

    2013-02-01

    Seven-core Ag/Fe sheathed Sr0.6K0.4Fe2As2 (Sr-122) superconducting wires were produced by the ex situ powder-in-tube method. The relationship between the cold-work deformation process and the superconducting properties of the wires was systematically studied. It was found that flat rolling can efficiently increase the mass density of the superconducting core, thus, significantly improving the transport critical current density (Jc) of the as-drawn wires. The transport Jc of the best sample achieved 21.1 kA/cm2 at 4.2 K in self field, and showed very weak magnetic field dependence at high fields. Our result suggested a promising future of multifilamentary iron-based superconductors in practical applications.

  17. Microwave study of Nd0.7Sr0.3MnO3 thin film resistivity

    NASA Astrophysics Data System (ADS)

    Claycomb, J. R.; Tralshawala, N.; Xie, L.-M.; Wosik, J.; Miller, J. H.

    1999-04-01

    We report on microwave studies of Nd0.7Sr0.3MnO3 thin film losses in a shielded TE011 dielectric cavity. The cavity quality (Q) factor and resonant frequency are measured as a function of temperature with the dielectric cavity loaded with a thin film on a LaAlO3 substrate. A reference Q measurement is then made without the film enabling the extraction of the film-Q factor Qfilm. Here the temperature dependence of the Q factor is discussed in terms of resistive losses in the thin film. A numerical finite difference time domain code is then used to extract the microwave resistivity as a function of temperature from the measured Q factors. The numerical method involves the discretization of Maxwell's equations on an axisymmetric space-time grid coupled to a discrete Fourier transform to determine the resonant frequency.

  18. Independent freezing of charge and spin dynamics in La1.5Sr0.5CoO4

    PubMed

    Zaliznyak; Hill; Tranquada; Erwin; Moritomo

    2000-11-13

    We present elastic and quasielastic neutron scattering measurements characterizing peculiar short-range charge-orbital and spin order in the layered perovskite material La1.5Sr0.5CoO4. We find that below T(c) approximately 750 K holes introduced by Sr doping lose mobility and enter a statically ordered charge glass phase with loosely correlated checkerboard arrangement of empty and occupied d(3z(2)-r(2)) orbitals ( Co3+ and Co2+). The dynamics of the resultant mixed spin system is governed by the anisotropic nature of the crystal-field Hamiltonian and the peculiar exchange pattern produced by the orbital order. It undergoes a spin freezing transition at a much lower temperature, T(s) less, similar30 K.

  19. Scaling law and flux pinning in polycrystalline La1.85Sr0.15CuO4

    NASA Astrophysics Data System (ADS)

    Hampshire, D. P.; Ikeda, J. A. S.; Chiang, Y.-M.

    1989-11-01

    The transport critical current density (Jct) of two hot-pressed bulk polycrystalline La1.85Sr0.15CuO4 superconducting samples has been measured over the temperature range 2 K to Tc in magnetic fields up to 27 T. It is demonstrated that these data have a separable variable form Fp=JctB=α(D)B2.4c2 (T)b [where α(D) is a constant and b=B/Bc2(T)], in agreement with the Fietz-Webb scaling law. This is strong evidence that in high magnetic fields, flux pinning is the mechanism that determines the critical current density. The authors suggest that the dissipative state is described by flux flow along the regions of weak flux pinning at the grain boundaries.

  20. First order phase transition in Sm0.53Sr0.47MnO3 films

    NASA Astrophysics Data System (ADS)

    Srivastava, Manoj K.; Singh, M. P.; Kaur, Amarjeet; Singh, H. K.

    2012-06-01

    In the present work Sm0.53Sr0.47MnO3 thin films were deposited on single crystal LAO (LaAlO3/(100)) substrates by DC magnetron sputtering. The θ-2 and ω-2θ scans show that these films are epitaxially grown and are under small compressive strain. The paramagnetic-ferromagnetic (insulator-metal) transition was found at TC˜126 K (at TIM˜128 K). The magnetic state at T

  1. 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.

  2. Magnetic, electronic, and thermal transport properties of Eu0.55Sr0.45MnO3

    NASA Astrophysics Data System (ADS)

    Wang, J. Z.; Sun, J. R.; Liu, G. J.; Xie, Y. W.; Wang, D. J.; Zhao, T. Y.; Shen, B. G.; Li, X. G.

    2007-09-01

    Magnetic, electronic, and thermal transport properties of Eu0.55Sr0.45MnO3 have been experimentally studied. The compound is found to exhibit a complex magnetic behavior with the change of temperature and magnetic field. Without magnetic field, it stays in a Griffiths-like state in a wide temperature range above ˜100K , characterized by the presence of ferromagnetic (FM) clusters of the size of ˜8 Mn ions, and an antiferromagnetic (AFM) state below ˜100K , evidenced by thermopower and heat conductivity. FM phase emerges and grows in the AFM matrix with applied field, resulting in a series of phase transitions from the paramagnetic (PM) state first to the AFM state, then to the FM and the AFM states upon cooling (˜0.8T˜2.3T) . The AFM state is unstable under high fields, and the high- and low-temperature AFM transitions are depressed by the fields above ˜1 and ˜2.3T , respectively. The FM transition is incomplete when the field is below ˜1.5T , leading to a coexistence of the FM and PM (or AFM) phases in the intermediate temperature range. A spin-glass-like behavior is observed in the AFM background below ˜50K . Significant response of resistance, thermopower, and heat conduction to magnetic transition, either FM or AFM transition, has been observed. Unlike the typical AFM manganites, for which usually a depression of thermal conduction occurs at the AFM state, the AFM transition in Eu0.55Sr0.45MnO3 enhances the thermal conduction. From the PM phase to the AFM phase and to the FM phase, thermal conductivity increases monotonically. A remarkable result of the present work is the different behaviors of thermopower and resistivity. The former displays a metallic behavior below a distinct temperature that is significantly lower than the metal-to-insulator transition temperature determined by resistivity. Furthermore, thermopower remains metallic while the resistivity shows up an upturn due to the AFM transition in the

  3. 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

    2015-04-06

    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.

  4. Microwave assisted hydrothermal synthesis and magnetocaloric properties of La0.67Sr0.33MnO3 manganite.

    PubMed

    Anwar, M S; Kumar, Shalendra; Ahmed, Faheem; Kim, G W; Koo, Bon Heun

    2012-07-01

    We report microwave assisted hydrothermal synthesis and magnetocaloric properties of La0.67Sr0.33MnO3 manganite. The synthesized La0.67Sr0.33MnO3 nanoparticles was characterized using X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), energy dispersive X-ray spectroscopy (EDS) and magnetization measurements. The XRD results indicated that La0.67Sr0.33MnO3 nanoparticles have polycrystalline nature with monoclinic structure. FE-SEM results suggested that La0.67Sr0.33MnO3 nanoparticles are assembled into rod like morphology. Magnetization measurements show that La0.67Sr0.33MnO3 nanoparticles exhibit transition temperature (Tc) above room temperature. The maximum magnetic entropy change (deltaS(M))max was found to be 0.52 J/kg K near Tc approximately 325 K at applied magnetc field of 20 kOe. This compound may considered as potential material for magnetic refrigeration near room temperature.

  5. A novel sol-gel route to synthesize (Sr0.5Ba0.5)Nb2O6 ceramics with enhanced electrocaloric effect

    NASA Astrophysics Data System (ADS)

    Chen, Ting; Wu, Shu Ya; Liu, Xiao Qiang; Chen, Xiang Ming

    (Sr0.5Ba0.5)Nb2O6 ultra-fine powders were synthesized by a novel sol-gel route, and the mechanism of the reaction was discussed. SrCO3, BaCO3, oxalate niobium and citric acid were used to initiate the sol-gel process, and ethylene glycol (EG) was added to further polymerize the cross-linking structure. The evolution of the (Sr0.5Ba0.5)Nb2O6 phase, the reaction process and the microstructures were investigated by X-ray diffraction (XRD), Raman spectroscopy, Fourier transform infrared spectroscopy, DSC-TG and scanning electron microscopy. The synthesis temperature of the (Sr0.5Ba0.5)Nb2O6 powders reached as low as 1200∘C, and the size and morphology of the powders were controlled by temperature. By adjusting the calcination temperature, we obtained (Sr0.5Ba0.5)Nb2O6 powders with uniform sizes of 20nm to 500nm. Then, dense (Sr0.5Ba0.5)Nb2O6 ceramics were successfully prepared using these ultrafine powders. Finally, an enhanced electrocaloric effect (ECE) value of 0.35∘C was obtained at 100kV/cm.

  6. Giant magnetoimpedance in Ag-doped La0.7Sr0.3MnO3

    NASA Astrophysics Data System (ADS)

    Ghatak, S. K.; Kaviraj, B.; Dey, T. K.

    2007-01-01

    The resistive and reactive parts of the magnetoimpedance of sintered ferromagnetic samples of La0.7Sr0.3-xAgxMnO3 (x=0.05,0.25) have been measured at room temperature (

  7. Effects of Ru substitution for Mn on La0.7Sr0.3MnO3 perovskites

    NASA Astrophysics Data System (ADS)

    Wang, L. M.; Lai, Jian-Hong; Wu, Jyh-Iuan; Kuo, Y.-K.; Chang, C. L.

    2007-07-01

    We report the investigations of crystal structure, electrical resistivity (ρ), magnetization (M), x-ray photoelectron spectroscopy (XPS), specific heat (CP), thermal conductivity (κ), and thermoelectric power (TEP) on La0.7Sr0.3(Mn1-xRux)O3 (LSMRO) compounds with x =0 to 0.90. From the analyzes of crystal structure and magnetization measurements, it is inferred that Ru should have a mixed valence of Ru3+ and Ru4+ for LSMRO with low level of Ru substitution, and an additional mixed valence of Ru4+ and Ru5+ with higher Ru substitution. Such a finding is further confirmed by the XPS measurements. Besides, it is found that all measured physical properties undergo pronounced anomalies due to the ferromagnetic-paramagnetic phase transition, and the observed transport properties of LSMRO can be reasonably understood from the viewpoint of polaronic transport. The Curie temperatures TC determined from the magnetization measurements are consistently higher than those of the metal-insulator transitions TMI determined from the transport measurements. By replacing Mn with Ru, both TC and TMI decrease concurrently and the studied materials are driven toward the insulating phase with larger value of x. It is also found that the entropy change during the phase transition is reduced with more Ru substitution. These observations indicate that the existence of Ru has the effect of weakening the ferromagnetism and metallicity of the LSMRO perovskites.

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

    PubMed Central

    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

    2016-01-01

    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. PMID:26928070

  9. [Spectroscopic properties of Er3+ : Ba0.65Sr0.35TiO nanopowders].

    PubMed

    Wu, Ji-qing; Zhang, Tian-jin; Wang, Jing-yang; Yu, Lin; Pan, Rui-kun

    2010-11-01

    Ba0.65Sr0.35TiO2 (BST) nanopowders doped with Er3+ were prepared by sol-gel method. The absorption spectrum and photoluminescence (PL) spectrum of Er3+ : BST nanopowders was measured at room temperature. Based on the Judd-Ofelt theory, the intensity parameters of Er3+ in BST nanopowders were determined, omega2 = 0.993 x 10(-20) cm2, omega4 = 1.665 x 10(-20) cm2 and omega = 0.540 x 10(-20) cm2, and then the values of the line strengths, radiative transition probabilities and branching ratios of Er3+ were calculated. According to the PL spectrum, the emission bands centered at about 522, 545, 654 and 851 nm corresponding to 2H(11/2)-->4S(3/2-->4I(15/2), 4F(9/2)-->4I(15/2), and 4S(3/2-->4I(13/2) transition were observed, and the emission properties were also discussed. The results show that the Er3+ : BST nanomaterials are prospective candidates for applications in new photoelectric devices.

  10. 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

  11. Investigation of ferromagnetic heterogeneities in La0.7Sr0.3MnO3 thin films

    NASA Astrophysics Data System (ADS)

    Mercone, S.; Belmeguenai, M.; Malo, S.; Ott, F.; Cayrel, F.; Golosovsky, M.; Leridon, B.; Adamo, C.; Monod, P.

    2017-02-01

    La0.7Sr0.3MnO3 manganite thin films are interesting since they have a fully spin-polarized conduction band at room temperature and this opens the way for applications in electronics. An important issue is their magnetic heterogeneity, which is very difficult to detect. We address here the heterogeneity detection issue in two epitaxial LSMO thin films (57 nm and 90 nm thick) on Si substrate fabricated by reactive molecular beam epitaxy (MBE) deposition. Combining three complementary analytic techniques, we measured structural and magnetic behavior of these films. The high frequency ferromagnetic resonance behavior observed in these two LSMO samples put in evidence a standard dynamic behaviour in the case of the homogeneous material and an uncommon multi-mode behavior in the heterogeneous bi-layered film. The multi-mode behavior can be attributed to the presence of two magnetic sub-layers inside the LSMO film. Indeed, transmission electron microscopy observations and neutron reflectivity measurements are essential to give a microscopic description of the structure and intrinsic magnetic homo/heterogeneity of the composite film.

  12. Effect of La0.67Sr0.33MnO3 electrodes on organic spin valves

    NASA Astrophysics Data System (ADS)

    Majumdar, Sayani; Huhtinen, H.; Majumdar, H. S.; Laiho, R.; Österbacka, R.

    2008-08-01

    We report the effect of La0.7Sr0.3MnO3 (LSMO) electrodes on the temperature dependence of the magnetoresistance (MR) of LSMO/polymer/cobalt spin valves (SVs). LSMO films have been prepared by pulsed laser deposition on three different single crystal substrates using different deposition parameters. The films were characterized for their surface morphologies, structural, magnetic, and magnetotransport properties. Low deposition rate is found to be detrimental for growth of good quality films and polycrystalline films with grain boundary effects are observed in thicker films. The films on MGO (100) substrate show a broad paramagnetic to ferromagnetic transition, accompanied with a metal-insulator transition below room temperature. This indicates growth of some strained structures due to large lattice mismatch (9%) between the substrate and the film and presence of polycrystalline grain boundaries. The deposited films on STO (100) and NGO (001) show much sharper magnetic transition and metallic behavior indicating higher spin polarization (SP) of LSMO on these substrates at room temperature. SVs made on STO (100) show improvement in switching behavior and better MR response compared to the devices made on MGO (100) at low temperatures. No difference in MR response was found at room temperature in either case. We conclude that the bulk spin polarization of LSMO films is not very important in the SV operation. The loss of most of the SP carriers at the LSMO/organic semiconductor interface at room temperature is a more dominant effect and drastically reduces the MR signal.

  13. Critical phenomena in Pr0.6Sr0.4MnO3 perovskite manganese oxide

    NASA Astrophysics Data System (ADS)

    Hcini, Sobhi; Zemni, Sadok; Baazaoui, M.ed; Dhahri, Jamila; Vincent, Henri; Oumezzine, M.ed

    2012-05-01

    We studied the critical phenomena of perovskite-manganite compound Pr0.6Sr0.4MnO3 around its Curie temperature. Experimental results based on magnetic measurements using Banerjee criterion revealed that the sample exhibits the second-order paramagnetic-ferromagnetic transition. It is found that the critical behaviour analysis and Kouvel-Fisher method show that the 3D- Heisenberg model is the best one to describe the critical phenomena around the critical point. Critical exponents β = 0.3785(6) and γ = 1.304(12) at TC = 320 K are obtained. The critical exponent δ = 4.7183(2) is determined separately from the isothermal magnetization at TC. These critical exponents fulfil the Widom scaling relation δ = 1 + γ/β. Based on the critical exponents, the magnetization-field-temperature (M-H-T) data around TC collapses into two curves obeying the single scaling equation M(H,ɛ)=|f(H/|) with ɛ = (T - TC)/TC is the reduced temperature.

  14. 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.

  15. Variation of the Ru moment in the Ca(0.3)Sr(0.7)Ru(1-x)Mn(x)O3 system.

    PubMed

    Mizusaki, S; Naito, M; Taniguchi, T; Nagata, Y; Itou, M; Sakurai, Y; Noro, Y; Ozawa, T C; Samata, H

    2010-04-14

    The variation of the magnetic moment on Ru and Mn atoms in the Ca(0.3)Sr(0.7)Ru(1-x)Mn(x)O(3) system was investigated by the magnetic Compton scattering technique using synchrotron radiation. The Ca(0.3)Sr(0.7)Ru(1-x)Mn(x)O(3) system has ferrimagnetism with an antiferromagnetic coupling between Ru and Mn, and the dominant magnetic component changes from ferromagnetic Ru to ferromagnetic Mn at x ∼0.25 as the Mn substitution proceeds. The mechanism for the change in the magnetism of Ca(0.3)Sr(0.7)Ru(1-x)Mn(x)O(3) is discussed.

  16. Sc-substituted La0.6Sr0.4FeO3-δ mixed conducting oxides as promising electrodes for symmetrical solid oxide fuel cells

    NASA Astrophysics Data System (ADS)

    Liu, Xuejiao; Han, Da; Zhou, Yucun; Meng, Xie; Wu, Hao; Li, Junliang; Zeng, Fanrong; Zhan, Zhongliang

    2014-01-01

    The main barrier to symmetrical solid oxide fuel cells (SOFCs), where the same catalytic materials are used simultaneously as the anodes and the cathodes, is to identify a redox-stable catalyst that exhibits superior catalytic activities for both fuel oxidation and oxygen reduction reactions. Here we report a Sc-substituted La0.6Sr0.4FeO3-δ oxide, La0.6Sr0.4Fe0.9Sc0.1O3-δ, that shows great promise as a new symmetrical electrode material with good structural stability and reasonable conductivities in air and hydrogen. We further demonstrate that nano-scale La0.6Sr0.4Fe0.9Sc0.1O3-δ catalysts impregnated into the porous La0.9Sr0.1Ga0.8Mg0.2O3-δ backbones exhibit good catalytic activities for oxygen reduction and hydrogen oxidation reactions and thereby yield low polarization resistances, e.g., 0.015 Ω cm2 in air and 0.29 Ω cm2 in hydrogen with appropriate current collection at 800 °C. Thin La0.9Sr0.1Ga0.8Mg0.2O3-δ electrolyte fuel cells with such symmetrical La0.6Sr0.4Fe0.9Sc0.1O3-δ catalysts showed maximum power densities of 0.56 and 0.32 W cm-2 when operating on 97% H2-3% H2O at 800 and 700 °C, respectively.

  17. Displacement waves in La2CuO(4-delta) and La(1.85)Sr(0.15)CuO(4-delta)

    NASA Astrophysics Data System (ADS)

    Kajitani, Tsuyoshi; Onozuka, Takashi; Yamaguchi, Yasuo; Hirabayashi, Makoto; Syono, Yasuhiko

    1987-11-01

    Structural investigation of orthorhombic La2CuO(4-delta) and La(1.85)Sr(0.15)CuO(4-delta) was carried out by means of X-ray and neutron diffraction on the basis of the space group Cmmm. The periodic expansion/contraction type distortion of CuO6 octahedra was found in both orthorhombic compounds. The distortion is nearly one-dimensional in La2CuO(4-delta) but is two-dimensional in La(1.85)Sr(0.15)CuO(4-delta). The existence of a charge-density wave is highly possible in the structures.

  18. Synthesis and photocatalytic property for H2 production of H1.78Sr0.78Bi0.22Nb2O7 nanosheets

    NASA Astrophysics Data System (ADS)

    Zhang, Bing; Li, Yingxuan; Luo, Jianmin; Zhao, He; Zhao, Jie; Dong, Guohui; Zhu, Yunqing; Wang, Chuanyi

    2017-01-01

    The SrBi2Nb2O9 platelets with a thickness of about 600 nm were synthesized by molten salt synthesis method. The treatment of the SrBi2Nb2O9 platelets with hydrochloric acid resulted in the formation of the protonated H1.78Sr0.78Bi0.22Nb2O7 platelets. Through a top-down approach in ethylamine solution, the H1.78Sr0.78Bi0.22Nb2O7 platelets were exfoliated into H1.78Sr0.78Bi0.22Nb2O7 nanosheets with a thickness of about 2.6 nm. The evolution of the structure, composition, morphology, optical, and photocatalytic properties of SrBi2Nb2O9 platelets was studied as it is converted into H1.78Sr0.78Bi0.22Nb2O7 platelets and subsequently exfoliated into H1.78Sr0.78Bi0.22Nb2O7 nanosheets. The absorption edge shifts to a lower wavelength accompanied by the protonation and exfoliation. The photocatalytic H2 evolution of the three samples were evaluated under the irradiation of a 300 W Xenon lamp from CH3OH/H2O solution, indicating that H1.78Sr0.78Bi0.22Nb2O7 nanosheets Exhibit 5.5 and 26.2 times higher activity than that of the H1.78Sr0.78Bi0.22Nb2O7 and SrBi2Nb2O9 platelets, respectively. The enhanced activity for the H1.78Sr0.78Bi0.22Nb2O7 nanosheets is mainly attributed to the higher separation efficiency of the photogenerated carriers and the larger specific surface area caused by the significant reduction in thickness.

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

    DOE PAGES

    Meyer, Tricia L; Jiang, Lu; Park, Sungkyun; ...

    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.

  20. Effect of strontium deficiency on the transport and magnetic properties of Pr 0.7Sr 0.3MnO 3

    NASA Astrophysics Data System (ADS)

    Abou-Ras, D.; Boujelben, W.; Cheikh-Rouhou, A.; Pierre, J.; Renard, J.-P.; Reversat, L.; Shimizu, K.

    2001-08-01

    Ceramic samples of Pr 0.7Sr 0.3- x□ xMnO 3 with x⩽0.2 have been investigated by various techniques including 55Mn nuclear magnetic resonance, SQUID magnetometry, resistivity and magnetoresistance measurements. On increasing x, the samples remain ferromagnetic at a low temperature with a decreasing Curie temperature, but a metal-insulator transition is observed. Besides, a positive magnetoresistance (MR) at very low temperatures with respect to a negative colossal MR at high temperatures is observed in the Pr 0.7Sr 0.2□ 0.1MnO 3 sample.

  1. Effect of Y doping on magnetic and transport properties of La0.7Sr0.3CoO3

    NASA Astrophysics Data System (ADS)

    Dwivedi, G. D.; Shukla, K. K.; Shahi, P.; Jha, O. K.; Ghosh, A. K.; Nigam, A. K.; Chatterjee, Sandip

    2013-02-01

    The temperature variation of magnetization, resistivity and thermo electric power of undoped and Y-doped La0.7Sr0.3CoO3 samples have been investigated. Y-doping decreases the magnetization possibly due to the spin state transition of Co-ions. The low temperature conduction in (La1-yYy)0.7Sr0.3CoO3 is consistent with the variable range hopping. With Y doping, value of the Seebeck coefficient increases, as Y doping decreases bandwidth and increases distortion.

  2. Structural and magnetic properties of Sr0.5Co0.5Fe2O4 nanoferrite

    NASA Astrophysics Data System (ADS)

    Abdallah, Hafiz M. I.; Moyo, Thomas; Ezekiel, Itegbeyogene P.; Osman, Nadir S. E.

    2014-09-01

    The nanoparticle Sr0.5Co0.5Fe2O4 powder was produced via glycol-thermal process from high-purity metal chlorides at a low reaction temperature of 200 °C. The phase identification of the as-synthesized powder reveals cubic spinel structure with an average crystallite size of 8 nm. Room-temperature Mössbauer spectra for the as-synthesized sample and samples annealed at different temperatures show different local environments of tetrahedral and octahedral coordinated iron cations. Magnetic properties of the as-synthesized sample and samples annealed at 300, 400, 450, 500, 600, 700 and 800 °C have been investigated using a vibrating sample magnetometer at room-temperature in applied magnetic fields of up to about 1.4 T. A substantial increase in coercive field at 300 K from 0.28 kOe to 2.897 kOe was obtained for the as-synthesized and annealed sample at 800 °C. Magnetic field dependence of magnetization curves measured on a mini-cryogen free VTI system operating at a base temperature of 2 K in magnetic fields of up to 5 T have been investigated. The variation of the saturation magnetization as a function of temperature follows modified Bloch's law. Coercive field increased from about 0.28 kOe and 1.04 kOe at 300 K to 11.14 kOe and 10.43 kOe at 2 K for the as-synthesized sample and sample annealed at 500 °C, respectively because of spin-freezing. The effect of exchange bias and Kneller's law are used to account for the temperature dependence of coercive fields.

  3. Crystal structures, strain analysis, and physical properties of Sr0.7Ce0.3MnO3

    NASA Astrophysics Data System (ADS)

    Zhang, Zhaoming; Kennedy, Brendan J.; Howard, Christopher J.; Carpenter, Michael A.; Miiller, Wojciech; Knight, Kevin S.; Matsuda, Motohide; Miyake, Michihiro

    2012-05-01

    We have studied the crystal structure of mixed-valence Sr0.7Ce0.3MnO3 from 4.2 to 973 K using high-resolution neutron powder diffraction. The crystal structure is tetragonal in space group I4/mcm at 4.2-923 K and cubic in Pm3¯m at T ≥ 948 K. Lattice parameters and Mn-O bond distances, obtained by Rietveld refinement, have been used to derive the spontaneous strains and MnO6 octahedral distortion, which are interpreted in terms of strain/order parameter coupling using a single Landau free-energy expansion for a Pm3¯m reference structure with two instabilities (R4+ and Γ3+). Two phase transitions were proposed: an octahedral tilting transition at Tc,φ ˜ 938 K (Pm3¯m↔ I4/mcm, R4+), and an isosymmetric, electronically driven (Jahn-Teller-like) transition at Tc,JT ˜ 770 K (I4/mcm, R4+ ↔ I4/mcm, R4+ and Γ3+). The nature of the tilting transition appears to be tricritical, while that of the Jahn-Teller-like transition is second order. In addition to the contributions from octahedral tilting and Jahn-Teller-like distortions, there is an excess octahedral distortion at temperatures below 250 K; this is speculated to be associated with an anomaly observed over the temperature range of 275-300 K in the heat-capacity measurements.

  4. Evidence for decoupled two-dimensional vortex behavior of YBa2Cu3O7-δ in La0.7Sr0.3MnO3/YBa2Cu3O7-δ/La0.7Sr0.3MnO3 trilayer

    NASA Astrophysics Data System (ADS)

    Samal, D.; Anil Kumar, P. S.

    2010-12-01

    We investigate the vortex behavior of YBa2Cu3O7-δ thin films sandwiched between two ferromagnetic layers (La0.7Sr0.3MnO3/YBa2Cu3O7-δ/La0.7Sr0.3MnO3). The magnetization study on La0.7Sr0.3MnO3/YBa2Cu3O7-δ/La0.7Sr0.3MnO3 trilayers conspicuously shows the presence of both ferromagnetic and diamagnetic phases. The magnetotransport study on the trilayers reveals a significant reduction in the activation energy (U) for the vortex motion in YBa2Cu3O7-δ. Besides, the "U" exhibits a logarithmic dependence on the applied magnetic field which directly indicates the existence of decoupled two-dimensional (2D) pancake vortices present in the CuO2 layers. The evidence of 2D decoupled vortex behavior in La0.7Sr0.3MnO3/YBa2Cu3O7-δ/La0.7Sr0.3MnO3 is believed to arise from (a) the weakening of superconducting coherence length along the c-axis and (b) enhanced intraplane vortex-vortex interaction due to the presence of ferromagnetic layers.

  5. Reduction properties of phases in the system La 0.5Sr 0.5MO 3 ( M=Fe, Co)

    NASA Astrophysics Data System (ADS)

    Berry, Frank J.; Marco, José F.; Ren, Xiaolin

    2005-04-01

    Phases formed by the reduction of compounds of the type La 0.5Sr 0.5MO 3 ( M=Fe, Co) have been characterized by means of temperature programmed reduction, X-ray powder diffraction, 57Fe Mössbauer spectroscopy and Fe K-, Co K-, Sr K-, and La L III-edge X-ray absorption spectroscopy. The results show that treatment of the material of composition La 0.5Sr 0.5FeO 3 (which contains 50% Fe 4+ and 50% Fe 3+) at 650 °C in a flowing 90% hydrogen/10% nitrogen atmosphere results in the formation of an oxygen-deficient perovskite-related phase containing only trivalent iron. Further heating in the gaseous reducing environment at 1150 °C results in the formation of the Fe 3+-containing phase SrLaFeO 4, which has a K 2NiF 4-type structure, and metallic iron. The material of composition La 0.5Sr 0.5CoO 3 is more susceptible to reduction than the compound La 0.5Sr 0.5FeO 3 since, after heating at 520 °C in the hydrogen/nitrogen mixture, all the Co 4+ and Co 3+ are reduced to metallic cobalt with the concomitant formation of strontium- and lanthanum-oxides.

  6. Microstructure and electrical properties of La 0.7Sr 0.3MnO 3 thin films deposited by metallo-organic decomposition method

    NASA Astrophysics Data System (ADS)

    Wang, Zhan Jie; Usuki, Hirokazu; Kumagai, Toshihide; Kokawa, Hiroyuki

    2006-07-01

    Lanthanum strontium manganate (La 0.7Sr 0.3MnO 3: LSMO) thin films were grown on SiO 2/Si substrates by a metallo-organic decomposition method, and their crystalline structure, microstructure and electrical properties were investigated. X-ray diffraction analysis indicated that La 0.7Sr 0.3MnO 3 films with a perovskite single phase could be obtained by annealing at 700 °C. Transmission electron microscopy (TEM) images showed that the films consisted of packed grains with a mean grain size of approximately 25 nm. The resistivity of the La 0.7Sr 0.3MnO 3 films decreased rapidly as the annealing temperature increased from 550 to 700 °C, and did not change greatly with increasing annealing temperature from 700 °C. The La 0.7Sr 0.3MnO 3 films annealed at 700 °C had a lower resistivity of 5.70×10 -4 Ω m.

  7. 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.

  8. 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.

  9. Dimensionality of the electronic states in Nd0.45Sr0.55MnO3 studied by soft X-ray photoemission

    NASA Astrophysics Data System (ADS)

    Fujiwara, H.; Sekiyama, A.; Yano, M.; Murakawa, T.; Miyamachi, T.; Tsunekawa, M.; Imada, S.; Schmid, B.; Sing, M.; Higashiya, A.; Muro, T.; Nakamura, T.; Noda, K.; Kuwahara, H.; Miyasaka, S.; Tokura, Y.; Suga, S.

    2007-03-01

    The electronic states of Nd0.45Sr0.55MnO3 in the two-dimensional metal phase have been revealed by the high-resolution Mn 2p-3d resonant photoemission. The vanishingly weak intensity at EF indicates an anomalous metal due to the two-dimensionality of the electronic states.

  10. 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. Copyright © 2015 John Wiley & Sons, Ltd.

  11. Blockage of domain growth by nanoscale heterogeneities in a relaxor ferroelectric Sr0.61Ba0.39Nb2O6

    NASA Astrophysics Data System (ADS)

    Pertsev, N. A.; Gainutdinov, R. V.; Bodnarchuk, Ya. V.; Volk, T. R.

    2015-01-01

    The growth of localized subsurface domains in a relaxor ferroelectric Sr0.61Ba0.39Nb2O6 is studied using the technique of piezoresponse force microscopy (PFM). Ferroelectric domains are created by applying moderate voltages of 10-50 V to the conductive tip of a scanning force microscope brought into contact with a nonpolar face of a Sr0.61Ba0.39Nb2O6 crystal. PFM images of written domains are acquired and analyzed quantitatively to determine the domain length along the polar axis and its width in the transverse direction. The dependences of domain sizes on the applied voltage, pulse duration, and the time passed after completion of the voltage pulse are reported and analyzed theoretically. It is shown that the observed kinetics of domain growth can be explained by the creep of domain boundaries occurring in the presence of random electric fields inherent in Sr0.61Ba0.39Nb2O6. The comparison of measured domain sizes with their equilibrium values calculated with the aid of the thermodynamic theory demonstrates that the growth of subsurface domains in Sr0.61Ba0.39Nb2O6 is blocked by nanoscale heterogeneities characteristic of this relaxor ferroelectric. These results may have important implications for the development of nonlinear optical devices based on nanoheterogeneous ferroelectrics.

  12. Self-construction of magnetic hollow La0.7Sr0.3MnO3 microspheres with complex units.

    PubMed

    Chu, Xuefeng; Huang, Keke; Han, Mei; Feng, Shouhua

    2013-04-15

    Perovskite structure La0.7Sr0.3MnO3 magnetic hollow microspheres with complex units were prepared via the hydrothermal route without hard and soft templates. The formation of hollow microspheres follows the self-construction mechanism involving oriented attachment, dissolution, and recrystallization processes. It exhibits a ferromagnetic behavior at room temperature.

  13. Effect of Heat Treatment on The Crystal Structur, Electrical Conductivity and Surface of Ba1.5Sr0.5Fe2O5 Composite

    NASA Astrophysics Data System (ADS)

    Purwanto, P.; Adi, WA; Yunasfi

    2017-05-01

    The Composite of Ba1,5Sr0,5Fe2O5 has been synthesized by using powder metallurgy technique. The Ba1.5Sr0.5Fe2O5 were prepared from BaCO3, SrCO3 and Fe2O3 raw materials with a specific weight ratio. The three materials were synthesized by powder metallurgy under heat treatment at 800 °C, 900 °C, and 1000 °C for 5 hours. All the three samples were characterized by using X-ray Diffraction (XRD) to determine the crystal structure and crystal size, LCR meter to determine the conductivity, and Scanning Electron Microscope (SEM) to observe the morphological of the composites. The phase analysis result showed that the composite consists of several minor phases such as BaO2, SrO2, and Fe2O3. The Crystal size of composite Ba1.5Sr0.5Fe2O5 decreased while increases the strain of crystal with increasing of sintering temperature. The crystal size of the Ba1.5Sr0.5Fe2O5 composite is 3.55 nm to 7.23 nm and value of strain is 8.47% until 3.90%. Based on the conductivity measurement, it was obtained that the conductivity of the Ba1.5Sr0.5Fe2O5 composite decreased with increasing sintering temperature. It was also noticed that the conductivity increased with increasing of frequency. The conductivity ranged from 6.619×10-7 S/cm to 65.659×10-7 S/cm. The energy dispersive spectroscopy (EDS) analysis showed that several dominant elements were a good agreement with the phase analysis.

  14. Influence of Co-substitution on the structural and magnetic properties of nanocrystalline Ba0.5Sr0.5Fe12O19

    NASA Astrophysics Data System (ADS)

    Ezhil Vizhi, R.; Harikrishnan, V.; Saravanan, P.; Rajan Babu, D.

    2016-10-01

    One-step citrate gel combustion method followed by annealing (800 °C/2 h) was employed to synthesize cobalt substituted barium strontium hexaferrite with a chemical composition of Ba0.5Sr0.5Fe12-xCoxO19 (x=0, 0.5, 0.7, and 0.9). A combination of thermo-gravimetric analysis and differential scanning calorimetry was employed to understand the thermo-chemical behavior of Ba0.5Sr0.5Fe12O19. X-ray diffraction (XRD) was used to evaluate the hexagonal phase evolution for the barium strontium ferrite nanopowders and a formation of secondary phase: α-Fe2O3 is evident for the Ba0.5Sr0.5Fe12O19. Raman spectroscopy confirmed the presence of different sublattices of Fe3+ present in the hexaferrite structure. Fourier transform infrared spectroscopy demonstrated the usual stretching vibrations of tetrahedral and octahedral M-O bands. The morphology and chemical composition of the samples were analyzed by transmission electron microscopy and field emission scanning electron microscopy attached with energy dispersive X-ray analysis, respectively. Selected area electron diffraction studies showed the nanocrystalline nature of the samples. The magnetic parameters such as saturation magnetization MS, coercivity, HC and remanent magnetization, MR were estimated from the hysteresis loops. Maximum value of MS (70.5 emu/g) was obtained for the Ba0.5Sr0.5Fe11.5Co0.5O19 nanoparticles. A possible growth mechanism on the crystallization of Ba0.5Sr0.5Fe12O19 hexagonal platelets during the citrate gel combustion synthesis is highlighted.

  15. 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.

  16. 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.

  17. 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.

  18. Oxygen diffusion in Sr0.75Y0.25CoO2.625 : A molecular dynamics study

    NASA Astrophysics Data System (ADS)

    Rupasov, D.; Chroneos, A.; Parfitt, D.; Kilner, J. A.; Grimes, R. W.; Istomin, S. Ya.; Antipov, E. V.

    2009-05-01

    Oxygen diffusion in Sr0.75Y0.25CoO2.625 is investigated using molecular dynamics simulations in conjunction with an established set of Born model potentials. We predict an activation energy of diffusion for 1.56 eV in the temperature range of 1000-1400 K. We observe extensive disordering of the oxygen ions over a subset of lattice sites. Furthermore, oxygen ion diffusion both in the a-b plane and along the c axis requires the same set of rate-limiting ion hops. It is predicted that oxygen transport in Sr0.75Y0.25CoO2.625 is therefore isotropic.

  19. Electrical properties of La0.67Sr0.33Mn0.7Ni0.3O3 synthesized by sol gel method

    NASA Astrophysics Data System (ADS)

    Widyaiswari, U.; Kurniawan, B.; Andika, R.; Laksanawati, W. D.; Fauziyah, I.; Imaduddin, A.

    2017-07-01

    Our previous study showed that La0.67Sr0.33MnO3 (LSMO) compound has Curie temperature, TC, above room temperature. In order to shift TC of the compound near room temperature, Ni doped was introduced to the Mn site of LSMO. In this paper, 30% Mn site was doped by Ni. La0.67Sr0.33Mn0.7Ni0.3O3 compound synthesized by sol-gel method and characterized by using X-ray Diffraction (XRD). Then single phase compound's resistivity was measured to see the electrical properties of this compound. The XRD result showed that the samples have a single phase with rhombohedral structure and R-3c space group. The resistivity measurement as a function of temperature did not show resistivity peak and metal-insulator transition. Below 300 K, the resistivity increased with decreasing of temperature which indicated insulator behavior.

  20. Atomic-Scale Electronic Spectra across BiFeO3/La0.7Sr0.3MnO3 Complex Oxide Heterointerfaces

    NASA Astrophysics Data System (ADS)

    Chiu, Ya-Ping; Huang, Bo-Chao; Yu, Pu; Ramesh, Ramamoorthy; Chu, Ying-Hao

    2014-03-01

    Atomic-scale evolution of electronic structures across BiFeO3/La0.7Sr0.3MnO3 complex oxide heterointerfaces has been revealed using cross-sectional scanning tunneling microscopy and spectroscopy. Analysis of scanning tunneling spectroscopy results exploits the interfacial valence mismatch to influence the electrostatic configurations across the BiFeO3/La0.7Sr0.3MnO0.3 heterointerfaces. Spatially unit-cell-by-unit-cell resolved electronic states at the atomic level reveal how the control of material interfaces at the atomic level to determine the ferroelectric polarization in BiFeO3. Department of Chemical Engineering, Tsinghua University, Beijing 100084, China.

  1. Tuning the dead-layer behavior of La0.67Sr0.33MnO3/SrTiO3 via interfacial engineering

    NASA Astrophysics Data System (ADS)

    Peng, R.; Xu, H. C.; Xia, M.; Zhao, J. F.; Xie, X.; Xu, D. F.; Xie, B. P.; Feng, D. L.

    2014-02-01

    The dead-layer behavior, deterioration of the bulk properties in near-interface layers, restricts the applications of many oxide heterostructures. We present the systematic study of the dead-layer in La0.67Sr0.33MnO3/SrTiO3 grown by ozone-assisted molecular beam epitaxy. Dead-layer behavior is systematically tuned by varying the interfacial doping, while unchanged with varied doping at any other atomic layers. In situ photoemission and low energy electron diffraction measurements suggest intrinsic oxygen vacancies at the surface of ultra-thin La0.67Sr0.33MnO3, which are more concentrated in thinner films. Our results show correlation between interfacial doping, oxygen vacancies, and the dead-layer, which can be explained by a simplified electrostatic model.

  2. Precise lattice parameter measurements of Sr0.72Ba0.25Nb2O5.97 single crystals

    NASA Astrophysics Data System (ADS)

    Paszkowski, R.; Wokulska, K. B.; Dec, J.; Łukasiewicz, T.

    2014-09-01

    Pure and undoped strontium-barium niobate Sr0.72Ba0.25Nb2O5.97 single crystals grown by the Czochralski method were investigated. Using X-ray Bond's method lattice parameters of this crystals are determined with high accuracy in the order of Δd/d=10-5. Based on the lattice parameter data measured at 298 K it was ascertained that the Sr0.72Ba0.25Nb2O5.97 single crystals belong to the tetragonal system. The additional analysis of the diffraction patterns performed by the Laue method confirmed the occurrence of a four-fold axis of symmetry.

  3. Growth and interface engineering in thin-film Ba0.6Sr0.4TiO3 /SrMoO3 heterostructures

    NASA Astrophysics Data System (ADS)

    Radetinac, Aldin; Ziegler, Jürgen; Vafaee, Mehran; Alff, Lambert; Komissinskiy, Philipp

    2017-04-01

    Epitaxial heterostructures of ferroelectric Ba0.6Sr0.4TiO3 and highly conducting SrMoO3 were grown by pulsed laser deposition on SrTiO3 (0 0 1) substrates. Surface oxidation of the SrMoO3 film is suppressed using a thin cap interlayer of Ba0.6Sr0.4TiO3-δ grown in reduced atmosphere. As shown by X-ray photoelectron spectroscopy, the Mo4+ valence state of the SrMoO3 films is stable upon annealing of the sample in oxygen up to 600 °C. The described oxygen interface engineering enables utilization of the highly conducting material SrMoO3 in multilayer oxide ferroelectric varactors.

  4. 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.

  5. Tailoring magnetic interlayer coupling in La0.7Sr0.3MnO3/SrRuO3 superlattices.

    PubMed

    Ziese, M; Vrejoiu, I; Pippel, E; Esquinazi, P; Hesse, D; Etz, C; Henk, J; Ernst, A; Maznichenko, I V; Hergert, W; Mertig, I

    2010-04-23

    The magnetic interlayer coupling in La0.7Sr0.3MnO3/SrRuO3 superlattices was investigated. High quality superlattices with ultrathin La0.7Sr0.3MnO3 and SrRuO3 layers were fabricated by pulsed laser deposition. The superlattices grew coherently with Mn/Ru intermixing restricted to about one interfacial monolayer. Strong antiferromagnetic interlayer coupling depended delicately on magnetocrystalline anisotropy and intermixing at interfaces. Ab initio calculations elucidated that the antiferromagnetic coupling is mediated by the Mn-O-Ru bond. The theoretical calculations allowed for a quantitative correlation between the total magnetic moment of the superlattice and the degree of Mn/Ru intermixing.

  6. The nanoscopic separation of magnetic phases in Cr-doped manganites Pr0.44Sr0.56MnO3

    NASA Astrophysics Data System (ADS)

    Knížek, K.; Jirák, Z.; Hejtmánek, J.; Maryško, M.; Martin, C.; Maignan, A.; Hervieu, M.

    2004-05-01

    Magnetic and electric transport investigation on a Pr0.44+y/2Sr0.56-y/2Mn1-yCryO3 (y=0-0.15) series reveal that the low-temperature state is at lower Cr doping composed of segregated FM and A-type AFM phases while for y>=0.9 a new non-uniform magnetic state is formed, characterized by distinctly higher TC and relatively low saturated moment.

  7. Synthesis crystal structure and ionic conductivity of Ca 0.5Bi 3V 2O 10 and Sr 0.5Bi 3V 2O 10

    NASA Astrophysics Data System (ADS)

    Porob, Digamber G.; Guru Row, T. N.

    2004-12-01

    Two new compounds Ca 0.5Bi 3V 2O 10 and Sr 0.5Bi 3V 2O 10 have been synthesized in the ternary system: MO-Bi 2O 3-V 2O 5 system ( M=M 2+). The crystal structure of Sr 0.5Bi 3V 2O 10 has been determined from single crystal X-ray diffraction data, space group P1¯ and Z=2, with cell parameters a=7.1453(3) Å, b=7.8921(3) Å, c=9.3297(3) Å, α=106.444(2)°, β=94.088(2)°, γ=112.445(2)°, V=456.72(4) Å 3. Ca 0.5Bi 3V 2O 10 is isostructural with Sr 0.5Bi 3V 2O 10, with, a=7.0810(2) Å, b=7.8447(2) Å, c=9.3607(2) Å, α=106.202(1)°, β=94.572(1)°, γ=112.659(1)°, V=450.38(2) Å 3 and its structure has been refined by Rietveld method using powder X-ray data. The crystal structure consists of infinite chains of (Bi 2O 2) along c-axis formed by linkage of BiO 8 and BiO 6 polyhedra interconnected by MO 8 polyhedra forming 2D layers in ac plane. The vanadate tetrahedra are sandwiched between these layers. Conductivity measurements give a maximum conductivity value of 4.54×10 -5 and 3.63×10 -5 S cm -1 for Ca 0.5Bi 3V 2O 10 and Sr 0.5Bi 3V 2O 10, respectively at 725 °C.

  8. Growth kinetics of induced domains in Ba0.8Sr0.2TiO3 ferroelectric thin films

    NASA Astrophysics Data System (ADS)

    Kiselev, D. A.; Afanasiev, M. S.; Levashov, S. A.; Chucheva, G. V.

    2015-06-01

    The possibility of the formation of stable domain states in Ba0.8Sr0.2TiO3 films on the initial surface and in a preliminarily polarized region of the film has been demonstrated using piezoresponse force microscopy. The velocity of lateral motion of a domain wall, coercive field, minimal domain size, and recording time for the domain formation under the applied voltage have been calculated.

  9. Temperature-dependent impedance spectroscopy of La0.8Sr0.2FeO3 nano-crystalline material

    NASA Astrophysics Data System (ADS)

    Kafa, C. A.; Triyono, D.; Laysandra, H.

    2017-04-01

    LaFeO3 is a material with perovskite structure which electrical properties frequently investigated. Research are done due to the exhibition of excellent gas sensing behavior through resistivity comparison from the p-type semiconductor. Sr doping on LaFeO3 or La1-xSrxFeO3 are able to improve the electrical conductivity through structural modification. Using Sr dopant concentration (x) of 0.2, La0.8Sr0.2FeO3 nano-crystal pellet was synthesized. The synthesis used sol-gel method, followed by gradual heat treatment and uniaxial compaction. XRD characterization shows that the structure of the sample is Orthorhombic Perovskite. Topography of the sample by SEM reveals grain and grain boundary existence with emerging agglomeration. The electrical properties of the material, as functions of temperature and frequency, were measured by Impedance Spectroscopy method using RLC meter, for temperatures of 303-373K. Through the Nyquist plot and Bode plot, the electrical conductivity of La0.8Sr0.2FeO3 is contributed by the grain and grain boundary. Finally, the electrical permittivities of La0.8Sr0.2FeO3 are increasing with temperature increase, with the highest achieved when measured at 1 kHz frequency.

  10. Synthesis and characterization of La0.8Sr0.2MO3-δ (M=Mn, Fe, or Co) cathode materials by induction plasma technology

    NASA Astrophysics Data System (ADS)

    Bouchard, D.; Sun, L.; Gitzhofer, F.; Brisard, G. M.

    2006-03-01

    In this work, nanopowders of perovskite cathode materials (La0.8Sr0.2MnO3-δ, La0.8Sr0.2FeO3-δ, and La0.8Sr0.2CoO3-δ), for use in solid oxide fuel cells (SOFC), were successfully synthesized, using induction plasma techniques. Their compositions, structures, morphology, particle size distributions, and BET specific surface areas were determined for comparison with their counterparts prepared by the Pechini method and by the glycine-nitrate combustion (GNC) technique. The particle sizes of the plasma-synthesized powders are mostly around 63 nm. These plasma-synthesized powders are generally globular, their BET specific surface areas being about 26 m2g-1, approximately twice those of powders prepared by the GNC and Pechini methods. These plasma-synthesized powders are readily reproducible and are not agglomerated. Their individual particle sizes and distributions are very independent of their composition.

  11. Spin state and magnetic ordering of half-doped Nd0.5Sr0.5CoO3 cobaltite

    NASA Astrophysics Data System (ADS)

    Reis, M. S.; Rocco, D. L.; Caraballo Vivas, R. J.; Pimentel, B.; Checca, N. R.; Torrão, R.; Paixão, L.; dos Santos, A. M.

    2017-01-01

    Cobaltites show intriguing magnetic and transport properties, when compared with manganites for instance, as they exhibit an additional degree of freedom: the spin state of the Co ions. For Nd0.5Sr0.5CoO3 this spin configuration is not well-established, as well as the magnetic ordering below the Curie temperature. Thus, in the present effort, magnetization measurements and a mean-field theoretical model were developed in order to understand in detail these aspects of the half-doped Nd0.5Sr0.5CoO3 cobaltite. These results show that the Co and Nd magnetic sub-lattices couple antiferromagnetically below Curie temperature Tc=215 K down to very low temperature. These findings clarify the presence of the plateau observed at 80 K on M(T) curve, which is erroneously attributed, in the literature, to the onset of an antiferromagnetic ordering. Magnetization data also clearly shows that Co3+ and Co4+ are in an intermediate spin state. In addition, experimental and theoretical magnetic entropy changes were determined and a comparative analysis among these two leads to ratify the results above claimed. Finally, from all those results, a magnetic phase diagram for Nd0.5Sr0.5CoO3. could be drawn.

  12. Electron-Phonon Anomaly Related to Charge Stripes: Static Stripe Phase Versus Optimally Doped Superconducting La1.85Sr0.15CuO4

    NASA Astrophysics Data System (ADS)

    Reznik, D.; Pintschovius, L.; Fujita, M.; Yamada, K.; Gu, G. D.; Tranquada, J. M.

    2007-05-01

    Inelastic neutron scattering was used to study the Cu-O bond-stretching vibrations in optimally doped La1.85Sr0.15CuO4 (Tc = 35 K) and in two other cuprates showing static stripe order at low temperatures, i.e. La1.48Nd0.4Sr0.12CuO4 and La1.875Ba0.125CuO4. All three compounds exhibit a very similar phonon anomaly, which is not predicted by conventional band theory. It is argued that the phonon anomaly reflects a coupling to charge inhomogeneities in the form of stripes, which remain dynamic in superconducting La1.85Sr0.15CuO4 down to the lowest temperatures. These results show that the phonon effect indicating stripe formation is not restricted to a narrow region of the phase diagram around the so-called 1/8 anomaly but occurs in optimally doped samples as well.

  13. Bond-stretching phonon mode in stripe ordered orthorhombic Nd1.67Sr0.33NiO4.

    NASA Astrophysics Data System (ADS)

    Hücker, M.; Fukuda, T.; Gu, G. D.; Tranquada, J. M.; Baron, A. Q. R.; Hill, J. P.

    2007-03-01

    Inelastic x-ray scattering (IXS) experiments on Nd1.67Sr0.33NiO4 have been performed to study electron-phonon interactions in this charge stripe ordered nickelate. Resurgent interest in such phenomena has been triggered by recent results on the high temperature superconductors, where a kink in the electron dispersion as well as striking anomalies in high- energy optical phonon modes have been observed. A significant softening of the bond-stretching-phonon mode for Q||[100] was also observed in the tetragonal nickelate La1.69Sr0.31NiO4 with inelastic neutron scattering. Moreover, this compound shows an apparent splitting of the bond-stretching mode along the [110] direction. Here we present first IXS results for Q||[110] on the orthorhombic compound Nd1.67Sr0.33NiO4, which is characterized by domains with unidirectional stripe order. By probing different spots on the sample with different domain distribution, a weak contrast between the phonon spectra has been observed. We discuss these differences in terms of phonons propagating parallel and perpendicular to the stripe direction, as well as the anisotropic, i.e. orthorhombic, lattice structure.

  14. Giant positive magnetoresistance in heterostructure (La0.7Sr0.3MnO3) coated with YBa2Cu3O7 composites

    NASA Astrophysics Data System (ADS)

    Lin, Y. B.; Huang, Z. G.; Yang, Y. M.; Wang, S.; Li, S. D.; Zhang, F. M.; Du, Y. W.

    2011-07-01

    (La0.7Sr0.3MnO3) x /(YBa2Cu3O7) y composites were prepared by mixing La0.7Sr0.3MnO3 powders and the sol-gel-derived YBa2Cu3O7 matrix, followed by high-temperature calcinations. Their structural, magnetic properties and magnetoresistance effect have been investigated systematically. A giant positive magnetoresistance (PMR) at low magnetic field is observed at low temperatures. In the case of (La0.7Sr0.3MnO3)1/(YBa2Cu3O7)9 composite, the PMR achieves 260% under a magnetic field of 5800 Oe. However, the PMR value sharply decreases with increasing temperature and no magnetoresistance effects are found above metal-insulator transition temperature. The enhancement of spin-dependent scattering at the grain boundaries should be responsible for the observed PMR. In addition, the temperature dependence of resistance under magnetic field could be explained by the competition between diamagnetism and paramagnetism in YBCO phase. At low temperature, the diamagnetism is predominant over paramagnetism and the interface scattering between LSMO grains is enhanced correspondingly. As a result, the low-temperature resistance increases and large PMR appears.

  15. 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.

  16. Ferroelectric domain wall relaxation in Ba0.25Sr0.75TiO3 films displaying Curie-Weiss behavior

    NASA Astrophysics Data System (ADS)

    Boikov, Yu. A.; Khamchane, K.; Claeson, T.

    2004-10-01

    Ferroelectric films may be used in integrated circuits for high frequency and memory applications. Losses and interfaces between films and electrodes are problematic. This work concerns the temperature and electric field response of the complex dielectric permittivity and the relaxation of domain walls in a ferroelectric layer that is of sufficient quality to show a Curie-Weiss behavior. Laser ablation was used to deposit 1200 nm thick Ba0.25Sr0.75TiO3 layers between metallic oxide, (100 nm) SrRuO3 and (120 nm) La0.67Ca0.33MnO3, films in epitaxial heterostructures. The electric field response (E ⩽80kV/cm) of the real ε' and imaginary ε″ parts of the complex permittivity of the intermediate Ba0.25Sr0.75TiO3 layer in these parallel plane film capacitors was studied at temperatures above and below the phase transition point TCurie. The latter was determined from the temperature dependence of the inverse dielectric permittivity and its value, TCurie=145K, agrees well with that of bulk single crystal. ε' of the Ba0.25Sr0.75TiO3 layer could be suppressed about 80% by a field E =80kV/cm at temperatures close to TCurieε'(T,E) and ε″(T,E) curves were used to gain insight into the relaxation dynamics of ferroelectric domain walls (DW) in the Ba0.25Sr0.75TiO3 layer. Their influence on ε' was noticed up to T =230K, well above TCurie. The most probable relaxation time τ of the DW in Ba0.25Sr0.75TiO3 follows a relation τ =τ0exp[(ϕ-β√E )/kT], where τ0=1.2×10-10sϕ=75-105meV, and β =4.7×10-24Jm1/2V-1/2.

  17. 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.

  18. Optical properties of Ag nanoparticles embedded Ba0.5Sr0.5TiO3 films prepared by alternating pulsed laser deposition.

    PubMed

    Kim, Ji-Suk; Lee, Kyeong-Seok; Kim, Sang Sub

    2006-11-01

    Nanocomposite thin films consisting of nanometer-sized Ag particles embedded in amorphous Ba0.5Sr0.5TiO3 matrix were prepared on fused silica substrates by an alternating pulsed laser deposition method. Their optical nonlinearities have been studied using the Z-scan method. The surface plasmon resonance (SPR) peak shifts to red and increases with the increasing the volume fraction of Ag in the nanocomposite films. The magnitude of the third-order nonlinear susceptibility of the nanocomposite with an Ag volume fraction of 3.3% was calculated to be approximately 2 x 10(-8) esu at the SPR wavelength.

  19. Relation between oxygen stoichiometry and thermodynamic properties and the electronic structure of nonstoichiometric perovskite La0.6Sr0.4CoO3-δ.

    PubMed

    Bychkov, S F; Sokolov, A G; Popov, M P; Nemudry, A P

    2016-10-26

    Continuous phase diagram 3 - δ - log pO2 - T of the nonstoichiometric perovskite La0.6Sr0.4CoO3-δ was obtained in a gas flow reactor by means of the quasi-equilibrium oxygen release technique. The thermodynamic properties of oxides were determined as a function of oxygen nonstoichiometry. Within the framework of the itinerant electron model, the dependence of the oxide nonstoichiometry on the oxygen activity was related to the density of electronic states near the Fermi level.

  20. 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.

  1. 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. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  2. Influence of damping constant on inverse spin hall voltage of La0.7Sr0.3MnO3(x)/platinum bilayers.

    PubMed

    Luo, G Y; Chang, C R; Lin, J G

    2014-05-07

    Pure spin transport via spin pumping in the condition of ferromagnetic resonance can be transformed to charge current in the ferromagnetic/paramagnetic bilayer systems, based on inverse spin Hall effect (ISHE). Here, we explore La0.7Sr0.3MnO(x)/Pt(5.5 nm) [x = 10 to 65 nm] bilayers to investigate the influence of damping constant on spin pumping efficiency. The results show that the ISHE voltage depend on the damping constant of magnetic moment, suggesting that the precession energy tansferred to lattice/electron of normal metal is a key parameter to control the magnitude of spin current.

  3. Bond-stretching-phonon anomalies in stripe-ordered La1.69Sr0.31NiO4.

    PubMed

    Tranquada, J M; Nakajima, K; Braden, M; Pintschovius, L; McQueeney, R J

    2002-02-18

    We report a neutron scattering study of bond-stretching phonons in La1.69Sr0.31NiO4, a doped antiferromagnet in which the added holes order in diagonal stripes at 45 to the Ni-O bonds. For the highest-energy longitudinal optical mode along the bonds, a softening of 20% is observed between the Brillouin zone center and the zone boundary. At 45 to the bonds, a splitting of the same magnitude is found across much of the zone. Surprisingly, the charge-ordering wave vector plays no apparent role in the anomalous dispersions. The implications for related anomalies in the cuprates are discussed.

  4. Hard X-ray diffraction study of charge stripe order in La1.48Nd0.4Sr0.12CuO4

    NASA Astrophysics Data System (ADS)

    Zimmermann, M. v.; Vigliante, A.; Niemöller, T.; Ichikawa, N.; Frello, T.; Madsen, J.; Wochner, P.; Uchida, S.; Andersen, N. H.; Tranquada, J. M.; Gibbs, D.; Schneider, J. R.

    1998-03-01

    High-energy photon diffraction is used to investigate the charge ordering previously studied by neutron diffraction in La1.48Nd0.4Sr0.12CuO4. Besides confirming the existence of superlattice peaks due to charge order, the temperature dependence of the peak intensity, width, and position has been determined with improved precision. Furthermore, we show that the scattered intensity has a sinusoidial modulation along c*, consistent with long-range Coulomb interactions between ordered charges within the CuO2 planes.

  5. Significant enhancement in energy density of polymer composites induced by dopamine-modified Ba0.6Sr0.4TiO3 nanofibers

    NASA Astrophysics Data System (ADS)

    Song, Yu; Shen, Yang; Hu, Penghao; Lin, Yuanhua; Li, Ming; Nan, C. W.

    2012-10-01

    Ba0.6Sr0.4TiO3 (BST) nanofibers prepared via electrospinning and modified by dopamine are used as dielectric fillers in polyvinylidene fluoride (PVDF)-based composites. With 4.4 vol. % of BST nanofibers, the extractable energy density of the BST/PVDF composites is more than doubled as compared with pure PVDF matrix. Such significant enhancement is attributed to the combined effect of both surface modification by dopamine and large aspect ratio of the BST nanofibers. Paraelectric or anti-ferroelectric fillers of large aspect ratio may serve as a general strategy for enhanced electric energy density in polymer composites.

  6. Temperature dependence of the mid-infrared absorption in La 1.84Sr 0.16NiO 4+δ

    NASA Astrophysics Data System (ADS)

    Crandles, D. A.; Timusk, T.; Garret, J. D.; Greedan, J. E.

    1993-10-01

    The reflectance of a La 1.84Sr 0.16Ni 4+δ crystal has been measured between 115 cm -1 and 5500 cm -1 with the electric-field vector in the ab-plane for several temperatures between 80 and 300 K. On the basis of the Kramers-Kronig derived optical conductivity data we show that it is unlikely that small-polaron absorption can account for the mid-infrared absorption, as had been previously suggested. A doped-semiconductor model is also considered.

  7. 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

    2015-10-07

    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.

  8. Low energy excitations and Drude-Smith carrier dynamics in Sm0.5Sr0.5MnO3

    NASA Astrophysics Data System (ADS)

    Kumar, K. Santhosh; Das, Sarmistha; Prajapati, G. L.; Philip, Sharon S.; Rana, D. S.

    2017-05-01

    We have performed terahertz time-domain spectroscopic measurements on half-doped charge-ordered manganite Sm0.5Sr0.5MnO3 in the temperature range of 5-300 K to explore the possibilities of the charge density wave (CDW) ground state and understand the low energy charge carrier dynamics. While a resonance absorption peak at 0.275 meV suggests formation of a CDW condensate, the increase in background conductivity due to uncondensed carriers obey the Drude-Smith model of carrier dynamics. This study confirms that CDW is a generic feature of charge-ordered manganites.

  9. Electric modulation of magnetization at the BaTiO3/La0.67Sr0.33MnO3 interfaces

    NASA Astrophysics Data System (ADS)

    Lu, H.; George, T. A.; Wang, Y.; Ketsman, I.; Burton, J. D.; Bark, C.-W.; Ryu, S.; Kim, D. J.; Wang, J.; Binek, C.; Dowben, P. A.; Sokolov, A.; Eom, C.-B.; Tsymbal, E. Y.; Gruverman, A.

    2012-06-01

    We report large (>10%) magnetization modulation by ferroelectric polarization reversal in the ferroelectric-ferromagnetic BaTiO3/La0.67Sr0.33MnO3 (BTO/LSMO) heterostructures. We find that the electrically induced change in magnetization is limited to the BTO/LSMO interface but extends about 3 nm deep into the LSMO layer—far beyond the expected screening length of metallic LSMO. It is suggested that this effect is due to a metal-insulator transition occurring at the BTO/LSMO interface as a result of electrostatic doping.

  10. Impact of interfacial coupling of oxygen octahedra on ferromagnetic order in La0.7Sr0.3MnO3/SrTiO3 heterostructures

    NASA Astrophysics Data System (ADS)

    Li, Xiaoyan; Lindfors-Vrejoiu, Ionela; Ziese, Michael; Gloter, Alexandre; van Aken, Peter A.

    2017-01-01

    La0.7Sr0.3MnO3, a half-metallic ferromagnet with full spin polarization, is generally used as a standard spin injector in heterostructures. However, the magnetism of La0.7Sr0.3MnO3 is strongly modified near interfaces, which was addressed as “dead-layer” phenomenon whose origin is still controversial. Here, both magnetic and structural properties of La0.7Sr0.3MnO3/SrTiO3 heterostructures were investigated, with emphasis on the quantitative analysis of oxygen octahedral rotation (OOR) across interfaces using annular-bright-field imaging. OOR was found to be significantly altered near interface for both La0.7Sr0.3MnO3 and SrTiO3, as linked to the magnetism deterioration. Especially in La0.7Sr0.3MnO3/SrTiO3 superlattices, the almost complete suppression of OOR in 4 unit-cell-thick La0.7Sr0.3MnO3 results in a canted ferromagnetism. Detailed comparisons between strain and OOR relaxation and especially the observation of an unexpected La0.7Sr0.3MnO3 lattice c expansion near interfaces, prove the relevance of OOR for the magnetic properties. These results indicate the capability of tuning the magnetism by engineering OOR at the atomic scale.

  11. Impact of interfacial coupling of oxygen octahedra on ferromagnetic order in La0.7Sr0.3MnO3/SrTiO3 heterostructures

    PubMed Central

    Li, Xiaoyan; Lindfors-Vrejoiu, Ionela; Ziese, Michael; Gloter, Alexandre; van Aken, Peter A.

    2017-01-01

    La0.7Sr0.3MnO3, a half-metallic ferromagnet with full spin polarization, is generally used as a standard spin injector in heterostructures. However, the magnetism of La0.7Sr0.3MnO3 is strongly modified near interfaces, which was addressed as “dead-layer” phenomenon whose origin is still controversial. Here, both magnetic and structural properties of La0.7Sr0.3MnO3/SrTiO3 heterostructures were investigated, with emphasis on the quantitative analysis of oxygen octahedral rotation (OOR) across interfaces using annular-bright-field imaging. OOR was found to be significantly altered near interface for both La0.7Sr0.3MnO3 and SrTiO3, as linked to the magnetism deterioration. Especially in La0.7Sr0.3MnO3/SrTiO3 superlattices, the almost complete suppression of OOR in 4 unit-cell-thick La0.7Sr0.3MnO3 results in a canted ferromagnetism. Detailed comparisons between strain and OOR relaxation and especially the observation of an unexpected La0.7Sr0.3MnO3 lattice c expansion near interfaces, prove the relevance of OOR for the magnetic properties. These results indicate the capability of tuning the magnetism by engineering OOR at the atomic scale. PMID:28074836

  12. 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.

  13. Structural, transport, magnetic and thermal properties of La0.7Ca0.24Sr0.06MnO3 single crystal

    NASA Astrophysics Data System (ADS)

    Bodhaye, Ashish; Sanyal, Sankar P.; Mukovskii, Y. M.

    2008-04-01

    La0.7Ca0.24Sr0.06MnO3 single crystals with high quality have been prepared by using floating zone technique. The structural, transport, magnetic and thermal properties of the hole doped La0.7Ca0.24Sr0.06MnO3 single crystal, have been studied using various experimental techniques. The resistivity data shows the metal to insulator transition (MI) occurs at TMI = 281 K along the c-axis and TMI = 270 K along the ab-plane. It is observed that the TMI data is higher along the C-axis as compared to that in the ab-plane, thus indicating more favourable hoping of electrons is along the c-axis. This MI transition and large magnetoresistance peak 79% is closely near to the ferromagnetic—paramagnetic transition Tc, which was confirmed from the magnetization data (at ˜275 K), it was also confirmed from the ac susceptibility data (at ˜275 K) and the specific heat data (at ˜270 K), which in term is indicative of the onset of long range order. The entropy change associated with this transition is found to be 2.3 J/mol K. For bolometric applications point of view, the temperature coefficient of resistance (TCR) along ab-plane is found ˜23%K-1.

  14. Atomic-Scale Tunneling Spectra across BiFeO3/La0.7Sr0.3MnO3 Heterointerfaces

    NASA Astrophysics Data System (ADS)

    Chiu, Ya-Ping; Huang, Bo-Chao; Yu, Pu; Chang, Chia-Seng; Chu, Ying-Hao

    2015-03-01

    Atomic-level evolution of electronic structures across BiFeO3/La0.7Sr0.3MnO3 complex oxide heterointerfaces has been demonstrated by cross-sectional scanning tunneling microscopy and spectroscopy in this work. Analysis of scanning tunneling spectroscopy results exploits how the change in the terminated interface brings the influence to the electrostatic configurations across the BiFeO3/La0.7Sr0.3MnO3 heterointerfaces. Spatially unit-cell-by-unit-cell resolved electronic states at the atomic level reveal that the control of material interfaces at the atomic level determines the ferroelectric polarization in BiFeO3. The precise electronic information therefore provides a clear realization about the electronic state at these complex-oxide heterointerfaces, which is crucial to understand and design a host of novel functionalities at complex oxide heterointerfaces. Affilication 2: Department of Physics, National Sun Yat-sen University, Kaohsiung 804, Taiwan.

  15. A New Ba0.6 Sr0.4 TiO3 -Silicon Hybrid Metamaterial Device in Terahertz Regime.

    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

    Metamaterials, offering unprecedented functionalities to manipulate electromagnetic waves, have become a research hotspot in recent years. Through the incorporation of active media, the exotic electromagnetic behavior of metamaterials can be dramatically empowered by dynamic control. Many ferroelectric materials such as BaSrTiO3 (abbreviated as BST), exhibiting strong response to external electric field, hold great promise in both microwave and terahertz tunable devices. A new active Ba0.6 Sr0.4 TiO3 -silicon hybrid metamaterial device, namely, a SRR (square split-ring resonator)-BaSrTiO3 thin film-silicon three-layer structure is fabricated and intensively studied. The active Ba0.6 Sr0.4 TiO3 thin film hybrid metamaterial, with nanoscale thickness, delivers a transmission contrast up to ≈79% due to electrically enabled carrier transport between the ferroelectric thin film and silicon substrate. This work has significantly increased the low modulation rate of ferroelectric based devices in terahertz range, a major problem in this field remaining unresolved for many years. The proposed BST metamaterial is promising in developing high-performance real world photonic devices for terahertz technology.

  16. Fabrication and Properties of Cr2O3 and La0.7Sr0.3MnO3 Thin Film Heterostructures Integrated on Si(001)

    NASA Astrophysics Data System (ADS)

    Punugupati, Sandhyarani

    Spintronics that utilizes both the spin and charge degrees of freedom of an electron is emerged as an alternate memory technology to conventional CMOS electronics. Many proposed spintronic devices require multifunctional properties in a single material. The oxides Cr2O3 and La0.7Sr0.3MnO3 are such materials which exhibit unique physical properties at room temperature. The Cr2O3 is an antiferromagnetic and magnetoelectric material below its Neel temperature 307K. The La0.7Sr0.3MnO3 is a ferromagnetic half metal with a Curie temperature of 360K and exhibits colossal magnetoresistance. However, the reach of this spintronic technology into more device applications is possible only when these materials in epitaxial thin film form are integrated with Si(001) which is the mainstay substrate in semiconductor industry. The primary objective of this dissertation was to integrate epitaxial Cr2O3, La0.7Sr0.3MnO3 and Cr2O3/La0.7Sr0.3MnO3 thin film heterostructure on Si(001) and, study their physical properties to investigate structure-processing-property relationship in these heterostructures. The epitaxial integration of Cr2O3 thin films on Si(001) was done using epitaxial cubic yttria stabilized zirconia (c-YSZ) buffer layer by pulsed laser deposition. Detailed structural characterizations XRD (2theta and phi) and TEM confirm the epitaxial nature of the films. Though bulk Cr2O3 is antiferromagnetic along the c-axis, the in-plane magnetization measurements on Cr2O3(0001) thin films showed ferromagnetic behavior up to 400K. The thickness dependent magnetization together with oxygen annealing results suggested that the in-plane ferromagnetism in Cr2O3 was due to the oxygen related defects whose concentration is controlled by strain in the films. The out-of-plane magnetic measurements on Cr2O3(0001) films showed magnetic behavior indicative of antiferromagnetic nature. To verify whether ferromagnetism can be induced by strain in Cr 2O3 thin films with orientation other than (0001

  17. 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.; hide

    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.

  18. In-plane structural order of domain engineered La0.7Sr0.3MnO3 thin films

    NASA Astrophysics Data System (ADS)

    Boschker, J. E.; Monsen, Å. F.; Nord, M.; Mathieu, R.; Grepstad, J. K.; Holmestad, R.; Wahlström, E.; Tybell, T.

    2013-05-01

    We present a detailed structural study of tensile-strained La0.7Sr0.3MnO3 thin films. We use the substrate miscut to control the number of rhombohedral variants in the films and study the in-plane order and structural distortions. Using high-resolution X-ray diffraction, we demonstrate that step-edge induced lattice modulations occur in 4-variant films, whereas periodic twinning is the dominant in-plane order for 2-variant films. We show that the in-plane twinning angle is almost completely relaxed. However, the relaxation of shear strain by the out-of-plane twinning angle and the monoclinic distortion is only partial. Furthermore, the film thickness dependence of the domain width reveals that domain formation is a universal mechanism for shear strain relaxation. Finally, we show that the structural response to the transition from the paramagnetic to the ferromagnetic phase of La0.7Sr0.3MnO3 at 345 K is smaller in 4-variant films compared to 2-variant films.

  19. Structure and magnetotransport properties in plasma-sprayed La 0.78Sr 0.22MnO 3 thick film

    NASA Astrophysics Data System (ADS)

    Orlando, M. T. D.; Cunha, A. G.; Freitas, J. C. C.; Orlando, C. G. P.; Bud'ko, S.; Giordanengo, B.; Sato, I. M.; Martinez, L. G.; Baggio-Saitovitch, E. M.

    2002-04-01

    Thick films of La 0.78Sr 0.22MnO 3 were produced by the plasma-spray technique onto stainless-steel substrate at 930°C. These films were obtained without the use of bond-layer, buffer-layer and annealing after deposition. The compound was deposited by a plasma-spray torch using nitrogen as the working gas. The films with thickness varying from 20 to 60 μm have good adherence and are composed of large splats with high degree of interconnection and small number of defects, as revealed by scanning electron microscopy. X-ray diffractometry analysis of the as-deposited film revealed that it had the same crystal structure as the original bulk. Measurements of electrical resistivity versus temperature for the film revealed a magnetic transition temperature near 340 K, with a ferromagnetic/metallic behavior below this temperature. The magnetoresistance of La 0.78Sr 0.22MnO 3 films exhibited similar magnetic field dependence as compared to the bulk sample, which indicates that the plasma-spray technique can be successfully employed for the deposition of thick films of manganites on large-area substrates while maintaining the main bulk properties.

  20. Phase transformation, dielectric and magnetic properties of Nb doped Bi0.8Sr0.2FeO3 multiferroics

    NASA Astrophysics Data System (ADS)

    Reetu, Agarwal, Ashish; Sanghi, Sujata; Ashima, Ahlawat, Neetu; Monica

    2012-06-01

    Bi0.8Sr0.2Fe1-xNbxO3 (x = 0.0, 0.05, and 0.10) multiferroics were prepared by solid state reaction method. X-ray diffraction and Rietveld analysis show that crystal structure is rhombohedral for x = 0.0, 0.05 samples and triclinic for x = 0.10 sample. These samples showed dispersion in dielectric constant (έ) and dielectric loss (tan δ) values at lower frequencies. For x = 0.05 sample, both έ and tan δ are lower than for Bi0.8Sr0.2FeO3 sample indicating its high resistivity. For x = 0.10 sample, the value of έ is enhanced which may be due to formation of stronger dipoles in triclinic structure. Temperature dependence of frequency exponent "s" of power law suggests that correlated barrier hopping (CBH) model is applicable at lower temperatures and quantum mechanical tunneling model is appropriate at higher temperatures for describing the conduction mechanism in x = 0.0 and x = 0.05 samples; while in x = 0.10 sample, CBH model is appropriate in studied temperature range. Significant enhancement observed in magnetization for x = 0.10 sample is due to the structural phase transition from rhombohedral to triclinic caused by Nb substitution. For this sample, values of remnant magnetization (Mr) and coercive field (Hc) are 0.155 emu/g and 2.695 kOe, respectively.

  1. Electrical Characteristics and Preparation of (Ba0.5Sr0.5)TiO3 Films by Spray Pyrolysis and Rapid Thermal Annealing

    NASA Astrophysics Data System (ADS)

    Koo, Horng-Show; Chen, Mi; Ku, Hong-Kou; Kawai, Tomoji

    2007-04-01

    Functional films of (Ba0.5Sr0.5)TiO3 on Pt (1000 Å)/Ti (100 Å)/SiO2 (2000 Å)/Si substrates are prepared by spray pyrolysis and subsequently rapid thermal annealing. Barium nitrate, strontium nitrate and titanium isopropoxide are used as starting materials with ethylene glycol as solvent. For (Ba0.5Sr0.5)TiO3 functional thin film, thermal characteristics of the precursor powder scratched from as-sprayed films show a remarkable peak around 300-400 °C and 57.7% weight loss up to 1000 °C. The as-sprayed precursor film with coffee-like color and amorphous-like phase is transformed into the resultant film with white, crystalline perovskite phase and characteristic peaks (110) and (100). The resultant films show correspondent increases of dielectric constant, leakage current and dissipation factor with increasing annealing temperatures. The dielectric constant is 264 and tangent loss is 0.21 in the resultant films annealed at 750 °C for 5 min while leakage current density is 1.5× 10-6 A/cm2 in the film annealed at 550 °C for 5 min.

  2. Effect of Synthesis Temperature on Structure and Magnetic Properties of (La,Nd)0.7Sr0.3MnO3 Nanoparticles

    NASA Astrophysics Data System (ADS)

    Shlapa, Yulia; Solopan, Sergii; Bodnaruk, Andrii; Kulyk, Mykola; Kalita, Viktor; Tykhonenko-Polishchuk, Yulia; Tovstolytkin, Alexandr; Belous, Anatolii

    2017-02-01

    Two sets of Nd-doped La0.7Sr0.3MnO3 nanoparticles were synthesized via sol-gel method with further heat treatment at 1073 and 1573 K, respectively. Crystallographic and magnetic properties of obtained nanoparticles were studied, and the effect of synthesis conditions on these properties was investigated. According to X-ray data, all particles crystallized in the distorted perovskite structure. Magnetic parameters, such as saturation magnetization, coercivity, Curie temperature, and specific loss power, which is released on the exposure of an ensemble of nanoparticles to AC magnetic field, were determined for both sets of samples. The correlation between the values of Curie temperature and maximal heating temperature under AC magnetic field was found. It was revealed that for the samples synthesized at 1573 K, the dependences of crystallographic and magnetic parameters on Nd content were monotonous, while for the samples synthesized at 1073 K, they were non-monotonous. It was concluded that Nd-doped La0.7Sr0.3MnO3 nanoparticles are promising materials for self-controlled magnetic hyperthermia applications, but the researchers should be aware of the unusual behavior of the particles synthesized at relatively low temperatures.

  3. Strain dependence of antiferromagnetic interface coupling in La0.7Sr0.3MnO3/SrRuO3 superlattices

    DOE PAGES

    Das, Sujit; Herklotz, Andreas; Pippel, Eckhard; ...

    2015-04-06

    We have investigated the magnetic response of La0.7Sr0.3MnO3/SrRuO3 superlattices to biaxial in-plane strain applied in situ. Superlattices grown on piezoelectric substrates of 0.72PbMg1/3Nb2/3O3-0.28PbTiO3(001) (PMN-PT) show strong antiferromagnetic coupling of the two ferromagnetic components. The coupling field of mu H-0(AF) = 1.8 T is found to change by mu(0)Delta H-AF/Delta epsilon similar to -520 mT %(-1) under reversible biaxial strain Delta epsilon at 80 K in a [La0.7Sr0.3MnO3(22 angstrom)/SrRuO3(55 angstrom)]15 superlattice. This reveals a significant strain effect on interfacial coupling. The applied in-plane compression enhances the ferromagnetic order in the manganite layers, which are under as-grown tensile strain, leading to amore » larger net coupling of SrRuO3 layers at the interface. It is thus difficult to disentangle the contributions from strain-dependent antiferromagnetic Mn-O-Ru interface coupling and Mn-O-Mn ferromagnetic double exchange near the interface for the strength of the apparent antiferromagnetic coupling. We discuss our results in the framework of available models.« less

  4. Effect of Synthesis Temperature on Structure and Magnetic Properties of (La,Nd)0.7Sr0.3MnO3 Nanoparticles.

    PubMed

    Shlapa, Yulia; Solopan, Sergii; Bodnaruk, Andrii; Kulyk, Mykola; Kalita, Viktor; Tykhonenko-Polishchuk, Yulia; Tovstolytkin, Alexandr; Belous, Anatolii

    2017-12-01

    Two sets of Nd-doped La0.7Sr0.3MnO3 nanoparticles were synthesized via sol-gel method with further heat treatment at 1073 and 1573 K, respectively. Crystallographic and magnetic properties of obtained nanoparticles were studied, and the effect of synthesis conditions on these properties was investigated. According to X-ray data, all particles crystallized in the distorted perovskite structure. Magnetic parameters, such as saturation magnetization, coercivity, Curie temperature, and specific loss power, which is released on the exposure of an ensemble of nanoparticles to AC magnetic field, were determined for both sets of samples. The correlation between the values of Curie temperature and maximal heating temperature under AC magnetic field was found. It was revealed that for the samples synthesized at 1573 K, the dependences of crystallographic and magnetic parameters on Nd content were monotonous, while for the samples synthesized at 1073 K, they were non-monotonous. It was concluded that Nd-doped La0.7Sr0.3MnO3 nanoparticles are promising materials for self-controlled magnetic hyperthermia applications, but the researchers should be aware of the unusual behavior of the particles synthesized at relatively low temperatures.

  5. Ferroelectric and magnetic properties of multiferroic BiFeO3-La0.7Sr0.3MnO3 heterostructures integrated with Si (100)

    NASA Astrophysics Data System (ADS)

    Singamaneni, Srinivasa Rao; Prater, J. T.; Nori, S.; Kumar, D.; Lee, Bongmook; Misra, V.; Narayan, J.

    2015-05-01

    We report on the electrical, ferroelectric, and magnetic properties of BiFeO3 (BFO)-La0.7Sr0.3MnO3 heterostructures deposited epitaxially onto Si(100) substrates. Temperature dependent (200-350 K) current-voltage (I-V), switching spectroscopy piezo-response force microscopy (SSPFM), and temperature dependent (5-300 K) anisotropic magnetization measurements have been performed. The BFO (100-nm thick)-based device structures were fabricated with a 250 nm thick La0.7Sr0.3MnO3 bottom electrode and 200 μm circular top Pt electrodes. I-V measurements performed at various temperatures indicated that the devices retained their as-deposited characteristics and exhibited non-leaky behavior up to at least 50 cycles. The temperature-dependent measurements showed clear diode-like behavior and resistive (hysteretic) switching behaviour. Characteristic butterfly loops (of several cycles) were observed in the PFM amplitude signals of the BFO film. In addition, the phase signal indicated a clear (180°) switching behavior at the switching voltage of 4-5 V, providing unambiguous evidence for the occurrence of ferroelectricity in BFO films integrated on Si (100). The temperature- and angle-dependent zero field cooled isothermal (5 K) magnetization measurements were consistent with the presence of uniaxial magnetic anisotropy. This work makes an important step for the fabrication of CMOS-compatible BFO devices for memory applications.

  6. Electrical Properties of La0.67Sr0.33Mn0.8Ni0.2O3 Synthesized by Sol Gel Method

    NASA Astrophysics Data System (ADS)

    Kurniawan, B.; Widyaiswari, U.; Fauziyah, I.; Imaduddin, A.

    2017-05-01

    The previous study of lanthanum manganites showed that physical properties of LaMnO3 compound has changed when Sr doped the La site. La0.67Sr0.33MnO3 compound give the highest TC = 370 K and showed metal insulator transition. It happens as a result of changed in Mn3+/Mn4+ ratio. Its indicated that Mn has the most important rule to the physical properties changed. In order to shift Tc of the compound to the near room temperature, Ni doped was given to Mn site of LSMO. In this paper, 20% Mn site was doped by Ni. La0.67Sr0.33Mn0.8Ni0.2O3 compound synthesized by sol gel method and characterized using XRD. Then, single phase compound resisitivity was measured to see the electrical properties this compound. The XRD result showed that sample have single phase with rhombohedral structure and R-3c space group. Resistivity as a temperature function graph does not show resistivity peak and metal insulator transition. The resistivity measurement showed that below 300 K, resistivity inscreased with decreased of temperature that indicates insulator behavior. It caused by decreased of double exchange interaction and increase of superexchange interaction. From this result, we can conclude that Ni doped decreased electrical properties of the sample.

  7. 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.

  8. Leakage current limiting mechanisms and ferroelectric properties of BiAlO3/La0.67Sr0.33MnO3 heterostructure

    NASA Astrophysics Data System (ADS)

    Zhao, Yanan; Luo, Bingcheng; Chen, Changle; Xing, Hui; Wang, Jianyuan; Jin, Kexin

    2017-03-01

    The BiAlO3/La0.67Sr0.33MnO3 heterostructure was deposited on LaAlO3 (111) substrate by pulse laser deposition technology. X-ray diffraction measurement indicates that BiAlO3 thin films belong to tetragonal phase. Two different leakage current mechanisms, i.e., Space Charge Limited Current and Schottky emission models are observed in J-E characteristics of BiAlO3/La0.67Sr0.33MnO3 heterostructure in different temperature regions, respectively. The ferroelectric hysteresis loops measured by positive-up negative-down method show intrinsic remnant polarization (2Pr = 2.4 μC/cm2) at the applied electric field of 750 kV/cm, with the 80 nm thickness of BiAlO3 thin films at room temperature. The domain imagines and local piezoelectric hysteresis loops obtained by Piezoresponse Force Microscopy technique further reveal the intrinsic ferroelectricity of. BiAlO3 thin films at room temperature.

  9. Field emission of silicon emitter arrays coated with sol-gel (Ba0.65Sr0.35)1-xLaxTiO3 thin films

    NASA Astrophysics Data System (ADS)

    Lu, H.; Pan, J. S.; Chen, X. F.; Zhu, W. G.

    2007-07-01

    (Ba0.65Sr0.35)1-xLaxTiO3 (BSLT) thin films with different La concentrations have been deposited on Si field emitter arrays (FEAs) using sol-gel technology for field electron emission applications. The films exhibit the perovskite structure at low La substitution level (x ≤0.5) and the pyrochlore phase at high La concentration (x ≥0.75). The 30-nm-thick BSLT (x =0.25) thin film has higher crystallinity of perovskite structure in the surface region. An x-ray photoelectron spectroscopy study indicates that the oxygen vacancy concentration decreases with La substitution. With respect to the undoped Ba0.65Sr0.35TiO3 thin film, the Fermi level shifts down for the BSLT sample with x =0.1 ascribed to the decreasing oxygen vacancy concentration, and then shifts up for the BSLT sample with x =0.25 attributed to the increasing La substitution level. In highly doped films with an x value over 0.5, it shifts down again associated with the second pyrochlore phase formation. The best enhancement in field emission is found for the BSLT-coated (x =0.25) Si FEAs due to the improved perovskite structure in the surface region and up-moved Fermi level of the coating.

  10. Estimation of Joule heating and its role in nonlinear electrical response of Tb0.5Sr0.5MnO3 single crystal

    NASA Astrophysics Data System (ADS)

    Nhalil, Hariharan; Elizabeth, Suja

    2016-12-01

    Highly non-linear I-V characteristics and apparent colossal electro-resistance were observed in non-charge ordered manganite Tb0.5Sr0.5MnO3 single crystal in low temperature transport measurements. Significant changes were noticed in top surface temperature of the sample as compared to its base while passing current at low temperature. By analyzing these variations, we realize that the change in surface temperature (ΔTsur) is too small to have caused by the strong negative differential resistance. A more accurate estimation of change in the sample temperature was made by back-calculating the sample temperature from the temperature variation of resistance (R-T) data (ΔTcal), which was found to be higher than ΔTsur. This result indicates that there are large thermal gradients across the sample. The experimentally derived ΔTcal is validated with the help of a simple theoretical model and estimation of Joule heating. Pulse measurements realize substantial reduction in Joule heating. With decrease in sample thickness, Joule heating effect is found to be reduced. Our studies reveal that Joule heating plays a major role in the nonlinear electrical response of Tb0.5Sr0.5MnO3. By careful management of the duty cycle and pulse current I-V measurements, Joule heating can be mitigated to a large extent.

  11. Field-induced magnetic phase transition in Pr3+ doped Sm0.5Sr0.5MnO3 manganites

    NASA Astrophysics Data System (ADS)

    Giri, S. K.; Nath, T. K.

    2013-05-01

    Magnetic properties of Pr3+ doped Sm0.5Sr0.5MnO3 manganite with the variation of particle size down to 30 nm have been investigated in detail. We have critically examined the magnetic field (H) dependence of the order of the ferromagnetic (FM) to paramagnetic (PM) phase transition in this Sm0.35Pr0.15Sr0.5MnO3 manganite. It has been shown that all the particle sizes (bulk to nano) exhibit first order FM → PM phase transition under low magnetic field accompanied by magnetization with thermal hysteresis in the field cooled cooling and warming cycle. However, the samples exhibit a second order magnetic phase transition above a critical field HCR. Again with decreasing the particle size, the ferromagnetic transition temperature, the thermal hysteresis width in the magnetizations, and the critical field HCR significantly decrease, which indicate that the ferromagnetism is weakened and the first-order magnetic phase transition is softened. We have also used the Banerjee criteria to distinguish the first-order magnetic phase transition from the second-order one. A detailed analysis of the magnetization measurements of this manganite reveal the disorder-induced softening of the first order phase transition in this phase separated manganite.

  12. La(0.8)Sr(0.2)MnO(3-δ) decorated with Ba(0.5)Sr(0.5)Co(0.8)Fe(0.2)O(3-δ): a bifunctional surface for oxygen electrocatalysis with enhanced stability and activity.

    PubMed

    Risch, Marcel; Stoerzinger, Kelsey A; Maruyama, Shingo; Hong, Wesley T; Takeuchi, Ichiro; Shao-Horn, Yang

    2014-04-09

    Developing highly active and stable catalysts based on earth-abundant elements for oxygen electrocatalysis is critical to enable efficient energy storage and conversion. In this work, we took advantage of the high intrinsic oxygen reduction reaction (ORR) activity of La(0.8)Sr(0.2)MnO(3-δ) (LSMO) and the high intrinsic oxygen evolution reaction (OER) activity of Ba(0.5)Sr(0.5)Co(0.8)Fe(0.2)O(3-δ) (BSCF) to develop a novel bifunctional catalyst. We used pulsed laser deposition to fabricate well-defined surfaces composed of BSCF on thin-film LSMO grown on (001)-oriented Nb-doped SrTiO3. These surfaces exhibit bifunctionality for oxygen electrocatalysis with enhanced activities and stability for both the ORR and OER that rival the state-of-the-art single- and multicomponent catalysts in the literature.

  13. 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.

  14. 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.

  15. Structural and dielectric relaxation behaviour of Ba0.8Sr0.2Zr0.1Ti0.9O3 ceramic

    NASA Astrophysics Data System (ADS)

    Mondal, Tanusree; Pada Majee, Bishnu; Ranjan Middya, Tapas; Sarun, P. M.

    2016-09-01

    Ba0.8Sr0.2Zr0.1Ti0.9O3 (BSZT) ceramic was prepared by conventional solid state reaction technique. The XRD pattern confirms single phase formation with cubic structure. The surface morphology was analysed by field emission scanning electron microscopy (FE-SEM). Detailed investigation of dielectric and electrical properties of the BSZT ceramic was done in the wide temperature (453K - 573K) and frequency range (40Hz - 5MHz). Dielectric studies of the compound revealed that dielectric parameters were strongly dependent on temperature and frequency. The complex impedance analysis confirms that the conduction of BSZT ceramic was mainly due to the grain in the lower temperature and with increasing temperature electrode effect was becoming prominent. The conductivity of the material was found to obey the power law.

  16. Effects of swift heavy ion irradiation on dielectric relaxation and conduction mechanism in Ba0.90Sr0.10TiO3

    NASA Astrophysics Data System (ADS)

    Mohan, C. R. K.; Dey, Ranajit; Patel, Shiv P.; Pandey, R. K.; Sharma, M. P.; Bajpai, P. K.

    2016-04-01

    The effects of 100 MeV O8+ ion beam irradiation on the structural and dielectric behavior of Ba0.90Sr0.10TiO3 ceramics have been analyzed. Ion irradiation does not change the crystalline structure, however the tetragonal distortion increases. The low frequency dielectric dispersion especially at high temperatures increases significantly after ion irradiation. The dielectric relaxation phenomenon has been probed through complex impedance and electric modulus approaches. The observed dielectric relaxation has distributed relaxation times and is a thermally activated process. Ion irradiation enhances the cationic disordering. The contributions of grains and grains boundaries towards impedance have been separated. It is inferred that the grain boundaries become more resistive due to ion irradiation and is associated to oxygen vacancies annihilation. Ion irradiation also decreases the bulk ferroelectric polarization demonstrating that the surface or near surface modifications may tune the bulk properties in polar dielectrics.

  17. Effect of iron oxide on the properties of La0.9Sr0.1ScO3-α protonics

    NASA Astrophysics Data System (ADS)

    Stroeva, A. Yu.; Gorelov, V. P.; Kuz'min, A. V.; Ponomareva, V. G.; Petrov, S. A.

    2015-07-01

    The effect of doping on the transport properties of solid electrolytes La0.9Sr0.1ScO2.95 + x FeO1.5 ( x = 0.1-15.0 wt % FeO1.5) has been elucidated by investigating the electrical conductivity of these materials by the four-probe method and the impedance method as a function of external parameters, namely, temperature T (150-900°C), oxygen partial pressure (0.21 × 104-10-15 Pa), and humidity (0.04-2.35 kPa). Samples of the solid electrolytes have been investigated using X-ray powder diffraction, electron microscopy, and Mössbauer spectroscopy.

  18. Ultra-sharp metamagnetic transitions in the half-doped manganite compound Eu0.5Sr0.5MnO3

    NASA Astrophysics Data System (ADS)

    Rana, D. S.; Nirmala, R.; Malik, S. K.

    2005-05-01

    Magnetization, electrical-resistance and specific-heat measurements have been performed on the ABO3-type half-doped Eu0.5Sr0.5MnO3 manganite compound. These studies reveal successive sharp step-like metamagnetic transitions at low temperatures. The steps are sharp at T <= 3 K but smeared above 3 K, signifying the transformation from a homogenous to an inhomogenous phase-separated state at 3 K. Earlier such successive sharp steps have been observed mostly in Pr-based manganites (in which Pr is magnetic). The observation of the similar steps in the present Eu-based system (in which Eu is non-magnetic), along with the irreversibility in the magnetization isotherms, suggests that rare-earth magnetism has no role in the occurrence of this fascinating property.

  19. Efficient carbon dioxide electrolysis with metal nanoparticles loaded La0·75Sr0·25Cr0·5Mn0·5O3-δ cathodes

    NASA Astrophysics Data System (ADS)

    Zhu, Changli; Hou, Linxi; Li, Shisong; Gan, Lizhen; Xie, Kui

    2017-09-01

    Solid oxide electrolysis cells with La0·75Sr0·25Cr0·5Mn0·5O3-δ (LSCM) cathode can electrolyze CO2 to generate chemical fuels. Nevertheless, the cathode performance is limited by its electrocatalytic activity. In this work, metal nanoparticles including Ni, Cu and NiCu metals are successfully impregnated in LSCM electrode to improve its activity. XRD, XPS, SEM and TEM together confirm the metal nanocatalysts are homogeneously distributed on LSCM backbone and therefore create active electrochemical interface for CO2 splitting. Electrical properties of LSCM with impregnated metal nanoparticles are investigated and correlated to electrode performances. Electrochemical measurements show that the NiCu-LSCM demonstrates the optimum performance without degradation after operation for ∼100 h and ∼10 redox cycles. It is believed that the enhanced performance of CO2 electrolysis may be attributed to the synergetic effect of metal nanocatalyst and LSCM ceramic electrode.

  20. Enhanced piezoresistive characteristics of Nb2O5 modified La0.8Sr0.2MnO3 ceramics

    NASA Astrophysics Data System (ADS)

    Sharma, Vaneet; Hossu, Maria R.; Lee, Woo Ho; Koymen, Ali R.; Priya, Shashank

    2006-11-01

    This letter reports the giant piezoresistance phenomenon in Nb2O5 modified La0.8Sr0.2MnO3 (LSMO) polycrystalline ceramics. LSMO modified with 2mol% Nb exhibited ˜2% change in resistivity at 19.2MPa pressure as compared to 0.5% for the pure LSMO. A dramatic improvement was obtained for 5mol% Nb-modified LSMO composition, which exhibited a linear change in resistivity with uniaxial stress and the fractional change was of the order of 3% at 19.2MPa stress. The origin of the giant piezoresistance was found to be related to Nb substitution on the Mn sites which distorts the Mn-O bond, lowering the magnitude of stress required for the manganite lattice transformation.

  1. Effect of Calcination Temperature on La0.7Sr0.3MnO3 Nanoparticles Synthesized with Modified Sol-gel Route

    NASA Astrophysics Data System (ADS)

    Ravi, S.; Karthikeyan, A.

    We report a modified route to synthesize La0.7Sr0.3MnO3 nanoparticle with oxalic acid as chelating agent and oleic acid as surfactant at different calcination temperatures. The synthesized nanoparticles were characterized using XRD, SEM, FTIR and VSM. XRD confirms the formation of phase pure perovskite structure with particle size of about 20 nm. SEM and HRSEM reveal a well refined structure with respect to calcination temperature. FTIR confirms the formation of perovskite with broad peak around 520 cm-1. Magnetic study reveals that these nanoparticle with irregular structure exhibit ferromagnetic nature with different value of magnetization except for 500 °C, which shows paramagnetic nature.

  2. 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.

  3. Suppression of the metal-insulator transition temperature in thin La0.7Sr0.3MnO3 films

    NASA Astrophysics Data System (ADS)

    Angeloni, M.; Balestrino, G.; Boggio, N. G.; Medaglia, P. G.; Orgiani, P.; Tebano, A.

    2004-12-01

    In this paper, we illustrate an approach to discriminate between epitaxial strain and other factors responsible for the decrease of the metal-insulator transition temperature (TP) in thin La0.7Sr0.3MnO3 films grown by pulsed laser deposition. Using this approach, we have estimated the effect of the biaxial strain on TP. Ultrathin films, independent of epitaxial strain, do not show any metal-insulator transition over the full temperature range. This finding confirms the existence of an interface dead layer. The strain-independent decrease in TP, relative to its bulk value, observed for a much wider thickness range (up to about 1000Å) can most likely be attributed to oxygen deficiency.

  4. Electric field modulated conduction mechanism in Al/BaTiO3/La0.67Sr0.33MnO3 heterostructures

    NASA Astrophysics Data System (ADS)

    Zheng, Dongxing; Li, Dong; Gong, Junlu; Jin, Chao; Li, Peng; Zhang, Xixiang; Bai, Haili

    2017-08-01

    Mediating a metastable state is a promising way to achieve a giant modulation of physical properties in artificial heterostructures. A metastable state La0.67Sr0.33MnO3 (LSMO) layer suffering tensile strain was grown on MgO substrates. Incorporating with the ferroelectric BaTiO3 (BTO) layer, an accumulation or depletion state controlled by electric fields can be formed at the BTO/LSMO interface, which drives a switching of the conduction mechanism between space charge limited conduction and Poole-Frenkel emission, corresponding to the low and high resistance states. Our results lighten an effective way for electric-field modulated resistance states in multiferroic magnetoelectric devices.

  5. Critical current densities of Sr0.6K0.4Fe2As2 superconductors estimated from AC susceptibilities

    NASA Astrophysics Data System (ADS)

    Setoyama, Subaru; Kinoshita, Junichi; Akune, Tadahiro; Sakamoto, Nobuyoshi; Murakami, Kouji; Yoshida, Nobuyuki; Kiuchi, Masaru; Otabe, Edmund Soji; Matsushita, Teruo; Ge, Jun; Ni, Baorong; Wang, Lei; Qi, Yanpeng; Zhang, Xianping; Gao, Zhaoshun; Ma, Yanwei

    2013-01-01

    AC susceptibilities (real χ‧ and imaginary χ″) of Sr0.6K0.4Fe2As2 (122 type) polycrystalline with Ag addition are analysed by the grained Bean model. A variety of characteristics, double peak in χ″ and shoulder transition in χ‧, appear in the model simulation. Comparing the measured χ‧ and χ″ with the model allows more clear insight on the polycrystalline structure. Estimated critical current densities Jcg and Jcℓ of the grain and the link in the iron-based pnictides show that the addition of 20 wt.% Ag increases Jcℓ 9 times larger. Improvement of intergrain characteristics with Ag addition is clearly indicated.

  6. 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.

  7. Elastic anomalies in a La 1.85Sr 0.15CuO 4 single crystal under high magnetic fields

    NASA Astrophysics Data System (ADS)

    Hanaguri, Tetsuo; Fukase, Tetsuo; Suzuki, Takao; Tanaka, Isao; Kojima, Hironao

    1994-02-01

    Temperature dependence of the sound velocity Vs in a La 1.85Sr 0.15CuO 4 single crystal has been measured in the ( c11 - c12)/2 mode and in the c33 mode under high magnetic fields up to 23T. In the field above 6T, Vs in the ( c11 - c12)/2 mode anomalously decreases with decreasing temperature, followed by the increase below about 10K. In the c33 mode, similar behavior of Vs can be observed above 20T. Such a temperature dependence of Vs may suggest the existence of a strain sensitive narrow band near the Fermi level or a phase transition related to the flux line lattice.

  8. Crystal-Orientation-Modulated Exchange Bias in Orthorhombic-YMnO3/La0.6Sr0.4MnO3 Multiferroic Heterostructures.

    PubMed

    Zheng, Dongxing; Gong, Junlu; Jin, Chao; Li, Peng; Bai, Haili

    2015-07-15

    The magnetic properties of the all-oxide multiferroic heterostructures composed of orthorhombic YMnO3 (YMO) with E-type antiferromagnetic and double-exchange ferromagnetic (FM) La0.6Sr0.4MnO3 (LSMO) were studied. An orientation-modulated exchange bias effect, which is related to the interfacial Mn-O-Mn bond angle, was discovered. Because of the large bond angle in YMO/LSMO(100) heterostructures, a strong exchange coupling at the interface is formed. This strong exchange coupling sustains an FM phase in YMO at the interface region. The FM phase with strong magnetocrystalline anisotropy contributes to the vertical shift and exchange bias effect in (100) orientation heterostructures. When LSMO (110) and (111) were layered with YMO, the Mn-O-Mn bond angle was reduced, leading to a weakened exchange coupling at the interface, and only a relatively small exchange bias at low temperatures was visible.

  9. Charge density wave excitations in stripe-type charge ordered Pr0.5Sr0.5MnO3 manganite

    NASA Astrophysics Data System (ADS)

    Rana, Rakesh; Rana, D. S.; Mavani, K. R.; Kawayama, I.; Murakami, H.; Tonouchi, M.

    2012-12-01

    We show that a charge-density wave mode submerged in large conductivity of the stripe-type charge-ordered (CO) crystal of Pr0.5Sr0.5MnO3 (PSMO) can be extracted by exciting selective crystallographic planes using polarized terahertz field. Low energy (1-7 meV) dynamics have been explored in the (100), (110), and (111) epitaxial films of PSMO manganite. Of (110) and (111) films representing bulk-like CO, the former exhibits a peak in the conductivity-energy spectrum with attributes of charge-density wave mode along a specific in-plane axis. On the contrary, the CO (111) and the phase-separated (100) films lack this low energy mode but exhibit a Drude-like spectral behavior in the metallic regime. These studies reveal a variety in isothermal charge dynamics originating from the anisotropic nature of the stripe charge-order.

  10. 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

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

    PubMed Central

    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/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. PMID:27001006

  12. Isotropic Kink and Quasiparticle Excitations in the Three-Dimensional Perovskite Manganite La_{0.6}Sr_{0.4}MnO_{3}.

    PubMed

    Horiba, Koji; Kitamura, Miho; Yoshimatsu, Kohei; Minohara, Makoto; Sakai, Enju; Kobayashi, Masaki; Fujimori, Atsushi; Kumigashira, Hiroshi

    2016-02-19

    In order to reveal the many-body interactions in three-dimensional perovskite manganites that show colossal magnetoresistance, we performed an in situ angle-resolved photoemission spectroscopy on La_{0.6}Sr_{0.4}MnO_{3} and investigated the behavior of quasiparticles. We observed quasiparticle peaks near the Fermi momentum in both the electron and the hole bands, and clear kinks throughout the entire hole Fermi surface in the band dispersion. This isotropic behavior of quasiparticles and kinks suggests that polaronic quasiparticles produced by the coupling of electrons with Jahn-Teller phonons play an important role in the colossal magnetoresistance properties of the ferromagnetic metallic phase of three-dimensional manganites.

  13. Electron Conduction of Nd0.6Sr0.4FeO3-δ Thin Film with Oxygen Vacancies Prepared by RF Magnetron Sputtering

    NASA Astrophysics Data System (ADS)

    Namiki, Wataru; Tsuchiya, Takashi; Takayanagi, Makoto; Furuichi, Shoto; Minohara, Makoto; Kobayashi, Masaki; Horiba, Koji; Kumigashira, Hiroshi; Higuchi, Tohru

    2017-07-01

    We have firstly studied the electrical conductivity and the electronic structure of the Nd0.6Sr0.4FeO3-δ (NSFO) thin film on Al2O3(0001) substrate deposited by RF magnetron sputtering. The prepared thin film has larger lattice constant than the bulk crystal due to the stress from the substrate and the oxygen vacancies. The Fe 2p photoemission spectrum exhibits the mixed valence states of Fe2+ and Fe3+. The electrical conductivity exhibits thermal activation-type behavior and increases with increasing film thickness. The band gap of charge transfer type is in a good agreement with the activation energy estimated from the Arrhenius plot. These results indicate the conducting carrier of the NSFO thin film is mainly electron, although the conductivity does not depend on oxygen gas partial pressure.

  14. Influence of strain on an epitaxial ferroelectric (Ba0.50Sr0.50)TiO3 nanodot under different electrical boundary conditions

    NASA Astrophysics Data System (ADS)

    Bin-Omran, S.

    2017-02-01

    A first-principles-derived effective Hamiltonian approach is used to reveal the temperature-versus-misfit strain phase diagram of an epitaxial (Ba0.50Sr0.50)TiO3 dot under different electrical boundary conditions. The results indicate that the electrical polarization and toroidal moment are highly sensitive to the applied strain and/or electrical boundary conditions, resulting in a wide variety of phases that are not found in a free-standing BST dot and in bulk. The calculations indicate that within a narrow range of surface charge screening an intermediate phase in which the polarization and toroidal moment coexist. The dependences of the electrical polarization, toroidal moment and dielectric permittivity on the misfit strain and electrical boundary conditions at room temperature are also investigated and compared with the available theoretical predictions and experimental measurements.

  15. The effect of post-annealing on the structure and magnetotransport properties of Pr0.5Sr0.5MnO3 thin film

    NASA Astrophysics Data System (ADS)

    Chen, Liping; Zeng, Jiali; Li, Miao; Tang, Zhenhua; Gao, Ju

    2017-05-01

    Pr0.5Sr0.5MnO3 (PSMO) thin film is epitaxially grown on (001)-oriented LaAlO3 single-crystal substrate using pulsed laser deposition (PLD). It is found that the as-grown PSMO film shows compressive strain in plane and tensile strain out of the plane. Upon annealing at 900°C in the air, the strain is significantly relaxed. The paramagnetic to ferromagnetic phase transition temperature TC shifts from 200 K to 220 K, and the antiferromagnetic insulating phase is suppressed in the phase separated state at low temperature. In addition, the magnetoresistance (MR) is found to increase around the ferromagnetic transition temperature, whereas it decreases from 99% to 60% at low temperature of 20 K.

  16. 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.

  17. Study of the domain structure evolution in single crystals of relaxor ferroelectric Sr0.61Ba0.39Nb2O6:Ce1

    NASA Astrophysics Data System (ADS)

    Shur, V. Ya.; Pelegov, D. V.; Shikhova, V. A.; Kuznetsov, D. K.; Nikolaeva, E. V.; Rumyantsev, E. L.; Yakutova, O. V.; Granzow, T.

    2010-02-01

    Optical visualization with simultaneous recording of the switching current was used for studying of domain structure evolution in single crystals relaxor ferroelectric strontium barium niobate (Sr0.61Ba0.39Nb2O6) doped by cerium (0.22 mol %) (SBN61:Ce). It was shown that the maze domain structures can be observed during polarization reversal due to local change of refractive index induced by formation of microscale domains with charged domain walls. It was proposed, that optical inhomogeneities occur in the switching regions, while the optical uniform areas correspond to regions where the switching either has not started yet or has already completed. The original mathematical treatment of the obtained images and switching currents has been used for quantitative characterization of the polarization reversal process.

  18. Dielectric characteristics of a Ce 3+-doped Sr 0.61Ba 0.39Nb 2O 6 single crystal with Cole-Cole plots technique

    NASA Astrophysics Data System (ADS)

    Şentürk, E.

    2004-04-01

    In this paper, we have investigated relaxation mechanisms and dielectric characteristics of an Sr 0.61- xBa 0.39Nb 2O 6Ce x (abbreviated as SBN61 and x=0.0066) single crystal with dielectric spectroscopy measurements. The crystal undergoes a ferroelectric phase transition at 340 K. The temperature dependence of the real and imaginary part of the complex dielectric susceptibility in the vicinity of ferroelectric-paraelectric phase transition has been studied in the frequency region 100 Hz-10 mHz. The measurement of the dielectric constants of the real and imaginary parts shows strong frequency dependence. The investigations of the dielectric constant using Cole-Cole plots revealed a non-Debye-type dielectric relaxation for Ce +3-doped SBN61. It reveals the coexistence of the two dielectric relaxators in the vicinity of the phase transition.

  19. Bosonic spectral density of epitaxial thin-film La1.83Sr0.17CuO4 superconductors from infrared conductivity measurements.

    PubMed

    Hwang, J; Schachinger, E; Carbotte, J P; Gao, F; Tanner, D B; Timusk, T

    2008-04-04

    We use optical spectroscopy to investigate the excitations responsible for the structure in the optical self-energy of thin epitaxial films of La(1.83)Sr(0.17)CuO(4). Using Eliashberg's formalism to invert the optical spectra we extract the electron-boson spectral function and find that at low temperature it has a two component structure closely matching the spin excitation spectrum recently measured by magnetic neutron scattering. We contrast the temperature evolution of the spectral density and the two-peak behavior in La(2-Sr(x)CuO(4) with another high temperature superconductor Bi(2)Sr(2)CaCu(2)O(8+delta). The bosonic spectral functions of the two materials account for the low T(c) of LSCO as compared to Bi-2212.

  20. Transmission electron microscopy characterization of protective La0.7Sr0.3MnO3-δ coatings prepared by electrostatic spray deposition on ferritic alloy

    NASA Astrophysics Data System (ADS)

    da Conceição, Leandro; Lay, Sabine; Robaut, Florence; Renou, Gilles; Muccillo, E. N. S.; Djurado, Elisabeth

    The effect of La0.7Sr0.3MnO3-δ (LSM) coating on SS446 steel on air oxidation at 800∘C was investigated by transmission electron microscopy. Dense and crack free thin LSM films were prepared by electrostatic spray deposition. The microstructural characterization was carried out on coated and uncoated interconnectors. A thin chromia scale at the alloy interface along with two spinel phases were observed after long term oxidation in both cases. Specimens exhibit, in addition, an SiO2 layer at the interface with steel due to the high content of Si in the steel. Significant changes in the thickness, morphology and composition occurred in the reaction layer for the LSM coated steel. These effects are explained on the basis of changes in the diffusive fluxes during exposure to the oxidation treatment. The implications of these effects for the degradation mechanism of LSM-based interconnects are discussed.

  1. Ultra-low magnetic damping of perovskite La0.7Sr0.3MnO3 thin films

    NASA Astrophysics Data System (ADS)

    Qin, Qing; He, Shikun; Song, Wendong; Yang, Ping; Wu, Qingyun; Feng, Yuan Ping; Chen, Jingsheng

    2017-03-01

    The perovskite La0.7Sr0.3MnO3 (LSMO) films grown on different substrates were investigated by an angle resolved broadband ferromagnetic resonance technique. All films exhibited a four-fold magnetocrystalline anisotropy, which is in accord with the crystal structure. Moreover, a perpendicular uniaxial anisotropy changed from the (001)pc easy plane to the [001]pc easy direction when the strain of LSMO films varies from tensile to compressive. The ultra-low magnetic damping constant of 5.2 × 10-4 was obtained for a 44.6 nm LSMO film on an NdGaO3 (110) substrate. The breathing Fermi surface model in which the damping constant is proportional to the density of states at Fermi energy is the dominant mechanism for the intrinsic magnetic relaxation.

  2. Synthesis, characterization and low field magnetotransport of Nd0.6Sr0.4MnO3/CrO3 composite

    NASA Astrophysics Data System (ADS)

    Ahmed, A. M.; Mohamed, H. F.; Diab, A. K.; Mohamed, Sara A.

    2017-02-01

    (Nd0.6Sr0.4MnO3)1-x/(CrO3)x with x = 0.0-0.030 step 0.005 weight% composites have been prepared by the solid state reaction process. The X-ray and scanning electron microscopic manifest that all composites are a single orthorhombic phase and there are no CrO3 grains separated from NdSrMnO matrix. The electrical measurements have revealed an increase of resistivity and a decrease of metal semiconductor transition with increasing CrO3. The composite x = 0.025 has largest magnetoresistance nearly one hundred percent at room temperature.

  3. Spin Gap in the Zigzag Spin-1/2 Chain Cuprate Sr0.9Ca0.1CuO2

    NASA Astrophysics Data System (ADS)

    Hammerath, F.; Nishimoto, S.; Grafe, H.-J.; Wolter, A. U. B.; Kataev, V.; Ribeiro, P.; Hess, C.; Drechsler, S.-L.; Büchner, B.

    2011-07-01

    We report a comparative study of Cu63 nuclear magnetic resonance spin lattice relaxation rates T1-1 on undoped SrCuO2 and Ca-doped Sr0.9Ca0.1CuO2 spin chain compounds. A temperature independent T1-1 is observed for SrCuO2 as expected for an S=1/2 Heisenberg chain. Surprisingly, we observe an exponential decrease of T1-1 for T<90K in the Ca-doped sample evidencing the opening of a spin gap. The data analysis within the J1-J2 Heisenberg model employing density-matrix renormalization group calculations suggests an impurity driven small alternation of the J2-exchange coupling as a possible cause of the spin gap.

  4. Energy-dependent crossover from anisotropic to isotropic magnetic dispersion in lightly-doped La1.96Sr0.04CuO4

    SciTech Connect

    Matsuda, Masaaki; Granroth, Garrett E; Fujita, M.; Yamada, K.; Tranquada, John M.

    2013-01-01

    Inelastic neutron scattering experiments have been performed on lightly-doped La$_{1.96}$Sr$_{0.04}$CuO$_{4}$, which shows diagonal incommensurate spin correlations at low temperatures. We previously reported that this crystal, with a single orthorhombic domain, exhibits the ``hourglass" dispersion at low energies [Phys. Rev. Lett. 101, 197001 (2008)]. In this paper, we investigate in detail the energy evolution of the magnetic excitations up to 65 meV. It is found that the anisotropic excitations at low energies, dispersing only along the spin modulation direction, crossover to an isotropic, conical dispersion that resembles spin waves in the parent compound La$_2$CuO$_{4}$. The change from two-fold to full symmetry on crossing the waist of the hourglass reproduces behavior first identified in studies of underdoped YBa$_2$Cu$_3$O$_{6+x}$. We discuss the significance of these results.

  5. Structure, the lattice dynamic, and the dielectric characteristics of Sr0.5Ba0.5Nb2O6 films

    NASA Astrophysics Data System (ADS)

    Pavlenko, A. V.; Zakharchenko, I. N.; Anokhin, A. S.; Kuprina, Yu. A.; Kiseleva, L. I.; Yuzyuk, Yu. I.

    2017-05-01

    Solid solution Sr0.5Ba0.5Nb2O6 films have been synthesized on a (111)Pt/(001)Si substrate by rf deposition in an oxygen atmosphere. The depolarized Raman spectra, the structure, and the dielectric characteristics of the films have been studied over a wide temperature range. It is found that the films were singlephase, had the tetragonal tungsten bronze structure, and had a pronounced axial texture with axis 001 directed perpendicular to the substrate surface. It is shown that the film material undergoes a diffuse phase transition to the state of a relaxor ferroelectric in the temperature range 300-425 K. Possible reasons of the regularities observed are discussed.

  6. Large oxygen-isotope effect in Sr0.4K0.6BiO3: Evidence for phonon-mediated superconductivity

    NASA Astrophysics Data System (ADS)

    Zhao, Guo-Meng; Conder, K.; Angst, M.; Kazakov, S. M.; Karpinski, J.; Maciejewski, M.; Bougerol, C.; Pshirkov, J. S.; Antipov, E. V.

    2000-11-01

    The oxygen-isotope effect has been investigated in a recently discovered superconductor Sr0.4K0.6BiO3. This compound has a distorted perovskite structure and becomes superconducting at about 12 K. Upon replacing 16O with 18O by 60-80 %, the Tc of the sample is shifted down by 0.32-0.50 K, corresponding to an isotope exponent of αO=0.40(5). This isotope exponent is very close to that for a similar bismuthate superconductor Ba1-xKxBiO3 with Tc=30 K. The very distinctive doping and Tc dependencies of αO observed in bismuthates and cuprates suggest that bismuthates should belong to conventional phonon-mediated superconductors while cuprates might be unconventional superconductors.

  7. An experimental and theoretical study of Ni impurity centers in Ba0.8Sr0.2TiO3

    NASA Astrophysics Data System (ADS)

    Sluchinskaya, I. A.; Lebedev, A. I.

    2017-08-01

    The local environment and the charge state of a nickel impurity in cubic Ba0.8Sr0.2TiO3 are studied by XAFS spectroscopy. According to the XANES data, the mean Ni charge state is 2.5+. An analysis of the EXAFS spectra and their comparison with the results of first-principle calculations of the defect geometry suggest that Ni2+ ions are in a high-spin state at the B sites of the perovskite structure and the difference of charges of Ni2+ and Ti4+ is mainly compensated by distant oxygen vacancies. In addition, a considerable amount of nickel in the sample is in a second phase BaNiO3 - δ. The measurements of the lattice parameter show a decrease in the unit cell volume upon doping, which can indicate the existence of a small amount of Ni4+ ions at the B site.

  8. Magnetic and calorimetric investigations of inverse magnetocaloric effect in Pr0.46Sr0.54MnO3

    NASA Astrophysics Data System (ADS)

    Naik, V. B.; Barik, S. K.; Mahendiran, R.; Raveau, B.

    2011-03-01

    We investigated magnetic entropy change (ΔSm) in the A-type antiferromagnet Pr0.46Sr0.54MnO3 by magnetic and differential scanning calorimetry (DSC) methods. The field-induced antiferromagnetic to ferromagnetic transition is first-order in nature and is accompanied by a large change in the latent heat as evidenced by the DSC data. The ΔSm shows an inverse magnetocaloric effect (ΔSm=+9 J kg-1 K-1 for ΔH =7 T) around the Neel temperature (TN=210±2 K) by magnetic measurement, which closely agrees with the calorimetric results. It is suggested that the large positive ΔSm results from a field-induced structural transition that accompanies the destruction of antiferromagnetism.

  9. A Raman scattering study of the antiferroelectric phase transition in (Sr0.70Ca0.30)TiO3

    NASA Astrophysics Data System (ADS)

    Mishra, Sanjay Kumar; Ranjan, Rajeev; Pandey, Dhananjai; Ouillon, R.; Pinan-Lucarre, J.-P.; Ranson, P.; Pruzan, Ph.

    2001-09-01

    The Raman scattering measurements on ceramic pellets of Sr0.70Ca0.30TiO3 (SCT 30) have been carried out as a function of temperature from 290 K to 8 K. It is shown that below (236+/-5 K), two additional lines appear around 79 and 128 cm-1. Further, there is enhancement in the intensity of the modes near 170 and 541 cm-1 below (236+/-5 K). The temperature at which these changes occur in the Raman spectra of SCT 30 correlates very well with the temperature at which the antiferroelectric superlattice reflections appear in the x-ray diffraction patterns. We propose that the additional modes are due to q≠0 phonons that have become Raman active due to the folding of the corresponding special points into the zone center below the cell-doubling antiferroelectric phase-transition temperature.

  10. Influence of applied electric field annealing on the microwave properties of (Ba0.5Sr0.5)TiO3 thin films

    NASA Astrophysics Data System (ADS)

    Cho, Kwang-Hwan; Lee, Chil-Hyoung; Kang, Chong-Yun; Yoon, Seok-Jin; Lee, Young-Pak

    2007-04-01

    The effect of heat treatment in electric field on the structure and dielectric properties at microwave range of rf magnetron sputtering derived (Ba0.5Sr0.5)TiO3 thin films have been studied. It has been demonstrated that postannealing in the proper electric field can increase the dielectric constant and the tunability. The increased out-of-plane lattice constant in the electric-annealed films indicated the formation of small polar regions with tetragonal structure, which are responsible for the increased dielectric constant and tunability. It was proposed that the segregation of Ti3+ ions caused by electric annealing could induce the formation of BaTiO3-like regions, which are ferroelectric at room temperature. And in dielectric loss, as the Ti-O bonding lengths increase, the energy scattering on the ferroelectric mode also increases. So, the value of dielectric loss is slightly increased.

  11. Ferroelectric and paraelectric Ba0.5Sr0.5TiO3 film structure distortions at room temperature and their effects on tunable microwave properties

    NASA Astrophysics Data System (ADS)

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

    2007-05-01

    Sputter-deposited Ba0.5Sr0.5TiO3 films on (001) MgO were characterized for their dielectric properties with different lattice structures. With varying Ar :O2 ratios during deposition, the films showed either in-plane (ca) tetragonal distortions, significantly affecting the dielectric constant and tunability. The dielectric constant exhibited clear hysteresis with dc bias at room temperature, indicating that the films were ferroelectric. The relationship between the dielectric properties and the distortions was the reverse of that observed in films deposited by pulsed laser deposition. The anisotropic in-plane dielectric behavior can be understood by relating polarization to film distortions and to the presence of permanent dipoles.

  12. The fabrication of thermoelectric La0.95Sr0.05CoO3 nanofibers and Seebeck coefficient measurement.

    PubMed

    Xu, Weihe; Shi, Yong; Hadim, Hamid

    2010-10-01

    The P-type perovskite oxides La(1-x)Sr(x)CoO(3) are a promising group of complex oxide thermoelectric (TE) materials. The thermoelectric properties of these oxides are expected to be significantly improved when their critical dimensions are reduced to the nanoscale. In this paper, the La(0.95)Sr(0.05)CoO(3) nanofibers, with diameters in the range of approximately 35 nm, were successfully prepared by the electrospinning process. X-ray diffraction (XRD) and scanning electron microscopy (SEM) were used to characterize these thermoelectric nanofibers. A micro-electromechanical (MEMS) tester was designed and fabricated to measure the Seebeck coefficient of the nanofibers. The measured voltage output was as large as 1.7 mV and the obtained Seebeck coefficient of the nanofibers reached 650 microV K(-1).

  13. Hollow spherical La0.8Sr0.2MnO3 perovskite oxide with enhanced catalytic activities for the oxygen reduction reaction

    NASA Astrophysics Data System (ADS)

    Lu, Fanliang; Sui, Jing; Su, Jianmin; Jin, Chao; Shen, Ming; Yang, Ruizhi

    2014-12-01

    A hollow spherical La0.8Sr0.2MnO3 (HS-LSM) perovskite oxide has been prepared using a new carbonate-template route, and characterized by XRD, SEM and TEM. SEM and TEM results show that the pre-prepared oxides consist of porous microspheres composed of submicrometer-sized subunits with a secondary particle diameter of ∼20-50 nm. The catalytic activity of the oxide for the oxygen reduction reaction (ORR) in 0.1 M KOH solution has been studied using a rotating ring-disk electrode (RRDE). In the ORR tests, a maximum cathodic current density of 6.4 mA cm-2 at -0.9 V (vs. Ag/AgCl) with 2500 rpm has been obtained, and the ORR mainly favors a direct four-electron pathway. The chronoamperometric test shows that the HS-LSM exhibits excellent stability for the ORR.

  14. Enhanced Shrinkage of Lanthanum Strontium Manganite (La0.90Sr0.10MnO3+δ) Resulting from Thermal and Oxygen Partial Pressure Cycling

    SciTech Connect

    McCarthy, Ben; Pederson, Larry R.; Anderson, Harlan U.; Zhou, Xiao Dong; Singh, Prabhakar; Coffey, Greg W.; Thomsen, Ed C.

    2007-10-01

    Exposure of La0.9Sr0.1MnO3+δ to repeated oxygen partial pressure cycles (air/10 ppm O2) resulted in enhanced densification rates, similar to behavior shown previously due to thermal cycling. Shrinkage rates in the temperature range 700 to 1000oC were orders of magnitude higher than Makipirtti-Meng model estimations based on stepwise isothermal dilatometry results at high temperature. A maximum in enhanced shrinkage due to oxygen partial pressure cycling occurred at 900oC. Shrinkage was greatest when LSM-10 bars that were first equilibrated in air were exposed to gas flows of lower oxygen fugacity than in the reverse direction. The former creates transient cation and oxygen vacancies well above the equilibrium concentration, resulting in enhanced mobility. These vacancies annihilate as Schottky equilibria is re-established, whereas the latter condition does not lead to excess vacancy concentrations.

  15. Growth diagram of La0.7Sr0.3MnO3 thin films using pulsed laser deposition

    NASA Astrophysics Data System (ADS)

    Guo, Hangwen; Sun, Dali; Wang, Wenbin; Gai, Zheng; Kravchenko, Ivan; Shao, Jian; Jiang, Lu; Ward, Thomas Z.; Snijders, Paul C.; Yin, Lifeng; Shen, Jian; Xu, Xiaoshan

    2013-06-01

    An experimental study was conducted on controlling the growth mode of La0.7Sr0.3MnO3 thin films on SrTiO3 substrates using pulsed laser deposition (PLD) by tuning growth temperature, pressure, and laser fluence. Different thin film morphology, crystallinity, and stoichiometry have been observed depending on growth parameters. To understand the microscopic origin, the adatom nucleation, step advance processes, and their relationship to film growth were theoretically analyzed and a growth diagram was constructed. Three boundaries between highly and poorly crystallized growth, 2D and 3D growth, stoichiometric and non-stoichiometric growth were identified in the growth diagram. A good fit of our experimental observation with the growth diagram was found. This case study demonstrates that a more comprehensive understanding of the growth mode in PLD is possible.

  16. A mechanical spectrum study of bilayer cuprate La 1.82Sr 0.18CaCu 2O 6+δ

    NASA Astrophysics Data System (ADS)

    Ying, X. N.; Yuan, Y. H.; Huang, Y. N.; Wang, Y. N.

    2007-05-01

    The mechanical spectrum of bilayer cuprate La 1.82Sr 0.18CaCu 2O 6+δ (La2126) was measured using the vibrating reed method from 30 K to room temperature at kilohertz frequency. A clear modulus softening was observed at 223 K accompanied by a sharp internal friction peak, which evidences a phase transition. Another broad internal friction peak around 250 K was observed, accompanied by a large modulus change. This contrasts with the broad internal friction peak of Ca doped Y Ba 2Cu 3O 7-δ (Y123) for which no clear modulus change was observed. The main contribution to the broad internal friction peak of La2126 is expected to be from the glass transition of the interstitial oxygen atoms.

  17. Structural evolution during calcination and sintering of a (La0.6Sr0.4)0.99CoO3-δ nanofiber prepared by electrospinning

    NASA Astrophysics Data System (ADS)

    Simonsen, S. B.; Shao, J.; Zhang, W.

    2017-06-01

    Design of three-dimensional metal oxide nanofibers by electrospinning is being widely explored. However, the impacts of calcination and sintering on the resulting morphology remain unknown. For the first time, (La0.6Sr0.4)0.99CoO3-δ (LSC) nanofiber, which is among the most promising electrode materials for solid oxide fuel cells, was synthesized by sol-gel electrospinning. By elevating the temperature in oxygen using in situ transmission electron microscopy, we discovered the structural transitions from nanofibers to nanotubes and then to nano-pearl strings. This facile and up-scalable method can be widely applied to design metal oxide one-dimensional nanomaterials with precise control in both geometry (nanofiber, nanotube and nano-pearl string) and surface area (by varying grain size).

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

    DOE PAGES

    Liu, Yaohua; Tornos, J.; te Velthuis, S. G. E.; ...

    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. The Ti dichroic reflectivity follows the Mn signal during the magnetization reversal, indicating exchange coupling between the Ti and Mn ions. However, the Ti dichroic reflectivity shows stronger temperature dependence than the Mn dichroic signal. Lastly, 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.

  19. Evidence for short-range-ordered charge stripes far above the charge-ordering transition in La1.67Sr0.33NiO4.

    PubMed

    Abeykoon, A M Milinda; Božin, Emil S; Yin, Wei-Guo; Gu, Genda; Hill, John P; Tranquada, John M; Billinge, Simon J L

    2013-08-30

    The temperature evolution of structural effects associated with charge order (CO) and spin order in La1.67Sr0.33NiO4 has been investigated using neutron powder diffraction. We report an anomalous shrinking of the c/a lattice parameter ratio that correlates with T(CO). The sign of this change can be explained by the change in interlayer Coulomb energy between the static-stripe-ordered state and the fluctuating-stripe-ordered state or the charge-disordered state. In addition, we identify a contribution to the mean-square displacements of Ni and in-plane O atoms whose width correlates quite well with the size of the pseudogap extracted from the reported optical conductivity, with a non-Debye-like component that persists below and well above T(CO). We infer that dynamic charge-stripe correlations survive to T∼2T(CO).

  20. Detailed structure of the low-energy magnetic dispersion of the diagonal incommensurate phase in La1.975Sr0.025CuO4

    NASA Astrophysics Data System (ADS)

    Matsuda, M.; Fernandez-Baca, J. A.; Fujita, M.; Yamada, K.; Tranquada, J. M.

    2011-09-01

    Inelastic neutron scattering experiments have been performed on lightly doped La1.975Sr0.025CuO4, which contains a hole concentration slightly higher than the critical concentration for three-dimensional long-range antiferromagnetic order. We previously found that the magnetic excitation spectrum in the insulating phase with a diagonal incommensurate spin modulation has similarities to that in the superconducting regime, where the spin modulation is bond parallel. In this study, we investigate the excitations in detail around Ecross, at which the excitations become most nearly commensurate. It is found that both the magnitude and the anisotropy of the momentum width of the excitations change abruptly at Ecross. Our experimental results suggest that the magnetic excitations rising from the pair of (diagonally) incommensurate wave vectors merge at Ecross into isotropic excitations.

  1. Evidence for Short-Range-Ordered Charge Stripes Far above the Charge-Ordering Transition in La1.67Sr0.33NiO4

    NASA Astrophysics Data System (ADS)

    Abeykoon, A. M. Milinda; Božin, Emil S.; Yin, Wei-Guo; Gu, Genda; Hill, John P.; Tranquada, John M.; Billinge, Simon J. L.

    2013-08-01

    The temperature evolution of structural effects associated with charge order (CO) and spin order in La1.67Sr0.33NiO4 has been investigated using neutron powder diffraction. We report an anomalous shrinking of the c/a lattice parameter ratio that correlates with TCO. The sign of this change can be explained by the change in interlayer Coulomb energy between the static-stripe-ordered state and the fluctuating-stripe-ordered state or the charge-disordered state. In addition, we identify a contribution to the mean-square displacements of Ni and in-plane O atoms whose width correlates quite well with the size of the pseudogap extracted from the reported optical conductivity, with a non-Debye-like component that persists below and well above TCO. We infer that dynamic charge-stripe correlations survive to T˜2TCO.

  2. Transmission-electron-microscopy study of charge-stripe order in La1.725Sr0.275NiO4

    NASA Astrophysics Data System (ADS)

    Li, Jianqi; Zhu, Yimei; Tranquada, J. M.; Yamada, K.; Buttrey, D. J.

    2003-01-01

    We characterize the local structure and correlations of charge stripes in La1.725Sr0.275NiO4 using transmission-electron microscopy. We present direct evidence that the stripe modulation is indeed one-dimensional within each NiO2 plane. Furthermore, we show that individual stripes tend to be either site centered or bond centered, with a bias towards the former. The spacing between stripes often fluctuates about the mean separation, contributing to a certain degree of frustration of the approximate body-centered stacking along the c axis. These results confirm ideas inferred from previous neutron-diffraction measurements on doped nickelates, and demonstrate that charge-stripe order is quite different from the conventional concept of charge-density-wave order.

  3. Bond-Stretching-Phonon Anomalies in Stripe-Ordered La1.69Sr0.31NiO4

    NASA Astrophysics Data System (ADS)

    Tranquada, J. M.; Nakajima, K.; Braden, M.; Pintschovius, L.; McQueeney, R. J.

    2002-02-01

    We report a neutron scattering study of bond-stretching phonons in La1.69Sr0.31NiO4, a doped antiferromagnet in which the added holes order in diagonal stripes at 45° to the Ni-O bonds. For the highest-energy longitudinal optical mode along the bonds, a softening of 20% is observed between the Brillouin zone center and the zone boundary. At 45° to the bonds, a splitting of the same magnitude is found across much of the zone. Surprisingly, the charge-ordering wave vector plays no apparent role in the anomalous dispersions. The implications for related anomalies in the cuprates are discussed.

  4. 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.

  5. Modified magnetic anisotropy at LaCoO3/La0.7Sr0.3MnO3 interfaces

    NASA Astrophysics Data System (ADS)

    Cabero, M.; Nagy, K.; Gallego, F.; Sander, A.; Rio, M.; Cuellar, F. A.; Tornos, J.; Hernandez-Martin, D.; Nemes, N. M.; Mompean, F.; Garcia-Hernandez, M.; Rivera-Calzada, A.; Sefrioui, Z.; Reyren, N.; Feher, T.; Varela, M.; Leon, C.; Santamaria, J.

    2017-09-01

    Controlling magnetic anisotropy is an important objective towards engineering novel magnetic device concepts in oxide electronics. In thin film manganites, magnetic anisotropy is weak and it is primarily determined by the substrate, through induced structural distortions resulting from epitaxial mismatch strain. On the other hand, in cobaltites, with a stronger spin orbit interaction, magnetic anisotropy is typically much stronger. In this paper, we show that interfacing La0.7Sr0.3MnO3 (LSMO) with an ultrathin LaCoO3 (LCO) layer drastically modifies the magnetic anisotropy of the manganite, making it independent of the substrate and closer to the magnetic isotropy characterizing its rhombohedral structure. Ferromagnetic resonance measurements evidence a tendency of manganite magnetic moments to point out-of-plane suggesting non collinear magnetic interactions at the interface. These results may be of interest for the design of oxide interfaces with tailored magnetic structures for new oxide devices.

  6. 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.

  7. Scintillation properties of a 2-inch diameter KCa0.8Sr0.2I3:Eu2+ single crystal

    NASA Astrophysics Data System (ADS)

    Wu, Yuntao; Lindsey, Adam C.; Loyd, Matthew; Stand, Luis; Zhuravleva, Mariya; Koschan, Merry; Melcher, Charles L.

    2017-09-01

    Inch-sized scintillating crystals are required for practical radiation detectors such as hand-held radio-isotope identification devices. In this work, a transparent and colorless 2-inch diameter KCa0.8Sr0.2I3: 0 . 5 mo% Eu2+ single crystal was grown by the vertical Bridgman method, and the scintillation properties of a ∅ 50 mm × 45 mm long sample were evaluated. The Eu2+ 5d1- 4 f emission under X-ray excitation is centered at 472 nm. Its scintillation decay time under 137 Cs source irradiation is 2 . 37 μs, and the absolute light output is 51,000 ± 3000 photons/MeV. The energy resolution at 662 keV was evaluated for different orientations of the crystals with respect to the PMT, and the effect of 40 K background subtraction on energy resolution was evaluated. The performance of the packaged crystal was also investigated.

  8. Optimization on photoelectric detection based on stacked La0.9Sr0.1MnO3-δ/LaAlO3-δ multijunctions

    NASA Astrophysics Data System (ADS)

    Xing, Jie; Ying Hao, Hui; Jia Guo, Er; Yang, Fang

    2011-08-01

    Three multijunctions consisting of La0.9Sr0.1MnO3-δ and LaAlO3-δ on Si substrate have been fabricated under different oxygen pressures by laser molecular beam epitaxy. They exhibit nonlinear and rectifying current-voltage characteristics and evident photocurrent response to He-Ne laser illumination. Experimental results indicate that the periodically stacked multijunction grown under lower oxygen pressure shows a better rectification behavior and a higher photocurrent. The photovoltaic responsivities of the multijunctions are enhanced greatly at reverse bias and are much higher than that of a similarly grown single p-n junction. Based on the band structure of the multilayers, a possible mechanism of the photovoltaic process was proposed. A high photovoltage responsivity of 168.6 mV/mW has been achieved at - 6 V bias; this demonstrates the potential of the present multijunction configuration for photodetectors operating at room temperature.

  9. 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.

  10. 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.

  11. Epitaxial growth and characterization of Eu0.5Sr0.5CoO3 thin films by off-axis sputtering

    NASA Astrophysics Data System (ADS)

    Kwon, Daeyoung; Wu, Youngsu; Kim, Bongju; Kim, Bog G.; Hwang, Harold Y.

    2009-09-01

    We report the epitaxial growth and physical properties of Eu0.5Sr0.5CoO3 (ESCO) thin films deposited on (001) LaAlO3 (LAO) and (001) SrTiO3 (STO) substrates by off-axis rf sputtering. The magnetic properties of a grown film are governed by the crystallinity of the thin film and strain effects due to the substrate. The temperature-dependent resistivity of an optimized ESCO thin film on a LAO substrate shows a characteristic sudden decrease near the ferromagnetic transition temperature, indicating metallic double-exchange-like behavior, while the resistivity of ESCO on a STO substrate displays insulatinglike behavior because of substrate strain. These results suggest that optimized ESCO film on LAO is ideal as a bottom electrode for strained dielectric and ferroelectric heterostructures.

  12. The pressure dependence of Tc in the infinite-layer electron-doped compound Sr 0.84Nd 0.16CuO 2

    NASA Astrophysics Data System (ADS)

    Wooten, C. L.; Beom-hoan, O.; Markert, J. T.; Smith, M. G.; Manthiram, A.; Zhou, J.; Goodenough, J. B.

    1992-03-01

    We report the effect of nearly hydrostatic pressure in the range 0-20 kbar on the resistively determined superconducting transition temperature Tc of the recently discovered infinite-layer electron-doped copper-oxide compound Sr 0.84ND 0.16CuO 2. In contrast to other electron-doped copper oxides, we observe a positive and appreciable change in Tc with pressure with value {dT c}/{dP }=+0.06±0.02 K/kbar. Thus the sign and magnitude of {dT c}/{dP} are not dominated by the carrier type; in this compound, we suggest they are determined by a pressure-induced enhancement of the interlayer coupling.

  13. Tailoring the solar absorptivity of thermochromic material La0.7Ca0.2Sr0.1MnO3

    NASA Astrophysics Data System (ADS)

    Fan, Desong; Li, Qiang; Xuan, Yimin

    2011-12-01

    La0.7Ca0.2Sr0.1MnO3 is a thermochromic material which can be used as thermal control device. However, its solar absorptivity is too high for that in spacecraft application. To reduce its solar absorptivity, an optical thin film is designed in this paper by using simulated annealing genetic algorithm. This film can effectively reflect the solar radiation at the short wave and can be transparent at long wave. A designed optical thin film is deposited on the surface of thermochromic material by electron beam evaporation. Experiments show that the solar absorptivity is reduced from 0.78 to 0.28 at short wave, and the transmissivity is 0.87 at long wave. The results match pretty well with the theoretical predictions in a global view.

  14. Flexoelectric Induced Caloric Effect in Truncated Pyramid Shaped Ba0.67Sr0.33TiO3 Ferroelectric Material

    NASA Astrophysics Data System (ADS)

    Patel, Satyanarayan; Chauhan, Aditya; Madhar, Niyaz Ahamad; Ilahi, Bouraoui; Vaish, Rahul

    2017-02-01

    Solid state refrigeration based on ferroelectric materials can potentially be competing in not-in-kind refrigeration technology. However, their functionality is currently limited to Curie temperatures. Through this article, authors have attempted to describe an unexplored component of the stress-driven caloric effect, obtainable beyond the Curie point. The phenomenon, termed as the flexocaloric effect (FCE), relies on inhomogeneous straining of the crystal lattice to induce polarization in centrosymmetric crystals (flexoelectricity). For this study, a truncated pyramid geometry was selected, and the dependence of sample height on caloric capacity was studied. A peak temperature change of 1.75 K (313 K) was estimated for Ba0.67Sr0.33TiO3 (BST) ceramics employing a truncated pyramid configuration.

  15. Direct Evidence for the Suppression of Charge Stripes in Epitaxial {La1.67Sr0.33NiO4} Films

    SciTech Connect

    Xie,C.; Budnick, J.; Hines, W.; Wells, B.; He, F.; Moodenbaugh, A.

    2008-01-01

    We have successfully grown epitaxial La1.67Sr0.33NiO4 films with a small crystalline mosaic using pulsed laser deposition. With synchrotron radiation, the x-ray-diffraction peaks associated with charge stripes have been successfully observed for relatively thick films. Anomalies due to the charge-ordering transition have been examined using four-point probe resistivity measurements. X-ray scattering provides direct evidence for suppression of the stripe phase in thinner samples; the phase disappears for film thicknesses 2600 Angstroms. The suppression appears to be a result of shrinking the stripe phase domains. This may reflect the stripe phase progressing from nematic to isotropic.

  16. Current dependence of the magnetoresistance in a colloidal-sphere-masked ion-milled La0.67Sr0.33MnO3 thin film

    NASA Astrophysics Data System (ADS)

    Li, J.; Zheng, D. N.; Rao, X. S.; Sow, C. H.; Chen, L.; Ong, C. K.

    2004-03-01

    An epitaxial La0.67Sr0.33MnO3 thin film covered with a monolayer of colloidal spheres was ion-milled so that structural discontinuities were involved. Nonlinear V-I characteristics have been observed, revealing that the zero-field resistance of the sample decreases with increasing measuring current I. In a magnetic field, however, the resistance varies non-monotonically with I. An inflexion appears around I = 50 nA. Accordingly, the magnetoresistance also correlates with I. A maximum value as high as - 700% (ΔR/RH) is recorded at liquid nitrogen in 1.5 T when I = 1 nA. The drastic current dependence of the magnetoresistance is believed to come from the ion-milling induced structural and magnetic disorders and to be related to the inelastic scattering of the spin-polarized electrons at the disorders. The possible underlying mechanisms are discussed in detail.

  17. Thickness and field dependent superconductivity in YBa2Cu3O7/La0.7Sr0.3MnO3 bilayers

    NASA Astrophysics Data System (ADS)

    Lin, J. G.; Hsu, Daniel; Song, M. Y.; Chiang, C. H.; Chan, W. C.

    2010-05-01

    Transport and magnetization properties of superconducting/ferromagnetic bilayers YBa2Cu3O7/La0.7Sr0.3MnO3 (YBCO/LSMO) are investigated with the thickness of bottom LSMO layer fixed at 50 nm and that of top YBCO (t) layer varied from 20 to 100 nm. Compared to bulk YBCO, the off set of superconducting temperature TSC-off is suppressed by 10 K for t =20 nm. The suppression rate of TSC versus magnetic field H is obtained as 1.2±0.2 K/T for all bilayers. Considering the polarization effect of LSMO on superconductivity is similar to the field effect, the internal field created by the LSMO in the YBCO(20nm)/LSMO(50nm) bilayer is estimated as 40 T.

  18. 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.

  19. Saturation of resistivity and Kohler's rule in Ni-doped La1.85Sr0.15CuO4 cuprate

    NASA Astrophysics Data System (ADS)

    Malinowski, A.; Bezusyy, V. L.; Nowicki, P.

    2017-01-01

    We present the results of electrical transport measurements of La1.85Sr0.15Cu1 -yNiyO4 thin single-crystal films at magnetic fields up to 9 T. Adding Ni impurity with strong Coulomb scattering potential to a slightly underdoped cuprate makes the signs of resistivity saturation at ρsat visible in the measurement temperature window up to 350 K. Employing the parallel-resistor formalism reveals that ρsat is consistent with the classical Ioffe-Regel-Mott limit and changes with carrier concentration n as ρsat∝1 /√{n } . Thermopower measurements show that Ni tends to localize mobile carriers, decreasing their effective concentration as n ≅0.15 -y . The classical unmodified Kohler's rule is fulfilled for magnetoresistance in the nonsuperconducting part of the phase diagram when applied to the ideal branch in the parallel-resistor model.

  20. Microwave dielectric and optical properties of amorphous and crystalline Ba0.5Sr0.5TiO3 thin films

    NASA Astrophysics Data System (ADS)

    Goud, J. Pundareekam; Joseph, Andrews; Ramakanth, S.; Naidu, Kuna Lakshun; Raju, K. C. James

    2016-05-01

    The thin films of composition Ba0.5Sr0.5TiO3 (BST5) were deposited by Pulsed Laser Deposition technique on amorphous fused silica substrates at room temperature (RT) and at 700°C. The film deposited at RT is amorphous while the other crystallized in cubic structure. The refractive index (n) and optical band gap (Eg) extracted from transmission spectra in the 190 -2500 nm range. Microwave dielectric properties were investigated using the Split Post Dielectric Resonators (SPDR) technique at spot frequencies of 10GHz and 20GHz. The experimental results show that thin films deposited at high temperature (700°C) shows very high dielectric constant for both 10GHz and 20 GHz. These high dielectric constant films can be used in a wide range of applications such as capacitors, non-volatile high speed random access memories, and electro-optic devices.

  1. Induced magnetization in La0.7Sr0.3MnO3/BiFeO3 superlattices.

    PubMed

    Singh, Surendra; Haraldsen, J T; Xiong, J; Choi, E M; Lu, P; Yi, D; Wen, X-D; Liu, J; Wang, H; Bi, Z; Yu, P; Fitzsimmons, M R; MacManus-Driscoll, J L; Ramesh, R; Balatsky, A V; Zhu, Jian-Xin; Jia, Q X

    2014-07-25

    Using polarized neutron reflectometry, we observe an induced magnetization of 75 ± 25 kA/m at 10 K in a La(0.7)Sr(0.3)MnO(3) (LSMO)/BiFeO(3) superlattice extending from the interface through several atomic layers of the BiFeO(3) (BFO). The induced magnetization in BFO is explained by density functional theory, where the size of band gap of BFO plays an important role. Considering a classical exchange field between the LSMO and BFO layers, we further show that magnetization is expected to extend throughout the BFO, which provides a theoretical explanation for the results of the neutron scattering experiment.

  2. Neutron scattering studies of the ferroelectric distortion and spin dynamics in the type-1 multiferroic perovskite Sr0.56Ba0.44MnO3

    NASA Astrophysics Data System (ADS)

    Pratt, Daniel K.; Lynn, Jeffrey W.; Mais, James; Chmaissem, Omar; Brown, Dennis E.; Kolesnik, Stanislaw; Dabrowski, Bogdan

    2014-10-01

    The magnetic order, spin dynamics, and crystal structure of the multiferroic Sr0.56Ba0.44MnO3 have been investigated using neutron and x-ray scattering. Ferroelectricity develops at TC=305 K with a polarization of 4.2 µC /cm2 associated with the displacements of the Mn ions, while the Mn4+ spins order below TN≈200 K into a simple G-type commensurate magnetic structure. Below TN the ferroelectric order decreases dramatically, demonstrating that the two order parameters are strongly coupled. The ground state spin dynamics is characterized by a spin gap of 4.6(5) meV and the magnon density of states peaking at 43 meV. Detailed spin wave simulations with a gap and isotropic exchange of J =4.8(2) meV describe the excitation spectrum well. Above TN strong spin correlations coexist with robust ferroelectric order.

  3. Flexoelectric Induced Caloric Effect in Truncated Pyramid Shaped Ba0.67Sr0.33TiO3 Ferroelectric Material

    NASA Astrophysics Data System (ADS)

    Patel, Satyanarayan; Chauhan, Aditya; Madhar, Niyaz Ahamad; Ilahi, Bouraoui; Vaish, Rahul

    2017-07-01

    Solid state refrigeration based on ferroelectric materials can potentially be competing in not-in-kind refrigeration technology. However, their functionality is currently limited to Curie temperatures. Through this article, authors have attempted to describe an unexplored component of the stress-driven caloric effect, obtainable beyond the Curie point. The phenomenon, termed as the flexocaloric effect (FCE), relies on inhomogeneous straining of the crystal lattice to induce polarization in centrosymmetric crystals (flexoelectricity). For this study, a truncated pyramid geometry was selected, and the dependence of sample height on caloric capacity was studied. A peak temperature change of 1.75 K (313 K) was estimated for Ba0.67Sr0.33TiO3 (BST) ceramics employing a truncated pyramid configuration.

  4. Electrical conduction mechanism and improved multiferroic properties of NFO/ (Pb0.50Sr0.50) TiO3 bilayer nanostructure composite thin film

    NASA Astrophysics Data System (ADS)

    Bala, Kanchan; Ram, Mast; Sharma, Hakikat; Negi, N. S.

    2016-05-01

    Multiferroic 2-2 type layered NFO/ (Pb0.50Sr0.50) TiO3 composite thin film on Pt/TiO2/Si substrate was prepared by novel metallo-Organic process using spin coating technique. The structural and surface morphology were confirmed by X-Ray diffraction (XRD) atomic force microscope (AFM). Significantly improved ferroelectric properties (Ps ˜ 8.69, Pr ˜ 3.19 µC/cm2 and Ec ˜ 419kV/cm) and magnetic properties (Ms), (Mr) and (Hc) is (104emu/cc, 0.8emu/cc and 25Oe.) were observed at room temperature. Our observation provides an effective way to manipulate the conduction behavior to understand the leakage current density of multiferroic composites film at the interface. Poole-Frankel tunneling conduction mechanism dominates the leakage current of films in the relatively high electric filed.

  5. Electronic conduction mechanism for NFO/(Pb0.80Sr0.20) TiO3 bi-layered nanostructure multiferroic composite thin film

    NASA Astrophysics Data System (ADS)

    Bala, Kanchan; Sharma, Hakikat; Negi, N. S.

    2016-05-01

    Multiferroic 2-2 type bi-layered NFO/(Pb0.80Sr0.20) TiO3 composite thin film on Pt/TiO2/Si substrate was prepared by novel metallo-Organic process using spin coating technique. The structural and surface morphology were confirmed by X-Ray diffraction (XRD) atomic force microscope (AFM). Significantly improved ferroelectric properties (Ps ~ 17.25, Pr ~ 8.02 µC/cm2 and Ec ~ 404kV/cm) and magnetic properties (Ms ~ 117emu/cc, Mr ~ 0.83emu/cc and Hc ~ 20Oe) were observed at room temperature. The leakage current densities in NFO/PST composites film have been studied. Poole-Frankel bulk limited conduction mechanism dominates of film at relatively high electric filed.

  6. CARRIER-LATTICE RELAXATION FOR BROADENING EPR LINEWIDTH IN Nd0.55Sr0.45MnO3

    NASA Astrophysics Data System (ADS)

    Fan, Jiyu; Zhang, Xiyuan; Tong, Wei; Zhang, Lei; Zhang, Weichun; Zhu, Yan; Shi, Yangguang; Hu, Dazhi; Hong, Bo; Ying, Yao; Ling, Langsheng; Pi, Li; Zhang, Yuheng

    2013-12-01

    In this paper, we report the electron paramagnetic resonance (EPR) study of perovskite manganite Nd0.55Sr0.45MnO3. Experimental data reveal that the EPR linewidth broadens with a quasilinear manner up to 480 K. The broadening of the EPR linewidth can be understood in terms of the shortening of carrier-lattice relaxation time due to the occurrence of strong carrier-phonon interactions. Two same activation energies obtained respectively from the temperature dependence of EPR intensity and resistivity indicate that the linewidth variation is correlated to the small polaron hopping. Therefore, the carrier-lattice coupling play a major role for deciding its magnetism in the present system.

  7. 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.

  8. Competition between quantum fluctuations and antiferroelectric order in Ru-doped Sr(0.8)Ca(0.2)Ti(1-x)Ru(x)O(3).

    PubMed

    Wei, T; Guo, Y Y; Guo, Y J; Luo, S J; Wang, K F; Liu, J-M; Wang, P W; Yu, D P

    2009-09-16

    The competition between quantum fluctuations and the antiferroelectric state in Sr(0.8)Ca(0.2)Ti(1-x)Ru(x)O(3) is investigated by measuring the low-temperature dielectric permittivity and by Raman spectroscopy. We demonstrate the significant impact of quantum fluctuations on the stability of the antiferroelectric polar order. It is revealed that the structural phase transitions can be modified by the quantum fluctuations, enhancing the stability of the high-symmetry phase and suppressing the antiferroelectric transitions. More importantly, a quantum antiferroelectric state, exhibiting similar behavior as the quantum ferroelectric state in terms of dielectric response, is identified. In addition, the effect of quantum fluctuations on the increasing permittivity at low temperature is also discussed.

  9. Surfactant-assisted synthesis of Ba0.7Sr0.3TiO3 nanoparticles by mechanical alloying and ultrasonic irradiation

    NASA Astrophysics Data System (ADS)

    Yustanti, Erlina; Hafizah, Mas Ayu Elita; Manaf, Azwar

    2017-01-01

    Ba0.7Sr0.3TiO3 nanoparticles were successfully synthesized by mechanical alloying and successive ultrasonic irradiation method with an addition of surfactant. Fine crystalline particles were first obtained after re-milled the sintered mechanically alloyed powders of BaCO3, TiO2 and SrCO3 precursors for 20 hours in which the size of particles was found below 300 nm. These fine particles were further refined their size under a high power ultrasonic treatment for 6 hours. Various types of surfactant namely amphoteric, cationic, anionic and non-ionic were brought into studies to find out their effectiveness in preventing the agglomeration due to strong attractive forces between fine particles. It was found that all surfactant prove effective to prevent the agglomeration. This was indicated in the distribution of particle size measurement in which mean size of particles added surfactants (139 nm-158 nm) was less than that of surfactant free (173 nm). However, among all surfactant which added in the media containing particles, only the non-ionic surfactant showed a particle size distribution with the smallest (139 nm) mean particle size. The effectiveness of surfactant in preventing the agglomeration depends on the concentration of surfactant and density of media containing particles. The study concluded that the addition of 0.1% non-ionic surfactant into media containing particles has resulted in Ba0.7Sr0.3TiO3 nanoparticles with the mean size of 139 nm.

  10. 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.

  11. 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.

  12. 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.

  13. Magnetron-sputtered La0.6Sr0.4Co0.2Fe0.8O3 nanocomposite interlayer for solid oxide fuel cells

    NASA Astrophysics Data System (ADS)

    Solovyev, A. A.; Ionov, I. V.; Shipilova, A. V.; Kovalchuk, A. N.; Syrtanov, M. S.

    2017-03-01

    A thin layer of a La0.6Sr0.4Co0.2Fe0.8O3 (LSCF) is deposited between the electrolyte and the La0.6Sr0.4Co0.2Fe0.8O3/Ce0.9Gd0.1O2 (LSCF/CGO) cathode layer of a solid oxide fuel cell (SOFC) by pulsed magnetron sputtering using an oxide target of LSCF. The films were completely dense and well adherent to the substrate. The effects of annealing in temperature range from 200 to 1000 °C on the crystalline structure of the LSCF films have been studied. The films of nominal thickness, 250-500 nm, are crystalline when annealed at temperatures above 600 °C. The crystalline structure, surface topology, and morphology of the films were determined using X-ray diffraction (XRD), atomic force microscopy (AFM), and scanning electron microscopy (SEM), respectively. To study the electrochemical characteristics of the deposited-film, solid oxide fuel cells using 325-nm LSCF films as interlayer between the electrolyte and the cathode have been fabricated. The LSCF interlayer improves the overall performance of the SOFC by increasing the interfacial area between the electrolyte and cathode. The electrolyte-supported cells with the interlayer have 30% greater, overall power output compared to that achieved with the cells without interlayer. The LSCF interlayer could also act as a transition layer that improves adhesion and relieves both thermal stress and lattice strain between the cathode and the electrolyte. Our results demonstrate that pulsed magnetron sputtering provides a low-temperature synthesis route for realizing ultrathin nanocrystalline LSCF film layers for intermediate- or low-temperature solid oxide fuel cells.

  14. Eu2+ concentration effects in KCa0.8Sr0.2I3:Eu2+: A novel high-performance scintillator

    NASA Astrophysics Data System (ADS)

    Wu, Yuntao; Zhuravleva, Mariya; Lindsey, Adam C.; Koschan, Merry; Melcher, Charles L.

    2016-06-01

    We report here the effect of Eu2+ concentration in KCa0.8Sr0.2I3:Eu2+ single crystal scintillators. KCa0.8Sr0.2I3:Eu2+ single crystals doped with 0.5, 1, 3, 5, and 7 mol% Eu2+ were grown by the Bridgman method. The effects of varying Eu2+concentration and crystal volume on the scintillation properties, including light yield, energy resolution, nonproportionality, scintillation decay time and afterglow level, were systematically investigated. For 5 mm×5 mm×5 mm samples, the best light yield of 86,000±4000 photons/MeV was achieved with a content of 5 mol% Eu2+; its energy resolution of 2.5% at 662 keV was comparable to that of LaBr3:Ce3+ and SrI2:Eu2+. With larger samples of about 2.2 cm3, the best performances achieved were for 3 mol% Eu2+ concentration, i.e. a light yield of 76,000±4000 photons/MeV and an energy resolution of 3% at 662 keV. A direct correlation between nonproportionality and Eu2+ concentration was found. A continuous lengthening of scintillation decay time and x-ray induced afterglow level with increasing Eu2+ concentration was observed. The self-absorption effect was evaluated by using the Stokes shift and the temperature dependence of the photoluminescence decay (PL) of the Eu2+ centers. The sample with the highest dopant concentration had more severe temperature quenching of the Eu2+5d-4f emission than the sample with the lowest dopant concentration, which could be ascribed to the thermally activated concentration quenching.

  15. Single crystalline La0.7Sr0.3MnO3 molecular sieve nanowires with high temperature ferromagnetism.

    PubMed

    Carretero-Genevrier, Adrián; Gázquez, Jaume; Idrobo, Juan Carlos; Oró, Judith; Arbiol, Jordi; Varela, María; Ferain, Etienne; Rodríguez-Carvajal, Juan; Puig, Teresa; Mestres, Narcís; Obradors, Xavier

    2011-03-23

    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(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 ε-MnO(2) nanoparticles with a new hexagonal structure is promoted. These nanoparticles generated up to 30 μm long and flexible hexagonal nanowires at mild growth temperatures (T(g) = 700 °C) as a consequence of the large crystallographic anisotropy of ε-MnO(2). The nanocrystallites of MnO(2) formed at low temperatures serve as seeds for the growth of La(0.7)Sr(0.3)MnO(3) nanowires at growth temperatures above 800 °C, through the diffusion of La and Sr into the empty 1D-channels of ε-MnO(2). Our particular growth method has allowed the synthesis of single crystalline molecular sieve (LaSr-2 × 4) monoclinic nanowires with composition La(0.7)Sr(0.3)MnO(3) and with ordered arrangement of La(3+) and Sr(2+) cations inside the 1D-channels. These nanowires exhibit ferromagnetic ordering with strongly enhanced Curie temperature (T(c) > 500 K) that probably results from the new crystallographic order and from the mixed valence of manganese.

  16. Hydrostatic pressure effect on the spin reorientation transition of ferromagnetic Sm0.7-xLaxSr0.3MnO3 (x = 0, 0.1) polycrystals

    NASA Astrophysics Data System (ADS)

    Thiyagarajan, R.; Arumugam, S.; Sivaprakash, P.; Kannan, M.; Saravanan, C.; Yang, Wenge

    2017-06-01

    The hydrostatic pressure effect on the resistivity and magnetization of the narrow band gap manganite Sm0.7-xLaxSr0.3MnO3 (x = 0, 0.1) systems has been investigated. At ambient pressure measurements, the parent compound Sm0.7Sr0.3MnO3 showed a ferromagnetic-insulating nature, whereas the 10% La-doped compound Sm0.6La0.1Sr0.3MnO3 showed a ferromagnetic-metallic nature. Furthermore, both samples showed a spin-reorientation transition (TSR) below Curie temperature, which originated from the Mn sublattice and was supported by an antiferromagnetic Sm(4f)-Mn(3d) interaction. Both samples exhibited a normal and inverse magnetocaloric effect as a result of these two different magnetic transitions. Magnetization measurements on Sm0.7Sr0.3MnO3 under pressure did not show an appreciable change in the Curie temperature, but enhanced TSR, whereas an insulator-metallic transition was observed during resistivity measurements under pressure. On the other hand, for Sm0.6La0.1Sr0.3MnO3, TC increased and TSR reduced upon the application of pressure. The metallic nature which is observed at ambient pressure resistivity measurement was further enhanced with 97% of piezoresistance. The pressure did not change the normal magnetocaloric effect of Sm0.7Sr0.3MnO3, but increased it in Sm0.6La0.1Sr0.3MnO3. However, there was not much change in the inverse magnetocaloric effect of both compounds. These studies were analyzed based on the pressure effect on the activation energy and scattering interaction factors.

  17. 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.

  18. A metal/Ba0.6Sr0.4TiO3/SiO2/Si single film device for charge trapping memory towards a large memory window

    NASA Astrophysics Data System (ADS)

    Zhang, Yuanyuan; Yang, Tao; Yan, Xiaobing; Zhang, Zichang; bai, Gang; Lu, Chao; Jia, Xinlei; Ding, Bangfu; Zhao, Jianhui; Zhou, Zhenyu

    2017-05-01

    In this study, we present a metal/Ba0.6Sr0.4TiO3/SiO2/Si (MBOS) structure for charge trapping memory, where the single Ba0.6Sr0.4TiO3 film acts as the blocking layer and charge trapping layer. This MBOS device structure demonstrates excellent charge trapping characteristics, a large memory window up to 8.4 V under an applied voltage of ±12 V, robust charge retention of only 4% charge loss after 1.08 × 104 s, fast switching rate, and great program/erase endurance. These attractive features are attributed to the high density of defect states in the Ba0.6Sr0.4TiO3 film and its inter-diffusion interface with SiO2. The properties of defect states in the Ba0.6Sr0.4TiO3 film are investigated through measurements of photoluminescence and photoluminescence excitation spectroscopy. The energy levels of these defect states are found to be distributed between 2.66 eV and 4.05 eV above the valence band. The inter-diffusion at the Ba0.6Sr0.4TiO3/SiO2 interface is observed by high-resolution transmission electron microscopy. More defect sites were created to obtain a better charge trapping capability and retention characteristics.

  19. 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.

  20. 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.

  1. 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.

  2. TECHNICAL NOTE: Structural and transport properties of the La1.85Sr0.15Cu1-xMxO4 superconducting system

    NASA Astrophysics Data System (ADS)

    Sedky, A.; Almulhem, Abdalaziz A.; Ibrahim, Sobhy S.

    2006-08-01

    X-ray diffraction and resistivity measurements were carried out on La1.85Sr0.15Cu1-xMxOy (La: 214) ceramic samples with different doping elements M and doping contents x (M = Li, Ni, Co and Mn, and x = 0.00,0.15 and 0.30). It is found that the substitutions of the above dopants at Cu sites cause lattice deformation and lead to the largest change in the transport properties of La: 214 systems. The pure sample with x = 0.00 exhibits superconductivity at 36 K, while the samples with x = 0.15 and 0.30 show semiconductor-like behavior with decreasing temperature from 300 K down to 20 K. The magnetic doping samples show a rapid increase in the resistivity more effectively than samples with the nonmagnetic dopants. The rate of increase in the resistivity with doping follows the order Mn>Co>Ni>Li. On the other hand, the activation energy Ea is calculated in the three different temperature regions characterized in the (ρ T) curve. A good correlation in the behavior of Ea as well as resistivity with dopants is reported. Our data fit well with the Arbrikosov and Gork'ov theory, but disagree with those of Huang et al (2005 Physica C 421 56). Our comments on Huang et al' s samples are reported.

  3. Structural imperfections and magnetoresistive properties of the ceramic La0.6Sr0.2Mn1,2-xFexO3±δ

    NASA Astrophysics Data System (ADS)

    Pashchenko, V. P.; Shemyakov, A. A.; Pashchenko, A. V.; Prokopenko, V. K.; Revenko, Yu. F.; Turchenko, V. A.; Varyukhin, V. N.; D'yakonov, V. P.; Szymczak, H.

    2007-08-01

    The x-ray structural, resistive, magnetic, and Mn55 NMR methods are used to investigate the ceramic magnetoresistive lanthanum manganite perovskites La0.6Sr0.2Mn1,2-xFexO3 (x =0, 0.02, 0.05, and 0.1) annealed at 1170 and 1500°C. It is found that increasing the Fe content decreases the metal-semiconductor phase transition temperature Tms and the Curie temperature TC, and increases the peak of the magnetoresistive effect near these phase transitions and results in growth of the peak at low temperatures, where the magnetoresistive effect is due to tunneling transitions of carriers between crystallites. The wide asymmetric Mn55 NMR spectrum, whose resonance frequency shifts with increasing x to lower frequencies, confirms the high-frequency electron-hole exchange between the Mn3+ and Mn4+ ions and the high degree of lattice imperfections, including not only vacancies but also clusters. The hysteresis in the field dependences of the magnetization at 4.2K is due to a change in the fraction of low-spin Mn2+ in clusters, whose magnetism appears below 42K. The increase of the activation energy with increasing Fe content is explained by the influence of these ions on the structural defect density, the charge carrier concentration, and the electron-hole exchange between heterovalent manganese ions in B positions.

  4. Photodiodes based in La0.7Sr0.3MnO3/single layer MoS2 hybrid vertical heterostructures

    NASA Astrophysics Data System (ADS)

    Niu, Yue; Frisenda, Riccardo; Svatek, Simon A.; Orfila, Gloria; Gallego, Fernando; Gant, Patricia; Agraït, Nicolás; Leon, Carlos; Rivera-Calzada, Alberto; Pérez De Lara, David; Santamaria, Jacobo; Castellanos-Gomez, Andres

    2017-09-01

    The fabrication of artificial materials by stacking of individual two-dimensional (2D) materials is amongst one of the most promising research avenues in the field of 2D materials. Moreover, this strategy to fabricate new man-made materials can be further extended by fabricating hybrid stacks between 2D materials and other functional materials with different dimensionality making the potential number of combinations almost infinite. Among all these possible combinations, mixing 2D materials with transition metal oxides can result especially useful because of the large amount of interesting physical phenomena displayed separately by these two material families. We present a hybrid device based on the stacking of a single layer MoS2 onto a lanthanum strontium manganite (La0.7Sr0.3MnO3) thin film, creating an atomically thin device. It shows a rectifying electrical transport with a ratio of 103, and a photovoltaic effect with V oc up to 0.4 V. The photodiode behaviour arises as a consequence of the different doping character of these two materials. This result paves the way towards combining the efforts of these two large materials science communities.

  5. Silver infiltrated La 0.6Sr 0.4Co 0.2Fe 0.8O 3 cathodes for intermediate temperature solid oxide fuel cells

    NASA Astrophysics Data System (ADS)

    Sakito, Y.; Hirano, A.; Imanishi, N.; Takeda, Y.; Yamamoto, O.; Liu, Y.

    Porous La 0.6Sr 0.4Co 0.2Fe 0.8O 3 (LSCF) electrodes on anode support cells were infiltrated with AgNO 3 solutions in citric acid and ethylene glycol. Two types of solid oxide fuel cells with the LSCF-Ag cathode, Ni-YSZ/YSZ/LSCF-Ag and Ni-Ce 0.9Gd 0.1O 1.95(GDC)/GDC/LSCF-Ag, were examined in a temperature range 530-730 °C under air oxidant and moist hydrogen fuel. The infiltration of about 18 wt.% Ag fine particles into LSCF resulted in the enhancement of the power density of about 50%. The maximum power density of Ni-YSZ/YSZ/LSCF was enhanced from 0.16 W cm -2 to 0.25 W cm -2 at 630 °C by infiltration of AgNO 3. No significant degradation of out-put power was observed for 150 h at 0.7 V and 700 °C. The Ni-GDC/GDC/LSCF-Ag cell showed the maximum power density of 0.415 W cm -2 at 530 °C.

  6. Strain induced x-ray absorption linear dichroism in La0.7Sr0.3MnO3 thin films

    NASA Astrophysics Data System (ADS)

    Aruta, C.; Ghiringhelli, G.; Tebano, A.; Boggio, N. G.; Brookes, N. B.; Medaglia, P. G.; Balestrino, G.

    2006-06-01

    Strain induced anisotropy in the electronic properties of La0.7Sr0.3MnO3 thin films was investigated by x-ray absorption spectroscopy at the Mn 2p and O 1s edges. Films on (100) SrTiO3 and (100) LaAlO3 substrates were grown by pulsed laser deposition with in situ reflection high energy electron diffraction diagnostic. At both absorption edges, clear features related to different anisotropic lattice strain effects as a function of the substrate were observed. On the average a negative (positive) linear dichroism was obtained for films grown under in-plane tensile (compressive) epitaxial strain conditions. Indeed, the structural macroscopic distortion induced by the substrate is responsible of the octahedra distortions with the resulting stabilization of x2-y2 (3z2-r2) orbitals. Enhanced linear dichroism at the Mn 2p edge in very thin films, only a few unit cells thick, is in agreement with a fully strained state which favors the formation of orbital ordered phase regions.

  7. Relaxation dynamics and thermodynamic properties of glassy Tb0.5Sr0.5MnO3 single crystal

    NASA Astrophysics Data System (ADS)

    Nhalil, Hariharan; Elizabeth, Suja

    2017-03-01

    Single crystals of Tb0.5Sr0.5MnO3 were grown in an optical float zone furnace and their magnetic and thermodynamic properties were studied. Temperature dependent DC magnetization measurements at different fields show strong irreversibility below the magnetic anomaly at 44 K. The upward deviation from ideal CW behavior well above the transition temperature and its field independent nature are signatures of non-Griffiths phase. The origin non-Griffiths phase owe to competition between the antiferromagnetic and ferromagnetic Mn3+-Mn4+ interactions mediated through intervening oxygen. Further, 44 K transition is confirmed as a magnetic glassy transition. The estimated dynamical spin flip time (τ0=2.11(3)×10-14 s) and zν(9.3(2)) values fall into the range of typical spin-glass systems. Detailed memory and temperature cycling relaxation measurements were performed and support the Hierarchical relaxation model. Low-temperature specific heat data displays a linear term, identifying the glassy magnetic phase contribution.

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

    DOE PAGES

    Jacobsen, H.; Zaliznyak, I. A.; Savici, A. T.; ...

    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

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

    DOE PAGES

    Zhang, B.; Sun, C. -J.; Lu, W.; ...

    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

  10. La(0.7)Sr(0.3)MnO3 nanoparticles based ultra-high sensitive ammonia chemical sensor.

    PubMed

    Al-Dossary, O; Umar, Ahmad; Al-Harbi, A A; Zaidi, Shabi Abbas; Dar, G N

    2012-08-01

    A facile, reliable, reproducible and ultra-high sensitive aqueous ammonia chemical sensor has been fabricated based on the utilization of La(0.7)Sr(0.3)MnO3 nanoparticles (LSMO NPs), as efficient electron mediators, and reported in this paper. The LSMO NPs were prepared by hydrothermal protocol followed by the annealing process and characterized in detail in terms of their mophological, structural and compositional properties. The I-V technique based aqueous ammonia sensor exhibits an ultra-high sensitivity of 494.68 +/- 0.01 microA cm(-2)mM(-1) and very low-detection limit of 0.2 microM with a response time less than 10 s. To the best of our knowledge, this is the first report in which LSMO is used as an efficient electron mediator for the fabrication of aqueous ammonia chemical sensor. Moreover, by comparing the literature, it is confirmed that the fabricated sensor exhibits highest sensitivity towards the detection of aqueous ammonia. This LSMO nanomaterial based research broadens the range of efficient electron mediators utilized for the fabrication of ultra-high sensitive chemical sensors.

  11. 55Mn NMR observation of colossal magnetoresistance effect in Sm0.55Sr0.45MnO3

    NASA Astrophysics Data System (ADS)

    Michalik, J. M.; Rybicki, D.; Tarnawski, Z.; Sikora, M.; De Teresa, J. M.; Ibarra, M. R.; Kapusta, Cz

    2017-07-01

    Temperature dependent 55Mn NMR study of Sm0.55Sr0.45MnO3 is reported. Previous bulk magnetization measurements have shown that below T C ~ 125 K the sample is ferromagnetic metallic (FMM) and above TC it is charge ordered and insulating. In present report, we show that from zero-field NMR a single line double-exchange (DE) signal is observed at temperatures up to 139 K, which is due to a presence of FMM clusters also above T C. The intensity of the DE line follows the temperature dependence of the magnetization measured at 0.01 T. When a magnetic field up to 2 T is applied at 139 K (i.e. 14 K above T C), a strong increase in NMR intensity of the DE line is observed indicating that content of FMM regions increases. This reveals that metallicity is induced in the material by the applied magnetic field and explains the observed colossal magnetoresistance (CMR) effect at the microscopic level. The observation agrees with previous results, which confirm that the percolation of the FMM clusters is responsible for the CMR effect. The shift of the resonant frequency in the applied field is three times smaller compared to decrease expected from gyromagnetic ratio, which indicates an antiferromagnetic coupling between the FMM clusters.

  12. 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.

  13. Dielectric relaxation in valence compensated solid solution Sr0.65La0.35Ti0.65Co0.35O3

    NASA Astrophysics Data System (ADS)

    Dwivedi, R. K.; Kumar, Devendra; Parkash, Om

    2000-01-01

    The valence compensated solid solution Sr0.65 La0.35 Ti0.65 Co0.35 O3 has been found to exhibit dielectric relaxor behaviour with a very high value of the dielectric constant. In the present investigation, this composition has been prepared using different processing parameters and routes, viz (a) solid-state sintering at 1350 °C followed by furnace cooling, (b) sintering at 1350 °C followed by annealing at 1000 °C, (c) sintering the sample prepared by the sol-gel route at 1100 °C and (d) sintering the powder prepared by the solid-state ceramic route at 1350 °C with 1 wt% SiO2 as a sintering aid. The dielectric characteristics were measured in the temperature range 300-500 K and frequency range 0.1 kHz-1 MHz. The dielectric characteristics of this composition are greatly influenced by processing parameters and routes. The dielectric relaxation in these materials was studied using impedance and modulus spectroscopic techniques.

  14. Energy storage properties of Dy3+ doped Sr0.5Ba0.5Nb2O6 thick film with nano-size grains

    NASA Astrophysics Data System (ADS)

    Yang, Daeyeol; Kang, Soo-Bin; Lim, Ji-Ho; Yoon, Songhyeon; Ryu, Jungho; Choi, Jong-Jin; Velayutham, Thamil Selvi; Kim, Hyungsun; Jeong, Dae-Yong

    2017-09-01

    We studied the temperature stable high-energy storage capacitors. Sr0.5Ba0.5Nb2O6 (SBN) is the lead-free ferroelectric solid solution between BaNb2O6 and SrNb2O6. By doping Dy into SBN, the Curie temperature was lowered and dielectric constant was increased. To improve the breakdown behavior of Dy-doped SBN, the aerosoldeposition(AD) was applied to fabricate the dense films with nano-sized grains. These nano-grain give a large number of grain boundaries, suppressing the electron conduction in ceramics. The dielectric constant and breakdown electric field of the AD films annealed at 650 °C were measured as 2307 and 9.9 MV/m, while bulk were 1080 and 4 MV/m. Energy density and efficiency of the AD films annealed at 650 °C were also enhanced as 0.65 J/cc and 90.2% and bulk were 0.08 J/cc and 72.1%, respectively. In addition, the dielectric constant of AD film annealed at 550 °C and 650 °C were quite stable up to 150 °C.

  15. Magnetic coupling in Epitaxial BiFeO3-La0.7Sr0.3MnO3 Heterostructures Integrated on Si(100)

    NASA Astrophysics Data System (ADS)

    Singamaneni, Srinivasa Rao; Prater, J. T.; Wu, Fan; Shelton, C. T.; Maria, J.-P.; Narayan, J.

    2014-03-01

    We present and discuss the magnetic characteristic of BiFeO3 (BFO)/La0.7Sr0.3MnO3 (LSMO) heterostructure, integrated on Si (100) using pulsed laser deposition (PLD) via the domain matching epitaxy (DME) paradigm. The magnetic behavior of this heterostructure, in which a d5 system (Fe3+) manifested in FE-AFM BFO is epitaxially conjoined at the interface to a multivalent transition metal ion such as Mn3+/Mn4+ in LSMO exhibits interesting magneto electric coupling phenomenon. The temperature- and magnetic field-dependent magnetization measurements reveal an unexpected enhancement in magnetization and improved magnetic hysteresis squareness originating from the BFO/LSMO interface. We observe a stronger temperature dependence of exchange coupling when the polarity of field cooling is negative as compared to positive field cooling. We believe such an enhancement in magnetization and magnetic coupling is likely directly related to an electronic orbital reconstruction at the interface and complex interplay between orbital and spin degrees of freedom.

  16. Contact resistance to SrRuO3 and La0.67Sr0.33MnO3 epitaxial films

    NASA Astrophysics Data System (ADS)

    Abuwasib, Mohammad; Lee, Hyungwoo; Gruverman, Alexei; Eom, Chang-Beom; Singisetti, Uttam

    2015-12-01

    Contact resistance to the metallic oxide electrodes, SrRuO3 (SRO) and La0.67Sr0.33MnO3 (LSMO), is an important parameter that affects the ferroelectric tunnel junction (FTJ) device performance. We have systematically studied the contact resistance between metallic oxide electrodes (SRO, LSMO) and contact metal overlayers (Ti, Pt) after exposure to various processing environments. Specific contact resistivity (ρc) for Ti and Pt contact metals and the sheet resistance (Rsh) of the metallic oxides are measured after exposure to different reactive ion plasma process steps. Sheet resistance degradation was observed for both SRO and LSMO films after exposure to plasma treatment. Severe contact resistance degradation was observed for Ti contacts as compared to Pt after reactive ion etching on LSMO films. The effect of oxygen (O2) plasma on LSMO was observed to be most severe with non-ohmic behavior with Ti contacts, which can affect the functionality of FTJ devices. Finally, the thermal stability of contacts was investigated, Pt contacts to SRO show low resistance ohmic behavior even after annealing at 900 °C, making it a suitable contact for FTJ devices.

  17. Complete vertical M-H loop shift in La0.7Sr0.3MnO3/SrRuO3 thin film heterostructures

    NASA Astrophysics Data System (ADS)

    Singamaneni, Srinivasa Rao; Fan, Wu; Prater, J. T.; Narayan, J.

    2015-05-01

    In the current work, we have epitaxially integrated La0.7Sr0.3MnO3/SrRuO3 (LSMO/SRO) BLs with the technologically important substrate Si (100) using pulsed laser deposition. Interestingly, at 4 K, under the magnetic field sweep of ±1500 Oe, a complete vertical M-H loop shift is observed in the sample prepared with 180 nm SRO thickness, which is unusual. This vertical shift persists even up to a field sweep range of ±6000 Oe, at which point the shift disappears and a symmetrical hysteresis loop centered at the origin is observed. In contrast, at the same temperature, under the same field sweep range, we observe a normal M-H loop (no or little vertical shift) from the sample with 45 nm SRO thickness. In both the cases, the LSMO thickness was held constant at ˜100 nm. It appears that SRO moment is frozen in place in the latter case, providing a clear demonstration of the effect that biasing layer (SRO) thickness can have on the magnetic characteristics of bilayer films. We attribute this vertical shift to the strong interplay between the uniaxial magnetocrystalline anisotropy and microscopic interface domain structure.

  18. Study of magnetic ordering in the perovskite manganites Pr0.6Sr0.4CrxMn1-xO3

    NASA Astrophysics Data System (ADS)

    Ge, X. S.; Wu, L. Q.; Li, S. Q.; Li, Z. Z.; Tang, G. D.; Qi, W. H.; Zhou, H. J.; Xue, L. C.; Ding, L. L.

    2017-04-01

    Powder samples of the ABO3 perovskite manganites Pr0.6Sr0.4CrxMn1-xO3 (0.00≤x≤0.30) were synthesized using the sol-gel method. X-ray diffraction analyses showed that all the samples had a single-phase orthorhombic structure. By analyzing magnetic parameters on the basis of the O2p itinerant electron model, we found that there are two magnetic transition temperatures, TCM and TCP, corresponding to changes in the magnetic ordering for the Mn and Pr cations, respectively. The magnetic moments of Mn3+ and Cr3+ cations within the B sublattice show canted ferromagnetic coupling, and the magnetic moments of the Pr cations within the A sublattice also show canted ferromagnetic coupling. However, the total magnetic moment of the A sublattice shows antiferromagnetic coupling against that of the B sublattice. The assumption of the canted ferromagnetic coupling within the B sublattice was confirmed using magnetoresistance experimental results.

  19. 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.

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

    DOE PAGES

    Gasparov, V. A.; Drigo, L.; Audouard, A.; ...

    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

  1. Non-saturating magnetoresistance of La0.7Sr0.3MnO3 thin films in pulsed magnetic fields up to 60T

    NASA Astrophysics Data System (ADS)

    Niu, Wei; Gao, Ming; Wang, Xuefeng

    The mixed-valence manganite La0.7Sr0.3MnO3 (LSMO) is an interesting material for spintronics due to its intrinsic magnetoresistance properties. In this work, high quality LSMO films with atomic terraces are epitaxially grown on SrTiO3 (100) substrates by laser molecular beam epitaxy. The magnetoresistance of LSMO thin films has been measured in pulsed magnetic fields up to 60T over a wide temperature range. Unsaturated magnetoresistances and resistance relaxation of LSMO thin films have been found at different temperatures. Unlike polycrystalline manganites, a linear increase with fields of the magnetoconductance at low temperature which is attributed to the spin-dependent tunneling via grain boundaries. However, the unsaturation magnetoresistances of our LSMO thin films at different temperature show two kinds of trends: quadratic at low temperature; qusi-linear at high temperature. We attribute the unsaturation behavior to the scattering of domain walls. National Laboratory of Solid State Microstructures, Collaborative Innovation Center of Advanced Microstructures, and School of Electronic Science and Engineering, Nanjing University, Nanjing 210093, China.

  2. Observation of reversible critical current performance under large compressive strain in Sr0.6K0.4Fe2As2 tapes

    NASA Astrophysics Data System (ADS)

    Liu, F.; Yao, C.; Liu, H.; Dai, C.; Qin, J.; Ci, L.; Mao, Z.; Zhou, C.; Shi, Y.; Jin, H.; Wang, D.; Ma, Y.

    2017-07-01

    Iron-based superconductors have caused great interest regarding high-field applications due to their good properties. A common fabrication route for 122-type wires and tapes is the ex situ powder-in-tube (PIT) process. From the point of application in the high magnetic field, where high electromagnetic forces are present, the conductor strength and its tolerance to the mechanical load are important issues. In order to understand the comparatively integrated critical current characterization of the Sr-122 tape under axial strain, the so-called U-spring setup was used to test a silver-sheathed Sr0.6K0.4Fe2As2 tape sample with a single core over a wide range of applied axial strain (-0.6% ˜ 0.3%). It was found that when the sample was compressed, the critical current performance showed reversiblity meanwhile the irreversible tensile strain limit was quite low. The Sr-122/Ag tape shows very good performance under compression, and a possible conductor design should be considered to make the superconductor work at proper compressive strain states for future applications.

  3. 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.

  4. Anisotropy of the upper critical fields and the paramagnetic Meissner effect in La1.85Sr0.15CuO4 single crystals

    NASA Astrophysics Data System (ADS)

    Felner, I.; Tsindlekht, M. I.; Drachuck, G.; Keren, A.

    2013-02-01

    Optimally doped La1.85Sr0.15CuO4 single crystals have been investigated by dc and ac magnetic measurements. These crystals have rectangular needle-like shapes with the long needle axis parallel to the crystallographic c axis (c-crystal) or parallel to the basal planes (a-crystal). In both crystals, the temperature dependence of the upper critical fields (HC2) and the surface critical field (HC3) were measured. The H-T phase diagram is presented. Close to TC = 35 K, for the c-crystal, {\\boldsymbol{\\gamma}}^{c}={H}_{{C3}}^{c}/{H}_{{C2}}^{c}=1.8 0(2), whereas for the a-crystal the {\\boldsymbol{\\gamma}}^{a}={H}_{{C3}}^{a}/{H}_{{C2}}^{a}=4.0(2) obtained is much higher than 1.69, predicted by the ideal mathematical model. At low applied dc fields, positive field-cooled branches known as the ‘paramagnetic Meissner effect’ (PME) are observed; their magnitude is inversely proportional to H. The anisotropic PME is observed in both a- and c-crystals, only when the applied field is along the basal planes. It is speculated that the high γa and the PME are connected to each other.

  5. Study of La0.67Sr0.33MnO3 Structure and Resistivity Synthesized by Using Sol Gel Method

    NASA Astrophysics Data System (ADS)

    Widyaiswari, U.; Kurniawan, B.; Imaduddin, A.; Saptari, S. A.

    2016-11-01

    In this study a colossal magnetoresistance La0.67Sr0.33MnO3 material was synthesized by using a sol gel method with different treatment heating process. First sample calcined at 850°C for 10 hours and pelletized, labelled as LSMO1, while another sample calcined at 850°C for 10 hours, pelletized, and sintered at 1200°C for 2 hours, labelled as LSMO2. The aim of this study was to learn a structure and resistivity of this material. The XRD results showed that both samples were single phase with no peak of impurity and formed a rhombohedral structure with space group R-3c. And the result showed that LSMO1 has smaller crystallite size than LSMO2. Result of resistivity measurement showed that LSMO1 has insulator behavior with resistivity several order of magnitude bigger than LSMO2. While LSMO2 had the peak of resistivity that showed a metal-insulator transition.

  6. Orientation Control of Interfacial Magnetism at La0.67Sr0.33MnO3/SrTiO3 Interfaces.

    PubMed

    Guo, Er-Jia; Charlton, Timothy; Ambaye, Haile; Desautels, Ryan D; Lee, Ho Nyung; Fitzsimmons, Michael R

    2017-06-07

    Understanding the magnetism at the interface between a ferromagnet and an insulator is essential because the commonly posited magnetic "dead" layer close to an interface can be problematic in magnetic tunnel junctions. Previously, degradation of the magnetic interface was attributed to charge discontinuity across the interface. Here, the interfacial magnetism was investigated using three identically prepared La0.67Sr0.33MnO3 (LSMO) thin films grown on different oriented SrTiO3 (STO) substrates by polarized neutron reflectometry. In all cases the magnetization at the LSMO/STO interface is larger than the film bulk. We show that the interfacial magnetization is largest across the LSMO/STO interfaces with (001) and (111) orientations, which have the largest net charge discontinuities across the interfaces. In contrast, the magnetization of LSMO/STO across the (110) interface, the orientation with no net charge discontinuity, is the smallest of the three orientations. We show that a magnetically degraded interface is not intrinsic to LSMO/STO heterostructures. The approach to use different crystallographic orientations provides a means to investigate the influence of charge discontinuity on the interfacial magnetization.

  7. Ferroelectric Properties of BaZrO3 Doped Sr0.8Bi2.2Ta2O9 Thin Films

    NASA Astrophysics Data System (ADS)

    Bozgeyik, Mehmet S.; Cross, Jeffrey S.; Ishiwara, Hiroshi; Shinozaki, Kazuo

    2009-06-01

    Novel sol-gel derived Sr0.8Bi2.2Ta2O9 (SBT) doped with 5 and 7% molar ratio BaZrO3 (BZ) thin films were fabricated, characterized, and electrical properties were evaluated with Pt electrodes. X-ray diffraction (XRD) analysis showed all the characteristic peaks of the layered perovskite structure with (115) orientation and slight peak broadening by BZ doping. X-ray photoelectron spectra (XPS) showed a small shift in the Sr 3d peak with BZ substitution. Scanning electron microscopy (SEM) cross-sectional photographs of the films show smaller grain size and greater porosity with BZ addition. The remanent polarization (2Pr) was significantly reduced from ˜16.4 µC/cm2 for SBT to ˜2.3 µC/cm2 for SBT with 7% BZ. Capacitance-voltage measurements performed at a frequency of 1 MHz showed butterfly type hysteresis loops, which is further evidence of ferroelectricity of the modified SBT, and dielectric constant of 135 for SBT with 7% BZ. Leakage current measurements showed one order of magnitude higher leakage current for SBT with 5% BZ compared to SBT. Lower film dielectric constant leads to higher leakage current in BZ doped SBT. Although leakage mechanisms predict this general trend, it runs counter to the objective of preparing ferroelectric films with low leakage and low dielectric constants for ferroelectric gate field-effect transistor (FeFET) type memory.

  8. Infield X-ray diffraction studies of field and temperature driven structural phase transition in Nd0.49Sr0.51MnO3+δ

    NASA Astrophysics Data System (ADS)

    Shahee, Aga; Sharma, Shivani; Singh, K.; Lalla, N. P.

    2017-07-01

    Comprehensive X-ray diffraction (XRD) studies have been performed at different temperature (T) (4.2-300 K) and magnetic field (H) (0-8 T) to understand the evolution of crystal structure of Nd0.49Sr0.51MnO3+δ (NSMO) under non ambient conditions. The T dependent XRD results show the abrupt change in the lattice parameters without any change in lattice symmetry at ∼200 K, which is associated with the first order structural phase transition from ferromagnetic to antiferromagnetic phase. This phase transition is strongly H dependent and shifted to lower temperature (∼150 K) on the application of 8 T field with phase coexistence (high temperature phase ∼18%), even down to 4.2 K. Isothermal XRD results at 150 K under different H clearly illustrate the H induced first order structural phase transition. The critical H at which this phase transformation starts is ∼1 T, with rapid growth above 4 T with hysteretic nature during increasing and decreasing H. These results are supported with the resistivity and magnetoresistance results and affirm the strong spin-lattice coupling in NSMO. Our detail studies reveal the structural correlations to the observed colossal magnetoresistance and magnetocaloric effect in this material.

  9. Magnetism and superconductivity in Eu0.2Sr0.8(Fe0.86Co0.14)2As2 probed by 75As NMR.

    PubMed

    Sarkar, R; Nath, R; Khuntia, P; Jeevan, H S; Gegenwart, P; Baenitz, M

    2012-02-01

    We report bulk superconductivity (SC) in Eu(0.2)Sr(0.8)(Fe(0.86)Co(0.14))(2)As(2) single crystals by means of electrical resistivity, magnetic susceptibility and specific heat measurements with T(c) is approximately equal to 20 K and an antiferromagnetic (AFM) ordering of Eu(2+) moments at T(N) is approximately equal to 2.0 K in zero field. (75)As NMR experiments have been performed in the two external field directions (H is parallel to ab) and (H is parallel to c). (75)As-NMR spectra are analysed in terms of first-order quadrupolar interaction. Spin-lattice relaxation rates (1/T(1)) follow a T(3) law in the temperature range 4.2-15 K. There is no signature of a Hebel-Slichter coherence peak just below the SC transition, indicating a non-s-wave or s(±) type of superconductivity. In the temperature range 160-18 K 1/T(1)T follows the C/(T+θ) law reflecting 2D AFM spin fluctuations.

  10. Colossal terahertz magnetoresistance at room temperature in epitaxial La0.7Sr0.3MnO3 nanocomposites and single-phase thin films

    DOE PAGES

    Lloyd-Hughes, James; Mosley, C. D. W.; Jones, S. P. P.; ...

    2017-03-13

    Colossal magnetoresistance (CMR) is demonstrated at terahertz (THz) frequencies by using terahertz time-domain magnetospectroscopy to examine vertically aligned nanocomposites (VANs) and planar thin films of La0.7Sr0.3MnO3. At the Curie temperature (room temperature), the THz conductivity of the VAN was dramatically enhanced by over 2 orders of magnitude under the application of a magnetic field with a non-Drude THz conductivity that increased with frequency. The direct current (dc) CMR of the VAN is controlled by extrinsic magnetotransport mechanisms such as spin-polarized tunneling between nanograins. In contrast, we find that THz CMR is dominated by intrinsic, intragrain transport: the mean free pathmore » was smaller than the nanocolumn size, and the planar thin-film exhibited similar THz CMR to the VAN. Surprisingly, the observed colossal THz magnetoresistance suggests that the magnetoresistance can be large for alternating current motion on nanometer length scales, even when the magnetoresistance is negligible on the macroscopic length scales probed by dc transport. This suggests that colossal magnetoresistance at THz frequencies may find use in nanoelectronics and in THz optical components controlled by magnetic fields. As a result, the VAN can be scaled in thickness while retaining a high structural quality and offers a larger THz CMR at room temperature than the planar film.« less

  11. Signatures of correlation between magnetic and electrical properties of Tb0.5Sr0.5MnO3 single crystals

    NASA Astrophysics Data System (ADS)

    Nhalil, Hariharan; Elizabeth, Suja

    2016-12-01

    Here, we report the dielectric, impedance and transport studies of non-charge-ordered magnetic glass, Tb0.5Sr0.5MnO3 single crystals. The temperature- and frequency-dependent real (ε') and imaginary (ε'' or tanδ) parts of the dielectric constant display large frequency dispersion. The colossal dielectric constant observed (≈ 3000) above 100 K is considered extrinsic. The activation energy of thermally activated relaxation is calculated using the Arrhenius law. Interestingly, two relaxation regions, each with different activation energies (E a ) are clearly evident, one occurring above and the other below the glassy magnetic transition temperature (Tg = 44 \\text{K}) . E a relates to the electron hopping between Mn3+ and Mn4+ ions and the origin of dielectric dispersion. E a in the glassy region is lower than that in paramagnetic region due to a lower energy spent in hopping between frozen spins. Bulk capacitance and resistivity derived from impedance measurements reveal anomalies around T g . Electrical transport data between 60 and 300 K shows insulating behavior and the calculated E a is in good agreement with the value obtained from dielectric measurements. Although, these results cannot be interpreted in terms of magneto-electric coupling, the correlation observed between magnetic and electronic states of the system is significant.

  12. 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.

  13. Interfacial Spin Glass State and Exchange Bias in the Epitaxial La0.7Sr0.3MnO3/LaNiO3 Bilayer

    NASA Astrophysics Data System (ADS)

    Zhou, Guo-wei; Guan, Xiao-fen; Bai, Yu-hao; Quan, Zhi-yong; Jiang, Feng-xian; Xu, Xiao-hong

    2017-05-01

    We study the magnetic properties of an epitaxial growth bilayer composed of ferromagnetic La0.7Sr0.3MnO3 (LSMO) and paramagnetic LaNiO3 (LNO) on SrTiO3 (STO) substrates. We find that the stack order of the bilayer heterostructure plays a key role in the interfacial coupling strength, and the coupling at the LSMO(top)/LNO(bottom) interface is much stronger than that at the LNO(top)/LSMO(bottom). Moreover, a strong spin glass state has been observed at the LSMO/LNO interface, which is further confirmed by two facts: first, that the dependence of the irreversible temperature on the cooling magnetic field follows the Almeida-Thouless line and, second, that the relaxation of the thermal remnant magnetization can be fitted by a stretched exponential function. Interestingly, we also find an exchange bias effect at the LSMO/LNO bilayer below the spin glass freezing temperature, indicating that the exchange bias is strongly correlated with the spin glass state at its interface.

  14. 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.

  15. Effect of particle size on magnetic and electric transport properties of La(0.67)Sr(0.33)MnO3 coatings.

    PubMed

    Zhou, Yu; Zhu, Xinde; Li, Shengli

    2015-12-14

    A systematic study of polycrystalline La0.67Sr0.33MnO3 (LSMO) manganite coatings has been undertaken to analyse the effect of various particle sizes on the magnetic and electric transport properties. In order to acquire a series of samples with different particle sizes, the samples were prepared by a sol-gel method and were subjected to annealing at four different temperatures. With decreasing particle sizes, the magnetization decreases while the coercivity increases, which is attributed to the magnetically disordered surface layer. More attractively, the electrical transport properties can be systematically manipulated by particle sizes and so can the low field magnetoresistance (LFMR) values. Emphasis is placed on how the particle size affects the temperature dependence of resistivity, and three conduction models are explored to describe the transport behaviours in three temperature regions. A minimum resistivity is observed in the low temperature region in the presence and absence of a magnetic field, which can be mainly explained as due to the intergranular spin polarized tunneling (ISPT) through the grain boundaries (GBs) in polycrystalline materials.

  16. Magnetic AC loss of a mono-Sr0.6K0.4Fe2As2 tape/Ag in perpendicular field

    NASA Astrophysics Data System (ADS)

    Liu, Qi; Zhang, Guomin; Yu, Hui; Huang, Miaomiao; Yuan, Weijia

    2016-12-01

    The magnetic AC losses of monofilament Sr0.6K0.4Fe2As2/Ag tapes are measured in the temperature range between 20 K and 30 K both in perpendicular and parallel field. The loss, measured by the standard magnetization technique, is determined from the area of the hysteresis loop using a vibrating sample magnetometer (VSM) in a cyclic field of amplitude up to 7 T. The results in perpendicular field are compared to that of the parallel-field loss and theoretical calculation of magnetization loss at various temperatures. There is a reasonable agreement between the theoretical model and the experimental results even in high field. The magnetic critical current density (Jc) of the tape, obtained by the magnetic hysteresis measurements M(H), are investigated in two field directions and in the temperature range from 5 K to 30 K. The comparison between the magnetic Jc in both field directions and the transport Jc of the tape are also done at various temperatures and fields. The anisotropy of Jc (Γ = Jcab /Jcc) is very small.

  17. Impact of Fe doping on radiofrequency magnetotransport in La0.7Sr0.3Mn1-xFexO3

    NASA Astrophysics Data System (ADS)

    Barik, S. K.; Mahendiran, R.

    2012-04-01

    We report four probe ac electrical impedance (Z) in La0.7Sr0.3Mn1-xFexO3 (x ≤ 0.15) as a function of temperature (T) and magnetic field (H) in response to radio frequency (f = 0.1-5 MHz) ac current flowing directly through the sample. It is found that Z(T,H = 0) shows an abrupt increase around Curie temperature with increasing f and this excess resistance is suppressed under an external magnetic field. A large magnetoimpedance of ΔZ/Z = -21% at f = 1 MHz for x = 0.05 and -8.5% at f = 5 MHz for x = 0.15 are observed for H = 500 Oe. We suggest that the magnetoimpedance results from suppression of the high frequency transverse permeability by an external magnetic field. Optimization of composition and frequency of ac current will enable us to obtain much larger low-field magnetoimpedance value suitable for practical applications at room temperature.

  18. Huge ac magnetoresistance of La0.7Sr0.3MnO3 in sub-kilogauss magnetic fields

    NASA Astrophysics Data System (ADS)

    Mahendiran, Ramanathan; Rebello, Alwyn; Naik, Vinayak B.; Barik, Sujit Kumar

    2010-03-01

    We report radio frequency (f = 0.1 5 MHz) magnetotransport of La0.7Sr0.3MnO3 in sub kilogauss magnetic fields (H = 0-1 kG). We measured ac resistance (R) and reactance (X) simultaneously. In zero field, R decreases smoothly around the Curie temperature TC when f = 100 kHz, but it increases abruptly and shows a peak close to TC for f = 0.5-5 MHz. The peak decreases in amplitude, broadens and shifts downward in temperature as the bias field increases. The peak is completely suppressed under Hdc = 1 kOe when f = 0.5 MHz. A huge low-field ac magnetoresistance (δR/R = 40 %) and magnetoinductance (δX/X = 12 %) are found in a field of Hdc = 700 Oe and f = 2 MHz. We suggest that the observed ac magnetoresistance arises from the suppression of ac permeability and enhanced magnetic skin depth under a magnetic field. The dynamical magnetotransport reported here will be interesting from view points of fundamental physics and applications.

  19. 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.

  20. Methane oxidation at redox stable fuel cell electrode La0.75Sr0.25Cr0.5Mn0.5O(3-delta).

    PubMed

    Tao, Shanwen; Irvine, John T S; Plint, Steven M

    2006-11-02

    Because of its widespread availability, natural gas is the most important fuel for early application of stationary fuel cells, and furthermore, methane containing biogases are one of the most promising renewable energy alternatives; thus, it is very important to be able to efficiently utilize methane in fuel cells. Typically, external steam reforming is applied to allow methane utilization in high temperature fuel cells; however, direct oxidation will provide a much better solution. Recently, we reported good electrochemical performance for an oxide anode La0.75Sr0.25Cr0.5Mn0.5O3 (LSCM) in low moisture (3% H2O) H2 and CH4 fuels without significant coking in CH4. Here, we investigate the catalytic activity of this oxide with respect to its ability to utilize methane. This oxide is found to exhibit fairly low reforming activity for both H2O and CO2 reforming but is active for methane oxidation. LSCM is found to be a full oxidation catalyst rather than a partial oxidation catalyst as CO2 production dominates CO production even in CH4-rich CH4/O2 mixtures. X-ray adsorption spectroscopy was utilized to confirm that Mn was the redox active species, clearly demonstrating that this material has the oxidation catalytic behavior that might be expected from a Mn perovskite and that the Cr ion is only present to ensure stability under fuel atmospheres.

  1. 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

  2. Anisotropic epitaxial strain effect on the charge-order phase of Nd0.5Sr0.5MnO3

    NASA Astrophysics Data System (ADS)

    Nakamura, Masao; Ogimoto, Yasushi; Tamaru, Hiroharu; Izumi, Makoto; Miyano, Kenjiro

    2005-03-01

    Strain effect in charge and orbital ordered state has been investigated for Nd0.5Sr0.5MnO3 thin films deposited on (100), (110), and (111)-oriented SrTiO3 (STO) substrates. Films on STO (001) and (111) substrates have monotonous temperature dependence for magnetic and transport properties showing no first-order phase transition. On the other hand, films on STO (110) show a clear ferromagnetic-antiferromagnetic and metal-insulator transition due to the onset of the charge and orbital order. Optical transmission spectra for the films on STO (110) show anisotry between the in-plane two axes. From the result, the orbital order plane of the film on STO (110) is deduced to be (100) or (010) plane, which lies out of the film surface. The reason for the difference in the magnetic and transport properties among the films on different substrate orientations, and why the clear metal-insulator transition occurs only on (110) substrates will be discussed.

  3. Heteroepitaxy of Nd(0.67)Sr(0.33)MnO3 on silicon for bolometric x-ray detector application.

    PubMed

    Yong, G J; Kolagani, Rajeswari M; Adhikari, S; Drury, O B; Gardner, C; Bionta, R M; Friedrich, S

    2010-11-01

    We have recently reported the design concept and sensor fabrication for a novel bolometric x-ray detector based on a rare earth manganite material for application as a total energy monitor for the Linac Coherent Light Source (LCLS) free electron laser at the Stanford Linear Accelerator Center (SLAC). The detector employs epitaxial thin films of Nd(0.67)Sr(0.33)MnO(3) grown on Si by pulsed laser deposition. In this paper we report details of the fabrication of the actual detector, its response characteristics under photon illumination from LCLS, and improvements in the growth scheme of the sensor material on Si using a buffer/template layer scheme that employs yttria-stabilized zirconia, cerium oxide (CeO(2)), and bismuth titanate (Bi(4)Ti(3)O(12)). The thermal sensor response changes linearly with the energy of an optical calibration laser as expected, and the signals from optical and x-ray pulses at LCLS are very similar, thereby validating the design concept. To the best of our knowledge, the LCLS detector application reported here is the first practical use of colossal magnetoresistive manganite bolometers.

  4. 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.

  5. 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.

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

    PubMed Central

    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

  7. Obtaining and characterization of La0.8Sr0.2CrO3 perovskite by the combustion method

    NASA Astrophysics Data System (ADS)

    Morales Rivera, A. M.; Gómez Cuaspud, J. A.; López, E. Vera

    2017-01-01

    This research is focused on the synthesis and characterization of a perovskite oxide based on La0.8Sr0.2CrO3 system by the combustion method. The material was obtained in order to contribute to analyse the effect of synthesis route in the obtaining of advanced anodic materials for solid oxide fuel cells (SOFC). The obtaining of solid was achieved starting from corresponding nitrate dissolutions, which were polymerized by temperature effect in presence of citric acid. The solid precursor as a foam citrate was characterized by infrared (FTIR) and ultraviolet (UV) spectroscopy, confirming the effectiveness in synthesis process. The solid was calcined in oxygen atmosphere at 800°C and characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive of X-ray spectroscopy (EDX) and solid state impedance spectroscopy (IS). Results confirm the obtaining of an orthorhombic solid with space group Pnma (62) and cell parameters a=5.4590Å, b=7.7310Å and c=5.5050Å. At morphological level the solid showed a heterogeneous distribution with an optimal correspondence with proposed and obtained stoichiometry. The electrical characterization, confirm a semiconductor behaviour with a value of 2.14eV Band-gap according with previous works.

  8. Increased saturation field as the origin of the giant electrocaloric effect in Ba0.8Sr0.2TiO3 thin films

    NASA Astrophysics Data System (ADS)

    Park, Y. A.; Sung, K. D.; Jung, J. H.; Hur, N.; Cheong, S. W.

    2015-08-01

    We investigated the electrocaloric (EC) effects in epitaxial Ba0.8Sr0.2TiO3 (BSTO) thin films grown on LaAlO3 and MgO substrates and in BSTO sol-gel thin films grown on Si substrates. We compared the EC effects in two forms of BSTO to confirm whether the giant EC effect recently observed in the polycrystalline thin film is an intrinsic effect or an extrinsic effect exclusively occurring in polycrystalline thin films with nano-sized grains. The EC effect in our BSTO single crystals exhibited a moderate EC temperature change over a broad temperature range. On the other hand, the EC effect in the BSTO sol-gel film was observed over a narrow temperature range with a giant Δ T of about 14 °C. We claim that this giant EC effect is due to the increased saturation field related to the small grain size in the sol-gel thin film.

  9. Enhanced dielectric constant and relaxor behavior realized by dual stage sintering of Sr0.5Ba0.5Nb2O6

    NASA Astrophysics Data System (ADS)

    Rathore, Satyapal S.; Vitta, Satish

    2014-04-01

    The relaxor ferroelectric compound, Sr0.5Ba0.5Nb2O6 (SBN50) was synthesized by solid state reaction followed by sintering under two different conditions: single and dual stage sintering. The impact of sintering process on structural and dielectric properties has been studied in detail using X-ray diffraction, scanning electron microscopy and broadband dielectric spectroscopy. The crystal structure determined by performing Rietveld refinement of X-ray diffractogram was found to be identical in both cases. SBN50 crystallizes in the ferroelectric tetragonal tungsten bronze, P4bm structure. It was observed that uniform grain growth can be controlled by dual stage sintering and relatively narrow distribution of grains can be achieved with an average grain size of ˜15 μm. The dielectric studies show that SBN50 exhibits a relaxor ferroelectric behavior with the transformation taking place at ˜ 380 K due to formation of polar nano regions. Although both single and dual stage sintered SBN50 exhibits relaxor behaviour, the maximum dielectric constant of dual stage sintered SBN50 is found to be 1550 compare to 1440 for single stage sintering.

  10. 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.

  11. Specific features of pulse and quasi-static remagnetization and relaxation properties of Nd0.5Sr0.5MnO3 single crystals

    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.; Davydeiko, N. V.; Linnik, T. A.; Popov, Yu. F.; Balbashov, A. M.

    2015-12-01

    The hysteresis features in the behavior of the magnetization and resistance of Nd0.5Sr0.5MnO3 single crystals in quasi-static (up to 9 T) and pulsed (up to 14 T) magnetic fields have been studied. Relaxation processes of magnetization and resistance after the action of a magnetic field of 9 T have also been investigated. It has been shown that relaxation curves are approximated by two exponents with different time constants, which are related to relaxation of the metastable ferromagnetic phase towards two different antiferromagnetic crystal structures ( I mma and p21/ m). Mechanism of the 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 determined by the structural transition, which is induced by a magnetic field (due to magnetostriction), and by a slow relaxation of the FM-phase (larger volume) to the stable AFM-phase (smaller volume) after field removal. It has been shown that, during pulse magnetization at the temperature 18 K, the time required for the AFM/I → FM/M phase transition is six-seven orders of magnitude shorter than that for the FM/M → AFM/I phase transition.

  12. Search for structural fluctuations in the disordered stripe state of Nd1:67 Sr 0:33 NiO 4

    NASA Astrophysics Data System (ADS)

    Abeykoon, A. M. Milinda; Bozin, Emil; Gu, Genda; Hill, John; Tranquada, John; Billinge, Simon

    2011-03-01

    We present a temperature series PDF and a Rietveld analysis of Nd 1:67 Sr 0:33 Ni O4 system to study the local structural response in the state above the charge-ordered state that has not been characterized in detail to date. We observed Ni O6 octahedral tilting patterns of different magnitude for short and long-range structure of the system. A sequential Rietveld refinement, and a T-series PDF analysis on the length scale (5-20)Å were carried out to characterize the long-range order of the system. A PDF analysis on the length scale (0-4.2) Å revealed a different magnitude local octahedral tilt pattern as a function of temperature. The correlation length of short-range ordered charge stripes existing above Tco was estimated using a Box-Car type PDF model. Combining this information with the refined isothermal atomic displacement parameters (ADPs) yields a much more complete picture of the nature of both atomic displacements and how they are correlated with each other in the system. This work was supported by US-DOE-BES.

  13. Energy-dependent crossover from anisotropic to isotropic magnetic dispersion in lightly doped La1.96Sr0.04CuO4

    NASA Astrophysics Data System (ADS)

    Matsuda, M.; Granroth, G. E.; Fujita, M.; Yamada, K.; Tranquada, J. M.

    2013-02-01

    Inelastic neutron-scattering experiments have been performed on lightly doped La1.96Sr0.04CuO4, which shows diagonal incommensurate spin correlations at low temperatures. We previously reported that this crystal, with a single orthorhombic domain, exhibits the “hourglass” dispersion at low energies [Phys. Rev. Lett.PRLTAO0031-900710.1103/PhysRevLett.101.197001 101, 197001 (2008)]. In this paper, we investigate in detail the energy evolution of the magnetic excitations up to 65 meV. It is found that the anisotropic excitations at low energies, dispersing only along the spin modulation direction, cross over to an isotropic, conical dispersion that resembles spin waves in the parent compound La2CuO4. The change from twofold to full symmetry on crossing the waist of the hourglass reproduces behavior first identified in studies of underdoped YBa2Cu3O6+x. We discuss the significance of these results.

  14. Evidence for Short-Range-Ordered Charge Stripes Far above the Charge-Ordering Transition in La1.67Sr0.33NiO4

    NASA Astrophysics Data System (ADS)

    Abeykoon, A. M. Milinda; Bozin, Emil S.; Yin, Wei-Guo; Gu, Genda; Hill, John P.; Tranquada, John M.; Billinge, Simon J. L.

    2015-03-01

    The temperature evolution of structural modulation associated with charge and spin order in La1.67Sr0.33NiO4 has been investigated using neutron powder diffraction. For the first time we report an anomalous shrinking of the c/a lattice parameter ratio that correlates with TCO at the temperature where long-range stacking order of charge stripes disappears. The sign of this change can be explained by the change in interlayer Coulomb energy between the static-stripe-ordered state and the fluctuating-stripe-ordered state or the charge-disordered state. In addition, we identify a contribution to the mean-square displacements of Ni and in-plane O atoms whose width correlates quite well with the size of the pseudogap extracted from the reported optical conductivity, with a non-Debye-like component that persists below and well above TCO. Local structural parameters in the atomic pair distribution function (PDF) well-agree with this result. We infer that dynamic charge-stripe correlations survive to T ~ 2TCO. This work was supported by the DOE Grant, DE- AC02-98CH10886.

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

    NASA Astrophysics Data System (ADS)

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

    2015-11-01

    The 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 Tc=20 K. At T ≪Tc 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. Furthermore, we observed a weak elastic (3 3 ¯0 ) superlattice peak that implies a reduced lattice symmetry. The presence of inequivalent O sites rationalizes various pieces of evidence for charge stripe order in underdoped La2 -xSrxCuO4 . The coexistence of superconductivity with quasistatic 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.

  16. Detection of charge scattering associated with stripe order in La1.775Sr0.225NiO4 by hard-x-ray diffraction

    NASA Astrophysics Data System (ADS)

    Vigliante, A.; von Zimmermann, M.; Schneider, J. R.; Frello, T.; Andersen, N. H.; Madsen, J.; Buttrey, D. J.; Gibbs, Doon; Tranquada, J. M.

    1997-10-01

    In the past few years neutron-scattering experiments have shown very intriguing stripe correlations of spins and holes in hole-doped La2NiO4 and La2CuO4. As yet, no x-ray-diffraction experiment has confirmed the neutron results and the topic is still controversial. In this paper we report the observation of stripe correlations of holes by x-ray diffraction. The experiments were performed in Laue geometry at the hard-x-ray beamline BW5 at HASYLAB on a crystal of La1.775Sr0.225NiO4 which was previously studied by neutron diffraction. Temperature dependences of the intensities and wave vectors of the charge-density-modulation peaks were characterized and found to be in good agreement with the neutron-scattering results. Interestingly, weak, temperature-dependent scattering was also observed at positions consistent with nonresonant x-ray magnetic scattering from the spin correlations; however, a definitive determination of its origin remains lacking.

  17. Observation of magnetism in La0.7Sr0.3MnO3—graphene nanoribbons complex: a probable magnetoelectronic material study

    NASA Astrophysics Data System (ADS)

    Joshi, Anupama; Datar, Suwarna; Kale, S. N.

    2017-07-01

    Incorporation of good magnetic moment and conductivity in a weakly magnetic matrix via doping of an impurity projects huge applications in the domain of magneto-electronics and spintronics. This is quite challenging because the system has to work in unison so that the there is an exchange of electrons and spins between the magnetic grains and the host matrix. Graphene-nano-ribbons (GNRs) possess defect states at their edges and shows good conductivity with weak magnetism. Such systems are studied as host matrix, in which 10% manganite (La0.7Sr0.3MnO3 (LSMO)) has been incorporated using octadecyl-amine (ODA) as the conjugating agent to form a GNR-LSMO complex. While Raman analysis of GNR shows reduction in disorder after complex formation, the system shows magnetic transition at 350 K. The magnetic-force-microscopy shows direct evidence of enhanced magnetism as compared to only GNR, especially in the regions where the manganite grains are in proximity to the GNR matrix. A novel magneto-electronic material can be envisaged with further careful grain-boundary engineering.

  18. Element specific and depth-resolved interface magnetism in BiFeO3/La0.67Sr0.33MnO3 thin films

    NASA Astrophysics Data System (ADS)

    Bertinshaw, Joel; Brück, Sebastian; Fritzsche, Helmut; Khaydukov, Yury; Soltwedel, Olaf; Keller, Thomas; Goering, Eberhard; Audehm, Patrick; Hutchison, Wayne; Maran, Ronald; Valanoor, Nagarajan; Klose, Frank; Ulrich, Clemens

    2013-03-01

    In recent years significant research has been conducted to probe the emergent physics of atomically sharp transition metal oxide layered systems. The spin, orbital and charge state at the interface has a drastic impact on the exhibited emergent physics. We have investigated epitaxial bi-layers of multiferroic BiFeO3 (BFO) / ferromagnetic La0.67Sr0.33MnO3 (LSMO). Polarized Neutron Reflectivity conducted at ANSTO, Chalk River, and FRM-II provided the absolute magnetic moment at the interface and X-ray Resonant Magnetic Reflectivity performed at BESSY II provided element specific magnetic information. We determined the precise magnetic properties of the bi-layer interface region, which indicated a region of depleted magnetization extending ~25Å into the LSMO at the interface, despite no FM in the BFO and in contrast to previous results on an inverse LSMO/BFO system. The importance of this result extends to the study and functionality of all strongly correlated thin film systems.

  19. 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.

  20. Orientation Control of Interfacial Magnetism at La0.67Sr0.33MnO3/SrTiO3 Interfaces

    DOE PAGES

    Guo, Er-Jia; Charlton, Timothy; Ambaye, Haile; ...

    2017-05-16

    Understanding the magnetism at the interface between a ferromagnet and an insulator is essential because the commonly posited magnetic “dead” layer close to an interface can be problematic in magnetic tunnel junctions. Previously, degradation of the magnetic interface was attributed to charge discontinuity across the interface. In this paper, the interfacial magnetism was investigated using three identically prepared La0.67Sr0.33MnO3 (LSMO) thin films grown on different oriented SrTiO3 (STO) substrates by polarized neutron reflectometry. In all cases the magnetization at the LSMO/STO interface is larger than the film bulk. We show that the interfacial magnetization is largest across the LSMO/STO interfacesmore » with (001) and (111) orientations, which have the largest net charge discontinuities across the interfaces. In contrast, the magnetization of LSMO/STO across the (110) interface, the orientation with no net charge discontinuity, is the smallest of the three orientations. We show that a magnetically degraded interface is not intrinsic to LSMO/STO heterostructures. Finally, the approach to use different crystallographic orientations provides a means to investigate the influence of charge discontinuity on the interfacial magnetization.« less

  1. Surface Chemistry of La0.99Sr0.01NbO4-d and Its Implication for Proton Conduction.

    PubMed

    Li, Cheng; Pramana, Stevin S; Ni, Na; Kilner, John; Skinner, Stephen J

    2017-09-06

    Acceptor-doped LaNbO4 is a promising electrolyte material for proton-conducting fuel cell (PCFC) applications. As charge transfer processes govern device performance, the outermost surface of acceptor-doped LaNbO4 will play an important role in determining the overall cell performance. However, the surface composition is poorly characterized, and the understanding of its impact on the proton exchange process is rudimentary. In this work, the surface chemistry of 1 atom % Sr-doped LaNbO4 (La0.99Sr0.01NbO4-d, denoted as LSNO) proton conductor is characterized using LEIS and SIMS. The implication of a surface layer on proton transport is studied using the isotopic exchange technique. It has shown that a Sr-enriched but La-deficient surface layer of about 6-7 nm thick forms after annealing the sample under static air at 1000 °C for 10 h. The onset of segregation is found to be between 600 and 800 °C, and an equilibrium surface layer forms after 10 h annealing. A phase separation mechanism, due to the low solubility of Sr in LaNbO4, has been proposed to explain the observed segregation behavior. The surface layer was concluded to impede the water incorporation process, leading to a reduced isotopic fraction after the D2(16)O wet exchange process, highlighting the impact of surface chemistry on the proton exchange process.

  2. Enhanced ferromagnetism and glassy state in phase separated La0.95Sr0.05MnO3 + δ

    NASA Astrophysics Data System (ADS)

    De, K.; Das, S.; Roy, A.; Dhak, P.; Willinger, M.; Amaral, J. S.; Amaral, V. S.; Giri, S.; Majumder, S.; Silva, C. J. R.; Gomes, M. J. M.; Mahapatra, P. K.

    2012-11-01

    Unusual high temperature ferromagentism is reported for La0.95Sr0.05MnO3+δ with Curie temperatures (TC1 and TC2) TC1 at 290 K and TC2 ˜ 150 K. Weak antiferromagnetism (AFM) is thought to give low moment, low temperature irreversibility, and non-saturation up to 10 T at 5 K. A short-range ferromagnetism is predicted from well-defined hysteresis at 5 K and field-cooled (FC) magnetization curves. Strong irreversibility between zero field-cooled (ZFC) and FC at 5 T is due to "hard" spins, not from ferromagnetic clusters. Field-dependent peak shift of spin freezing temperature in ZFC, memory effect, magnetic relaxation shows cluster glass like transition in the system. A metal-insulator transition at 115 K also implies a completion of percolation of short range ferromagnetic clusters, giving an onset of metallic state at 115 K. A complete magnetic phase diagram is presented showing its temperature dependent rich magnetic behavior.

  3. Effects of oxygen partial pressure on the ferroelectric properties of pulsed laser deposited Ba0.8Sr0.2TiO3 thin films

    NASA Astrophysics Data System (ADS)

    Silva, J. P. B.; Sekhar, K. C.; Almeida, A.; Agostinho Moreira, J.; Pereira, M.; Gomes, M. J. M.

    2013-11-01

    The Ba0.8Sr0.2TiO3 thin films were grown on the Pt-Si substrate at 700 °C by using a pulsed laser deposition technique at different oxygen partial pressure (PO2) in the range of 1-20 Pa and their properties were investigated. It is observed that the PO2 during the deposition plays an important role on the tetragonal distortion ratio, surface morphology, dielectric permittivity, ferroelectric polarization, switching response, and leakage currents of the films. With an increase in PO2, the in-plane strain for the BST films changes from tensile to compressive. The films grown at 7.5 Pa show the optimum dielectric and ferroelectric properties and also exhibit the good polarization stability. It is assumed that a reasonable compressive strain, increasing the ionic displacement, and thus promotes the in-plane polarization in the field direction, could improve the dielectric permittivity. The butterfly features of the capacitance-voltage ( C- V) characteristics and the bell shape curve in polarization current were attributed to the domain reversal process. The effect of pulse amplitude on the polarization reversal behavior of the BST films grown at PO2 of 7.5 Pa was studied. The peak value of the polarization current shows exponential dependence on the electric field.

  4. Influence of electron beam irradiation on electrical, structural, magnetic and thermal properties of Pr0.8Sr0.2MnO3 manganites

    NASA Astrophysics Data System (ADS)

    Christopher, Benedict; Rao, Ashok; Petwal, Vikash Chandra; Verma, Vijay Pal; Dwivedi, Jishnu; Lin, W. J.; Kuo, Y.-K.

    2016-12-01

    In this communication, the effect of electron beam (EB) irradiation on the structural, electrical transport and thermal properties of Pr0.8Sr0.2MnO3 manganites has been investigated. Rietveld refinement of XRD data reveals that all samples are single phased with orthorhombic distorted structure (Pbnm). It is observed that the orthorhombic deformation increases with EB dosage. The Mn-O-Mn bond angle is found to increase with increase in EB dosage, presumably due to strain induced by these irradiations. Analysis on the measured electrical resistivity data indicates that the small polaron hopping model is operative in the high temperature region for pristine as well as EB irradiated samples. The electrical resistivity in the entire temperature region has been successfully fitted with the phenomenological percolation model which is based on phase segregation of ferromagnetic metallic clusters and paramagnetic insulating regions. The Seebeck coefficient (S) of the pristine as well as the irradiated samples exhibit positive values, indicating that holes is the dominant charge carriers. The analysis of Seebeck coefficient data confirms that the small polaron hopping mechanism governs the thermoelectric transport in the high temperature region. In addition, Seebeck coefficient data also is well fitted with the phenomenological percolation model. The behavior in thermal conductivity at the transition is ascribed to the local anharmonic distortions associated with small polarons. Specific heat measurement indicates that electron beam irradiation enhances the magnetic inhomogeneity of the system.

  5. Room temperature insulating ferromagnetism induced by charge transfer in ultrathin (110) La0.7Sr0.3MnO3 films

    NASA Astrophysics Data System (ADS)

    Quan, Zhiyong; Wu, Biao; Zhang, Fei; Zhou, Guowei; Zang, Julu; Xu, Xiaohong

    2017-02-01

    The achievement of high temperature ferromagnetism in perovskite manganites has proved both fundamentally and technologically important for spintronics devices. However, high operating temperatures have not been achieved due to the depression of the Curie temperature and the rapid spin filtering efficiency loss, which are the main obstacles for practical applications. Here, we report unexpected room temperature insulating ferromagnetism in ultrathin (110) oriented La0.7Sr0.3MnO3 (LSMO) films. The relationships between room temperature ferromagnetism, charge transfer, and orbital occupancy are investigated, with X-ray absorption spectroscopy (XAS) and X-ray linear dichroism (XLD) measurements. Our results suggest that the room temperature insulating ferromagnetism is originated from super-exchange interaction between Mn2+ and Mn3+. The formation of Mn2+ ions is related to the charge transfer induced by oxygen vacancies. Moreover, a preferential orbital occupancy of eg(3z2-r2) in Mn3+ ions is crucial to the in-plane super-exchange coupling in ultrathin (110) LSMO films, resulting in insulating ferromagnetic behavior. This work may lead to the development of barrier materials in spin filter tunnel junctions and understanding of ferromagnetic coupling in insulating perovskite films.

  6. 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.

  7. Thermophysical and Microwave Shielding Properties of La0.5Sr0.5CoO3- δ and its Composite with Epoxy

    NASA Astrophysics Data System (ADS)

    Dijith, Kesavapillai Sreedeviamma; Pillai, Saju; Surendran, Kuzhichalil Peethambharan

    2017-08-01

    The microwave shielding properties of the perovskite oxide conductors, La0.5Sr0.5CoO3- δ (LSCO), were investigated. The sintered LSCO sheets were showing excellent microwave shielding properties up to 35-42 dB in the entire X and Ku bands. Towards getting a light-weight and easily processable structure, an attempt was made to composite LSCO with the easily mouldable polymer, epoxy. The thermal, dielectric and electromagnetic wave shielding properties of the composites were studied. The mechanical strength, thermal expansivity and thermal conductivity of the composites were progressively improved with LSCO addition. An improvement in the shielding effectiveness was observed with filler addition and attained a value of 10 dB in the range of 8.2-10 GHz for a maximum loaded LSCO-epoxy composite and the value spans from 3 dB to 9 dB in the Ku band region. The improvement in the shielding effectiveness with filler addition was supplemented by the gradual improvement in the dielectric permittivity, dielectric loss and AC conductivity.

  8. Strain induced ferromagnetism and large magnetoresistance of epitaxial La1.5Sr0.5CoMnO6 thin films

    NASA Astrophysics Data System (ADS)

    Krishna Murthy, J.; Jyotsna, G.; N, Nileena; Anil Kumar, P. S.

    2017-08-01

    In this study, the structural, magnetic, and magneto-transport properties of La1.5Sr0.5CoMnO6 (LSCMO) thin films deposited on a SrTiO3 (001) substrate were investigated. A normal θ/2θ x-ray diffraction, rocking curve, ϕ-scan, and reciprocal space mapping data showed that prepared LSCMO thin films are single phase and highly strained with epitaxial nature. Temperature vs. magnetization of LSCMO films exhibits strain-induced ferromagnetic ordering with TC ˜ 165 K. In contrast to the bulk samples, there was no exchange bias and canted type antiferromagnetic and spin glass behavior in films having thickness (t) ≤ 26 nm. Temperature dependent resistivity data were explained using Schnakenberg's model and the polaron hopping conduction process. The slope change in resistivity and magnetoresistance maximum (˜65%) around TC indicates the existence of a weak double exchange mechanism between the mixed valence states of transition metal ions. Suppression of spin dependent scattering with the magnetic field is attributed for the large negative magnetoresistance in LSCMO films.

  9. Superconductivity suppression in YBa2Cu3O7-δ/La0.7Sr0.3MnO3 bilayer films

    NASA Astrophysics Data System (ADS)

    Sharma, Minaxi; Sharma, K. K.; Choudhary, R. J.; Kumar, Ravi

    2014-12-01

    We study the thickness effect of YBa2Cu3O7-δ (YBCO) in YBCO/La0.7Sr0.3MnO3 (LSMO) bilayer films, fabricated on LaAlO3 (001) substrate using pulsed laser deposition technique. The thickness dependent transport behavior of YBCO layer in considered bilayer systems demonstrate a clear onset critical temperature at 60 K and 80 K for 100 nm and 200 nm thick YBCO layer systems, respectively, whereas 50 nm thick YBCO system reveals complete suppression in the superconductivity. With the increase in thickness of YBCO layer, the magnetoresistance (MR) data show both positive and negative MR. The positive MR in superconducting regime dominates the negative MR, suppress the double exchange interaction. The maximum magnetoresistance ratio ˜81% at 64 K and ˜47% at 30 K temperature are observed for 200 nm and 100 nm YBCO layers, respectively. In YBCO(200 nm)/LSMO(200 nm) bilayer specimen, the temperature co-efficient of resistance is ˜8.4% K-1 at 72 K which can be practical for bolometric performances and temperature sensors.

  10. 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

  11. Quantitative analysis of the magnetic domain structure in polycrystalline La(0.7)Sr(0.3)MnO3 thin films by magnetic force microscopy.

    PubMed

    Li, Zhenghua; Wei, Fulin; Yoshimura, Satoru; Li, Guoqing; Asano, Hidefumi; Saito, Hitoshi

    2013-01-14

    The nanoscale magnetic domain structure of the polycrystalline La(0.7)Sr(0.3)MnO(3) granular thin films was imaged with a developed magnetic force microscopy technique by simultaneously detecting both the perpendicular and in-plane components of magnetic field gradients during the same scan of the tip oscillation. The characteristics of both the perpendicular and in-plane magnetic field gradient at the grain edges or the nonmagnetic grain boundary phase for LSMO films were demonstrated and can be used to evaluate the magnetic domain structure and magnetic isolation between neighboring grains. A two dimensional signal transformation algorithm to reconstruct the in-plane magnetization distribution of the polycrystalline LSMO thin films from the measured raw MFM images with the aid of the deconvolution technique was presented. The comparison between the experimental and simulated MFM images indicates that the magnetic grains or clusters are in the single domain (SD) or multi-domain (MD) state with the magnetic moments parallel or anti-parallel to the effective magnetic field of each grain, possibly due to the need for minimizing the total energy. The quantitative interpretation of the magnetic domain structure indicates that the large magnetoresistance in the studied LSMO films is mainly due to tunnel effect and scattering of conducted electrons at the nonmagnetic grain boundary phase related to the different configurations of magnetic domain states between neighboring grains.

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

    DOE PAGES

    Shen, Xuan; Yamada, Tomoaki; Lin, Ruoqian; ...

    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

  13. Critical analysis of the paramagnetic to ferromagnetic phase transition in Pr0.55K0.05Sr0.4MnO3

    NASA Astrophysics Data System (ADS)

    Thaljaoui, R.; Pękała, M.; Fagnard, J.-F.; Vanderbemden, Ph.

    2016-02-01

    The critical properties of monovalent doped manganite Pr0.55K0.05Sr0.4MnO3 around the paramagnetic to ferromagnetic phase transition were investigated through various methods: the modified Arrott plots (MAP), the Kouvel-Fisher method and the critical isotherm analysis. Data obtained near Tc were examined in the framework of the mean field theory, the 3D-Heisenberg model, the 3D-Ising model, and tricritical mean field. The deduced critical exponents values obtained using MAP method were found to be β=0.44(4) with TC≈303 K and γ=1.04(1) with TC≈302 K. Kouvel-Fisher method supplies the critical values to be β=0.41(2) with TC≈302 K and γ=1.09(1) with TC≈302 K. The obtained critical parameters show a tendency towards the mean-field behavior, suggesting the existence of long-range ferromagnetic order in the compound studied. The exponent δ deduced separately from isotherm analysis at T=303 K was found to obey to the Widom scaling relation δ=1+γ/β. The reliability of obtained exponents was confirmed by using the universal scaling hypothesis. The itinerant character of ferromagnetism in the present system was also tested by using Rhodes-Wohlfarth's criterion.

  14. Critical behavior and long-range ferromagnetic order in perovskite manganite Nd0.55Sr0.45MnO3

    NASA Astrophysics Data System (ADS)

    Xu, Lisha; Fan, Jiyu; Shi, Yangguang; Zhu, Yan; Bärner, Klaus; Yang, Changping; Shi, Daning

    2015-10-01

    The critical behavior of perovskite manganite Nd0.55Sr0.45MnO3 has been investigated based on the static magnetization measurement around the paramagnetic-ferromagnetic transition temperature 273 K. A large critical exponent β = 0.4816 and a small one γ = 1.0846 have been obtained by calculating the magnetic-field dependence of the magnetic-entropy change and the Widom scaling relation. These critical exponents not only obey the scaling hypothesis, but also corroborate the results obtained from the Kouvel-Fisher method. In comparison with the values given by standard models, these obtained exponents are very close to those expected from the mean-field model (β = 0.5 and γ = 1 ) and its magnetic-coupling type belongs to nearly long-range interaction. We suggest that the A-site spin disorder and localized magnetic phase competition are the main reasons for the actual critical exponents to show a slight deviation from the theoretical model.

  15. Tuning of Cr3+ ions doping on the magnetic and magnetocaloric properties of La0.5Sr0.5Mn1-xCrxO3

    NASA Astrophysics Data System (ADS)

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

    2016-12-01

    The effects of Cr3+ ions doping on the magnetic and magnetocaloric properties of manganites La0.5Sr0.5Mn1-xCrxO3 (x=0.05, 0.1, 0.15, and 0.2) have been investigated. The magnetization measurements show that a ferromagnetic cluster behavior is induced by Cr3+ dopants and the paramagnetic to ferromagnetic transition temperature TC decreases from 319 to 251 K with increasing Cr3+ content from 0.05 to 0.2. The positive slope of the Arrott plots near TC indicates a second order phase transition. The magnetic entropy change (-ΔSM) is estimated from the isothermal magnetization measurements, and the maximum of the magnetic entropy change (-ΔSmaxM) near TC shows a power law dependence of magnetic field: -ΔSmaxM = m(μ0 H) n with n being close to the predicted value 2/3. The experimental results suggest that the magnetic entropy change and TC can be tuned by changing the Cr3+ ions doping level, which offers an effective method for finding an optimal doping level for magnetic refrigeration near room temperature.

  16. Aberration-corrected STEM-EELS studies of epitaxial La0.5Sr0.5CoO3 thin films

    NASA Astrophysics Data System (ADS)

    Varela, Maria; Gazquez, Jaume; Biskup, Neven; Pennycook, Stephen; Torija, Maria; Sharma, Manish; Bose, Shameek; Leighton, Chris

    2012-02-01

    Cobaltite thin films provide a unique opportunity to study magneto-electronic phase separation, which can be strong in this reduced dimensionality environment. Here we present an investigation of epitaxial La0.5Sr0.5CoO3 thin films on SrTiO3 and LaAlO3 substrates by scanning transmission electron microscopy and electron energy loss spectroscopy. The different degrees of strain and also different orientations of the substrates (such as (001) vs. (110)) induce major changes of the crystal structure and the depth profile of the chemical composition, observed both in the La/Sr and O sub-lattices. These effects can lead to lower effective doping level at the interface, favoring interfacial magneto-electronic phase separation. Research Council Starting Investigator Award (JS, NB) and the U.S. Dept. of Energy, Office of Basic Energy Sciences, Materials Sciences and Engineering Div. (MV, SJP). Work at UMN supported by NSF and DOE (scattering).

  17. 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

  18. 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

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

    PubMed

    Huber, Tobias M; Navickas, Edvinas; Friedbacher, Gernot; Hutter, Herbert; Fleig, Jürgen

    2015-10-01

    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. (18)O 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 (18)O 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 (18)O 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 (18)O 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.

  20. Impact of substrate on magnetic phase coexistence in bicritical Sm 0.53Sr 0.47MnO 3 thin films

    NASA Astrophysics Data System (ADS)

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

    2012-01-01

    Sm 0.53Sr 0.47MnO 3 thin films were deposited on single crystal LaAlO 3 (LAO/(001)) and SrTiO 3 (STO/(001)) substrates by DC magnetron sputtering. The θ-2θ and ω-2θ scans show that these films have very good crystallinity and the films on LAO and STO are under compressive and tensile strain, respectively. The films on LAO and STO substrates show ferromagnetic (insulator-metal) transition at TC˜126 K (at T˜128 K) and 120 K ( T˜117 K), respectively. The magnetic state at T

  1. Critical phenomena in La0.6Pr0.1Sr0.3MnO3 perovskite manganese oxide

    NASA Astrophysics Data System (ADS)

    Cherif, R.; Hlil, E. K.; Ellouze, M.; Elhalouani, F.; Obbade, S.

    2015-09-01

    We report a study of the critical phenomena of perovskite-manganite compound La0.6Pr0.1Sr0.3MnO3 around the Curie temperature. Experimental results based on magnetic measurements using Banerjee criterion reveals that the sample exhibits a second-order paramagnetic-ferromagnetic transition. The critical behavior analysis and the Kouvel-Fisher method suggests that the critical phenomena around the critical point can be correctly described by the 3D-Heisenberg model. Critical exponents were estimated and found β=0.354±0.009 and γ=1.264±0.035 at TC=325.5±0.443 K. The critical exponent δ is determined separately from the isothermal magnetization at TC and evaluated to δ=4.934±0.0004. These critical exponents obey the Widom scaling relation δ=1‏+γ/β. Based on the critical exponents, the magnetization-field-temperature (M-H-T) data around TC collapses into two curves obeying the single scaling equation M (H , ε) =| ε | β f ± (H /| ε | β + γ) where ε=(T-TC)/TC is the reduced temperature.

  2. 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

  3. Magneto-electric properties and magnetic entropy change in perovskite La0.7Sr0.3Mn1-xTixO3

    NASA Astrophysics Data System (ADS)

    Bau, Le Viet; An, Nguyen Manh

    2016-12-01

    The ceramic samples of La0.7Sr0.3Mn1-xTixO3(x=0; 0.05; 0.1; 0.2 and 0.3) were synthesized by the conventional solid state reaction method. Their electric, magnetic and magnetocaloric properties have been investigated. The transition temperature declines and a significant influence on the width of the ferro-paramagnetic phase transition is observed as increasing Ti concentration. Moreover, the sign of spin-glass is expected to exist in the high concentration samples. For fully replacing Ti4+ for Mn4+, the canted spin state is formed. The substitution Ti for Mn increases resistivity quickly and the insulating-metallic transition temperature shifts toward lower temperature. For x>0.1 samples, the insulating state is observed even in ferromagnetic phase. The substitution Ti shifts the CME to room temperature while almost persists the value of entropy change. Although the maximum value of CME reduces slightly, the temperature range happening MCE is expended and then improves the relative cooling power. These properties could be explained in term of DE interaction and phase separation phenomenon.

  4. 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.

  5. Towards understanding surface chemistry and electrochemistry of La0.1Sr0.9TiO3-α based solid oxide fuel cell anodes

    NASA Astrophysics Data System (ADS)

    Yurkiv, Vitaliy; Constantin, Guillaume; Hornes, Aitor; Gondolini, Angela; Mercadelli, Elisa; Sanson, Alessandra; Dessemond, Laurent; Costa, Rémi

    2015-08-01

    In the present contribution, we combine modeling and experimental study of electrochemical hydrogen oxidation at an alternative perovskite based mixed-conducting SOFC anode. Composite electrodes were produced by conventional wet ceramic processing (screen printing - spraying) and sintering on YSZ electrolytes (La0.1Sr0.9TiO3-α-Ce1-xGdxO2-α|YSZ) with different compositions and microstructure, and were electrochemically characterized using symmetrical button-cells configuration. An elementary kinetic model was developed and applied to explore the performance of LST based SOFC anode. A detailed multi-step heterogeneous chemical and electrochemical reaction mechanism was established taking into account transport of ions in all ionic phases, and gas transport in channel and porous media. It was found that heterogeneous chemistry at LST surface has capacitive behavior that alters the impedance spectra. In addition, surface charge-transfer reaction, which describes partial oxygen ionization, caused impedance feature and is rate-limiting at high temperature. The gas transport in the supply chamber (gas conversion) is significant only at moderate temperatures.

  6. 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.

  7. Interface magnetism in epitaxial BiFeO3-La0.7Sr0.3MnO3 heterostructures integrated on Si(100).

    PubMed

    Rao, S S; Prater, J T; Wu, Fan; Shelton, C T; Maria, J-P; Narayan, J

    2013-01-01

    We report on the heteroepitaxial growth of ferroelectric (FE)-antiferromagnetic (AFM) BiFeO3 (BFO) on ferromagnetic La0.7Sr0.3MnO3 (LSMO), integrated on Si(100) using pulsed laser deposition via the domain matching epitaxy paradigm. The BFO/LSMO films were epitaxially grown on Si(100) by introducing epitaxial layers of SrTiO3/MgO/TiN. X-ray diffraction, scanning electron microscopy, high-resolution transmission electron microscopy, X-ray photo absorption spectroscopy, and atomic force microscopy were employed to fully characterize the samples. Furthermore, we have investigated the magnetic behavior of this five layer heterostructure, in which a d(5) system (Fe(3+)) manifested in FE-AFM BFO is epitaxially conjoined at the interface to a multivalent transition metal ion such as Mn(3+)/Mn(4+) in LSMO. The temperature- and magnetic field-dependent magnetization measurements reveal an unexpected enhancement in magnetic moment and improved magnetic hysteresis squareness originating from the BFO/LSMO interface. We observe a stronger temperature dependence of HEB when the polarity of field cooling is negative as compared to positive field cooling. We believe such an enhancement in magnetic moment and magnetic coupling is likely directly related to an electronic orbital reconstruction at the interface and complex interplay between orbital and spin degrees of freedom, similar to what has previously been reported in the literature. Future work will involve the linearly polarized X-ray absorption measurements to prove this hypothesis. This work represents a starting step toward the realization of magneto-electronic devices integrated with Si(100).

  8. Impact of Jahn-Teller active Mn3+ on strain effects and phase transitions in Sr0.65Pr0.35MnO3

    NASA Astrophysics Data System (ADS)

    Tan, Teck-Yee; Kennedy, Brendan J.; Zhou, Qingdi; Ling, Christopher D.; Miiller, Wojciech; Howard, Christopher J.; Carpenter, Michael A.; Knight, Kevin S.

    2012-03-01

    The mixed-valence manganite Sr0.65Pr0.35MnO3 has been prepared and its crystal and magnetic structure investigated between 7 and 1200 K using high-resolution powder neutron diffraction. The structural and lattice parameter data have been used to determine the octahedral tilting and spontaneous strains associated with the structural, electronic, and magnetic phase transitions. At room temperature, the structure is tetragonal and is characterized by cooperative out-of-phase tilts of the MnO6 octahedra about the c axis and a large Jahn-Teller-type distortion due to the presence of Mn3+. The sample exhibits a reversible phase transition from the cubic Pm3¯m perovskite to a tetragonal I4/mcm structure at 750 K. The Pm3¯m ↔ I4/mcm phase transition is continuous, and the tetragonal strain, which is dominated by the Jahn-Teller-type distortion of the MnO6 octahedra, exhibits an unusual et0.5 ∝ (Tc - T) temperature dependence. At low temperatures, a C-type antiferromagnetic structure develops with a Neel temperature TN of 250 K. The Mn magnetic moment at 7 K is 2.99(2) μB/Mn. The magnetic ordering introduces additional tetragonal strain, and this strain shows the expected quadratic dependence on the magnetic moment at low temperatures. An increase in the octahedral tilt angle at TN demonstrates an effective coupling between the magnetic ordering process and octahedral tilting.

  9. Surface electronic structure transitions at high temperature on perovskite oxides: the case of strained La0.8Sr0.2CoO3 thin films.

    PubMed

    Cai, Zhuhua; Kuru, Yener; Han, Jeong Woo; Chen, Yan; Yildiz, Bilge

    2011-11-09

    In-depth probing of the surface electronic structure on solid oxide fuel cell (SOFC) cathodes, considering the effects of high temperature, oxygen pressure, and material strain state, is essential toward advancing our understanding of the oxygen reduction activity on them. Here, we report the surface structure, chemical state, and electronic structure of a model transition metal perovskite oxide system, strained La(0.8)Sr(0.2)CoO(3) (LSC) thin films, as a function of temperature up to 450 °C in oxygen partial pressure of 10(-3) mbar. Both the tensile and the compressively strained LSC film surfaces transition from a semiconducting state with an energy gap of 0.8-1.5 eV at room temperature to a metallic-like state with no energy gap at 200-300 °C, as identified by in situ scanning tunneling spectroscopy. The tensile strained LSC surface exhibits a more enhanced electronic density of states (DOS) near the Fermi level following this transition, indicating a more highly active surface for electron transfer in oxygen reduction. The transition to the metallic-like state and the relatively more enhanced DOS on the tensile strained LSC at elevated temperatures result from the formation of oxygen vacancy defects, as supported by both our X-ray photoelectron spectroscopy measurements and density functional theory calculations. The reversibility of the semiconducting-to-metallic transitions of the electronic structure discovered here, coupled to the strain state and temperature, underscores the necessity of in situ investigations on SOFC cathode material surfaces.

  10. Two-dimensional incommensurately modulated structure of (Sr0.13Ca0. 87)2CoSi2O7 crystals.

    PubMed

    Bagautdinov, B; Hagiya, K; Kusaka, K; Ohmasa, M; Iishi, K

    2000-10-01

    The incommensurate structure of (Sr(0.13)Ca(0.87))(2)CoSi(2)O(7) at room temperature has been determined from single-crystal X-ray diffraction data. The compound has a non-centrosymmetric tetragonal basic cell of a = 7.8743 (4) and c = 5.0417 (2) A with the space group P4;2(1)m. The refinements of the basic structure converged to R = 0.038 for 757 main reflections. The two-dimensional incommensurate structure is characterized by the wavevectors q(1) = 0.286 (3)(a* + b*) and q(2) = 0.286 (3)(-a* + b*), where a*, b* are the reciprocal lattice vectors of the basic structure. With the (3 + 2)-dimensional superspace group P(p4mg)(P4;2(1)(m)), the refinements converged to R = 0.071 for 1697 observed reflections (757 main and 940 satellite reflections). The structure is described in terms of displacement of the atoms, rotation, distortion of CoO(4) and SiO(4) tetrahedra, and the partial ordering of the Sr and Ca atoms accompanied with the modulation. Correlated evolution of these features throughout the crystal gives rise to various oxygen coordination around Ca/Sr. Comparison of the derived modulated structure to that of Ca(2)CoSi(2)O(7) clarified that the partial substitution of Ca by large alkaline-earth atoms such as Sr should decrease the distortion of the polyhedra around the cations.

  11. Dielectric properties of tape cast Ba0.65Sr0.35TiO3 derived from sol gel for application in multilayered capacitors

    NASA Astrophysics Data System (ADS)

    Sharma, Pramod K.; Varadan, V. V.; Varadan, V. K.

    2003-10-01

    The tape casting technique using a doctor-blade is used to fabricate thin dielectric sheets of barium strontium titanate (Ba1-xSrxTiO3) with x = 0.35 (abbreviated as BST). Initially, fine powder of Ba0.65Sr0.35TiO3 is prepared by the sol-gel method. Two kinds of tape are used for the stacks, i.e. ∥ (the direction of the layer is along the tape direction (in the casting direction)) and perp (the direction of the layer is perpendicular to the tape direction (across the tape)). Further, two stacking sequences are used for stacking layers of tape, i.e. ∥ layers. It has been observed that the green density remains unaffected by any change of sequence. However, the density of fired tape cast BST changes significantly with change of sequence. For example, the density of multilayered BST with eleven layers is enhanced from approx 3.5 g cm-3 to approx 4 g cm-3 when the sequence changes from ∥ and perp. Observations of the microstructure of multilayered BST under the scanning electron microscope suggest that the packings of particles and pores are strongly dependent on the sequence. The dielectric permittivity of sintered tape cast BST is found to increase with increasing number of layers and temperature; however, it is higher for the perp sequence. A comparison has also been made of the dielectric properties of tape cast BST derived from powders obtained from sol-gel and by conventional methods. Investigations on BST are highly desirable in relation to applications in multilayered capacitors in the electronics and communications industries.

  12. 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

    2015-04-08

    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.

  13. 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.

  14. Magnetic, electrical, magnetoelectrical, and magnetoelastic properties of La0.9Sr0.1MnO3 - y manganites

    NASA Astrophysics Data System (ADS)

    Koroleva, L. I.; Zashchirinskiĭ, D. M.; Khapaeva, T. M.; Gurskiĭ, L. I.; Kalanda, N. A.; Trukhan, V. M.; Szymczak, R.; Krzumanska, B.

    2010-01-01

    This paper reports on a study of the influence of oxygen deficiency on the magnetization, paramagnetic susceptibility, electrical resistivity, magnetoresistance, and volume magnetostriction of the La0.9Sr0.1MnO3 - y manganite with y = 0.03, 0.10, and 0.15. The magnetization M( T) behaves in a complex way with temperature; for T < 80 K, it only weakly depends on T, and at 80 ≤ T ≤ 300 K, the M( T) curve shows a falloff. Within the interval 240 K ≤ T ≤ 300 K, the long-range magnetic order breaks up into superparamagnetic clusters. For T < 80 K, the magnetic moment per formula unit is about one-fourth that which should be expected for complete ferromagnetic alignment of Mn ion moments. Although the composition with y = 0.03, in which part of acceptor centers is compensated by donors (oxygen vacancies), the negative magnetoresistance Δρ/ρ and volume magnetostriction ω are observed to pass through maxima near the Curie point, their values are one to two orders of magnitude smaller than those for the y = 0 composition. In compositions with y = 0.10 and 0.15 with electronic doping, the values of Δρ/ρ and ω are smaller by one to two orders of magnitude than those observed for the y = 0.03 composition. They do not display giant magnetoresistance and volume magnetostriction effects, which evidences the absence of ferrons near unionized oxygen vacancies. This allows the conclusion that the part played by both compensated and uncompensated doubly charged donors consists in forming dangling Mn-O-Mn bonds, which lead to a decrease in the Curie temperature with increasing y and to the formation above it of superparamagnetic clusters of the nonferron type.

  15. Spin-state transition of iron in (Ba0.5Sr0.5)(Fe0.8Zn0.2)O perovskite

    NASA Astrophysics Data System (ADS)

    Feldhoff, Armin; Martynczuk, Julia; Arnold, Mirko; Myndyk, Maxym; Bergmann, Ingo; Šepelák, Vladimir; Gruner, Wolfgang; Vogt, Ulrich; Hähnel, Angelika; Woltersdorf, Jörg

    2009-11-01

    The redox behavior of iron during heating of a high-performance perovskite for ceramic oxygen separation membranes was studied by combined electron energy-loss (EELS, esp. ELNES) and Mössbauer spectroscopical in situ methods. At room temperature, the iron in (Ba0.5Sr0.5)(Fe0.8Zn0.2)O (BSFZ) is in a mixed valence state of 75% Fe in the high-spin state and 25% Fe predominantly in the low-spin state. When heated to 900C, a slight reduction of iron is observed that increases the quantity of Fe species. However, the dominant occurrence is a gradual transition in the spin-state of trivalent iron from a mixed low-spin/high-spin to a pure high-spin configuration. In addition, a remarkable amount of hybridization is found in the Fe-O bonds that are highly polar rather than purely ionic. The coupled valence/spin-state transition correlates with anomalies in thermogravimetry and thermal expansion behavior observed by X-ray diffraction and dilatometry, respectively. Since the effective cationic radii depend not only on the valence but also on the spin-state, both have to be considered when estimating under which conditions a cubic perovskite will tolerate specific cations. It is concluded that an excellent phase stability of perovskite-based membrane materials demands a tailoring, which enables pure high-spin states under operational conditions, even if mixed valence states are present. The low spin-state transition temperature of BSFZ provides that all iron species are in a pure high-spin configuration already above ca. 500C making this ceramic highly attractive for intermediate temperature applications ( 500-800C).

  16. 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.

  17. 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.

  18. Upconversion luminescence of Ca1-x Ho x F2+x and Sr0.98-x Er0.02Ho x F2.02+x powders upon excitation by an infrared laser

    NASA Astrophysics Data System (ADS)

    Lyapin, A. A.; Kuznetsov, S. V.; Ryabochkina, P. A.; Merculov, A. P.; Chernov, M. V.; Ermakova, Yu A.; Luginina, A. A.; Fedorov, P. P.

    2017-07-01

    Fluorite-type Ca1-x Ho x F2+x and Sr0.98-x Er0.02Ho x F2.02+x powders were synthesized using the co-precipitation from water solution technique. The upconversion luminescence of Ca1-x Ho x F2+x and Sr0.98-x Er0.02Ho x F2.02+x powders in the visible spectral region upon excitation of 5I7 level Ho3+ ions and 4I13/2 level Er3+ ions were studied for the first time. The possibility of visualizing near IR laser radiation using Ca1-x Ho x F2+x and Sr0.98-x Er0.02Ho x F2.02+x powders is proposed. Optimal compositions of Ca1-x Ho x F2+x and Sr0.98-x Er0.02Ho x F2.02+x powders for application as visualizers are discussed.

  19. Effect of the thickness of BiFeO3 layers on the magnetic and electric properties of BiFeO3/La0.7Sr0.3MnO3 heterostructures

    NASA Astrophysics Data System (ADS)

    Wang, Le; Wang, Zhen; Jin, Kui-juan; Li, Jian-qi; Yang, Huai-xin; Wang, Can; Zhao, Rui-qiang; Lu, Hui-bin; Guo, Hai-zhong; Yang, Guo-zhen

    2013-06-01

    BiFeO3 layers with various thicknesses were fabricated on La0.7Sr0.3MnO3 covered SrTiO3 substrates by a laser molecular-beam epitaxy system. The ferromagnetic transition temperature (Tc) and magnetic coercive field (Hc) of BiFeO3/La0.7Sr0.3MnO3 heterostructures are larger than those of the La0.7Sr0.3MnO3 film. With increasing the thickness of the BiFeO3 layer, Tc, Hc, and ferroelectric coercive field of the BiFeO3/La0.7Sr0.3MnO3 heterostructures decrease, while the dielectric permittivity, remanent polarization, and resistance ratio of the ON and OFF states increase. The variations of the magnetic and electric properties with the thickness could be due to the effects of the epitaxial strain and the interface layer.

  20. Sr0.95Zn0.05Se:Eu2+ and CdSe/ZnS nanocrystals hybrid phosphors for enhancing color rendering index of white light emitting diode.

    PubMed

    Chung, Wonkeun; Jung, Hyunchul; Lee, Chang Hun; Kim, Sung Hyun

    2012-07-01

    In this study, the yellow emitting cubic structure of Sr0.95Zn0.05Se:Eu2+ phosphors were prepared by high temperature solid state reaction. The Sr0.95Zn0.05Se:Eu2+ phosphors exhibited strong excitation intensity under 400-460 nm region, and broad band emission appeared at around 545-600 nm due to the d-f transition of Eu2+. To enhance the red emission, HDA/TOP/TOPO capped CdSe/ZnS NCs were synthesized via fast nucleation and slow growth method. The narrow emission peak was located at 615 nm with 69% of high quantum yield. Bright white emission was generated by combining a 460 nm InGaN LED chip with CdSe/ZnS NCs and Sr0.95Zn0.05Se:Eu2+ hybrid phosphors. The fabricated white LEDs showed warm white light with acceptable CIE chromaticity coordinate variation from (0.343, 0.255) at 20 mA to (0.335, 0.250) at 50 mA. The addition of CdSe/ZnS NCs contributed to the extension of white light spectrum by supplement of the red region. The color rendering index was largely enhanced from 41.7 to 79.7 compared to the Sr0.95Zn0.05Se:Eu2+ based phosphors white LED.

  1. Novel lead-free ferroelectric film by ultra-small Ba0.8Sr0.2TiO3 nanocubes assembled for a large electrocaloric effect.

    PubMed

    Su, Ran; Zhang, Dawei; Liu, Yang; Lu, Jiangbo; Wang, Zhipeng; Li, Linglong; Bian, Jihong; Wu, Ming; Lou, Xiaojie; Yang, Yaodong

    2016-10-26

    A giant electrocaloric effect (ECE) can be achieved in ferroelectric thin films, which demonstrates the applications of thin films in alternative cooling. However, electrocaloric thin films fabricated by conventional techniques, such as the pulsed laser deposition or sol-gel methods, may be limited by high costs, low yield and their dependence on substrates. In this study, we present a new bottom-up strategy to construct electrocaloric Ba0.8Sr0.2TiO3 thin films by assembling precisely designed building blocks of ferroelectric nanocubes, which is supported by detailed structural characterization. Moreover, it is found that our assembled Ba0.8Sr0.2TiO3 films differ remarkably from both individual Ba0.8Sr0.2TiO3 NPs and bulk Ba0.8Sr0.2TiO3 ceramics in terms of new collective ferroelectric properties, including superior and diffused permittivity constants and polarization-electric field loops. Benefiting from these unique ferroelectric properties, a giant ECE (9.1 K) over a broad temperature range (20 °C to 60 °C) is achieved, which is very large in the lead-free oxide film. Clearly, this bottom-up strategy provides a promising pathway for developing high electrocaloric effect devices.

  2. In situ formation of oxygen vacancy in perovskite Sr0.95Ti0.8Nb0.1M0.1O3 (M = Mn, Cr) toward efficient carbon dioxide electrolysis

    PubMed Central

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

    2014-01-01

    In this work, redox-active Mn or Cr is introduced to the B site of redox stable perovskite Sr0.95Ti0.9Nb0.1O3.00 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 Sr0.95Ti0.9Nb0.1O3.00 to reduced Sr0.95Ti0.9Nb0.1O2.90 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 Sr0.95Ti0.8Nb0.1M0.1O3.00 (M = Mn, Cr) to Sr0.95Ti0.8Nb0.1M0.1O2.85. 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. PMID:25403738

  3. 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

    2015-12-09

    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.

  4. 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).

  5. Electronic structure of La0.7Sr0.3Mn1-xCuxO3 (0.0<=x<=0.30)

    NASA Astrophysics Data System (ADS)

    Kim, M. S.; Yang, J. B.; Medvedeva, J.; Yelon, W. B.; Parris, P. E.; James, W. J.

    2008-06-01

    We have investigated the electronic structure of Cu-substituted La0.7Sr0.3MnO3 (LSMO) by x-ray photoelectron spectroscopy and using density functional theory within local spin-density approximations (LSDA) and LSDA+U. We find that there is a coexistence of mixed-valent Cu ions, Cu3+ with Cu2+ dominant, in all Cu-substituted LSMO samples. From a deconvolution of the XPS spectra of Cu-2p3/2, we determined the ratios of Cu2+/Cu3+ and Mn3+/Mn4+, and in turn calculated the change in the tolerance factors of Cu-substituted LSMO. Valence-band photoelectron spectra show that the density of states at the Fermi level is made up mainly of the O-2p and Mn-3d states with a small contribution near EF from the Cu-3d states. We find that LSDA+U calculations for La1/2Sr1/2Mn1-xCuxO3 describe the half-metallicity and ground state ferromagnetic ordering with no evidence of antiferromagnetism for all systems consistent with experimental neutron diffraction data. Two electron transport channels of the major Mn-O-Mn and the minor Cu-O-Cu chains are found. This suggests that the electronic transport behavior of Cu-substituted LSMO systems may be explained by a combination of two different transport mechanisms: (i) a σpd hybridization between the eg states in a majority spin-up Mn-d channel with O-2p orbitals in the Mn-O-Mn chain and (ii) a σpd hybridization between the eg states in a dominant minority spin-down Cu-d channel with O-2p orbitals in the Cu-O-Cu chain. We also find that the half-metallicity of the compounds is lost upon Cu-substitution with a resulting anisotropic electronic transport of the Cu-pair electrons in the basal plane and along the c axis.

  6. Superconductivity and charge-carrier localization in ultrathin La1.85Sr0.15CuO4/La2CuO4 bilayers

    NASA Astrophysics Data System (ADS)

    Sen, K.; Marsik, P.; Das, S.; Perret, E.; de Andres Prada, R.; Alberca, A.; Biškup, N.; Varela, M.; Bernhard, C.

    2017-06-01

    La1.85Sr0.15CuO4 /La2CuO4 (LSCO15/LCO) bilayers with a precisely controlled thickness of N unit cells (UCs) of the former and M UCs of the latter ([LSCO15_N /LCO _M ] ) were grown on (001)-oriented SrLaAlO4 (SLAO) substrates with pulsed laser deposition (PLD). X-ray diffraction and reciprocal space map (RSM) studies confirmed the epitaxial growth of the bilayers and showed that a [LSCO15_2/LCO_2] bilayer is fully strained, whereas a [LSCO15_2/LCO_7] bilayer is already partially relaxed. The in situ monitoring of the growth with reflection high energy electron diffraction (RHEED) revealed that the gas environment during deposition has a surprisingly strong effect on the growth mode and thus on the amount of disorder in the first UC of LSCO15 (or the first two monolayers of LSCO15 containing one CuO2 plane each). For samples grown in pure N2O gas (growth type B), the first LSCO15 UC next to the SLAO substrate is strongly disordered. This disorder is strongly reduced if the growth is performed in a mixture of N2O and O2 gas (growth type A). Electric transport measurements confirmed that the first UC of LSCO15 next to the SLAO substrate is highly resistive and shows no sign of superconductivity for growth type B, whereas it is superconducting for growth type A. Furthermore, we found, rather surprisingly, that the conductivity of the LSCO15 UC next to the LCO capping layer strongly depends on the thickness of the latter. A LCO capping layer with 7 UCs leads to a strong localization of the charge carriers in the adjacent LSCO15 UC and suppresses superconductivity. The magnetotransport data suggest a similarity with the case of weakly hole doped LSCO single crystals that are in a so-called `cluster-spin-glass state.' We discussed several mechanisms that could lead to such a localization of holes that are embedded in a short-range ordered antiferromagnetic background for the case of a thick LCO capping layer with M =7 but not for a thin one with M =2 .

  7. Effect of La0.7Sr0.3MnO3 crystal structures on magnetization of (1 1 1) oriented La0.7Sr0.3MnO3-SrRuO3 superlattices

    NASA Astrophysics Data System (ADS)

    Behera, B. C.; Padhan, P.; Prellier, W.

    2016-05-01

    A series of superlattices consisting of 15 bilayers of ferromagnetic La0.7Sr0.3MnO3 (LSMO) and SrRuO3 (SRO) were grown with either stacking order on (1 1 1) oriented SrTiO3 (STO) substrates using the pulsed laser deposition technique. The Raman spectra of these superlattices show the existence of rhombohedral and orthorhombic crystal structures of LSMO in (111)STO/[11-unit cell (u.c.) LSMO/n-u.c. SRO]X15 superlattices with n  =  2 and 3. Interestingly, the Raman spectra of (1 1 1)STO/[11-u.c. SRO/n-u.c. LSMO]X15 superlattices with n  =  2 and 3 show only the orthorhombic structure of LSMO. The (1 1 1)STO/[11-u.c. LSMO/n-u.c. SRO]X15 superlattices exhibit enhanced magnetization with weak antiferromagnetic coupling whereas reduced magnetization with strong antiferromagnetic coupling is observed in (1 1 1)STO/[11-u.c. SRO/n-u.c. LSMO]X15 superlattices. The observed magnetic properties of these superlattices can be explained by the interfacial structural coupling, as evident from their Raman spectra which suggest a modification in the stereochemistry of Mn at the interfaces.

  8. Effect of La0.7Sr0.3MnO3 crystal structures on magnetization of (1 1 1) oriented La0.7Sr0.3MnO3-SrRuO3 superlattices.

    PubMed

    Behera, B C; Padhan, P; Prellier, W

    2016-05-18

    A series of superlattices consisting of 15 bilayers of ferromagnetic La0.7Sr0.3MnO3 (LSMO) and SrRuO3 (SRO) were grown with either stacking order on (1 1 1) oriented SrTiO3 (STO) substrates using the pulsed laser deposition technique. The Raman spectra of these superlattices show the existence of rhombohedral and orthorhombic crystal structures of LSMO in (111)STO/[11-unit cell (u.c.) LSMO/n-u.c. SRO]X15 superlattices with n  =  2 and 3. Interestingly, the Raman spectra of (1 1 1)STO/[11-u.c. SRO/n-u.c. LSMO]X15 superlattices with n  =  2 and 3 show only the orthorhombic structure of LSMO. The (1 1 1)STO/[11-u.c. LSMO/n-u.c. SRO]X15 superlattices exhibit enhanced magnetization with weak antiferromagnetic coupling whereas reduced magnetization with strong antiferromagnetic coupling is observed in (1 1 1)STO/[11-u.c. SRO/n-u.c. LSMO]X15 superlattices. The observed magnetic properties of these superlattices can be explained by the interfacial structural coupling, as evident from their Raman spectra which suggest a modification in the stereochemistry of Mn at the interfaces.

  9. Transport properties of YBa2Cu3Ox /La0.67Sr0.33MnO3 nanostrips and YBa2Cu3Ox/La0.67Sr0.33MnO3/YBa2Cu3Ox nanojunctions

    NASA Astrophysics Data System (ADS)

    Štrbík, V.; Beňačka, Š.; Gaži, Š.; Španková, M.; Šmatko, V.; Chromik, Š.; Gál, N.; Knoška, J.; Sojková, M.; Pisarčík, M.

    2016-03-01

    A metallic ferromagnet (F) in proximity with a superconductor (S) can transport supercurrent on a long distance through conversion of opposite-spin singlet Cooper pairs (CP) into equal-spin triplet CP (long range triplet component, LRTC), which are not broken by the exchange energy of F. The optimal conditions for the conversion are yet to be clarified; however, it is accepted that the key point to this process include high interface transparency and magnetic inhomogeneity at the SF interface. The aim of our paper is to study SF nanostrips (length of about 1500 nm and width down to 300 nm) and lateral SFS nanojunctions based on high critical temperature YBa2Cu3Ox (YBCO) and half-metallic La0.67Sr0.33MnO3 (LSMO) thin films. We applied a focused Ga+ ion beam (FIB) for patterning the SF nanostrips, as well as lateral SFS nanojunctions, by creating a slot in the nanostrip after removing the YBCO film in the slot along a length of about 200 nm. The temperature dependences of the samples resistance R(T) show critical temperature TCn ≈ 89 K of the SF nanostrips; however, the SFS nanojunctions at T < TCn show a residual resistance R < 100 Ω corresponding to a dirty LSMO (ρ≈ 10 mΩ cm) in the slot. The LRTC was not observed in our lateral SFS nanojunctions until now.

  10. Electrochemical performance and carbon deposition resistance of Ce-doped La0.7Sr0.3Fe0.5Cr0.5O3-δ anode materials for solid oxide fuel cells fed with syngas

    NASA Astrophysics Data System (ADS)

    Sun, Yi-Fei; Li, Jian-Hui; Chuang, Kart T.; Luo, Jing-Li

    2015-01-01

    Ce-doped La0.7Sr0.3Fe0.5Cr0.5O3-δ (Ce-LSFC) perovskite anode catalysts for solid oxide fuel cells are successfully synthesized by a modified combustion method for the first time. The pure perovskite structure without formation of CeO2 is obtained when the content of Ce ≤ 10%. Compared with La0.7Sr0.3Fe0.5Cr0.5O3-δ anode, Ce-LSFC anode not only shows much higher catalytic activity towards the oxidation of syngas with less carbon deposition, but also displays better regeneration from coking. The enhanced performance is attributed to the more available oxygen vacancies in lattice and better oxygen mobility after doping with Ce.

  11. Enhanced second-harmonic generation in Pr0.5Ca0.5MnO3/La0.5Sr0.5MnO3 superlattices

    NASA Astrophysics Data System (ADS)

    Lee, J. S.; Nakamura, M.; Kawasaki, M.; Tokura, Y.

    2013-12-01

    We investigated second harmonic generation for manganite superlattices composed of Pr0.5Ca0.5MnO3 and La0.5Sr0.5MnO3. While the second harmonic intensity shows a strong variation as a function of the constituent layer thickness, it is dramatically enhanced when each layer has a same thickness of about 1.4 nm and endows its own ground state nature, i.e., a charge-orbital ordered antiferromagnetic insulator for Pr0.5Ca0.5MnO3 and a ferromagnetic metal for La0.5Sr0.5MnO3. From the detailed symmetry analysis, we discuss a possible role of the coexisting phases and their boundaries in the enhancement of the polar character in this manganese oxide superlattice.

  12. Correlation between electrical, magnetocaloric properties and critical behavior in (La0.75Nd0.25)2/3(Ca0.8Sr0.2)1/3MnO3

    NASA Astrophysics Data System (ADS)

    Khelifi, J.; Dhahri, E.; Hlil, E. K.

    2017-01-01

    An investigation of the critical behavior and magnetic entropy from resistivity of (La0.75Nd0.25)2/3(Ca0.8Sr0.2)1/3MnO3 is presented. The magnetocaloric properties of the polycrystalline manganite (La0.75Nd0.25)2/3(Ca0.8Sr0.2)1/3MnO3 based on resistivity measurements were investigated. Using, the equation ΔS = - α∫0H ∂Ln (ρ)/∂T) H dH relates magnetic order to the transport behavior of the compound, we measure the magnetic entropy change ΔSM from the resistivity which is similar to that calculated from the magnetic measurement. Moreover, we have found an excellent estimation of critical behavior from resistivity and magnetic analysis.

  13. Ce electronic states in Nd(0.45-x)Ce(x)Sr0.55MnO3 probed by x-ray absorption spectroscopy and photoemission.

    PubMed

    Shirai, T; Imada, S; Higashiya, A; Sekiyama, A; Suga, S; Muro, T; Tanaka, Y; Tamasaku, K; Yabashi, M; Ishikawa, T; Miyasaka, S; Tokura, Y

    2013-10-16

    We have investigated the Ce 4f electronic states in the Ce-doped manganites Nd(0.45-x)Ce(x)Sr0.55MnO3 (NCSMO) by means of x-ray absorption spectroscopy (XAS) and hard x-ray photoelectron spectroscopy (HAXPES). The Ce 3d XAS shows that the Ce ions exist in the form of the Ce(3+) and Ce(4+) mixed-valent states, and we have found that the XAS spectral features change with temperature. The Ce 3d XAS and HAXPES spectra for NCSMO agree reasonably well with calculated results based on the single-impurity Anderson model, which takes into account the atomic multiplets and two valence bands. The estimated Ce bulk valence of Nd0.15Ce0.3Sr0.55MnO3 decreases from 3.44 to 3.30 with cooling.

  14. Internal residual stress studies and enhanced dielectric properties in La0.7Sr0.3CoO3 buffered (Ba,Sr)TiO3 thin films

    NASA Astrophysics Data System (ADS)

    Lu, Shengbo; Xu, Zhengkui

    2009-09-01

    Ba0.6Sr0.4TiO3 (BST) thin films were deposited on La0.7Sr0.3CoO3 (LSCO) buffered and unbuffered Pt (111)/Ti/SiO2/Si substrates by pulsed laser deposition. The former exhibits a (100) preferred orientation and the latter a random orientation, respectively. Grazing incident x-ray diffraction study revealed that the tensile residual stress observed in the latter is markedly reduced in the former. As a result, the dielectric property of the LSCO buffered BST thin film is greatly improved, which shows a larger dielectric constant and tunability, smaller loss tangent, and lower leakage current than those of the unbuffered BST thin film. The relaxation of the larger tensile residual stress is attributed to the larger grain size in the buffered BST thin film and to a closer match of thermal expansion coefficient between the BST and the LSCO buffer layer.

  15. Optical spectroscopy study of charge density wave order in Sr3Rh4Sn13 and (Sr0.5Ca0.5)3Rh4Sn13

    NASA Astrophysics Data System (ADS)

    Ban, W. J.; Wang, H. P.; Tseng, C. W.; Kuo, C. N.; Lue, C. S.; Wang, N. L.

    2017-04-01

    We perform optical spectroscopy measurement on single-crystal samples of Sr3Rh4Sn13 and (Sr0.5Ca0.5)3Rh4Sn13. Formation of CDW energy gap was clearly observed for both single-crystal samples when they undergo the phase transitions. The existence of residual Drude components in σ 1( ω) below T CDW indicates that the Fermi surface is only partially gapped in the CDW state. The obtained value of 2Δ/ k B T CDW is roughly 13 for both Sr3Rh4Sn13 and (Sr0.5Ca0.5)3Rh4Sn13 compounds, which is considerably larger than the mean-field value based on the weak-coupling BCS theory. The measurements provide optical evidence for the strong coupling characteristics of the CDW phase transition.

  16. Stripe order of La1.64Eu0.2Sr0.16CuO4 in magnetic fields studied by resonant soft x-ray scattering

    NASA Astrophysics Data System (ADS)

    Zwiebler, M.; Schierle, E.; Weschke, E.; Büchner, B.; Revcolevschi, A.; Ribeiro, Patrick; Geck, J.; Fink, J.

    2016-10-01

    We present results on the magnetic field dependence of the stripe order in La1.64Eu0.2Sr0.16CuO4 (LESCO). Using resonant soft x-ray scattering at the oxygen K edge to probe the (0.259,0,0.648) superlattice reflection, which is commonly associated to charge stripes, we found no pronounced difference in the wave vector, peak widths, and integrated intensity for magnetic fields up to B =6 T. This is in strong contrast to the behavior observed for La1.875Sr0.125CuO4 , where a stabilization of the charge modulation in high magnetic fields has been demonstrated.

  17. Interrelation of transport properties, defect structure and spin state of Ni3+ in La1.2Sr0.8Ni0.9Fe0.1O4+δ

    NASA Astrophysics Data System (ADS)

    Gilev, A. R.; Kiselev, E. A.; Zakharov, D. M.; Cherepanov, V. A.

    2017-10-01

    The total conductivity, Seebeck coefficient and oxygen non-stoichiometry for La1.2Sr0.8Ni0.9Fe0.1O4+δ have been measured vs temperature and oxygen partial pressure P(O2). The measurements were carried out at 800, 850, 900 and 950 °C within the P(O2) range of 10-5-0.21 atm. La1.2Sr0.8Ni0.9Fe0.1O4+δ was shown to be oxygen deficient in all temperature and P(O2) ranges studied. The calculated values of the partial molar enthalpy of oxygen depend very slightly on oxygen content (δ), indicating that La1.2Sr0.8Ni0.9Fe0.1O4+δ with the oxygen deficiency can be considered an ideal solution. The model of point defect equilibria in La1.2Sr0.8Ni0.9Fe0.1O4+δ has been proposed and fitted to experimental dependencies. Subsequent joint analysis of the defect structure and transport properties revealed that electron holes can coexist in both localized and quasi-delocalized states in the oxide: the former corresponded to high-spin state Ni3+ and the latter - to low-spin state Ni3+. The mobilities of localized electron holes were shown to be significantly lower in comparison to quasi-delocalized ones. The behavior of localized electron holes was explained in terms of a small polaron conduction mechanism; in contrast, quasi-delocalized electron holes were described in terms of a band conduction approach. The small polaron conduction mechanism was shown to be predominant in the Sr- and Fe-co-doped lanthanum nickelate.

  18. Direct Observation of Magnetic-Ion Off-Centering-Induced Ferroelectricity in Multiferroic Manganite Pr(Sr0.1Ca0.9)2 Mn2O7.

    PubMed

    Ma, Chao; Lin, Yue; Yang, Huaixin; Tian, Huanfang; Shi, Lei; Zeng, Jie; Li, Jianqi

    2015-11-04

    Ferroelectricity in multiferroic Pr(Sr0.1 Ca0.9)2 Mn2 O7 is found to originate from the off-centering of Mn ions. This polar displacement is energetically stabilized by the cooperative interplay of lattice deformation induced by orbital ordering and oxygen octahedral tilting. This mechanism implies that magnetism and ferroelectricity arise from the same magnetic ions, providing direct evidence for the magnetic-ion off-centering-driven ferroelectricity.

  19. Novel high temperature proton conducting fuel cells: Production of La 0.995Sr 0.005NbO 4- δ electrolyte thin films and compatible cathode architectures

    NASA Astrophysics Data System (ADS)

    Fontaine, M.-L.; Larring, Y.; Haugsrud, R.; Norby, T.; Wiik, K.; Bredesen, R.

    For breakthrough development in solid oxide fuel cells, novel cell architectures integrating better performing materials and cost-effective manufacturing processes with potential for mass production must be realised. The present work addresses this on the basis of the recent discovery of acceptor doped rare-earth ortho-niobate proton conductors and the development of a versatile fabrication process. La 0.995Sr 0.005NbO 4- δ/NiO anodes are produced by tape-casting and co-lamination of green layers. Their porosity is finely tuned by using a pyrolyzable pore former. La 0.995Sr 0.005NbO 4- δ electrolytes are spin-coated using ceramic-based suspensions. Fully dense electrolytes with thickness ranging from 9 μm to 26 μm are obtained after sintering in air at 1350 °C. The cathode layers are then screen-printed. To match thermal expansion and to avoid chemical reaction between the functional layers, special attention is paid to the design of cathode architectures. CaTi 0.9Fe 0.1O 3- δ, La 2NiO 4+ δ and La 4Ni 3O 10 mixed oxygen ion and electron conducting oxides are investigated as either monophase or La 0.995Sr 0.005NbO 4- δ-based composite electrodes. The latter gives the whole cell an innovative "semi-monolithic" concept, which can take advantage of the chemical and mechanical stability of La 0.995Sr 0.005NbO 4- δ, as well as of inherent material integration. Most promising cell architectures are finally selected based on thermo-mechanical and chemical compatibility of all functional layers.

  20. Comparison of stripe modulations in La1.875Ba0.125CuO4 and La1.48Nd0.4Sr0.12CuO4

    NASA Astrophysics Data System (ADS)

    Wilkins, S. B.; Dean, M. P. M.; Fink, Jörg; Hücker, Markus; Geck, J.; Soltwisch, V.; Schierle, E.; Weschke, E.; Gu, G.; Uchida, S.; Ichikawa, N.; Tranquada, J. M.; Hill, J. P.

    2011-11-01

    We report combined soft and hard x-ray scattering studies of the electronic and lattice modulations associated with stripe order in La1.875Ba0.125CuO4 and La1.48Nd0.4Sr0.12CuO4. We find that the amplitude of both the electronic modulation of the hole density and the strain modulation of the lattice is significantly larger in La1.875Ba0.125CuO4 than in La1.48Nd0.4Sr0.12CuO4 and is also better correlated. The in-plane correlation lengths are isotropic in each case; for La1.875Ba0.125CuO4, ξhole=255±5 Å, whereas for La1.48Nd0.4Sr0.12CuO4, ξhole=111±7 Å. We find that the modulations are temperature independent in La1.875Ba0.125CuO4 in the low temperature tetragonal phase. In contrast, in La1.48Nd0.4Sr0.12CuO4, the amplitude grows smoothly from zero, beginning 13 K below the LTT phase transition. We speculate that the reduced average tilt angle in La1.875Ba0.125CuO4 results in reduced charge localization and incoherent pinning, leading to the longer correlation length and enhanced periodic modulation amplitude.

  1. Transport studies of Nb-doped Pr0.7Sr0.3Mn1-xNbxO3 (0≤x≤0.05) manganites

    NASA Astrophysics Data System (ADS)

    Choithrani, Renu; Bhat, Masroor A.; Gaur, N. K.

    2014-09-01

    We have investigated the transport studies of the Nb-doped Pr0.7Sr0.3Mn1-xNbxO3 (0≤x≤0.05) manganites for the first time for identifying the transport properties as a function of the composition and temperature. Pr0.7Sr0.3Mn1-xNbxO3 (0≤x≤0.05) samples exhibit a single phase nature with an orthorhombic structure and a Pbnm space group. These materials show colossal magnetoresistance effect (CMR) and have wide technological applications such as magnetic sensors, reading head devices, spintronics, bolometers, magnetic refrigeration, etc. The computed transport properties such as cohesive energy, Reststrahlen frequency, Debye temperature, Grüneisen parameter and temperature dependence of specific heat of Pr0.7Sr0.3Mn1-xNbxO3 (0≤x≤0.05) manganites are discussed in detail in the present work by applying extended rigid ion model (ERIM) and have shown significant agreement with the corresponding available results.

  2. Sharp ferroelectric phase transition in strained single-crystalline SrRuO3/Ba0.7Sr0.3TiO3/SrRuO3 capacitors

    NASA Astrophysics Data System (ADS)

    Dittmann, R.; Plonka, R.; Vasco, E.; Pertsev, N. A.; He, J. Q.; Jia, C. L.; Hoffmann-Eifert, S.; Waser, R.

    2003-12-01

    Single-crystalline all-perovskite SrRuO3/Ba0.7Sr0.3TiO3/SrRuO3 thin-film capacitors epitaxially grown on SrTiO3 exhibit a sharp paraelectric-to-ferroelectric phase transition at 350 K with a maximum permittivity of about 6660. This value is comparable to that of bulk ceramics and exceeds by several times the highest values reported for Ba0.7Sr0.3TiO3 thin film capacitors. The observed thickness dependence of the dielectric response is analyzed with the aid of a thermodynamic theory. It is shown that a weak decrease of the permittivity with the Ba0.7Sr0.3TiO3 thickness decreasing from 200 to 10 nm can be explained solely by the thickness-dependent strain relaxation in epitaxial films without assuming the presence of low-permittivity layers at the film/electrode interfaces.

  3. Growth and electrical transport properties of La0.7Sr0.3MnO3 thin films on Sr2IrO4 single crystals

    DOE PAGES

    Moon, E. J.; May, A. F.; Shafer, P.; ...

    2017-04-20

    Here, we report the physical properties of La 0.7 Sr 0.3 MnO 3 thin films on Sr 2 IrO 4 single crystals. We also deposited the manganite films using oxide molecular beam epitaxy on flux-grown (001)-oriented iridate crystals. Temperature-dependent magnetotransport and x-ray magnetic circular dichroism measurements reveal the presence of a ferromagnetic metallic ground state in the films, consistent with films grown on SrTiO 3 and La 0.3 Sr 0.7 Al 0.65 Ta 0.35 O 3 . A parallel resistance model is used to separate conduction effects within the Sr 2 IrO 4 substrate and the La 0.7 Sr 0.3more » MnO 3 thin films, revealing that the measured resistance maximum does not correspond to the manganite Curie temperature but results from a convolution of properties of the near-insulating substrate and metallic film. Furthermore, the ability to grow and characterize epitaxial perovskites on Sr 2 IrO 4 crystals enables a new route for studying magnetism at oxide interfaces in the presence of strong spin-orbit interactions.« less

  4. Dielectric properties of xNa0.5Bi0.5TiO3-(1 ‑ x)Ba0.66Mg0.04Sr0.3TiO3 composite ceramics

    NASA Astrophysics Data System (ADS)

    Wang, Jing; Cheng, Haiyan; Gao, Lan; Wang, Xianling; Duan, Ruijie; Li, Jiali

    2017-02-01

    The ceramics with the composition of xNa0.5Bi0.5TiO3-(1 ‑ x)Ba0.66Mg0.04Sr0.3TiO3 (NBT-BMST) in which x = 0.2, 0.3, 0.4 and 0.5 were prepared successfully by the solid-state reaction method. The effects of NBT-doping on phase structure, morphology, temperature stability and dielectric properties had been investigated in detail. The XRD results show that the composites are composed of tetragonal perovskite. The phase structure of NBT-BMST is observed by scanning electron microscopy. The dielectric constant of 0.3Na0.5Bi0.5TiO3-0.7Ba0.66Mg0.04Sr0.3TiO3 ceramic is ˜4100, the temperature coefficients of capacitance are ‑15%, 15% and 22% at ‑55∘C, 60∘C and 200∘C, respectively. And the dielectric loss is less than 0.13, which is obviously superior to other compositions. The results of this work showed that the component of 0.3Na0.5Bi0.5TiO3-0.7Ba0.66Mg0.04Sr0.3TiO3 is a promising candidate to high-temperature stable materials.

  5. 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.

  6. A-site ordering and its effect on tilting transition in perovskite La0.75Sr0.25FeO3-δ investigated by mechanical spectroscopy

    NASA Astrophysics Data System (ADS)

    Chen, C. C.; Ying, X. N.

    2017-05-01

    La0.75Sr0.25FeO3-δ polycrystalline samples were prepared by the solid state reaction at different sintering temperatures. An octahedral tilting Pnma ↔ R 3 ¯ c transition in La0.75Sr0.25FeO3-δ was detected by mechanical spectroscopy, where a dip of reduced modulus was observed and accompanied by a sharp internal friction peak. The modulus softening is due to the strain/order parameters coupling at this improper ferroelastic transition. The tilting transition shifts toward lower temperature with reducing sintering temperature in La0.75Sr0.25FeO3-δ samples, which is due to the detriment of A-site ordering in the ABO3 perovskite. A higher degree of A-site ordering favors more homogenous structural modulation, which stabilizes the low temperature Pnma phase and results in the shift of the transition to higher temperature. Another internal friction peak just below the tilting transition was observed, which is attributed to domain wall motions. A correlation between the mobility of ferroelastic domain walls in Pnma perovskite and the existence of the high temperature R 3 ¯ c phase was suggested.

  7. Preparation and characterization of BiFeO3/La0.7Sr0.3MnO3 heterostructure grown on SrTiO3 substrate

    NASA Astrophysics Data System (ADS)

    Zhao, Chenwei; Zhou, Chaochao; Chen, Changle

    2017-09-01

    In this paper, BiFeO3/La0.7Sr0.3MnO3 heterostructure is fabricated on the SrTiO (100) substrate using the pulsed laser deposition method (PLD). Magnetization hystersis loops of the BiFeO3/La0.7Sr0.3MnO3 heterostructure are obtained at 300 K and 80 K. The heterostructure exhibits evident ferromagnetic characteristic at both room temperature and 80 K. At 80 K, magnetization of the heterostructure is stronger than room temperature magnetic measure. The temperature dependence of resistance of the heterostructure with different currents is also studied. With different currents, there appears to be a peak resistance about 180 K. When I is 50 uA, ΔR is 68.4%. And when I is 100 uA, ΔR is 79.3%. The BiFeO3/La0.7Sr0.3MnO3 heterostructure exhibits a positive colossal magnetoresistance (MR) effect over a temperature range of 80-300 K. In our heterostructure, maximum magnetic resistance appears in 210 K, and MR = 44.34%. Mechanism analysis of the leakage current at room temperature shows that the leakage current is the interface-limited Schottky emission, but not dominated by the Poole-Frenkel emission or SCLC.

  8. Solution processed Ni-doped TiO2 p-type channel in field effect transistor assembly with <10 nm thin Ba0.5Sr0.5TiO3 dielectric layer

    NASA Astrophysics Data System (ADS)

    Das, Soumen; Kim, Jin-Hwan; Park, Yong-Kyu; Hahn, Yoon-Bong

    2011-05-01

    Solution processed field effect transistor structures were fabricated by inserting a Ba0.5Sr0.5TiO3 layer to form Ag/ZnO/Ba0.5Sr0.5TiO3/Ni2+:TiO2/n-Si assembly. Such assembly registered an on-to-off current ratio as large as 103 with very low off-state current ˜10-12 A. The low leakage current is attributed to the appreciably higher values of valence/conduction band off-set of Ba0.5Sr0.5TiO3/semiconductor heterojunction. The device response was studied as a function of temperature in the range of 25-175 °C. The hole diffusion coefficient and mobility of p-TiO2 was calculated ˜10-3 cm2/s and ˜0.13-0.15 cm-2 V-1 s-1, respectively.

  9. 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.

  10. High performing BaCe0.8Zr0.1Y0.1O3-δ-Sm0.5Sr0.5CoO3-δ based protonic ceramic fuel cell

    NASA Astrophysics Data System (ADS)

    Dailly, J.; Taillades, G.; Ancelin, M.; Pers, P.; Marrony, M.

    2017-09-01

    The electrochemical performances of a composite cathode consisted of Sm0.5Sr0.5CoO3-δ and BaCe0.8Zr0.1Y0.1O3-δ coated onto a BaCe0.8Zr0.1Y0.1O3-δ-based half-cell are evaluated in the intermediate temperature range 600-700 °C. Powders for the manufacture of anode substrate and electrolyte are commercial products, whereas a glycine-nitrate process is used to synthesize the cathode material. The complete cell is manufactured by wet chemical routes, using the combination of tape-casting for the anode substrate NiO-BaCe0.8Zr0.1Y0.1O3-δ and wet powder spraying for the elaboration of the electrolyte BaCe0.8Zr0.1Y0.1O3-δ and air electrode Sm0.5Sr0.5CoO3-δ-BaCe0.8Zr0.1Y0.1O3-δ. Thin electrolytes and porous electrodes are successfully elaborated for a cell size of 3 × 3 cm2. A high open circuit voltage of 1.11 V at 600 °C indicates an excellent gas-tightness of the protonic ceramic electrolyte. A maximum power density of 370-530 mW cm-2 in the range 600-700 °C is measured validating Sm0.5Sr0.5CoO3-δ material as promising cathode for protonic-based cells.

  11. Reversible magnetocaloric effect in materials with first order phase transitions in cyclic magnetic fields: Fe48Rh52 and Sm0.6Sr0.4MnO3

    NASA Astrophysics Data System (ADS)

    Aliev, A. M.; Batdalov, A. B.; Khanov, L. N.; Kamantsev, A. P.; Koledov, V. V.; Mashirov, A. V.; Shavrov, V. G.; Grechishkin, R. M.; Kaul', A. R.; Sampath, V.

    2016-11-01

    The magnetocaloric effect (MCE) in an Fe48Rh52 alloy and Sm0.6Sr0.4MnO3 manganite was studied in cyclic magnetic fields. The adiabatic temperature change in the Fe48Rh52 alloy for a magnetic field change (ΔB) of 8 T and a frequency (f) of 0.13 Hz reaches the highest value of (ΔTad) of -20.2 K at 298 K. The magnitude of the MCE in Sm0.6Sr0.4MnO3 reaches ΔTad = 6.1 K at the same magnetic field change at 143 K. The temperature regions, where a strong MCE is exhibited in an alternating magnetic field, are bounded in both compounds. In the case of the Fe48Rh52 alloy, the temperature range for this phenomenon is bounded above by the ferromagnetic to antiferromagnetic transition temperature in the zero field condition during cooling. In the case of the Sm0.6Sr0.4MnO3 manganite, the temperature range for the MCE is bounded below by the ferromagnetic-paramagnetic transition temperature in zero field during heating. The presence of these phase boundaries is a consequence of the existence of areas of irreversible magnetic-field-induced phase transitions. It is found that the effect of long-term action of thousands of cycles of magnetization/demagnetization degrades the magnetocaloric properties of the Fe48Rh52 alloy. This can be explained by the gradual decrease in the size of the ferromagnetic domains and increasing role of the domain walls due to giant magnetostriction at the ferromagnetic to antiferromagnetic transition temperature. The initial magnetocaloric properties can be restored by heating of the material above their Curie temperature.

  12. 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.

  13. Microwave and electrical characterization of M-type Ba0.5Sr0.5CoxRuxFe(12-2x)O19 hexaferrite for practical applications

    NASA Astrophysics Data System (ADS)

    Kaur, Rajvir; Dhillon, Naveen; Singh, Charanjeet; Narang, S. Bindra; Chandra, Madhu

    2015-01-01

    The microwave absorption of Ba0.5Sr0.5CoxRuxFe(12-2x)O19 (x=0.0,0.2,0.4,0.8,1.0) ferrite has been investigated as a function of frequency, substitution and thickness. The static I-V characteristics have been studied as a function of substitution. The results exhibit reflection loss of -12.02 dB at 9.0 GHz in x=0.2. The electrical current density increases at higher substitution. The microwave and electrical properties show dependence on microstructure. The ferrite compositions for different electromagnetic applications are also suggested.

  14. 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.

  15. 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.

  16. Structural, transport and magnetotransport properties of Ru-doped La0.5Sr0.5Mn1-xRuxO3 (x = 0.0 & 0.05) manganite

    NASA Astrophysics Data System (ADS)

    Jethva, Sadaf; Katba, Savan; Udeshi, Malay; Kuberkar, D. G.

    2017-09-01

    We report the results of the structural, transport and magnetotransport studies on polycrystalline La0.5Sr0.5Mn1-xRuxO3 (x = 0.0 and 0.05) manganite investigated using XRD and resistivity (with and without field) measurements. Rietveld refinement of XRD patterns confirms the single phasic tetragonal structure for both the samples crystalizing in I4/mcm space group (No. 140). Low-temperature resistivity and MR measurements with H = 0 T & 5 T field show thermal hysteresis which has been attributed to the first order phase transition. The increase in resistivity and decrease in metal - insulator transition temperature (TMI) with Ru - doping concentration in La0.5Sr0.5MnO3 (LSMO) has been understood in the context of superexchange interaction between Mn and Ru ions. The observed upturn in resistivity at low temperature under field has been explained using combined effect of electron - electron (e - e) interaction, Kondo-like spin-dependent scattering and electron - phonon interaction while the variation in resistivity at high temperature (T > Tp) has been explained using adiabatic small polaron hopping model.

  17. Data Retention and Readout Degradation Properties of Pt/Sr0.7Sm0.07Bi2.2Ta2O9/HfO2/Si Structure Ferroelectric-Gate Field Effect Transistors

    NASA Astrophysics Data System (ADS)

    Saiki, Hirokazu; Tokumitsu, Eisuke

    2007-01-01

    We discuss the data retention and readout degradation properties of ferroelectric-gate field-effect transistors (FeFETs) with Pt/Sr0.7Sm0.07Bi2.2Ta2O9/HfO2/Si structures. We first point out that to read out the stored data correctly, unselected FeFETs should be turned off during the readout process and that this process causes a significant reduction of ON readout current. We next characterize the data retention properties of Pt/Sr0.7Sm0.07Bi2.2Ta2O9/HfO2/Si structure n-channel FeFET by taking the readout process into account. It is shown that the retention property measured by applying positive readout pulses after holding at VG=0 V for 30 s, is similar to that measured by the conventional method in which drain current is continuously measured at a positive hold voltage.

  18. 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.

  19. Magnetic and magnetocaloric properties of La0.6Pr0.1Sr0.3Mn1-xFexO3 (0≤x≤0.3) manganites

    NASA Astrophysics Data System (ADS)

    Cherif, R.; Hlil, E. K.; Ellouze, M.; Elhalouani, F.; Obbade, S.

    2014-07-01

    The La0.6Pr0.1Sr0.3Mn1-xFexO3 (x=0, 0.1, 0.2 and 0.3) samples have been elaborated by the solid-state reaction method. X-ray powder diffraction shows that all the samples crystallize in a rhombohedric phase with R3barc space group. The variation of magnetization as a function of temperature and applied magnetic field was carried out. The samples for x=0 and 0.1 exhibit a FM-PM transition at the Curie temperature TC, however, for x=0.2 and 0.3 exhibit an AFM-PM one at the Neel temperature TN, when the temperature increases. A magneto-caloric effect has been calculated in terms of isothermal magnetic entropy change. A large magneto-caloric effect has been observed, the maximum entropy change, |ΔSMmax|, reaches the highest value of 3.28 J/kgK under a magnetic field change of 5 T with an RCP value of 220 J/kg for La0.6Pr0.1Sr0.3MnO3 composition, which will be an interesting compound for application materials working as magnetic refrigerants near room temperature.

  20. 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.

  1. Electrical-transport, magnetoresistance and magnetic properties of La0.7Ca0.3MnO3 and La0.7Ca0.24Sr0.06MnO3 single crystals

    NASA Astrophysics Data System (ADS)

    Tank, Tejas M.; Bodhaye, Ashish; Mukovskii, Ya. M.; Sanyal, S. P.

    2015-06-01

    We report the electrical-transport, magnetoresistance and magnetic properties of the hole doped La0.7Ca0.3MnO3 (LCMO) and La0.7Ca0.24Sr0.06MnO3 (LCSMO) single crystals. It was prepared using floating zone technique. The resistivity data shows the metal to insulator transition (TMI) occurs at 211 K along c-axis and TMI = 185 K the ab-plane for LCMO and TMI = 290 K along the c-axis and TMI = 280 K along the ab-plane for LCSMO single crystals. It is observed that the TMI is higher along the c-axis as compared to that in the ab-plane, consequently signifying more favorable hoping of electrons is along the c-axis. The ac-susceptibility measurement shows that this material exhibits ferromagnetic to paramagnetic transition temperature (TC) at 206 K for LCMO and TC = 277 K for LCSMO single crystals. For magnetic memory device application point of view, the sample shows the maximum MR of 98% for LCMO and 80% for LCSMO single crystals at 8T applied magnetic field. Doping small amount of Sr (0.06%) reveals that the electronic and magnetic phase transition in CMR single crystal increases substantially and useful for device application. This is first time such type of comparative study in these manganite single crystals.

  2. Effect of trivalent rare earth doping on magnetic and magnetocaloric properties of Pr0.5(Ce,Eu,Y)0.1Sr0.4MnO3 manganites

    NASA Astrophysics Data System (ADS)

    Sakka, A.; M'nassri, R.; Chniba-Boudjada, N.; Ommezzine, M.; Cheikhrouhou, A.

    2016-06-01

    Experimental studies of the structural, magnetic and magnetocaloric properties of the three compounds Pr0.5X0.1Sr0.4MnO3 (X = Ce, Eu and Y) are reported. Our samples were synthesized using the Pechini sol-gel method. X-ray powder diffraction at room temperature indicates that our materials crystallize in the orthorhombic structure with Pbnm space group. The compounds undergo a second-order magnetic transition from paramagnetic to ferromagnetic state around their own Curie temperatures T C ~ 310, 270 and 230 K for X = Ce, Eu and Y, respectively. A considerable magnetocaloric effect (MCE) is observed around room temperature. The maximum values of magnetic entropy change ∆ S max are 3.54, 3.81 and 2.99 J/kgK for the samples with X = Ce, Eu and Y, respectively, when a magnetic field of 5 T was applied. The relative cooling power (RCP) values for the corresponding materials are 246.60, 261.66 and 298 J/kg. It is shown that for Pr0.5X0.1Sr0.4MnO3 the exponent n and the magnetic entropy change follow a master curve behavior. With the universal scaling curve, the experimental ∆ S at several temperatures and fields can be extrapolated.

  3. 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.

  4. Solid-State (29)Si NMR and neutron-diffraction studies of Sr(0.7)K(0.3)SiO(2.85) oxide ion conductors.

    PubMed

    Xu, Jungu; Wang, Xiaoming; Fu, Hui; Brown, Craig M; Jing, Xiping; Liao, Fuhui; Lu, Fengqi; Li, Xiaohui; Kuang, Xiaojun; Wu, Mingmei

    2014-07-07

    K/Na-doped SrSiO3-based oxide ion conductors were recently reported as promising candidates for low-temperature solid-oxide fuel cells. Sr0.7K0.3SiO2.85, close to the solid-solution limit of Sr1-xKxSiO3-0.5x, was characterized by solid-state (29)Si NMR spectroscopy and neutron powder diffraction (NPD). Differing with the average structure containing the vacancies stabilized within the isolated Si3O9 tetrahedral rings derived from the NPD study, the (29)Si NMR data provides new insight into the local defect structure in Sr0.7K0.3SiO2.85. The Q(1)-linked tetrahedral Si signal in the (29)Si NMR data suggests that the Si3O9 tetrahedral rings in the K-doped SrSiO3 materials were broken, forming Si3O8 chains. The Si3O8 chains can be stabilized by either bonding with the oxygen atoms of the absorbed lattice water molecules, leading to the Q(1)-linked tetrahedral Si, or sharing oxygen atoms with neighboring Si3O9 units, which is consistent with the Q(3)-linked tetrahedral Si signal detected in the (29)Si NMR spectra.

  5. 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).

  6. Effect of hydrostatic pressure on magnetic entropy change and critical behavior of the perovskite manganite La0.4Bi0.3Sr0.3MnO3

    NASA Astrophysics Data System (ADS)

    Thiyagarajan, R.; Esakki Muthu, S.; Barik, S. K.; Mahendiran, R.; Arumugam, S.

    2013-01-01

    We report the effect of magnetic field (H) and hydrostatic pressure (P) on the order of magnetic transition of polycrystalline La0.4Bi0.3Sr0.3MnO3 which undergoes a first-order paramagnetic (PM) to ferromagnetic (FM) transition in La0.7-xBixSr0.3MnO3 series. The ferromagnetic Curie temperature (TC) increases with increasing H (12.01 K/T-cooling and 10.28 K/T-warming) and P (8.1 K/kbar-cooling and 6 K/kbar-warming). The first-order FM transition becomes second-order under the applied magnetic field of 9 T and pressure of 9.1 kbar. We have analyzed the critical behavior associated with the second order PM-FM transition at 9.1 kbar. The estimated critical exponents (β = 0.5217, γ = 1.209, and δ = 3.162) are found to be close to the mean-field model. Pressure suppresses metamagnetic transition in magnetization isotherms observed above TC in ambient pressure and enhances the magnetic entropy change (ΔSm). The ΔSm was found to increase by 50% under hydrostatic pressure of 9.1 kbar at TC = 240 K. This study suggested that hydrostatic pressure can be used to enhance magnetocaloric values in phase separated manganites.

  7. Effect of Fe substitution on magnetocaloric effect in La 0.7Sr 0.3Mn 1- xFe xO 3 (0.05≤ x≤0.20)

    NASA Astrophysics Data System (ADS)

    Barik, S. K.; Krishnamoorthi, C.; Mahendiran, R.

    2011-04-01

    We have studied the effect of Fe substitution on magnetic and magnetocaloric properties in La0.7Sr0.3Mn1-xFexO3 (x=0.05, 0.07, 0.10, 0.15, and 0.20) over a wide temperature range (T=10-400 K). It is shown that substitution by Fe gradually decreases the ferromagnetic Curie temperature (TC) and saturation magnetization up to x=0.15 but a dramatic change occurs for x=0.2. The x=0.2 sample can be considered as a phase separated compound in which both short-range ordered ferromagnetic and antiferromagnetic phases coexist. The magnetic entropy change (-ΔSm) was estimated from isothermal magnetization curves and it decreases with increase of Fe content from 4.4 J kg-1 K-1 at 343 K (x=0.05) to 1.3 J kg-1 K-1 at 105 K (x=0.2), under ΔH=5 T. The La0.7Sr0.3Mn0.93Fe0.07O3 sample shows negligible hysteresis loss, operating temperature range over 60 K around room temperature with refrigerant capacity of 225 J kg-1, and magnetic entropy of 4 J kg-1 K-1 which will be an interesting compound for application in room temperature refrigeration.

  8. 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.

  9. 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.

  10. Robust Interfacial Exchange Bias and Metal-Insulator Transition Influenced by the LaNiO3 Layer Thickness in La0.7Sr0.3MnO3/LaNiO3 Superlattices.

    PubMed

    Zhou, Guowei; Song, Cheng; Bai, Yuhao; Quan, Zhiyong; Jiang, Fengxian; Liu, Wenqing; Xu, Yongbing; Dhesi, Sarnjeet S; Xu, Xiaohong

    2017-01-25

    Artificial heterostructures based on LaNiO3 (LNO) have been widely investigated with the aim to realize the insulating antiferromagnetic state of LNO. In this work, we grew [(La0.7Sr0.3MnO3)5-(LaNiO3)n]12 superlattices on (001)-oriented SrTiO3 substrates by pulsed laser deposition and observed an unexpected exchange bias effect in field-cooled hysteresis loops. Through X-ray absorption spectroscopy and magnetic circular dichroism experiments, we found that the charge transfer at the interfacial Mn and Ni ions can induce a localized magnetic moment. A remarkable increase of exchange bias field and a transition from metal to insulator were simultaneously observed upon decreasing the thickness of the LNO layer, indicating the antiferromagnetic insulator state in 2 unit cells LNO ultrathin layers. The robust exchange bias of 745 Oe in the superlattice is caused by an interfacial localized magnetic moment and an antiferromagnetic state in the ultrathin LNO layer, pinning the ferromagnetic La0.7Sr0.3MnO3 layers together. Our results demonstrate that artificial interface engineering is a useful method to realize novel magnetic and transport properties.

  11. The temperature evolution of NiO6 octahedral tilts as a probe to study charge stripes in Ln1:67Sr0:33NiO4 (Ln=La/Nd)

    NASA Astrophysics Data System (ADS)

    Abeykoon, Milinda; Bozin, Emil; Gu, Genda; Hill, John; Tranquada, John; Billinge, Simon

    2012-02-01

    Nd1:67Sr0:33NiO4 and La1:67Sr0:33NiO4 exhibit long range ordered (LRO) charge stripes below Tco˜240K. When the charge stripes are static and long-range ordered, they have been seen as superlattice Bragg peaks in single crystal neutron and x-ray diffraction. We used neutron atomic pair distribution function (NPDF) technique to investigate the possibility of existence of localized charges above Tco, where, the LRO of the stripes disappears. Rigid body type NiO6 octahedral tilts were used as a probe to study the local and average structural response to charge order. The amplitude of rotation of the octahedral units was used to investigate the observed large apical oxygen thermal ellipsoids (anisotropic thermal displacement parameters) in the a-b crystal plane. We measured enhanced tilt amplitudes in the local structure, compared to the average. We will discuss the temperature dependence of the tilt amplitudes and of the correlation length of the local tilt order and explore the potential relationship to local stripe order.

  12. 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.

  13. Simple synthesis and characterization of vertically aligned Ba0.7Sr0.3TiO3-CoFe2O4 multiferroic nanocomposites from CoFe2 nanopillar arrays.

    PubMed

    Basov, Sergey; Elissalde, Catherine; Simon, Quentin; Maglione, Mario; Castro-Chavarria, Christopher; Herisson de Beauvoir, Thomas; Payan, Sandrine; Temst, Kristiaan; Lazenka, Vera; Antohe, Vlad Andrei; Pereira de Sa, Pedro; Sallagoity, David; Piraux, Luc

    2017-09-29

    A new strategy to elaborate (1-3) type multiferroic nanocomposites with controlled dimensions and vertical alignment is presented. The process involves a supported nanoporous alumina layer as a template for growth of free-standing and vertically aligned CoFe2 nanopillars using a room temperature pulsed electrodeposition process. Ba0.70Sr0.30TiO3-CoFe2O4 multiferroic nanocomposites were grown through direct deposition of Ba0.7Sr0.3TiO3 films by radio-frequency sputtering on the top surface of the pillar structure, with in-situ simultaneous oxidation of CoFe2 nanopillars. The vertically aligned multiferroic nanocomposites were characterized using various techniques for their structural and physical properties. The large interfacial area between the ferrimagnetic and ferroelectric phases leads to a magnetoelectric voltage coefficient as large as ~320 mV cm-1 Oe-1 at room temperature, reaching the highest values reported so far for vertically architectured nanocomposite systems. This simple method has great potential for large-scale synthesis of many other hybrid vertically aligned multiferroic heterostructures. © 2017 IOP Publishing Ltd.

  14. 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.

  15. Evidence for monoclinic distortion in the ground state phase of underdoped La1.95Sr0.05CuO4: A single crystal neutron diffraction study

    DOE PAGES

    Singh, Anar; Schefer, Jurg; Sura, Ravi; ...

    2016-03-24

    The existing controversy about the symmetry of the crystal structure of the ground state of the critical doped La1.95Sr0.05CuO4 has been resolved by analyzing the single crystal neutron diffraction data collected between 5 and 730 K. We observed small but significant intensities for "forbidden" reflections given by extinction rules of the orthorhombic Bmab space group at low temperatures. A careful investigation of neutron diffraction data reveals that the crystal structure of La1.95Sr0.05CuO4 at 5 K is monoclinic with B2/m (2/m 1 1) space group. The monoclinic structure emerges from the orthorhombic structure in a continuous way; however, the structure ismore » stable below similar to 120K which agrees with other observed phenomena. Lastly, our results on symmetry changes are crucial for the interpretation of physical properties also in other high temperature superconductors with similar structures.« less

  16. 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

  17. 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.

  18. The novel dielectric relaxation behavior around the Curie point of (Ba0.7Sr0.3)0.96Y0.04TiO3 ceramics with giant effective permittivity

    NASA Astrophysics Data System (ADS)

    Yan, Shiguang; Mao, Chaoliang; Wang, Genshui; Yao, Chunhua; Cao, Fei; Dong, Xianlin; Meng, Xiangjian

    2016-10-01

    The temperature (80 K ˜ 423 K) and frequency (40 Hz ˜ 5 MHz) dependence of the permittivity were studied in (Ba0.7Sr0.3)0.96Y0.04TiO3 ceramics. A giant effective permittivity over 105 with a certain frequency and temperature stability and Debye-type dielectric relaxation behavior was observed. The complex impedance spectrum analysis reveals that the giant permittivity is due to the heterogeneous structure with a semiconducting bulk and high resistance electrode-ceramic interface. Deviating from low temperature (below 200 K) thermal activated behavior, the odd change of the characteristic relaxation frequency around the Curie point is observed and proven to be induced by the competition between the positive temperature coefficient of the resistance effect of the bulk ceramic and the dielectric anomaly of the surface layer capacitance, both of which originate from the ferroelectric-paraelectric phase transition.

  19. Structures and phase transition in the layered perovskite La0.6Sr0.1TiO3: a new orthorhombic structure solved from high-resolution diffraction in combination with group theoretical analysis

    NASA Astrophysics Data System (ADS)

    Howard, Christopher J.; Zhang, Zhaoming

    2003-07-01

    The crystal structure of the layered perovskite La0.6Sr0.1TiO3 at room temperature has been solved by synchrotron x-ray powder diffraction in combination with group theoretical analysis. The structure is orthorhombic in Cmmm, on a cell with a = 7.7556(1), b = 7.7349(1) and c = 7.7910(1) Å. It is believed that this is also the structure adopted by La2/3TiO3. Pertinent features are the alternation of fully and partly occupied layers of La (Sr) cations, and out-of-phase tilting of the TiO6 octahedra around an axis perpendicular to the direction of the cation ordering. The compound undergoes a second order transition to a tetragonal structure, the transition temperature being estimated as 360 °C.

  20. Prediction of La0.6Sr0.4Co0.2Fe0.8O3 cathode microstructures during sintering: Kinetic Monte Carlo (KMC) simulations calibrated by artificial neural networks

    NASA Astrophysics Data System (ADS)

    Yan, Zilin; Kim, Yongtae; Hara, Shotaro; Shikazono, Naoki

    2017-04-01

    The Potts Kinetic Monte Carlo (KMC) model, proven to be a robust tool to study all stages of sintering process, is an ideal tool to analyze the microstructure evolution of electrodes in solid oxide fuel cells (SOFCs). Due to the nature of this model, the input parameters of KMC simulations such as simulation temperatures and attempt frequencies are difficult to identify. We propose a rigorous and efficient approach to facilitate the input parameter calibration process using artificial neural networks (ANNs). The trained ANN reduces drastically the number of trial-and-error of KMC simulations. The KMC simulation using the calibrated input parameters predicts the microstructures of a La0.6Sr0.4Co0.2Fe0.8O3 cathode material during sintering, showing both qualitative and quantitative congruence with real 3D microstructures obtained by focused ion beam scanning electron microscopy (FIB-SEM) reconstruction.

  1. Electrostatic tuning of magnetism at the conducting (111) (La0.3Sr0.7)(Al0.65Ta0.35)/SrTiO3 interface

    NASA Astrophysics Data System (ADS)

    Bal, V. V.; Huang, Z.; Han, K.; Ariando, Venkatesan, T.; Chandrasekhar, V.

    2017-08-01

    We present measurements of the low temperature electrical transport properties of the two dimensional carrier gas that forms at the interface of (111) (La0.3Sr0.7)(Al0.65Ta0.35)/SrTiO3 as a function of applied back gate voltage, Vg. As is found in (111) LaAlO3/SrTiO3 interfaces, the low-field Hall coefficient is electron-like but shows a sharp reduction in magnitude below V g ˜ 20 V, indicating the presence of hole-like carriers in the system. This same value of Vg correlates approximately with the gate voltage below which the magnetoresistance evolves from nonhysteretic to hysteretic behavior at millikelvin temperatures, signaling the onset of magnetic order in the system. We believe our results can provide insight into the mechanism of magnetism in SrTiO3 based systems.

  2. 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.

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

    PubMed Central

    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, PrBa0.5Sr0.5Co2−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. PMID:23945630

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

    DOE PAGES

    Fitzsimmons, Michael R.; Jia, Quanxi X.; Singh, Surendra; ...

    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

  5. 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.

  6. Thermodynamic stability maps for the La0.6Sr0.4Co0.2Fe0.8O3±δ-CO2-O2 system for application in solid oxide fuel cells

    NASA Astrophysics Data System (ADS)

    Darvish, Shadi; Gopalan, Srikanth; Zhong, Yu

    2016-12-01

    Thermodynamic and electrochemical predictions on the formation of secondary phases in CO2 containing atmosphere on the La0.6Sr0.4Co0.2Fe0.8O3±δ (LSCF-6428) surface have been carried out utilizing the CALculation of Phase Diagram (CALPHAD) approach. The effect of temperature, CO2 partial pressure, O2 partial pressure as well as the cathode composition on the formation of secondary phases have been investigated and correlated with the previous investigations in the literature. It is predicted that SrCO3 has the possibility to form on the surface as a result of CO2 exposure to the system. In addition, it is seen that LSCF-6428 experiences higher degradation due to the larger amount of segregated phases than LSM-20 at the same operating condition.

  7. Growth and characterization of charge carrier spatially confined SrMnO3/La0.7Sr0.3MnO3/SrMnO3 trilayers

    NASA Astrophysics Data System (ADS)

    Galdi, A.; Sacco, C.; Orgiani, P.; Romeo, F.; Maritato, L.

    2017-02-01

    (SrMnO3)x/(La0.7Sr0.3MnO3)y/(SrMnO3)z (x,y,z=number of unit cells) trilayers have been grown using a Reflection High Energy Electron Diffraction calibrated layer-by-layer molecular beam epitaxy technique. X-Ray Reflectivity and X-Ray Diffraction measurements confirm the structural quality and the abruptness of the interfaces. Electrical transport property analysis as a function of temperature show effects related to the spatial confinement of the charge carriers induced by the layering. These results are important in view of future developments of oxide based heterostructures for innovative quantum devices.

  8. Novel metal-supported solid oxide fuel cells with impregnated symmetric La0.6Sr0.4Fe0.9Sc0.1O3-δ electrodes

    NASA Astrophysics Data System (ADS)

    Zhou, Yucun; Liu, Xuejiao; Li, Junliang; Nie, Huaiwen; Ye, Xiaofeng; Wang, Shaorong; Zhan, Zhongliang

    2014-04-01

    This paper reports on the fabrication of novel metal-supported solid oxide fuel cells containing porous 430L stainless steel substrates, YSZ electrolytes and porous YSZ cathode backbones. Such tri-layer structures are obtained by the tape casting, lamination and co-firing techniques. Redox-stable La0.6Sr0.4Fe0.9Sc0.1O3-δ (LSFSc) oxides are introduced as symmetric electrode catalysts onto the internal surfaces of porous 430L substrates and YSZ backbones using the solution impregnation method. The maximum power density is 0.65 W cm-2 measured at 800 °C. Impedance analyses show that the anode polarizations are the largest losses while the cathode polarizations make negligible contribution to the total cell resistances.

  9. 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.

  10. 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

  11. Electrical transport and giant magnetoresistance in La0.75Sr0.25Mn1-xCrxO3 (0.15, 0.20 and 0.25) manganite oxide.

    PubMed

    Dhahri, Ah; Jemmali, M; Dhahri, E; Hlil, E K

    2015-03-28

    We have investigated the influence of chromium (Cr) doping on the magneto-electrical properties of polycrystalline samples La0.75Sr0.25Mn1-xCrxO3 (0.15 ≤ x ≤ 0.25), prepared by the sol-gel method. Comparison of experimental data with the theoretical models shows that in the metal-ferromagnetic region, the electrical behavior of the three samples is quite well described by a theory based on electron-electron, electron-phonon and electron-magnon scattering and Kondo-like spin dependent scattering. For the high temperature paramagnetic insulating regime, the adiabatic small polaron hopping (SPH) model is found to fit well the experimental curves.

  12. Manganite based hetero-junction structure of La0.7Sr(0.7-x)CaxMnO3 and CaMnO(3-δ) for cross-point arrays.

    PubMed

    Lee, Hong-Sub; Park, Hyung-Ho

    2015-07-10

    Resistive random access memory and the corresponding cross-point array (CPA) structure have received a great deal of attention for high-density next generation non-volatile memory. However, the cross-talk issue of CPA structure by sneak current should be overcome to realize the highest density integration. To accomplish this, the sneak current can be minimized by high, nonlinear characteristic behaviors of resistive switching (RS). Therefore this study fabricated pnp bipolar hetero-junction structure using the perovskite manganite family, such as La0.7Sr(0.3-x)CaxMnO3 (LSCMO) and CaMnO(3-δ) (CMO), to obtain nonlinear RS behavior. The pnp structure not only shows nonlinear characteristics, but also a tunable characteristic with Ca substitution.

  13. Sm0.5Sr0.5CoO3-δ infiltrated Ce0.9Gd0.1O2-δ composite cathodes for high performance protonic ceramic fuel cells

    NASA Astrophysics Data System (ADS)

    Zhao, Ling; Li, Geng; Chen, Kongfa; Ling, Yihan; Cui, Yuexiao; Gui, Liangqi; He, Beibei

    2016-11-01

    Sm0.5Sr0.5CoO3-δ (SSC) infiltrated Ce0.9Gd0.1O2-δ (GDC) composite cathodes are developed for protonic ceramic fuel cells (PCFCs). Although the SSC infiltrated GDC cathodes make little contribute to expending the reaction sites of water formation, it can significantly improve the oxygen reduction dynamics among the whole electrochemical reaction. The symmetric half cell and single cell testing results demonstrate the high electrochemical activity of SSC infiltrated GDC cathodes. Moreover, the single cell is stable at 600 °C for 120 h in humidified H2 and humidified H2sbnd CO. The encouraging results indicate that the SSC infiltrated GDC could be the promising composite cathodes for application in PCFCs.

  14. 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.

  15. Flash microwave synthesis and sintering of nanosized La 0.75Sr 0.25Cr 0.93Ru 0.07o 3-δ for fuel cell application

    NASA Astrophysics Data System (ADS)

    Combemale, L.; Caboche, G.; Stuerga, D.

    2009-10-01

    Perovskite-oxide nanocrystals of La 0.75Sr 0.25Cr 0.93Ru 0.07O 3-δ with a mean size around 10 nm were prepared by microwave flash synthesis. This reaction was performed in alcoholic solution using metallic salts, sodium ethoxide and microwave autoclave. The obtained powder was characterised after purification by energy dispersive X-ray analysis (EDX), X-ray powder diffraction (XRD), BET adsorption technique, photon correlation spectroscopy (PCS) and transmission electron microscopy (TEM). The results show that integrated perovskite-type phase and uniform particle size were obtained in the microwave treated samples. At last the synthesised powder was directly used in a sintering process. A porous solid, in accordance with the expected applications, was then obtained at low sintering temperature (1000 °C) without use of pore forming agent.

  16. Magnetic field reversal of electric polarization and magnetoelectric phase diagram of the hexaferrite Ba1.3Sr0.7Co0.9Zn1.1Fe10.8Al1.2O22

    NASA Astrophysics Data System (ADS)

    Shen, Shipeng; Yan, Liqin; Chai, Yisheng; Cong, Junzhuang; Sun, Young

    2014-01-01

    Low magnetic field reversal of electric polarization has been demonstrated in the multiferroic Y-type hexaferrite Ba1.3Sr0.7Co0.9Zn1.1Fe10.8Al1.2O22 single crystal. The maximum magnetoelectric coefficient at 200 K reaches 1065 ps/m near zero magnetic field. By a systematic investigation of magnetic field dependence of magnetic and dielectric responses at various temperatures, we obtained the magnetoelectric phase diagram describing the detailed evolution of the spin-induced ferroelectric phases with temperature and magnetic field. Below 225 K, the transverse spin cone can be stabilized at zero magnetic field, which is responsible for the reversal behavior of electric polarization. Our study reveals how to eventually achieve magnetic field reversal of electric polarization in hexaferrites at room temperature.

  17. 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).

  18. Robust high-temperature magnetic pinning induced by proximity in YBa2Cu3O7-δ/La0.67Sr0.33MnO3 hybrids

    NASA Astrophysics Data System (ADS)

    Chen, C. Z.; Liu, Z. Y.; Lu, Y. M.; Zeng, L.; Cai, C. B.; Zeng, R.; Dou, S. X.

    2011-04-01

    An elaborately designed bilayer consisting of superconducting YBa2Cu3O7-δ (YBCO) and ferromagnetic La0.67Sr0.33MnO3-δ (LSMO) was prepared on a single crystal LaAlO3 substrate by pulsed laser deposition (PLD), with a view to understanding the mechanism behind the influence of superconductor/ferromagnet proximity on the critical current density, Jc. The present bilayer system shows significant modifications in Jc, as evidenced by the suppressed decay of its temperature dependence, as well as the crossing behavior of the magnetic field dependence of Jc at high temperatures. This indicates that enhanced flux pinning emerges at high temperatures, and it is believed to arise from the special magnetic inhomogeneity, i.e., the ferromagnet/antiferromagnet clusters caused by phase separation due to the epitaxial stress between LSMO and the substrate.

  19. Valence-sensitive determination of Cr3+ and Ce3+ concentration in doped Sr0.61 Ba0.39 Nb2 O6 from magnetization studies and paramagnetic relaxation of Ce3+

    NASA Astrophysics Data System (ADS)

    Schaniel, D.; Woike, Th.; Weckwerth, G.; Schefer, J.; Imlau, M.; Wöhlecke, M.; Pankrath, R.

    2004-10-01

    Magnetization- and susceptibility measurements are used as a method to determine the number density of the photorefractive centers Ce3+ and Cr3+ in Sr0.61Ba0.39Nb2O6 (SBN61). The number densities nmacr Ce3+=0.73(1)·1020cm-3 and nmacr Cr3+=1.58(8)·1020cm-3 were determined for crystals doped with 1.6wt.%Ce and 20000ppmCr , respectively. Frequency dependent susceptibility measurements in the temperature range 3-10K on SBN61: Ce show that the spin-lattice relaxation in this compound is dominated by the Orbach process. The crystal field splitting of the two lowest ground state doublets is determined to 1.77meV . The susceptibility of SBN61: Cr shows no frequency dependence in the range 10-104Hz .

  20. Effect of Cu doping on Ba0.5Sr0.5Fe1-xCuxO3-δ perovskites for solid oxide fuel cells: A first-principles study

    NASA Astrophysics Data System (ADS)

    Vázquez, Santiago; Suescun, Leopoldo; Faccio, Ricardo

    2016-04-01

    Nowadays a rational design of solid oxide fuel cells (SOFCs) cathodes is possible thanks to first-principles calculations based on density functional theory (DFT). We study the effect of Cu-doping in the bulk properties for the perovskite Ba0.5Sr0.5Fe1-xCuxO3-δ (with x = 0, 0.25 and 0.50) and correlate the results with previous experimental characterization. Bulk properties such as geometric structure, charge analysis, thermodynamic stability, vacancy formation energy, oxygen diffusion and electronic structure where studied in detail to provide an explanation of the oxygen reduction reaction (ORR) activity enhancement with Cu-doping. The results obtained here, using GGA+U, demonstrate the first-principles approach gives useful information that allows the prediction and explanation of experimental characterizations.

  1. 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.

  2. Self-Poling-Induced Magnetoelectric Effect in Highly Strained Epitaxial BiFeO3/La0.67Sr0.33MnO3-δ Multiferroic Heterostructures.

    PubMed

    Li, Dong; Zheng, Dongxing; Gong, Junlu; Zheng, Wanchao; Jin, Chao; Bai, Haili

    2017-07-19

    Highly strained epitaxial BiFeO3/La0.67Sr0.33MnO3-δ (BFO/LSMO) heterostructures were fabricated on LaAlO3 substrates by magnetron sputtering. The as-grown downward self-polarization of BFO capping layers was confirmed by piezoelectric force microscopy. Using the electrostatic field-induced charge screening, a hole depletion state was induced in ultrathin (8 nm) LSMO films. As a result of the interfacial charge coupling, appreciable saturated magnetization (MS) increase of about 500 and 100% can be observed in LSMO with BFO capping at 5 and 300 K, respectively. Besides, LSMO phase translations can be revealed by the BFO thickness-related exchange bias field (HE) and MS of the BFO/LSMO heterostructures. The results established a new approach in achieving interfacial magnetoelectric couplings with thin self-polarized multiferroic layers.

  3. Characteristics of metal-ferroelectric-insulator-semiconductor diodes composed of Pt electrodes and epitaxial Sr0.8Bi2.2Ta2O9(001)/SrTiO3(100)/Si(100) structures

    NASA Astrophysics Data System (ADS)

    Lu, Xubing; Ishiwara, Hiroshi; Gu, Xing; Lubyshev, Dmitri; Fastenau, Joel; Pelzel, Rodney

    2009-01-01

    Epitaxial metal-ferroelectric-insulator-semiconductor diodes were fabricated by depositing a chemical-solution-decomposed Sr0.8Bi2.2Ta2O9 (SBT) film on an SrTiO3-coated Si(100) wafer. X-ray diffraction analysis revealed that the SBT film was composed mostly of c-axis-oriented grains. In Pt/SBT(300 nm)/SrTiO3(23 nm)/Si diodes, a memory window as wide as 1.1 V was obtained for a voltage sweep of ±7 V in capacitance-voltage measurement. The capacitance change in per decade increase in the retention time was approximately 10% up to 24 h. The origin of the ferroelectricity in a c-axis-oriented SBT film is discussed.

  4. 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

  5. Modulation of ultrafast laser-induced magnetization precession in BiFeO3-coated La0.67Sr0.33MnO3 thin films

    NASA Astrophysics Data System (ADS)

    Wan, Qian; Jin, KuiJuan; Wang, JieSu; Yao, HongBao; Gu, JunXing; Guo, HaiZhong; Xu, XiuLai; Yang, GuoZhen

    2017-04-01

    The ultrafast laser-excited magnetization dynamics of ferromagnetic (FM) La0.67Sr0.33MnO3 (LSMO) thin films with BiFeO3 (BFO) coating layers grown by laser molecular beam epitaxy are investigated using the optical pump-probe technique. Uniform magnetization precessions are observed in the films under an applied external magnetic field by measuring the time-resolved magneto-optical Kerr effect. The magnetization precession frequencies of the LSMO thin films with the BFO coating layers are lower than those of uncoated LSMO films, which is attributed to the suppression of the anisotropy field induced by the exchange interaction at the interface between the antiferromagnetic order of BFO and the FM order of LSMO.

  6. Two regimes behavior in the resistivity of the La 1.85Sr 0.15Cu 1- xLi xO 4 system: A signature of different electronic states for holes

    NASA Astrophysics Data System (ADS)

    García, S.; Musa, J. E.; Giordanengo, B.; Baggio-Saitovitch, E. M.

    1998-01-01

    The variations of the normal-state resistivity and the superconducting transition temperature Tc of the La 1.85Sr 0.15(Cu 1- xLi x)O 4 system for 0 ≤ x ≤ 0.05 reveal a two regimes behavior, with x ≅ 0.03 being the critical concentration for a transition from a delocalized state, with a reduction of the resistivity values while Tc remains unchanged, to an early stage of a spin compensation process, characterized by Tc suppression without broadening. Disorder at the CuO 2 planes is proposed to be the source of localization and Tc depletion, as supported by fitting of the normal-state curves according to different conduction models.

  7. Normal-state magnetic properties and their correlation with Tc suppression and the resistivity anomalies in the (La1-xPrx)1.85Sr0.15CuO4 series

    NASA Astrophysics Data System (ADS)

    Musa, J. E.; García, S.; Rothier de Amaral, M.; Salim de Amorim, H.; Giordanengo, B.; Baggio-Saitovitch, E. M.; Pagliuso, P. J. G.; Rettori, C.; Yelon, W. B.; Malik, S. K.

    1999-04-01

    We have investigated the normal-state anomalies observed in the magnetic and transport properties of the (La1-xPrx)1.85Sr0.15CuO4 system with 0⩽x⩽0.5. The resistivity curves showed an increasing deviation from linearity below ˜100 K. This behavior is properly accounted by a logarithmic term, whose coefficient C linearly increases with x. The normal-state magnetic susceptibility measurements evidenced a departure from the Pr3+ Curie-Weiss dependence in the same temperature range for which the resistivity anomaly occurs. A comprehensive picture of the conduction mechanism is presented in terms of a Kondo-like scattering of the mobile holes by the spin fluctuations.

  8. Structure and dielectric tunability of (Pb 0.5Ba 0.5)ZrO 3 thin films derived on (Sr 0.95La 0.05)TiO 3 buffer-layered substrates

    NASA Astrophysics Data System (ADS)

    Hao, Xihong; Zhai, Jiwei; Zhou, Jing; Yang, Jichun; Song, Xiwen; An, Shengli

    2010-02-01

    In present work, (Pb 0.5Ba 0.5)ZrO 3 (PBZ) thin films with a thickness of 840 nm were successfully fabricated on (Sr 0.95La 0.05)TiO 3 (SLT) buffer-layered Pt(1 1 1)/TiO 2/SiO 2/Si(1 0 0) substrates via the sol-gel technique. The effects of SLT buffer layer on the microstructure and electrical properties of PBZ thin films were investigated systemically. X-ray diffraction (XRD) and scanning electron microscopy (SEM) results indicated that PBZ thin films on SLT buffer-layered substrates showed a more uniform structure with a random orientation. Dielectric measurements illustrated that PBZ films with SLT buffer layer displayed larger dielectric constant, improved tunability and enhanced figure of merit (FOM). Moreover, leakage current of PBZ films was also reduced by SLT buffer layer.

  9. Structural and transport characterization of ultra thin Ba0.05Sr0.95TiO3 layers grown over Nb electrodes for the development of Josephson junctions

    NASA Astrophysics Data System (ADS)

    Sirena, M.; Avilés Félix, L.; Carvacho Vera, G. A.; Navarro Fernández, H. L.; Steren, L. B.; Bernard, R.; Briático, J.; Bergeal, N.; Lesueur, J.; Faini, G.

    2012-01-01

    A phenomenological approach was used to obtain critical information about the structure and electrical properties of ultra thin Ba0.05Sr0.95TiO3 (BSTO) layers over Nb electrodes. The method allows, in a simple way, to study and to optimize the growth of the barrier in order to improve the performance and application of Josephson junctions. A very good control of the layer thickness with a low roughness was achieved during the deposition process. The BSTO layers present an energy barrier of 0.6 eV and an attenuation length of 0.4 nm, indicating its good insulating properties for the development of Josephson junctions with improved performance.

  10. Investigation of Carbon ion-implanted waveguides in tungsten bronze (Ca0.28Ba0.72)0.25(Sr0.6Ba0.4)0.75Nb2O6 single crystal

    NASA Astrophysics Data System (ADS)

    Jiao, Yang; Wang, Chuan-Kui; Li, Zong-Liang; Ren, Ying-Ying

    2014-09-01

    Planar optical waveguides were fabricated in (Ca0.28Ba0.72)0.25(Sr0.6Ba0.4)0.75Nb2O6 (CSBN25) crystal by 6.0-MeV C+ ion implantation with fluences of 2, 4 and 6 × 1014 ions/cm2 at room temperature. The mode parameters, refractive indices profiles are measured and the refractive indices behavior in the waveguide region is discussed. The shape of nuclear energy loss distribution of the C+ implantation was similar to those of the waveguide refractive index profiles, which means an inherent relationship between the waveguide formation and the energetic energy deposition. The extraordinary refractive index has a small positive change in the surface region after the implantation.

  11. Nano-structured cathodes based on La 0.6Sr 0.4Co 0.2Fe 0.8O 3- δ for solid oxide fuel cells

    NASA Astrophysics Data System (ADS)

    Kim, Ju Hee; Park, Young Min; Kim, HaeKyoung

    Lanthanum-based iron- and cobalt-containing perovskite is a promising cathode material because of its electrocatalytic activity at a relatively low operating temperature in solid oxide fuel cells (SOFCs), i.e., 700-800 °C. To enhance the electrocatalytic reduction of oxidants on La 0.6Sr 0.4Co 0.2Fe 0.8O 3- δ (LSCF), nanocrystalline LSCF materials are successfully fabricated using a complexing method with chelants and inorganic nano dispersants. When inorganic dispersants are added to the synthesis process, the surface area of the LSCF powder increases from 18 to 88 m 2 g -1, which results in higher electrocatalytic activity of the cathode. The performance of a unit cell of a SOFC with nanocrystalline LSCF powders synthesized with nano dispersants is increased by 60%, from 0.7 to 1.2 W cm -2.

  12. 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.

  13. 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

    2015-09-07

    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.

  14. Large tunneling anisotropic magnetoresistance in La0.7Sr0.3MnO3/pentacene/Cu structures prepared on SrTiO3 (110) substrates

    NASA Astrophysics Data System (ADS)

    Kamiya, Takeshi; Miyahara, Chihiro; Tada, Hirokazu

    2017-01-01

    We investigated tunneling anisotropic magnetoresistance (TAMR) at the interface between pentacene and La0.7Sr0.3MnO3 (LSMO) thin films prepared on SrTiO3 (STO) (110) substrates. The dependence of the TAMR ratio on the magnetic field strength was approximately ten times larger than that of the magnetic field angle at a high magnetic field. This large difference in the TAMR ratio is explained by the interface magnetic anisotropy of strain-induced LSMO thin films on a STO (110) substrate, which has an easy axis with an out-of-plane component. We also note that the TAMR owing to out-of-plane magnetization was positive at each angle of the in-plane magnetic field. This result implies that active control of the interface magnetic anisotropy between organic materials and ferromagnetic metals should realize nonvolatile and high-efficiency TAMR devices.

  15. 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.

  16. The onset of ferromagnetism and superconductivity in [La0.7Sr0.3MnO3(n u.c.)/YBa2Cu3O7(2 u.c.)]20 superlattices.

    PubMed

    Dybko, K; Aleshkevych, P; Sawicki, M; Paszkowicz, W; Przyslupski, P

    2013-09-18

    With the aim of studying the interface magnetism, the onset of ferromagnetism and the onset of the transition to the superconducting state a series of [La0.7Sr0.3MnO3(n u.c.)/YBa2Cu3O7(2 u.c.)]20 (LSMO/YBCO) superlattices with nominally varying layer thickness of the LSMO from one to four unit cells (u.c.) was prepared and characterized by x-ray diffraction, electronic transport, magnetization and ferromagnetic resonance measurements. Spontaneous magnetization was observed for a superlattice with four u.c. LSMO layer thickness in a multilayer structure. Superlattices with 3 u.c. of LSMO and lower layer thicknesses did not show a signature of ferromagnetism. The onset of superconductivity was observed for superlattices with one and two LSMO layer u.c. thickness.

  17. A comparative study of magnetic field induced meta-magnetic transition in nanocrystalline and bulk Pr0.65(Ca0.7Sr0.3)0.35MnO3 compound

    NASA Astrophysics Data System (ADS)

    Saha, Suvayan; Das, Kalipada; Bandyopadhyay, Sudipta; Das, I.

    2017-06-01

    In our present study we highlight the observations of external magnetic field induced sharp meta-magnetic transition in polycrystalline bulk as well as nanocrystalline form of Pr0.65(Ca0.7Sr0.7)0.35MnO3 compound. Interestingly, such behavior persists in the nanoparticles regardless of the disorder broadened transition. However, higher magnetic field is required for nanoparticles having average particle size ∼40 nm for such meta-magnetic transition, which differs from the general trends of the pure charge ordered nano materials. The interfacial strain between the different magnetic domains plays the important role in magnetic isothermal properties of nanoparticles, when the samples are cooled down in different cooling field. Additionally, both the bulk and nanoparticle compounds exhibit spontaneous phase separation and significantly large magnetoresistance at the low temperature region due to the melting of charge ordered fraction.

  18. Antiferromagnetic interlayer exchange coupling in all-perovskite La0.7Sr0.3MnO3/SrRu1-xTixO3 superlattices

    NASA Astrophysics Data System (ADS)

    Xu, Haoran; Wan, Siyuan; Chen, Binbin; Ma, Chao; Jin, Feng; Guo, Zhuang; Lan, Da; Chen, Feng; Wu, Wenbin

    2017-02-01

    An unambiguous antiferromagnetic interlayer exchange coupling (IEC) is realized in all-perovskite oxide La0.7Sr0.3MnO3(LSMO)/SrRu1-xTixO3(SR1-xTxO) (x < 0.3) superlattices above the Curie temperature of the SR1-xTxO spacer layer, which is different from the traditional interfacial antiferromagnetic coupling. For 0.3 ≤ x ≤ 0.5, the superlattices behave as a ferromagnetic coupling. Meanwhile, this antiferromagnetic IEC between the ferromagnetic LSMO layers across the SR1-xTxO spacer can be further modulated by changing the thickness of SR1-xTxO spacer. Combining the high Curie temperature of LSMO, these findings may have potential applications in future spintronic devices.

  19. Study of the electrical and dielectric measurements of a rare-earth doped perovskite La0.6Nd0.1Sr0.3Mn0.7Ti0.3O3

    NASA Astrophysics Data System (ADS)

    Abassi, A.; Kallel, N.; Kallel, S.; Khirouni, K.; Peña, O.

    2016-12-01

    Electrical and dielectric properties of a polycrystalline La0.6Nd0.1Sr0.3Mn0.7Ti0.3O3 sample prepared by standard solid state reaction technique are presented. FTIR studies have showed the vibration of (Mn/Ti)O6 octahedra. The complex impedance is investigated in a temperature range 120-340 K and in frequency range 40 Hz-10 MHz. The impedance spectra have indicated that the electrical properties are strongly dependent on temperature and frequency, showing a good correlation with the sample microstructure. Ac conductivity is found to obey Jonscher power law. The value of activation energy estimated from the conductivity analysis is slightly higher than that deduced from relaxation analysis.

  20. Modulation of ultrafast laser-induced magnetization precession in BiFeO3-coated La0.67Sr0.33MnO3 thin films

    NASA Astrophysics Data System (ADS)

    Wan, Qian; Jin, KuiJuan; Wang, JieSu; Yao, HongBao; Gu, JunXing; Guo, HaiZhong; Xu, XiuLai; Yang, GuoZhen

    2017-04-01

    The ultrafast laser-excited magnetization dynamics of ferromagnetic (FM) La0.67Sr0.33MnO3 (LSMO) thin films with BiFeO3 (BFO) coating layers grown by laser molecular beam epitaxy are investigated using the optical pump-probe technique. Uniform magnetization precessions are observed in the films under an applied external magnetic field by measuring the time-resolved magneto-optical Kerr effect. The magnetization precession frequencies of the LSMO thin films with the BFO coating layers are lower than those of uncoated LSMO films, which is attributed to the suppression of the anisotropy field induced by the exchange interaction at the interface between the antiferromagnetic order of BFO and the FM order of LSMO.

  1. Er0.4Bi1.6O3-δ - La0.8Sr0.2MnO3-δ nano-composite as a low-temperature firing cathode of solid oxide fuel cell

    NASA Astrophysics Data System (ADS)

    Kim, Sun Jae; Dayaghi, Amir Masoud; Kim, Kun Joong; Choi, Gyeong Man

    2017-03-01

    Er0.4Bi1.6O3-δ (ESB) composited with La0.8Sr0.2MnO3-δ (LSM) (2:3 or 3:2 wt:wt) with a bonding aid to decrease firing temperature TF are screen-printed on symmetric single cells composed of a Gd0.2Ce0.8O2-δ (GDC) interlayer/yttria-stabilized zirconia (YSZ) electrolyte/GDC interlayer, and their impedance spectra are compared. Addition of 5 wt % CuO to ESB-LSM (3:2 wt:wt) decreases the cathode TF to 650 °C without increasing cathodic polarization resistance (Rp ∼0.19 Ω cm2 at 650 °C). This ESB-LSM composite can be used as a cathode that can be fired at low temperature.

  2. Room temperature ferroelectric and ferromagnetic properties of multiferroics xLa0.7Sr0.3MnO3-(1-x )ErMnO3 (weight percent x =0.1, 0.2) composites

    NASA Astrophysics Data System (ADS)

    Dey, P.; Nath, T. K.; Nanda Goswami, M. L.; Kundu, T. K.

    2007-04-01

    A different kind of multiferroics with composite character, xLa0.7Sr0.3MnO3 (LSMO )-(1-x)ErMnO3 (EMO) (x =0.1, 0.2), where EMO is the ferroelectric (FE) and LSMO is the ferromagnetic (FM) component, has been studied. Magnetization versus magnetic field measurements at 300K show prominent hysteresis loops, attesting room temperature FM behavior of these multiferroic composites. Dielectric constant (ɛ) as a function of temperature reveals that paraelectric-FE transition temperature TC* (525K) and maximum value of ɛ (318) remain almost unaffected for x =0.1 composite compared to pure EMO. Polarization versus electric field study at 300K give conclusive evidence of the presence of spontaneous polarization in this x =0.1 composite. For x =0.2 composite, decreasing TC* (430K) with increase in ɛ value (774) indicates diffusive FE character.

  3. In situ study of electrochemical activation and surface segregation of the SOFC electrode material La0.75Sr0.25Cr0.5Mn0.5O(3±δ).

    PubMed

    Huber, Anne-Katrin; Falk, Mareike; Rohnke, Marcus; Luerssen, Bjoern; Gregoratti, Luca; Amati, Matteo; Janek, Jürgen

    2012-01-14

    Mixed-conducting perovskite-type electrodes which are used as cathodes in solid oxide fuel cells (SOFCs) exhibit pronounced performance improvement after cathodic polarization. The current in situ study addresses the mechanism of this activation process which is still unknown. We chose the new perovskite-type material La(0.75)Sr(0.25)Cr(0.5)Mn(0.5)O(3±δ) which is a potential candidate for use in symmetrical solid oxide fuel cells (SFCs). We prepared La(0.75)Sr(0.25)Cr(0.5)Mn(0.5)O(3±δ) thin film model electrodes on YSZ (111) single crystals by pulsed laser deposition (PLD). Impedance spectroscopy (EIS) measurements show that the kinetics of these electrodes can be drastically improved by applying a cathodic potential. To understand the origin of the enhanced electrocatalytic activity the surfaces of operating LSCrM electrodes were studied in situ (at low pressure) with spatially resolving X-ray photoelectron spectroscopy (μ-ESCA, SPEM) and quasi static secondary ion mass spectrometry (ToF-SIMS) after applying different electrical potentials in the SIMS chamber. We observed that the electrode surfaces which were annealed at 600 °C are enriched significantly in strontium. Subsequent cathodic polarization decreases the strontium surface concentration while anodic polarization increases the strontium accumulation at the electrode surface. We propose a mechanism based on the reversible incorporation of a passivating SrO surface phase into the LSCrM lattice to explain the observed activation/deactivation process.

  4. Effect of natural homointerfaces on the magnetic properties of pseudomorphic La0.7Sr0.3MnO3 thin film: Phase separation vs split domain structure

    NASA Astrophysics Data System (ADS)

    Congiu, Francesco; Sanna, Carla; Maritato, Luigi; Orgiani, Pasquale; Geddo Lehmann, Alessandra

    2016-12-01

    We studied the effect of naturally formed homointerfaces on the magnetic and electric transport behavior of a heavily twinned, 40 nm thick, pseudomorphic epitaxial film of La0.7Sr0.3MnO3 deposited by molecular beam epitaxy on ferroelastic LaAlO3(001) substrate. As proved by high resolution X-ray diffraction analysis, the lamellar twin structure of the substrate is imprinted in La0.7Sr0.3MnO3. In spite of the pronounced thermomagnetic irreversibility in the DC low field magnetization, spin-glass-like character, possibly related to the structural complexity, was ruled out, on the base of AC susceptibility results. The magnetic characterization indicates anisotropic ferromagnetism, with a saturation magnetization Ms = 3.2 μB/Mn, slightly reduced with respect to the fully polarized value of 3.7 μB/Mn. The low field DC magnetization vs temperature is non bulklike, with a two step increase in the field cooled MFC(T) branch and a two peak structure in the zero field cooled MZFC(T) one. Correspondingly, two peaks are present in the resistivity vs temperature ρ(T) curve. With reference to the behavior of epitaxial manganites deposited on bicrystal substrates, results are discussed in terms of a two phase model, in which each couple of adjacent ferromagnetic twin cores, with bulklike TC = 370 K, is separated by a twin boundary with lower Curie point TC = 150 K, acting as barrier for spin polarized transport. The two phase scenario is compared with the alternative one based on a single ferromagnetic phase with the peculiar ferromagnetic domains structure inherent to twinned manganites films, reported to be split into interconnected and spatially separated regions with in-plane and out-of-plane magnetization, coinciding with twin cores and twin boundaries respectively.

  5. 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.

  6. High-Temperature Thermoelectric Properties of Perovskite-Type Pr0.9Sr0.1Mn1-x Fe x O3 (0 ≤ x ≤ 1)

    NASA Astrophysics Data System (ADS)

    Nakatsugawa, H.; Saito, M.; Okamoto, Y.

    2017-02-01

    Polycrystalline samples of Pr0.9Sr0.1Mn1-x Fe x O3 (0 ≤ x ≤ 1) have been synthesized using a conventional solid-state reaction method, and the crystal structure studied at room temperature. The magnetic susceptibility was measured from 5 K to 350 K. The electrical resistivity, Seebeck coefficient, and thermal conductivity were investigated as functions of temperature below 850 K. For all samples, the perovskite structure at room temperature exhibited orthorhombic Pbnm phase. While the Pr0.9Sr0.1MnO3 (x = 0) sample exhibited ferromagnetic-like ground state below T C = 145 K (Curie temperature), the ferromagnetic transition temperature T C decreased with increasing x. The Seebeck coefficient of the samples with 0 ≤ x ≤ 0.8 decreased with increasing temperature because of double-exchange interaction of Mn ions. In fact, the carrier type for x = 0 changed from hole-like to electron-like behavior above 800 K. On the other hand, the samples with x ≥ 0.9 showed large positive Seebeck coefficient over the entire temperature range, indicating that the low-spin state of Fe ions dominated the electronic structure for this x range. In particular, the sample with x = 1 exhibited p-type thermoelectric properties with relatively high Seebeck coefficient, moderate electrical resistivity, and low thermal conductivity. Thus, the sample with x = 1 showed power factor of 20 μW m-1 K-2 at 850 K leading to ZT of 0.024 at this temperature, indicating that hole-doped perovskite-type iron oxide is a good candidate high-temperature thermoelectric p-type oxide.

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

    PubMed Central

    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

  8. Crystal Chemical and Thermodynamic Study on CaUO 4- x, (Ca 0.5Sr 0.5)UO 4- x, and α-SrUO 4- x ( x = 0 ˜ 0.5)

    NASA Astrophysics Data System (ADS)

    Takahashi, Kazuo; Fujino, Takeo; Morss, Lester R.

    1993-07-01

    A crystallographic and thermochemical study of CaUO 4- x, (Ca 0.5Sr 0.5)UO 4- x, and αSrUO 4- x with x values ranging from nearly 0 to 0.5 was carried out. As the crystal radius of the divalent cations increases, a (rhomb) of nearly stoichiometric compounds increases, accompanied by an increase in the cell volume, whereas α(rhomb) decreases. With nonstoichiometry, the lattice parameters of (Ca 0.5Sr 0.5)UO 4- x and α-SrUO 4- x discontinuously change at 4 ˜ x = 3.79 and 3.77, respectively, although each compound is a single phase in the entire range from 4 - x = 4.00 to 3.50. For CaUO 4- x, the products were two-phase mixtures between 4 ˜ x = 3.98 and 3.70. These crystal structures are discussed taking into account the lattice parameters and interatomic distances. In the nonstoichiometric crystals, oxygen vacancies exist on the O II sites but not on the O I sites. The enthalpy of formation of α-SrUO 4- x was measured for several specimens with different x values by solution calorimetry, and was expressed in a second-order polynomial of x by least-squares calculation. This quantity and its derivative, i.e., partial molar enthalpy of oxygen, suggest the change of defect species with x and the existence of repulsive vacancy-vacancy interaction.

  9. (Bi0.15La0.27Sr0.53)(Co0.25Fe0.75)O3-δ perovskite: A novel cathode material for intermediate temperature solid oxide fuel cells

    NASA Astrophysics Data System (ADS)

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

    2016-12-01

    Perovskite oxides (Bi0.15La0.27Sr0.53)x(Co0.25Fe0.75)O3-δ (BiLSCFx, x = 0.8, 0.9, 1.0, 1.1) have been synthesized by solid state reaction and evaluated as a novel cathode material for intermediate-temperature solid oxide fuel cells (IT-SOFCs). The effects of A-site variations on lattice structure, calcination temperature, oxygen desorption and electrochemical properties of BiLSCFx are investigated. This kind of material has perfectly cubic structure based on the Pm-3m space group whose lattice size increases with x, which is thermally stable after calcination and shows desirable chemical compatibility with La0.8Sr0.2Ga0.8Mg0.2O3-δ electrolyte at 1150 °C for 8 h under air atmosphere. Among those A-site variations, it is found that BiLSCF0.9 demonstrates the best cathode performance. It has the minimum polarization resistance value of 0.039 Ω cm2 at 700 °C and α-oxygen desorbed about 0.031 mmol g-1, indicating a good reactivity and strong adsorbate of O2. The single cell with BiLSCF0.9 cathode delivers a power density of 0.66 W cm-2 at 700 °C with humidified H2 (∼3% H2O) as the fuel and ambient air as the oxidant. In addition, the cell shows sufficient stability with ∼9% degradation over 75 h at 600 °C. It indicates that BiLSCF0.9 is a promising candidate for application as cathode material in IT-SOFCs.

  10. 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.

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

    DOE PAGES

    Song, Xueyan; Lee, Shiwoo; Chen, Yun; ...

    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

  12. 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.

  13. 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

    2015-04-24

    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.

  14. Preparation and characterization of Ba0.2Sr0.2La0.6MnO3 nanoparticles and investigation of size & shape effect on microwave absorption

    NASA Astrophysics Data System (ADS)

    Peymanfar, Reza; Javanshir, Shahrzad

    2017-06-01

    In this paper, the design and characterization of a radar absorbing material (RAM) was investigated at microwave frequency. Ba0.2Sr0.2La0.6MnO3 magnetic nanoparticles was synthesized thru a facile hydrothermal method in the presence of polymethyl methacrylate (PMMA) and the possibility of shape and size-controlled synthesis of nanoparticles (NPs) over the range 15-50 Nm was also explored. Afterward, the effect of shape and size of the synthesized Ba0.2Sr0.2La0.6MnO3 NPs on microwave absorption properties was investigated in KU-band. The crystal structures and morphology of as-synthesized nanoparticles were characterized and confirmed by FESEM, XRD, VSM, FTIR analysis. The RAM samples were prepared by dispersion of magnetic NPs in silicone rubber in an ultrasonic bath. The maximum reflection loss (RL) values NPs were 12.04 dB at 14.82 GHz and a broad absorption band (over 1.22 GHz) with RL values <-10 dB are obtained and the maximum reflection loss (RL) values of decrease and shaped NPs were 22.36 dB at 14.78 GHz and a broad absorption band (over 2.67 GHz) with RL values <-10 dB are obtained. The results indicated that the particle size and shape play a major role on the absorption properties of the composites in the 12.4-18 GHz frequency range. It is observed that microwave absorption properties increased with the decrease in average particle size of NPs.

  15. Stability and performance of La0.6Sr0.4Co0.2Fe0.8O3-δ nanostructured cathodes with Ce0.8Gd0.2O1.9 surface coating

    NASA Astrophysics Data System (ADS)

    dos Santos-Gómez, L.; Porras-Vázquez, J. M.; Losilla, E. R.; Martín, F.; Ramos-Barrado, J. R.; Marrero-López, D.

    2017-04-01

    La0.6Sr0.4Co0.2Fe0.8O3-δ is considered as one of the most promising cathodes for Solid Oxide Fuels Cells (SOFCs) operating at intermediate temperatures, however, its performance degrades significantly over time mainly due to phase segregations on the surface. In this work, the surface of La0.6Sr0.4Co0.2Fe0.8O3-δ-Ce0.8Gd0.2O1.9 (LSCF-CGO) nanostructured cathode is coated with CGO particles via a simple and economic spray-pyrolysis deposition process. The electrode polarization resistance (Rp) and the microstructure evolution of the uncoated and CGO-coated cathodes are investigated by impedance spectroscopy and scanning electron microscopy, respectively. The CGO-coated cathodes exhibit improved stability and performance, with Rp values varying from 0.27 to 0.30 Ωcm2 at an annealing temperature of 600 °C for 400 h. On the contrary, the uncoated cathode shows a faster degradation rate, with a continuous increase of Rp from 2.8 to 8.5 Ωcm2. Above 800 °C, the particle coarsening of the CGO layer results in a significant increase of Rp over time, reaching steady values of 0.04 Ωm2 at 800 °C. An anode-supported cell with the CGO-coated cathode shows a remarkable power density of 0.72 Wcm-2 at 650 °C in comparison to 0.56 Wcm-2 for the cell with uncoated cathode.

  16. Magnetocaloric effect and critical behavior in La0.8-xPrxSr0.2MnO3 (x = 0.2, 0.4, 0.5) manganites

    NASA Astrophysics Data System (ADS)

    Zarifi, M.; Kameli, P.; Mansouri, M.; Ahmadvand, H.; Salamati, H.

    2017-08-01

    This paper reports on an investigation carried out to determine the effects of Pr substitution on the magnetocaloric and critical behavior of La0.8-xPrxSr0.2MnO3 (x = 0.2, 0.4, 0.5) manganites. Structural studies show that all the compositions are single phase with a rhombohedral structure. Moreover, the lattice parameters and unit cell volume decrease with increasing Pr concentration while the Curie temperature (TC) decreases with Pr3+ substitution for La3+ ions. Arrot's plots are used to determine the nature of the second order magnetic transition; no obvious hysteresis loss is observed in the vicinity of TC in any of the samples. An exhaustive study of the critical behavior of the paramagnetic to ferromagnetic transition is conducted to determine the values of the critical exponents (β, γ, and δ) based on the modified Arrot's plot and using the Kouvel-Fisher method. We have obtained the critical exponents used 3D-Heisenberg and 3D-Ising models. It was found that with increasing Pr doping the values of β and γ decrease and increase, respectively. This suggests an increase in the ferromagnetic short-range order as a result of increasing Pr content in the La0.8-xPrxSr0.2MnO3 samples. Maximum changes in the magnetic entropy were found to be 4.16, 3.88, and 3.8 J kg-1 K-1 under an applied magnetic field of 5 T while the Relative Cooling Power (RCP) values reached 174.7, 252.3, and 255 J kg-1 for x = 0.2, 0.4, and 0.5, respectively.

  17. Structure defects, phase transitions, magnetic resonance and magneto-transport properties of La0.6-xEuxSr0.3Mn1.1O3-δ ceramics

    NASA Astrophysics Data System (ADS)

    Liedienov, N. A.; Pashchenko, A. V.; Pashchenko, V. P.; Prokopenko, V. K.; Revenko, Yu. F.; Mazur, A. S.; Sycheva, V. Ya.; Kamenev, V. I.; Levchenko, G. G.

    2016-12-01

    Structure and its defects, magnetic resonance and magneto-transport properties of La0.6-xEuxSr0.3Mn1.1O3-δ magnetoresistive ceramics were investigated by x-ray diffraction, thermogravimetric, resistance, magnetic, 55Mn NMR and magnetoresistance methods. It was found that isovalent substitution of lanthanum by europium A-cation of a smaller ionic radius increases the structural imperfection and leads to a symmetry change from the rhombohedrally distorted perovskite structure of R 3 ¯ c symmetry to the pseudocubic type. It was shown that the real structure contains anionic and cationic vacancies, the concentrations of which increases with the Eu concentration and the sintering temperature tann. A decrease in the temperature of the metal-semiconductor Tms and ferromagnetic-paramagnetic TC phase transitions as well as an increase in the resistivity ρ and the activation energy Ea with increasing x are due to an increase in vacancy concentration, which weakens the high-frequency electron double exchange Mn3+ ↔ O2- ↔ Mn4+. The crystal structure of the compositions x = 0 and 0.1 contains nanostructured planar clusters, causing anomalous magnetic hysteresis at T = 77 K. Broad asymmetric 55Mn NMR spectra confirm high-frequency electron double exchange Mn3+(3d4) ↔ O2-(2p6) ↔ Mn4+(3d3) and indicate inhomogeneity of the manganese environment due to the surrounding ions and vacancies. The effective local fields of the hyperfine interaction HHF at 55Mn nuclei have been calculated by decomposing asymmetric NMR spectra into three Gaussian components. The constructed experimental phase diagram of the magnetic and conducting states of the La0.6-xEuxSr0.3Mn1.1O3-δ ceramics revealed strong correlation between the composition, structural imperfection, phase state, and magnetotransport properties of rare-earth manganites.

  18. High-Temperature Thermoelectric Properties of Perovskite-Type Pr0.9Sr0.1Mn1- x Fe x O3 (0 ≤ x ≤ 1)

    NASA Astrophysics Data System (ADS)

    Nakatsugawa, H.; Saito, M.; Okamoto, Y.

    2017-05-01

    Polycrystalline samples of Pr0.9Sr0.1Mn1- x Fe x O3 (0 ≤ x ≤ 1) have been synthesized using a conventional solid-state reaction method, and the crystal structure studied at room temperature. The magnetic susceptibility was measured from 5 K to 350 K. The electrical resistivity, Seebeck coefficient, and thermal conductivity were investigated as functions of temperature below 850 K. For all samples, the perovskite structure at room temperature exhibited orthorhombic Pbnm phase. While the Pr0.9Sr0.1MnO3 ( x = 0) sample exhibited ferromagnetic-like ground state below T C = 145 K (Curie temperature), the ferromagnetic transition temperature T C decreased with increasing x. The Seebeck coefficient of the samples with 0 ≤ x ≤ 0.8 decreased with increasing temperature because of double-exchange interaction of Mn ions. In fact, the carrier type for x = 0 changed from hole-like to electron-like behavior above 800 K. On the other hand, the samples with x ≥ 0.9 showed large positive Seebeck coefficient over the entire temperature range, indicating that the low-spin state of Fe ions dominated the electronic structure for this x range. In particular, the sample with x = 1 exhibited p-type thermoelectric properties with relatively high Seebeck coefficient, moderate electrical resistivity, and low thermal conductivity. Thus, the sample with x = 1 showed power factor of 20 μW m-1 K-2 at 850 K leading to ZT of 0.024 at this temperature, indicating that hole-doped perovskite-type iron oxide is a good candidate high-temperature thermoelectric p-type oxide.

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

    NASA Astrophysics Data System (ADS)

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

    2015-12-01

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

  20. 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.

  1. Coexistence of superconductivity and ferromagnetism in Sr0.5Ce0.5FBiS2-xSex (x = 0.5 and 1.0), a non-U material with Tc < TFM

    PubMed Central

    Thakur, Gohil S.; Fuchs, G.; Nenkov, K.; Haque, Zeba; Gupta, L. C.; Ganguli, A. K.

    2016-01-01

    We have carried out detailed magnetic and transport studies of the new Sr0.5Ce0.5FBiS2-xSex (0.0 ≤ x ≤ 1.0) superconductors derived by doping Se in Sr0.5Ce0.5FBiS2. Se–doping produces several effects: it suppresses semiconducting–like behavior observed in the undoped Sr0.5Ce0.5FBiS2, the ferromagnetic ordering temperature, TFM, decreases considerably from 7.5 K (in Sr0.5Ce0.5FBiS2) to 3.5 K and the superconducting transition temperature, Tc, gets enhanced slightly to 2.9–3.3 K. Thus in these Se–doped materials, TFM is marginally higher than Tc. Magnetization studies provide evidence of bulk superconductivity in Sr0.5Ce0.5FBiS2-xSex at x ≥ 0.5 in contrast to the undoped Sr0.5Ce0.5FBiS2 (x = 0) where magnetization measurements indicate a small superconducting volume fraction. Quite remarkably, as compared with the effective paramagnetic Ce–moment (~2.2 μB), the ferromagnetically ordered Ce–moment in the superconducting state is rather small (~0.1 μB) suggesting itinerant ferromagnetism. To the best of our knowledge, Sr0.5Ce0.5FBiS2-x Sex (x = 0.5 and 1.0) are distinctive Ce–based bulk superconducting itinerant ferromagnetic materials with Tc < TFM. Furthermore, a novel feature of these materials is that they exhibit a dual and quite unusual hysteresis loop corresponding to both the ferromagnetism and the coexisting bulk superconductivity. PMID:27892482

  2. Coexistence of superconductivity and ferromagnetism in Sr0.5Ce0.5FBiS2-xSex (x = 0.5 and 1.0), a non-U material with Tc < TFM

    NASA Astrophysics Data System (ADS)

    Thakur, Gohil S.; Fuchs, G.; Nenkov, K.; Haque, Zeba; Gupta, L. C.; Ganguli, A. K.

    2016-11-01

    We have carried out detailed magnetic and transport studies of the new Sr0.5Ce0.5FBiS2-xSex (0.0 ≤ x ≤ 1.0) superconductors derived by doping Se in Sr0.5Ce0.5FBiS2. Se–doping produces several effects: it suppresses semiconducting–like behavior observed in the undoped Sr0.5Ce0.5FBiS2, the ferromagnetic ordering temperature, TFM, decreases considerably from 7.5 K (in Sr0.5Ce0.5FBiS2) to 3.5 K and the superconducting transition temperature, Tc, gets enhanced slightly to 2.9–3.3 K. Thus in these Se–doped materials, TFM is marginally higher than Tc. Magnetization studies provide evidence of bulk superconductivity in Sr0.5Ce0.5FBiS2-xSex at x ≥ 0.5 in contrast to the undoped Sr0.5Ce0.5FBiS2 (x = 0) where magnetization measurements indicate a small superconducting volume fraction. Quite remarkably, as compared with the effective paramagnetic Ce–moment (~2.2 μB), the ferromagnetically ordered Ce–moment in the superconducting state is rather small (~0.1 μB) suggesting itinerant ferromagnetism. To the best of our knowledge, Sr0.5Ce0.5FBiS2-x Sex (x = 0.5 and 1.0) are distinctive Ce–based bulk superconducting itinerant ferromagnetic materials with Tc < TFM. Furthermore, a novel feature of these materials is that they exhibit a dual and quite unusual hysteresis loop corresponding to both the ferromagnetism and the coexisting bulk superconductivity.

  3. Coexistence of superconductivity and ferromagnetism in Sr0.5Ce0.5FBiS2-xSex (x = 0.5 and 1.0), a non-U material with Tc < TFM.

    PubMed

    Thakur, Gohil S; Fuchs, G; Nenkov, K; Haque, Zeba; Gupta, L C; Ganguli, A K

    2016-11-28

    We have carried out detailed magnetic and transport studies of the new Sr0.5Ce0.5FBiS2-xSex (0.0 ≤ x ≤ 1.0) superconductors derived by doping Se in Sr0.5Ce0.5FBiS2. Se-doping produces several effects: it suppresses semiconducting-like behavior observed in the undoped Sr0.5Ce0.5FBiS2, the ferromagnetic ordering temperature, TFM, decreases considerably from 7.5 K (in Sr0.5Ce0.5FBiS2) to 3.5 K and the superconducting transition temperature, Tc, gets enhanced slightly to 2.9-3.3 K. Thus in these Se-doped materials, TFM is marginally higher than Tc. Magnetization studies provide evidence of bulk superconductivity in Sr0.5Ce0.5FBiS2-xSex at x ≥ 0.5 in contrast to the undoped Sr0.5Ce0.5FBiS2 (x = 0) where magnetization measurements indicate a small superconducting volume fraction. Quite remarkably, as compared with the effective paramagnetic Ce-moment (~2.2 μB), the ferromagnetically ordered Ce-moment in the superconducting state is rather small (~0.1 μB) suggesting itinerant ferromagnetism. To the best of our knowledge, Sr0.5Ce0.5FBiS2-x Sex (x = 0.5 and 1.0) are distinctive Ce-based bulk superconducting itinerant ferromagnetic materials with Tc < TFM. Furthermore, a novel feature of these materials is that they exhibit a dual and quite unusual hysteresis loop corresponding to both the ferromagnetism and the coexisting bulk superconductivity.

  4. X-ray photoelectron spectroscopic study of direct reforming catalysts Ln0.5Sr0.5Ti0.5Mn0.5O3±d (Ln = La, Nd, and Sm) for high temperature-operating solid oxide fuel cell

    NASA Astrophysics Data System (ADS)

    Kim, Keunsoo; Jeong, Jihoon; Azad, Abul K.; Jin, Sang Beom; Kim, Jung Hyun

    2016-03-01

    Chemical states of lanthanide doped perovskite for direct reforming anode catalysts, Ln0.5Sr0.5Ti0.5Mn0.5O3±d (Ln = La, Nd, and Sm) have been studied by X-ray Photoelectron Spectroscopy (XPS) in order to determine the effects of various lanthanide substitution in complex perovskites for high temperature-operating solid oxide fuel cells (HT-SOFC). The charge state of lanthanide ions remained at 3+ and the binding energies of the lanthanide ions in Ln0.5Sr0.5Ti0.5Mn0.5O3±d were located in a relatively lower range compared to those of conventional lanthanide oxides. Mn and Ti were regarded as charge compensation components in Ln0.5Sr0.5Ti0.5Mn0.5O3±d; Mn was more influential than Ti. In the cases of substituting Nd and Sm into Ln0.5Sr0.5Ti0.5Mn0.5O3±d, some portion of Ti showed metallic behavior; the specific Mn satellite peak indicating an electro-catalytic effect had occurred. Three types of oxygen species comprised of lattice oxygen, carbonate species, and adsorbed oxygen species were observed in Ln0.5Sr0.5Ti0.5Mn0.5O3±d from the O 1s spectra; a high portion of lattice oxygen was observed in both Nd0.5Sr0.5Ti0.5Mn0.5O3±d (NSTM) and Sm0.5Sr0.5Ti0.5Mn0.5O3±d (SSTM). In various respects, NSTM and SSTM will be desirable reforming catalysts and anode candidates for high temperature solid oxide fuel cell.

  5. 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.; ...

    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

  6. Ln 0.6Sr 0.4Co 1- yFe yO 3- δ (Ln = La and Nd; y = 0 and 0.5) cathodes with thin yttria-stabilized zirconia electrolytes for intermediate temperature solid oxide fuel cells

    NASA Astrophysics Data System (ADS)

    Torres-Garibay, Claudia; Kovar, Desiderio; Manthiram, Arumugam

    The electrochemical performances of the solid oxide fuel cells (SOFC) fabricated with Ln 0.6Sr 0.4Co 1- yFe yO 3- δ (Ln = La, Nd; y = 0, 0.5) perovskite cathodes, thin yttria-stabilized zirconia (YSZ) electrolytes, and YSZ-Ni anodes by tape casting, co-firing, and screen printing are evaluated at 600-800 °C. Peak power densities of ∼550 mW cm -2 are achieved at 800 °C with a La 0.6Sr 0.4CoO 3- δ (LSC) cathode that is known to have high electrical conductivity. Substitution of La by Nd (Nd 0.6Sr 0.4CoO 3- δ) to reduce the thermal expansion coefficient (TEC) results in only a slight decrease in power density despite a lower electrical conductivity. Conversely, substitution of Fe for Co (La 0.6Sr 0.4Co 0.5Fe 0.5O 3- δ or Nd 0.6Sr 0.4Co 0.5Fe 0.5O 3- δ) to reduce the TEC further reduces the cell performance greatly due to a significant decrease in electrical conductivity. However, infiltration of the Fe-substituted cathodes with Ag to increase the electrical conductivity increases the cell performance while preserving the low TEC.

  7. 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.

  8. Effects of cation-size disorder in (La0.67Ca0.15Sr0.18)1-x(Gd0.67Ba0.33)xCoO3 perovskites

    NASA Astrophysics Data System (ADS)

    Sun, J. R.; Wong, H. K.

    1999-07-01

    Effects of the A-cation disorder on the structural, magnetic and transport properties of the ABO3-type (La0.67Ca0.15Sr0.18)1-x(Gd0.67Ba0.33)xCoO3 (x=0.0, 0.1, 0.2, 0.3, and 0.4) are studied. Based on x-ray diffraction, two crystallographic phases coexist in the compounds, and a progressive transition from rhombohedral structure to orthorhombic structure takes place with increasing x, with which the cation disorder increases. Two resistive transitions, a metal-to-metal and a metal-to-semiconductor, occur subsequently with decreasing temperature, with the upper resistive transition coinciding with a magnetic one. Both resistive transitions vary against x, with the upper one from ~223 to ~190 K and the lower one from ~95 to ~160 K corresponding to a change of x from 0.0-0.3. The presence of cation-size disorder drives the system from the cluster-glass state into the spin-glass state, accompanied by an enhancement of the semiconducting character of the compounds. The weak Jahn-Teller effects and the spin state transition could be responsible for the special cation disorder effects in the Co-based perovskites.

  9. 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.; ...

    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

  10. 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.

  11. Electrostatic doping limits and control of magnetism in electrolyte gated LaAlO3(001)/La0.5Sr0.5CoO3-δ thin films

    NASA Astrophysics Data System (ADS)

    Walter, Jeff; Wang, Helin; Leighton, Chris

    Recently developed ionic liquid/gel gating techniques have proven remarkably expedient in the study of charge density effects in a variety of conductors, ranging from organics to complex oxides. Here we present electrolyte gate control of magnetism in ultrathin (8 u.c.) La0.5Sr0.5CoO3-δ (LSCO) films, using ion gels in electric double layer transistors. The LSCO films are initially metallic and ferromagnetic (Tc ~ 170 K), with anomalous Hall conductivity up to 40 S/cm, and strong perpendicular magnetic anisotropy. Based on extensive temperature and gate voltage dependences we first determined the limits for electrostatic vs. electrochemical operation, concluding that negative bias enables reversible hole accumulation, whereas positive bias irreversibly induces oxygen vacancies. Following this we demonstrated clear voltage-control of resistivity, magnetoresistance, andTc. Utilizing the anomalous Hall conductivity as an exceptional probe of the magnetic order parameter in the gated surface region, a 12 K shift in Tc is obtained. This compares favorably to the state-of-the-art and exhibits potential for much larger modulation in films of lower Sr content. Work supported by NSF MRSEC.

  12. 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.

  13. 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+) .

  14. 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.

  15. Signatures of a Two-Dimensional Ferromagnetic Electron Gas at the La0.7Sr0.3MnO3/ SrTiO3 Interface Arising From Orbital Reconstruction

    NASA Astrophysics Data System (ADS)

    Calderon, Maria J.; Nemes, Norbert; Beltran, Juan Ignacio; Bruno, Flavio; Garcia-Barriocanal, Javier; Sefrioui, Zouhair; Leon, Carlos; Garcia-Hernandez, Mar; Muñoz, Carmen; Brey, Luis; Santamaria, Jacobo

    2015-03-01

    The interface between two different oxides has properties different from the ones corresponding to the constituent layers in bulk. Different orders can arise due to the complexity of these materials in which the orbital degree of freedom, magnetism and lattice are strongly interdependent. Here we present a joint theoretical-experimental effort to understand the properties of a multilayer formed by a metallic ferromagnetic manganite oxide (La0.7Sr0.3MnO3) and the insulating SrTiO3. Magnetoresistance measurements as a function of the relative angle between the magnetic field and the interface plane have shown an unexpected in-plane peak. Calculations of resistivity in a model system including spin-orbit coupling reveal that the unexpected in-plane maximum is due to transport through a two-dimensional ferromagnetic electron gas formed by orbital reconstruction at the manganite interface. These orbital and magnetic reconstructions are supported by X-ray linear dichroism and ab-initio calculations. Advanced Materials DOI:10.1002/adma.201402829. MINECO-Spain through grants FIS2012-33521, MAT2011-27470-C02-01, MAT2011-27470-C02-02, MAT2012-38045-C04-04, CSD2009-00013, and Ramon y Cajal program.

  16. Thickness dependence of microstructure in thin La0.7Sr0.3MnO3 films grown on (1 0 0) SrTiO3 substrate

    NASA Astrophysics Data System (ADS)

    Mirzadeh Vaghefi, P.; Baghizadeh, A.; Willinger, M.-G.; Pereira, M. J.; Mota, D. A.; Almeida, B. G.; Agostinho Moreira, J.; Amaral, V. S.

    2017-10-01

    This study investigates the nanostructure of perovskite thin films, and its influence on magnetic properties. Epitaxial thin films of perovskite La0.7 Sr0.3 MnO3 with thickness ranging from 13.5 nm to 320 nm were deposited on SrTiO3 (1 0 0) substrates using pulsed laser deposition techniques. X-ray diffraction, along with high-resolution transmission electron microscopy (HRTEM) investigations were carried out, and showed the presence of a second, La-rich phase in thick film. Scanning electron microscopy analysis showed thinner films to have smooth surfaces, while thicker films presented large triangular shapes emerging out of the film surface. Also HRTEM images revealed epitaxial growth for thinner films. Thicker films grow with numerous misfit dislocations leading to columnar structure, where the thickest film presents branched structure with an intermediate La-rich layer. Lattice mismatch, diffusion of Mn ions into the substrate and substituting Ti ions are known as sources of strain in films near interfaces. Magnetic properties in the structure mentioned are described by double-exchange interaction, which is very sensitive to local structure. Hence, the nanostructure of films reported here has a remarkable effect on their magnetic properties.

  17. 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

    2014-11-17

    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.

  18. 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.

  19. 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.

  20. La 0.6Sr 0.4Co 0.2Fe 0.8O 3- δ cathodes infiltrated with samarium-doped cerium oxide for solid oxide fuel cells

    NASA Astrophysics Data System (ADS)

    Nie, Lifang; Liu, Mingfei; Zhang, Yujun; Liu, Meilin

    Porous La 0.6Sr 0.4Co 0.2Fe 0.8O 3- δ (LSCF) cathodes are coated with a thin film of Sm 0.2Ce 0.8O 1.95- δ (SDC) using a one-step infiltration process. Examination of the microstructures reveals that small SDC particles are formed on the surface of LSCF grains with a relatively narrow size distribution. Impedance analysis indicates that the SDC infiltration has dramatically reduced the polarization of LSCF cathode, reaching interfacial resistances of 0.074 and 0.44 Ω cm 2 at 750 °C and 650 °C, respectively, which are about half of those for LSCF cathode without infiltration of SDC. The activation energies of the SDC infiltrated LSCF cathodes are in the range of 1.42-1.55 eV, slightly lower than those for a blank LSCF cathode. The SDC infiltrated LSCF cathodes have also shown improved stability under typical SOFC operating conditions, suggesting that SDC infiltration improves not only power output but also performance stability and operational life.

  1. High performance La2NiO4+δ-infiltrated (La0.6Sr0.4)0.995Co0.2Fe0.8O3-δ cathode for solid oxide fuel cells

    NASA Astrophysics Data System (ADS)

    Zhang, Xinxin; Zhang, Hui; Liu, Xingbo

    2014-12-01

    In this paper, we reported our effort on improving electrochemical performance of (La0.6Sr0.4)0.995Co0.2Fe0.8O3-δ (LSCF) cathode in solid oxide fuel cell (SOFC) by infiltration of La2NiO4+δ (LNO). It is found that a porous LSCF backbone coated with LNO nanoparticles is an attractive way to acquire a noticeable decrease in the polarization resistance and activation energy of LSCF cathode, thereby showing high surface activity and enhanced oxygen transport capability. The key contributions of the LNO nanoparticles also lead to a 67% increase in peak power density and operation stability at a constant current density of 250 mA cm-2 with a low degradation rate of 0.39% for about 500 h at 750 °C. Although extended durability of LNO-infiltrated LSCF might be concerned, based on coarsening of the LNO nanoparticles, a greatly increased power density and voltage output after a cell operation of 500 h engenders substantial confidence in the beneficial effect of LNO-infiltrated LSCF materials on cell properties. The enhancement of ORR kinetics could be ascribed to the increase of active surface area and active reaction regions from the heterostructured LSCF/LNO interface architecture, and/or favorable cation diffusion from LSCF to LNO.

  2. 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.

  3. A robust high performance cobalt-free oxygen electrode La0.5Sr0.5Fe0.8Cu0.15Nb0.05O3-δ for reversible solid oxide electrochemical cell

    NASA Astrophysics Data System (ADS)

    Zhou, Ning; Yin, Yi-Mei; Li, Jingcheng; Xu, Lei; Ma, Zi-Feng

    2017-02-01

    A novel cobalt-free perovskite oxide La0.5Sr0.5Fe0.8Cu0.15Nb0.05O3-δ (LSFCN) has been synthesized and evaluated as oxygen electrode for reversible solid oxide electrochemical cells (RSOCs). The performance and stability of the LSFCN based RSOCs have been characterized in fuel cell and electrolysis modes, and the reversibility of the cells has been proven. In FC mode, the cell exhibits the maximum power density of 1.10 Wcm-2 at 800 °C, and a stable output under 0.7 V at 700 °C during 108 h. The performance and stability of the cell in electrolysis mode are also remarkable. An electrolysis current of 0.85 A cm-2 is achieved at 750 °C with an applied voltage of 1.3 V, and no degradation as well as delamination are observed for the cell after 50 h electrolysis under voltage of 1.60 V (∼1.27 A cm-2) at 800 °C. The high performance of the LSFCN at both cathodic and anodic conditions may be attributed to the inherent high electrochemical activity of copper-iron based perovskites; and the incorporation of Nb5+ cations into perovskite lattice is responsible for the stability of LSFCN, which leads to the more stable crystal structure, lower thermal expansion coefficient and the reduced Sr segregation at surface.

  4. 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.

  5. Evaluation of La0.6Sr0.4Co0.2Fe0.8O3-Gd0.1Ce0.9O1.95 composite cathode with three dimensional microstructure reconstruction

    NASA Astrophysics Data System (ADS)

    Kim, Y. T.; Jiao, Z.; Shikazono, N.

    2017-02-01

    In the present study, the polarization characteristics of La0.6Sr0.4Co0.2Fe0.8O3 (LSCF) - Gd0.1Ce0.9O1.95 (GDC) composite cathodes with different volume ratios were investigated. Samples with volume ratios of 20:80, 30:70, 50:50, 70:30 and 100:0 vol % were tested. The electrochemical impedance spectroscopy tests and current voltage curve measurements were carried out for the current densities from 0 to 0.2 Acm-2 with an interval of 0.05 Acm-2. The results showed that a volume ratio of LSCF:GDC = 30:70 composite cathode led to the lowest overpotential, and the overpotential increased in the order of 30:70, 50:50, 70:30, 100:0, 20:80 vol %. Three dimensional microstructures of composite cathodes were reconstructed and quantified by dual beam focused ion beam-scanning electron microscope (FIB-SEM). The results showed that neither LSCF surface area nor triple phase boundary (TPB) alone could explain the dependence of polarization characteristics on volume ratios. Current and electrochemical potential distributions were simulated by the Lattice Boltzmann method, in which both surface and TPB reactions were considered. Prediction considering both surface and TPB reactions could predict qualitatively the dependence of overpotentials on LSCF - GDC cathode composition.

  6. 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; ...

    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

  7. 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.

  8. Landau theory and critical behavior near the ferromagnetic-paramagnetic transition temperature in Pr0.63A0.07Sr0.3MnO3 (A=Pr, Sm and Bi) manganites

    NASA Astrophysics Data System (ADS)

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

    2017-09-01

    In this work, we are interested in the study of the critical behavior and the Landau theory of Pr0.63A0.07Sr0.3MnO3 (A=Pr, Sm and Bi) compounds. The critical exponents of all our samples were studied using the magnetic field dependent isothermal magnetization around Curie temperature TC, based on various techniques. The validity of our critical exponents is confirmed by the scaling analysis. The study revealed that tricritical mean field model is the best for calculating the critical exponents for all our samples. The substitution of praseodymium by samarium and bismuth does not change the universality class. Using Landau theory, we have confirmed that the magnetic transition around TC is of second-order. An agreement was found between the (-ΔS) values estimated by Landau theory and those obtained using Maxwell relation for a magnetic field equal to 2 T, which shows the validity of this theory for all our compounds. The deviation obtained for bismuth and samarium based samples below TC can be attributed to the existence of some antiferromagnetic domains in the ferromagnetic phase.

  9. Electrical properties and transport mechanisms of Au/Ba0.6Sr0.4TiO3/GaN metal-insulator-semiconductor (MIS) diode at high temperature range

    NASA Astrophysics Data System (ADS)

    Rajagopal Reddy, V.

    2016-05-01

    The electrical and transport mechanisms of a fabricated Au/Ba0.6Sr0.4TiO3 (BST)/GaN metal-insulator-semiconductor (MIS) diode have been studied in the temperature range of 280-430 K by current-voltage ( I- V) and capacitance-voltage ( C- V) measurements. The barrier heights (BHs) of the Au/BST/GaN MIS diode are found to be 0.85 eV ( I- V)/1.35 ( C- V) at 280 K and 1.14 eV ( I- V)/1.17 ( C- V) at 430 K. The series resistance ( R S) values determined by Cheung's functions are in good agreement with each other. The difference between BHs estimated by I- V and C- V methods are also discussed. Results show that the estimated interface state density ( N SS) of MIS diode decreases with an increase in temperature. Observations have indicated that the BH increases whereas ideality factor R S and N SS decreases with increasing temperature. Results have demonstrated that the reverse leakage current is dominated by Poole-Frenkel emission at temperatures of 280-340 K and by Schottky emission at temperatures of 370-430 K. It is also noted that there is a transition of the conduction mechanism in Au/BST/GaN MIS diode from Poole-Frenkel to Schottky emission at temperatures of 340-370 K.

  10. 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.

  11. 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 %.

  12. 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.

  13. 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.

  14. 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.

  15. Exsolution of Fe and SrO Nanorods and Nanoparticles from Lanthanum Strontium Ferrite La0.6Sr0.4FeO3-δ Materials by Hydrogen Reduction.

    PubMed

    Thalinger, Ramona; Gocyla, Martin; Heggen, Marc; Klötzer, Bernhard; Penner, Simon

    2015-09-24

    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.

  16. Ferromagnetic-Antiferromagnetic Coupling by Distortion of Fe/Mn Oxygen Octahedrons in (BiFeO3 )m (La0.7 Sr0.3 MnO3 )n Superlattices.

    PubMed

    Xiong, Jie; Lei, Tianyu; Chu, Junwei; Yang, Chao; Wei, Jiake; Zhuo, Mujin; Choi, Eun-Mi; Tao, Bowan; Zhang, Wanli; Wang, Yongqiang; Li, Yanrong

    2017-03-10

    Interface enhanced magnetism attracts much attention due to its potential use in exploring novel structure devices. Nevertheless, the magnetic behavior at interfaces has not been quantitatively determined. In this study, abnormal magnetic moment reduction is observed in La0.7 Sr0.3 MnO3 (LSMO)/BiFeO3 (BFO) superlattices, which is induced by ferromagnetic (FM)/antiferromagnetic (AFM) coupling in the interface. With reduced repetition of the superlattice's unit cell [(LSMO)n /(BFO)n ]60/n (n = 1, 2, 5, 10) on a SrTiO3 substrate, magnetic moment reduction from 25.5 emu cc(-1) ([(LSMO)10 /(BFO)10 ]6 ) to 1.5 emu cc(-1) ([(LSMO)1 /(BFO)1 ]60 ) is obtained. Ab initio simulations show that due to the different magnetic domain formation energies, the magnetic moment orientation tends to be paramagnetic in the FM/AFM interface. The work focuses on the magnetic domain formation energy and provides a pathway to construct artificial heterostructures that can be an effective way to tune the magnetic moment orientation and control the magnetization of ultrathin films.

  17. 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.

  18. Preparation and electrochemical properties of urchin-like La0.8Sr0.2MnO3 perovskite oxide as a bifunctional catalyst for oxygen reduction and oxygen evolution reaction

    NASA Astrophysics Data System (ADS)

    Jin, Chao; Cao, Xuecheng; Zhang, Liya; Zhang, Cong; Yang, Ruizhi

    2013-11-01

    An urchin-like La0.8Sr0.2MnO3 (LSM) perovskite oxide has been synthesized through a co-precipitation method with urea as a precipitator, and characterized by thermogravimetric analysis (TGA), X-ray diffraction (XRD), scanning electron microscopy (SEM) and BET analysis. SEM results show that a micro/nanocomposite with an urchin-like morphology has been obtained. The as-synthesized LSM perovskite oxide has a high specific surface area of 48 m2 g-1. The catalytic activity of the oxide for the oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER) in 0.1 M KOH solution has been studied by using a rotating-ring-disk electrode (RRDE). In the ORR test, a maximum cathodic current density of 5.2 mA cm-2 at -1.0 V (vs. Ag/AgCl) with 2500 rpm was obtained, and the ORR mainly favors a direct four-electron pathway. The results of anodic linear scanning voltammograms indicate that the urchin-like LSM perovskite oxide exhibits an encouraging catalytic activity for the OER. All electrochemical measurements suggest that the urchin-like LSM perovskite oxide could be used as a bifunctional catalyst for the ORR and the OER.

  19. 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.

  20. The effect of Bi substitution on the microstructure and magnetic properties of the Sr0.4Ba0.3La0.3Fe12-xBixO19 hexagonal ferrites

    NASA Astrophysics Data System (ADS)

    Yang, Yujie; Wang, Fanhou; Liu, Xiansong; Shao, Juxiang; Feng, Shuangjiu; Huang, Duohui; Li, Mingling

    2017-01-01

    Bi3+ ions doped M-type hexaferrites, Sr0.4Ba0.3La0.3Fe12-xBixO19 (0≤x≤0.7), were prepared by the ceramic process. The phase components of the magnetic powders were investigated by X-ray diffraction. The results show that a single magnetoplumbite phase is obtained for the magnetic powders with x from 0 to 0.2, and BiFeO3 as a second phase appears when Bi content (x)≥0.3. The micrographs of the sintered magnets were observed by a field emission scanning electron microscopy. The sintered magnets are formed of hexagonal-shaped crystals. The magnetic properties of the sintered magnets were measured at room temperature by a permanent magnetic measuring system. The remanence (Br) first increases with x from 0 to 0.2, and then decreases when Bi content (x)≥0.2. The intrinsic coercivity (Hcj) and magnetic induction coercivity (Hcb) firstly decrease quickly with x from 0 to 0.1, and then increase linearly when Bi content (x)≥0.1. The maximum energy product [(BH)max] increases with x from 0 to 0.3, and then decreases when Bi content (x)≥0.3. The ratio Hk/Hcj ratio first increases with Bi content (x) from 0 to 0.4. And the Hk/Hcj ratio decreases when x≥0.4.

  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. 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.

  3. Electrochemical properties of ceria-based intermediate temperature solid oxide fuel cell using microwave heat-treated La0.1Sr0.9Co0.8Fe0.2O3-δ as a cathode

    NASA Astrophysics Data System (ADS)

    Choi, M.-B.; Lee, K.-T.; Yoon, H.-S.; Jeon, S.-Y.; Wachsman, E. D.; Song, S.-J.

    2012-12-01

    The temperature dependence of the chemical diffusion coefficient and the surface exchange coefficient of LSCF1982 is successfully determined from the D.C. conductivity relaxation in the temperature range of 500 ≤ T/°C ≤ 700 and an oxygen partial pressure of 0.21 atm. The kinetic values of chemical diffusion coefficient (D˜) and surface exchange coefficient (k) are 1.85 × 10-5 cm2 s-1 and 2.42 × 10-4 cm s-1 at 650 °C, respectively. The electrochemical properties of La0.1Sr0.9Co0.8Fe0.2O3-δ (LSCF1982) as a cathode for ceria based IT-SOFC are successfully characterized by I-V performance measurement and electrochemical impedance spectroscopy (EIS) in terms of cathode microstructure effects by using microwave heat treatment. The cell with microwave heat-treated cathode shows the higher performance than conventional heat treated cathode. At 650 °C the open circuit potential (OCP) and maximum power density are respectively 0.753 V and 1.79 W cm-2 under 150 sccm of wet hydrogen and air gas flow conditions, and the ohmic and electrode area specific resistance (ASR) are 0.037 and 0.014 Ω cm2, respectively.

  4. CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES: Improvement in Dielectric Tunability of Ba0.6Sr0.4TiO4-Mg2TiO4 Composite Ceramics via Heterogeneous Nucleation Processing

    NASA Astrophysics Data System (ADS)

    Wang, Zhuo; Li, Yong-Xiang

    2009-11-01

    Dielectric tunable composite ceramics Ba0.6Sr0.4 TiO3-Mg2TiO4 (BST-MT) are prepared with a heterogeneous nucleation sol-gel approach. The Mg2TiO4 powders are synthesized by the conventional solid-state reaction method. The micro-sized MT powders with dispersant Ciba-4010 are introduced into Ba-Sr-Ti sol to obtain uniform and homogeneous mixture compounds with nano-sized BST particles synthesized via heterogeneous nucleation (HN) in the sol-gel process. Thus, the microstructural and dielectric properties can be tailored. The dielectric constants of BST-MT composite ceramics can be adjusted in a large range from 294 to 1790, and the dielectric tunability can be adjusted from 29.4% to 37.0% with different MT contents from 60 wt% to 20 wt%. Compared to the samples prepared by the conventional solid-state (SS) process, the BST-MT composite ceramics by the heterogeneous nucleation sol-gel process exhibit a more uniform microstructure, and improve dielectric properties.

  5. La0.7Sr0.3MnO3 thin films on SrTiO3 and CaTiO3 buffered Si substrates: structural, static, and dynamic magnetic properties

    NASA Astrophysics Data System (ADS)

    Belmeguenai, M.; Mercone, S.; Adamo, C.; Chauveau, T.; Méchin, L.; Monod, P.; Moch, P.; Schlom, D. G.

    2011-11-01

    Nearly 50-nm thick La0.7Sr0.3MnO3 (LSMO) films were grown on Si substrates using molecular beam epitaxy on (001) Si substrates over-layered by a 20 nm thick SrTiO3 (STO) or by a 20 nm thick CaTiO3 (CTO) film. In addition, a reference LSMO film was directly deposited on a (001) STO substrate by pulsed laser deposition. For all the samples, X-ray diffraction revealed an excellent epitaxy of the LSMO film and small mosaicity around (001), with in-plane [100] and [010] cubic axes. The LSMO/CTO films are in-plane compressed while the LSMO/STO ones are in-plane extended. The temperature dependence of their static magnetic properties was studied using a SQUID, showing a Curie temperature overpassing 315 K for all the samples. Hysteresis loops performed at room temperature (294 K) with the help of a vibrating sample magnetometer (VSM) are also discussed. At 294 K Micro-strip ferromagnetic resonance (MS-FMR) was used to investigate the dynamic magnetic properties. It allows concluding to a strong anisotropy perpendicular to the films and to a weak fourfold in-plane anisotropy with easy axes along the [110] and [ 1bar{1}0 ] directions. Their values strongly depend on the studied sample and are presumably related to the strains suffered by the films.

  6. One-pot synthesis of La0.7Sr0.3MnO3 supported on flower-like CeO2 as electrocatalyst for oxygen reduction reaction in aluminum-air batteries

    NASA Astrophysics Data System (ADS)

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

    2017-08-01

    A novel La0.7Sr0.3MnO3-CeO2 (LSM-CeO2) hybrid catalyst for oxygen reduction reaction (ORR) has been synthesized by a facile one-pot method. The flower-like CeO2 with the diameter of about 3 μm is formed by the agglomeration of nanosheets with the thickness of about 40 nm. The LSM particles with the diameter of about 150 nm are well distributed on the flower-like CeO2, thus the interaction between LSM and CeO2 is built. Therefore, the LSM-CeO2 composite catalyst exhibits the much higher catalytic activity toward ORR with the direct four-electron transfer mechanism in alkaline solution than LSM or CeO2. Furthermore, the stability of LSM-CeO2 is superior to that of Pt/C, and the current retention is 93% after 100000 s. The maximum power density of the aluminum-air battery using LSM-CeO2 as the ORRC can reach 238 mW cm-2, which is about 29% higher than that with LSM (184 mW cm-2). It indicates that LSM-CeO2 composite material is a promising cathodic electrocatalyst for metal-air batteries.

  7. Chemical characterization of surface precipitates in La0.7Sr0.3Co0.2Fe0.8O3-δ as cathode material for solid oxide fuel cells

    NASA Astrophysics Data System (ADS)

    Yu, Yang; Nikiforov, Alexey Y.; Kaspar, Tiffany C.; Woicik, Joseph C.; Ludwig, Karl F.; Gopalan, Srikanth; Pal, Uday B.; Basu, Soumendra N.

    2016-11-01

    In this study, a strontium doped lanthanum cobalt ferrite thin film with 30% Sr on A-site, denoted as La0.7Sr0.3Co0.2Fe0.8O3-δ or LSCF-7328, is investigated before and after annealing at 800 °C under CO2 containing atmosphere for 9 h. The formation of secondary phases on surface of post-annealed LSCF-7328 is observed using atomic force microscope (AFM) and scanning electron microscope (SEM). The extent of Sr segregation at the film surface is monitored using the synchrotron-based total reflection X-ray fluorescence (TXRF) technique. The bonding environment of the secondary phases formed on the surface is investigated by synchrotron-based hard X-ray photoelectron spectroscopy (HAXPES). Scanning transmission electron microscopy (STEM) and related spectroscopy techniques are used for microstructural and quantitative elemental analyses of the secondary phases on surface. These studies reveal that the secondary phases on surface consist of SrO covered with a capping layer of SrCO3. The formation of Co-rich phases is observed on the surface of post-annealed LSCF-7328.

  8. The effects of minor elements in La0.6Sr0.4Co0.2Fe0.8O3-δ cathodes on oxygen reduction reaction

    NASA Astrophysics Data System (ADS)

    Oishi, Junya; Otomo, Junichiro; Oshima, Yoshito; Koyama, Michihisa

    2015-03-01

    It is known that the minor elements affect the performance of solid oxide fuel cell (SOFC). In this study, we focus on the influence of minor elements on the SOFC cathode properties. The Ca, Ba, Al, and Si, which originate from raw materials and production processes for SOFC cathodes, are investigated as minor elements that may have effect on the properties of La0.6Sr0.4Co0.2Fe0.8O3-δ (LSCF) cathode. To examine the effects of minor elements on the cathode properties, Ca, Ba, Al, and Si with a controlled concentration are added to the LSCF reference sample. Conductivity relaxation measurements are conducted to determine the chemical diffusion coefficient (Dchem) and surface exchange coefficient (ktr), which governs the overpotential characteristics of the LSCF cathode. The results show that Al and Si have negative effects on both Dchem and ktr while Ca and Ba do not alter Dchem and show weakly positive effects on ktr. The effects of Ca and Ba for the cathode properties are discussed on the basis of XPS measurements.

  9. 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.

  10. Origin of insulating weak-ferromagnetic phase in ultra-thin La0.67Sr0.33MnO3 films on SrTiO3 substrate

    NASA Astrophysics Data System (ADS)

    Li, Yun; Choi, Euiyoung; Kim, Shin-Ik; Baek, Seung-Hyub; Park, Seung-Young; Jo, Younghun; Seo, Jiwon

    2017-08-01

    We investigate the origin of insulating weak-ferromagnetic phase in ultra-thin epitaxial La0.67Sr0.33MnO3 (LSMO) films on SrTiO3 substrate using density functional theory calculation together with X-ray linear dichroism (XLD). The calculations show that symmetry breaking of the crystal field at the LSMO surface largely lowers the energy level of Mn d3z2 orbital at the surface and leads to full occupancy of the d3z2 orbital in majority spin channel, and XLD spectra clearly show the preferential occupation of Mn d3z2 orbital at the surface. Such an orbital reconstruction and charge redistribution in the ultra-thin films largely suppresses double-exchange interaction and favors super-exchange interaction, resulting in G-type antiferromagnetic spin ordering and insulating state. The anisotropic exchange interaction due to spin-orbital interaction leads to spin canting, and thus the films show weak ferromagnetism.

  11. Improved electrical properties of Sr0.8Bi2.2Ta2O9 films by ZrSiO4 doping for low voltage operations of metal-ferroelectric-insulator-Si devices

    NASA Astrophysics Data System (ADS)

    Lu, Xubing; Ishiwara, Hiroshi

    2009-03-01

    Sr0.8Bi2.2Ta2O9 (SBT) films were prepared by chemical solution deposition in which ZrSiO4 (ZSO) with concentration ranging from 0 to 10 wt % was incorporated for improving dielectric and leakage current characteristics of the films. X-ray diffraction analysis revealed that no secondary phase and clear degradation of crystallization can be found in ZSO-doped SBT films. Smaller grain size and reduced surface roughness were found for the samples with higher ZSO doping concentration as observed by atomic force microscopy and scanning electron microscopy. The dielectric constant was observed to be much reduced for ZSO-doped SBT films as well as the remnant polarization and coercive field. Films preannealed at 400 °C have a much smaller dielectric constant when compared with that of the films preannealed at 750 °C. Furthermore, a clear reduction in the leakage current and improved fatigue characteristics were observed for ZSO-doped SBT films preannealed at 400 °C. Such improved electrical properties as reduced dielectric constant, leakage current, and coercive field for the ZSO-doped SBT films will be very beneficial for the low voltage operations in metal-ferroelectric-insulator-Si devices.

  12. Fabrication and Characterization of ZnO:Al/Sr0.8Bi2.2Ta2O9/Y2O3:Eu Structures for Ferroelectric-Electroluminescent Devices

    NASA Astrophysics Data System (ADS)

    Aizawa, Koji; Inagaki, Hiroyuki; Takatsuka, Yushi; Hoko, Koichi; Otani, Yusuke; Tokunaga, Yoshiaki

    2009-09-01

    ZnO:Al (AZO)/Sr0.8Bi2.2Ta2O9 (SBT)/Pt and AZO/SBT/Y2O3:Eu/Pt structures were fabricated, and their crystallinity, ferroelectric, and electroluminescent (EL) properties were investigated for the first time. The AZO/SBT/Pt structures showed a typical hysteresis loop, in which their double remnant polarization was approximately 5.3 µC/cm2. The polycrystalline SBT/Y2O3:Eu structures were grown on a Pt-coated substrate, in which ferroelectric phases were formed on an Y2O3:Eu film with cubic crystals. The electrical and EL properties of the AZO/SBT/Y2O3:Eu/Pt structures were measured, and then EL emission peaks associated with the 5D0-7F1 (λ=601 nm) and 5D0-7F2 (λ=617 nm) transitions of Eu3+ were observed. The EL emission pattern of the AZO/SBT/Y2O3:Eu/Pt structure was different from the PL emission pattern of the Y2O3:Eu film. Furthermore, polarization-voltage characteristics with counterclockwise hysteresis loops and an asymmetric behavior of current-voltage characteristics were observed in the fabricated AZO/SBT/Y2O3/Pt:Eu structures.

  13. Intermediate temperature single-chamber methane fed SOFC based on Gd doped ceria electrolyte and La 0.5Sr 0.5CoO 3- δ as cathode

    NASA Astrophysics Data System (ADS)

    Morales, M.; Piñol, S.; Segarra, M.

    Single-chamber fuel cells with electrodes supported on an electrolyte of gadolinium doped ceria Ce 1- xGd xO 2- y with x = 0.2 (CGO) 200 μm thickness has been successfully prepared and characterized. The cells were fed directly with a mixture of methane and air. Doped ceria electrolyte supports were prepared from powders obtained by the acetyl-acetonate sol-gel related method. Inks prepared from mixtures of precursor powders of NiO and CGO with different particle sizes and compositions were prepared, analysed and used to obtain optimal porous anodes thick films. Cathodes based on La 0.5Sr 0.5CoO 3 perovskites (LSCO) were also prepared and deposited on the other side of the electrolyte by inks prepared with a mixture of powders of LSCO, CGO and AgO obtained also by sol-gel related techniques. Both electrodes were deposited by dip coating at different thicknesses (20-30 μm) using a commercial resin where the electrode powders were dispersed. Finally, electrical properties were determined in a single-chamber reactor where methane, as fuel, was mixed with synthetic air below the direct combustion limit. Stable density currents were obtained in these experimental conditions. Temperature, composition and flux rate values of the carrier gas were determinants for the optimization of the electrical properties of the fuel cells.

  14. Influence of Y3+ substitution on the structural and magnetic properties of Sr0.7La0.3 Fe11.75- x Y x Co0.25O19 hexagonal ferrites

    NASA Astrophysics Data System (ADS)

    Zhang, Cong; Liu, Xiansong; Rehman, Khalid Mehmood Ur; Liu, Chaocheng; Li, Haohao; Meng, Xiangyu

    2017-08-01

    In this study, the Y3+ ion-substituted M-type Sr0.7La0.3Fe11.75- x Y x Co0.25O19 (0 ≤ x ≤ 0.2) hexagonal ferrites were synthesized by the traditional ceramic method. The structural, morphological, and magnetic properties were investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM), and vibrating sample magnetometer techniques. The results show that a single M-type strontium ferrite was obtained with the Yttrium content ( x) from 0 to 0.08, and the impure phase appeared when x is above 0.08. SEM images indicate the hexagonal platelet-like particles, and the size of the materials is about 3-5 μm. The saturation magnetization ( M s) and coercivity ( H c) of the magnetic powders both increased with the increase of x from 0 to 0.12, then decreased with the increase of x from 0.16 to 0.2.

  15. 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.

  16. Effect of Screen-Printing Mesh Opening Diameter on Microstructural and Electrical Properties of La0.6Sr0.4Co0.2Fe0.8O3- δ Thick Films

    NASA Astrophysics Data System (ADS)

    Jamale, Atul P.; Bhosale, C. H.; Jadhav, L. D.

    2016-01-01

    The performance of solid oxide fuel cells (SOFCs) is hampered by the large polarization and ohmic losses across the cathode-electrolyte interface. To minimize these losses, in most SOFCs the cathode is obtained by thick-film deposition techniques. Since the properties of such films depend upon the starting materials and screen-printing parameters, the effect of the mesh opening diameter on the physiochemical properties of cathodes for intermediate-temperature (IT)-SOFCs has been studied. Combustion-synthesized La0.6Sr0.4Co0.2Fe0.8O3- δ powder with specific surface area of 11.64 m2 g-1 was utilized in film formation. All films were porous in nature, and the thickness was observed to increase with the mesh opening diameter. The electrical conductivity showed a decreasing trend with film thickness. Typically, film with 7 μm thickness showed moderate conductivity of 16.4 S cm-1 with E a = 0.1 eV.

  17. 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.

  18. Effect of coupling agents on the dielectric properties and energy storage of Ba0.5Sr0.5TiO3/P(VDF-CTFE) nanocomposites

    NASA Astrophysics Data System (ADS)

    Wu, Peixuan; Zhang, Min; Wang, Han; Tang, Hui; Bass, Patrick; Zhang, Lin

    2017-07-01

    Dielectric materials with high electric energy density and low dielectric loss are critical for electric applications in modern electronic and electrical power systems. To obtain desirable dielectric properties and energy storage, nanocomposites using Ba0.5Sr0.5TiO3 (BST) as the filler and poly(vinylidene fluoride-chlorotrifluoroethylene) as the matrix material are prepared with a uniform microstructure by using a newly developed process that combines the bridge-linked action of a coupling agent, solution casting, and a hot-pressing method. When a proper amount of coupling agent is used to modify the surface of the nanoparticles, the composite exhibits a higher dielectric constant and a more uniform microstructure. A dielectric constant of 95, dielectric loss of 0.25, and energy density of 2.7 J/cm3 is obtained in the nanocomposite with 30 vol.% of BST and 15 wt.% of coupling agent. The results suggest that the energy storage ability of the composites could be improved by the surface modification of the fillers and from the interface compatibility between the fillers and the polymer matrix.

  19. Magnetic structure and effect of magnetic field on its domain structure in magnetoelectric Ba1.3Sr0.7CoZnFe11AlO22

    NASA Astrophysics Data System (ADS)

    Ueda, H.; Tanaka, Y.; Nakajima, H.; Mori, S.; Ohta, K.; Haruki, K.; Hirose, S.; Wakabayashi, Y.; Kimura, T.

    2016-10-01

    The magnetic structure and the effect of a magnetic field on its domain structure were investigated in a magnetoelectric Y-type hexaferrite, Ba1.3Sr0.7CoZnFe11AlO22, by means of mapping with a micro-focused and circularly polarized X-ray beam in the resonant X-ray diffraction. It was revealed that this hexaferrite exhibits a magnetic order characterized by two distinct antiferromagnetic components: incommensurate helical and commensurate collinear ones, which can be explained as the development of the so-called alternating longitudinal conical structure. A multi-domain state due to the handedness of the helical component, i.e., spin-chirality, is transformed into nearly a mono-domain one by using only a magnetic field. Furthermore, the sign of the spin-chirality in the mono-domain state is reversed by reversing the sign of a magnetic field. These results demonstrate that the spin-chirality in this hexaferrite can be manipulated by a magnetic field alone at room temperature.

  20. 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.