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Sample records for modulu sr-0 jaderneho

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

    NASA Astrophysics Data System (ADS)

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

    2016-01-01

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

  2. Magnetoresistance of La0.5Sr0.5MnO3 nanoparticle compact

    NASA Astrophysics Data System (ADS)

    Wang, Zhi-Hong; Ji, Tian-Hao; Wang, Yi-Qian; Chen, Xin; Li, Run-Wei; Cai, Jian-Wang; Sun, Ji-Rong; Shen, Bao-Gen; Yan, Chun-Hua

    2000-05-01

    Magnetization, resistance, and current-voltage (I-V) measurements have been performed in La0.5Sr0.5MnO3 compact prepared by pressing sol-gel nanoparticles (46 nm) at 723 K with a high pressure (4 GPa). The pressed compound orders ferromagnetically at 340 K (TC) and has a substantial drop in the thermomagnetic curve below 158 K (TDP). After undergoing a metal-to-semiconductor transition at 140 K (TMS), the compound reenters into a strong semiconducting state below 60 K, demonstrating a charge localized behavior induced by the small grain rather than the magnetic disorder which is related with the frozen spin clusters below TDP. Instead of showing a feature near TMS, the magnetoresistance (MR) ratio increases almost linearly with decreasing temperature. The large low field MR corresponding to the sharp rise of magnetization is obtained at 5 K and, evidenced as the spin polarized intergrain tunneling (SPIT) effect by the nolinear I-V curve. Although La0.5Sr0.5MnO3 has a relatively high TC, the SPIT MR decays rapidly from 17.6% (5 K, 0.3 T) to 7.6% (150 K, 0.3 T), indicating that if trying to put the low field sensitivity of SPIT MR into application at room temperature, the selected compound having a higher TC seems to be a prerequisite.

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

    NASA Astrophysics Data System (ADS)

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

    2016-05-01

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

  4. 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.

  5. Strain dependent magnetocaloric effect in La0.67Sr0.33MnO3 thin-films

    NASA Astrophysics Data System (ADS)

    Kumar, V. Suresh; Chukka, Rami; Chen, Zuhuang; Yang, Ping; Chen, Lang

    2013-05-01

    The strain dependent magnetocaloric properties of La0.67Sr0.33MnO3 thin films deposited on three different substrates (001) LaAlO3 (LAO), (001) SrTiO3 (STO), and (001) La0.3Sr0.7Al0.65Ta0.35O9 (LSAT) have been investigated under low magnetic fields and around magnetic phase transition temperatures. Compared to bulk samples, we observe a remarkable decrease in the ferromagnetic transition temperature that is close to room temperature, closely matched isothermal magnetic entropy change and relative cooling power values in tensile strained La0.67Sr0.33MnO3 films. The epitaxial strain plays a significant role in tuning the peak position of isothermal magnetic entropy change towards room temperature with improved cooling capacity.

  6. 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

  7. Tunnelling anisotropic magnetoresistance at La0.67Sr0.33MnO3-graphene interfaces

    NASA Astrophysics Data System (ADS)

    Phillips, L. C.; Lombardo, A.; Ghidini, M.; Yan, W.; Kar-Narayan, S.; Hämäläinen, S. J.; Barbone, M.; Milana, S.; van Dijken, S.; Ferrari, A. C.; Mathur, N. D.

    2016-03-01

    Using ferromagnetic La0.67Sr0.33MnO3 electrodes bridged by single-layer graphene, we observe magnetoresistive changes of ˜32-35 MΩ at 5 K. Magneto-optical Kerr effect microscopy at the same temperature reveals that the magnetoresistance arises from in-plane reorientations of electrode magnetization, evidencing tunnelling anisotropic magnetoresistance at the La0.67Sr0.33MnO3-graphene interfaces. Large resistance switching without spin transport through the non-magnetic channel could be attractive for graphene-based magnetic-sensing applications.

  8. 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.

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

    PubMed

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

    2015-11-01

    The spectroscopic properties of trivalent samarium doped Sr0.5Ca0.5TiO3 perovskite phosphor material (Sr0.5Ca0.5TiO3:xSm(3+), x=0.05, 0.1, 0.5, 1, 1.5) synthesized by the solid state method have been studied. The X-Ray Diffraction profile confirms the orthorhombic perovskite Sr0.5Ca0.5TiO3 structure of the prepared samples. The SEM study reveals the surface morphology. The Judd-Ofelt intensity parameters were calculated for 0.5 wt% Sm(3+) doped Sr0.5Ca0.5TiO3. Transition probabilities, branching ratios and radiative lifetime were evaluated by using Judd-Ofelt analysis. The emission spectra under 405 nm excitation shows five emission peaks at 564 nm, 599 nm, 645 nm, 707 nm and 776 nm corresponding to the transitions (4)G5/2→(6)Hj (j=5/2, 7/2, 9/2, 11/2 and 13/2) respectively. The higher values of branching ratio and stimulated emission cross-section for (4)G5/2→(6)H7/2 transition of Sr0.5Ca0.5TiO3:0.5 wt% Sm(3+) shows its suitability in the field of visible lasers and optical fiber amplifiers. The experimental lifetimes of Sm(3+) doped samples were estimated using the decay curves corresponding to (4)G5/2→(6)H7/2 transition upon 405 nm excitation. Concentration dependence on emission intensity and experimental lifetime were also studied. From the CIE diagram we can see that as the concentration of Sm(3+) ions increases from 0.05 wt% to 1.5 wt% the CIE color co-ordinates changes from greenish yellow to yellowish orange. PMID:26057096

  10. 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.

  11. Magnetocaloric effect in La 0.67Sr 0.33MnO 3 manganite above room temperature

    NASA Astrophysics Data System (ADS)

    Rostamnejadi, A.; Venkatesan, M.; Kameli, P.; Salamati, H.; Coey, J. M. D.

    2011-08-01

    The La0.67Sr0.33MnO3 composition prepared by sol-gel synthesis was studied by dc magnetization measurements. A large magnetocaloric effect was inferred over a wide range of temperature around the second-order paramagnetic-ferromagnetic transition. The change of magnetic entropy increases monotonically with increasing magnetic field and reaches the value of 5.15 J/kg K at 370 K for Δμ0H=5 T. The corresponding adiabatic temperature change is 3.3 K. The changes in magnetic entropy and the adiabatic temperature are also significant at moderate magnetic fields. The magnetic field induced change of the specific heat varies with temperature and has maximum variation near the paramagnetic-ferromagnetic transition. The obtained results show that La0.67Sr0.33MnO3 could be considered as a potential candidate for magnetic refrigeration applications above room temperature.

  12. Pressure-induced reemergence of superconductivity in topological insulator Sr0.065Bi2Se3

    NASA Astrophysics Data System (ADS)

    Zhou, Yonghui; Chen, Xuliang; Zhang, Ranran; Shao, Jifeng; Wang, Xuefei; An, Chao; Zhou, Ying; Park, Changyong; Tong, Wei; Pi, Li; Yang, Zhaorong; Zhang, Changjin; Zhang, Yuheng

    2016-04-01

    The recently discovered SrxBi2Se3 superconductor provides an alternative and ideal material base for investigating possible topological superconductivity. Here, we report that in Sr0.065Bi2Se3 , the ambient superconducting phase is gradually depressed upon the application of external pressure. At high pressure, a second superconducting phase emerges at above 6 GPa, with a maximum Tc value of ˜8.3 K. The joint investigations of the high-pressure synchrotron x-ray diffraction and electrical transport properties reveal that the reemergence of superconductivity in Sr0.065Bi2Se3 is closely related to the structural phase transition from an ambient rhombohedral phase to a high-pressure monoclinic phase around 6 GPa, and further to another high-pressure tetragonal phase above 25 GPa.

  13. Interrelation between Structure Magnetic Properties in La0.5Sr0.5CoO3

    SciTech Connect

    Biegalski, Michael D; Takamura, Y; Mehta, A; Gai, Zheng; Kalinin, Sergei; Ambaye, Hailemariam; Lauter, Valeria; He, Jun; Kim, Young Min; Borisevich, Albina Y; Siemons, Wolter; Christen, Hans M

    2014-01-01

    Differing anisotropic strain induced from the underlying substrates not only control the long-range structural symmetries in La0.5Sr0.5CoO3 but also impact the magnetic properties of these epitaxial thin films. The two dominant structural distortions: oxygen octahedral tilts and epitaxial strain, however, have complex and non-intuitive effects on the splitting of the t2g states and consequently on magnetization.

  14. Critical behavior and magnetic relaxation dynamics of Nd0.4Sr0.6MnO3 nanoparticles

    NASA Astrophysics Data System (ADS)

    Kundu, S.; Nath, T. K.

    2013-07-01

    Detailed DC and AC magnetic properties of chemically synthesized Nd0.4Sr0.6MnO3 with different particle size (down to 27 nm) have been studied in details. We have found ferromagnetic state in the nanoparticles, whereas the bulk Nd0.4Sr0.6MnO3 is known to be an A-type antiferromagnet. A Griffiths-like phase has also been identified in the nanoparticles. Further, critical behaviour of the nanoparticles has been studied around the second-order ferromagnetic-paramagnetic transition region (|(T-T C)/T C| ⩽ 0.04) in terms of modified Arrott plot, Kouvel-Fisher plot and critical isotherm analysis. The estimated critical exponents (β, γ, δ) are quite different from those predicted according to three-dimensional mean-field, Heisenberg and Ising models. This signifies a quite unusual nature of the size-induced ferromagnetic state in Nd0.4Sr0.6MnO3. The nanoparticles are found to be interacting and do not behave like ideal superparamagnet. Interestingly, we find spin glass like slow relaxation of magnetization, aging and memory effect in the nanometric samples. These phenomena have been attributed to very broad distribution of relaxation time as well as to inter-particle interaction. Experimentally, we have found out that the dynamics of the nanoparticle systems can be best described by hierarchical model of spin glasses.

  15. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2016-08-01

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

  17. Microwave properties of Ba0.5Sr0.5TiO3 thin film coplanar phase shifters

    NASA Astrophysics Data System (ADS)

    Suherman, P. M.; Jackson, T. J.; Tse, Y. Y.; Jones, I. P.; Chakalova, R. I.; Lancaster, M. J.; Porch, A.

    2006-05-01

    Coplanar waveguide transmission lines have been used to show that the temperature dependent properties of Ba0.5Sr0.5TiO3 thin films used for microwave phase shifters in the frequency range 45 MHz-50 GHz are correlated strongly with the microstructure of the films. The highest tunability and figure of merit of the phase shifters were obtained for films with the narrowest ferroelectric-paraelectric phase transition range, lowest mosaic spread, and widest columnar microstructure. The study also showed that the operating temperature plays an important role in achieving the optimum phase shift for microwave applications.

  18. 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.

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

    PubMed

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

    2008-12-12

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

  20. Effect of injected spins with different polarized orientations on the vortex phase transition in La0.7Sr0.3MnO3/La1.85Sr0.15CuO4 heterostructure

    NASA Astrophysics Data System (ADS)

    Zhang, M. J.; Teng, M. L.; Hao, F. X.; Yin, Y. W.; Zeng, Z.; Li, X. G.

    2015-05-01

    The current-voltage (I-V) characteristics with spin injection were investigated for the epitaxial La0.7Sr0.3MnO3/La1.85Sr0.15CuO4 heterostructure rotated from H//c to H//ab in magnetic fields up to 14 T. It is found that all the I-V curves in various magnetic fields can be scaled with a three dimensional (3D) vortex glass model, and the spin injection can induce a better 3D scaling behavior, which is closely related to the decrease of the anisotropy parameter. A vortex phase diagram for the evolution of vortex glass transition field (Hg) and upper critical field (Hc2) indicates that both Hg and Hc2 are suppressed by spin injection, and this effect becomes more obvious in the case of H//ab, which probably originates from the different suppression on the superconducting pairing strength by different injected spins' orientations.

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

    DOE PAGESBeta

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

    2015-10-06

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

  2. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2016-04-01

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

  4. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2016-04-01

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

  6. 139La NMR investigation in underdoped La1.93Sr0.07CuO4

    NASA Astrophysics Data System (ADS)

    Baek, S.-H.; Erb, A.; Büchner, B.; Grafe, H.-J.

    2012-05-01

    We report 139La and 63Cu nuclear magnetic and quadrupole resonance (NMR/NQR) studies in an underdoped La1.93Sr0.07CuO4 single crystal, focusing on the 139La NMR in the normal state. We demonstrate that the local structural distortions in the low-temperature orthorhombic structure cause the tilting of the direction of the electric field gradient (EFG) at the nuclei from the c axis, resulting in two NMR central transition spectra at both the 139La and 63Cu nuclei in an external field. Taking into account the tilt angle of the EFG, the temperature dependence of the 139La spectra allowed us to determine the 139La Knight shift and the structural order parameter. The angle and temperature dependence of the 139La spectrum is in perfect agreement with the macroscopic average structure and proves a displacive transition. The 139La nuclear spin-lattice relaxation rates, T1-1, suggest that La1.93Sr0.07CuO4 undergoes a gradual change to a temperature-independent paramagnetic regime in the high-temperature region. Both the spectra and T1-1 of the 139La as a function of temperature reveal a sharp anomaly around TS=387(1) K, implying a first-order-like structural transition, and a dramatic change below ˜70 K arising from collective glassy spin freezing.

  7. Enhanced refrigeration capacity and magnetic entropy change in La0.55Ce0.15Sr0.3MnO3 manganite

    NASA Astrophysics Data System (ADS)

    Anwar, M. S.; Koo, Bon Heun

    2015-07-01

    The temperature dependent of the isothermal magnetic entropy change, Δ S M ( T), and the field dependence of the refrigeration capacity, RC, have been investigated in La0.7- x Ce x Sr0.30MnO3 ( x = 0.0 and 0.15). An enhanced RC and Δ S M ( T) were observed in La0.55Ce0.15Sr0.30MnO3. Under a magnetic field change of 2 T, the maximum improvement of 20% of Δ S M ( T) and 40% of RC, in comparison with La0.7Sr0.30MnO3, was observed. Moreover, Curie temperature of the La0.7Sr0.30MnO3 can tuned by adjusting the Ce concentration and makes this attractive for magnetic refrigeration at desired temperature. [Figure not available: see fulltext.

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

    PubMed

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

    2010-07-01

    Ba(0.6)Sr(0.4)TiO(3)-Mg(2)SiO(4)-MgO composite ceramics were prepared by a solid-state reaction method and their dielectric tunable characteristics were investigated for the potential application as microwave tunable materials. The addition of Mg(2)SiO(4)-MgO into Ba(0.6)Sr(0.4)TiO(3) forms ferroelectric (Ba(0.6)Sr(0.4)TiO(3))-dielectric (Mg(2)SiO(4)-MgO) composites and shifts the Curie temperature to a lower temperature. The dielectric constant and loss tangent of Ba(0.6)Sr(0.4)TiO(3)-Mg(2)Si(O4)- MgO composites have been decreased and the overall tunability is maintained at a sufficiently high level. The microwave dielectric properties of Ba(0.6)Sr(0.4)TiO(3)-Mg(2)Si(O4)-MgO composites were evaluated. Ba(0.6)Sr(0.4)TiO(3)-Mg(2)SiO(4)-MgO composites have tunability of 9.2 to 10.5% at 100 kHz under 2 kV/mm, indicating that it is a promising candidate material for tunable microwave applications requiring a low dielectric constant. PMID:20639146

  9. Vortex glass melting in single crystal La 1.825Sr 0.075CuO 4

    NASA Astrophysics Data System (ADS)

    Herbsommer, J. A.; Luzuriaga, J.; Cheong, S.-W.

    1996-02-01

    The vortex phase diagram in single crystalline La 1.85Sr 0.075CuO 4 has been studied using an AC-susceptibility technique. A peak in the out-of-phase ( χ“) component of the susceptibility indicates a transition from a pinned flux lattice (FLL) to an unpinned one. This peak is frequency dependent for all the values of the magnetic field measured (0.01 to 4 T), and this, as well as the general behavior found in the cuprates, has prompted us to interpret our data as evidence for a vortex-glass to liquid transition in the FLL. The activation energies obtained can be fitted to a theory developed by Vinokur et al. Measurements with the magnetic field at an angle with the Cu-O planes may also be understood qualitatively within this framework.

  10. Study of La0.9Sr0.1MnO3 manganite at different temperature

    NASA Astrophysics Data System (ADS)

    Patil, Swapnilkumar S.; Jha, Prafulla K.; Bhargava, Parag

    2015-05-01

    In this paper, the effect of sintering temperature on the structural properties of Sr doped lanthanum manganites is studied. The Sr doped manganites are synthesized using solid state reaction method. The structural properties of the sintered powders are examined by X-ray diffraction. The La0.9Sr0.1MnO3 powder samples exhibit a dominant peak along with increased peak intensity corresponding to the (104), (202), (204) reflections and some new peaks also appeared along (116),(036) and (0210) reflections compared to first sintering temperature (1250°C). This confirms a more polycrystalline nature of the powder at higher sintering temperature. The crystallite size varies between 45 nm to 50 nm. For relative study, the calculated average crystallite size and lattice parameters are noted in tabulated form.

  11. Magnetocaloric effect in epitaxial La0.56Sr0.44MnO3 alloy and digital heterostructures

    NASA Astrophysics Data System (ADS)

    Belyea, Dustin D.; Santos, Tiffany S.; Miller, Casey W.

    2012-04-01

    This work investigates the magnetocaloric effect of two epitaxial manganite heterostructures, one being a single layer La0.56Sr0.44MnO3 alloy with randomly distributed La and Sr cations, the other a digitally synthesized superlattice of LaMnO3 and SrMnO3 fabricated to be compositionally identical to the alloy. The magnetic entropy change and relative cooling power were larger for the alloy than the superlattice, though both are suppressed relative to bulk materials. These results indicate that disorder of the A-site cation species in the perovskite structure may play a crucial role in defining the magnetocaloric effect in complex oxide materials.

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

    NASA Astrophysics Data System (ADS)

    Yahyaoui, Samia; Diep, H. T.

    2016-09-01

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

  13. Thermal gradient induced flexoelectric effects in bulk Ba0.67Sr0.33TiO3

    NASA Astrophysics Data System (ADS)

    Kim, Taeyang; Huang, Wenbin; Huang, Shujin; Jiang, Xiaoning

    2016-05-01

    Flexoelectric effect, denoting electric field gradient induced mechanical strain or mechanical strain gradient induced electric polarization, is a universal phenomenon in all dielectrics. Although research on the topic of flexoelectricity under stress fields and electric fields has advanced significantly, information regarding the phenomenon under thermal fields is rather limited. In this letter, the flexoelectricity field of Ba0.67Sr0.33TiO3 (BST) was investigated by generating temperature gradients along the lengths of samples with symmetric geometry. An electric field gradient induced by a thermal gradient was analyzed based on the temperature-dependent dielectric property of BST. The strain was then experimentally verified due to the electric field gradient. Experimental results suggest converse flexoelectric effect of BST samples with symmetric geometry in a thermal field. This result was not only consistent with the theoretical prediction, but it also followed the scaling effect of flexoelectricity.

  14. Large magnetocaloric effect in single crystal Pr0.63Sr0.37MnO3

    NASA Astrophysics Data System (ADS)

    Phan, Manh-Huong; Peng, Hua-Xin; Yu, Seong-Cho

    2005-05-01

    This article reports the magnetocaloric effect in a single crystal Pr0.63Sr0.37MnO3, which undergoes a very sharp ferromagnetic-to-paramagnetic phase transition at ˜300K. A large magnetic entropy change of 8.52J/kgK and a large adiabatic temperature change of 5.65K for an applied field change of 50kOe were observed around 300K; this allows water to be used as a heat transfer fluid in the room-temperature magnetic refrigeration regime. The distribution of entropy change (ΔSM) was found to be very uniform and which is desirable for an Ericson-cycle magnetic refrigerator. The large magnetic entropy change induced by a relatively low magnetic field change is beneficial for household application.

  15. Strain modulated large magnetocaloric effect in Sm0.55Sr0.45MnO3 epitaxial films

    NASA Astrophysics Data System (ADS)

    Giri, S. K.; Dasgupta, Papri; Poddar, A.; Sahoo, R. C.; Paladhi, D.; Nath, T. K.

    2015-01-01

    Epitaxial Sm0.55Sr0.45MnO3 thin films were deposited on LAO (001), LSAT (001), and STO (001) single crystalline substrates by pulsed laser deposition technique to investigate the correlation between the substrate induced film lattice strain and magnetocaloric effect (MCE). The film on LAO substrate (S_LAO), which is under compressive strain, undergoes ferromagnetic → paramagnetic transition at TC ˜ 165 K. The films on STO (S_STO) and LSAT (S_LSAT) substrates are under tensile strain and have TC ˜ 120 K and 130 K, respectively. At T < TC, the zero field cooled and field cooled magnetization curves of all the films show huge bifurcation. In case of S_STO and S_LSAT films, hysteresis is also observed between field cooled cooling and warming cycle in magnetization versus temperature measurement at low magnetic field similar to first order-like magnetic phase transition. No signature of first order magnetic phase transition has been observed in the case of S_LAO film. Most interestingly, both normal (i.e., negative ΔSM) and inverse (i.e., positive ΔSM) MCE around TC and above Tp, respectively, for S_STO and S_LSAT films have been observed with maximum value of MCE ˜ 10 J kg-1 K-1. The S_STO film also exhibits a large relative cooling power of 142 J/kg for a magnetic field change of 1 T. Our findings of substrate-induced strain modulated large MCE in epitaxial Sm0.55Sr0.45MnO3 films have been well explained through the substrate induced film lattice strain, and it may be useful for active magnetic refrigerant materials.

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

    PubMed

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

    2015-04-01

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

  17. 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.

  18. Synthesis of Sr0.9K0.1FeO3-δ electrocatalysts by mechanical activation

    NASA Astrophysics Data System (ADS)

    Monteiro, J. F.; Waerenborgh, J. C.; Kovalevsky, A. V.; Yaremchenko, A. A.; Frade, J. R.

    2013-02-01

    Potassium-substituted SrFeO3-δ for possible application as oxygen evolution electrode in alkaline or molten salt media was prepared by mechanical activation and characterized by X-ray diffraction, dilatometric and thermogravimetric analysis, Mössbauer spectroscopy, and electrical conductivity measurements. Room temperature mechanical activation of a mixture of oxide precursors with subsequent thermal treatments at 700-900 °C results in the formation of Sr0.9K0.1FeO3-δ with tetragonal perovskite-like structure. Such allows to decrease the synthesis temperature, if compared to the conventional solid-state route, and to prevent possible volatilization of potassium. The results of Mössbauer spectroscopy studies indicate that the oxygen nonstoichiometry in the samples annealed in air at 900-1100 °C with subsequent rapid cooling vary in the range δ=0.30-0.32. The electrical conductivity in air exhibits a metal-like behaviour at temperatures above 400 °C and semiconductor behaviour in the low-temperature range, reaching 13-30 S/cm under prospective operation conditions for alkaline electrolyzers (≤90 °C).

  19. Critical behavior in single-crystalline La0.67Sr0.33CoO3

    NASA Astrophysics Data System (ADS)

    Khan, N.; Midya, A.; Mydeen, K.; Mandal, P.; Loidl, A.; Prabhakaran, D.

    2010-08-01

    The critical behavior of La0.67Sr0.33CoO3 single crystal has been investigated from the bulk magnetization measurements around the Curie temperature (TC) . The detailed analysis of the magnetization indicates the occurrence of a continuous ferromagnetic to paramagnetic phase transition at 223.0 K. The critical exponents β=0.361±0.007 , γ=1.31±0.001 , and δ=4.64±0.01 characterizing this second order phase transition, have been estimated using different techniques such as the Kouvel-Fisher plot, the Arrott-Noaks plot, and critical isotherm analysis. With these values of TC , β , and γ , one can scale the magnetization below and above TC following a single equation of state. The consistency in the values of the critical exponents obtained from different methods and the well-obeyed scaling behavior confirm that the calculated exponents are unambiguous and purely intrinsic to the system. These values of the exponents match well with those theoretically predicted for the three-dimensional Heisenberg model with nearest-neighbor interaction.

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

    NASA Astrophysics Data System (ADS)

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

    2016-05-01

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

  1. Dielectric dynamics of the polycrystalline Ba0.5Sr0.5TiO3 thin films

    NASA Astrophysics Data System (ADS)

    Pečnik, Tanja; Eršte, Andreja; Matavž, Aleksander; Bobnar, Vid; Ivanov, Maksim; Banys, Juras; Xiang, Feng; Wang, Hong; Malič, Barbara; Glinšek, Sebastjan

    2016-05-01

    Polycrystalline Ba0.5Sr0.5TiO3 films, with thicknesses between 90 and 600 nm, were prepared on alumina substrates at 900 °C by chemical solution deposition (CSD) and a dielectric spectroscopy investigation of the in-plane properties was performed. The 5-kHz permittivity ε‧ shows a non-monotonic thickness dependence, reaching 1230 at room temperature for the 310-nm-thick film, whose grain size is ∼75 nm. Its 15-GHz-value and losses are 1105 and 0.05, respectively. The temperature of the permittivity maximum T max at 5 kHz decreases with increasing thickness from 277 to 250 K for the 170- and 600-nm-thick films, respectively, which has been linked to the residual biaxial stress. A hysteresis is observed in the permittivity ε‧-electric field E DC characteristics in all the films up to ∼50 K above T max . Frequency dispersion in which permittivity decreases with increasing frequency is present below T max in films thicker than 90 nm. The high permittivity values of the thinnest films, which are among the highest reported in the (Ba,Sr)TiO3 films with grain sizes below 75 nm, are a direct proof of the optimized CSD processing conditions.

  2. 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

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

    NASA Astrophysics Data System (ADS)

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

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

  4. Structural and magnetic properties of Y0.33Sr0.67CoO2.79

    NASA Astrophysics Data System (ADS)

    Goossens, D. J.; Wilson, K. F.; James, M.; Studer, A. J.; Wang, X. L.

    2004-04-01

    The perovskite-based oxide Y0.33Sr0.67CoO2.79 has been magnetically and structurally characterized. The material shows a unit cell of 2×2×4 simple perovskite cubes with space group I4/mmm. This is a different structure to that observed in the much-studied (La,Sr)CoO3 oxides. Oxygen stoichiometry is established through thermogravimetric analysis and correlated with ac and dc magnetic measurements and magnetic neutron diffraction. Hysteresis with field and temperature is observed in the dc magnetization measurements, yet the absence of an imaginary component in the ac susceptibility suggests a time-independent cause for these effects such as the presence of independently ordering ferromagnetic regions due to compositional inhomogeneities within the (single-phase) sample. Rietveld magnetic refinements suggest that the Co moments are arranged antiferromagnetically below 320 K, with the ferromagnetic regions existing within the long-range ordered antiferromagnetic matrix. The staggered moments are (anti)parallel with the c axis and of magnitude 2μB, a moment most typical of intermediate spin Co3+. The material does not enter a spin glass or cluster glass phase, but appears to undergo a broad spin-state transition below 100 K.

  5. Tunable magnetic and magnetocaloric properties of La0.6Sr0.4MnO3 nanoparticles

    NASA Astrophysics Data System (ADS)

    Ehsani, M. H.; Kameli, P.; Ghazi, M. E.; Razavi, F. S.; Taheri, M.

    2013-12-01

    Nanoparticles of La0.6Sr0.4MnO3 with different particle sizes are synthesized by the nitrate-complex auto-ignition method. The structural and magnetic properties of the samples are investigated by X-Ray diffraction (XRD), Fourier transform infra-red (FT-IR) spectroscopy, transmission electron microscopy (TEM), and DC magnetization measurements. The XRD study coupled with the Rietveld refinement shows that all samples crystallize in a rhombohedral structure with the space group of R-3 C. The FT-IR spectroscopy and TEM images indicate formation of the perovskite structure with the average sizes of 20, 40, and 100 nm for the samples sintered at 700, 800, and 1100 °C, respectively. The DC magnetization measurements confirm tuning of the magnetic properties due to the particle size effects, e.g., reduction in the ferromagnetic moment and increase in the surface spin disorder by decreasing the particle size. The magnetocaloric effect (MCE) study based on isothermal magnetization vs. filed measurements in all samples reveals a relatively large MCE around the Curie temperature of the samples. The peak around the Curie temperature gradually broadens with reduction of the particle size. The data obtained show that although variations in the magnetic entropy and adiabatic temperature decrease by lowering the particle size, variation in the relative cooling power values are the same for all samples. These results make this material a proper candidate in the magnetic refrigerator application above room temperature at moderate fields.

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

    NASA Astrophysics Data System (ADS)

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

    2015-03-01

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

  7. Reversible aging behavior of La0.8Sr0.2MnO3 electrodes at open circuit

    SciTech Connect

    Abernathy, H.; Finklea, H.; Mebane, D.; Chen, X.; Gerdes, K.; Salazar, M.

    2012-01-01

    La0.8Sr0.2MnO3 (LSM) electrodes on yttria-stabilized zirconia (YSZ) electrolytes were characterized at open circuit by impedance spectroscopy. An initial irreversible change in the polarization resistance is observed for cells aged with no prior current activation. After the initial break-in, the polarization resistance rises with time at 700 #1;C and decays at 800 #1;C, reversibly, over repeated temperature cycles. The initial irreversible break-in and subsequent reversible cycling behavior suggests multiple processes happening within the time and temperatures measured. The authors propose that these processes are (1) changes in the wetting behavior of the LSM on the YSZ and (2) the reversible segregation/desegregation of cations within LSM. Between 700 #1;C and 800 #1;C, there is a transition temperature at which the segregation behavior of cations to the cathode surface changes. These measurable changes in the impedance behavior of LSM indicate that cation segregation, while considered by some to be part of the cathode activation process, may be dictated by thermodynamic factors, and thus not strictly dependent on the passage of current through the cathode.

  8. Low field anisotropic colossal magnetoresistance in Sm0.53Sr0.47MnO3 thin films

    NASA Astrophysics Data System (ADS)

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

    2011-12-01

    Sm0.53Sr0.47MnO3 (SSMO) thin films (thicknesses ˜200 nm) were deposited by on-axis dc magnetron sputtering on the single crystal LSAT (001) substrates. These films are oriented along the out of plane c-direction. The ferromagnetic and insulator-metal transition occurs at TC ˜ 96 and TIM ˜ 91 K, respectively. The magnetization easy axis is observed to lie in the plane of the film while the magnetic hard axis is found to be along the normal to this. The magnetotransport of the SSMO films, which was measured as a function of angle (θ) between the magnetic field (H) and plane of the film, shows colossal anisotropy. Magnetoresistance (MR) decreases drastically as θ increases from 0° (H//easy axis) to 90° (H//hard axis). The out-of-plane anisotropic MR is as high as 88% at H = 3.6 kOe and 78 K. The colossal anisotropy has been explained in terms of the magnetic anisotropies at play and the magnetic domain motion in applied magnetic field.

  9. 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

  10. Spectroellipsometric studies of sol-gel derived Sr0.6Ba0.4Nb2O6 films

    NASA Astrophysics Data System (ADS)

    Ho, Melanie M. T.; Tang, T. B.; Mak, C. L.; Pang, G. K. H.; Chan, K. Y.; Wong, K. H.

    2006-10-01

    Sr0.6Ba0.4Nb2O6 (SBN) films have been fabricated on (001)Si substrates by a sol-gel technique. The annealing process was carried out in air at various temperatures ranging from 200to700°C. Studies using x-ray diffractometry, high resolution transmission electron microscopy, and scanning electron microscopy showed that polycrystalline films, with a grain size of about 100nm, were obtained only for annealing temperatures ⩾600°C. The optical properties of these sol-gel derived SBN films were studied by spectroscopic ellipsometry (SE). In the analysis of the measured SE spectra, a triple-layer Lorentz model has been developed and used to deduce the optical properties of the SBN films. Our systematic SE measurements revealed that the refractive indices of the SBN films increase with the annealing temperature. This increase is more pronounced at around the crystallization temperature, i.e., between 500 and 600°C. The extinction coefficients of the films also exhibit a similar trend, showing a zero value for amorphous films and larger values for films annealed at above 600°C. Our results demonstrate that while crystallization helps to raise the refractive index of the film due to film densification, it also promotes scattering by grain boundary, resulting in a larger extinction coefficient.

  11. Critical behavior near the ferromagnetic - paramagnetic phase transition in La0.7Sr0.3MnO3+d nanowires synthesized by hydrothermal method

    NASA Astrophysics Data System (ADS)

    Datta, Subarna; Ghosh, Barnali

    2015-06-01

    We report here the synthesis, characterization and magnetic properties of functional oxide nanowire (NW) of hole doped manganite La0.7Sr0.3MnO3+d (LSMO). The nanowires (NWs) are fabricated by hydrothermal method using autoclave at a temperature of 240°C. Due to size reduction of the NWs the volume of the unit cell decreases ~ 1% with respect to the bulk La0.7Sr0.3MnO3. The LSMO NWs have a ferromagnetic - paramagnetic transition temperature or Curie temperature (TC) at 311 K and it shows second order phase transition at TC as seen in bulk.

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

    DOE PAGESBeta

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

    2015-12-08

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

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

    PubMed

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

    2016-05-01

    A giant terahertz modulation based on a Ba0.6 Sr0.4 TiO3 -silicon hybrid metamaterial is reported by L. Wu, W. Zhang, and co-workers on page 2610. The proposed nanoscale Ba0.6 Sr0.4 TiO3 (BST) hybrid metamaterial, delivering a transmission contrast of up to ≈79% due to electrically enabled carrier transport between the ferroelectric thin film and silicon substrate, is promising in developing high-performance real world photonic devices for terahertz technology. PMID:27167323

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

    NASA Astrophysics Data System (ADS)

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

    2016-05-01

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

  15. Critical exponents and irreversibility lines of La0.9Sr0.1CoO3 single crystal

    NASA Astrophysics Data System (ADS)

    Khan, N.; Midya, A.; Mandal, P.; Prabhakaran, D.

    2013-05-01

    We have studied the dynamic and static critical behavior of spin glass transition in insulating La0.9Sr0.1CoO3 single crystal by ac susceptibility and dc magnetization measurements in the vicinity of its freezing temperature (Tf). The dynamic scaling analysis of the frequency dependence of ac susceptibility data yields the characteristic time constant τ0=1.6(9)×10-12 s, the dynamic critical exponent zν=9.5(2), and a frequency dependence factor K =ΔTf/Tf(Δlogf)=0.017, indicating that the sample enters into a canonical spin-glass phase below Tf = 34.8(2) K. The scaling analysis of non-linear magnetization in the vicinity of Tf through the static scaling hypothesis yields critical exponents β = 0.89(1) and γ = 2.9(1), which match well with that observed for well known three-dimensional (3D) Heisenberg spin glasses. From the longitudinal component of zero-field-cooled and field-cooled magnetization measurement, we have constructed the H-T phase diagram which represents the field evolution of two characteristic temperatures: the upper one, Tw(H), indicates the onset of spin freezing in a uniform external field H, while the lower one, Ts(H), marks the onset of strong irreversibility of the frozen state. The low field Ts(H) follows the critical line suggested by d'Almeida-Thouless model for canonical spin glass, whereas the Tw(H) exhibits a re-entrant behavior with a maximum in the Tw(H) at a nonzero field above which it follows the Gabay-Toulouse (GT) critical line which is a characteristic of Heisenberg spin glass. The reentrant behavior of the GT line resembles that predicted theoretically for n-component vector spin glasses in the presence of a uniaxial anisotropy field.

  16. Effect of sol-gel method on structural and electron magnetic resonance properties of Pr0.6Sr0.4MnO3 manganite

    NASA Astrophysics Data System (ADS)

    Thaljaoui, R.; Boujelben, W.; Pękała, M.; Szydłowska, J.; Cheikhrouhou, A.

    2012-06-01

    Structural and electron magnetic resonance studies in a broad temperature range are reported for Pr0.6Sr0.4MnO3 manganite synthesized by sol-gel method. Temperature dependence of magnetic resonance spectra is analyzed in the paramagnetic state and compared to similar systems. Using the temperature variation of signal intensity the activation energy is calculated.

  17. Reversible control of magnetism in La0.67Sr0.33MnO3 through chemically-induced oxygen migration

    NASA Astrophysics Data System (ADS)

    Grutter, A. J.; Gilbert, D. A.; Alaan, U. S.; Arenholz, E.; Maranville, B. B.; Borchers, J. A.; Suzuki, Y.; Liu, Kai; Kirby, B. J.

    2016-02-01

    We demonstrate reversible control of magnetization and anisotropy in La0.67Sr0.33MnO3 films through interfacial oxygen migration. Gd metal capping layers deposited onto La0.67Sr0.33MnO3 leach oxygen from the film through a solid-state redox reaction to form porous Gd2O3. X-ray absorption and polarized neutron reflectometry measurements show Mn valence alterations consistent with high oxygen vacancy concentrations, resulting in suppressed magnetization and increased coercive fields. Effects of the oxygen migration are observed both at the interface and also throughout the majority of a 40 nm thick film, suggesting extensive diffusion of oxygen vacancies. After Gd-capped La0.67Sr0.33MnO3 is exposed to atmospheric oxygen for a prolonged period of time, oxygen diffuses through the Gd2O3 layer and the magnetization of the La0.67Sr0.33MnO3 returns to the uncapped value. These findings showcase perovskite heterostructures as ideal candidates for developing functional interfaces through chemically-induced oxygen migration.

  18. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2016-06-01

    The aim of this paper is to study performance enhancement of the dielectric properties of polycrystalline Ba_{0.8} Sr_{0.2} Ti_(1 - x) Snx O3, with 0 ≤ x ≤ 0.2 . The material was characterized by x-ray diffraction, scanning electron microscopy (SEM), micro-Raman spectroscopy and impedance spectroscopy technique. The results have been analyzed by studying the effects of substituting Sn4+ for Ti4+. The observed diffraction peaks have been indexed to a cubic structure with space group Pm3m. The calculated lattice parameters increase from 3.9834 Å to 4.0091 Å with increasing Sn concentration. The SEM micrographs show that with increasing Sn an increase of the grain size from x = 0 up to x = 0.15 was observed. The dielectric measurements confirm the relaxor behavior of all the concentrations of Ba_{0.8} Sr_{0.2} Ti_(1 - x) Sn}x O3 compounds. The Ba_{0.8} Sr_{0.2} Ti_{0.95} Sn_{0.05} O3 compound presents the most interesting properties, namely high dielectric constant value (ɛ^'(T_{{m}} ) = 5017 ) and a Curie temperature slightly above room temperature (T_{{c}} = 317 K) . An important dielectric constant value persists for a wide range of temperatures around room temperature. This is considered as an advantage of the Ba_{0.8} Sr_{0.2} Ti_{0.95} Sn_{0.05} O3 relaxor ferroelectrics.

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

    PubMed

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

    2016-02-01

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

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

    PubMed

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

    2016-10-01

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

  2. Electric polarization of Sr0.5Ba0.5MnO3: a multiferroic Mott insulator

    NASA Astrophysics Data System (ADS)

    Nourafkan, Reza

    2015-03-01

    Multiferroics, materials which display simultaneous magnetic and ferroelectric orders, are interesting both for their rich physics and for their promising practical applications. The search for multiferroic materials with strong-magnetoelectric coupling is challenging and requires an understanding of how the magnetic order, or more specifically the correlations, influence the electric polarization and vice versa. A calculations of the electric polarization in the paramagnetic (PM) insulating phase of multiferroics is essential to address this mutual influence. Ab inito calculations of the electric polarization are based on the modern theory of polarization, which is a single-electron theory. Thus, a correlation driven insulating state is beyond the scope of this approach. Here we show that combining correlated band structure calculations (DFT+DMFT) with a formula for the electric polarization of interacting insulators, expressed in terms of the full Green and vertex functions, allows for the first time to reliably calculate the polarization in the PM phase. We focus on the Mott insulator Sr0.5Ba0.5MnO3, in which both magnetic and ferroelectric instabilities are related to the Mn ions. We predict a ferroelectric polarization of ~= 16 . 5 μC / cm2 in the high temperature paramagnetic phase and recover the measured value of ~= 13 . 3 μC / cm2 in the low temperature antiferromagnetic phase. Our calculations reveal that the the driving force behind the ferroelectric distortion comes from the tendency of Mn eg states to establish a stronger covalency with the surrounding oxygens. This covalency is reduced by correlations, in particular by Hund coupling. On the other hand, the half-filled Mn t2 g orbitals give rise to the magnetic ordering which decreases the ionic displacement, hence its contribution to the polarization. For fixed ionic displacement, the magnetic order also slightly decreases the electronic contribution to the electric polarization by partially

  3. 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.

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

    NASA Astrophysics Data System (ADS)

    Torija, M. A.; Sharma, M.; Fitzsimmons, M. R.; Varela, M.; Leighton, C.

    2008-07-01

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

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

    PubMed

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

    2015-10-28

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

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

    PubMed

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

    2014-12-01

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

  7. 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.

  8. Single crystalline La0.5Sr0.5MnO3 microcubes as cathode of solid oxide fuel cell

    SciTech Connect

    Mingjia Zhi; Guangwen Zhou; Zhanglian Hong; Jin Wang; Randall Gemmen; Kirk Gerdes; Ayyakkannu Manivannan; Dongling Mae; Nianqiang Wu

    2010-09-13

    The efficiency of solid oxide fuel cells (SOFCs) is heavily dependent on the electrocatalytic activity of the cathode toward the oxygen reduction reaction (ORR). In order to achieve better cathode performance, single crystalline La0.5Sr0.5MnO3 (LSM) microcubes with the {200} facets have been synthesized by the hydrothermal method. It is found that the LSM microcubes exhibit lower polarization resistance than the conventional polycrystalline La0.8Sr0.2MnO3 powder in air from 700 #2;C to 900 #2;C. The ORR activation energy of the LSM microcubes is lower than that of the conventional powder. The ORR kinetics for the microcubes is limited by the charge transfer step while that for the conventional powder is dominated by the oxygen adsorption and dissociation on the cathode surface.

  9. 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.

  10. Dielectric resonance effect with negative permittivity in a La1.5Sr0.5NiO4+ δ ceramic

    NASA Astrophysics Data System (ADS)

    Thanh, Tran Dang; Van Dang, Nguyen; Van Hong, Le; Phan, The-Long; Yu, Seong-Cho

    2014-11-01

    A polycrystalline sample of La1.5Sr0.5NiO4+ δ was prepared by using a solid-state reaction. X-ray diffraction proved the sample to be a single phase with a tetragonal structure (space group: I4/mmm). By using an iodometric titration method to determine the non-stoichiometric oxygen concentration ( δ) in La1.5Sr0.5NiO4+ δ , we found δ = -0.017, which corresponds to a doping level of n h = x + 2 δ = 0.466. Also, a strong increase of the magnetization in the M( T) curve at temperatures below the spin-ordering temperature ( T SO ~ 100 K) was observed. The M( H) curves show very small magnetic moments, which proves the weak ferromagnetic nature of La1.5Sr0.5NiO4+ δ . The dependences of the dielectric constant on the frequency and the temperature, ɛ( ω, T) = ɛ'( ω, T) + iɛ″( ω, T), was investigated in the frequency range of 1-13 MHz. At temperatures around room temperature, the maximum of the real part ( ɛ') was higher than 105. Particularly, an abnormal dependence of the permittivity on frequency was observed. Depending on temperature, a dielectric resonance was observed at about 500 kHz or 8 MHz. Interestingly, we observed the dielectric-resonance effect with a negative permittivity. Such a feature is very similar to that observed in left-handed materials. The fitting of the experimental data for the dielectric constant at frequencies around the resonance frequency to the equations associated with an equivalent RLC series circuit proves that La1.5Sr0.5NiO4+ δ belongs to the class of multiferroic materials.

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

    NASA Astrophysics Data System (ADS)

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

    2016-06-01

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

  12. 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.

  13. Tracing the origin of oxygen for La0.6Sr0.4MnO3 thin film growth by pulsed laser deposition

    NASA Astrophysics Data System (ADS)

    Chen, J.; Döbeli, M.; Stender, D.; Lee, M. M.; Conder, K.; Schneider, C. W.; Wokaun, A.; Lippert, T.

    2016-02-01

    We report on the semi-quantitative analysis of pulsed laser induced plasma species as well as thin film compositions of La0.6Sr0.4MnO3 grown on SrTiO3 substrates under various background pressure regimes using an 18O isotope labelled La0.6Sr0.4MnO3 target. The importance of negative metal-oxygen or positive metal-oxygen ions to influence the final oxygen composition of the thin film is illustrated through the use of mass spectrometry, where the chemical reactions between the laser ablated target species with the oxygen background molecules are directly characterized. We find that the influence of metal-oxygen negative ions is not as important as the metal-oxygen positive ions to the final oxygen composition of the LSMO film, due to their low stability in high background partial pressures. Furthermore, we observe that the oxygen incorporated in La0.6Sr0.4MnO3 thin films coming from the target is ~44%, 29% and 1% at 2  ×  10-3 mbar, 1  ×  10-2 mbar and 2  ×  10-1 mbar, respectively. When growing films at 10-1 mbar on 18O2 exchanged substrates, almost all oxygen originates from the background and almost none from the substrate or target.

  14. Sintering and Mixed Electronic-Ionic Conducting Properties of LA1.9SR0.1NIO4+δ Derived from a Polyaminocarboxylate Complex Precursor

    NASA Astrophysics Data System (ADS)

    Huang, Duan-Ping; Xu, Qing; Zhang, Feng; Chen, Wen; Liu, Han-Xing; Zhou, Jian

    2006-06-01

    La1.9Sr0.1NiO4+δ with a pure K2NiF4 phase was synthesized from a polyaminocarboxylate complex precursor with diethylenetriaminepentaacetic acid (H5DTPA) as ligand, and the effect of sintering temperature on the microstructure and mixed electronic-ionic conducting properties of La1.9Sr0.1NiO4+δ ceramic was investigated in the range of 1400-1600 °C. Homogeneous and fine powder (100-200 nm) with a pure K2NiF4 phase was produced by calcining the complex precursor at 900 °C for 2 h in air. The increase of sintering temperature promoted the microstructural densification. Compared with a gradual increase of grain size with sintering temperature in the range of 1400-1500 °C, there is an exaggerated grain growth in the specimens sintered at 1550 °C and 1600 °C, respectively. Increasing sintering temperature from 1400 °C to 1500 °C resulted in an enhancement of electrical and ionic conducting properties. Further increase of the sintering temperature above 1500 °C declined the electrical and ionic conducting properties. The variation of the mixed conducting properties with sintering temperature was interpreted for the viewpoint of microstructural evolution. With respect to the mixed conducting properties, the preferred sintering temperature was ascertained to be 1500 °C for La1.9Sr0.1NiO4+δ. The specimen sintered at 1500 °C exhibits an electrical conductivity of 86 S/cm and an oxygen ionic conductivity of 3.8×10-2 S/cm at 800 °C.

  15. Application of antiferromagnetic-Fermi-liquid theory to NMR experiments in La1.85Sr0.15CuO4

    NASA Astrophysics Data System (ADS)

    Monien, H.; Monthoux, P.; Pines, D.

    1991-01-01

    NMR experiments on La1.85Sr0.15CuO4 by Kitaoka et al. and Imai et al. are analyzed using the phenomenological antiferromagnetic (AF) Fermi liquid theory of Millis, Monien, and Pines, and the results are compared with those previously obtained for YBa2Cu3O7 and YBa2Cu3O6.63. A one-component model, with hyperfine couplings that are unchanged from those found previously for YBa2Cu3O7 and YBa2Cu3O6.63, and parameters obtained from experiment, provide a quantitative fit to the data. At all temperatures the antiferromagnetic correlations found in La1.85Sr0.15CuO4 are stronger than those found for the Y-Ba-Cu-O samples with the result that the characteristic energy for the antiferromagnetic paramagnons that describe the AF spin dynamics is quite low (Sr0.15CuO4, YBa2Cu3O7, and YBa2Cu3O6.63, and find that it displays a linear temperature dependence for all three materials. Our results support the proposal that the properties of a nearly antiferromagnetic Fermi liquid are genuinely novel, and suggest that both the spin and charge aspects of the normal-state properties of the cuprate oxide superconductors can be quantitatively explained in terms of quasiparticles coupled to antiferromagnetic paramagnons whose characteristic energy scale is

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

    NASA Astrophysics Data System (ADS)

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

    2016-06-01

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

  17. Unexpected luminescence properties of Sr(0.25)Ba(0.75)Si2O2N2:Eu(2+)--a narrow blue emitting oxonitridosilicate with cation ordering.

    PubMed

    Seibald, Markus; Rosenthal, Tobias; Oeckler, Oliver; Fahrnbauer, Felix; Tücks, Andreas; Schmidt, Peter J; Schnick, Wolfgang

    2012-10-15

    Owing to a parity allowed 4f(6)((7)F)5d(1)→4f(7)((8)S(7/2)) transition, powders of the nominal composition Sr(0.25)Ba(0.75)Si(2)O(2)N(2):Eu(2+) (2 mol% Eu(2+)) show surprising intense blue emission (λ(em)=472 nm) when excited by UV to blue radiation. Similarly to other phases in the system Sr(1-x)Ba(x)Si(2)O(2)N(2):Eu(2+), the described compound is a promising phosphor material for pc-LED applications as well. The FWHM of the emission band is 37 nm, representing the smallest value found for blue emitting (oxo)nitridosilicates so far. A combination of electron and X-ray diffraction methods was used to determine the crystal structure of Sr(0.25)Ba(0.75)Si(2)O(2)N(2):Eu(2+). HRTEM images reveal the intergrowth of nanodomains with SrSi(2)O(2)N(2) and BaSi(2)O(2)N(2)-type structures, which leads to pronounced diffuse scattering. Taking into account the intergrowth, the structure of the BaSi(2)O(2)N(2)-type domains was refined on single-crystal diffraction data. In contrast to coplanar metal atom layers which are located between layers of condensed SiON(3)-tetrahedra in pure BaSi(2)O(2)N(2), in Sr(0.25)Ba(0.75)Si(2)O(2)N(2):Eu(2+) corrugated metal atom layers occur. HRTEM image simulations indicate cation ordering in the final structure model, which, in combination with the corrugated metal atom layers, explains the unexpected and excellent luminescence properties. PMID:22968845

  18. Significantly enhanced ferroelectricity and magnetic properties in (Sr0.5Ca0.5)TiO3-modified BiFeO3 ceramics

    NASA Astrophysics Data System (ADS)

    Liu, Juan; Liu, Xiao Qiang; Chen, Xiang Ming

    2015-05-01

    BiFeO3 multiferroic ceramics were modified by introducing (Sr0.5Ca0.5)TiO3 to form solid solutions. The single phase structure was easy to be obtained in Bi1-x(Sr0.5Ca0.5)xFe1-xTixO3 (x = 0.2, 0.25, 0.3, and 0.4) solid solutions. Rietveld refinement of X-ray diffraction data revealed a transition from rhombohedral R3c (x = 0.2, 0.25, and 0.3) to orthorhombic Pnma (x = 0.4). Current density-field (J-E) characteristics indicated that the leakage current density was reduced by three orders of magnitude in Bi1-x(Sr0.5Ca0.5)xFe1-xTixO3 ceramics. Both the ferroelectricity and magnetic properties were significantly enhanced in the present solid solutions. P-E hysteresis loop measurements with dynamic leakage current compensation methods showed the significantly enhanced ferroelectric properties for x = 0.25 and 0.3 and the paraelectric behavior for x = 0.4. The best ferromagnetic characteristics were achieved in the composition of x = 0.25, where the saturated M-H loop was determined with Mr = 34.8 emu/mol. The improvement of ferroelectricity was mainly due to the suppressed leakage current, and the enhanced magnetism originated from the partial substitution of Fe3+ by Ti4+, which destroyed its previous spiral structure to allow the appearance of a macroscopic magnetization.

  19. Structural studies of zirconium doped Ba0.70Sr0.30TiO3 lead free ferroelectric thin films

    NASA Astrophysics Data System (ADS)

    Sharma, Sarita; Ram, Mast; Thakur, Shilpa; Sharma, Hakikat; Negi, N. S.

    2016-05-01

    Ba0.7Sr0.3(ZrxTi1-x)O3(BSZT, x=0,0.05,0.10,0.15,0.20) thin films were prepared by using sol gel method. Structural and microstructural properties were studied by using XRD, Raman Spectroscopy and atomic force microscopy (AFM) respectively. XRD and Raman Spectroscopy show the presence of tetragonal phase in multilayer BSZT thin film. The experimental results demonstrate that structural and microstructural properties of BSZT thin film were significantly dependent on variation of Zr content.

  20. Giant zero field cooled spontaneous exchange bias effect in phase separated La1.5Sr0.5CoMnO6

    NASA Astrophysics Data System (ADS)

    Krishna Murthy, J.; Venimadhav, A.

    2013-12-01

    We report a giant zero field cooled exchange bias (ZEB) effect (˜0.65 T) in La1.5Sr0.5CoMnO6 sample. Magnetic study has revealed a reentrant spin glass ˜90 K, phase separation to spin glass and ferromagnetic phases below 50 K and canted antiferromagnetic transition ˜10 K. A small conventional exchange bias (CEB) is established with the advent of spontaneous phase separation down to 10 K. Giant ZEB and enhanced CEB effects are found only below 10 K and are attributed to the large unidirectional anisotropy at the interface of isothermally field induced ferromagnetic phase and canted antiferromagnetic background.

  1. Strain induced enhanced ferromagnetic behavior in inhomogeneous low doped La0.95Sr0.05MnO3+δ

    NASA Astrophysics Data System (ADS)

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

    2013-03-01

    We report an unusual high-temperature ferromagnetic transition in bulk single-phase nanocrystalline La0.95Sr0.05MnO3+δ, achieved through localized strain and inhomogeneous Sr-doping. Magnetization measurements show a well defined transition at 290 K and a broad one at ˜150 K. HRTEM imaging reveals the strain on the highly crystalline nanometer sized grains and Sr-doping gradients, while oxygen homogeneity at the grain interfaces is confirmed by EELS-spectra. The magnetic behavior, far from the expected bulk phase diagram, shows how local doping and strain can strongly tune the macroscopic properties of a bulk material.

  2. The effect of interface roughness on exchange bias in La0.7Sr0.3MnO3-BiFeO3 heterostructures

    NASA Astrophysics Data System (ADS)

    Vafaee, Mehran; Finizio, Simone; Deniz, Hakan; Hesse, Dietrich; Zabel, Hartmut; Jakob, Gerhard; Kläui, Mathias

    2016-02-01

    We characterized the interfaces of heterostructures with different stack sequences of La0.7Sr0.3MnO3/BiFeO3 (LSMO/BFO) and BFO/LSMO using TEM revealing sharp and rough interfaces, respectively. Magnetometry and magnetoresistance measurements do not show a detectable exchange bias coupling for the multistack with sharp interface. Instead, the heterostructures with rough and chemically intermixed interfaces exhibit a sizable exchange bias coupling. Furthermore, we find a temperature-dependent irreversible magnetization behavior and an exponential decay of coercive and exchange bias fields with temperature suggesting a possible spin-glass-like state at the interface of both stacks.

  3. Elastic Moduli of detwinned orthorhombic optimally doped LSCO (La2-0.16 Sr 0.16 CuO4)

    NASA Astrophysics Data System (ADS)

    Fanelli, Victor; Betts, Jonathan; Migliori, Albert; Suzuki, Yoko; Yan, Jiaqiang

    2010-03-01

    Accurate elastic modulus characterization of the superconducting phase transition (SC) in La2-0.16 Sr 0.16 CuO4 is difficult because the discontinuities in moduli are much smaller than fluctuations from twin boundary motion. Thus detwinning is required for a useful measurement and was achieved using mechanical stress along the tetragonal [110] direction (or equivalently, along the orthorhombic [100] direction) below the orthorhombic phase transition that is well below ambient temperature. Using resonant ultrasound spectroscopy (RUS) on the detwinned monocrystal, the discontinuities and moduli around the SC transition were measured.

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

    NASA Astrophysics Data System (ADS)

    Priolkar, K. R.; Rawat, R.

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

  5. 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.

  6. Sensitive electrochemical detection of glucose based on electrospun La(0.88)Sr(0.12)MnO3 naonofibers modified electrode.

    PubMed

    Xu, Duo; Luo, Liqiang; Ding, Yaping; Xu, Pengyu

    2015-11-15

    Electrochemical detection of glucose in alkaline solution was performed on La0.88Sr0.12MnO3 (LSMO) nanofibers modified carbon paste electrode. Perovskite-type oxide LSMO nanofibers were prepared by an electrospinning and calcination process. The morphologies, structures, and electrochemical behavior of the nanofibers were characterized by scanning electron microscope, energy dispersive spectrometer, X-ray diffraction, Fourier transform infrared spectrum, and cyclic voltammetry. The modified electrode shows excellent electrocatalytic activity toward glucose. Under optimal conditions, the linear response was obtained in the range of 0.05-100 μM with high sensitivity and rapid response. PMID:26297817

  7. Preparation and Characterization of (Ba0.8Sr0.2)TiO3-Al2O3 Composite Oxide for Thin Film Capacitor

    NASA Astrophysics Data System (ADS)

    Jang, Joo-Hee; Kim, Tae-Yoo; Lee, Chang-Hyoung; Zhang, JingJing; Park, Eun-Mi; Park, Chan; Suh, Su-Jeong

    2011-07-01

    Barium strontium titanate-alumina composites were fabricated using a sol-gel and anodizing process for high performance thin film capacitors and the properties of the films were studied. The (Ba0.8Sr0.2)TiO3 (BST) films were formed by spin coating and subsequent annealing at 150-550 °C. The respective annealed films were anodized in a neutral borate solution. The capacitance density increased with increasing annealing temperature up to 450 °C but decreased at 550 °C. The capacitance density was approximately 28.46% higher with the BST coating than without the BST layer.

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

    SciTech Connect

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

    2009-01-01

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

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

    PubMed

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

    2012-08-01

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

  10. Extreme sensitivity of magnetic properties on the synthesis routes in La0.7Sr0.3MnO3

    NASA Astrophysics Data System (ADS)

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

    2016-05-01

    La0.7Sr0.3MnO3 polycrystalline samples have been prepared using different synthesis routes. X-ray Diffraction (XRD) confirms that the samples are of single phase with R-3c space group. The surface morphology and particle size has been observed using Field Emission Scanning Electron Microscopy (FESEM). Magnetic measurement shows that the magnetization in the materials are affected by low crystallite size which destroys the spin ordering due to strain at grain boundaries and this also leads to reduction in magnetization as well as high coercivity in the material.

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

    NASA Astrophysics Data System (ADS)

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

    2016-05-01

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

  12. Effect of biaxial strain on the electrical and magnetic properties of (001) La0.7Sr0.3MnO3 thin films

    NASA Astrophysics Data System (ADS)

    Adamo, C.; Ke, X.; Wang, H. Q.; Xin, H. L.; Heeg, T.; Hawley, M. E.; Zander, W.; Schubert, J.; Schiffer, P.; Muller, D. A.; Maritato, L.; Schlom, D. G.

    2009-09-01

    We have studied the effect of biaxial strain on thin films of (001) La0.7Sr0.3MnO3. We deposited films by reactive molecular-beam epitaxy on different single crystalline substrates, varying the substrate-induced biaxial strain from -2.3% to +3.2%. Magnetization and electrical transport measurements reveal that the dependence of the Curie temperature on biaxial strain is in very good agreement with the theoretical predictions of Millis et al. [J. Appl. Phys. 83, 1588 (1998)].

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

    NASA Astrophysics Data System (ADS)

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

    2016-05-01

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

  14. Nickel-Doped La0.8Sr0.2Mn(1-x)Ni(x)O3 Nanoparticles Containing Abundant Oxygen Vacancies as an Optimized Bifunctional Catalyst for Oxygen Cathode in Rechargeable Lithium-Air Batteries.

    PubMed

    Wang, Zhaodong; You, Ya; Yuan, Jing; Yin, Ya-Xia; Li, Yu-Tao; Xin, Sen; Zhang, Dawei

    2016-03-01

    In this work, Ni-doped manganite perovskite oxides (La0.8Sr0.2Mn(1-x)Ni(x)O3, x = 0.2 and 0.4) and undoped La0.8Sr0.2MnO3 were synthesized via a general and facile sol-gel route and used as bifunctional catalysts for oxygen cathode in rechargeable lithium-air batteries. The structural and compositional characterization results showed that the obtained La0.8Sr0.2Mn(1-x)Ni(x)O3 (x = 0.2 and 0.4) contained more oxygen vacancies than did the undoped La0.8Sr0.2MnO3 as well as a certain amount of Ni(3+) (eg = 1) on their surface. The Ni-doped La0.8Sr0.2Mn(1-x)Ni(x)O3 (x = 0.2 and 0.4) was provided with higher bifunctional catalytic activities than that of the undoped La0.8Sr0.2MnO3. In particular, the La0.8Sr0.2Mn0.6Ni0.4O3 had a lower total over potential between the oxygen evolution reaction and the oxygen reduction reaction than that of the La0.8Sr0.2MnO3, and the value is even comparable to that of the commercial Pt/C yet is provided with a much reduced cost. In the lithium-air battery, oxygen cathodes containing the La0.8Sr0.2Mn0.6Ni0.4O3 catalyst delivered the optimized electrochemical performance in terms of specific capacity and cycle life, and a reasonable reaction mechanism was given to explain the improved performance. PMID:26900959

  15. Disorder induced superconductor-insulator transition in epitaxial La1.85Sr0.15CuO4 thin films

    NASA Astrophysics Data System (ADS)

    Jang, Han-Byul; Yang, Chan-Ho

    La2-xSrxCuO4is a well-known superconducting system showing various electronic properties as a function of Sr content. Especially, epitaxial thin layers of the compound show enormous increase of superconducting critical temperature (Tc) by a compressive strain. It has been reported that Tc can be controlled by misfit strain, thickness, and oxygen annealing. In this study, we report structural and transport properties of high quality epitaxial La1.85Sr0.15CuO4thin films. According to x-ray diffraction study, c-axis lattice parameter shows no significant change for various film thicknesses and the in-plane lattice parameters of the films are coherently matched with that of substrate. Electronic transport measurements show a clear superconductor-to-insulator transition (SIT), accompanying variation of Tc depending on film thickness. These results are analyzed by using the McMillan equation to find the relation between the Tc and a disorder correlating with film thickness. We have found the disorder exhibits an explicit power-law behavior with respect to film thickness in our La1.85Sr0.15CuO4 thin films.

  16. 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.

  17. Evidence of spin glass like ordering and electronic phase arrest in Pr3+ doped Sm0.5Sr0.5MnO3 bulk manganites

    NASA Astrophysics Data System (ADS)

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

    2012-06-01

    The effect of doping of rare earth Pr3+ ion replacing Sm3+ in Sm0.5Sr0.5MnO3 is investigated in details. Measurements of linear and non linear ac magnetic susceptibility, resistivity, magnetoresistance on chemically synthesized (Sm0.5-xPrx)Sr0.5MnO3 shows various interesting features with doping level x=0.15. Here we observe the frequency independent FM-PM transition at higher temperature followed by a frequency dependent re-entered magnetic transition at lower temperature through complex ac susceptibility measurements. We have ascribed our observation to the formation of finite size ferromagnetic clusters which are formed as a consequence of intrinsic phase separation and undergo Spin glass-like freezing below certain temperature in this manganite. The magnetoresistance of the samples also show strong irreversibility with respect to sweeping of the field between highest positive and negative values. All these experimental results have been attributed to phase separation effect and kinetic arrest of electronically phase separated system.

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

    NASA Astrophysics Data System (ADS)

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

    2015-12-01

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

  19. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2016-04-01

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

  1. 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. PMID:27007192

  2. 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.

  3. Effects of fluorine doping on thermoelectric properties of Sr0.61Ba0.39Nb2O6 ceramics

    NASA Astrophysics Data System (ADS)

    Li, Yi; Liu, Jian; Wang, Zhen; Zhou, YuCheng; Wang, Chunlei; Li, Jichao; Zhu, Yuanhu; Li, Maokui; Mei, Liangmo

    2015-02-01

    The thermoelectric properties of Sr0.61Ba0.39Nb2O6 ceramics, doped with different contents of fluorine at the oxygen sites, were investigated in the temperature range of 323 to 1073 K. The electrical resistivity is reduced significantly after fluorine doping. However, the magnitudes of electrical resistivity, Seebeck coefficient (S), and slope of S at high temperatures (dS/dT) vary non-monotonically with increasing doping contents, indicating that doped fluorine ions not only act as electron donors, but also influence band structure. The lattice thermal conductivity decreases when fluorine ions are slightly doped, and increases with increasing fluorine content because of the increasing average grain size. The thermoelectric performance is enhanced by slight fluorine doping due to the increase of the power factor and the reduction of thermal conductivity. The thermoelectric figure of merit reaches maximum value (0.21 at 1073 K) in the Sr0.61Ba0.39Nb2O5.95F0.05 sample.

  4. Effect of oxygen vacancies on the magnetic structure of the La0.6Sr0.4FeO3-δ perovskite: A neutron diffraction study

    NASA Astrophysics Data System (ADS)

    Chu, Z.; Yelon, W. B.; Yang, J. B.; James, W. J.; Anderson, H. A.; Xie, Y.; Malik, S. K.

    2002-05-01

    Magnetic interactions in perovskite compounds of the type La1-xSrxMO3-δ (M=3d transition such as Mn and Fe) are presumed to arise through a super exchange between 3d electrons of the magnetic ions via oxygen orbitals. The magnetic structure of La0.6Sr0.4FeO3-δ has been studied with neutron diffraction. Oxygen vacancies were created by annealing samples under various gases including N2, air and mixtures of CO/CO2. All La0.6Sr0.4FeO3-δ compounds maintain the rhombohedral structure (space group R3¯c). The air- or oxygen-annealed samples have almost no oxygen vacancies while those made in the reducing atmosphere show 7%-11% oxygen vacancies. The rhombohedral distortion decreases in the reduced samples. All the samples exhibit antiferromagnetic ordering at room temperature, although a small ferromagnetic moment may also be present. The samples with little or no oxygen vacancies show a room temperature magnetic moment of ˜1.4μB at the Fe site while those having >7% oxygen vacancies show a moment of ˜4.0μB. Magnetization measurements reveal a much higher magnetic ordering temperature in samples with oxygen vacancies

  5. Dual Extraction of Photogenerated Electrons and Holes from a Ferroelectric Sr0.5Ba0.5Nb2O6 Semiconductor.

    PubMed

    Fan, Dayong; Zhu, Jian; Wang, Xiuli; Wang, Shengyang; Liu, Yong; Chen, Ruotian; Feng, Zhaochi; Fan, Fengtao; Li, Can

    2016-06-01

    The separation of photogenerated charges is a critical factor in photocatalysis. Recently, anomalous photovoltaic (APV) field effects (Voc ∼ 10(3) V/cm) in ferroelectrics, with their strong driving force for charge separation, have attracted much attention in photocatalysis and photoelectrocatalysis. However, it is still unknown whether photogenerated electrons and holes can be simultaneously extracted by the strong driving force toward the surface of ferroelectrics and can become available for surface reactions. This issue becomes critically important in photocatalysis because the surface reaction utilizes both the electrons and holes that reach the surface. In this work, a model lateral symmetric structure, metal/Sr0.5Ba0.5Nb2O6/metal (metal = Ag or Pt), as an electrode was fabricated. The dual extractions of photogenerated electrons and holes on the two opposite metal electrodes were achieved, as revealed by photovoltaic and ferroelectrical hysteresis measurements and photoassisted Kelvin probe force microscopy (KPFM). It was found that the high Schottky barriers of the two opposite Sr0.5Ba0.5Nb2O6-Pt electrodes are key factors that alter the two space charge regions (SCRs) by a poling effect. The resulting built-in electrical fields with parallel directions near both electrodes significantly enhance the charge separation ability. Our model unravels the driving force of charge separation in ferroelectric semiconductors, thus demonstrating the potential for highly efficient charge separation in photocatalysis. PMID:27183145

  6. 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.

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

    NASA Technical Reports Server (NTRS)

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

    1999-01-01

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

  8. Spark Plasma Sintering Temperature Effect on Structural, Dielectric and Ferroelectric Properties of Ba0.9Sr0.1TiO3 Nanocrystalline Ceramics

    NASA Astrophysics Data System (ADS)

    Mudinepalli, Venkata Ramana; Lin, Wen-Chin; Song, S.-H.; Murty, B. S.

    2015-11-01

    A combination of mechanical alloying and spark plasma sintering (SPS) was used to process Ba0.9Sr0.1TiO3 (abbreviated as BST) with a high-density and homogeneous microstructure, at a temperature 300°C to 400°C lower than that used in conventional sintering. The SPS technique was employed to prepare dense Ba0.9Sr0.1TiO3 nano-ceramics at different temperatures ranging from 800°C to 1000°C within a very short time. The SPS samples were characterized by x-ray diffraction, scanning electron microscopy, transmission electron microscopy, electrical, ferroelectric and piezoelectric property measurements. The dielectric constant both at room temperature and Curie temperature increased with increasing SPS temperature. The coercive field increased continuously with rising SPS temperature, but the spontaneous polarization increased gradually up to 900°C and then decreased considerably with further increases in SPS temperature. In addition, the prepared nano-ceramic exhibited excellent piezoelectric properties.

  9. Enhanced Microwave Absorption Properties of Intrinsically Core/shell Structured La0.6Sr0.4MnO3Nanoparticles

    PubMed Central

    2009-01-01

    The intrinsically core/shell structured La0.6Sr0.4MnO3nanoparticles with amorphous shells and ferromagnetic cores have been prepared. The magnetic, dielectric and microwave absorption properties are investigated in the frequency range from 1 to 12 GHz. An optimal reflection loss of −41.1 dB is reached at 8.2 GHz with a matching thickness of 2.2 mm, the bandwidth with a reflection loss less than −10 dB is obtained in the 5.5–11.3 GHz range for absorber thicknesses of 1.5–2.5 mm. The excellent microwave absorption properties are a consequence of the better electromagnetic matching due to the existence of the protective amorphous shells, the ferromagnetic cores, as well as the particular core/shell microstructure. As a result, the La0.6Sr0.4MnO3nanoparticles with amorphous shells and ferromagnetic cores may become attractive candidates for the new types of electromagnetic wave absorption materials. PMID:20596374

  10. 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.

  11. Substrate-related structural, electrical, magnetic and optical properties of La0.7Sr0.3MnO3 films

    NASA Astrophysics Data System (ADS)

    Liu, G. Z.; Yang, Y. Y.; Qiu, J.; Chen, X. X.; Jiang, Y. C.; Yao, J. L.; Zhao, M.; Zhao, R.; Gao, J.

    2016-02-01

    La0.7Sr0.3MnO3 (LSMO) film exhibits certain unique properties which make it an ideal material for heterostructure-based multifunctional devices. In this paper, La0.7Sr0.3MnO3 thin films were grown epitaxially on SrTiO3, LaAlO3(LAO) and (LaAlO3)0.3-(SrAl0.5Ta0.5O3)0.7(LSAT) substrates, and their structural, electrical, magnetic and optical properties were examined and compared, aiming at revealing and explaining the effects of substrate on fundamental physical properties of LSMO films. Results show that (i) the effects of substrate materials on the electrical conductivity and paramagnetic-ferromagnetic transition temperature of the LSMO films could be ignored, and (ii) the LSMO film on LAO substrate has much higher coercive field and slower photoinduced relaxation process than other samples. This unusual behavior observed in the LSMO film on the LAO substrate could be related to the nature of the LAO substrate itself, on which the LSMO film showed different easy magnetization direction, and the film also exhibited relatively poor crystalline quality due to the twin domain structure of LAO crystal. Our results may help to understand the substrate-related electrical, magnetic and optical properties for perovskite manganite films.

  12. Influence of Cu substitution for Mn on the structure, magnetic, magnetocaloric and magnetoresistance properties of La 0.7Sr 0.3MnO 3 perovskites

    NASA Astrophysics Data System (ADS)

    Chau, Nguyen; Niem, Pham Quang; Nhat, Hoang Nam; Luong, Nguyen Hoang; Tho, Nguyen Duc

    2003-04-01

    Structural, magnetic, magnetocaloric and magnetoresistance (MR) studies on La 0.7Sr 0.3Mn 0.95Cu 0.05O 3 (No. 1) and La 0.7Sr 0.3Mn 0.9Cu 0.1O 3 (No. 2) perovskites are reported. The crystal structure of the samples is rhombohedral with a change of the lattice constants depending on the Cu content. FC and ZFC thermomagnetic measurements for both compositions at low field indicate that a spin-glass-like state (or cluster glass) occurs at low temperatures and a very sharp change of magnetization around the phase-transition point. The Curie temperature, TC, does almost not depend on the content of Cu substitution. A maximum magnetic-entropy change, Δ Sma x, of 1.96 and 2.07 J/kg K at 13.5 kOe and 350 K is observed for sample No. 1 and No. 2, respectively. Therefore, they can be considered as active magnetic refrigerant materials for room-temperature applications. Electrical-resistance measurements show that both samples are metallic conductor for T< TC and semiconductor for T> TC; moreover, the MR is maximal around TC.

  13. Multiferroic properties of Pb0.90Sr0.10TiO3-CoFe2O4 nanostructured bilayered thin film

    NASA Astrophysics Data System (ADS)

    Bala, Kanchan; Kotnala, R. K.; Negi, N. S.

    2015-05-01

    Pb0.90Sr0.10TiO3-CoFe2O4(PST10-CFO) nanostructured bilayered thin film were grown on Si (100) substrate by using metallo-organic decomposition chemical route and spin coating technique. Results show that PST (pervoskite structure) and CFO (spinel) phase coexist in the bilayered thin films, annealed at 650°C for 2hr and no obvious impurity phase can be detected. The structural, surface morphology and micro structural properties were confirmed by X-Ray diffraction (XRD), atomic force microscope (AFM) respectively. Excellent ferroelectric behavior at different voltage was observed, with two platinum electrodes only at surface of the bilayer thin film. A room temperature ferromagnetic behavior was observed in the bilayered Pb0.90Sr0.10TiO3-CoFe2O4 nanostructured thin film. The saturation magnetization and variation in coercivity value of the bilayer thin film is lower than that of the pure CFO film in the presence of non ferromagnetic PST layer which is the attributed that the significant coupling between the two phases.

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

    NASA Astrophysics Data System (ADS)

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

    2016-05-01

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

  15. Fluctuations of the order parameter in R 0.55Sr0.45MnO3 manganites near the metal-insulator phase transition

    NASA Astrophysics Data System (ADS)

    Bukhanko, F. N.; Bukhanko, A. F.

    2013-06-01

    The magnetic phase transformations induced by changes of the composition, external magnetic field strength, and temperature in manganites with a nearly half-filled conduction band in the vicinity of the metal-insulator phase transition have been investigated experimentally. It has been found that the substitution of rare-earth ions (Sm) for Nd ions with a larger ionic radius in R 0.55Sr0.45MnO3 manganites leads to a linear decrease in the Curie temperature T C from 270 to 130 K and a transformation of the second-order ferromagnetic (FM) phase transition into a first-order phase transition. The results of measurements of the alternating-current (ac) magnetic susceptibility in the (Nd1 - y Sm y )0.55Sr0.45MnO3 system indicate the existence of a Griffiths-like phase in samples with a samarium concentration y > 0.5 in the temperature range T C < T < T* (where T* ˜ 220 K). For samples with y > 0.5, the magnetization isotherms at temperatures above T C exhibit specific features in the form of reversible metamagnetic phase transitions associated with strong fluctuations of the short-range ferromagnetic order in the system of Mn spins in the high-temperature Griffiths phase consisting of ferromagnetic clusters. According to the results of measurements of the ac magnetic susceptibility in the (Sm1 - y Gd y )0.55Sr0.45MnO3 system for a gadolinium concentration y = 0.5, there is an antiferromagnetic (AFM) phase with an unusually low critical temperature of the spin ordering T N ≊ 48.5 K. An increase in the external static magnetic field at 4.2 K leads to an irreversible induction of the ferromagnetic phase, which is stable in the temperature range 4.2-60 K. In the temperature range 60 K < T < 150 K, there exists a high-temperature Griffiths-like phase consisting of clusters (correlations) with a local charge/orbital ordering. The metastable antiferromagnetic structure is retained in samples with gadolinium concentrations y = 0.6 and 0.7, but it is destroyed with a further

  16. Interfacial Ion Intermixing Effect on Four-Resistance States in La0.7Sr0.3MnO3/BaTiO3/La0.7Sr0.3MnO3 Multiferroic Tunnel Junctions.

    PubMed

    Huang, Weichuan; Lin, Yue; Yin, Yuewei; Feng, Lei; Zhang, Dalong; Zhao, Wenbo; Li, Qi; Li, Xiaoguang

    2016-04-27

    A multiferroic tunnel junction (MFTJ), employing a ferroelectric barrier layer sandwiched between two ferromagnetic layers, presents at least four resistance states in a single memory cell and therefore opens an avenue for the development of the next generation of high-density nonvolatile memory devices. Here, using the all-perovskite-oxide La0.7Sr0.3MnO3/BaTiO3/La0.7Sr0.3MnO3 as a model MFTJ system, we demonstrate asymmetrical Mn-Ti sublattice intermixing at the La0.7Sr0.3MnO3/BaTiO3 interfaces by direct local measurements of the structure and valence, which reveals the relationship between ferroelectric polarization directions and four-resistance states, and the low temperature anomalous tunneling behavior in the MFTJ. These findings emphasize the crucial role of the interfaces in MFTJs and are quite important for understanding the electric transport of MFTJs as well as designing high-density multistates storage devices. PMID:27055530

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

    NASA Astrophysics Data System (ADS)

    Fan, Baoan; Yan, Jiabao; Yan, Xiaochao

    2011-10-01

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

  18. Pb0.3Sr0.7TiO3 thin films for high-frequency phase shifter applications

    NASA Astrophysics Data System (ADS)

    Jain, M.; Karan, N. K.; Katiyar, R. S.; Bhalla, A. S.; Miranda, F. A.; Keuls, F. W. Van

    2004-07-01

    Pb0.3Sr0.7TiO3(PST30) thin films were synthesized on platinized silicon (Pt /Si) and lanthanum aluminate (LAO) substrates using chemical solution deposition technique. The films on LAO substrate were highly (100) oriented, whereas the films on Pt /Si substrate were polycrystalline. The low dielectric loss in the PST30/LAO films makes them attractive for fabricating tunable dielectric devices. An eight-element coupled microstrip phase shifter was fabricated on PST30/LAO film and tested in the frequency range ˜15-17GHz. The maximum figure of merit (κ =phase shift per dB loss) of ˜56°/dB was obtained for PST30 film, which was better than commonly observed value in pure barium strontium titanate films. This makes PST30 a potential candidate material for further investigations for microwave applications.

  19. Orientation effect on microwave dielectric properties of Si-integrated Ba0.6Sr0.4TiO3 thin films for frequency agile devices

    NASA Astrophysics Data System (ADS)

    Kim, Hyun-Suk; Hyun, Tae-Seon; Kim, Ho-Gi; Kim, Il-Doo; Yun, Tae-Soon; Lee, Jong-Chul

    2006-07-01

    The effect of texture with (100) and (110) preferred orientations on dielectric properties of Ba0.6Sr0.4TiO3 (BST) thin films grown on SrO (9nm) and CeO2 (70nm ) buffered Si substrates, respectively, was investigated. The coplanar waveguide (CPW) phase shifter using (100) oriented BST films on SrO buffered Si exhibited a much-enhanced figure of merit of 24.7°/dB, as compared to that (10.2°/dB) of a CPW phase shifter using (110) oriented BST films on CeO2 buffered Si at 12GHz. This work demonstrates that the microwave properties of the Si-integrated BST thin films are highly correlated with crystal orientation.

  20. Crystal structure of La 0.4Sr 0.6CoO 2.71 investigated by TEM and XRD

    NASA Astrophysics Data System (ADS)

    Gspan, C.; Grogger, W.; Bitschnau, B.; Bucher, E.; Sitte, W.; Hofer, F.

    2008-11-01

    The structure of the oxygen-deficient perovskite La 0.4Sr 0.6CoO 3-δ ( δ=0.29) was investigated by transmission electron microscopy (TEM) and X-ray powder diffraction (XRD). Domains between 50 and 250 nm in size were observed in the electron microscope. Weak superstructure reflections were found with both X-ray and electron diffraction. Investigations of these superstructure reflections by selected area electron diffraction (SAED) and convergent beam electron diffraction (CBED) showed that the domains in a crystal are orientated in a 90° relationship. High-resolution transmission electron microscopy (HRTEM) images from the domain boundary also revealed a 90° orientation dependency. Using the symmetry of CBED patterns, the point group 4/ mmm was determined. By comparing reflections from the SAED pattern with possible reflections, the space group I4/ mmm (No. 139) could be isolated and finally the crystal structure was refined by Rietveld refinement.

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

    NASA Astrophysics Data System (ADS)

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

    2013-10-01

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

  2. Effect of Quenching on Magnetoresistance Properties in the Pr 0.5Sr 0.5MnO 3 Perovskite Manganite

    NASA Astrophysics Data System (ADS)

    Boujelben, W.; Ellouze, M.; Cheikh-Rouhou, A.; Pierre, J.; Joubert, J. C.

    2002-05-01

    We report on the magnetization, resistivity and magnetoresistance (MR) measurements on polycrystalline Pr0.5Sr0.5MnO3. Quenching samples from 1400°C to room temperature in water (sample I) or in air (sample II) leads to different behaviors. Powder X-ray diffraction patterns for samples I and II could be indexed, respectively, in rhombohedral perovskite structure with R3c space group and in the orthorhombic one with Imma space group. Magnetization measurements show that both samples exhibit a paramagnetic-ferromagnetic transition at 280 K (sample I) and 265 K (sample II). At low temperature, sampleI presents a ferromagnetic spin-canted state, while sample II behaves as an antiferromagnet below 160 K. Resistivity and magnetoresistance studies show a net difference as a function of the quenching conditions.

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

    PubMed

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

    2014-11-12

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

  4. Structural and dielectric properties of Ba0.7Sr0.3TiO3 thin films grown by PLD

    NASA Astrophysics Data System (ADS)

    James, K. K.; Satish, B.; Jayaraj, M. K.

    2014-01-01

    Ferroelectric thin films of Ba0.7Sr0.3TiO3 (BST) were deposited on Si/SiO2/TiO2/Pt (PtSi) substrate by pulsed laser deposition (PLD). Crystalline films with perovskite structure were obtained without post-deposition annealing. Phase purity of the deposited films was confirmed by x-ray diffraction. The lowest value of FWHM obtained for the film deposited at oxygen pressure 5.4×10-4 mbar and substrate temperature 600°C, indicates the high crystallinity of the film. The room temperature dielectric constant at 100 kHz was 85. Butterfly loop, which is the characteristic of ferroelectric materials, was obtained in the regime of -4 to +4V. The leakage current density was nearly 9×10-13 Acm-2.

  5. Memory effects and magnetic relaxation in single-crystalline La0.9Sr0.1CoO3

    NASA Astrophysics Data System (ADS)

    Khan, N.; Mandal, P.; Prabhakaran, D.

    2014-07-01

    We report a detailed investigation of magnetic relaxation and memory effects in La0.9Sr0.1CoO3 single crystal from dc magnetization measurements. The analysis of magnetic relaxation at different temperatures and magnetic fields below the freezing temperature Tf reveals the characteristics of the spin-glass phase. Below Tf, striking memory effects have been clearly observed in different experimental protocols. The memory effect in the zero-field-cooled magnetization further establishes that the glassy magnetic state arises from the cooperative spin-spin interaction but not due to the independent relaxation of metastable phase clusters. The asymmetric response with respect to negative and positive temperature changes favors the hierarchical model of memory effects rather than the droplet model discussed in other works for different insulating and metallic Heisenberg spin glasses.

  6. Size dependence in magnetic memory, relaxation and interaction of La0.67Sr0.33MnO3

    NASA Astrophysics Data System (ADS)

    Ghosh, Nilotpal; Datta, Subarna; Ghosh, Barnali

    2015-05-01

    We report the study of memory effect, relaxation and interaction of La0.67Sr0.33MnO3 (LSMO) particles of two different sizes, bulk (~60-150 μm) and nano (~80 nm) synthesized by using polymeric precursor route. Magnetic relaxation measurement has been carried out and the analysis shows the existence of two relaxation times in both the cases. Our dynamic light scattering (DLS) studies indicate the presence of two different size distributions in LSMO nano particle sample. This is attributed to the fact that particles of two different sizes can relax separately. It has been observed that both the samples show signature of magnetic memory effect. Because, the effect of disordered surface layer is more in LSMO nano than LSMO bulk particles, LSMO nano particles are found to favor demagnetized state where as LSMO bulk prefer magnetized state.

  7. Structure, magnetic and magnetoresistance properties of Pr0.67Sr0.33MnO3 manganite oxide prepared by ball milling method

    NASA Astrophysics Data System (ADS)

    Chérif, W.; Ellouze, M.; Lehlooh, A.-F.; Elhalouani, F.; Mahmood, S. H.

    2012-07-01

    A sample of Pr0.67Sr0.33MnO3 nanoparticles was synthesized by the ball milling method. X-ray diffraction pattern of the sample showed orthorhombic system with Pnma space group. The average crystallite size of 110 nm was obtained by both Scanning Electron Microscopy and X-ray diffraction. Magnetic measurements showed para-to-ferromagnetic transition with a Curie temperature of TC=269 K. Electrical investigations showed that all our samples exhibit a semi-conducting behavior above TC and a metallic-like one at lower temperatures. The sample exhibited a large magnetoresistance of 30% at room temperature in an applied magnetic field of 2 T. The transport and the magnetic properties were interpreted in terms of the existence of magnetic polarons in the sample.

  8. Electrospun La0.8Sr0.2MnO3 nanofibers for a high-temperature electrochemical carbon monoxide sensor

    NASA Astrophysics Data System (ADS)

    Zhi, Mingjia; Koneru, Anveeksh; Yang, Feng; Manivannan, Ayyakkannu; Li, Jing; Wu, Nianqiang

    2012-08-01

    Lanthanum strontium manganite (La0.8Sr0.2MnO3, LSM) nanofibers have been synthesized by the electrospinning method. The electrospun nanofibers are intact without morphological and structural changes after annealing at 1050 °C. The LSM nanofibers are employed as the sensing electrode of an electrochemical sensor with yttria-stabilized zirconia (YSZ) electrolyte for carbon monoxide detection at high temperatures over 500 °C. The electrospun nanofibers form a porous network electrode, which provides a continuous pathway for charge transport. In addition, the nanofibers possess a higher specific surface area than conventional micron-sized powders. As a result, the nanofiber electrode exhibits a higher electromotive force and better electro-catalytic activity toward CO oxidation. Therefore, the sensor with the nanofiber electrode shows a higher sensitivity, lower limit of detection and faster response to CO than a sensor with a powder electrode.

  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. Influence of heat treatment on the magnetic and magnetocaloric properties in Nd0.6Sr0.4MnO3 compound

    NASA Astrophysics Data System (ADS)

    Ahmed, A. M.; Mohamed, H. F.; Diab, A. K.; Mohamed, Sara A.; García-Granda, S.; Martínez-Blanco, D.

    2016-07-01

    In the present investigation, the effect of annealing temperature on the structural, electrical transport and the magnetocaloric effect of Nd0.6Sr0.4MnO3 manganites have been studied. Rietveld refinement of XRD data reveals that all samples are single phase with a space group (Pnma). Heat treatment enhances the grain size and decreases the porosity. All samples suffer Curie transition from ferromagnetic to paramagnetic. Magnetocaloric parameters have been determined by the analysis of isothermal M (H) curves around Curie temperature (ΔH = 2 T) for samples. Heat treatment enhances magnetic entropy, which reaches a maximum at Tan = 900 °C. In addition, the rate cooling power records highest value at Tan = 700 °C.

  11. 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.

  12. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2010-11-01

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

  14. 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

  15. Strain Effects in La0.7Sr0.3MnO3 Films by X-ray Absorption Spectroscopy

    SciTech Connect

    Ramos, A.Y.; Neto, N.M. Souza; Giacomelli, C.; Tolentino, H.C.N.; Ranno, L.; Favre-Nicolin, E.

    2003-01-24

    We report on Mn K-edge X-ray absorption study, in plane and out of plane, of La0.7Sr0.3MnO3 films, epitaxially grown on a tensile substrate SrTiO3 by laser ablation. From Extended X-ray Absorption Fine Structure in the film plane we observe a small increase of Mn-Mn distances with respect to relaxed film. In addition, a small distortion of the MnO6 octahedron is evidenced from Extended and Near Edge Absorption measurements. The respective amplitudes found for these two effects are on the same order, so that no modification of the Mn-O-Mn angle is evidenced.

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

    NASA Astrophysics Data System (ADS)

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

    2016-07-01

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

  17. Planar-type spin valves based on low-molecular-weight organic materials with La0.67Sr0.33MnO3 electrodes

    NASA Astrophysics Data System (ADS)

    Ikegami, Tomonori; Kawayama, Iwao; Tonouchi, Masayoshi; Nakao, Satoru; Yamashita, Yoshiro; Tada, Hirokazu

    2008-04-01

    The spin injection and transport properties of low-molecular-weight organic semiconductors such as pentacene and bis(l,2,5-thiadiazolo)-p-quinobis(l,3-dithiole) (BTQBT) were investigated utilizing planar-type spin-valve devices with half-metallic La0.67Sr0.33MnO3 electrodes. The devices showed clear spin-valve characteristics with a magnetoresistance (MR) ratio of up to 29% at 5K. The MR ratio was found to depend on the gap spacing of the electrodes, the applied bias voltage, temperature, and the crystallinity of the films. It was also affected by gas adsorption onto the films, indicating that the spins were scattered by carriers and/or radical ions in the films generated through charge transfer from gas molecules.

  18. Silica-coated La0.75Sr0.25MnO3 nanoparticles for magnetically driven DNA isolation.

    PubMed

    Trachtová, Stěpánka; Kaman, Ondřej; Spanová, Alena; Veverka, Pavel; Pollert, Emil; Rittich, Bohuslav

    2011-11-01

    Magnetic La(0.75)Sr(0.25)MnO(3) nanoparticles possessing an approximately 20-nm-thick silica shell (LSMO(0.25)@SiO(2) ) were characterised and tested for the isolation of PCR-ready bacterial DNA. The results presented here show that the nanoparticles do not interfere in PCR. DNA was apparently reversibly adsorbed on their silica shell from the aqueous phase system (16% PEG 6000-2 M NaCl). The method proposed was used for DNA isolation from complex food samples (dairy products and probiotic food supplements). The isolated DNA was compatible with PCR. The main advantages of the nanoparticles tested for routine use were their high colloidal stability allowing a more precise dosage and therefore high reproducibility of DNA isolation. PMID:21919199

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

    NASA Astrophysics Data System (ADS)

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

    2005-03-01

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

  20. 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.

  1. Thermal hysteresis in the luminescence of Cr3+ ions in Sr0.6Ba0.4 (NbO3)2

    NASA Astrophysics Data System (ADS)

    Ramirez, M. O.; Jaque, D.; Montes, M.; García Solé, J.; Bausá, L. E.; Ivleva, L.

    2004-04-01

    The temperature dependence of the emission spectrum of Cr3+ ions in Sr0.6Ba0.4 (NbO3)2 has been systematically investigated around the ferroelectric phase transition of this crystal (≈370 K). In spite of the strong thermal quenching of the luminescence occurring at these temperatures, the emission spectrum is still clearly detectable and shows dramatic changes in both line shape and intensity when passing through the phase transition temperature. A redshift of about 6 nm occurs when the crystal is driven from the polar to the nonpolar phase. In addition, this shift displays a thermal hysteresis, then providing the possibility of realizing a bistable spectral system based on this material.

  2. Turning antiferromagnetic Sm0.34Sr0.66MnO3 into a 140 K ferromagnet using a nanocomposite strain tuning approach

    NASA Astrophysics Data System (ADS)

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

    2016-04-01

    Ferromagnetic insulating thin films of Sm0.34Sr0.66MnO3 (SSMO) on (001) SrTiO3 substrates with a TC of 140 K were formed in self-assembled epitaxial nanocomposite thin films. High TC ferromagnetism was enabled through vertical epitaxy of the SSMO matrix with embedded, stiff, ~40 nm Sm2O3 nanopillars giving a c/a ratio close to 1 in the SSMO. In contrast, bulk and single phase SSMO films of the same composition have much stronger tetragonal distortion, the bulk having c/a >1 and the films having c/a <1, both of which give rise to antiferromagnetic coupling. The work demonstrates a unique and simple route to creating ferromagnetic insulators for spintronics applications where currently available ferromagnetic insulators are either hard to grow and/or have very low TC.

  3. 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.

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

    PubMed

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

    2016-04-21

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

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

    PubMed

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

    2015-10-01

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

  7. Debye’s temperature and heat capacity for Sr0.15Ba0.85Bi2Nb2O9 relaxor ferroelectric ceramic

    NASA Astrophysics Data System (ADS)

    Peláiz-Barranco, A.; González-Abreu, Y.; Saint-Grégoire, P.; Guerra, J. D. S.; Calderón-Piñar, F.

    2016-02-01

    A lead-free relaxor ferroelectric, Sr0.15Ba0.85Bi2Nb2O9, was synthesized via solid-state reaction and the temperature-dependence of the heat capacity was measured in a wide temperature range. The dielectric permittivity was also measured between 500Hz and 5MHz in the same temperature range. No anomaly has been detected in the heat capacity curve for the whole temperature range covered in the present experiments, while broad peaks have been observed in the dielectric permittivity with high frequency dispersion. A typical relaxor behavior has been observed from the dielectric analysis. The Debye’s temperature has showed a minimum value near the freezing temperature. The results are discussed considering the spin-glass model and the high frequency dispersion, which has been observed for the studied relaxor system.

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

    DOE PAGESBeta

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

    2016-04-01

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

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

    PubMed

    Chai, Xiaojie; Xing, Hui; Jin, Kexin

    2016-01-01

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

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

    NASA Astrophysics Data System (ADS)

    Chai, Xiaojie; Xing, Hui; Jin, Kexin

    2016-03-01

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

  11. Ordered La0.7Sr0.3MnO3 nanohole arrays fabricated on a nanoporous alumina template by pulsed laser ablation

    NASA Astrophysics Data System (ADS)

    Kumaresavanji, M.; Gomes, I. T.; Apolinario, A.; Rolo, A. G.; Almeida, B. G.; Lopes, A. M. L.; Araujo, J. P.

    2016-03-01

    Highly ordered nanohole arrays of {{La}}0.7{{Sr}}0.3{{MnO}}3 manganite have been synthesized using pulsed laser deposition on nanoporous alumina template. Their structure and phase formation were characterized by scanning electron microscopy (SEM), atomic force microscopy (AFM), energy dispersive x-ray spectroscopy (EDX) and x-ray diffraction (XRD). The magnetic measurements were performed with respect to temperature and field and exhibit a ferromagnetic to paramagnetic transition at 284 K. In addition, the temperature dependence of electrical resistance was measured at different magnetic fields and an insulating phase throughout all the temperatures was observed. The low temperature ferromagnetic insulating state is discussed by the presence of a canted ferromagnetic state induced by the nanoholes. The present work shows the feasibility of combining both the nanoporous alumina template and pulsed laser ablation for the fabrication of perovskite manganite nanohole arrays which can also be extended to fabricate other multicomponent oxide nanohole materials.

  12. Anisotropy of the Electron-Doped Infinite-Layer Superconductor Sr0.9La0.1CuO2

    NASA Astrophysics Data System (ADS)

    Kim, Heon-Jung; Park, Min-Seok; Jung, C. U.; Lee, Sung-Ik; Kim, Mun-Seog

    Anisotropy of a c-axis aligned Sr0.9La0.1CuO2 infinite-layer superconductor was studied by measuring the magnetization in different temperature (M(T)) and angle (M(θ)). The M(θ) and the critical temperature as a function of the angle (Tc2(θ)) deduced from M(T) was well described by the anisotropic Ginzburg-Landua theory with a moderate anisotropy value γ≈9. This low value, which is comparable to that of YBa2Cu3O7-δ implied strong interlayer coupling between CuO2 planes. In this compound, the strong interlayer coupling was thought to solely result from the crystal structure without charge reservoir blocks.

  13. Possible surface antiferromagnetism and no evidence for intergranular tunneling magnetoresistance in La0.5Sr0.5CoO3-δ cobaltites

    NASA Astrophysics Data System (ADS)

    Troyanchuk, I. O.; Bushinsky, M. V.; Lobanovsky, L. S.

    2013-12-01

    The magnetization and magnetoresistance (MR) of La0.5Sr0.5CoO3-δ have been studied as function of surface/volume ratio and oxygen deficit. All the samples have positive and negative components of MR at low temperature. The small positive component is predominated in low field regime below and well above the coercive field. The positive MR under magnetic moment reorientation is in contradiction with scenario of negative intergranular tunneling magnetoresistance being the hallmark of half-metallic polycrystalline oxides. The oxygen deficit leads to a gradual stabilization of antiferromagnetic phase in bulk and concomitant enhancement of the MR. The decrease in value of magnetization and enhancement of the negative MR component in compacted at high pressure/room temperature powder with a large surface/volume ratio can be ascribed to antiferromagnetism at the surface.

  14. Magnetic and structural investigations on La0.6Sr0.4MnO3 nanostructured manganite: Evidence of a ferrimagnetic shell

    NASA Astrophysics Data System (ADS)

    Andrade, V. M.; Caraballo-Vivas, R. J.; Costas-Soares, T.; Pedro, S. S.; Rocco, D. L.; Reis, M. S.; Campos, A. P. C.; Coelho, A. A.

    2014-11-01

    This paper presents the structural and magnetic properties of La0.6Sr0.4MnO3 nanoparticles with sizes from 21 to 106 nm, which have been prepared using the sol-gel method. The reduction of the nanoparticles' size tends to broaden the paramagnetic to ferromagnetic transition, as well as to promote magnetic hysteresis and a remarkable change on the magnetic saturation. In order to better understand the magnetic behavior of those nanoparticles, a simple model based on a ferromagnetic core and a ferrimagnetic shell was considered, where the magnetization was described in terms of the standard mean-field Brillouin function. This model matches the experimental data, leading to conclusion the nanoparticles with size <40 nm are single magnetic domain. In addition, the output fitting parameters give information on the Landé factor of the core and shell.

  15. Nanoscale Mapping of the Magnetic Properties of (111)-Oriented La(0.67)Sr(0.33)MnO3.

    PubMed

    O'Shea, Kerry J; MacLaren, Donald A; McGrouther, Damien; Schwarzbach, Danny; Jungbauer, Markus; Hühn, Sebastian; Moshnyaga, Vasily; Stamps, Robert L

    2015-09-01

    Spatially resolved analysis of magnetic properties on the nanoscale remains challenging, yet strain and defects on this length-scale can profoundly affect a material's bulk performance. We present a detailed investigation of the magnetic properties of La0.67Sr0.33MnO3 thin films in both free-standing and nanowire form and assess the role of strain and local defects in modifying the films' magnetic properties. Lorentz transmission electron microscopy is used to measure the magnetocrystalline anisotropy and to map the Curie temperature and saturation magnetization with nanometric spatial resolution. Atomic-scale defects are identified as pinning sites for magnetic domain wall propagation. Measurement of domain wall widths and crystalline strain are used to identify a strong magnetoelastic contribution to the magnetic anisotropy. Together, these results provide unique insight into the relationship between the nanostructure and magnetic functionality of a ferromagnetic complex oxide film. PMID:26252745

  16. Strain Relaxation in Thin Films of La1.85Sr0.15CuO4 Grown by Pulsed Laser Deposition

    NASA Astrophysics Data System (ADS)

    Zaytseva, I.; Cieplak, M. Z.; Abal'Oshev, A.; Berkowski, M.; Domukhovski, V.; Paszkowicz, W.; Shalimov, A.

    2007-01-01

    X-ray diffraction, resistivity, and susceptibility measurements are used to examine the effects of film thickness d (from 17 to 250 nm) on the structural and superconducting properties of La1.85Sr0.15CuO4 films grown by pulsed laser deposition on SrLaAlO4 substrates. For each d the film sgrow with a variable strain, ranging from a large compressive strain in the thinnest films to a negligible or tensile strain in thick films. Our results indicate that the tensile strain is not caused by the off-stoichiometric layer at the substrate-film interface. Instead, it may be caused by the extreme oxygen deficiency in some of the films.

  17. 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

  18. Electromagnetic transport properties and magnetoresistance of La 0.7Ca 0.2Sr 0.1MnO 3-Ag composites prepared by electroless process

    NASA Astrophysics Data System (ADS)

    Xiong, C. S.; Cui, Y. F.; Xiong, Y. H.; Pi, H. L.; Bao, X. C.; Huang, Q. P.; Zeng, Y.; Wei, F. F.; Zheng, C. F.; Zhu, J.

    2008-09-01

    A series of bulk polycrystalline La 0.7Ca 0.2Sr 0.1MnO 3 (LCSMO)-Ag composites were prepared by electroless plating process and several kinds of physical properties have been studied systemically. According to the results of X-ray diffraction (XRD), scanning electron microscopy (SEM), and electromagnetic transport properties, we can see that Ag-added segregated at the surfaces or interfaces of LCSMO grains. The metal-insulator transition temperature ( TP) and Curie temperature ( Tc) were almost unchanged but ρ decreased with increasing plating time. We also observed Ag-added can significantly enhance the magnetoresistance (MR) near TP under a low applied field (3000 Oe) and the room temperature MR reached to 35% under 20 kOe, which is encouraging for practical applications. We can suggest that improved grain boundary effect by Ag-added is responsible for the enhancement.

  19. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2016-04-01

    In artificial multiferroics hybrids consisting of ferromagnetic La0.7Sr0.3MnO3 (LSMO) and ferroelectric BaTiO3 epitaxial layers, net Ti moments are found from polarized resonant soft x-ray reflectivity and absorption. 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. 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.

  1. Epitaxial growth and properties of La0.7Sr0.3MnO3 thin films with micrometer wide atomic terraces

    NASA Astrophysics Data System (ADS)

    Yuan, Wei; Zhao, Yuelei; Tang, Chi; Su, Tang; Song, Qi; Shi, Jing; Han, Wei

    2015-07-01

    La0.7Sr0.3MnO3 (LSMO) films with extraordinarily wide atomic terraces are epitaxially grown on SrTiO3 (100) substrates by pulsed laser deposition. Atomic force microscopy measurements on the LSMO films show that the atomic step is ˜4 Å and the atomic terrace width is more than 2 μm. For a 20 monolayers (MLs) LSMO film, the magnetization is determined to be 255 ± 15 emu/cm3 at room temperature, corresponding to 1.70 ± 0.11 μB per Mn atom. As the thickness of LSMO increases from 8 MLs to 20 MLs, the critical thickness for the temperature dependent insulator-to-metal behavior transition is shown to be 9 MLs. Furthermore, post-annealing in oxygen environment improves the electron transport and magnetic properties of the LSMO films.

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

    NASA Astrophysics Data System (ADS)

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

    2004-06-01

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

  3. Hierarchical mesoporous perovskite La0.5Sr0.5CoO2.91 nanowires with ultrahigh capacity for Li-air batteries

    PubMed Central

    Zhao, Yunlong; Xu, Lin; Mai, Liqiang; Han, Chunhua; An, Qinyou; Xu, Xu; Liu, Xue; Zhang, Qingjie

    2012-01-01

    Lithium-air batteries have captured worldwide attention due to their highest energy density among the chemical batteries. To provide continuous oxygen channels, here, we synthesized hierarchical mesoporous perovskite La0.5Sr0.5CoO2.91 (LSCO) nanowires. We tested the intrinsic oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) activity in both aqueous electrolytes and nonaqueous electrolytes via rotating disk electrode (RDE) measurements and demonstrated that the hierarchical mesoporous LSCO nanowires are high-performance catalysts for the ORR with low peak-up potential and high limiting diffusion current. Furthermore, we fabricated Li-air batteries on the basis of hierarchical mesoporous LSCO nanowires and nonaqueous electrolytes, which exhibited ultrahigh capacity, ca. over 11,000 mAh⋅g –1, one order of magnitude higher than that of LSCO nanoparticles. Besides, the possible reaction mechanism is proposed to explain the catalytic activity of the LSCO mesoporous nanowire. PMID:23150570

  4. Hierarchical mesoporous perovskite La0.5Sr0.5CoO2.91 nanowires with ultrahigh capacity for Li-air batteries.

    PubMed

    Zhao, Yunlong; Xu, Lin; Mai, Liqiang; Han, Chunhua; An, Qinyou; Xu, Xu; Liu, Xue; Zhang, Qingjie

    2012-11-27

    Lithium-air batteries have captured worldwide attention due to their highest energy density among the chemical batteries. To provide continuous oxygen channels, here, we synthesized hierarchical mesoporous perovskite La(0.5)Sr(0.5)CoO(2.91) (LSCO) nanowires. We tested the intrinsic oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) activity in both aqueous electrolytes and nonaqueous electrolytes via rotating disk electrode (RDE) measurements and demonstrated that the hierarchical mesoporous LSCO nanowires are high-performance catalysts for the ORR with low peak-up potential and high limiting diffusion current. Furthermore, we fabricated Li-air batteries on the basis of hierarchical mesoporous LSCO nanowires and nonaqueous electrolytes, which exhibited ultrahigh capacity, ca. over 11,000 mAh⋅g(-1), one order of magnitude higher than that of LSCO nanoparticles. Besides, the possible reaction mechanism is proposed to explain the catalytic activity of the LSCO mesoporous nanowire. PMID:23150570

  5. Anomalous field-induced magnetoresistance behavior in Pr0.5Sr0.5MnO3 at low temperatures

    NASA Astrophysics Data System (ADS)

    Kumar, Dhirendra; Shahee, Aga; Rawat, Rajeev; Lalla, N. P.

    2012-06-01

    Low-temperature (LT) XRD and magnetoresistance (MR) have been studied in the single phase polycrystalline Pr0.5Sr0.5MnO3 with space-group I4/mcm. The resistance-vs-temperature (R-T) variation at zero-field show a broad paramagnetic to ferromagnetic metallic (FMM) transition at Tc ˜ 240K and it further undergoes FMM to antiferromagnetic insulating (AFMI) transition at TN ˜ 90K with a broad hysteresis indicates a disorder broadened first order phase transition (FOPT). The zero-field cooled (ZFC) MR at 5K shows an open loop with virgin curve lying outside the envelope curve. This anomalous behavior vanishes with increasing temperature. This has been attributed to field-induced transformation of AFMI to FMM phase, which remains arrested down to zero magnetic field at 5K.

  6. Dielectric and enhanced pyroelectric properties of (Pb0.325Sr0.675)TiO3 ceramics under direct current bias field

    NASA Astrophysics Data System (ADS)

    Lei, Xiuyun; Dong, Xianlin; Mao, Chaoliang; Chen, Ying; Cao, Fei; Wang, Genshui

    2012-12-01

    (Pb0.325Sr0.675)TiO3 (PST) ceramics were prepared by a traditional solid-state reaction technique. The dielectric and enhanced pyroelectric properties of PST ceramics were investigated under a DC bias field. The dielectric permittivity and dielectric loss of PST ceramics at Curie temperature were 2.97 × 10-4 and 0.006 without DC bias field, respectively. With a DC electric field of 0-500 V/mm, the maximum pyroelectric coefficient and the largest figure of merit (Fd) of PST ceramics were obtained, about 60 × 10-8 C cm-2 K-1 and 26 × 10-5 Pa-1/2, respectively. PST ceramics with such superior electric field enhanced pyroelectric properties have the potential for uncooled focal plane array detectors application.

  7. Magnetoelectric properties of (Pb0.60Sr0.40)TiO3-CFO composite thin film synthesized by metallo-organic decomposition

    NASA Astrophysics Data System (ADS)

    Bala, Kanchan; Kotnala, R. K.; Negi, N. S.

    2015-06-01

    (Pb0.60Sr0.40) TiO3-CFO composite thin films were grown on Pt/TiO2/Si substrate by novel metallo-Organic process using spin coating technique. The structural, surface morphology and micro structural properties were confirmed by X-Ray diffraction (XRD), Raman spectroscopy, atomic force microscope (AFM) and TEM respectively. The lattice constant of the composite thin film crystallized in the pervoskite and spinel phase was 3.9531 and 8.571 Å. Excellent ferroelectric behavior at 10V was observed, a room temperature magnetic hysteresis shows good results. The saturation magnetization value of the bilayer thin film is lower than that of the pure CFO film which is may be attributed to presence of non ferromagnetic PST layer A high initial behavior of dynamic ME response coefficient for the film was observed. The ME effect of the film strongly depends on the magnetic bias.

  8. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2016-04-01

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

  10. Large magnetic entropy change above 300 K in a La 0.7Ca 0.2Sr 0.1MnO 3 single crystal

    NASA Astrophysics Data System (ADS)

    Phan, Manh-Huong; Peng, Hua-Xin; Yu, Seong-Cho; Hwi Hur, Nam

    2005-04-01

    A detailed study of the magneto-caloric effect in a single crystal of La0.7Ca0.2Sr0.1MnO3 has been made. The magnetic entropy change (Δ SM) reaches a maximum value of ∼7.45 J/kg K at ∼308 K for a 50 kOe field change, which is ideal for room-temperature magnetic refrigeration applications. Due to the absence of grains in the manganite single crystal, the Δ SM distribution of this sample is much more uniform than that of gadolinium and polycrystalline manganites, which is desirable for an Ericson-cycle magnetic refrigerator. The single crystal has the large magnetic entropy change induced by low magnetic field change, which is beneficial for the household application of active magnetic refrigerant (AMR) materials. These results indicate that the present single crystal is an excellent candidate as a working material for room-temperature AMR.

  11. 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.

  12. 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.

  13. Suppression of superconductivity in La1.85Sr0.15Cu1-yNiyO4: The relevance of local lattice distortions

    NASA Astrophysics Data System (ADS)

    Haskel, D.; Stern, E. A.; Polinger, V.; Dogan, F.

    2001-02-01

    The effect of Ni substitution upon the local structure of La1.85Sr0.15Cu1-yNiyO4 is commonly neglected when addressing the Ni-induced destruction of the superconducting state at y≈0.03 and a metal-insulator transition at y≈0.05. It is also sometimes assumed that direct substitution of a dopant into the CuO2 planes has a detrimental effect on superconductivity due to in-plane lattice distortions around the dopants. We present here results from angular-dependent x-ray absorption fine structure (XAFS) measurements at the Ni, La and Sr K-edges of oriented powders of La1.85Sr0.15Cu1-yNiyO4 with y=0.01, 0.03, 0.06. A special magnetic alignment geometry allowed us to measure pure ĉ and ab̂ oriented XAFS at the Ni K-edge in identical fluorescence geometries. Both the near-edge absorption spectra (XANES) and the XAFS unequivocally show that the NiO6 octahedra are largely contracted along the c-axis, by ≈ 0.16 Å. Surprisingly, the Ni-O planar bonds and the Ni-O-Cu/Ni planar buckling angle are nearly identical to their Cu counterparts. The NiO6 octahedral contraction drives the macroscopic ĉ-axis contraction observed with Ni-doping. The local ĉ-axis strongly fluctuates, due to the different NiO6 and CuO6 octahedral configurations and the much stronger bonding of a La+3 ion than a Sr+2 ion to the O(2) apical oxygens. We discuss the relevance of these findings to the mechanisms of Tc suppresion and hole-localization by Ni dopants.

  14. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2016-06-01

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

  16. 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.

  17. Comparative study of magnetic and magnetotransport properties of Sm0.55Sr0.45MnO3 thin films grown on different substrates

    NASA Astrophysics Data System (ADS)

    Srivastava, Manoj K.; Singh, Sandeep; Siwach, P. K.; Kaur, Amarjeet; Awana, V. P. S.; Maurya, K. K.; Singh, H. K.

    2013-05-01

    Highly oriented polycrystalline Sm0.55Sr0.45MnO3 thin films (thickness ˜100 nm) deposited on LaAlO3 (LAO, (001)), SrTiO3 (STO, (001)) and (La0.18Sr0.82) (Al0.59Ta0.41)O3 (LSAT, (001)) single crystal substrates by ultrasonic nebulized spray pyrolysis have been studied. The out of plane lattice parameter (OPLP) of the film on LAO is slightly larger than that of the corresponding bulk. In contrast, the OPLP of the films on STO and LSAT are slightly smaller than the corresponding bulk value. This suggests that the film on LAO is under compressive strain while LSAT and STO are under tensile strain. The films on LAO and LSAT show simultaneous paramagnetic-ferromagnetic (PM-FM) and insulator-metal transition (IMT) temperature at TC/TIM ˜ 165 K and 130 K, respectively. The PM-FM and IM transition occur at TC ˜ 120 K and TIM ˜ 105 K, respectively in the film on STO substrate. At T < TC, the zero field cooled-field cooled (ZFC-FC) magnetization of all the films shows strong bifurcation. This suggests the presence of a metamagnetic state akin to cluster glass formed due to coexisting FM and antiferromagnetic-charge order (AFM-CO) clusters. All the films show colossal magnetoresistance but its temperature and magnetic field dependence are drastically different. The films on LAO and STO show peak CMR around TC/TIM, while the film on LSAT shows MR > 99 % over a very wide temperature range of ˜40 K centred on TC/TIM. In the lower temperature region the magnetic field dependent isothermal resistivity also shows signature of metamagnetic transitions. The observed results have been explained in terms of the variation of the relative fractions of the coexisting FM and AFM-CO phases as a function of the substrate induced strain and oxygen vacancy induced quenched disorder.

  18. Electrochemical properties of the Sm 0.5Sr 0.5CoO 3-La 0.8Sr 0.2Ga 0.8Mg 0.15Co 0.05O 3 (LSGMC5)/LSGMC5 interface modified by an LSGMC5 interlayer synthesized using the citrate method

    NASA Astrophysics Data System (ADS)

    Wang, Shizhong; Zhong, Hao; Zou, Yuman

    A La 0.8Sr 0.2Ga 0.8Mg 0.15Co 0.05O 3 (LSGMC5) interlayer synthesized using the citrate method was added between an Sm 0.5Sr 0.5CoO 3 (SSC)-LSGMC5 electrode and an LSGMC5 electrolyte pellet synthesized using a solid-state reaction, and we found that the electrode activity was improved dramatically. The SEM images of the samples demonstrated that the contact between the electrode and the interlayer was much better than the contact between the electrode and electrolyte without the interlayer. The addition of the interlayer resulted in an increased three-phase boundary length and electrode/electrolyte two-phase interfacial area. An SSC-LSGMC5 electrode sintered at 1123 K deposited onto an interlayer sintered at 1673 K exhibited the highest performance among the samples studied. The electrode resistance was about 0.08 Ω cm 2 at near equilibrium conditions, and the cathodic overpotential at a current density of 1 A cm -2 was only about 70 mV at 973 K in oxygen. The introduction of the interlayer did not change the oxygen reaction mechanism, and the significant increase in electrode performance was due to the increase in the number of active sites for oxygen reduction.

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

    DOE PAGESBeta

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

    2015-11-20

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

  20. Magnetic properties of BaTiO3/La0.7Sr0.3MnO3 thin films integrated on Si(100)

    NASA Astrophysics Data System (ADS)

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

    2014-12-01

    Two-phase multiferroic heterostructures composed of room-temperature ferroelectric BaTiO3 (BTO) and ferromagnetic La0.7Sr0.3MnO3 (LSMO) epitaxial thin films were grown on technologically important substrate Si (100). Bilayers of BTO/LSMO thin films display ferromagnetic Curie transition temperatures of ˜350 K, close to the bulk value, which are independent of BTO films thickness in the range of 25-100 nm. Discontinuous magnetization jumps associated with BTO structural transitions were suppressed in M(T) curves, probably due to substrate clamping effect. Interestingly, at cryogenic temperatures, the BTO/LSMO structure with BTO layer thickness of 100 nm shows almost 2-fold higher magnetic coercive field, 3-fold reduction in saturation magnetization, and improved squareness compared to the sample without BTO. We believe that the strong in-plane spin pinning of the ferromagnetic layer induced by BTO layer at BTO/LSMO interface could cause such changes in magnetic properties. This work forms a significant step forward in the integration of two-phase multiferroic heterostructures for CMOS applications.

  1. 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.

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

    PubMed Central

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

    2016-01-01

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

  3. Microstructures and electrical properties of La 0.8Sr 0.2MnO 3 films synthesized by sol-gel method

    NASA Astrophysics Data System (ADS)

    Zhu, Xinde; Li, Shengli; Yang, Xiaojie; Qiu, Jie

    2007-11-01

    La 0.8Sr 0.2MnO 3 (LSMO) thin films were fabricated on alumina substrates by an improved sol-gel dip-coating process. It was found that multiple dip-coating process could not be performed until the pre-firing temperature reached 600 °C. Different amounts of LSMO powders were added to precursor solution with an aim to avoid cracks in LSMO thin films during calcining caused by the shrinkage mismatch between the film and the substrate. The structure and surface morphology of the films prepared from precursors with and without LSMO powders were characterized using X-ray diffraction (XRD) and scanning electron microscopy (SEM). It was found that the addition of 56.4 wt.% LSMO powders into the sol-gel precursor solution significantly modified the microstructure of films. A single LSMO perovskite phase was obtained on alumina substrate after calcining at 800 °C for 4 h by the improved sol-gel method. The sheet resistance of the films prepared with different processing parameters was measured by four-point dc method. Results indicated that the sheet resistance of films decreased with increasing the number of coating applications and the amount of LSMO powders.

  4. Ultrafast Dynamics of the Symmetry Breaking in Charge-ordered La1.75Sr0.25NiO4 Single Crystals

    NASA Astrophysics Data System (ADS)

    Coslovich, Giacomo; Kemper, Alexander F.; Behl, Sascha; Huber, Bernhard; Bechtel, Hans A.; Sasagawa, Takao; Martin, Michael C.; Kaindl, Robert A.

    We report equilibrium and ultrafast optical pump-THz probe spectroscopy of the stripe-phase rare-earth nickelate compound La1.75Sr0.25NiO4, unveiling the ultrafast dynamics of the crystal symmetry breaking and of local electronic arrangements. At low temperatures the folding of finite momenta vibrations due to symmetry breaking lead to the appearance of new IR-active resonances, particularly around the phonon bending mode frequency (~11 THz). Ultrafast experiments in the multi-THz spectral range show sharp THz reflectivity modulations associated with the phonon zone-folding dynamics, while the background conductivity is reminiscent of the opening of the mid-IR pseudogap. We combine experimental data with DFT calculations of the phonon dispersion to reveal the distinct dynamics of the LO and TO phonon modes at finite momenta. This work provides new insight in the role of polar electron-phonon coupling and symmetry breaking in charge-ordered systems. This work was supported by the US Department of Energy, Office of Basic Energy Sciences, Division of Materials Sciences and Engineering.

  5. 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.

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

    DOE PAGESBeta

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

    2015-05-26

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

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

    SciTech Connect

    Jacobsen, H; Zaliznyak, Igor; Savici, Andrei T; Winn, Barry L; Chang, S; Hucker, M.; Gu, Genda; Tranquada, John M.

    2015-01-01

    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 nearly energy-independent 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 (33 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 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.

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

    DOE PAGESBeta

    Jacobsen, H; Zaliznyak, Igor; Savici, Andrei T; Winn, Barry L; Chang, S; Hucker, M.; Gu, Genda; Tranquada, John M.

    2015-01-01

    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 nearly energy-independent 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 Omore » sites within the CuO2 planes. Furthermore, we observed a weak elastic (33 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 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. Combinatorial studies in Ba0.45Sr0.55TiO3 thin films for microwave components by radio frequency magnetron sputtering

    NASA Astrophysics Data System (ADS)

    Alema, Fikadu; Reinholz, Aaron; Pokhodnya, Konstantin

    2014-03-01

    The optimization of dielectric properties of ferroelectric thin films for microwave applications can be limited due to the time and resources consumption of the corresponding device fabrication and testing for each doping level. We report the use of a combinatorial technique to achieve the optimal doping level of Ba0.45Sr0.55TiO3 (BST) thin film with three dopants, Mg, Nb and lanthanide (Ln) metal. The process uses two R.F. magnetron sputtering BST sources doped with few at. % of MgII/NbV in charge compensating concentration and LnIV, respectively. The guns were shifted and tilted each by 30° in opposite directions to realize the dopants gradient across a static wafer. The film is reactively co-sputtered on the static 4'' platinized Al2O3 wafer. The film crystallinity and phase purity were analyzed and correlated to its dielectric properties measured on 2432 MIM capacitors that are of lithographically fabricated using Pt top electrode. After electrical testing, the wafer was diced into 22 16x16 mm2 samples, and the elemental analysis of each piece was performed. The correlation between the composition and dielectric properties was established and the optimal dopant concentrations for obtaining maximum tunability of 75% and minimum loss of 0.02 were determined.

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

    PubMed

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

    2014-04-23

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

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

    PubMed

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

    2015-01-01

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

  13. 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.

  14. 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. PMID:23464509

  15. 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.

  16. Selective electrochemical decomposition of outgrowths and nanopatterning in La 0.7 Sr 0.3 MnO3 perovskite thin films.

    PubMed

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

    2014-01-01

    The outgrowth formation in inorganic thin films is a dramatic problem that has limited the technological impact of many techniques and materials. Outgrowths are often themselves part of the films, but are detrimental for vertical junctions since they cause short-circuits or work as defects, compromising the reproducibility and in some cases the operation of the corresponding devices. The problem of outgrowth is particularly relevant in ablation-based methods and in some complex oxides, but is present in a large variety of systems and techniques. Here we propose an efficient local electrochemical method to selectively decompose the outgrowths of conductive oxide thin films by electrochemical decomposition, without altering the properties of the background film. The process is carried out using the same set-up as for local oxidation nanolithography, except for the sign of the voltage bias and it works at the nanoscale both as serial method using a scanning probe and as parallel method using conductive stamps. We demonstrated our process using La 0.7 Sr 0.3 MnO3 perovskite as a representative material but in principle it can be extended to many other conductive systems. PMID:25491921

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

    NASA Astrophysics Data System (ADS)

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

    2014-12-01

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

  18. Thermoelectric and electrical properties of Ba0.5Sr0.5Co x Ru x Fe(12-2 x)O19 ferrite*

    NASA Astrophysics Data System (ADS)

    Singh, Charanjeet; Jaroszewski, Maciej; Bindra Narang, Sukhleen; Ravinder, D.

    2016-04-01

    Thermoelectric and electrical characteristics investigation of M-type hexagonal ferrite, Ba0.5Sr0.5CoxRuxFe(12-2x)O19 (x = 0.0, 0.2, 0.4, 0.6, 0.8, 1.0, 1.2), have been carried out from 303 K to 473 K. The static current density-electric field characteristics have been measured at room temperature. The Seebeck coefficient indicates n-type behavior at lower substitution and p-type conduction at higher substitution. The different electrical parameters are affected by change in grain size with substitution of Co2+ and Ru4+ ions. The existence of polarons is confirmed from increase in conductivity with frequency. The static conduction due to applied electric field is discussed qualitatively in terms of space charge limited current, ionic hopping, Poole-Frenkel and Schottky-Richardson mechanisms. The large current density has been observed at higher substitution. Contribution to the Topical Issue "Materials for Dielectric Applications", edited by Maciej Jaroszewski and Sabu Thomas.

  19. Dielectric properties of low-temperature sintered Ba0.6Sr0.4TiO3 derived from citrate method

    NASA Astrophysics Data System (ADS)

    Zhang, X. F.; Xu, Q.; Huang, Y. H.; Huang, D. P.; Kim, B. H.

    2011-03-01

    Superfine and uniform Ba0.6Sr0.4TiO3 powder with average particle size of 56 nm was derived from citrate method at calcining temperature of 550 °C. The desired morphological feature of the powder was found to be effective in reducing sintering temperature of the ceramic specimens. Sintering at 1260 °C produced ceramic specimen with a fine-grained (about 0.5 μn) microstructure and reasonable densification around 95% of the theoretical density. The dielectric properties of the ceramic specimen were investigated in terms of dielectric thermal spectrum, polarization versus electric-field relation and dielectric nonlinearity under bias electric-field. The ceramic specimen exhibited a dielectric constant (epsilonr) of 3530 and a dielectric loss (tan δ) of 0.47% at 10 kHz and zero bias field together with a tunability of 39.3% at 10 kHz and 20 kV/cm. Moreover, the dielectric nonlinearity was detected to be sensitive to the field history. This sensitivity was tentatively explained with respect to the existence of polar nano-regions (PNRs) superimposed on macroscopically paraelectric background of the ceramic matrix.

  20. Influence of Calcining Temperature on CuO-Modified (Ba0.8Sr0.2)(Ti0.9Zr0.1)O3 Ceramics

    NASA Astrophysics Data System (ADS)

    Yang, Cheng-Fu; Wu, Long; Wu, Tien-Shou

    1992-07-01

    The sintering of (Ba0.8Sr0.2)(Ti0.9Zr0.1)O3 (abbreviated as BSTZ) with different amounts of CuO, which is used as the liquid phase promoter for lowering the temperature required to densify BSTZ, is studied using two types of calcined powders. For 1050°C calcination, the calcined powder contains BaTiO3, SrTiO3 and some raw materials such as ZrO2 and BaCO3. With sintering, some residual raw materials form unknown phases or low-dielectric-constant compounds with CuO, causing the liquid phase effect of CuO to disappear. For 1170°C calcination, the calcined powder completely forms ABO3 phases containing (Ba, Sr)TiO3 and BaZrO3. The sintering temperature for densification of ceramics is lowered, and the firing characteristics critically depend on the amount of CuO added and the sintering temperature.

  1. Al3+ doping effects and high-field phase diagram of La0.5Sr0.5Mn1-x Al x O3

    NASA Astrophysics Data System (ADS)

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

    2016-01-01

    Magnetization measurements of La0.5Sr0.5Mn1-x Al x O3 (0  ⩽  x  ⩽  0.25) under pulsed high magnetic fields up to 50 T have been carried out, in which the Al3+ ions doping and magnetic field effects on the charge-ordering/antiferromagnetic to ferromagnetic phase transitions have been discussed. A triple-phase diagram with the critical field, doping level and temperature has been determined, in which the antiferromagntic and ferromagnetic phase boundaries were clearly defined. The change from long-range charge-ordered/antiferromagnetic phases to the robust short-range ones upon the Al3+-doping was observed. According to the experimental results, we assume that Al3+ ion doping at the Mn sites dilutes the Mn3+-O-Mn4+ network, weakens the double-exchange interaction and further suppresses the FM phase (metallic conduction), which leads to the critical magnetic fields destroying the antiferromagnetic order increase with the increase of the doping level.

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

    PubMed

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

    2013-11-01

    Surface of La(0.7)Sr(0.3)MnO3 (LSMO) magnetic nanoparticles (MNPs) is functionalized with polymer (dextran) and their colloidal stability in various mediums is carried out. The influence of the surface functionalization of LSMO MNPs on their colloidal stability in physiological media is studied and correlated with their hyperthermia properties. Many studies have concerned the colloidal stability of MNPs coated with polymer, but their long-term stability when such complexes are exposed to physiological media is still not well understood. After zeta potential study, it is found that the dextran coating on MNPs improves the colloidal stability in water as well as in physiological media like PBS. The specific absorption rates (SAR) of these MNPs are found to be in 50-85 W/g in different concentrations of glucose and NaCl; and there values are suitable for hyperthermia treatment of cancer cells under AC magnetic field. After incorporation of MNPs up to 0.2-1mg/mL in 2 × 10(5)cells/mL (L929), the apoptosis and necrosis studies are carried out by acridine orange and ethidium bromide (AO and EB) staining and followed by visualization of microstructures under a fluorescence microscope. It is found that there are no morphological changes (i.e. no signs of cell rounding, bubble formation on the membrane and nuclear fragmentation) suggesting biocompatibility of dextran coated LSMO nanoparticles up to these concentrations. PMID:23838191

  3. Broad-band dielectric spectroscopy and ferroelectric soft-mode response in the Ba(0.6)Sr(0.4)TiO(3) solid solution.

    PubMed

    Ostapchuk, T; Petzelt, J; Hlinka, J; Bovtun, V; Kužel, P; Ponomareva, I; Lisenkov, S; Bellaiche, L; Tkach, A; Vilarinho, P

    2009-11-25

    Ceramic Ba(0.6)Sr(0.4)TiO(3) (BST-0.6) samples were studied in the broad spectral range of 10(6)-10(14) Hz by using several dielectric techniques in between 20 and 800 K. The dominant dielectric dispersion mechanism in the paraelectric phase was shown to be of strongly anharmonic soft-phonon origin. The whole soft-mode response in the vicinity of the ferroelectric transition was shown to consist of two coupled overdamped THz excitations, which show classical features of a coupled soft and central mode, known from many ferroelectric crystals with a dynamics near the displacive and order-disorder crossover. Similar behaviour has been recently revealed and theoretically simulated in pure BaTiO(3) (see Ponomareva et al 2008 Phys. Rev. B 77 012102 and Hlinka et al 2008 Phys. Rev. Lett. 101 167402). Also for the BST system, this feature was confirmed by the theory based on molecular dynamics simulations with an effective first-principles Hamiltonian. In all the ferroelectric phases, additional relaxation dispersion appeared in the GHz range, assigned to ferroelectric domain-wall dynamics. The microwave losses were analysed from the point of view of applications. The paraelectric losses above 1 GHz are comparable with those in single crystals and appear to be of intrinsic multi-phonon origin. The ceramic BST system is therefore well suited for applications in the whole microwave range. PMID:21832494

  4. Influence of Ga doping on rare earth moment ordering and ferromagnetic transition in Nd0.7Sr0.3Co1-xGaxO3

    NASA Astrophysics Data System (ADS)

    Kumar, Pawan; Maheswar Repaka, D. V.; Aparnadevi, M.; Tripathi, T. S.; Mahendiran, R.

    2013-05-01

    We report the impact of dilution of Co sublattice by non-magnetic Ga3+ ion on the magnetic, electrical, and magnetoresistive properties in Nd0.7Sr0.3Co1-xGaxO3 for x = 0-0.12. Field-cooled magnetization of the parent compound (x = 0) shows an anomalous maximum at T* = 54.6 K much below the onset of ferromagnetic transition (TC = 160 K) of the Co sublattice, which is attributed to the polarization of Nd-4f moments antiparallel to the Co-3d sublattice. Both TC and T* shift to low temperature with increasing x and the Nd-4f spin reverses from antiparallel to parallel with increasing strength of the magnetic field. While the value of high field magnetization is not seriously affected by Ga doping, coercive field at 10 K increases dramatically with increasing x. Ga substitution transforms ferromagnetic metallic state into ferromagnetic insulating state for x ≥ 0.03 and decreases the magnitude of magnetoresistance from 6% for x = 0% to 0.5% for x = 0.12.

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

    NASA Astrophysics Data System (ADS)

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

    2005-08-01

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

  6. 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.

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

    PubMed

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

    2013-02-13

    Optimally doped La(1.85)Sr(0.15)CuO(4) 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 (H(C2)) and the surface critical field (H(C3)) were measured. The H-T phase diagram is presented. Close to T(C) = 35 K, for the c-crystal, γ(C) = H(C3)(c)/H(C2)(c) = 1.80(2), whereas for the a-crystal the γ(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 γ(a) and the PME are connected to each other. PMID:23315336

  8. Surface stoichiometry of La0.7Sr0.3MnO3 during in vacuo preparation; A synchrotron photoemission study

    NASA Astrophysics Data System (ADS)

    Monsen, Å. F.; Song, F.; Li, Z. S.; Boschker, J. E.; Tybell, T.; Wahlström, E.; Wells, J. W.

    2012-09-01

    We present a study of the surface stoichiometry and contamination of La0.7Sr0.3MnO3 thin films following exposure to air and subsequent in vacuo preparation. Samples were studied using both soft X-ray synchrotron photoemission (hν = 150 to 350 eV) and traditional Mg-Kα XPS (hν = 1253.6 eV) whilst annealing incrementally to ≈ 510°C in low pressures of O2. In all cases, a Mn depleted and Sr rich surface oxide layer is observed, it is of reduced crystalline quality and is charge depleted. This surface layer is weakly affected by subsequent annealing, and is partially reversed by annealing in higher O2 pressure. Surface carbon contamination is incrementally removed by annealing at increased temperatures, and at 270 °C, it is reduced to ≈ 0.4% of the topmost unit cell. The modification of the surface stoichiometry and electronic properties is consistent with the reported loss of magnetic properties in thin LSMO films.

  9. Magnetic and Mössbauer studies on oxygen deficient perovskite, La0.6Sr0.4FeO3-δ

    NASA Astrophysics Data System (ADS)

    Yang, J. B.; Yelon, W. B.; James, W. J.; Zhou, X. D.; Xie, Y. X.; Anderson, H. U.; Chu, Z.

    2002-05-01

    Samples of La0.6Sr0.4Fe3-δ with varying oxygen vacancy contents were prepared by heating them in different gas flows. Magnetization measurement showed that samples with low oxygen vacancies have a magnetic ordering temperature in the range of 300-325 K while those with 9%-12% oxygen vacancies have a magnetic ordering temperature of 800 K and higher. Mössbauer spectra at 300 K exhibit paramagnetic or weak magnetic characteristics for the N2, O2, and air-quenched samples, whereas an average hyperfine field of 52 T is found for the CO/CO2 reduced samples. The heat treatment in the reducing atmosphere creates oxygen vacancies and increases unit cell volume. However, the Fe-O bond length remains nearly constant, resulting in distortion/rotation of the oxygen octahedra which increases the Fe-O-Fe bond angle as much as 12 degrees. This dramatically affects the Fe-O-Fe superexchange coupling and plays a key role in the increase of the Nèel temperatures.

  10. Magnetocaloric effect of monovalent K doped manganites Pr0.6Sr0.4-xKxMnO3 (x=0 to 0.2)

    NASA Astrophysics Data System (ADS)

    Thaljaoui, R.; Boujelben, W.; Pękała, M.; Pękała, K.; Fagnard, J.-F.; Vanderbemden, P.; Donten, M.; Cheikhrouhou, A.

    2014-02-01

    Magnetic and magnetocaloric properties are reported for polycrystalline monovalent potassium doped manganites Pr0.6Sr0.4-xKxMnO3 (x=0, 0.05, 0.1, 0.15 and 0.2) crystallized in orthorhombic structure with Pnma space group. The increasing K content shifts the paramagnetic to ferromagnetic transition temperature from 310 K for x=0 to 269 K for x=0.2. The magnetic entropy change under magnetic field variation of 2 T is found to be 1.95, 3.09, 2.89, 3.05 and 3.2 J/kgK for x varying from 0 to 0.2, respectively. The highest relative cooling power of 102 J/kg is observed for the undoped sample. The sensitivity of magnetic entropy change to magnetic field is estimated by a local N(T) exponent exhibiting the characteristic temperature variation. Phenomenological universal curves of entropy change and Arrott plots confirm the second order phase transition.

  11. Influences of spark plasma sintering temperature on the microstructures and thermoelectric properties of (Sr0.95Gd0.05)TiO3 ceramics

    NASA Astrophysics Data System (ADS)

    Li, Liang-Liang; Qin, Xiao-Ying; Liu, Yong-Fei; Liu, Quan-Zhen

    2015-06-01

    (Sr0.95Gd0.05)TiO3 (SGTO) ceramics are successfully prepared via spark plasma sintering (SPS) respectively at 1548, 1648, and 1748 K by using submicron-sized SGTO powders synthesized from a sol-gel method. The densities, microstructures, and thermoelectric properties of the SGTO ceramics are studied. Though the Seebeck coefficient shows no obvious difference in the case that SPS temperatures range from 1548 K to 1648 K, the electrical conductivity and the thermal conductivity increase remarkably due to the increase in grain size and density. The sample has a density higher than 98% theoretical density as the sintering temperature increases up to 1648 K and shows average grain sizes increasing from ˜ 0.7 μm to 7 μm until 1748 K. As a result, the maximum of the dimensionless figure of merit of ˜ 0.24 is achieved at ˜ 1000 K for the samples sintered at 1648 K and 1748 K, which was ˜ 71% larger than that (0.14 at ˜ 1000 K) for the sample sintered at 1548 K due to the enhancement of the power factor. Project supported by the National Natural Science Foundation of China (Grant Nos. 11174292, 51101150, and 11374306).

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

    NASA Astrophysics Data System (ADS)

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

    2016-08-01

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

  13. Alignment of energy levels at the Alq3/La0.7Sr0.3MnO3 interface for organic spintronic devices

    NASA Astrophysics Data System (ADS)

    Zhan, Y. Q.; Bergenti, I.; Hueso, L. E.; Dediu, V.; de Jong, M. P.; Li, Z. S.

    2007-07-01

    The electronic structure of the interface between tris(8-hydroxyquinolino)-aluminum (Alq3) and La0.7Sr0.3MnO3 (LSMO) manganite was investigated by means of photoelectron spectroscopy. As demonstrated recently, this interface is characterized by efficient spin injection in organic spintronic devices. We detected a strong interface dipole of about 0.9eV that shifts down the whole energy diagram of the Alq3 with respect to the vacuum level. This modifies the height of the barrier for the injection into highest occupied molecular orbital level to 1.7eV , indicating more difficult hole injection at this interface than expected for the undistorted energy level diagram. We believe that the interface dipole is due to the intrinsic dipole moment of the Alq3 layer. The presented data lead to significant progress in understanding the electronic structure of LSMO/Alq3 interface and represent a step toward the description of spin transport in organic spin valves.

  14. Twinned domain induced magnonic modes in La0.7Sr0.3MnO3/SrTiO3(001) thin films

    NASA Astrophysics Data System (ADS)

    Wahlström, Erik; Macia, Ferran; Boschker, Jos E.; Monsen, Åsmund; Norblad, Per; Mathieu, Roland; Kent, Andrew D.; Tybell, Thomas

    2015-03-01

    By defining a periodic magnetic structure it iss possible to excite magnonic modes other than standard uniform magnetodynamic modes. However, a traditional top-down approach to define structures at length scales <100 nm is often challenging. Here we present a bottom up approach to such magnonic lattices. In order to achieve this we rely on epitaxial thin films of a prototypical perovskite, La0.7Sr0.3MnO3, on top of SrTiO3(001), with an intended structural twinned domain geometry, acting as a periodic perturbation for the magnonic lattice. Variable temperature ferromagnetic resonance spectroscopy (FMR) gives evidence for additional magnonic modes. We will show that the origin of these modes can be related to a spatial modulation of the Curie temperature induced by the twin domain formation. This yields a temperature dependent magnetic variation in the saturation magnetization that forms the magnonic structure. We will discuss how film thickness and structural domain periodicity affects the excited modes. In particular the temperature dependence of the magnetic structure will be discussed and used in a model description of the system that accounts for the major features of FMR spectra.

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

    PubMed Central

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

    2014-01-01

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

  16. 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

  17. 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.

  18. 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

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

    PubMed

    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 T(1/2) 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

  20. 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. PMID:25643075

  1. Avalanches and hysteresis at the structural transition in stripe-ordered La1.48Nd0.4Sr0.12CuO4

    NASA Astrophysics Data System (ADS)

    Baity, P. G.; Saraswat, Garima; Popović, Dragana; Sasagawa, T.

    The coupling or intertwining of lattice, spin and charge orders and their effects on superconductivity are of great current interest in the physics of cuprates. The rare-earth-doped cuprate La1.48Nd0.4Sr0.12CuO4 (LNSCO), for example, exhibits a first-order structural phase transition (SPT) from the low-temperature orthorhombic (LTO) to the low-temperature tetragonal (LTT) phase, with the onset of the static charge stripe order roughly coinciding with the SPT. We present out-of-plane magnetoresistance measurements around the LTO-LTT transition in LNSCO single crystals with H ∥ c up to 12 T and H ∥ ab up to 9 T. Hysteresis is observed for both field orientations, but for H ∥ c we also find evidence for the existence of metastable states and collective dynamics in the form of avalanches and return point memory. Such behavior indicates that, in LNSCO, the LTO-LTT structural transition can be driven with H. A detailed analysis of the avalanche statistics is used to determine their size and field dependence, and to extract information about the domain structure and dynamics of domain walls. Our results shed light on the interplay of lattice, spin and charge degrees of freedom in stripe-ordered La-based cuprates. Supported by NSF DMR-1307075 and NHMFL via NSF DMR-1157490 and the State of Florida.

  2. 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

  3. Electron microscopic studies of the antiferroelectric phase in Sr 0.60Ca 0.40TiO 3 ceramic

    NASA Astrophysics Data System (ADS)

    Anwar, Shahid; Lalla, N. P.

    2008-05-01

    The structural variants and their coexistence across the antiferroelectric phase transition in Sr 0.60Ca 0.40TiO 3 ceramic has been studied through transmission electron microscopy (TEM) at room temperature and ˜100 °C. A clear evidence of the presence of superlattice reflections, corresponding to the cell doubling along the c-axis of Pbnm (or b-axis along Pnma), occurring during paraelectric to antiferroelectric transition, has been obtained through selected area electron diffraction, convergent beam electron diffraction and lattice-resolution imaging. Coexistence of the Pbnm and Pbcm phases at room temperature has been observed and attributed to the strain/disorder-induced broadening of the first-order antiferroelectric phase transition. Drastic changes in the domain structure during Pbnm to Pbcm transformation have been observed. This clearly indicates that the antiferrodistortive transition responsible for the occurrence of the antiferroelectric phase is of completely different origin and it is not just an additional follow-up of the already-existing ordering due to a-a-c+ tilt schemes in the Pbnm domain. Thermal cycling studies on microstructural changes indicate some kind of memory mechanism, which retains the memory of the original a-a-c+ tilt schemes in the Pbnm phase. This has been attributed to the symmetry conforming short-range order (SC-SRO) of the point defects.

  4. Understanding the origin of photoluminescence in disordered Ca 0.60Sr 0.40WO 4: An experimental and first-principles study

    NASA Astrophysics Data System (ADS)

    Longo, V. M.; Orhan, E.; Cavalcante, L. S.; Porto, S. L.; Espinosa, J. W. M.; Varela, J. A.; Longo, E.

    2007-04-01

    Visible photoluminescence (PL) was observed for the first time at room temperature in structurally disordered calcium strontium tungstate powder, Ca 0.60Sr 0.40WO 4 (CSW), obtained by the polymeric precursor method. The PL behavior of CSW powders has been analyzed as a function of the disorder rate, based on experimental and theoretical studies. Quantum mechanical theory based on density functional theory at the B3LYP level has been employed to study the electronic structure of two periodic models representing both crystalline and disordered powders. Their electronic structures have been analyzed in terms of density of states, band dispersion and charge densities. The calculations indicate a break in symmetry when passing from crystalline to disordered models, creating localized electronic levels above the valence band. Moreover, a negative charge transfer process takes place from the [WO 3] cluster to the [WO 4] cluster. The polarization induced by the break in symmetry and the existence of localized levels favors the creation of trapped holes and electrons, originating the PL phenomenon.

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

    DOE PAGESBeta

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

    2015-10-08

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

  6. 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.

  7. 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.

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

    PubMed

    Fan, Hui; Han, Minfang

    2015-01-01

    Composite SSC (Sm(0.5)Sr(0.5)CoO(3-δ))-YSZ (yttria stabilized zirconia) oxygen electrodes were prepared by an infiltration process. X-ray diffraction (XRD) analysis and scanning electron microscopy (SEM) of the composite electrodes showed the formation of SSC perovskite and a well-connected network of SSC particles in the porous YSZ backbone, respectively. The electrochemical performance of the cell was investigated under both fuel cell and steam electrolysis modes using polarization curves and electrochemical impedance spectroscopy (EIS). The cell experienced a large degradation rate at 700 °C with a constant voltage of 0.7 V for over 100 h under power generation operation. The subsequent post-cell SEM micrograph revealed that agglomeration of the infiltrated SSC particles was possibly the cause for the performance deterioration. Furthermore, the long-term stability of the cell was examined at 700 °C with a constant voltage of 1.3 V under steam electrolysis mode. SEM associated with energy dispersive X-ray spectroscopy (EDS) was employed to characterize the post-test cell after the long-term electrolysis operation and it indicated that besides the agglomeration of SSC particles, the delamination of the SSC-YSZ oxygen electrode from the YSZ electrolyte, as well as segregation of cobalt-enriched particles (particularly cobalt oxides) at the interface, was probably responsible for the cell degradation under the steam electrolysis mode. PMID:26212177

  9. Effects of oxygen content on the structural and transport properties in epitaxial Nd0.7Sr0.3MnO thin films

    NASA Astrophysics Data System (ADS)

    Meng, Ying; He, Wenlan; Li, Aixia; Li, Guang; Jin, Shaowei

    2012-07-01

    Epitaxial Nd0.7Sr0.3MnO3-x (NSMO) thin films, 120 nm thickness, were grown coherently on the (0 0 1) (LaAlO3)0.3 (Sr2AlTaO6)0.7 (LSAT) substrates by using pulsed-laser deposition (PLD). Effects of oxygen contents controlled by post-annealing in vacuum on the structural and transport properties of the NSMO films were carefully studied by x-ray reciprocal space maps (RSMs) and resistivity measurements. It is clearly shown that both the out-of-plane lattice parameters of the films and the transition temperatures Tp (peak resistance) can simultaneously change as the oxygen contents, the in-plane lattice coherency is maintained consistently with that of the LSAT substrate at the same time. The larger altered transport properties are chiefly ascribed to the increase of Mn3+ ions and the distortion of MnO6 octahedra in films. The oxygen compositions are deduced from the out-of-plane lattice parameters of coherency epitaxy NSMO films. The Kröger-Vink notation was used for explaining the correlation of oxygen vacancy and transport properties.

  10. 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

  11. Influence of epitaxial growth on phase competition in Pr 0.5Sr 0.5MnO 3 films

    NASA Astrophysics Data System (ADS)

    Chen, Liping; Chen, Yuansha; Ma, Yubin; Lian, Guijun; Zhang, Yan; Xiong, Guangcheng

    2012-03-01

    A series of Pr0.5Sr0.5MnO3 (PSMO) films with various thickness were epitaxially grown on substrates of (0 0 1)-oriented (LaAlO3)0.3(SrAl0.5Ta0.5O3)0.7 (LSAT), LaAlO3 (LAO) and SrTiO3 (STO), and (0 1 1)-oriented STO using pulse laser deposition. Influence of epitaxial growth on phase competition was investigated. A ferromagnetic metal to antiferromagnetic insulator (FMM-AFI) transition upon cooling is present in both largely compressed situations deposited on LAO (0 0 1) and tensile cases deposited on STO (0 0 1) but absent in little strained films grown on LSAT (0 0 1), indicating that the antiferromagnetic insulating state is favored by strains. On the other hand, the 400 nm films deposited on (0 1 1)-oriented STO as well as LAO substrates show FMM-AFI transition. These results reveal that both the orientation of epitaxial growth and substrate-induced strain affect the FMM-AFI transition.

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

    DOE PAGESBeta

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

    2016-07-11

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

  13. 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.

  14. Band gap formation in La0.7Sr0.3MnO3 (LSMO) thin films measured by reflectivity/absorption and ultrafast spectroscopy

    NASA Astrophysics Data System (ADS)

    Cabrera, Guerau; Trappen, Robbyn; Chu, Ying-Hao; Holcomb, Mikel

    Thin film La0.7Sr0.3MnO3 (LSMO) is a prime candidate for highly spin-polarized magnetic-tunnel-junction memories. Due to its magnetic properties, it is also a good candidate for applications utilizing electrical control of magnetism when grown adjacent to a ferroelectric layer such as Pb(Zr/Ti)O3 (PZT). Recently, Wu and others have seen the emergence of a band gap (about 1eV) in LSMO thin films, when grown adjacent to PZT. Currently, it is understood that LSMO is a half-metal, with a pseudo-gap due to a low desity of states (DOS) near the Fermi level. The transition from pseudo-gap to band gap is not yet fully understood. It is therefore our aim to investigate the formation of this band gap through optical reflectivity/absorption and ultrafast carrier dynamics for a variety of thicknesses ranging from a few nanometers to thicker films (about 100 nm).

  15. Microporous La0.8Sr0.2MnO3 perovskite nanorods as efficient electrocatalysts for lithium-air battery

    NASA Astrophysics Data System (ADS)

    Lu, Fanliang; Wang, Yarong; Jin, Chao; Li, Fan; Yang, Ruizhi; Chen, Fanglin

    2015-10-01

    Efficient electrocatalyst for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) is the most critical factor to influence the performance of lithium-air batteries. We present La0.8Sr0.2MnO3 (LSM) perovskite nanorods as high active electrocatalyst fabricated via a soft template method for lithium-air batteries. The as-prepared LSM nanorods are microporous with numerous defects and large surface area (20.6 m2 g-1), beneficial to the ORR and OER in the discharge and charge processes, respectively. Lithium-air batteries based on the microporous LSM nanorods electrocatalysts show enhanced electrochemical performances, including high first discharge specific capacity (6890 mAh g-1(electrode) at 200 mA g-1), low overpotential, good rate capability (up to 400 mA g-1), and cycle stability (only 1.1% voltage loss after 30 circles of specific capacity limit of 1000 mAh g-1 tested at 200 mA g-1). The improved performance might be due to the synergistic effect of the unique microporous and one-dimensional structure and numerous defects of the prepared LSM catalyst.

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

    NASA Astrophysics Data System (ADS)

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

    2015-04-01

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

  17. 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

  18. 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.

  19. A modified liquid-phase-assisted sintering mechanism for La0.8Sr0.2Cr1-xFexO3-δ-A high density, redox-stable perovskite interconnect for solid oxide fuel cells

    NASA Astrophysics Data System (ADS)

    Wei, Tao; Liu, Xiaojuan; Yuan, Chun; Gao, Qingyu; Xin, Xianshuang; Wang, Shaorong

    2014-03-01

    Fe-doped lanthanum strontium chromites, i.e., La0.8Sr0.2Cr1-xFexO3-δ (x = 0.1, 0.2, 0.3, 0.4, and 0.5), are synthesised and evaluated as potential interconnect materials for SOFCs. A modified liquid-phase-assisted sintering mechanism is employed to improve the sintering abilities of La0.8Sr0.2Cr1-xFexO3-δ powders. A distinct transient liquid phase forms during the sintering process, which spreads into a uniform layer and covers the grain boundaries, thereby enhancing densification. Additionally, it is determined that the amount of liquid phase formed during liquid-phase-assisted sintering significantly affects the densification of doped lanthanum chromites. Relative densities of 94.6% and 96.6% are successfully obtained for La0.8Sr0.2Cr0.6Fe0.4O3-δ and La0.8Sr0.2Cr0.5Fe0.5O3-δ, respectively. Furthermore, these compounds are also redox-stable after being heated to 900 °C in flowing H2 for 6 h. The electrical conductivity increases with Fe-doping levels, and the conductivity of La0.8Sr0.2Cr0.5Fe0.5O3-δ is measured to be 21.88 S cm-1 in air and 6.45 S cm-1 in 5% H2/Ar at 800 °C. Therefore, dense La0.8Sr0.2Cr0.5Fe0.5O3-δ is a promising interconnect alternative for solid oxide fuel cells.

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

    PubMed

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

    2016-08-23

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

  1. Structural and magnetic properties of La0.7Sr0.1AgxMnO3-δ perovskite manganites

    NASA Astrophysics Data System (ADS)

    Hou, Xue; Ji, Deng-Hui; Qi, Wei-Hua; Tang, Gui-De; Li, Zhuang-Zhi

    2015-05-01

    Ag-doped manganite powder samples, La0.7Sr0.1AgxMnO3-δ (x = 0.00, 0.025, 0.05, 0.075, and 0.10) were synthesized using the sol-gel method. X-ray diffraction patterns indicated that the samples had two phases with the perovskite being the dominant phase and Mn3O4 being the second phase. X-ray energy dispersive spectra indicated that the ratio of Ag to La was very close to that of the nominal composition in the samples. The specific saturation magnetizations at 300 K increased from 32.0 A·m2/kg when x = 0.00 to 46.8 A·m2/kg when x = 0.10. The Curie temperature, TC, of the samples increased from 310 K when x = 0.00 to 328 K when x = 0.10. Because the atomic concentration ratios of La, Sr, and Mn in the five samples were all the same and only the Ag concentration changed, the variations of the specific saturation magnetizations at 300 K and the Curie temperatures suggested that the Ag cations have been doped into the A sites of the perovskite phase in the samples. Project supported by the National Natural Science Foundation of China (Grant No. NSF-11174069), the Natural Science Foundation of Hebei Province, China (Grant No. E2011205083), the Key Item Science Foundation of Hebei Province, China (Grant No. 10965125D), the Key Item Science Foundation of the Education Department of Hebei Province, China (Grant No. ZD2010129), and the Young Scholar Science Foundation of the Education Department of Hebei Province, China (Grant No. QN20131008).

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

    NASA Astrophysics Data System (ADS)

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

    2016-06-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2013-01-01

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

  4. Investigations on the spin-glass state in Dy0.5Sr0.5MnO3 single crystals through structural, magnetic and thermal properties

    NASA Astrophysics Data System (ADS)

    Harikrishnan, S.; Naveen Kumar, C. M.; Bhat, H. L.; Elizabeth, Suja; Rößler, U. K.; Dörr, K.; Rößler, S.; Wirth, S.

    2008-07-01

    Single crystals of Dy0.5Sr0.5MnO3 are grown using the optical floating zone technique, and their structural, magnetic, transport and thermal properties have been investigated. Magnetization measurements under field-cooled and zero-field-cooled conditions display irreversibility below 35 K. The magnetization does not saturate up to fields of 5 T in the temperature range 5-350 K. AC susceptibility shows a cusp around 32 K that shifts to higher temperature with increasing frequency. This frequency dependence of the peak temperature follows a critical slowing down with exponent zν = 3.6. Electrical resistivity shows insulating behavior, and the application of magnetic fields up to 10 T does not change this qualitative behavior. However, a marked negative magnetoresistance is observed in the paramagnetic phase reaching 80% at 70 K and 10 T. The observed resistivity behavior does not obey an activated type of conduction. These features are characteristic of spin-glass behavior in this half-doped insulating manganite. It is argued that the spin-glass-like state originates from the A-site disorder, which in turn results from the random distribution of cations with different ionic radii. Specific-heat measurements reveal a sizable linear contribution at low temperature that may be associated with the glassy magnetic ordering and a Schottky-like anomaly in a wide temperature range between 8 and 40 K. The distribution of Schottky levels is explained by the inhomogeneity of the molecular field in the spin-glass state that leads to variable splitting of the Kramers ground-state doublets in Dy3+.

  5. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2016-04-01

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

  7. Composite anode La0.8Sr0.2MnO3 impregnated with cobalt oxide for steam electrolysis

    NASA Astrophysics Data System (ADS)

    Li, Shisong; Cheng, Jigui; Xie, Kui; Li, Peipei; Wu, Yucheng

    2013-12-01

    Oxygen-ion conducting solid oxide electrolyzer (SOE) has attracted a great deal of interest because it converts electrical energy into chemical energy directly. The oxygen evolution reaction (OER) is occurred at the anode of solid oxide electrolyzer as the O2- being oxidized and form O2 gas, which is considered as one of the major cause of overpotentials in steam electrolyzers. This paper investigates the electrolysis of steam based on cobalt oxide impregnated La0.8Sr0.2MnO3 (LSM) composite anode in an oxide-ion-conducting solid oxide electrolyzer. The conductivity of LSM is studied versus temperature and oxygen partial pressure and correlated to the electrochemical properties of the composite electrodes in symmetric cells at 800 °C. Different contents of Co3O4 (wt.1%, 2%, 4%, 6%, 8%, 10%) were impregnated into LSM electrode and it was found that the polarization resistance (Rp) of symmetric cells gradually improved from 1.16 Ω•cm2 (LSM) to 0.24 Ω•cm2 (wt.10%Co3O4-LSM). Steam electrolysis based on LSM and wt.6%Co3O4-LSM anode electrolyzers are tested at 800°C and the AC impedance spectroscopy results indicated that the Rp of high frequency process significantly decreased from1.1 Ω•cm2 (LSM) to 0.5 Ω•cm2 (wt.6%Co3O4-LSM) under 1.8V electrolysis voltage and the Rp of low frequency process decreased from 14.9 Ω•cm2 to 5.7 Ω•cm2. Electrochemical catalyst Co3O4 can efficiently improve the electrode and enhance the performance of high temperature solid oxide electrolyzer.

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

    PubMed

    Tsvetkov, Nikolai; Lu, Qiyang; Yildiz, Bilge

    2015-01-01

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

  9. 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.

  10. Chromium deposition and poisoning of La(0.8)Sr(0.2)MnO3 oxygen electrodes of solid oxide electrolysis cells.

    PubMed

    Chen, Kongfa; Hyodo, Junji; Dodd, Aaron; Ai, Na; Ishihara, Tatsumi; Jian, Li; Jiang, San Ping

    2015-01-01

    The effect of the presence of an Fe-Cr alloy metallic interconnect on the performance and stability of La(0.8)Sr(0.2)MnO3 (LSM) oxygen electrodes is studied for the first time under solid oxide electrolysis cell (SOEC) operating conditions at 800 °C. The presence of the Fe-Cr interconnect accelerates the degradation and delamination processes of the LSM oxygen electrodes. The disintegration of LSM particles and the formation of nanoparticles at the electrode/electrolyte interface are much faster as compared to that in the absence of the interconnect. Cr deposition occurs in the bulk of the LSM oxygen electrode with a high intensity on the YSZ electrolyte surface and on the LSM electrode inner surface close to the electrode/electrolyte interface. SIMS, GI-XRD, EDS and XPS analyses clearly identify the deposition and formation of chromium oxides and strontium chromate on both the electrolyte surface and electrode inner surface. The anodic polarization promotes the surface segregation of SrO and depresses the generation of manganese species such as Mn(2+). This is evidently supported by the observation of the deposition of SrCrO4, rather than (Cr,Mn)3O4 spinels as in the case under the operating conditions of solid oxide fuel cells. The present results demonstrate that the Cr deposition is essentially a chemical process, initiated by the nucleation and grain growth reaction between the gaseous Cr species and segregated SrO on LSM oxygen electrodes under SOEC operating conditions. PMID:26206416

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

    PubMed

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

    2015-04-01

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

  12. 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. PMID:11006557

  13. A novel solution-phase approach to nanocrystalline niobates: selective syntheses of Sr0.4H1.2Nb2O6.H2O nanopolyhedrons and SrNb2O6 nanorods photocatalysts.

    PubMed

    Liang, Shijing; Wu, Ling; Bi, Jinhong; Wang, Wanjun; Gao, Jian; Li, Zhaohui; Fu, Xianzhi

    2010-03-01

    A novel solution-phase route using Nb(2)O(5).nH(2)O as precursor was developed to selectively synthesize single-crystalline Sr(0.4)H(1.2)Nb(2)O(6).H(2)O nanopolyhedrons and SrNb(2)O(6) nanorods photocatalysts via simply adjusting pH values of the reactive solutions. PMID:20162143

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

    NASA Astrophysics Data System (ADS)

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

    2014-11-01

    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.

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

    PubMed

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

    2015-12-01

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

  16. Dielectric properties of Ba0.6Sr0.4TiO3-La(B0.5Ti0.5)O3 (B=Mg, Zn) ceramics.

    PubMed

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

    2009-11-01

    Ba(0.6)Sr(0.4)TiO(3)-La(B(0.5)Ti(0.5))O(3) (B = Mg, Zn) ceramics were prepared by a solid-state reaction method, and their microwave dielectric characteristics and tunability were investigated. The ferroelectric-dielectric solid solutions with cubic perovskite structures were obtained for compositions of 10 to 60 mol% La(Mg(0.5)Ti(0.5))O(3) and 10 to 50 mol% La(Zn(0.5)Ti(0.5))O(3). With the increase of linear oxide dielectric content, the dielectric constant and tunability were decreased and Qf was increased. Ba(0.6)Sr(0.4)TiO(3)-La(Mg(0.5)Ti(0.5))O(3) has better dielectric properties than Ba(0.6)Sr(0.4)TiO(3)-La(Zn(0.5)Ti(0.5))O(3). 0.9Ba(0.6)Sr(0.4)TiO(3)-0.1La(Mg(0.5)Ti(0.5))O(3) has a dielectric constant epsilon = 338.2, Qf = 979 GHz and a tunability of was 3.7% at 100 kHz under 1.67 kV/mm. The Qf value of 0.5Ba(0.6)Sr(0.4)TiO(3)- 0.5La(Mg(0.5)Ti(0.5))O(3) reached 9367 GHz, but the tunable properties were lost. PMID:19942521

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

    PubMed

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

    2008-11-01

    Ba(0.6)Sr(0.4)TiO(3)-Sr(Ga(0.5)Ta(0.5))O(3) solid solutions are prepared by a solid-state reaction method, and their dielectric and tunable characteristics are investigated. The solid solutions with cubic perovskite structures are obtained for compositions of 10-50 mol% Sr(Ga(0.5)Ta(0.5))O(3). It is observed that the addition of Sr(Ga(0.5)Ta(0.5))O(3) into Ba(0.6)Sr(0.4)TiO(3) causes a shift in the phase transition peak to a lower temperature. Ba(0.6)Sr(0.4)TiO(3)-Sr(Ga(0.5)Ta(0.5))O(3) solid solutions exhibit depressed and broadened phase transition peaks, resulting in decreased dielectric constants and dielectric losses at room temperature. With the increase of Sr(Ga(0.5)Ta(0.5))O(3) content, the dielectric constant, loss tangent, and tunability are decreased. 0.9Ba(0.6)Sr(0.4)TiO(3)-0.1Sr(Ga(0.5)Ta(0.5))O(3) has a dielectric constant epsilon = 534 and a tunability of 16% at 100 kHz under 2.63 kV/mm. The dielectric characteristics of Ba(0.6)Sr(0.4)TiO(3)-Sr(Ga(0.5)Ta(0.5))O(3) ceramics at microwave frequencies are also evaluated. PMID:19049916

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

    PubMed

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

    2014-01-01

    In this work, redox-active Mn or Cr is introduced to the B site of redox stable perovskite Sr(0.95)Ti(0.9)Nb(0.1)O3.00 to create oxygen vacancies in situ after reduction for high-temperature CO2 electrolysis. Combined analysis using X-ray diffraction, X-ray photoelectron spectroscopy, transmission electron microscopy and thermogravimetric analysis confirms the change of the chemical formula from oxidized Sr(0.95)Ti(0.9)Nb(0.1)O3.00 to reduced Sr(0.95)Ti(0.9)Nb(0.1)O2.90 for the bare sample. By contrast, a significant concentration of oxygen vacancy is additionally formed in situ for Mn- or Cr-doped samples by reducing the oxidized Sr(0.95)Ti(0.8)Nb(0.1)M(0.1)O3.00 (M = Mn, Cr) to Sr(0.95)Ti(0.8)Nb(0.1)M0.1O2.85. The ionic conductivities of the Mn- and Cr-doped titanate improve by approximately 2 times higher than bare titanate in an oxidizing atmosphere and 3-6 times higher in a reducing atmosphere at intermediate temperatures. A remarkable chemical accommodation of CO2 molecules is achieved on the surface of the reduced and doped titanate, and the chemical desorption temperature reaches a common carbonate decomposition temperature. The electrical properties of the cathode materials are investigated and correlated with the electrochemical performance of the composite electrodes. Direct CO2 electrolysis at composite cathodes is investigated in solid-oxide electrolyzers. The electrode polarizations and current efficiencies are observed to be significantly improved with the Mn- or Cr-doped titanate cathodes. PMID:25403738

  19. Specific features of magnetic states of impurity iron ions in the perovskite La0.75Sr0.25Co0.98 57Fe0.02O3

    NASA Astrophysics Data System (ADS)

    Pokatilov, V. S.; Rusakov, V. S.; Makarova, A. O.; Pokatilov, V. V.; Matsnev, M. E.

    2016-02-01

    Single-phase polycrystalline La0.75Sr0.25Co0.98 57Fe0.02O3 samples have been prepared by solidstate ceramic technology. The samples have the rhombohedral structure (space group Rbar 3c). The studies of perovskite La0.75Sr0.25Co0.98 57Fe0.02O3 by Mössbauer spectroscopy on impurity 57Fe nuclei in the temperature range of 5-293 K have revealed the existence of a superparamagnetic relaxation in the temperature range of 100-210 K. The parameters of hyperfine interactions (hyperfine magnetic fields, line shifts, and quadrupole shifts) and the anisotropy energy have been measured, and the frequencies of magnetic moment relaxation of iron ions have been estimated.

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

    NASA Astrophysics Data System (ADS)

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

    2016-03-01

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

  1. 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.

  2. Ferroelectric control of spin injection in La0.7 Sr0.3 MnO3 /BaTiO3 /La0.5 Ca0.5 MnO3 /La0.7 Sr0.3 MnO3 multiferroic tunnel junctions with a bilayer barrier

    NASA Astrophysics Data System (ADS)

    Yin, Yuewei; Miao, L. D.; Du, R. Z.; Li, Q.

    2015-03-01

    Using a ferroelectric (FE) barrier with ferromagnetic electrodes has become a promising method for controlling spin injection by purely electrical means, which is an important challenge in spintronics. Recently, we have designed a La0.7Sr0.3MnO3(LSMO) /BaTiO3(BTO) /La0.5Ca0.5MnO3(LCMO) /LSMO tunnel junctions in which the reversal of FE polarization of BTO will magnetoelectrically lead to a FM metallic - antiferromagnetic insulating phase transition in LCMO and result in an enhanced tunneling electroresistance (TER). Using the bilayer barrier, we observed that the spin injection can be controlled by barrier polarization reversal as shown in the change of tunneling magnetoresistance (TMR). The temperature evolution of tunnel electromagnetoresistance (TEMR) (percentage ratio between the TMR values for the two polarization states), which is directly proportional to the change of tunnel-current spin polarization, was studied and larger TEMR was obtained with increasing temperature. Meanwhile, TEMR increases with TER effect for samples with different LCMO insertion thicknesses, suggesting a controllable strong electric control of tunnel-current spin polarization using a designed structure with proper interfaces.

  3. 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.

  4. Synthesis and performance of Y-doped La 0.7Sr 0.3CrO 3- δ as a potential anode material for solid oxygen fuel cells

    NASA Astrophysics Data System (ADS)

    Zhu, Xiufang; Zhong, Qin; Zhao, Xuejun; Yan, Han

    2011-01-01

    Y-doped La 0.7Sr 0.3CrO 3- δ is a promising anode catalyst for solid oxygen fuel cell (SOFC). The performances of chemical and physical are measured by SEM, XRD and FT-IR. The conductivities of catalyst are measured by DC four-probe method in 20% H 2S-N 2, 3% H 2-N 2 and air from 573 K to 1173 K, respectively. The results show that Y-doped La 0.7Sr 0.3CrO 3- δ powders have perfect perovskite phase structure with no extra peaks and exhibit good chemical compatibility with Ce 0.8Sm 0.2O 1.9 (as electrolyte) in air. Through XRD and FT-IR analysis no sulfur-containing species is detected after exposure to the 20% H 2S at 1173 K for 5 h. Meanwhile, Y-doped La 0.7Sr 0.3CrO 3- δ shows that the highest conductivity is 0.21 S/cm at 1173 K in H 2S. The open circuit voltages are 0.85 V at 1173 K in H 2S and 1.04 V at 823 K in H 2. The maximal power densities are 12.4 mW/cm 2 in H 2S and 1.59 W/cm 2 in H 2 for cells comprising Y-doped La 0.7Sr 0.3CrO 3- δ-Sm 0.2Ce 0.8O 1.9/Sm 0.2Ce 0.8O 1.9/Ag.

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

    PubMed

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

    2016-04-28

    Reducing operating temperatures is a key step in making solid oxide fuel cell (SOFC) technology viable. A promising strategy for accomplishing this goal is employing mixed ion-electron conducting (MIEC) cathodes. La1-xSrxCo1-yFeyO3-δ (LSCF) is the most widely employed MIEC cathode material; however, rational optimization of the composition of LSCF requires fundamental insight linking its electronic structure to its defect chemistry. To provide the necessary insight, density functional theory plus U (DFT+U) calculations are used to investigate the electronic structure of LSCF (xSr = 0.50, yCo = 0.25). The DFT+U calculations show that LSCF has a significantly different electronic structure than La1-xSrxFeO3 because of the addition of cobalt, but that minimal electronic structure differences exist between La0.5Sr0.5Co0.25Fe0.75O3 and La0.5Sr0.5Co0.5Fe0.5O3. The oxygen vacancy formation energy (ΔEf,vac) is calculated for residing in different local environments within La0.5Sr0.5Co0.25Fe0.75O3. These results show that configurations have the highest ΔEf,vac, while have the lowest ΔEf,vac and may act as traps for . We conclude that compositions with more Fe than Co are preferred because the additional sites would lead to higher overall ΔEf,vac (and lower concentrations), while the trapping strength of the sites is relatively weak (∼0.3 eV). PMID:27079696

  6. 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

    2015-11-01

    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. PMID:26390084

  7. Fabrication of Ba0.5Sr0.5Co0.8Fe0.2O(3-δ) catalysts with enhanced electrochemical performance by removing an inherent heterogeneous surface film layer.

    PubMed

    Jung, Jae-Il; Jeong, Hu Young; Kim, Min Gyu; Nam, Gyutae; Park, Joohyuk; Cho, Jaephil

    2015-01-14

    A heat-treatment approach for Ba0.5Sr0.5Co0.8Fe0.2O(3-δ) (BSCF5582) is introduced as a way of enhancing the electrocatalytic performance of perovskite catalysts. The perovskite made by heat-treatment in oxygen atmosphere loses around 30 nm of spinel layer on the surface relative to the untreated version, and demonstrates enhanced oxygen reduction reaction and oxygen evolution reaction catalytic activities. PMID:25413252

  8. Synthesis of nano-crystalline (Ba 0.5Sr 0.5)Co 0.8Fe 0.2O 3- δ cathode material by a novel sol-gel thermolysis process for IT-SOFCs

    NASA Astrophysics Data System (ADS)

    Subramania, A.; Saradha, T.; Muzhumathi, S.

    Nano-crystalline (Ba 0.5Sr 0.5)Co 0.8Fe 0.2O 3- δ powder has been successfully synthesized by a novel sol-gel thermolysis method using a unique combination of PVA and urea. The decomposition and crystallization behaviour of the gel precursor was studied by TG/DTA analysis. The gel precursor was calcined at different temperatures and the phase evoluation was studied by X-ray diffraction (XRD) analysis. From the result of X-ray diffraction patterns, it is found that a cubic perovskite (Ba 0.5Sr 0.5)Co 0.8Fe 0.2O 3- δ was formed by calcining the precursor at 450 °C for 5 h, but the well-crystalline cubic perovskite (Ba 0.5Sr 0.5)Co 0.8Fe 0.2O 3- δ was obtained by calcining the precursor at 650 °C for 5 h. Morphological analysis of the powder calcined at various temperatures was done by scanning electron microscope (SEM). Thermogravimetric (TG) results showed the lattice oxygen loss of the product was about ∼2% in its original weight in the temperature range 40-900 °C. Finally, thermal expansion and electrical conductivity of the synthesized material were measured by dilatometer and four-probe dc method, respectively.

  9. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2016-04-01

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

  11. 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

    2016-06-01

    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.

  12. Enhanced cycle stability at high rate and excellent high rate capability of La0.7Sr0.3Mn0.7Co0.3O3-coated LiMn2O4

    NASA Astrophysics Data System (ADS)

    Shi, Ting; Dong, Yue; Wang, Chun-Mei; Tao, Fen; Chen, Li

    2015-01-01

    La0.7Sr0.3Mn0.7Co0.3O3-coated spinel LiMn2O4 with excellent cycle stability and high rate capability is successfully prepared by a sol-gel method. The 3 wt.% La0.7Sr0.3Mn0.7Co0.3O3-coated LiMn2O4 shows the optimum electrochemical performance. It can deliver 101 mAh g-1 at 10 C even after 100 cycles with a capacity retention of 93.5%. In contrast, the bare LiMn2O4 delivers 83.6 mAh g-1 at the same condition, only 84.5% capacity left. The rate capability of 3 wt.% La0.7Sr0.3Mn0.7Co0.3O3-coated LiMn2O4 is also obviously enhanced, especially at high rates (10 C, 20 C and 30 C). It can deliver 74.3 mAh g-1 at 30 C which is much higher than that of the bare sample (47.2 mAh g-1). The bare and coated LiMn2O4 samples are studied with various techniques. Both powder X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) measurements demonstrate the existence of the La0.7Sr0.3Mn0.7Co0.3O3, and it has no influence on the crystal structure of the pristine LiMn2O4. Transmission electron microscopy (TEM) shows that La0.7Sr0.3Mn0.7Co0.3O3 coating layer with good crystallinity can cover the surface of LiMn2O4 to form a core-shell structure. Electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV) demonstrate that the coating layer can improve the kinetics of electrodes.

  13. Magnetocaloric effect in manganite perovskites La 0.77Sr 0.23Mn 1- xCu xO 3(0.1≤ x≤0.3)

    NASA Astrophysics Data System (ADS)

    El-Hagary, M.; Shoker, Y. A.; Emam-Ismail, M.; Moustafa, A. M.; Abd El-Aal, A.; Ramadan, A. A.

    2009-02-01

    The magnetocaloric properties of the polycrystalline manganites perovskite La 0.77Sr 0.23Mn 1- xCu xO 3 with 0.1≤x≤0.3 have been investigated. The maximum magnetic entropy change, ΔSMmax, of Cu doped manganites increases gradually with increasing applied magnetic field. The maximum values of magnetic entropy changes of Cu doped manganites samples is found to decrease with the further increasing of Cu concentration in the romboherderal phase ( x≤0.2). However, with increasing Cu contents ( x≥ 0.3) structure transformed into orthorhombic phase and, hence ΔSMmax, start to increase again with increasing Cu doped concentration. It was found that the maximum value of the magnetic entropy change increases near their respective TC from 3.09 J/kg K at 0.1 T and reached highest value of 4.41 J/kg K at 1 T for compound with x=0.1. ΔSMmax in La 0.77Sr 0.23Mn 0.9Cu 0.1O 3 at 1 T is found to be 26% higher than that known for the prototype magnetic refrigerant with pure Gd. The relative cooling power (RCP) of La 0.77Sr 0.23Mn 1- xCu xO 3 is nearly 60% of pure Gd. Thus, due to the high ΔSMmax and RCP values, sample with x=0.1 (at μoΔH=1 T) is the most promising compound to be used as magnetomechnical materials.

  14. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2014-11-01

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

  16. Controllable-permittivity and low-loss of Ba0.5Sr0.5TiO3/MgO composites prepared by citrate gel derived core-shell powders

    NASA Astrophysics Data System (ADS)

    Zhang, Jingji; Ji, Ludong; Xu, Yu; Gao, Yafeng; Bai, Wangfeng; Chen, Zhi; Wang, Jiangying

    2015-11-01

    Core-shell Ba0.5Sr0.5TiO3(BST)/MgO nano-composites have been synthesized by using an oleic acid modified citrate gel in situ process. The nano-composites exhibit a spherical microstructure consisting of large amounts of small particles with average sizes of 50-100 nm, which results in high F center levels in the composite ceramics. Interestingly, microwave permittivity of the composite can be reduced significantly with increasing volume fraction of MgO, while microwave loss and tunability remain almost unchanged, which is in good agreement with the results of the columnar model.

  17. Investigations of sol gel-derived highly (100)-oriented Ba0.5Sr0.5TiO3 : MgO composite thin films for phase-shifter applications

    NASA Astrophysics Data System (ADS)

    Jain, M.; Majumder, S. B.; Katiyar, R. S.; Bhalla, A. S.; Miranda, F. A.; van Keuls, F. W.

    2005-02-01

    Sol gel deposition of highly oriented Ba0.5Sr0.5TiO3 : MgO composite thin films has shown desirable dielectric constant reduction and higher figure of merit for phase-shifter applications. In this multilayer configuration, MgO distributed homogeneously through the Ba0.5Sr0.5TiO3 (BST50) matrix, and it helped in tailoring the dielectric constant and reducing the loss tangent significantly. In the present study, the high-frequency dielectric behavior of the films has been evaluated by fabricating an eight-element coupled microstrip phase shifter and measuring the degree of phase shift and insertion loss as a function of applied voltage at room temperature. An increase in phase-shifter figure of merit (degree of phase shift per dB insertion loss) from 28°/dB for pure BST50 to 71°/dB for a BST50 : MgO film (at 14 GHz and 333 kV/cm) has been observed.

  18. Synthesis and Characterization of La0.8Sr0.2Co0.8Fe0.2O3 Nanoparticles for Intermediate-low Temperature Solid Oxide Fuel Cell Cathodes

    NASA Astrophysics Data System (ADS)

    Ding, C.; Lin, H.; Sato, K.; Hashida, T.

    2008-02-01

    Nanoparticles of La0.8Sr0.2Co0.8Fe0.2O3, which are being investigated as cathode materials for intermediate-low temperature solid oxide fuel cells, were successfully synthesized by a novel sol-gel process. The thermal decomposition behavior of gel precursor was examined using TG/DTA analysis. Development of crystalline phases in the powders calcined at various temperatures was monitored by x-ray diffraction. Single phase La0.8Sr0.2Co0.8Fe0.2O3 could be obtained after calcining at 800 °C. A small amount of impurity phase existed in the powders calcined at the temperature below 700 °C. Morphological analysis of the powders calcined at various temperatures was done by scanning electron microscopy. The synthesized powders had an average particle size of 30˜90 nm at 600-1100 °C. The average particle size of the powders increased with increase in calcination temperature. Noticeable changes occurred at temperature above 800 °C, and the coarse particles existed in the powders calcined at high temperatures.

  19. 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.

  20. Oxygen vacancies induced switchable and nonswitchable photovoltaic effects in Ag/Bi0.9La0.1FeO3 /La0.7Sr0.3MnO3 sandwiched capacitors

    NASA Astrophysics Data System (ADS)

    Gao, R. L.; Yang, H. W.; Chen, Y. S.; Sun, J. R.; Zhao, Y. G.; Shen, B. G.

    2014-01-01

    The short circuit photocurrent (Isc) was found to be strongly dependent on the oxygen vacancies (VOs) distribution in Ag/Bi0.9La0.1FeO3/La0.7Sr0.3MnO3 heterostructures. In order to manipulate the VOs accumulated at either the Ag/Bi0.9La0.1FeO3 or the Bi0.9La0.1FeO3/La0.7Sr0.3MnO3 interface by pulse voltages, switchable or nonswitchable photocurrent can be observed without or with changing the polarization direction. The sign of photocurrent could be independent of the direction of polarization when the variation of diffusion current and the modulation of the Schottky barrier at the Ag/Bi0.9La0.1FeO3 interface induced by oxygen vacancies are large enough to offset those induced by polarization. Our work provides deep insights into the nature of photovoltaic effects in ferroelectric films, and will facilitate the advanced design of switchable devices combining spintronic, electronic, and optical functionalities.

  1. High Dielectric, Piezoelectric, Upconversion Photoluminescence and Low-Temperature Sensing Properties in Ba0.7Sr0.3TiO3-BaZr0.2Ti0.8O3:Ho/Yb Ceramics

    NASA Astrophysics Data System (ADS)

    Zuo, Qianghui; Luo, Laihui; Yao, Yongjie

    2016-02-01

    In the present work, we have synthesized pure and Ho/Yb-co-doped 0.5Ba0.7Sr0.3TiO3-0.5BaZr0.2Ti0.8O3 ceramics using a solid-state reaction technique. The prepared pure 0.5Ba0.7Sr0.3TiO3-0.5BaZr0.2Ti0.8O3 ceramics were found in the morphotropic phase boundary region, and exhibit high piezoelectric and dielectric properties. Under a 980-nm excitation, strong green, red and near-infrared (NIR) upconversion (UC) photoluminescence is observed in Ho/Yb-co-doped samples. It is found that the color of UC emission could be tuned by changing the concentration of sensitizer Yb ions in the host matrix. Furthermore, optical temperature sensing properties based on the green and NIR UC emissions of BSZT:0.005Ho/0.01Yb were investigated. Fluorescence intensity ratio (FIR) between green (5F4,5S2) → 5I8 and NIR (5F4,5S2) → 5I7 UC emissions of Ho ions was studied as a function of temperature in the range of 78 K-373 K, and a maximum sensitivity 0.0206 K-1 at 97 K was obtained.

  2. Reversible magnetization measurements of the anisotropic superconducting parameters of the infinite-layer electron-doped compound Sr 0.90La 0.10CuO 2 apparent anisotropy crossover

    NASA Astrophysics Data System (ADS)

    Cobb, J. L.; Markert, J. T.

    1994-06-01

    We report the results and analysis of DC magnetization studies of grain-aligned powders of the infinite-layer electron-doped compounds Sr 0.90La 0.10CuO 2. Magnetization data in the reversible temperature regime were analyzed to obtain the anisotropic superconducting parameters for this system. Three samples of Sr 0.90La 0.10CuO 2 were studied, presumably with very slightly diffrent La or O concentrations. Typically, the extracted values of the coherence lengths (ξ ∥=46 Å, ξ ⊥=30 Å), the penetration depths (λ ∥=290 nm, λ ⊥=450 nm), the mass anisotrophy ( ( {m ⊥}/{m ∥}) {1}/{2}≈1.5 ), and the lower and upper critical fields are appreciably less anisotropic than reported values for the electron-doped T‧ phase materials, possibly because the infinite-layer compound has a significantly shorter interplanar spacing (3.4 Å versus 6.0 Å). One notable sample, moreover, exhibits an inverse anisotropy (( ( {m ⊥}/{m ∥}) {1}/{2}≈0.6 ), further suggesting that this system behaves much like a three-dimensional metal.

  3. Evidence of glassy ferromagnetic phase and kinetic arrest of electronic phase in Sm0.35Pr0.15Sr0.5MnO3 manganites

    NASA Astrophysics Data System (ADS)

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

    2012-07-01

    The effect of doping of rare earth Pr3+ ion as a replacement of Sm3+ in Sm0.5Sr0.5MnO3 is investigated. Temperature dependent dc and ac magnetic susceptibility, resistivity, magnetoresistance measurements on chemically synthesized (Sm0.5-xPrx)Sr0.5MnO3 show various unusual features with doping level x=0.15. The frequency independent ferromagnetic to paramagnetic transition at higher temperature (∼191 K) followed by a frequency dependent reentrant magnetic transition at lower temperature (∼31 K) has been observed. The nature of this frequency dependent reentrant magnetic transition is described by a critical slowing down model of spin glasses. From non-linear ac susceptibility measurements it has been confirmed that the finite size ferromagnetic clusters are formed as a consequence of intrinsic phase separation, and undergo spin glass-like freezing below a certain temperature. There is an unusual observation of a 2nd harmonic peak in the non-linear ac susceptibility around this reentrant magnetic transition at low temperature (∼31 K). Arrott plots at 10 and 30 K confirm the existence of glassy ferromagnetism below this low temperature reentrant transition. Electronic- and magneto-transport measurements show a strong magnetic field-temperature history dependence and strong irreversibility with respect to the sweeping of magnetic field. These results are attributed to the effect of phase separation and kinetic arrest of the electronic phase in this phase separated manganite at low temperatures.

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

    NASA Astrophysics Data System (ADS)

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

    2016-08-01

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

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

    NASA Astrophysics Data System (ADS)

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

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

  6. 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.

  7. Dependence of luminescence efficiency on dopant concentration and sintering temperature in the erbium-doped Ba0.7Sr0.3TiO3 thin films

    NASA Astrophysics Data System (ADS)

    Kuo, Shou-Yi; Chen, Chin-Sheng; Tseng, Tseung-Yuen; Chang, S.-C.; Hsieh, Wen-Feng

    2002-08-01

    We found the dependence of luminescence efficiency on Er3+ concentration and sintering temperature in the Er-doped Ba0.7Sr0.3TiO3 (BST) thin films is governed by crystallinity and ion-ion interaction. X-ray diffraction and Raman studies of the sol-gel prepared samples show that the BST polycrystalline phase occurred when the sintering temperature reaches 700 degC, whereas, it becomes worse for temperature above 700 degC resulting from phase separation and the Er3+ concentration exceeding 3 mol % due to charge compensation mechanism. The observed green emission reaches maximum at sintering temperature 700 degC and 3 mol % Er3+ ions concentration. We also showed the Er dopant does not affect the dielectric property of BST thin films in C-V measurement and the Ba0.7Sr0.3TiO3 films doped with Er3+ ions may have potential use for electroluminescence devices.

  8. Microwave Dielectric Properties of Ba0.2Sr0.8La4Ti4O15 Ceramic with La2O3-B2O3-TiO2 Doping

    NASA Astrophysics Data System (ADS)

    Li, Ying-xiang; Si, Feng; Tang, Bin; Wang, Ya; Zhang, Shu-ren

    2016-02-01

    The effects of La2O3-B2O3-TiO2 (LBT) glass addition on the phase composition, microstructure, and microwave dielectric properties of Ba0.2Sr0.8La4Ti4O15 (BSLT) ceramic were investigated in this study. X-ray diffraction results showed that a small amount of SrLaBO4 secondary phase was formed in the LBT-doped BSLT ceramics. Scanning electron microscopy indicated that addition of LBT glass restrained grain growth of the main phase. Samples doped with LBT showed strong promotion of both ɛ r and Q × f values. Typically, the LBT (La2O3:B2O3:TiO2 = 1:0.5:0.5)-doped Ba0.2Sr0.8La4Ti4O15 ceramic sintered at 1550°C for 3 h in air exhibited good microwave dielectric properties of ɛ r = 50.7, Q × f = 72,700 GHz, and τ f = -7.3 ppm/°C.

  9. Point contact investigations of film and interface magnetoresistance of La0.7Sr0.3MnO3 heterostructures on Nb:SrTiO3

    NASA Astrophysics Data System (ADS)

    Monsen, Åsmund; Boschker, Jos E.; Nordblad, Per; Mathieu, Roland; Tybell, Thomas; Wahlström, Erik

    2015-01-01

    STM based magnetotransport measurements of epitaxial La0.7Sr0.3MnO3 31 nm thick films with and without an internal LaMnO3 layer (0-3.1 nm thick) grown on Nb doped SrTiO3 are presented. The measurements reveal two types of low field magnetoresistance (LFMR) with a magnitude of ~0.1-1.5%. One LFMR contribution is identified as a conventional grain boundary/domain wall scattering through the symmetric I-V characteristics, high dependence on tip placements and insensitivity to introduction of LaMnO3 layers. The other contribution originates from the reverse biased Nb doped SrTiO3 interface and the interface layer of La0.7Sr0.3MnO3. Both LFMR contributions display a field dependence indicative of a higher coercivity (~200 Oe) than the bulk film. LaMnO3 layers are found to reduce the rectifying properties of the junctions, and sub-micron lateral patterning by electron beam lithography enhances the diodic properties, in accordance with a proposed transport model based on the locality of the injected current.

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

    NASA Astrophysics Data System (ADS)

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

    2005-01-01

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

  11. 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.

  12. 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.

  13. Progress in understanding and development of Ba 0.5Sr 0.5Co 0.8Fe 0.2O 3- δ-based cathodes for intermediate-temperature solid-oxide fuel cells: A review

    NASA Astrophysics Data System (ADS)

    Zhou, Wei; Ran, Ran; Shao, Zongping

    Solid-oxide fuel cells (SOFCs) convert chemical energy directly into electric power in a highly efficient way. Lowering the operating temperature of SOFCs to around 500-800 °C is one of the main goals in current SOFC research. The associated benefits include reducing the difficulties associated with sealing and thermal degradation, allowing the use of low-cost metallic interconnectors and suppressing reactions between the cell components. However, the electrochemical activity of the cathode deteriorates dramatically with decreasing temperature for the typical La 0.8Sr 0.2MnO 3-based electrodes. The cathode becomes the limiting factor in determining the overall cell performance. Therefore, the development of new electrodes with high electrocatalytic activity for oxygen reduction becomes a critical issue for intermediate-temperature (IT)-SOFCs. Ba 0.5Sr 0.5Co 0.8Fe 0.2O 3- δ (BSCF) perovskite oxide was first reported as a potential IT-SOFC cathode material in 2004 by Shao and Haile. After that, the BSCF cathode has attracted considerable attention. This paper reviews the current research activities on BSCF-based cathodes for IT-SOFCs. Emphasis will be placed on the understanding and optimization of BSCF-based materials. The issues raised by the BSCF cathode are also presented and analyzed to provide some guidelines in the search for the new generation of cathode materials for IT-SOFCs.

  14. 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.

  15. 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. PMID:24737665

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

    NASA Astrophysics Data System (ADS)

    Yamane, Hisanori; Shimooka, Satoshi; Uheda, Kyota

    2012-06-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2016-05-01

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

  18. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2016-06-01

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

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

    PubMed

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

    2016-05-18

    From temperature and magnetic field dependent point-contact spectroscopy on the ferromagnetic superconductor Sr0.5Ce0.5FBiS2 (bulk superconducting [Formula: see text] K) we observe (a) a pseudogap in the normal state that sustains to a remarkably high temperature of 40 K and (b) two-fold enhancement of T c upto 5 K in the point-contact geometry. In addition, Andreev reflection spectroscopy reveals a superconducting gap of 6 meV for certain point-contacts suggesting that the mean field T c of this system could be approximately 40 K, the onset temperature of pseudo-gap. Our results suggest that quantum fluctuations originating from other competing orders in Sr0.5Ce0.5FBiS2 forbid a global phase coherence at high temperatures thereby suppressing T c. Apart from the known ordering to a ferromagnetic state, our first-principles calculations reveal nesting of a multi-band Fermi surface and a significant electron-phonon coupling that could result in charge density wave-like instabilities. PMID:27089948

  1. Ramp-edge junctions between superconducting Nd1.85Ce0.15CuO4 and La1.85Sr0.15CuO4

    NASA Astrophysics Data System (ADS)

    Hoek, M.; Coneri, F.; Renshaw Wang, X.; Hilgenkamp, H.

    2016-03-01

    We have fabricated in-plane ramp-edge junctions between Nd1.85Ce0.15CuO4 (NCCO) and La1.85Sr0.15CuO4 (LSCO) where both layers are superconducting. At the interface, we find an insulating barrier in electronic transport. The barrier is shown to be a tunneling barrier with a combination of inelastic and elastic tunneling, the former is indicated by the appearance of the LSCO phonon density of states in {{{d}}}2I/{{d}}{V}2 measurements and the latter is inferred from the temperature dependence of the conductance. The energy scale of the barrier is smaller than would be expected from band alignment found by considering the cuprates as degenerate semiconductors. It is closest to the scenario where hybridization of the O 2p valence band states dictate band alignment. Additional experiments with overdoped interlayers of Nd1.8Ce0.2CuO4 and La1.75Sr0.25CuO4 show that the origin of the barrier is most likely a combination of electronic depletion mainly in the NCCO and a strain effect in the LSCO.

  2. Electrolysis of H2O and CO2 in an oxygen-ion conducting solid oxide electrolyzer with a La0.2Sr0.8TiO3+δ composite cathode

    NASA Astrophysics Data System (ADS)

    Li, Shisong; Li, Yuanxin; Gan, Yun; Xie, Kui; Meng, Guangyao

    2012-11-01

    Solid oxide electrolyzers have attracted a great deal of interest in recent years because they can convert electrical energy into chemical energy with high efficiency. Ni/YSZ cathodes are generally utilized for high temperature electrolysis of H2O and CO2 in oxygen-ion conducting solid oxide electrolyzers; however, such electrodes can only operate under reducing conditions. In an atmosphere without a flow of reducing gas, cathodes based on La0.2Sr0.8TiO3+δ (LST) are a promising alternative. Solid Oxide Electrolyzers with LST cathodes without pre-reduction were used at 700 °C for the electrolysis of 3%H2O/97%N2 and 100%CO2, and promising polarization impedance data were obtained in both atmospheres. The electrochemical results indicated that the electrochemical reduction of the La0.2Sr0.8TiO3+δ cathode was the main process at low electrical voltages, while the electrolysis was the main process at high voltages because ion transportation in the electrolyte limited the overall efficiency. The electrolysis of H2O was determined to be more efficient than the electrolysis of CO2 under the same conditions. The Faraday efficiencies of H2O and CO2 were 85.0% and 24.7%, respectively, at 700 °C and a 2 V applied potential.

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

    NASA Astrophysics Data System (ADS)

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

    2014-01-01

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

  4. 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.

  5. Systematic study of magnetotransport properties and enhanced low-field magnetoresistance in thin films of La0.67Sr0.33MnO3 + Mg(O)

    NASA Astrophysics Data System (ADS)

    Staruch, M.; Cantoni, C.; Jain, M.

    2013-02-01

    La, Sr, Mn, and Mg precursors were mixed in stoichiometric ratio 0.67/0.33/1/x with solvent and were spin-coated onto (001) LaAlO3 substrates. X-ray diffraction and elemental mapping of these films indicate that for small addition of Mg precursor, Mg2+ acts as a dopant in La0.67Sr0.33MnO3 phase and for higher concentrations, MgO phase separates out. Curie temperature and metal-insulator transition temperature systematically decrease with increasing molar concentration of Mg(O). Low-field magnetoresistance of films significantly enhanced by Mg addition and for the highest amount of Mg at 10 K, values were -35.5% and -83.2% with 0.5 T and 3 T applied fields, respectively.

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

    NASA Astrophysics Data System (ADS)

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

    2016-05-01

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

  7. Ferromagnetism and adiabatic to non-adiabatic switching process in La0.33Sr0.67Mn1-xFexO3 (0≤x≤0.02) manganite

    NASA Astrophysics Data System (ADS)

    Ahmed, Hilal; Khan, Shakeel; Khan, Wasi; Nongjai, Razia; Khan, Imran

    2014-11-01

    We have systematically investigated structural, electrical and magnetic properties of Fe doped La0.33Sr0.67MnO3 manganites synthesized through solid-state reaction-route. All the samples are found to have rhombohedral crystal structure. The crystallite sizes obtained by XRD data are much smaller than the average grain size obtained by scanning electron microscope (SEM). Temperature dependent resistivity data were fitted using Mott's variable-range hopping (VRH) and small polaron hopping (SPH) models for obtaining different parameters. The adiabatic SPH conduction mechanism is followed almost for both samples in the absence of magnetic field but a switching from adiabatic to non-adiabatic SPH conduction mechanism is found in the presence of magnetic field. Temperature dependent magnetization (M-T) measurements confirm the decrease in Curie-temperature (TC) with Fe doping. Both the samples exhibited ferromagnetic behavior at 10 K and 300 K with a small hysteresis loop and low coercivity.

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

    DOE PAGESBeta

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

    2015-12-02

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

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

    NASA Astrophysics Data System (ADS)

    Hirai, Daigorou; Matsuno, Jobu; Takagi, Hidenori

    2015-04-01

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

  10. 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. PMID:26206522

  11. Double Exchange via t2g Orbitals and the Jahn-Teller Effect in Ferromagnetic La0.7Sr0.3CoO3 Probed by Epitaxial Strain

    NASA Astrophysics Data System (ADS)

    Fuchs, D.; Merz, M.; Nagel, P.; Schneider, R.; Schuppler, S.; von Löhneysen, H.

    2013-12-01

    The magnetic exchange in hole-doped ferromagnetic cobaltates is investigated by studying the magnetic and electronic properties of La0.7Sr0.3CoO3 films as a function of epitaxial strain. We found a strong-coupling double exchange mechanism between Co3+(4t2g2eg) and Co4+(3t2g2eg) high-spin states mediated by t2g electrons—in contrast to the moderate coupling provided by the eg exchange in manganites. The strong sensitivity of the Curie temperature TC to the bulk compression can be explained by the small bandwidth of the t2g-derived states. A strain-induced Jahn-Teller effect is likewise observed. The experimental results clarify the magnetic exchange mechanism in the cobaltates.

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

    PubMed

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

    2015-09-01

    An exchange bias effect with perpendicular anisotropy is of great interest owing to potential applications such as read heads in magnetic storage devices with high thermal stability and reduced dimensions. Here we report a novel approach for achieving perpendicular exchange bias by orienting the ferromagnetic/antiferromagnetic coupling in the vertical geometry through a unique vertically aligned nanocomposite (VAN) design. Our results demonstrate robust perpendicular exchange bias phenomena in micrometer-thick films employing a prototype material system of antiferromagnetic BiFeO3 and ferromagnetic La0.7Sr0.3MnO3. The unique response of exchange bias to a perpendicular magnetic field reveals the existence of exchange coupling along their vertical heterointerfaces, which exhibits a strong dependence on their strain states. This VAN approach enables a large selection of material systems for achieving perpendicular exchange bias, which could lead to advanced spintronic devices. PMID:26222013

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

    NASA Astrophysics Data System (ADS)

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

    1996-02-01

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

  14. Evolution of microstructure and magnetoresistive properties of (La0.65Sr0.35)0.8Mn1.2O3±Δ ceramics sintered at 800-1500 °C

    NASA Astrophysics Data System (ADS)

    Novokhatska, A.; Akimov, G.; Prylypko, S.; Revenko, Yu.; Burkhovetsky, V.

    2013-05-01

    An effect of microstructure on magnetoresistive properties of manganite ceramics (La0.65Sr0.35)0.8Mn1.2O3±Δ with superstoichiometric manganese has been studied after sintering in the temperature range of 800-1500 °C. Increase in sintering temperature to 1400 °C, an enormous growth of grains, densification of material, and rise in magnetoresistance peak from 1% to 4.8% are observed. At the same time, sintering at 1500 °C leads to a sharp increase in the grain size more than 100 μm, release of excess manganese on grain boundaries, and almost two times magnetoresistance peak rise. We propose that such radical changes are due to the presence of superstoichiometric manganese which plays a crucial role in the formation of ceramics microstructure and properties.

  15. Luminescent properties of sol-gel processed red-emitting phosphor Ca0.6 Sr0.4-1.5x-0.5y Mo0.4  W0.6 O4:Eux Liy.

    PubMed

    Li, Fei; Xie, Huidong; Xi, Haihong; Dang, Fangfang; Wang, Xiaochang

    2015-08-01

    A series of red-emitting phosphors Ca0.6Sr(0.4-1.5x-0.5y)Mo0.4W0.6O4:Eux Liy (x = 0.02-0.12, y = 0-0.12) has been synthesized by a sol-gel method. The effects of calcining temperature, concentrations of Li(+) and Eu(3+) , and compensation ions on the luminescent properties were investigated. X-ray diffraction and scanning electron microscopic results showed that as-prepared phosphors were of single phase with several microns. The Li(+) compensated compositions showed remarkably intense red emission at 619 nm. The emission intensity of the series reached maximum for compositions at x = 0.08 and y = 0.08 when the calcining temperature was 900 °C. PMID:25339264

  16. Microstructure of screen-printed (Tl 0.5,Pb 0.5)(Sr 0.8,Ba 0.2) 2Ca 2Cu 3O y superconducting films on untextured silver substrate

    NASA Astrophysics Data System (ADS)

    Kim, Bong-Jun; Kim, Hyun-Tak; Matsui, Yoshio; Jeong, Dae-Yong; Deinhofer, Christian; Gritzner, Gerhard

    2007-09-01

    Highly c-axis oriented (Tl 0.5,Pb 0.5)(Sr 0.8,Ba 0.2) 2Ca 2Cu 3O y films with a thickness of ∼1.5 μm and ∼4 μm were prepared by screen printing method on untextured silver substrates. Tl-1223 films have the critical temperatures around 116 K with transition widths, Δ T, of 2 K, The microstructures have been investigated by high-resolution transmission electron microscopy. Tl-1223 film deposited on well-polished Ag substrate shows large single domains in the lateral direction including secondary phases and intergrowth of Tl-1212, 2201 and 1234. From selected area electron diffraction (SAED) pattern, secondary phase is determined as BaCuO 2, which plays an important role in flux pinning to improve magnetic properties. And the relationships between the domain size, alignment and the surface roughness are studied.

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

    NASA Astrophysics Data System (ADS)

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

    2016-04-01

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

  18. The crystal structure, oxygen nonstoichiometry and chemical stability of Ba(0.5)Sr(0.5)Co(0.8)Fe(0.2)O(3-δ) (BSCF).

    PubMed

    Wang, Fang; Nakamura, Takashi; Yashiro, Keiji; Mizusaki, Junichiro; Amezawa, Koji

    2014-04-28

    The oxygen nonstoichiometry and the crystal structure of Ba0.5Sr0.5Co0.8Fe0.2O3-δ (BSCF) were investigated by using coulometric titration, high-temperature gravimetry and in situ HT-XRD. The chemical stability diagram of BSCF was established as a function of temperature between room temperature and 1373 K and oxygen partial pressure, p(O2), between 1 and 1 × 10(-21) bar. The results showed that the cubic BSCF had poor chemical stability both under highly oxidative conditions at low temperatures and highly reductive conditions at high temperatures. The phase analysis of the decomposition products showed that the chemical instability of BSCF was mainly owing to the oxidation/reduction of trivalent Co ions. PMID:24619453

  19. 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.

  20. 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).

  1. Low-temperature crystallization of high performance Pb0.4Sr0.6TiO3 films compatible with the current silicon-based microelectronic technology

    NASA Astrophysics Data System (ADS)

    Li, Kui; Rémiens, Denis; Dong, Xianlin; Costecalde, Jean; Sama, Nossikpendou; Li, Tao; Du, Gang; Chen, Ying; Wang, Genshui

    2013-05-01

    This investigation presents a simple approach to realize the low temperature crystallization of Pb0.4Sr0.6TiO3 thin films at 400 °C by taking advantage of well controlled lead excess and kinetic-driving-force compensated thermodynamics crystalline via sputtering deposition. The thin films prepared at low temperature show fine-grained micro-structure because of the suppressed grain growth, furthermore, the intrinsic dielectric response can be modulated by the distinct level of crystallinity. The film processed at 450 °C exhibited a dielectric constant of 435 and high figure merit of 130 at 400 kV/cm, superior ferroelectric property, and stable performance with temperature and frequency.

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

    NASA Astrophysics Data System (ADS)

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

    2014-05-01

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

  3. 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

  4. Microwave losses in MgO, LaAlO3, and (La0.3Sr0.7)(Al0.65Ta0.35)O3 dielectrics at low power and in the millikelvin temperature range

    NASA Astrophysics Data System (ADS)

    Arzeo, M.; Lombardi, F.; Bauch, T.

    2014-05-01

    We have investigated both the temperature and the power dependence of microwave losses for various dielectrics commonly used as substrates for the growth of high critical temperature superconductor thin films. We present measurement of niobium superconducting λ/2 coplanar waveguide resonators, fabricated on MgO, LaAlO3, and (La0.3Sr0.7)(Al0.65Ta0.35)O3 (LSAT), at the millikelvin temperature range and at low input power. By comparing our results with the two-level system model, we have discriminated among different dominant loss mechanisms. LSAT has shown the best results as regards the dielectric losses in the investigated regimes.

  5. Large magnetic-entropy change above room temperature in the colossal magnetoresistance La 0.7Sr 0.3Mn 1- xNi xO 3 materials

    NASA Astrophysics Data System (ADS)

    Choudhury, Md. A.; Akhter, S.; Minh, D. L.; Tho, N. D.; Chau, N.

    2004-05-01

    Magnetic and magnetocaloric properties of the series La 0.7Sr 0.3Mn 1- xNi xO 3 ( x=0.00, 0.01, 0.02, 0.03, and 0.05) have been investigated. The X-ray diffraction analysis shows that all perovskites studied have the rhombohedral structure. The field-cooled and zero-field-cooled thermomagnetic curves measured at low field show that there is spin-glass (or cluster-glass)-like state in the samples. It is found that the magnetic-entropy change |Δ Smax| has reached the highest value of 3.54 J/kg K at 13.5 kOe for the composition with x=0.02.

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

    NASA Astrophysics Data System (ADS)

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

    2016-05-01

    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.

  7. 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.

  8. 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.

  9. 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

  10. The effect of Mg doping on the dielectric and tunable properties of Pb0.3Sr0.7TiO3 thin films prepared by sol-gel method

    NASA Astrophysics Data System (ADS)

    Sun, Xiaohua; Li, Xiuneng; Hou, Shuang; Huang, Caihua; Zou, Jun; Li, Meiya; Peng, Tianyou; Zhao, Xing-zhong

    2014-03-01

    Mg doped Pb0.3Sr0.7TiO3 (PST) thin films were fabricated by the sol-gel method on a Pt/Ti/SiO2/Si substrate. The microstructure, surface morphology, dielectric and tunable properties of PST thin films were investigated as a function of Mg concentration. It is found that proper Mg doping dramatically improves the dielectric loss (0.0088 @ 1 MHz), furthermore, the crystallinity, dielectric constant, and tunability of films simultaneously decrease with the increase of Mg content. The 2 mol% Mg doped PST thin film shows the highest figure of merit (FOM) value of 36.8 for its the smallest dielectric loss and upper tunability. The dependence of Rayleigh coefficient on the doping concentration was examined, which indicated that the reduction of dielectric constant and tunability of films should be related to the - defect dipoles pinning the domain wall motion of residual polar clusters in PST.

  11. 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

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

    PubMed

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

    2016-01-01

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

  13. 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. PMID:26086277

  14. 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. PMID:23962975

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

    DOE PAGESBeta

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

    2015-06-18

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

  16. Evidence of electronic phase arrest and glassy ferromagnetic behaviour in (Nd0.4Gd0.3)Sr0.3MnO3 manganite: comparative study between bulk and nanometric samples

    NASA Astrophysics Data System (ADS)

    Kundu, S.; Nath, T. K.

    2011-09-01

    The effect of the doping of rare earth Gd3+ ions replacing Nd3+ in Nd0.7Sr0.3MnO3 is investigated in detail. Measurements of resistivity, magnetoresistance, magnetization, and linear and nonlinear ac magnetic susceptibility on chemically synthesized (Nd0.7-xGdx)Sr0.3MnO3 show various interesting features with doping level x = 0.3. A comparative study has been carried out between a bulk and a nanometric sample (grain size ˜60 nm) synthesized from the same as a prepared powder to maintain an identical stoichiometry. The resistivity of the samples shows strong dependence on the magnetic field-temperature history. The magnetoresistance of the samples also shows strong irreversibility with respect to sweeping of the field between the highest positive and negative values. Moreover, the resistivity is found to increase with time after field cooling and then switching off the field. All these phenomena have been attributed to phase separation effects and the arrest of phases in the samples. Furthermore, the bulk sample displays a spin glass like behaviour as evident from the frequency dependence of linear ac magnetic susceptibility and critical divergence of the nonlinear ac magnetic susceptibility. The experimentally obtained characteristic time τ0 after dynamical scaling analysis of the frequency dependence of the ac susceptibility is found to be 10-17 s which implies that the system is different from a canonical spin glass. An unusual frequency dependence of the second harmonic of ac susceptibility around the magnetic transition temperature led us to designate the magnetic state of the sample to be glassy ferromagnetic. On reduction of the grain size low field magnetoresistance and phase arrest phenomena are found to enhance but the glassy state is observed to be destabilized in the nanometric sample.

  17. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2014-01-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2014-12-01

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

  20. Exchange bias and enhanced coercivity in phase separated La0.45Sr0.55MnO3 and Pr0.55(Ca0.65S0.35)0.45MnO3 films

    NASA Astrophysics Data System (ADS)

    Kim, Byeong-geon; Kumar, Ashvani; Ki, Sanghoon; Kim, Sangwoo; Dho, Joonghoe

    2011-12-01

    An epitaxial La0.45Sr0.55MnO3 (LSMO) film, which has a paramagnetic-to-ferromagnetic transition at ˜260 K and a partial ferromagnetic-to-antiferromagnetic transition at ˜150 K upon cooling, was synthesized on (001) (La0.18Sr0.82)(Al0.59Ta0.41)O3 with pulsed laser deposition. The x-ray diffraction pattern showed interference fringes around the (002) LSMO peak, indicating a successful growth of a high quality and smooth film. When the LSMO film was cooled down in a magnetic field of 5 kOe, it exhibited a large exchange bias (HEX) of ˜490 Oe and an enhanced coercivity (HC) of ˜800 at 10 K, respectively. The observed exchange bias effect, which is associated with phase coexistence of the ferromagnetic (FM) and antiferromagnetic (AF) phases, displayed a distinctive training effect, which is probably due to a competing spin order at the boundary between the FM and AF phases. Similarly, we also observed a large exchange bias and enhanced coercivity in a phase separated Pr0.55(Ca0.65S0.35)0.45MnO3 film, which had simultaneous FM and AF transitions at ˜150 K. Our results show that the exchange bias effect can be induced even in single layer films with a magnetic phase coexistence state of FM and AF phases, which may be exploited as a very simple structure for spin-valve devices.

  1. 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).

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

    PubMed

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

    2015-01-01

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

  3. 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.

  4. 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.

  5. 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.

  6. 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 PAGESBeta

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

    2015-02-17

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

  7. The power of in situ pulsed laser deposition synchrotron characterization for the detection of domain formation during growth of Ba0.5Sr0.5TiO3 on MgO.

    PubMed

    Bauer, Sondes; Lazarev, Sergey; Molinari, Alan; Breitenstein, Andreas; Leufke, Philipp; Kruk, Robert; Hahn, Horst; Baumbach, Tilo

    2014-03-01

    A highly sophisticated pulsed laser deposition (PLD) chamber has recently been installed at the NANO beamline at the synchrotron facility ANKA (Karlsruhe, Germany), which allows for comprehensive studies on the PLD growth process of dielectric, ferroelectric and ferromagnetic thin films in epitaxial oxide heterostructures or even multilayer systems by combining in situ reflective high-energy diffraction with the in situ synchrotron high-resolution X-ray diffraction and surface diffraction methods. The modularity of the in situ PLD chamber offers the opportunity to explore the microstructure of the grown thin films as a function of the substrate temperature, gas pressure, laser fluence and target-substrate separation distance. Ba0.5Sr0.5TiO3 grown on MgO represents the first system that is grown in this in situ PLD chamber and studied by in situ X-ray reflectivity, in situ two-dimensional reciprocal space mapping of symmetric X-ray diffraction and acquisition of time-resolved diffraction profiles during the ablation process. In situ PLD synchrotron investigation has revealed the occurrence of structural distortion as well as domain formation and misfit dislocation which all depend strongly on the film thickness. The microstructure transformation has been accurately detected with a time resolution of 1 s. The acquisition of two-dimensional reciprocal space maps during the PLD growth has the advantage of simultaneously monitoring the changes of the crystalline structure as well as the formation of defects. The stability of the morphology during the PLD growth is demonstrated to be remarkably affected by the film thickness. A critical thickness for the domain formation in Ba0.5Sr0.5TiO3 grown on MgO could be determined from the acquisition of time-resolved diffraction profiles during the PLD growth. A splitting of the diffraction peak into two distinguishable peaks has revealed a morphology change due to modification of the internal strain during growth

  8. Crystal structure, magnetic properties, and Mössbauer studies of La0.6Sr0.4FeO3- δ prepared by quenching in different atmospheres

    NASA Astrophysics Data System (ADS)

    Yang, J. B.; Yelon, W. B.; James, W. J.; Chu, Z.; Kornecki, M.; Xie, Y. X.; Zhou, X. D.; Anderson, H. U.; Joshi, Amish G.; Malik, S. K.

    2002-11-01

    Samples of La0.6Sr0.4FeO3-δ compounds prepared by quenching in different gaseous environments were studied by x-ray diffraction, neutron diffraction, magnetization measurements, and Mössbauer spectroscopy (MS). All materials are single phase and crystallize in the rhombohedral perovskite structure. Samples prepared in flowing air, N2, and O2 yielded oxygen vacancies ranging from 0% to 1%. The oxygen vacancy concentration increases from 6.8% to 9.6% as the ratio of CO/CO2 changes from 10:90 to 90:10. The air-, N2-, and O2-quenched samples have a magnetic ordering temperature in the range of 300-325 K. The magnetic ordering temperature increases for all the samples subjected to the reducing CO/CO2 atmosphere. The neutron data refinements and magnetization data indicate that the Fe sublattice of La0.6Sr0.4FeO3-δ has an antiferromagnetic structure below the magnetic ordering temperature. The Fe atoms possess a magnetic moment of 3.8μB and a hyperfine field of 53 T in the CO/CO2-quenched samples. It is found that the heat treatment in the CO/CO2 atmosphere creates more oxygen vacancies, changes the Fe valence states, and increases the unit cell volume. In the meantime, the Fe-O-Fe bond angle increases. These dramatically affect the Fe-O-Fe superexchange coupling. The change of the Fe-O-Fe bond angle and the change of the Fe valence states in the CO/CO2 heat treatment play a key role in the increase of the magnetic ordering temperatures and the magnetic moment. Therefore by creating oxygen vacancies or having excess oxygen, the exchange interaction of Fe-O and the valence state of Fe ions are affected, and lead to large changes in the magnetic properties, such as the magnetic ordering temperature, the magnetic moments, and the hyperfine interactions in the pervoskite structure.

  9. High-tunability and low-microwave-loss Ba0.6Sr0.4TiO3 thin films grown on high-resistivity Si substrates using TiO2 buffer layers

    NASA Astrophysics Data System (ADS)

    Kim, Hyun-Suk; Kim, Ho-Gi; Kim, Il-Doo; Kim, Ki-Byoung; Lee, Jong-Chul

    2005-11-01

    In this Letter, we report on high-tunability and low-microwave-loss properties of Ba0.6Sr0.4TiO3 (BST) thin films by use of atomic-layer-deposited TiO2 films as the microwave buffer layer between BST and high-resistivity Si substrate. The interdigital capacitor fabricated on BST films grown on TiO2/high resistivity Si (2kΩcm) substrates showed the much enhanced tunability value of 33.2% while retaining an appropriate Q factor, as compared to the tunability values of BST (21%) films grown on MgO single-crystal substrates and BST (8.2%) films grown on TiO2/normal Si (10Ωcm) substrates. The coplanar waveguide BST phase shifter fabricated on TiO2/high resistivity Si exhibited a phase shift of 95° and insertion loss of 3.09 dB at 15 GHz and an applied voltage of 50 V. ALD-grown TiO2 buffer layers enable the successful integration of BST-based microwave tunable devices onto high-resistivity Si wafers.

  10. Finite gap behaviour in the superconductivity of the 'infinite layer' n-doped high-Tc superconductor Sr0.9La0.1CuO2

    NASA Astrophysics Data System (ADS)

    White, J. S.; Forgan, E. M.; Laver, M.; Häfliger, P. S.; Khasanov, R.; Cubitt, R.; Dewhurst, C. D.; Park, M.-S.; Jang, D.-J.; Lee, H.-G.; Lee, S.-I.

    2008-03-01

    We report on the first small-angle neutron scattering measurements from the flux line lattice (FLL) in the high-Tc cuprate superconductor Sr0.9La0.1CuO2. Using a polycrystalline sample, the scattered intensity decreases monotonically with scattering angle away from the undiffracted beam, independently of the azimuthal angle around the beam. The absence of clear peaks in the intensity suggests the establishment of a highly disordered FLL within the grains. We find that the intensity distribution may be represented by the form factor for a single flux line in the London approximation, with some contribution from crystal anisotropy. Most interestingly however, we find that, over the observed field range, the temperature dependence of the diffracted intensity is best represented by s-wave pairing, with lower limits of the gap values being very similar to the Bardeen-Cooper-Schrieffer value of Δ(0) = 1.76 kBTc. However, a qualitative consideration of corrections to the observed intensity suggests that these gap values are likely to be higher, implying strong-coupling behaviour.

  11. Dielectric properties of (Na0.5Bi0.5)TiO3-Ba0.7Sr0.3Sn0.02Ti0.98O3 composite ceramics

    NASA Astrophysics Data System (ADS)

    Wang, Jing; Rong, Guijuan; Liu, Lei; Cheng, Haiyan; Jiang, Qi; Li, Chuangchuang; Wang, Mengmeng

    2016-05-01

    Lead-free x(Na0.5Bi0.5)TiO3-(1 ‑ x)Ba0.7Sr0.3Sn0.02Ti0.98O3 (NBT-BSST) ceramics are prepared by a wet solid-phase reaction method. The effect of NBT/BSST ratio on phase structure, microstructure and dielectric properties has been investigated in detail. The X-ray diffraction (XRD) analysis illustrates that the composites are composed of tetragonal perovskite. With increasing NBT content, the ceramic capacitors display stronger temperature stability in its dielectric behavior. A great enhance of dielectric properties and other electric parameters is obtained in this system by properly modulating the compositions. For example, the composite ceramics with 30% NBT content possess a large dielectric constant (𝜀r) of 3200 and a low dielectric loss (tan δ) of 0.09. The temperature coefficient of capacitance of NBT-BSST varies from ‑50% to 20% while the NBT content is 30% at the whole range of measured temperature. The results show that NBT-BSST ceramics are a good candidate of lead-free dielectric materials.

  12. Magnetocaloric effect and magnetic refrigeration in La0.7Ca0.15Sr0.15Mn1-xGaxO3 (0 ≤ x ≤ 0.1)

    NASA Astrophysics Data System (ADS)

    Othmani, S.; Balli, M.

    2012-06-01

    In this paper we report magnetic and magnetocaloric effect (MCE) properties for La0.7 (CaSr)0.3Mn1-xGaxO3 (x =0, 0.025, 0.05, 0.075 and 0.1) manganites. Our compounds were prepared by sol-gel method and characterized by X-ray diffraction and magnetization measurements. The temperature dependence of the magnetization M(T) reveals a decrease of M with increasing Ga content. The same behavior was observed for the Curie temperature TC. MCE was calculated according to the Maxwell relation based on magnetic measurements. The magnetic entropy change (∆SM) reaches a maximum value witch decreases with increasing Ga content. It is found to decrease from 5.15 J/kgK for x = 0 to 1.86 J/kgK for x = 0.1 under an applied magnetic field of 5T. So, the studied samples could be considered as good materials for magnetic refrigeration for a large temperature interval near room temperature.

  13. The coexistence of cluster glass behavior and long-range ferromagnetic ordering in La0.7Sr0.25Na0.05Mn0.7Ti0.3O3 manganite

    NASA Astrophysics Data System (ADS)

    Kossi, S. El.; Mnefgui, S.; Dhahri, J.; Hlil, E. K.

    2015-11-01

    The electron-doped La0.7Sr0.25Na0.05Mn0.7Ti0.3O3 (LSNMTi0.3) sample was synthesized by a conventional solid-state reaction. Rietveld analysis of the X-ray diffraction (XRD) data showed that the compound crystallized in the space group R 3 barc. Magnetic characterization present a signature of a coexisting AFM-FM ordering and a cluster-glass phase. The M2 vs. H/M curves prove that the samples exhibit a second-order magnetic phase transition and the critical properties near the ferromagnetic-paramagnetic phase transition temperature have been analyzed from data of the static magnetization measurements for the sample, through various techniques such as the modified Arrott plot and the critical isotherm analysis. The critical exponent values estimated from the isothermal magnetization measurements are found to be consistent and comparable to those predicted by the long-range mean-field theory.

  14. Analysis of magnetic and structural properties in La0.6Sr0.4MnO3 ferromagnetic particles under the influence of mechanical ball milling effect

    NASA Astrophysics Data System (ADS)

    Campillo, G.; Gil, A.; Arnache, O.; Beltrán, J. J.; Osorio, J.; Sierra, G.

    2013-11-01

    We have investigated the magnetic, structural and morphological properties of La0.6Sr0.4MnO3 (LSMO-40) manganite particles, synthesized by solid state reaction method. The resulting LSMO-40 powders were milled in air atmosphere during 3, 6 and 12 hours, by using a planetary ball milling. Samples obtained were characterized by X-ray diffraction, scanning electron microscopy - SEM and magnetization measurements as a function of temperature and magnetic field. A Rietveld analysis was carried on each XRD pattern, and was observed a reduction in crystallite average size (Dv) with increased ball milling time, tM. This is associated with a decrease in particle size. A characteristic rhombohedral crystal structure for the LSMO-40 phase was identified (space group R3C), independent of the milling time of the powders. However, from SEM microstructure was observed more homogeneity in the grain distribution by milling process. The results of magnetic characterization, showed that samples with higher tM (smaller grain size), presented the lowest value of the saturation magnetization, which is attributed to surface effects that induce magnetically disordered states with decreasing particle sizes. This magnetic anisotropy surface is evidenced also on the changes of coercive fields, HC, measured at low temperatures, which increased with increasing tM.

  15. La0.6Sr0.4Co0.2Fe0.8O3 cathodes incorporated with Sm0.2Ce0.8O2 by three different methods for solid oxide fuel cells

    NASA Astrophysics Data System (ADS)

    Shen, Fengyu; Lu, Kathy

    2015-11-01

    The incorporation of Sm0.2Ce0.8O2 (SDC) into La0.6Sr0.4Co0.2Fe0.8O3 (LSCF) is carried out by three methods: mechanical mixing, infiltration, and dip coating. The effects of SDC on the electrochemical performance of the LSCF cathodes are studied by electrochemical impedance spectroscopy (EIS) at 800 °C for 100 h. LSCF mechanically mixed with SDC as the cathode decreases the electrochemical performance of the half-cell; the LSCF cathode infiltrated with SDC offers faster activation and decreased resistance with thermal treatment time; and the LSCF cathode dip coated with SDC has the smallest polarization resistance. These cathodes also show clear microstructure differences at the cathode/interconnect interface after 100 h of thermal treatment. SrCrO4 phase forms on all the cathodes near the interconnect. Reactions between the mechanically mixed cathode and the YSZ electrolyte destroy the electrolyte. The influence of SDC catalyst on oxygen adsorption, dissociation, and incorporation is explained for each type of cathodes. Overall, dip coating method is recommended for incorporation of SDC into the LSCF cathode.

  16. Magnetic and structural properties of Sr0.75La0.25FexCu0.20O19 (10.40≤x≤11.80) hexagonal ferrites prepared by the solid-state reaction

    NASA Astrophysics Data System (ADS)

    Yang, Yujie; Shao, Juxiang; Wang, Fanhou; Liu, Xiansong; Feng, Shuangjiu; Huang, Duohui; Yang, Junsheng; Jin, Chengguo

    2016-05-01

    In this study, the hexaferrite magnetic powders and magnets according to the formula Sr0.75La0.25FexCu0.20O19, where x ranging from 10.40 to 11.80 with a step of 0.2 were prepared by the solid-state reaction. X-ray diffraction was performed to investigate the microstructures of the magnetic powders. The results show that a single magnetoplumbite phase is obtained for the magnetic powders with Fe content (10.60≤x≤11.60). For the magnetic powders with Fe content (x) of 10.40 or 11.80, magnetic impurities appear in the structure. A field emission scanning electron microscopy was hired to explore the micrographs of the magnets. The hexaferrite magnets are formed of hexagonal-shaped crystals. A magnetic properties test instrument was used in order to study the magnetic properties of the magnets. The remanence and maximum energy product first increase with Fe content (x) from 10.40 to 11.00 and then begin to decrease when Fe content (x) continues to increase. While the intrinsic coercivity and magnetic induction coercivity first increase with Fe content (x) from 10.40 to 11.20 and then decrease when Fe content (x)>11.20.

  17. 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.

  18. 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.

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

    DOE PAGESBeta

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

    2015-01-13

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

  20. Stability of La0.6Sr0.4Co0.2Fe0.8O3/Ce0.9Gd0.1O2 cathodes during sintering and solid oxide fuel cell operation

    NASA Astrophysics Data System (ADS)

    Kiebach, Ragnar; Zhang, Wei-Wei; Zhang, Wei; Chen, Ming; Norrman, Kion; Wang, Hsiang-Jen; Bowen, Jacob R.; Barfod, Rasmus; Hendriksen, Peter Vang

    2015-06-01

    Degradation phenomena of La0.58Sr0.4Co0.2Fe0.8O3/Ce0.9Gd0.1O2 (LSCF/CGO) cathodes were investigated via post-mortem analyses of an experimental solid oxide fuel cell (SOFC) stack tested at 700 °C for 2000 h using advanced electron microscopy (SEM-EDS, HR-TEM-EDS) and time-of-flight secondary ion mass spectrometry (TOF-SIMS). Similar studies were carried out on non-tested reference cells for comparison. The analysis focused on the LSCF/CGO cathode and the CGO barrier layer, as the cathode degradation can be a major contributor to the overall degradation in this type of SOFC. SEM-EDS and TOF-SIMS were used to investigate inter-diffusion across the barrier layer-electrolyte interface and the barrier layer-cathode interface. In addition, TOF-SIMS data were employed to investigate impurity distribution before and after testing. HR-TEM-EDS was used to investigate possible phase segregation in the LSCF and to look for reaction between the phases. The results show that phase separation and inter-diffusion across the cathode-barrier layer interface and the barrier layer-electrolyte interface happened mainly during sintering and cathode firing, and to a very little degree during the test period.

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

    NASA Astrophysics Data System (ADS)

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

    2016-01-01

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

  2. Influence of calcium content on the structural and magnetic properties of Sr0.70-xCaxLa0.30Fe11.75Zn0.25O19 hexagonal ferrites

    NASA Astrophysics Data System (ADS)

    Yang, Yujie; Wang, Fanhou; Shao, Juxiang; Liu, Xiansong; Feng, Shuangjiu; Yang, Junsheng

    2016-03-01

    Hexagonal ferrite Sr0.70-xCaxLa0.30Fe11.75Zn0.25O19 (0≤x≤0.70) magnetic powder and magnets were prepared by the ceramic process. The phase characterization of the calcined powders was investigated by X-ray diffraction. There is a single magnetoplumbite phase in the magnetic powders with x from 0 to 0.60, and for the magnetic powders with x of 0.70, the α-Fe2O3 phase is observed. The morphology of the sintered magnets was examined by a field emission scanning electron microscopy. The magnets have formed the hexagonal structures and the particles are distributed evenly. Magnetic properties of the calcined powders and sintered magnets were measured by a vibrating sample magnetometer and a magnetic properties test instrument, respectively. The saturation magnetization, remanent magnetization and coercivity of the magnetic powders increase with the increase of x from 0 to 0.2, and then begin to decrease when x>0.2. The remanence, intrinsic coercivity, magnetic induction coercivity and maximum energy product of the sintered magnets first increase with x from 0 to 0.20, and then, start to decrease when x continues to increase. The magnetic properties of the sintered magnet at x=0.20 reach the maximum values.

  3. Effect of Ga substitution on magnetocaloric effect in La0.7(Ba, Sr)0.3Mn1-xGaxO3 (0.0≤x ≤0.20) polycrystalline at room temperature

    NASA Astrophysics Data System (ADS)

    Tlili, R.; Omri, A.; Bekri, M.; Bejar, M.; Dhahri, E.; Hlil, E. K.

    2016-02-01

    In this paper, we have investigated the effect of the non-magnetic (d10) Ga3+ doping on structural, magnetic and magnetocaloric properties of La0.7(Ba, Sr)0.3Mn1-xGaxO3 (x=0.0, 0.1 and 0.2) manganites prepared by solid state reaction method. The XRD study has revealed that all samples crystallized in the orthorhombic symmetry with Pnma space group. Magnetization measurements have confirmed that when the temperature increases, all the compositions exhibit a ferromagnetic to paramagnetic transition. The substitution of Mn by gallium Ga leads to a tune of the magnetic transition temperature (TC) to room temperature and the Curie temperature decreases from 314 K for x=0.0 to 299 K for x=0.2. Moreover, the obtained results of the magnetocaloric effect are in accordance with the reported values of other doped manganites, leading to the conclusion that our sample can be used as a magnetic refrigerant at room temperature. Finally, using Arrott plots, the phase transition from ferromagnetic to paramagnetic was found to be of a second order. The second order magnetic phase transition has been confirmed by the construction of the universal curve of the magnetic entropy change.

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

    PubMed

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

    2014-11-01

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

  5. La0.7Sr0.3MnO3-coated SS444 alloy by dip-coating process for metallic interconnect supported Solid Oxide Fuel Cells

    NASA Astrophysics Data System (ADS)

    da Conceição, Leandro; Dessemond, Laurent; Djurado, Elisabeth; Souza, Mariana M. V. M.

    2013-11-01

    Sol-gel and dip-coating technologies have been used to deposit La0.7Sr0.3MnO3 (LSM) porous thin films on stainless steel SS444-Cr-17% interconnect plates. Single and double LSM layers were fired in air at 800 °C for 2 h to achieve a sufficient adhesion on the substrate. The microstructure and composition of oxide scales were investigated using X-ray diffraction, scanning electron microscopy and energy dispersive X-ray analysis. The area specific resistance (ASR) for coated and uncoated plates was evaluated during long term oxidation in air at 800 °C for 200 h, and between 600 and 900 °C, by DC two point measurements. The formation of an interfacial oxide scale based on (Cr,Mn)3O4 spinel and Cr2O3 has been evidenced for uncoated and LSM-coated SS444. The results indicate that the oxidation resistance of the alloy is enhanced by a protective coating consisting of one single LSM layer. ASR values as low as 0.6 mΩ cm2 were recorded after 200 h at 800 °C. The effectiveness of the LSM layer as a protective coating depends on the stability of the film and its adherence on the alloy substrate.

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

    PubMed

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

    2014-06-25

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

  7. 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.

  8. 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.

  9. 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.

  10. Core-shell structure of nanoscaled Ba0.5Sr0.5TiO3 self-wrapped by MgO derived from a direct solution synthesis at room temperature

    NASA Astrophysics Data System (ADS)

    Tian, H. Y.; Qi, J. Q.; Wang, Y.; Wang, J.; Chan, H. L. W.; Choy, C. L.

    2005-01-01

    A nanoscaled Ba0.5Sr0.5TiO3 (BST) powder was successfully synthesized using a modified hydrothermal process at a low temperature ({\\sim }80\\,^{\\circ }{\\mathrm {C}} ). By dissolving Ba(OH)2·8H2O and Sr(OH)2·8H2O in deionized water as a base solution, nanocrystalline BST powder can be obtained by mixing an ethanol solution of tetrabutyl titanate with a hot base solution by stirring. The grain size of BST is close to 17-20 nm, as calculated by XRD patterns and confirmed by TEM and SEM measurements. A perovskite structure core material of the nanoscaled BST was successfully self-wrapped by a non-ferroelectric oxide MgO derived from a magnesium nitrate (Mg(NO3)2·6H2O) solution under ultrasonic dispersion. A small amount of ammonia solution was added to this mixture to adjust it to a proper level of acidity in order to form a homogeneous core-shell structure. Straightforward experimental results revealed the formation of a core-shell structure. High-resolution transmission electron microscopy (HRTEM) combined with EDX was used to confirm the composition and its variation. TEM, SEM, and XRD results showed that the average particle size of a core-shell structure was less than 150 nm up to sintering at 1100 °C, depending on the core BST powder and its dispersion.

  11. 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.

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

    PubMed

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

    2016-07-13

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

  13. Atomic ordering in the doped rare earth cobaltates Ln0.33Sr 0.67CoO 3- δ ( Ln=Y 3+, Ho 3+ and Dy 3+)

    NASA Astrophysics Data System (ADS)

    Withers, R. L.; James, M.; Goossens, D. J.

    2003-08-01

    The perovskite-based rare earth cobaltates ( Ln0.33Sr 0.67CoO 3- δ) ( Ln=Y 3+, Ho 3+ and Dy 3+) have been synthesized at 1100°C under 1 atm oxygen. A thermogravimetric study has determined the overall oxygen content in each case while a combined electron diffraction (ED) and synchrotron X-ray diffraction study has revealed the presence of a complex, previously unreported, perovskite-related superstructure phase. ED gave a resultant C1 c1 but most probably Cmcm ( a=2a p-2c p, b=4b p, c=2a p+2c p) perovskite-related superstructure, describable as a modulated I4/ mmm intermediate parent structure. Synchrotron X-ray data has been used to refine the intermediate parent structures of all three compounds. Coupled Ln/Sr and O/vacancy ordering and associated structural relaxation is shown to be responsible for the observed superstructure.

  14. Effects of Interface Layers and Domain Walls on the Ferroelectric-Resistive Switching Behavior of Au/BiFeO3/La0.6Sr0.4MnO3 Heterostructures.

    PubMed

    Feng, Lei; Yang, Shengwei; Lin, Yue; Zhang, Dalong; Huang, Weichuan; Zhao, Wenbo; Yin, Yuewei; Dong, Sining; Li, Xiaoguang

    2015-12-01

    The electric field effects on the electric and magnetic properties in multiferroic heterostructures are important for not only understanding the mechanisms of certain novel physical phenomena occurring at heterointerfaces but also offering a route for promising spintronic applications. Using the Au/BiFeO3/La0.6Sr0.4MnO3 (Au/BFO/LSMO) multiferroic heterostructure as a model system, we investigated the ferroelectric-resistive switching (RS) behaviors of the heterostructure. Via the manipulation of the BFO ferroelectric polarizations, the nonvolatile tristate of RS is observed, which is closely related to the Au/BFO and BFO/LSMO interface layers and the highly conducting BFO domain walls (DWs). More interestingly, according to the magnetic field dependence of the RS behavior, the negative magnetoresistance effect of the third resistance state, corresponding to the abnormal current peak in current-pulse voltage hysteresis near the electric coercive field, is also observed at room temperature, which mainly arises from the possible oxygen vacancy accumulation and Fe ion valence variation in the DWs. PMID:26554671

  15. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2016-07-01

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

  17. 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.

  18. Effect of atmospheric CO2 on surface segregation and phase formation in La0.6Sr0.4Co0.2Fe0.8O3-δ thin films

    NASA Astrophysics Data System (ADS)

    Yu, Yang; Luo, Heng; Cetin, Deniz; Lin, Xi; Ludwig, Karl; Pal, Uday; Gopalan, Srikanth; Basu, Soumendra

    2014-12-01

    The effects of atmospheric CO2 on surface segregation and phase formation in La0.6Sr0.4Co0.2Fe0.8O3-δ (LSCF-6428) were investigated. (0 0 1)-oriented LSCF-6428 thin films were deposited on lattice matched (1 1 0)-oriented NdGaO3 (NGO) substrates by pulsed laser deposition (PLD). Using the synchrotron technique of total reflection X-ray fluorescence (TXRF), it was found that the kinetics of Sr surface segregation was enhanced when annealing at 800 °C in a high-CO2 partial pressure, as compared to a similar anneal in a CO2-free atmosphere, with the oxygen partial pressure being constant in both cases. Hard X-ray photoelectron spectroscopy (HAXPES) measurements showed that the contribution of the surface carbonate to surface oxide phases increased significantly for the sample annealed in the high-CO2 atmosphere. Atomic force microscopy (AFM) studies showed enhanced surface phase formation during the high-CO2 partial pressure anneal. Density functional theory (DFT) calculations provide a thermodynamic basis for the enhanced kinetics of surface segregation in the presence of atmospheric CO2.

  19. Electron channeling contrast imaging of anti-phase boundaries in coherently strained La0.7Sr0.3MnO3 thin films on (110)-oriented SrTiO3

    NASA Astrophysics Data System (ADS)

    Yan, Miaolei; De Graef, Marc; Picard, Yoosuf N.; Salvador, Paul A.

    2015-07-01

    Electron channeling contrast imaging (ECCI) was used to characterize coherently strained La0.7Sr0.3MnO3 (LSM) films grown on (110)cubic-SrTiO3 (STO) and ( 100 ) orthorhombic -NdGaO3 (NGO). We focus on the characterization of a relatively low density (1-3 μm/μm2) of meandering loops (MLs) found in the LSM film on STO and absent in the film on NGO. The MLs exhibit a uniform contrast variation from the background and a strong contrast dependence on the diffraction vector g. The MLs are quantitatively consistent with LSM anti-phase boundaries (APBs) having a displacement vector R = /1 2 [ 001 ] L S M . These APBs are consistent with a "double positioning" degeneracy of tilted octahedra along [ 001 ] L S M on untilted octahedra along [ 001 ] S T O . The results highlight the non-destructive capacity of ECCI to characterize extended defects in oxide films.

  20. Effect of the deposition temperature on the electrochemical properties of La0.6Sr0.4Co0.8Fe0.2O3-δ cathode prepared by conventional spray-pyrolysis

    NASA Astrophysics Data System (ADS)

    Marrero-López, D.; Romero, R.; Martín, F.; Ramos-Barrado, J. R.

    2014-06-01

    La0.6Sr0.4Co0.8Fe0.2O3-δ (LSCF) cathodes have been deposited by conventional spray pyrolysis on Ce0.8Gd0.2O1.9 (CGO) electrolytes at different temperatures between 250 and 450 °C, obtaining electrodes with different microstructure and porosity. Highly porous and macroporous electrodes are obtained at deposition temperatures of 250 °C and 450 °C, respectively, with an average grain size of 30-50 nm. The influence of the post-annealing treatment on the microstructure and on the electrochemical properties is investigated by scanning electron microscopy and impedance spectroscopy in air and as a function of the oxygen partial pressure to identify the different contributions to the polarization. Samples annealed at 650 °C show similar values of area specific resistance 0.04-0.06 Ω cm2 at a measured temperature of 650 °C. However, after annealing the samples at 850 °C, the ASR values increase up to 0.1-0.6 Ω cm2 with the lowest value corresponding to the film deposited at 250 °C due to the large porosity and surface area of this film. The performance degradation upon annealing is attributed to decreasing reaction sites induced by grain growth and densification.

  1. Self-Arranged Misfit Dislocation Network Formation upon Strain Release in La0.7Sr0.3MnO3/LaAlO3(100) Epitaxial Films under Compressive Strain.

    PubMed

    Santiso, José; Roqueta, Jaume; Bagués, Núria; Frontera, Carlos; Konstantinovic, Zorica; Lu, Qiyang; Yildiz, Bilge; Martínez, Benjamín; Pomar, Alberto; Balcells, Lluis; Sandiumenge, Felip

    2016-07-01

    Lattice-mismatched epitaxial films of La0.7Sr0.3MnO3 (LSMO) on LaAlO3 (001) substrates develop a crossed pattern of misfit dislocations above a critical thickness of 2.5 nm. Upon film thickness increases, the dislocation density progressively increases, and the dislocation spacing distribution becomes narrower. At a film thickness of 7.0 nm, the misfit dislocation density is close to the saturation for full relaxation. The misfit dislocation arrangement produces a 2D lateral periodic structure modulation (Λ ≈ 16 nm) alternating two differentiated phases: one phase fully coherent with the substrate and a fully relaxed phase. This modulation is confined to the interface region between film and substrate. This phase separation is clearly identified by X-ray diffraction and further proven in the macroscopic resistivity measurements as a combination of two transition temperatures (with low and high Tc). Films thicker than 7.0 nm show progressive relaxation, and their macroscopic resistivity becomes similar than that of the bulk material. Therefore, this study identifies the growth conditions and thickness ranges that facilitate the formation of laterally modulated nanocomposites with functional properties notably different from those of fully coherent or fully relaxed material. PMID:27280493

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

    PubMed Central

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

    2016-01-01

    The Mn K edge X-ray absorption near edge structure (XANES) of Pr0.67Sr0.33MnO3 films with different thicknesses on (001) LaAlO3 substrate was measured, and the effects of strain relaxation on film properties were investigated. The films showed in-plane compressive and out-of-plane tensile strains. Strain relaxation occurred with increasing film thickness, affecting both lattice constant and MnO6 octahedral rotation. In polarization dependent XANES measurements using in-plane (parallel) and out-of-plane (perpendicular) geometries, the different values of absorption resonance energy Er confirmed the film anisotropy. The values of Er along these two directions shifted towards each other with increasing film thickness. Correlating with X-ray diffraction (XRD) results it is suggested that the strain relaxation decreased the local anisotropy and corresponding probability of electronic charge transfer between Mn 3d and O 2p orbitals along the in-plane and out-of-plane directions. The XANES results were used to explain the film-thickness dependent magnetic and transport properties. PMID:26818583

  3. 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. PMID:26549423

  4. Thermoelectric power and resistivity of La1.8Sr0.2CaCu2O6-δ and the effects of O2 hot-isostatic-press annealing

    NASA Astrophysics Data System (ADS)

    Liu, C.-J.; Yamauchi, H.

    1995-05-01

    We have measured the resistivity and thermoelectric power of La1.8Sr0.2CaCu2O6-δ for 15<=T<=340 K. For the as-sintered sample heated under one atmosphere of oxygen, a minimum resistivity occurs at ca. 100 K, and the conductivity can be fitted to the form exp(T-1/2) or exp(T-1/4) for 30.3<=T<=86.8 K. The thermoelectric power varies as T1/2 for 20<=T<=200 K and exhibits a saturated value of ca. 100 μV/K for T>=230 K. Upon O2 HIP (hot isostatic press) treatment, the upturn of resistivity (metal- nonmetal transition) is suppressed and superconductivity ensues, and the thermoelectric power decreases in magnitude and displays a broad maximum at ca. 190 K in a manner similar to La2-xSrxCuO4-δ. It is conceivable that the O2 HIP treatment suppresses the metal-nonmetal transition as a result of increasing carrier concentration and possibly enhancing cation ordering. The possible origin of the metal-nonmetal transition is discussed.

  5. The impact of Co/La ratios on microstructure and magnetic properties of the Sr0.75-xCa0.25LaxFe12-yCoyO19 hexaferrites

    NASA Astrophysics Data System (ADS)

    Yang, Yujie; Wang, Fanhou; Shao, Juxiang; Huang, Duohui; Liu, Xiansong; Feng, Shuangjiu; Wen, Cuie

    2015-06-01

    Hexagonal ferrite Sr0.75-xCa0.25LaxFe12-yCoyO19 magnetic powder and magnets were synthesized according to a ceramic process. The phase compositions of the magnetic powder samples were determined by X-ray diffraction. There is a single magnetoplumbite phase in the samples with y/x from 0.3 to 0.6, and when y/x>0.6, the CoFe2O4 phase is observed. The micrographs of the sintered magnets were observed by a field emission scanning electron microscopy. The magnets have formed the hexagonal structures and the particles are distributed inhomogeneously. The impact of Co/La ratios on magnetic properties of the magnets was studied systematically. The remanence, magnetic induction coercivity and maximum energy product of the magnets first increase with y/x from 0.3 to 0.6, and then decrease when y/x>0.6. However, the intrinsic coercivity of the magnets first increases with y/x from 0.3 to 0.9, and decreases when y/x>0.9. The rectangularity of the demagnetizing curves for the magnets decreases with increasing y/x.

  6. Influence of heat treatment temperatures on structural and magnetic properties of Sr0.50Ca0.20La0.30Fe11.15Co0.25O19 hexagonal ferrites

    NASA Astrophysics Data System (ADS)

    Yang, Yujie; Liu, Xiansong; Jin, Dali

    2014-09-01

    M-type ferrite Sr0.50Ca0.20La0.30Fe11.15Co0.25O19 magnetic powders and magnets were prepared by a ceramic process. The phase identification of magnetic powders was performed by X-ray diffraction. At calcination temperatures ranging from 1170 to 1270 °C, the phase compositions of the magnetic powders consist of M-type hexaferrites together with small amount of impurity phases such as α-Fe2O3, LaFeO3 and CoFe2O4. At calcination temperatures above 1270 °C, single-phase M-type hexaferrites can be obtained. The microstructures of the magnets were investigated by field emission scanning electron microscopy. The particles appear in hexagonal plate-like shape and the particles are distributed homogeneously. The radial shrinkage of the magnets increases with the increase of calcination or sintering temperature. The magnetic properties of the magnets and magnetic powders were measured by a permanent magnetic measure equipment and a vibrating sample magnetometer, respectively. For high remanence, intrinsic coercivity, magnetic induction coercivity and maximum energy product, the optimized calcination and sintering temperatures are 1250 °C and 1190 °C, respectively.

  7. 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.

  8. Assessment of perovskite-type La0.8Sr0.2ScxMn1-xO3-δ oxides as anodes for intermediate-temperature solid oxide fuel cells using hydrocarbon fuels

    NASA Astrophysics Data System (ADS)

    Sengodan, S.; Yeo, H. J.; Shin, J. Y.; Kim, G.

    2011-03-01

    Composites formed by the infiltration of 40 wt% La0.8Sr0.2ScxMn1-xO3-δ (LSSM) oxides (x = 0.1, 0.2, 0.3) into 65% porous yttria-stabilized zirconia (YSZ) are investigated as anode materials for intermediate-temperature solid oxide fuel cells for hydrocarbon oxidation. The oxygen non-stoichiometry and electrical conductivity of each LSSM-YSZ composite are determined by coulometric titration. As the concentration of Sc increases, the composites show higher phase stability and the electrical conductivity of LSSM is significantly affected by the Sc doping, the non-stoichiometric oxygen content, and oxygen partial pressure (p(O2)). To achieve better electrochemical performance, it is necessary to add ceria-supported palladium catalyst for operation with humidified CH4. Anode polarization resistance increases with Sc doping due to a decrease in electrical conductivity. An electrolyte-supported cell with a LSSM-YSZ composite anode delivers peak power densities of 395 and 340 mW cm-2 at 923 K in humidified (3% H2O) H2 and CH4, respectively, at a flow rate of 20 mL min-1.

  9. Abnormal percolative transport and colossal electroresistance induced by anisotropic strain in (011)-Pr0.7(Ca0.6Sr0.4)0.3MnO3/PMN-PT heterostructure

    NASA Astrophysics Data System (ADS)

    Zhao, Ying-Ying; Wang, Jing; Kuang, Hao; Hu, Feng-Xia; Zhang, Hong-Rui; Liu, Yao; Zhang, Ying; Wang, Shuan-Hu; Wu, Rong-Rong; Zhang, Ming; Bao, Li-Fu; Sun, Ji-Rong; Shen, Bao-Gen

    2014-11-01

    Abnormal percolative transport in inhomogeneous systems has drawn increasing interests due to its deviation from the conventional percolation picture. However, its nature is still ambiguous partly due to the difficulty in obtaining controllable abnormal percolative transport behaviors. Here, we report the first observation of electric-field-controlled abnormal percolative transport in (011)-Pr0.7(Ca0.6Sr0.4)0.3MnO3/0.7Pb(Mg1/3Nb2/3)O3-0.3PbTiO3 heterostructure. By introducing an electric-field-induced in-plane anisotropic strain-field in a phase separated PCSMO film, we stimulate a significant inverse thermal hysteresis (~ -17.5 K) and positive colossal electroresistance (~11460%), which is found to be crucially orientation-dependent and completely inconsistent with the well accepted conventional percolation picture. Further investigations reveal that such abnormal inverse hysteresis is strongly related to the preferential formation of ferromagnetic metallic domains caused by in-plane anisotropic strain-field. Meanwhile, it is found that the positive colossal electroresistance should be ascribed to the coactions between the anisotropic strain and the polarization effect from the poling of the substrate which leads to orientation and bias-polarity dependencies for the colossal electroresistance. This work unambiguously evidences the indispensable role of the anisotropic strain-field in driving the abnormal percolative transport and provides a new perspective for well understanding the percolation mechanism in inhomogeneous systems.

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

    PubMed

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

    2016-08-23

    Among standard high-temperature cathode materials for solid oxide fuel cells, La0.8 Sr0.2 MnO3-δ (LSM) displays the least reactivity with the oxide-ion conductor La2 Mo2 O9 (LMO), yet a reaction is observed at high processing temperatures, identified by using XRD and focused ion beam secondary-ion mass spectrometry (FIB-SIMS) after annealing at 1050 and 1150 °C. Additionally, Sr and Mn solutions were deposited and annealed on LMO pellets, as well as a Mo solution on a LSM pellet. From these studies several reaction products were identified by using XRD and located by using FIB-SIMS on the surface of pelletised samples. We used depth profiling to show that the reactivity extended up to ∼10 μm from the surface region. If Sr was present, a SrMoO4 -type scheelite phase was always observed as a reaction product, and if Mn was present, LaMnO3+δ single crystals were observed on the surface of the LMO pellets. Additional phases such as La2 MoO6 and La6 MoO12 were also detected depending on the configuration and annealing temperature. Reaction mechanisms and detailed reaction formulae are proposed to explain these observations. The strongest driving force for cationic diffusion appears to originate from Mo(6+) and Mn(3+) cations, rather than from Sr(2+) . PMID:27478975

  11. 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.

  12. 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.

  13. XPS study of surface state of novel perovskite system Dy0.5Sr0.5Co0.8Fe0.2O3-δ as cathode for solid oxide fuel cells

    NASA Astrophysics Data System (ADS)

    Kautkar, Pranay R.; Acharya, Smita A.; Tumram, Priya V.; Deshpande, U. P.

    2016-05-01

    In the present attempt,novel perovskite oxide Dy0.5Sr0.5Co0.8Fe0.2O3-δ (DSCF) as cathode material has been synthesized by an Ethylene glycol-citrate combined sol-gel combustion route. Orthorhombic symmetry structure is confirmed by X-ray diffraction (XRD) and data is well fitted using Rietveld refinement by Full-Prof software suite. Chemical natureof surface of DSCF has been analyzed by using X-ray photoelectron spectroscopy (XPS). XPS result shows that Dy ions are in +3 oxidation state and Sr in +2 states. However Co2p and Fe2p spectra indicates partial change in oxidation state from Co3+/Fe3+ to Co4+/Fe4+. These attribute to develop active sites on the surface for oxygen ions. O1s XPS spectra shows two oxygen peaks relatedto lattice oxygen in perovskite and absorbed oxygen in oxygen vacancy are detected. O1s spectra demonstrate the existence of adsorbed oxygen species on the surface of DSCF oxide which is quite beneficial for intermediate temperature of Solid Oxide Fuel Cell.

  14. High permittivity and near-zero τɛ dielectrics Ca0.36Sr0.64TiO3-Li0.5Nd0.5TiO3 for multilayer ceramic capacitors

    NASA Astrophysics Data System (ADS)

    Wang, Xiaochuan; Liu, Yawen; Wang, Xiaohong; Lu, Wenzhong

    2015-11-01

    The microstructure and dielectric properties of (1 - x)Ca0.36Sr0.64TiO3-xLi0.5Nd0.5TiO3 (0 ≤ x ≤ 1) [abbreviated as (1 - x)CST-xLNT] solid solutions were investigated in this study. X-ray diffraction results showed that the samples exhibited a single cubic phase with x ≤ 0.5, whereas increasing LNT content resulted in a structural change from cubic to tetragonal phase in when x > 0.5. The permittivity (ɛr) decreased with increasing x, while the dielectric loss (tan δ) increased and then decreased at x = 1.0. The temperature dependence of ɛr and tan δ at 1 MHz for the (1 - x)CST-xLNT ceramics was also investigated. The temperature coefficient of the permittivity (τɛ) increased from highly negative values to positive values with increasing x. A near-zero τɛ was achieved at x = 0.57. Optimised dielectric properties were estimated to be ɛr = 227, tan δ = 0.043 and τɛ = 12 ppm/°C. Therefore, the 0.43CST-0.57LNT ceramic is proposed as a promising candidate material for multilayer ceramic capacitors with good temperature stability and high capacitance.

  15. Low-Temperature Sintering of Ba0.5Sr0.5TiO3-SrMoO4 Dielectric Tunable Composite Ceramics for LTCC Applications

    NASA Astrophysics Data System (ADS)

    Tang, Linjiang; Wang, Jinwen; Zhai, Jiwei

    2013-08-01

    A sintering-aid system using melting of B-Li glass for barium strontium titanate (BST)-based compositions to be used in low-temperature cofired ceramic (LTCC) layers is introduced. The effects of the sintering aid on the microstructure, dielectric properties, and application in LTCC were investigated. The composition Ba0.5Sr0.5TiO3-SrMoO4 with 3 wt.% B-Li glass sintered at 950°C exhibits optimized dielectric properties, including low dielectric constant (368), low dielectric loss (0.007), and moderate tunability (13%, 60 kV/cm) at 10 kHz. At 1.44 GHz, it possesses a dielectric constant of 218 and Q value of 230. LTCC multilayer ceramic capacitors fabricated by the tape-casting process have steady relative tunability of 12% at 300 V, suggesting that BST50-SrMoO4-B-Li glass composite ceramic is a promising candidate for electrically tunable LTCC microwave device applications.

  16. Electrical surface-resistivity, dielectric resonance, polarization and magnetic properties of Bi0.5Sr0.5FeO3-δ thin films grown by pulsed laser deposition

    NASA Astrophysics Data System (ADS)

    Balamurugan, K.; Ramachandran, B.; Krishna Surendra, M.; Kumar, N. Harish; Ramachandra Rao, M. S.; Santhosh, P. N.

    2014-09-01

    Polycrystalline and highly preferred (1\\,0\\,\\bar{{2}}) orientated Bi0.5Sr0.5FeO3-δ thin films were grown by pulsed laser deposition (PLD) on n-Si (2 0 0) and MgO (2 0 0) single crystalline substrates respectively. The thin films were inspected using x-ray diffraction, scanning electron microscopy, energy dispersive x-ray spectroscopy and atomic force microscopy techniques. The electrical surface-resistivity, dielectric resonance, electric polarization, and magnetic properties of the thin films were studied. At room temperature, depending on deposition conditions, the polycrystalline thin films grown on n-Si substrates were found to exhibit an electrical surface-resistivity of the order of 103-106 Ω, a piezoelectric resonance in the frequency range of about 25-26 MHz, a relaxor-type ferroelectric hysteresis with a maximum polarization of 0.015-0.055 µC cm-2 and magnetic hysteresis. Similarly, the thin films grown on MgO substrates exhibited an electrical surface-resistivity of the order of 109 Ω, multiple piezoelectric resonances in the frequency range of about 8-45 MHz, a linear variation of polarization with applied electric field and either a linearly varying magnetization or magnetic hysteresis which depends on the deposition conditions.

  17. Resonant inelastic x-ray scattering study of the spin and charge excitations in the overdoped superconductor La1.77Sr0.23CuO4

    NASA Astrophysics Data System (ADS)

    Monney, C.; Schmitt, T.; Matt, C. E.; Mesot, J.; Strocov, V. N.; Lipscombe, O. J.; Hayden, S. M.; Chang, J.

    2016-02-01

    We present a resonant inelastic x-ray scattering (RIXS) study of spin and charge excitations in overdoped La1.77Sr0.23CuO4 along two high-symmetry directions. The line shape of these excitations is analyzed and they are shown to be highly overdamped. Their spectral weight and damping are found to be strongly momentum dependent. Qualitative agreement between these observations and a calculated random-phase approximation susceptibility is obtained for this overdoped compound, implying that a significant contribution to the RIXS signal stems from a continuum of charge excitations. Furthermore, this suggests that the spin excitations in the overdoped regime can be captured qualitatively by an itinerant picture. Our calculations also predict a low-energy spin-excitation branch to exist along the nodal direction near the zone center. With the energy resolution of the present experiment, this branch is not resolvable, but we show that the next generation of high-resolution spectrometers will be able to test this prediction.

  18. PbZr0.4Ti0.6O3 and Ba0.9Sr0.1TiO3 reflectors derived from chemical solutions containing polymers.

    PubMed

    Hu, G J; Shang, J L; Sun, Y; Zhang, T; Wu, J; Xie, J

    2008-09-15

    Ba(0.9)Sr(0.1)TiO3 (BST)-based and PbZr(0.4)Ti(0.6)O(3)-based quasi-periodic multilayers consisting of dense and porous ferroelectric layers have been fabricated by solgel technique using chemical solutions containing polyethylene glycol (PEG) or polyvinylpyrrolidone k30 (PVP). All multilayers exhibit good performance as dielectric mirrors. For each multilayer, the maximum peak reflectivity is over 90% and the photonic stopband width is no less than 30 nm at room temperature. The reflection-band position can be easily tuned by varying the thickness of the bilayer. With the same processing conditions and number of periods, the Bragg reflection performance is almost the same for quasi-periodic PZT multilayers derived from two precursors containing different polymers. The BST multilayers deposited by using a PVP-containing precursor are superior in optical properties, including peak reflectivities and stop-band width, to those deposited by using the PEG-containing solution. PMID:18794931

  19. Strain effect caused by substrates on phase separation and transport properties in Pr0.7(Ca0.8Sr0.2)0.3MnO3 thin films

    NASA Astrophysics Data System (ADS)

    Zhao, Y. Y.; Hu, F. X.; Wang, J.; Chen, L.; Gao, W. W.; Shen, J.; Sun, J. R.; Shen, B. G.

    2012-04-01

    Tensile and compressive strains were introduced by epitaxially growing Pr(Ca0.8Sr0.2)0.3MnO3 thin films on different substrates with different lattice constants. The large tensile strain in films on SrTiO3 enhances the stability of the long-range charge-orbital (CO) phase and a 5 T magnetic field cannot melt the CO phase. However, the CO phase in the film on (LaAlO3)0.3(Sr2AlTaO6)0.7 (LSAT) is less robust due to a smaller tensile strain and can be partially melt by a 5T field. On the other hand, compressive strained films on LaAlO3 (LAO) show different behavior. Sharp metal-insulator transition with pronounced hysteresis was observed, indicating that the long-range CO is suppressed, whereas the short-rang ferromagnetic (FM)/CO is favored. Upon magnetic field application, resistance reduces remarkably, whereas the insulator-metal (IM) transition and hysteresis becomes broader and insignificant.

  20. Effect of misfit strain on multiferroic and magnetoelectric properties of epitaxial La0.7Sr0.3MnO3/BaTiO3 bilayer

    NASA Astrophysics Data System (ADS)

    Li, T. X.; Zhang, M.; Yu, F. J.; Hu, Z.; Li, K. S.; Yu, D. B.; Yan, H.

    2012-02-01

    La0.7Sr0.3MnO3/BaTiO3 (LSMO/BTO) bilayer films were grown on (0 0 1) oriented SrTiO3 (STO), LaAlO3 (LAO) and (LaAlO3)0.3(SrAl0.5Ta0.5O3)0.7 (LSAT) substrates by pulsed laser deposition. The bilayer deposited on the LSAT substrate presented the best ferromagnetic properties due to the smallest lattice mismatch between LSAT and LSMO. However, the best ferroelectric properties and strongest magnetoelectric (ME) effect existed in the bilayer on the STO substrate due to the minimal compressive strain in the BTO film. All these showed similar frequency-dependent ME behaviour from 0.1 to 100 kHz, and the largest value of ME voltage coefficient (αE) was obtained on the STO substrate. The values of αE were around 263 mV cm-1 Oe-1, 202 mV cm-1 Oe-1 and 169 mV cm-1 Oe-1 at 1 kHz on STO, LSAT and LAO substrates, respectively, which were at least one order of magnitude higher than previously reported values for similar composites and were ascribed mainly to the rather low dielectric constant of the BTO film.

  1. Large enhancement of magnetic anisotropy and laser induced resistive switching effect in La0.7Sr0.3MnO3 films due to strain from BaTiO3 substrates

    NASA Astrophysics Data System (ADS)

    Kalappattil, V.; Das, R.; Srikanth, H.; Phan, M. H.; Moya, X.

    Multifunctional oxide materials are interesting for their fundamental physical properties and technological applications. Epitaxial films of La0.7Sr0.3MnO3 (LSMO) on BaTiO3 (BTO) show intriguing properties such as a giant magnetoelectric effect due to strain from BTO substrate. The LSMO film shows sharp jumps in magnetization M(T) and resistance R(T) at first-order structural phase transitions of BTO (TR-O 200K and TO-T 270 K) due to strain coupling from BTO. A temperature evolution of effective in-plane anisotropy field (HK) measured using the radio-frequency transverse susceptibility (TS) shows a sharp increase in HK around TR-O, which vanishes around TO-T.The in-plane magnetic anisotropy plays an important role in changing the magnetic and resistive states around TO-T. A switchable laser-induced resistive change of up to 300 %, which is about 10 times greater than those of conventional oxide systems, has been achieved in LSMO films using a 0.5 W violet laser just below the TO-T.The repeatability and stability of the laser-induced resistive switching effect reveal potential applications of LSMO/BTO heterostructures in developing new type of temperature sensors and memory devices. Work at USF supported by ARO Grant No. W911NF-15-1-0626.

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

    NASA Astrophysics Data System (ADS)

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

    2016-05-01

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

  3. Influence of structural disorder on magnetic and transport properties of (La0.7Sr0.3)0.5(Pr0.65Ca0.35)0.5MnO3 films

    NASA Astrophysics Data System (ADS)

    Prokhorov, V. G.; Flis, V. S.; Kaminsky, G. G.; Lee, Y. P.; Park, J. S.; Svetchnikov, V. L.

    2005-02-01

    Magnetic and transport properties of (La0.7Sr0.3)0.5(Pr0.65Ca0.35)0.5MnO3 films prepared by a "co-deposition" utilizing the laser-ablation technique are investigated in a wide temperature range. The film deposited at 300 °C has a nanocrystalline disordered structure and exhibits a paramagnetic temperature dependence of the magnetization with a narrow peak (ΔT≃10 K) at TG≃45 K, which can be interpreted as a paramagnetic→superparamagnetic transition. A short-term annealing of the as-deposited film at 750 °C leads to the formation of a high-textured polycrystalline microstructure and to the appearance of ferromagnetic (FM) and metal-insulator (MI) transitions at TC≃240 K and TP≃140 K, respectively. The observed discrepancy between TP and TC values can be ascribed to a percolating nature of the MI transition, with an exponent of 5.3 for the percolating conductivity. The film deposited at Tsub≃740 °C is composed of lattice-strain-free and the lattice-strained crystallites with different lattice parameters and TC's, and is consistently described in the framework of the Millis model [A. J. Millis, T. Darling, and A. Migliori, J. Appl. Phys. 83, 1588 (1998)]. For a single-phase crystalline film the values TC≃270 K and TP≃260 K are obtained.

  4. Electrical conductivity and complex impedance analysis of La0.7-xNdxSr0.3Mn0.7Ti0.3O3 (x≤0.30) perovskite

    NASA Astrophysics Data System (ADS)

    Abassi, Amel; Kallel, Nabil; Kallel, Sami; Khirouni, Kamel; Peña, Octavio

    2016-03-01

    Polycrystalline samples La0.7-xNdxSr0.3Mn0.7Ti0.3O3 (x=0.10; 0.20 and 0.30) were prepared by a high-temperature solid-state reaction technique. The X-ray diffraction shows that all the samples crystallize in the orthorhombic structure, Pbnm space group, with presence of a minor unreacted Nd2O3. The electrical response was studied by impedance complex spectroscopy over a broad frequency range (40-100 MHz) at room temperature. The values of ac conductivity for all samples were fitted by the Jonscher law σ (ω) = σdc + Aωs . For x=0.10 and 0.20, hopping occurs between neighboring sites, whereas for x=0.30 the hopping process occurs through longer distance. Complex impedance plots exhibit semicircular arcs described by an electrical equivalent circuit, which indicates that the Nd-doped compounds obey a non-Debye relaxation process.

  5. Temperature evolution of superparamagnetic clusters in single-crystal La0.85Sr0.15CoO3 characterized by nonlinear magnetic ac response and neutron depolarization

    NASA Astrophysics Data System (ADS)

    Lazuta, A. V.; Ryzhov, V. A.; Runov, V. V.; Khavronin, V. P.; Deriglazov, V. V.

    2015-07-01

    The representative measurements of the second harmonic in ac magnetization complemented by neutron depolarization have been performed for single-crystal La0.85Sr0.15CoO3 in the temperature range 97 K

  6. 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.

  7. Co-electrolysis of steam and CO2 in a solid oxide electrolysis cell with La0.75Sr0.25Cr0.5Mn0.5O3-δ -Cu ceramic composite electrode

    NASA Astrophysics Data System (ADS)

    Xing, Ruimin; Wang, Yarong; Zhu, Yongqiang; Liu, Shanhu; Jin, Chao

    2015-01-01

    Cu impregnation has been performed to improve electronic conductivity of La0.75Sr0.25Cr0.5Mn0.5O3-δ (LSCM) material in reducing atmosphere, and solid oxide electrolysis cells (SOECs) with the configuration of LSCF|LSGM|LSCM-Cu are prepared and evaluated for high temperature steam and carbon dioxide co-electrolysis. Electrochemical impedance spectra (EIS) and voltage-current curves are carried out to characterize the cell performances. Compared with LSCF|LSGM|LSCM cell without Cu impregnation for steam electrolysis under the same conditions, EIS results show that LSCF|LSGM|LSCM-Cu cell not only displays lower ohmic resistance and better electrochemical performances, but also their resistance increases with the percentage of the fed CO2 under open circuit voltage, in which the polarization resistance dominates. With the applied electrolysis voltage of 1.65 V and the operating temperature of 750 °C, the maximum consumed current density increases from 1.31 A cm-2 without CO2 to 1.82 A cm-2 with 37.5% CO2. Although there is an increase of 2.0% in the applied electrolysis voltage, the cell has exhibited an excellent durability test for more than 50 h with the electrolysis current density of 0.33 A cm-2 and the gas mixture of 50% AH-25% H2-25% CO2 at 750 °C.

  8. Spin glass-like state, charge ordering, phase diagram and positive entropy change in Nd 0.5-xPr xSr 0.5MnO 3 perovskites

    NASA Astrophysics Data System (ADS)

    Chau, N.; Tho, N. D.; Luong, N. H.; Giang, B. H.; Cong, B. T.

    2006-08-01

    The mixed rare earth manganites Nd 0.5-xPr xSr 0.5MnO 3 ( x=0.1-0.5) have been prepared using solid state reaction technique. All samples are of single phase with orthorhombic structure. The microstructure of the samples was determined by SEM. The field-cooled (FC) and zero-field-cooled (ZFC) curves showed that samples with x⩾0.25 exhibit the spin glass-like state at low field and low temperatures, whereas, in the samples with x<0.25, there is the charge ordering (coexisting with FM-AFM transition) established at low temperatures. The Curie temperature of the samples increases with increasing Pr content due to increase of < rA>. Interesting feature is that at the FM-AFM transition region, the magnetic entropy change has positive value, in contrary to that at FM-PM transition region. The electrical property of the samples from 10 K to room temperature is examined in detail.

  9. Large magnetic entropy change above 300 K in a colossal magnetoresistive material La0.7Sr0.3Mn0.98Ni0.02O3

    NASA Astrophysics Data System (ADS)

    Phan, Manh-Huong; Tho, Nguyen Duc; Chau, Nguyen; Yu, Seong-Cho; Kurisu, M.

    2005-05-01

    A thorough study of the magnetocaloric effect (MCE) in a colossal magnetoresistive compound of La0.7Sr0.3Mn0.98Ni0.02O3 has been made. The large magnetic entropy change of 7.65 J/kg K upon an applied field of 70 kOe has been found to occur at 350 K, which allows magnetic refrigeration at room temperature. It is interesting to note that, even in high magnetic fields, the magnetic entropy change versus temperature distribution is much more uniform than that of gadolinium and several polycrystalline perovskite manganites, which is desirable for an Ericson-cycle magnetic refrigerator. It is found that such a small amount (˜2%) of substitution of Mn3+ by a magnetic ion (Ni3+ or Co3+) in the perovskite manganite can favor the spin order and hence the MCE. Undoubtedly, this observation opens a window to explore the active magnetic refrigeration at high temperatures.

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

    DOE PAGESBeta

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

    2016-01-28

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

  11. Mass synthesis of high performance (La0.75Sr0.25)0.95MnO3±δ nano-powder prepared via a low-carbon chemical solution method

    NASA Astrophysics Data System (ADS)

    Wang, Jian Xin; Sun, Jia Long; He, Chang Rong; Wang, Qin; Wang, Wei Guo

    2014-05-01

    A novel low-carbon chemical solution method is established and successfully scaled up to prepare (La0.75Sr0.25)0.95MnO3±δ(LSM) nano-powders, in which acetate and acrylic acid have been used as raw materials. Distinguish from the traditional chemical solution methods, nitrate and amino compound are non-used in this method and without causing any fire hazard or explosion condition which are usually found in most of the solution synthesis reactions. The organic compound emission is reduced to a quarter of that in the citric acid-nitrate method. This optimization is attributed to the low application amount and high effect of acrylic acid by means of the co-operation of ethylenic linkage and carboxyl group. As-prepared powders are high purity, single phase, slight aggregation with grain size less than 100 nm. The conductivity of the sintered LSM sample is measured about 220 S cm-1 in air at 700-1000 °C. The polarization resistance of LSM-YSZ cathode is less than 0.1 Ω cm2 at 800 °C. Anode supported Cells with configuration of Ni + YSZ/YSZ/LSM + YSZ exhibit the power density of 0.54 W cm-2 at 800 °C and 0.7 V. These results indicate that the novel acetate-acrylic method is very suitable for mass synthesis of high performance LSM powders.

  12. Photoluminescence Properties of Efficient Blue-Emitting Phosphor α-Ca1.65Sr0.35SiO4:Ce(3+): Color Tuning via the Substitutions of Si by Al/Ga/B.

    PubMed

    Li, Kai; Shang, Mengmeng; Lian, Hongzhou; Lin, Jun

    2015-08-17

    A series of Ce(3+)-doped α-Ca1.65Sr0.35SiO4 (CSSO) phosphors without and with the substitutions of Si by Al/Ga/B were synthesized via the high-temperature solid-state reaction process. X-ray diffraction patterns and Rietveld refinements were used to demonstrate the successful incorporations of Al/Ga/B into CSSO:Ce(3+). Without Al/Ga/B, the Ce(3+) singly doped CSSO phosphors present intense blue emission, which correspond to the broad emission bands in visible region with the wavelength range from 360 to 580 nm upon 350 nm excitation. The optimal emission intensity occurs in CSSO:0.05Ce(3+) sample with the emission peak wavelength at 436 nm. With the introduction of Al/Ga/B into the CSSO:0.05Ce(3+), the emission peak shifts from 436 to 457/465/446 nm under 365 nm excitation, respectively. The red shift of Ce(3+) emission is attributed to the polyhedral distortion of the cations, resulting in the enhancement of crystal field spitting due to the variations of the adjacent (Al/Ga/B,Si)O4 polyhedron. Moreover, the temperature-dependent photoluminescence was determined to be of light impact to CSSO:Ce(3+) with the introduction of Al/Ga/B. This research is useful for enriching the emission colors of Ce(3+)-activated phosphors. PMID:26247562

  13. Preparation and characterization of La0.75Sr0.25Cr0.5Mn0.5O3-δ-yttria stabilized zirconia cathode supported solid oxide electrolysis cells for hydrogen generation

    NASA Astrophysics Data System (ADS)

    Xing, Ruimin; Wang, Yarong; Liu, Shanhu; Jin, Chao

    2012-06-01

    La0.75Sr0.25Cr0.5Mn0.5O3-δ (LSCM)-YSZ cathode supported solid oxide electrolysis cells (SOECs), with the LSM-YSZ|YSZ|LSCM-YSZ configuration, have been prepared and evaluated for high temperature hydrogen generation. Electrochemical impedance spectra (EIS) and voltage-current curves were recorded out to characterize the cell performance. EIS results showed that the cell resistance increased as the proportion of steam in the feed supply increased, at open circuit voltage. The hydrogen generation rate calculated from Faraday's law is 561 ml cm-2 h-1 at 850 °C with 80 vol.% absolute humidity (AH) at a 1.6 V electrolysis voltage. Although there is a 8.2% increase of the applied electrolysis voltage, the cell has endured a test lasting more than 103 h with 45 vol.% AH and 0.33 A cm-2 electrolysis current density at 850 °C. Energy-dispersive X-ray (EDX) spectroscopy analysis showed that there is no elemental diffusion between the electrode and electrolyte interface after the durability test. Scanning electron microscopy (SEM) images indicate that the slight split between the LSCM-YSZ cathode and the YSZ electrolyte is responsible for the increase of ohmic resistance of the cell; this resistance rise led to the degradation of the cell performance.

  14. Magnetron sputtering derived (1 0 0) oriented Pb0.4Sr0.6(Ti0.97Mg0.03)O2.97 thin film on inducing-layer/glass substrate with outstanding tunability

    NASA Astrophysics Data System (ADS)

    Fang, Junfei; Hu, Tao; Chen, Jingfeng; Han, Gaorong; Weng, Wenjian; Ma, Ning; Du, Piyi

    2013-12-01

    Pb0.4Sr0.6(Ti0.97Mg0.03)O2.97 (PST) thin films were deposited on ITO/glass substrates with (1 0 0)/(0 0 1) oriented Tb-doped-PbTiO3 (Tb-PT) layer inserted by magnetron sputtering method at room temperature. And the PST thin film is well-crystallized in (1 0 0) direction at annealing temperature of 600 °C for 30 min. The oriented Tb-PT layer promotes a (1 0 0) orientation, restrains structural distortion and improves phase quality of PST thin film. The (1 0 0) oriented PST thin film has higher permittivity and lower dielectric loss compared with the randomly oriented one. The tunability of the PST thin film is dramatically improved by 90% compared to that of randomly oriented PST without Tb-PT inserting layer, from 33% for randomly oriented PST without the inserting layer to 62.66% for the oriented one with the inserting layer. It is attractable to be used in high quality dielectric tunable devices.

  15. The effect of Mg doping on the dielectric and tunable properties of Pb0.3Sr0.7TiO3 thin films prepared by sol-gel method

    NASA Astrophysics Data System (ADS)

    Sun, Xiaohua; Li, Xiuneng; Hou, Shuang; Huang, Caihua; Zou, Jun; Li, Meiya; Peng, Tianyou; Zhao, Xing-zhong

    2013-03-01

    Mg doped Pb0.3Sr0.7TiO3 (PST) thin films were fabricated by the sol-gel method on a Pt/Ti/SiO2/Si substrate. The microstructure, surface morphology, dielectric and tunable properties of PST thin films were investigated as a function of Mg concentration. It is found that proper Mg doping dramatically improves the dielectric loss (0.0088 @ 1 MHz), furthermore, the crystallinity, dielectric constant, and tunability of films simultaneously decrease with the increase of Mg content. The 2 mol% Mg doped PST thin film shows the highest figure of merit (FOM) value of 36.8 for its the smallest dielectric loss and upper tunability. The dependence of Rayleigh coefficient on the doping concentration was examined, which indicated that the reduction of dielectric constant and tunability of films should be related to the Mg''_{Ti}-VO^{bulletbullet} defect dipoles pinning the domain wall motion of residual polar clusters in PST.

  16. Hierarchical Mesoporous/Macroporous Perovskite La0.5Sr0.5CoO3-x Nanotubes: A Bifunctional Catalyst with Enhanced Activity and Cycle Stability for Rechargeable Lithium Oxygen Batteries.

    PubMed

    Liu, Guoxue; Chen, Hongbin; Xia, Lu; Wang, Suqing; Ding, Liang-Xin; Li, Dongdong; Xiao, Kang; Dai, Sheng; Wang, Haihui

    2015-10-14

    Perovskites show excellent specific catalytic activity toward both oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) in alkaline solutions; however, small surface areas of the perovskites synthesized by traditional sol-gel methods lead to low utilization of catalytic sites, which gives rise to poor Li-O2 batteries performance and restricts their application. Herein, a hierarchical mesporous/macroporous perovskite La0.5Sr0.5CoO3-x (HPN-LSC) nanotube is developed to promote its application in Li-O2 batteries. The HPN-LSC nanotubes were synthesized via electrospinning technique followed by postannealing. The as-prepared HPN-LSC catalyst exhibits outstanding intrinsic ORR and OER catalytic activity. The HPN-LSC/KB electrode displays excellent performance toward both discharge and charge processes for Li-O2 batteries, which enhances the reversibility, the round-trip efficiency, and the capacity of resultant batteries. The synergy of high catalytic activity and hierarchical mesoporous/macroporous nanotubular structure results in the Li-O2 batteries with good rate capability and excellent cycle stability of sustaining 50 cycles at a current density of 0.1 mA cm(-2) with an upper-limit capacity of 500 mAh g(-1). The results will benefit for the future development of high-performance Li-O2 batteries using hierarchical mesoporous/macroporous nanostructured perovskite-type catalysts. PMID:26418118

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

    NASA Astrophysics Data System (ADS)

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

    2016-05-01

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

  18. High performance La2NiO4+δ-infiltrated (La0.6Sr0.4)0.995Co0.2Fe0.8O3−δ cathode for solid oxide fuel cells

    DOE PAGESBeta

    Zhang, Xinxin; Zhang, Hui; Liu, Xingbo

    2014-12-01

    In this paper, we reported our effort on improving electrochemical performance of (La0.6Sr0.4)0.995Co0.2Fe0.8O3d (LSCF) cathode in solid oxide fuel cell (SOFC) by infiltration of La2NiO4þd (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 cm2 with a low degradationmore » 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.« less

  19. 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.

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

    PubMed

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

    2016-01-01

    The Mn K edge X-ray absorption near edge structure (XANES) of Pr0.67Sr0.33MnO3 films with different thicknesses on (001) LaAlO3 substrate was measured, and the effects of strain relaxation on film properties were investigated. The films showed in-plane compressive and out-of-plane tensile strains. Strain relaxation occurred with increasing film thickness, affecting both lattice constant and MnO6 octahedral rotation. In polarization dependent XANES measurements using in-plane (parallel) and out-of-plane (perpendicular) geometries, the different values of absorption resonance energy Er confirmed the film anisotropy. The values of Er along these two directions shifted towards each other with increasing film thickness. Correlating with X-ray diffraction (XRD) results it is suggested that the strain relaxation decreased the local anisotropy and corresponding probability of electronic charge transfer between Mn 3d and O 2p orbitals along the in-plane and out-of-plane directions. The XANES results were used to explain the film-thickness dependent magnetic and transport properties. PMID:26818583

  1. Ni-induced local distortions in La1.85Sr0.15Cu1-yNiyO4 and their relevance to Tc suppression: An angular-resolved XAFS study

    NASA Astrophysics Data System (ADS)

    Haskel, Daniel; Stern, Edward A.; Polinger, Victor; Dogan, Fatih

    2001-09-01

    We present results from angular-resolved x-ray-absorption fine-structure (XAFS) measurements at the Ni, La, and Sr K edges of oriented powders of La1.85Sr0.15Cu1-yNiyO4, with y=0.01, 0.03, 0.06. A special magnetic alignment procedure allowed us to measure pure ĉ- and ab-oriented XAFS at the Ni K edge in identical fluorescence geometries. Both the x-ray-absorption near-edge structure and the XAFS unequivocally show that the NiO6 octahedra are contracted along the c axis by ~0.32 Å relative to CuO6 octahedra while the in-plane distances of NiO6 and CuO6 octahedra are the same within 0.01 Å. The NiO6 octahedral contraction drives the average ĉ axis contraction measured by diffraction with increasing content of Ni. The local ĉ axis shows strong spatial fluctuations, due to the different NiO6 and CuO6 octahedral configurations and the stronger bonding of a La3+ ion than a Sr2+ ion to the O(2) apical oxygens of such octahedra. We discuss the relevance of these findings to the mechanisms of loss of superconductivity at y~0.03 and hole localization above y~0.05 by Ni dopants.

  2. Effect of the symmetric cell preparation temperature on the activity of Ba0.5Sr0.5Fe0.8Cu0.2O3-δ as cathode for intermediate temperature Solid Oxide Fuel Cells

    NASA Astrophysics Data System (ADS)

    Vázquez, Santiago; Basbus, Juan; Soldati, Analía L.; Napolitano, Federico; Serquis, Adriana; Suescun, Leopoldo

    2015-01-01

    In this work we studied the electrochemical performance of Ba0.5Sr0.5Fe0.8Cu0.2O3-δ (BSFCu) as cathode for Intermediate Temperature Solid Oxide Fuel Cells (IT-SOFC) with Ce0.9Gd0.1O1.95 (CGO) electrolyte and the effect of the symmetric cell preparation temperature on the oxygen reduction reaction (ORR) activity. Symmetrical cells with the configuration BSFCu/CGO/BSFCu were prepared at 900 °C, 950 °C and 1000 °C to perform the electrochemical characterization in the 500-700 °C temperature range. The resultant area specific resistance (ASR) of the cells with different preparation temperatures followed the tendency: ASR900°C < ASR950°C < ASR1000°C. The symmetric cell constructed at 900 °C showed ASR values of 0.18, 0.078 and 0.035 Ω cm2 at 600, 650 and 700 °C respectively, which demonstrated superior electrochemical activities than previous reports. Additional, X-ray diffraction (XRD), scanning and transmission electron microscopies (SEM and TEM) techniques were used to characterize the microstructure of the original and fired BSFCu materials and correlate it with the cell preparation temperature.

  3. Electric and Magnetic Characterization of patterned La0.6Sr0.4MnO3/SrTiO3/Si junctions using strained SrTiO3 as a Ferroelectric Barrier

    NASA Astrophysics Data System (ADS)

    Jalili Shafighi, Parisa; Cottier, Ryan; Currie, Daniel. A.; Koehne, Barry. D.; Johnson, Andrew; Veazey, Joshua. P.; Theodoropoulou, Nikoleta; Texas State University, San Marcos, TX Team; Hope College, Holland, MI Team

    Controlling a magnetic device via electrical means is a sought-after goal for technological devices and can be achieved through magnetoelectric coupling between ferroelectric and ferromagnetic materials. We investigate such as possibility through a by epitaxially growing a magnetic oxide, La0.6Sr0.4MnO3 (LSMO) as an active magnetic electrode on a ferroelectric oxide, strained SrTiO3(STO) on Si. STO thin films grown on Si are compressively strained (1.7 %) and can be ferroelectric at T =300 K when less than 5nm thick. LSMO is ferromagnetic up to 340 K (in bulk), has an in-plane crystal constant of a = 0.3870 nm, and is closely lattice matched to STO (a = 0.3905 nm) with a 0.9% in-plane tensile strain. Since STO is compressively strained in Si, an even smaller lattice mismatch is expected between LSMO and STO/Si. We investigate the epitaxial growth of LSMO/STO/Si and electrical characteristics in a capacitor type structure fabricated using photolithography as a function of Temperature and Magnetic Field. Acknowledgements: Support by the NSF-Career grant, DMR-1255629, Hope College Frissel Research Fund, NSF-MRI Grant, CHE-1126462 is gratefully acknowledged.

  4. Evidence for a tricritical point coinciding with the triple point in (Pb0.94Sr0.06)(ZrxTi1-x)O3: A combined synchrotron x-ray diffraction, dielectric, and Landau theory study

    NASA Astrophysics Data System (ADS)

    Solanki, Ravindra Singh; Mishra, S. K.; Kuroiwa, Yoshihiro; Moriyoshi, Chikako; Pandey, Dhananjai

    2013-11-01

    We present here results of high-resolution synchrotron x-ray diffraction (SXRD) and dielectric studies in conjunction with Landau theory considerations on (Pb0.94Sr0.06)(ZrxTi1-x)O3 compositions in the vicinity of the morphotropic phase boundary (MPB) to find evidence for the flattening of the free-energy surface at the MPB proposed in recent ab initio studies on strongly piezoelectric ceramics. SXRD results reveal that the tetragonal and pseudorhombohedral monoclinic compositions with x = 0.515 and 0.550 transform directly into the cubic paraelectric phase, whereas for 0.520 ≤ x ≤ 0.545, the pseudotetragonal and pseudorhombohedral monoclinic compositions transform first to the tetragonal phase and then to the cubic phase. Our results reveal the existence of a triple point at x ≃ 0.550. It is shown that the tetragonal-to-cubic transition, irrespective of the composition, up to x ≃ 0.545 is accompanied with a discontinuous change in the unit cell volume and thermal hysteresis, confirming the first-order nature of this transition. However, the pseudorhombohedral monoclinic composition for x = 0.550 transforms directly into the cubic phase in a second-order manner. Our experimental results thus reveal a crossover from a first-order to a second-order phase transition through a tricritical point around x = 0.550. Landau theory calculations also confirm gradual flattening of the free-energy surface on approaching the tricritical composition x = 0.550. We conclude that the triple point in the Pb(ZrxTi1-x)O3 phase diagram is a tricritical point.

  5. Temperature-dependent and time-dependent effects of hyperthermia mediated by dextran-coated La0.7Sr0.3MnO3: in vitro studies

    PubMed Central

    Haghniaz, Reihaneh; Umrani, Rinku D; Paknikar, Kishore M

    2015-01-01

    Background The purpose of this study was to investigate the therapeutic efficacy of dextran-coated (Dex) La0.7Sr0.3MnO3 (LSMO) nanoparticles-mediated hyperthermia at different temperatures (43°C, 45°C, and 47°C) based on cell killing potential and induction of heat shock proteins in a murine melanoma cell (B16F1) line. Methods LSMO nanoparticles were synthesized by a citrate-gel method and coated with dextran. B16F1 cells were exposed to the Dex-LSMO nanoparticles and heated using a radiofrequency generator. After heating, the morphology and topology of the cells were investigated by optical microscopy and atomic force microscopy. At 0 hours and 24 hours post heating, cells were harvested and viability was analyzed by the Trypan blue dye exclusion method. Apoptosis and DNA fragmentation were assessed by terminal deoxynucleotidyl transferase-dUTP nick end labeling (TUNEL) assay and agarose gel electrophoresis, respectively. An enzyme-linked immunosorbent assay was used to quantify heat shock protein levels. Results Our data indicate that cell death and induction of heat shock proteins in melanoma cells increased in a time-dependent and temperature-dependent manner, particularly at temperatures higher than 43°C. The mode of cell death was found to be apoptotic, as evident by DNA fragmentation and TUNEL signal. A minimum temperature of 45°C was required to irreversibly alter cell morphology, significantly reduce cell viability, and result in 98% apoptosis. Repeated cycles of hyperthermia could induce higher levels of heat shock proteins (more favorable for antitumor activity) when compared with a single cycle. Conclusion Our findings indicate a potential use for Dex-LSMO-mediated hyperthermia in the treatment of melanoma and other types of cancer. PMID:25759583

  6. The impact of disorder on magnetocaloric properties in Ti-doped manganites of La0.7Sr0.25Na0.05Mn(1-x)TixO3 (0≤x≤0.2)

    NASA Astrophysics Data System (ADS)

    Kossi, S. EL.; Ghodhbane, S.; Mnefgui, S.; Dhahri, J.; Hlil, E. K.

    2015-12-01

    This work reports the effect of Ti doping on the structural, magnetic and magnetocaloric properties of La0.7Sr0.25Na0.05Mn(1-x)TixO3 (LSNMTix) (0≤x≤0.2) manganese perovskite prepared by the conventional solid-state reaction. Rietvelds' refinement result of X-ray power diffraction using the FullProf refinement program indicates that these compounds have a rhombohedrally distorted structure with a space group R 3 ̅c. Magnetization as a function of temperature shows that all samples exhibit a paramagnetic (PM) - ferromagnetic (FM) phase transition at the Curie temperature TC which decreases from 363 K to 125 K for x=0-0.2, respectively. The magnetic entropy change (ΔSM) deduced from the measured magnetization M (μ0H) data using Maxwell relation, strongly depends on the Ti content. The maximum value of magnetic entropy change has been observed in our samples with a peak centered around their respective TC decrease from 4.34 J kg-1 K-1 to 2.03 J kg-1 K-1 for x=0 and x=0.2 at μ0H=5 T respectively. In addition, the relative cooling power (RCP) values inferred from the |ΔSM| vs. T peak broadening, vary slightly with the titanium content reaching values between 298 and 273 J kg-1 for an applied magnetic field of 5 T when x increases from 0 to 0.2. Technically, these results suggest that the material can be considered as suitable candidate as working substance in magnetic refrigeration.

  7. Nano-ceria pre-infiltration improves La0.6Sr0.4Co0.8Fe0.2O3-x infiltrated Solid Oxide Fuel Cell cathode performance

    NASA Astrophysics Data System (ADS)

    Burye, Theodore E.; Nicholas, Jason D.

    2015-12-01

    Here, scanning electron microscopy, X-ray diffraction, and thermo-gravimetric analysis experiments show that the pre-infiltration of Ce0.9Gd0.1O1.95 (GDC) nano-particles reduces the average size of La0.6Sr0.4Co0.8Fe0.2O3-x (LSCF) produced from the subsequent infiltration of precursor nitrate solutions containing the surfactant Triton X-100 or the chelating agent citric acid. In contrast, GDC pre-infiltration has no effect on the average size of LSCF particles produced from precursor solutions containing only lanthanum, strontium, cobalt, and iron nitrate. Consistent with the observed particle size trends, electrochemical impedance spectroscopy measurements show that GDC pre-infiltration improves the performance of Triton X-100 Derived (TXD) LSCF-GDC cathodes and Citric Acid Derived (CAD) LSCF-GDC cathodes, but has no effect on the performance of Pure Nitrate Derived (PND) LSCF-GDC cathodes. In particular, TXD LSCF-GDC cathodes with more than ∼5 vol% of GDC pre-infiltration display average LSCF particle sizes of 21 nm and open-circuit polarization resistance values of 0.10 Ωcm2 at 540 °C, compared to 48 nm and 640 °C without GDC pre-infiltration. Results suggest that this 100 °C reduction in cathode operating temperature is caused solely by LSCF particle size reductions. 7.4 vol% GDC pre-infiltrated TXD LSCF-GDC cathodes also display lower 540 °C degradation rates than conventionally infiltrated PND LSCF-GDC cathodes.

  8. Magnetocaloric effect and critical behavior in Pr0.5Sr0.5MnO3: an analysis of the validity of the Maxwell relation and the nature of the phase transitions.

    PubMed

    Caballero-Flores, R; Bingham, N S; Phan, M H; Torija, M A; Leighton, C; Franco, V; Conde, A; Phan, T L; Yu, S C; Srikanth, H

    2014-07-16

    The Maxwell relation, the Clausius-Clapeyron equation, and a non-iterative method to obtain the critical exponents have been used to characterize the magnetocaloric effect (MCE) and the nature of the phase transitions in Pr0.5Sr0.5MnO3, which undergoes a second-order paramagnetic to ferromagnetic (PM-FM) transition at TC ~ 247 K, and a first-order ferromagnetic to antiferromagnetic (FM-AFM) transition at TN ~ 165 K. We find that around the second-order PM-FM transition, the MCE (as represented by the magnetic entropy change, ΔSM) can be precisely determined from magnetization measurements using the Maxwell relation. However, around the first-order FM-AFM transition, values of ΔSM calculated with the Maxwell relation deviate significantly from those calculated by the Clausius-Clapeyron equation at the magnetic field and temperature ranges where a conversion between the AFM and FM phases occurs. A detailed analysis of the critical exponents of the second-order PM-FM transition allows us to correlate the short-range type magnetic interactions with the MCE. Using the Arrott-Noakes equation of state with the appropriate values of the critical exponents, the field- and temperature-dependent magnetization [Formula: see text] curves, and hence the [Formula: see text] curves, have been simulated and compared with experimental data. A good agreement between the experimental and simulated data has been found in the vicinity of the Curie temperature TC, but a noticeable discrepancy is present for [Formula: see text]. This discrepancy arises mainly from the coexistence of AFM and FM phases and the presence of ferromagnetic clusters in the AFM matrix. PMID:24945593

  9. Performance and sulfur poisoning of Ni/CeO2 impregnated La0.75Sr0.25Cr0.5Mn0.5O3-δ anode in solid oxide fuel cells

    NASA Astrophysics Data System (ADS)

    Li, Yiqian; Zhang, Yaohui; Zhu, Xingbao; Wang, Zhihong; Lü, Zhe; Huang, Xiqiang; Zhou, Yongjun; Zhu, Lin; Jiang, Wei

    2015-07-01

    In this study, comparison experiments are conducted based on yttria-stabilized zirconia (YSZ) electrolyte supported single solid oxide fuel cells (SOFCs) with pure La0.75Sr0.25Cr0.5Mn0.5O3-δ (LSCrM) or Ni/CeO2 impregnated LSCrM anodes. The single cells are tested in dry H2 and H2/H2S (50 ppm) mixture, respectively. Compared with the pure LSCrM anode, the cell with Ni/CeO2 impregnated LSCrM presents a significant performance improvement when the pure H2 is fueled to the anode, and shows a good stability during a constant-current discharge testing (398 mA cm-2). When the fuel is switched to H2/H2S mixture, the cell with Ni/CeO2 impregnated LSCrM anode still shows a remarkable constant-current discharge (120 mA cm-2) performance compared with pure LSCrM anode. The Ni/CeO2 impregnation can improve the electrochemical performance of the LSCrM anode without any sacrifice of sulfur tolerance ability. The Ni/CeO2 impregnated LSCrM might be a potential anode material for solid oxide fuel cell operating in sulfur-containing fuels. The XRD and XPS results demonstrate that the anode poisoning product is composed of adsorbed sulfur, metal sulfides and sulfate radical. The mass spectrum result confirms that the poisoning mechanism involves the reaction of sulfur with anode rather than the direct reaction between H2S gas and anode.

  10. Performance of Y0.9Sr0.1Cr0.9Fe0.1O3-δ as a sulfur-tolerant anode material for intermediate temperate solid oxide fuel cells

    NASA Astrophysics Data System (ADS)

    Bu, Yun-Fei; Zhong, Qin; Xu, Dan-Dan; Zhao, Xiao-Lu; Tan, Wen-Yi

    2014-03-01

    Perovskite-type Y0.9Sr0.1Cr0.9Fe0.1O3-δ maintained good chemical stability under a H2S-containing atmosphere based on results from X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FT-IR) in our previous study. In this research, the YSCF-based anode was studied using H2 and H2S-containing fuels. The activity of an electrode is closely related to its material composition, lattice structure, physic-chemical properties, and morphologic structure. Therefore, the characteristics of the YSCF powders and the cell were analyzed by XRD, Brunauer-Emmett-Teller (BET) surface area analysis, and scanning electron microscopy (SEM). The conductivities of YSCF were evaluated by four-probe method in 10% H2-N2, 1% H2S-N2 and air, respectively. Thermodynamic calculations and X-ray photoelectron spectroscopy (XPS) analysis have been used to investigate the stability of the elements in YSCF upon exposure to hydrogen sulfide (H2S) in hydrogen (H2) over a range of partial pressures of sulfur (pS2) and oxygen (pO2) that are representative of fuel cell operating conditions. In addition, the performance of the complete cell (YSCF-SDC|SDC|Ag) under H2S and H2 fuel mixtures was also evaluated by electrochemical impedance spectra (EIS) and I-V and I-P curves. The emergence of FeSO4 in the sulfur treatment should play an important role in preventing further sulfur-poisoning.

  11. Impregnation of La0.4Ce0.6O1.8-La0.4Sr0.6TiO3 as solid oxide fuel cell anode in H2S-containing fuels

    NASA Astrophysics Data System (ADS)

    Afshar, Milad R.; Yan, Ning; Zahiri, Beniamin; Mitlin, David; Chuang, Karl T.; Luo, Jing-Li

    2015-01-01

    Active anodes were fabricated via wet chemical impregnation of optimized amount of La0.4Sr0.6TiO3 (L4ST) into La0.4Ce0.6O1.8 (LDC) pre-infiltrated porous yttria-stabilized zirconia (YSZ) matrix. Impregnations of 10 wt% LDC with 16 wt% L4ST significantly improved the performance of the fuel cell from 48 mW cm-2 for pure L4ST to 161 mW cm-2 for LDC-L4ST at 900 °C in H2. The contribution of the pre-loaded LDC to this improvement was investigated using electrochemical impedance spectroscopy (EIS), scanning electron microscopy (SEM) as well as transmission electron microscopy (TEM). The measurement results indicated that pre-infiltrated LDC increased the activity of the anode more effectively by decreasing the total polarization resistance of the cell from 3.3 Ω cm2 to 1.0 Ω cm2 in humidified H2 at 900 °C. More importantly, the LDC nano-deposits (<20 nm) behaved as an effective "adhesive" that substantially enhanced the wettability of L4ST on YSZ matrix, resulting in finer and more uniform structure of L4ST infiltrates. The LDC-L4ST cells also demonstrated significantly improved performances in 0.5% H2S-H2 and 0.5% H2S-CH4 with higher stability than cells with pure L4ST anode.

  12. Effects of pre-oxidation on the microstructural and electrical properties of La0.67Sr0.33MnO3-δ coated ferritic stainless steels

    NASA Astrophysics Data System (ADS)

    Yang, Peng; Liu, Chien-Kuo; Wu, Jin-Yu; Shong, Wei-Ja; Lee, Ruey-Yi; Sung, Chia-Chi

    2012-09-01

    LaxSr1-xMnO3 (LSM) is commonly used as a protective layer on the metallic interconnects of solid oxide fuel cells (SOFCs) to prevent surface oxidation and chromium poisoning. However, the volume shrinkage at elevated temperatures causes the LSM coatings to crack, resulting in chromium diffusion. Therefore, this paper investigates the effects of pre-oxidation on the microstructure and electrical properties of ferritic stainless steels coated with La0.67Sr0.33MnO3 (LSM). Four ferritic stainless steels were selected for use as interconnect substrates: Crofer22APU, Crofer22H, ss441, and ZMG232L. The candidate materials were pre-oxidised at 850 °C for 25 and 50 h, respectively. After the pre-oxidation process, the LSM films with a thickness of 3-4 μm were deposited on the surface of samples by using Pulsed DC magnetron sputtering. After aging the coated specimens at elevated temperatures, the morphologies and crystalline structures were examined using SEM/EDX and XRD, respectively. The results indicated that the pre-oxidised layer, (Mn, Cr)3O4, could significantly suppress chromium penetration from the interior to the surface of the specimens. Moreover, the area specific resistance (ASR) values for the 25-h pre-oxidised specimens were 2.24, 12.21, 2.30, and 6.77 mΩ cm2 for Crofer22APU, Crofer22H, ss441, and ZMG232L, respectively, at 800 °C for 500 h in an air atmosphere.

  13. Nano-ceria pre-infiltration improves La0.6Sr0.4Co0.8Fe0.2O3-x infiltrated Solid Oxide Fuel Cell cathode performance

    NASA Astrophysics Data System (ADS)

    Burye, Theodore E.; Nicholas, Jason D.

    2015-12-01

    Here, scanning electron microscopy, X-ray diffraction, and thermo-gravimetric analysis experiments show that the pre-infiltration of Ce0.9Gd0.1O1.95 (GDC) nano-particles reduces the average size of La0.6Sr0.4Co0.8Fe0.2O3-x (LSCF) produced from the subsequent infiltration of precursor nitrate solutions containing the surfactant Triton X-100 or the chelating agent citric acid. In contrast, GDC pre-infiltration has no effect on the average size of LSCF particles produced from precursor solutions containing only lanthanum, strontium, cobalt, and iron nitrate. Consistent with the observed particle size trends, electrochemical impedance spectroscopy measurements show that GDC pre-infiltration improves the performance of Triton X-100 Derived (TXD) LSCF-GDC cathodes and Citric Acid Derived (CAD) LSCF-GDC cathodes, but has no effect on the performance of Pure Nitrate Derived (PND) LSCF-GDC cathodes. In particular, TXD LSCF-GDC cathodes with more than ˜5 vol% of GDC pre-infiltration display average LSCF particle sizes of 21 nm and open-circuit polarization resistance values of 0.10 Ωcm2 at 540 °C, compared to 48 nm and 640 °C without GDC pre-infiltration. Results suggest that this 100 °C reduction in cathode operating temperature is caused solely by LSCF particle size reductions. 7.4 vol% GDC pre-infiltrated TXD LSCF-GDC cathodes also display lower 540 °C degradation rates than conventionally infiltrated PND LSCF-GDC cathodes.

  14. Exsolution of Fe and SrO Nanorods and Nanoparticles from Lanthanum Strontium Ferrite La0.6Sr0.4FeO3−δ Materials by Hydrogen Reduction

    PubMed Central

    2015-01-01

    Formation of uniform Fe and SrO rods as well as nanoparticles following controlled reduction of La0.6Sr0.4FeO3−δ (LSF) and Ni-LSF samples in dry and moist hydrogen is studied by aberration-corrected electron microscopy. Metallic Fe and SrO precipitate from the perovskite lattice as rods of several tenths of nm and thicknesses up to 20 nm. Based on a model of Fe whisker growth following reduction of pure iron oxides, Fe rod exsolution from LSF proceeds via rate-limiting lattice oxygen removal. This favors the formation of single iron metal nuclei at the perovskite surface, subsequently growing as isolated rods. The latter is only possible upon efficient removal of reduction-induced water and, subsequently, reduction of Fe +III/+IV to Fe(0). If water remains in the system, no reduction or rod formation occurs. In contrast, formation of SrO rods following reduction in dry hydrogen is a catalytic process aided by Ni particles. It bears significant resemblance to surface diffusion-controlled carbon whisker growth on Ni, leading to similar extrusion rods and filaments. In addition to SrO rod growth, the exsolution of Fe nanoparticles and, subsequently, Ni–Fe alloy particles is observed. The latter have also been observed under static hydrogen reduction. Under strict control of the experimental parameters, the presented data therefore open an attractive chemically driven pathway to metal nanoarchitectures beyond the formation of “simple” nanoparticles. PMID:26435764

  15. Interfacial Analysis of (La0.6Sr0.4)(Co0.2Fe0.8)O3-δ Substrates Wetted by Ag-CuO

    SciTech Connect

    Weil, K. Scott; Kim, Jin Yong Y.; Hardy, John S.

    2005-05-01

    Recently a new method of brazing has been developed to hermetically seal high-temperature, solid-state electrochemical devices, such as as oxygen and hydrogen separators, fuel gas reformers, solid oxide fuel cells, and chemical sensors. Based on a two-phase liquid composed of silver and copper oxide, brazing is conducted directly in air without the need of an inert cover gas or the use of surface reactive fluxes. A key issue in the development of this joining technique is understanding the effect of braze composition on wetting behavior. In the present paper we consider the wetting behaviors of two candidate braze filler materials, Ag-CuO and Ag-CuO-TiO2, on a protoypical mixed ionic/electronic conducting oxide substrate, lanthanum strontium cobalt ferrite [(La0.6Sr0.4)(Co0.2Fe0.8)O3-δ]. It was found that additions of CuO to silver exhibit a tremendous effect on both the wettability and joint strength characteristics of the subsequent braze relative to polycrystalline alumina substrates. The effect is particularly significant at low CuO content, with substantial improvements in wetting observed in the 1 – 8 mol% range. The corresponding strength of the brazed polycrystalline alumina joints appears to be maximized at a copper oxide content of 8 mol%, with a maximum room temperature flexural strength approaching that of monolithic alumina. While further increases in oxide content lead to improved wetting on polycrystalline alumina, the effect on joint strength is deleterious. It appears that the formation of a continuous brittle copper-based oxide layer along the interface between the braze and alumina faying surface is responsible for the poor mechanical behavior observed in joints fabricated with higher CuO content brazes.

  16. Effect of Bi doping on magnetic and magnetocaloric properties of La0.7-xBixSr0.3MnO3 (0<=x<=0.4)

    NASA Astrophysics Data System (ADS)

    Barik, S. K.; Mahendiran, R.

    2010-05-01

    We investigated the effect of Bi doping on magnetic and magnetocaloric properties of La0.7-xBixSr0.3MnO3 (x=0.0-0.4). It is shown that the low temperature ground state changes from a ferromagnet (x=0) to a charge-ordered antiferromagnet for x=0.4. While the paramagnetic-ferromagnetic (PM-FM) transition is second-order in x≤0.25, it changes into first-order for x=0.3 which is at the magnetic phase boundary. The changes in the magnetic ground state affect magnetic entropy. The magnitude of the isothermal magnetic entropy (|ΔSM|) at the FM Curie temperature increases from 4.56 J/kg K for x=0 to a maximum value of 5.02 J/kg K for x=0.05 and then decreases to nearly zero for x=0.4 at the charge order transition. In contrast to x≤0.25, the ΔSM of x=0.3 is magnetic history dependent and its temperature dependence exhibits a clear step at TCO=260 K followed by a plateau between 240 and 185 K. Although |ΔSM|=3.1 J/kg K of x=0.3 is small compared to other compositions, it has a high relative cooling power (325 J/kg) which is desirable for magnetic refrigeration over a wide temperature. The unusual magnetic and magnetocaloric properties of x=0.3 are attributed to the existence of short-range charge-orbital (CO) correlations in the PM state. It is suggested that harnessing competition between FM spin ordering and CO correlations may provide a strategy to enhance magnetic refrigeration capacity over a wide temperature range.

  17. Investigation of oxygen reduction reaction kinetics on Sm 0.5Sr 0.5CoO 3- δ cathode supported on Ce 0.85Sm 0.075Nd 0.075O 2- δ electrolyte

    NASA Astrophysics Data System (ADS)

    Gao, Zhan; Liu, Xingmin; Bergman, Bill; Zhao, Zhe

    Sm 0.5Sr 0.5CoO 3- δ (SSC) cathode prepared by a glycine-nitrate process (GNP) is investigated for solid oxide fuel cells (SOFCs) based on Ce 0.85Sm 0.075Nd 0.075O 2- δ (SNDC) electrolyte. SSC forms cubic perovskite structure after being annealed at 1100 °C for 5 h. SSC cathode and SNDC electrolyte can retain their own structure and there is no reaction between the two compositions. The microstructure of the cathode and the interfaces between cathodes and SNDC electrolytes are studied by scanning electron microscopy (SEM) after sintering at various temperatures. Impedance spectroscopy measurements reveal that area specific resistances (ASRs) of SSC-SNDC30 cathode are much lower than those of SSC cathode. Kinetics of oxygen reduction reaction (ORR) on porous SSC cathode is investigated by analysis of impedance spectra. Medium-frequency conductivities show no dependency on oxygen partial pressure (PO2) , which can be attributed to the oxygen ions transfer across the electrode/electrolyte interface. The dependencies of low-frequency conductivities on oxygen partial pressure (PO2) vary in the range from ca. 0.31 to ca. 0.34 and increase with the increasing temperatures. The low-frequency electrode process is a mixing process involving oxygen reduction reaction related to atomic oxygen and oxygen ions conduction step together with total charge-transfer step. IR-compensated current density (i)-overpotential (η) relationship is established and the exchange current densities i o originated from high-field approximations are much higher than those of low-field approximations and a.c. impedance data under OCV state. It demonstrates the polarization overpotential has great effect on the kinetics of ORR. The polarization current is observed to increase with time in the long-term stability measurement, which can be ascribed to the propagation process of oxygen vacancies.

  18. Abnormal percolative transport and colossal electroresistance induced by anisotropic strain in (011)-Pr(0.7)(Ca(0.6)Sr(0.4))(0.3)MnO₃/PMN-PT heterostructure.

    PubMed

    Zhao, Ying-Ying; Wang, Jing; Kuang, Hao; Hu, Feng-Xia; Zhang, Hong-Rui; Liu, Yao; Zhang, Ying; Wang, Shuan-Hu; Wu, Rong-Rong; Zhang, Ming; Bao, Li-Fu; Sun, Ji-Rong; Shen, Bao-Gen

    2014-01-01

    Abnormal percolative transport in inhomogeneous systems has drawn increasing interests due to its deviation from the conventional percolation picture. However, its nature is still ambiguous partly due to the difficulty in obtaining controllable abnormal percolative transport behaviors. Here, we report the first observation of electric-field-controlled abnormal percolative transport in (011)-Pr(0.7)(Ca(0.6)Sr(0.4))(0.3)MnO3/0.7Pb(Mg(1/3)Nb(2/3))O3-0.3PbTiO3 heterostructure. By introducing an electric-field-induced in-plane anisotropic strain-field in a phase separated PCSMO film, we stimulate a significant inverse thermal hysteresis (~ -17.5 K) and positive colossal electroresistance (~11460%), which is found to be crucially orientation-dependent and completely inconsistent with the well accepted conventional percolation picture. Further investigations reveal that such abnormal inverse hysteresis is strongly related to the preferential formation of ferromagnetic metallic domains caused by in-plane anisotropic strain-field. Meanwhile, it is found that the positive colossal electroresistance should be ascribed to the coactions between the anisotropic strain and the polarization effect from the poling of the substrate which leads to orientation and bias-polarity dependencies for the colossal electroresistance. This work unambiguously evidences the indispensable role of the anisotropic strain-field in driving the abnormal percolative transport and provides a new perspective for well understanding the percolation mechanism in inhomogeneous systems. PMID:25399635

  19. Abnormal percolative transport and colossal electroresistance induced by anisotropic strain in (011)-Pr0.7(Ca0.6Sr0.4)0.3MnO3/PMN-PT heterostructure

    PubMed Central

    Zhao, Ying-Ying; Wang, Jing; Kuang, Hao; Hu, Feng-Xia; Zhang, Hong-Rui; Liu, Yao; Zhang, Ying; Wang, Shuan-Hu; Wu, Rong-Rong; Zhang, Ming; Bao, Li-Fu; Sun, Ji-Rong; Shen, Bao-Gen

    2014-01-01

    Abnormal percolative transport in inhomogeneous systems has drawn increasing interests due to its deviation from the conventional percolation picture. However, its nature is still ambiguous partly due to the difficulty in obtaining controllable abnormal percolative transport behaviors. Here, we report the first observation of electric-field-controlled abnormal percolative transport in (011)-Pr0.7(Ca0.6Sr0.4)0.3MnO3/0.7Pb(Mg1/3Nb2/3)O3-0.3PbTiO3 heterostructure. By introducing an electric-field-induced in-plane anisotropic strain-field in a phase separated PCSMO film, we stimulate a significant inverse thermal hysteresis (~ -17.5 K) and positive colossal electroresistance (~11460%), which is found to be crucially orientation-dependent and completely inconsistent with the well accepted conventional percolation picture. Further investigations reveal that such abnormal inverse hysteresis is strongly related to the preferential formation of ferromagnetic metallic domains caused by in-plane anisotropic strain-field. Meanwhile, it is found that the positive colossal electroresistance should be ascribed to the coactions between the anisotropic strain and the polarization effect from the poling of the substrate which leads to orientation and bias-polarity dependencies for the colossal electroresistance. This work unambiguously evidences the indispensable role of the anisotropic strain-field in driving the abnormal percolative transport and provides a new perspective for well understanding the percolation mechanism in inhomogeneous systems. PMID:25399635

  20. La 2NiO 4+ δ potential cathode material on La 0.9Sr 0.1Ga 0.8Mg 0.2O 2.85 electrolyte for intermediate temperature solid oxide fuel cell

    NASA Astrophysics Data System (ADS)

    Escudero, María José; Fuerte, Araceli; Daza, Loreto

    La 2NiO 4+ δ, a mixed ionic-electronic conducting oxide with K 2NiF 4 type structure, has been studied as cathode material with La 0.9Sr 0.1Ga 0.8Mg 0.2O 2.85 (LSGM) electrolyte for intermediate solid oxide fuel cells (IT-SOFCs). XRD results reveal excellent chemical compatibility between the La 2NiO 4+ δ sample and LSGM electrolyte. A single cell (0.22 cm 2 active area) was fabricated with La 2NiO 4+ δ as cathode, Ni-Sm 0.2Ce 0.8O 1.9 (2:1; w/w) as anode and LSGM as electrolyte. A thin buffer layer of Sm 0.2Ce 0.8O 1.9 (SDC) between anode and electrolyte was used to avoid possible interfacial reactions. The cell was tested under humidified H 2 and stationary air as fuel and oxidant, respectively. The electrochemical behaviour was evaluated by means of current-voltage curves and impedance spectroscopy. Microstructure and morphology of the cell components were analysed by SEM-EDX after testing. The maximum power densities were 160, 226, and 322 mW cm -2 at 750, 800 and 850 °C, respectively with total polarisation resistances of 0.77, 0.48 and 0.31 Ω cm 2 at these temperatures. Cell performance remained stable when a current density of 448 mA cm -2 was demanded for 144 h at 800 °C, causing no apparent degradation in the cell. The performance of this material may be further improved by reducing the electrolyte thickness and optimisation of the electrode microstructure.

  1. Synthesis and characterization of La0.75Ca0.15Sr0.05Ba0.05MnO3-Ni0.9Zn0.1Fe2O4 multiferroic composites

    NASA Astrophysics Data System (ADS)

    Rahaman, Md. D.; Setu, S. H.; Saha, S. K.; Akther Hossain, A. K. M.

    2015-07-01

    In the present work, we report on structural, dielectric, impedance spectroscopic studies and magnetoelectric properties of (1-x) La0.75Ca0.15Sr0.05Ba0.05MnO3 (LCSBMO)+(x) Ni0.9Zn0.1Fe2O4 (NZFO) (x=0.0, 0.1, 0.2, 0.4, 0.6, 0.8 and 1.0) composites. The composites were prepared by the solid state reaction route. The coexistence of a cubic spinel NZFO phase and a tetragonal LCSBMO phase in the composites is confirmed by the X-ray diffraction measurement. Scanning electron microscopy images reveal that NZFO particles were distributed non-uniformly with some porosity in the LCSBMO matrix. Frequency dependent dielectric constant shows usual dielectric dispersion behavior, which may be attributed to the Maxwell-Wagner type interfacial polarization. At higher frequencies (≥105 Hz), due to electronic and ionic polarizations only, the dielectric constant is independent of frequency. Complex impedance shows semicircular arc due to the domination of grain boundary resistance and electric modulus confirms the presence of hopping conduction. The AC conductivity (σAC) obeys the power law and the linearity of logω2 versus logσAC plots indicates that the conduction mechanism is due to small polaron hopping. Low frequency dispersion in permeability is due to domain wall motion and the frequency stability of permeability indicates that the arrangement of the magnetic moment in the polarization process can keep up with the external field. The maximum magnetoelectric voltage coefficient of ~40 mV Oe-1 cm-1 for x=0.8.

  2. Thickness dependent functional properties of PbZr0.52Ti0.48O3/La0.67Sr0.33MnO3 heterostructures

    NASA Astrophysics Data System (ADS)

    Barrionuevo, D.; Ortega, N.; Kumar, A.; Chatterjee, R.; Scott, J. F.; Katiyar, R. S.

    2013-12-01

    The ultra thin ferroelectric PbZr0.52Ti0.48O3 (PZT) films with various thicknesses ranging from 100 (P100) to 10 (P10) nm were grown on La0.67Sr0.33MnO3/(LaAlO3)0.3(Sr2AlTaO6)0.7 (LSMO/LSAT) (001) substrates deposited by pulsed laser deposition technique. The x-ray diffraction patterns of the heterostructures show only (00l) (l = 1 and/or 2) reflections corresponding to the LSAT substrate, PZT, and LSMO layers. The atomic force microscopy studies show that the root mean square surface roughnesses of P100 and P10 films are 2.39 and 0.99 nm, respectively. An increase of both real (ɛ') and imaginary (ɛ″) permittivities was observed when thickness of PZT increases from 10 nm to 100 nm. Temperature dependent ɛ' presents an anomaly, related to ferromagnetic-metal to paramagnetic-insulator transition of the LSMO, in the range of 350-500 K. The dielectric anomalies and magnetic phase transition temperature shifted to the lower temperature values with decrease in the PZT films thicknesses. The values of the remanent polarization (Pr) and coercive field (Ec) of the heterostructures were in the range of 24-42 μC/cm2-170-1300 kV/cm. An appreciable increase of saturated magnetization (Ms) was observed with increase of PZT layer thickness. The average Ms values of PZT/LSMO heterostructure were 170, 150, 100, and 45 emu/cm3 for 100, 50, 25, and 10 nm at 300 K, respectively. Enhancement in magnetization with increase in PZT thickness may be due to the interface effect between PZT/LSMO layers.

  3. Chromium deposition and poisoning at La0.6Sr0.4Co0.2Fe0.8O(3-δ) oxygen electrodes of solid oxide electrolysis cells.

    PubMed

    Wei, Bo; Chen, Kongfa; Zhao, Ling; Lü, Zhe; Jiang, San Ping

    2015-01-21

    The degradation of solid oxide electrolysis cells (SOECs) is an issue of both scientific and technical importance. In this study, chromium deposition and poisoning at the La0.6Sr0.4Co0.2Fe0.8O(3-δ) (LSCF) anode or the oxygen electrode of SOECs are studied for the first time under a current density of 200 mA cm(-2) at 900 and 800 °C. After polarization in the presence of the Fe-Cr interconnect at 900 °C for 20 h, electrode polarization resistance and overpotential of the O2 evolution reaction (OER) on the LSCF electrode are 0.413 Ω cm(-2) and 127 mV, respectively, which is nearly 7 and 18 times the initial values of the electrode before the polarization. Significant performance degradation was also observed for the reaction at 800 °C in the presence of the Fe-Cr alloy. XRD and XPS analyses clearly identified the deposition of SrCrO4, CrO2.5 and Cr2O3 phases on the surface of LSCF oxygen electrodes and their formation is closely related to the increased segregation of the SrO species under anodic polarization conditions. Sr segregation leads to Sr deficiency at the A-site, thus deteriorating the electrocatalytic activity of the LSCF oxygen electrodes for OER. The results indicate that Cr deposition is essentially a chemical reaction and is initiated by the nucleation reaction between the gaseous Cr species and segregated SrO on the surface region of the LSCF oxygen electrode. PMID:25435014

  4. Degradation of (La(0.8)Sr(0.2))(0.98)MnO(3-δ)-Zr(0.84)Y(0.16)O(2-γ) composite electrodes during reversing current operation.

    PubMed

    Hughes, Gareth A; Railsback, Justin G; Yakal-Kremski, Kyle J; Butts, Danielle M; Barnett, Scott A

    2015-01-01

    Reversing-current operation of solid oxide cell (La(0.8)Sr(0.2))(0.98)MnO(3-δ)-Zr(0.84)Y(0.16)O(2-γ) (LSM-YSZ) oxygen electrodes is described. Degradation was characterized by impedance spectroscopy in symmetric cells tested at 800 °C in air with a symmetric current cycle with a period of 12 hours. No change in cell resistance could be detected, in 1000 h tests with a sensitivity of ∼1% per kh, at a current density of 0.5 A cm(-2) corresponding to an overpotential of 0.18 V. At a current density to 0.6 A cm(-2) (0.33 V overpotential) measurable resistance degradation at a rate of 3% per kh was observed, while higher current/overpotential values led to faster degradation. Degradation was observed mainly in the ohmic resistance for current densities of 0.6, 0.8 and 0.9 A cm(-2), with little change in the polarization resistance. Polarization degradation, mainly observed at higher current density, was present as an increase in an impedance response at ∼30 kHz, apparently associated with the resistance of YSZ grain boundaries within the electrode. Microstructural and chemical analysis showed significant changes in electrode structure after the current cycling, including an increase in LSM particle size and a reduction in the amount of YSZ and LSM at the electrode/electrolyte interface - the latter presumably a precursor to delamination. PMID:26211999

  5. Evaluation of the effect of various mechanisms on the magnetoresistance of lanthanum manganites La0.85Sr0.15MnO3 with activation-type conductivity

    NASA Astrophysics Data System (ADS)

    Gudin, S. A.; Kurkin, M. I.; Neifel'd, E. A.; Korolev, A. V.; Gapontseva, N. N.; Ugryumova, N. A.

    2015-11-01

    A method is proposed that allows one to divide the magnetoresistance (MR) observed in manganites into three mechanisms: dimensional, orientational, and magnetic. The first two mechanisms are associated with the stratification of a substance into ferromagnetic and nonferromagnetic phases, which significantly differ in electric resistivity. The dimensional mechanism of MR is attributed to the effect of a magnetic field on the size of magnetic inclusions. The orientational mechanism of MR is determined by the dependence of electric resistivity on the mutual orientation of the magnetizations of magnetic inclusions. The magnetic mechanism of MR is determined by the properties of the magnetization of a ferromagnet, in particular, by the Curie-Weiss singularity on the temperature dependence of magnetic susceptibility at the Curie point. This mechanism exists in homogeneous substances, although its value may depend on the magnetic properties of inhomogeneities. The method is developed for substances with activation-type conductivity and is applied to the analysis of MR of La0.85Sr0.15MnO3 manganite near the Curie point, where the MR attains its maximum. The dimensional mechanism turns out to be dominant in magnetic fields H greater than the saturation field H s ( H > H s ). The orientational, dimensional, and magnetic mechanisms have a comparable effect on the MR for H < H s . The effect of the orientational mechanism on MR is relatively weak (does not exceed the third part of the total MR), although this mechanism determines the giant MR in multilayered metal films. The possibility of application of the method to the analysis of MR near the insulator-metal transition is analyzed.

  6. Dielectric properties of BaMg1/3Nb2/3O3 doped Ba0.45Sr0.55Tio3 thin films for tunable microwave applications

    NASA Astrophysics Data System (ADS)

    Alema, Fikadu; Pokhodnya, Konstantin

    2015-11-01

    Ba(Mg1/3Nb2/3)O3 (BMN) doped and undoped Ba0.45Sr0.55TiO3 (BST) thin films were deposited via radio frequency magnetron sputtering on Pt/TiO2/SiO2/Al2O3 substrates. The surface morphology and chemical state analyses of the films have shown that the BMN doped BST film has a smoother surface with reduced oxygen vacancy, resulting in an improved insulating properties of the BST film. Dielectric tunability, loss, and leakage current (LC) of the undoped and BMN doped BST thin films were studied. The BMN dopant has remarkably reduced the dielectric loss (˜38%) with no significant effect on the tunability of the BST film, leading to an increase in figure of merit (FOM). This is attributed to the opposing behavior of large Mg2+ whose detrimental effect on tunability is partially compensated by small Nb5+ as the two substitute Ti4+ in the BST. The coupling between MgTi″ and VO•• charged defects suppresses the dielectric loss in the film by cutting electrons from hopping between Ti ions. The LC of the films was investigated in the temperature range of 300-450K. A reduced LC measured for the BMN doped BST film was correlated to the formation of defect dipoles from MgTi″, VO•• and NbTi• charged defects. The carrier transport properties of the films were analyzed in light of Schottky thermionic emission (SE) and Poole-Frenkel (PF) emission mechanisms. The result indicated that while the carrier transport mechanism in the undoped film is interface limited (SE), the conduction in the BMN doped film was dominated by bulk processes (PF). The change of the conduction mechanism from SE to PF as a result of BMN doping is attributed to the presence of uncoupled NbTi• sitting as a positive trap center at the shallow donor level of the BST.

  7. Calcioferrite with composition (Ca3.94Sr0.06)Mg1.01(Fe2.93Al1.07)(PO4)6(OH)4·12H2O

    PubMed Central

    Lafuente, Barbara; Downs, Robert T.; Yang, Hexiong; Jenkins, Robert A.

    2014-01-01

    Calcioferrite, ideally Ca4MgFe3+ 4(PO4)6(OH)4·12H2O (tetra­calcium magnesium tetrairon(III) hexakis-phosphate tetra­hydroxide dodeca­hydrate), is a member of the calcioferrite group of hydrated calcium phosphate minerals with the general formula Ca4 AB 4(PO4)6(OH)4·12H2O, where A = Mg, Fe2+, Mn2+ and B = Al, Fe3+. Calcioferrite and the other three known members of the group, montgomeryite (A = Mg, B = Al), kingsmountite (A = Fe2+, B = Al), and zodacite (A = Mn2+, B = Fe3+), usually occur as very small crystals, making their structure refinements by conventional single-crystal X-ray diffraction challenging. This study presents the first structure determination of calcioferrite with composition (Ca3.94Sr0.06)Mg1.01(Fe2.93Al1.07)(PO4)6(OH)4·12H2O based on single-crystal X-ray diffraction data collected from a natural sample from the Moculta quarry in Angaston, Australia. Calcioferrite is isostructural with montgomeryite, the only member of the group with a reported structure. The calcioferrite structure is characterized by (Fe/Al)O6 octa­hedra (site symmetries 2 and -1) sharing corners (OH) to form chains running parallel to [101]. These chains are linked together by PO4 tetra­hedra (site symmetries 2 and 1), forming [(Fe/Al)3(PO4)3(OH)2] layers stacking along [010], which are connected by (Ca/Sr)2+ cations (site symmetry 2) and Mg2+ cations (site symmetry 2; half-occupation). Hydrogen-bonding inter­actions involving the water mol­ecules (one of which is equally disordered over two positions) and OH function are also present between these layers. The relatively weaker bonds between the layers account for the cleavage of the mineral parallel to (010). PMID:24764934

  8. Weak ferromagnetism and magnetoelectric effect in multiferroic xBa0.95Sr0.05TiO3-(1-x)BiFe0.9Gd0.1O3 relaxors

    NASA Astrophysics Data System (ADS)

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

    2016-03-01

    Multiferroic xBa0.95Sr0.05TiO3-(1-x)BiFe0.9Gd0.1O3 [xBST-(1-x)BFGO], where x=0.00-0.40, have been synthesized by the conventional solid-state reaction method. The crystalline phase, microstructure, relaxor behavior, ac conductivity, impedance spectroscopy, dc magnetic properties, complex initial permeability and magnetoelectric coefficient of these solid solutions have been investigated. The crystal structure is found to change from rhombohedral in BFGO rich compositions to cubic when x≥0.30. Room temperature dielectric properties are investigated within the frequency range from 1 kHz to 1 MHz and found to increase with BST content. The frequency dependence of high temperature dielectric measurements indicated that the composites with x≥0.20, exhibit relaxor ferroelectric behavior. The ac conductivity obeys the Jonscher's universal power law and BST helps to enhance the electrical conductivity of the composites. Studies of impedance spectroscopy suggest that only grains have the contribution to the conductivity mechanism in this material. Magnetizations as a function of applied magnetic field measurements show weak ferromagnetism for 0.10≤x≤0.30 composites. The maximum value of remnant magnetization is found to be 0.565×103 A/m (=0.08 emu/g) for x=0.25 which is better than previously reported BaTiO3-BiFeO3 systems. The complex initial permeability is found to improve with the increase in BST concentration due to the reduction of oxygen vacancies. In addition, an enhanced magnetoelectric (ME) coupling is also observed and determined by the ME coefficient. The maximum value of ME coefficient is found to be 21.71×10-4 V/A (=1.67 mV/cm Oe) for the x=0.25 composition. The BST-BFGO solid solutions show high-performance multiferroic properties and can be selected for further investigation.

  9. High-Performance Microchanneled Asymmetric Gd(0.1)Ce(0.9)O(1.95-δ)-La(0.6)Sr(0.4)FeO(3-δ)-Based Membranes for Oxygen Separation.

    PubMed

    Cheng, Shiyang; Huang, Hua; Ovtar, Simona; Simonsen, Søren B; Chen, Ming; Zhang, Wei; Søgaard, Martin; Kaiser, Andreas; Hendriksen, Peter Vang; Chen, Chusheng

    2016-02-01

    A microchanneled asymmetric dual phase composite membrane of 70 vol % Gd(0.1)Ce(0.9)O(1.95-δ)-30 vol % La(0.6)Sr(0.4)FeO(3-δ) (CGO-LSF) was fabricated by a "one step" phase-inversion tape casting. The sample consists of a thin dense membrane (100 μm) and a porous substrate including "finger-like" microchannels. The oxygen permeation flux through the membrane with and without catalytic surface layers was investigated under a variety of oxygen partial pressure gradients. At 900 °C, the oxygen permeation flux of the bare membrane was 1.6 (STP) ml cm(-2) min(-1) for the air/He-case and 10.10 (STP) ml cm(-2) min(-1) for the air/CO-case. Oxygen flux measurements as well as electrical conductivity relaxation show that the oxygen flux through the bare membrane without catalyst is limited by the oxygen surface exchange. The surface exchange can be enhanced by introduction of catalyst on the membrane surface. An increase of the oxygen flux of ∼1.49 (STP) mL cm(-2) min(-1) at 900 °C was observed when catalyst is added for the air/He-case. Mass transfer polarization through the finger-like support was confirmed to be negligible, which benefits the overall performance. A stable flux of 7.00 (STP) ml cm(-2) min(-1) was observed between air/CO/CO2 over 200 h at 850 °C. Partial surface decomposition was observed on the permeate side exposed to CO, in line with predictions from thermodynamic calculations. In a mixture of CO, CO2, H2, and H2O at similar oxygen activity the material will according to the calculation not decompose. The microchanneled asymmetric CGO-LSF membranes show high oxygen permeability and chemical stability under a range of technologically relevant oxygen potential gradients. PMID:26829707

  10. Structural and magnetic inhomogeneities, phase transitions, 55Mn nuclear magnetic resonance, and magnetoresistive properties of La0.6 - x Nd x Sr0.3Mn1.1O3-δ ceramics

    NASA Astrophysics Data System (ADS)

    Pashchenko, A. V.; Pashchenko, V. P.; Prokopenko, V. K.; Revenko, Yu. F.; Kisel, N. G.; Kamenev, V. I.; Sil'cheva, A. G.; Ledenev, N. A.; Burkhovetskii, V. V.; Levchenko, G. G.

    2014-05-01

    The structure, lattice imperfection, and properties of ceramic samples La0.6 - x Nd x Sr0.3Mn1.1O3-δ ( x = 0-0.4) have been investigated using the X-ray diffraction, resistive, magnetic (χac, 55Mn NMR), magnetoresistive and microscopic methods. It has been shown that there is a satisfactory agreement between the concentration decrease in the lattice parameters a of the rhombohedral ( x = 0, 0.1, 0.2) and cubic ( x = 0.3, 0.4) perovskite structures and the average ionic radii for the lattice containing anion vacancies, cation vacancies, and nanostructured clusters with Mn2+ ions in A-positions. With an increase in the neodymium concentration x, the vacancy-type imperfection increases, the cluster-type imperfection decreases, the temperatures of metal-semiconductor phase transition T ms and ferromagnetic-paramagnetic phase transition T C decrease, and the content of the ferromagnetic phase decreases. The anomalous hysteresis is associated with the appearance of unidirectional exchange anisotropy induced in a clustered perovskite structure consisting of a ferromagnetic matrix and a planar antiferromagnetic cluster coherently coupled with it. An analysis of the asymmetrically broadened 55Mn NMR spectra has revealed a high-frequency electronic double exchange (Mn3+-O2--Mn4+) ↔ (Mn4+-O2--Mn3+) and an inhomogeneity of the magnetic and charge states of manganese due to the heterogeneous environment of the manganese ions by other ions and defects. The observed changes in the resonant frequency and width of the resonance curve are caused by changes in the ratio Mn3+/Mn4+ and magnetic inhomogeneity. An increase in the neodymium concentration x leads to a decrease in the ferromagnetic phase content determined from the dependences 4π Nχac( T) and the 55Mn NMR curves. The phase diagram characterizes an interrelation between the composition, the imperfection of the structure, and the transport, magnetic, and magnetoresistive properties of lanthanum neodymium manganite

  11. Synthesis and enhancement of multiferroic properties of (x)Ba0.95Sr0.05TiO3-(1-x)BiFe0.90Dy0.10O3 ceramics

    NASA Astrophysics Data System (ADS)

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

    2016-01-01

    Polycrystalline (x)Ba0.95Sr0.05TiO3-(1-x)BiFe0.90Dy0.10O3 [(x)BST-(1-x)BFDO] ceramics were synthesized by the standard solid-state reaction method. Samples prepared from these powders were sintered at various temperatures (900-1000 °C). The crystal structure, microstructure, magnetic, dielectric, complex impedance and magnetoelectric properties of the (x)BST-(1-x)BFDO ceramics were systematically investigated. The X-ray diffraction pattern indicated that (x)BST-(1-x)BFDO ceramics showed a structural transition from rhombohedral to cubic phase. The average grain size increased to a maximum 2.86 μm for x=0.20 and then decreased. M-H plot showed weak ferromagnetism for x=0.00 to 0.30. The magnetization value increased for increasing BST substitution up to x=0.20 due to the modification of crystal structure and then decreased for further increasing due to the nonmagnetic behavior of BST. A significant remnant magnetization (0.086 emu/g) and a coercive magnetic field (103.62 Oe) were also obtained for this solid solution. The complex initial permeability increased with the increase of both BST content (up to x=0.20) and sintering temperatures. The room-temperature dielectric constant increased whereas dielectric loss decreased with increasing BST content because of reducing oxygen vacancies. Impedance spectroscopy analysis confirmed the conducting grains and highly resistive grain boundaries affecting the conductivity but the grains had major contribution in the conduction mechanism. Magnetoelectric voltage coefficient (αME) increased with the increase of BST content because of strong interaction between magnetic and ferroelectric domains. The highest value of αME=1.67 mV cm-1 Oe-1 was observed for x=0.20 solid solution sintered at Ts=1000 °C because of uniform grains in size and shape at this composition.

  12. Influence of microstructure and interfacial strain on the magnetic properties of epitaxial Mn3O4/La0.7Sr0.3MnO3 layered-composite thin films

    NASA Astrophysics Data System (ADS)

    Mukherjee, Devajyoti; Bingham, Nicholas; Hordagoda, Mahesh; Phan, Manh-Huong; Srikanth, Hariharan; Witanachchi, Sarath; Mukherjee, Pritish

    2012-10-01

    Epitaxial Mn3O4/La0.7Sr0.3MnO3 (Mn3O4/LSMO) bilayer thin films were grown on lattice-matched single crystal substrates of SrTiO3 (STO) (100) and MgO (100), with Mn3O4 as the top layer, using a pulsed laser deposition technique. X-ray diffraction (XRD) patterns revealed the single crystalline nature and epitaxial relationship between the layers. A detailed analysis of strains using XRD asymmetric/symmetric scans indicated an increasing in-plane compressive strain in the LSMO layer with increasing thicknesses of the Mn3O4 layer, resulting in a tetragonal distortion of the LSMO lattice in the Mn3O4/LSMO films in comparison to the tensile strains in LSMO single-layer films grown on both STO and MgO substrates. Cross-sectional high resolution transmission electron microscope (HRTEM) images showed atomically sharp interfaces in all films. However, as opposed to a flat interface between LSMO and STO, the Mn3O4 and LSMO interface was undulating and irregular in the bilayer films. Magnetic measurements revealed that relative to LSMO, the presence of Mn3O4 in Mn3O4/LSMO reduced the saturation magnetization at T > 50 K (the ferrimagnetic ordering temperature of Mn3O4) but enhanced it at T < 50 K. The decrease of the saturation magnetization in Mn3O4/LSMO for T > 50 K was associated with the appearance and increase of the compressive strain with the increase in Mn3O4 thickness. These observations point to the importance of a ferromagnetic-ferrimagnetic interfacial coupling between the LSMO and Mn3O4 layers in enhancing the surface magnetism of LSMO in the Mn3O4/LSMO bilayers. Our study provides useful information regarding the development of manganite composite thin films with improved magnetic properties for a wide range of technological applications, such as in spintronics and sensor devices.

  13. Systematic evaluation of cobalt-free Ln0.5Sr0·5Fe0·8Cu0·2O3-δ (Ln = La, Pr, and Nd) as cathode materials for intermediate-temperature solid oxide fuel cells

    NASA Astrophysics Data System (ADS)

    Pang, Shengli; Wang, Wenzhi; Chen, Tao; Shen, Xiangqian; Wang, Yonggang; Xu, Kaijie; Xi, Xiaoming

    2016-09-01

    Cobalt-free perovskites, Ln0.5Sr0·5Fe0·8Cu0·2O3-δ (Ln = La, Pr, and Nd), are systematically evaluated as the cathode materials for intermediate-temperature solid oxide fuel cells (IT-SOFCs) using Gd0.1Ce0·9O1.95 as the electrolyte. The samples exhibit an orthorhombic perovskite structures, and their cell volumes decrease as the ionic radius of Ln decreases. Both the oxygen vacancy content and the magnitude of lattice oxygen release per formula unit increase in the temperature range from 370 °C to 850 °C as the ionic radius of Ln decreases. Ln0.5Sr0.5Fe0.8Cu0.2O3-δ is chemically and thermally compatible with the Gd0.1Ce0·9O1.95 electrolyte. In the temperature range of 600 °C-750 °C, Nd0.5Sr0·5Fe0·8Cu0·2O3-δ possesses the highest catalytic activity for the oxygen reduction reaction with area specific resistance values of 0.071 Ω cm2 and 0.141 Ω cm2 at 750 °C and 700 °C, respectively. The maximum power densities of the anode-supported single cells at 800 °C and 700 °C are 1003.7 mW cm-2 and 516.7 mW cm-2 for Pr0.5Sr0·5Fe0·8Cu0·2O3-δ and 944.5 mW cm-2 and 530.2 mW cm-2 for Nd0.5Sr0·5Fe0·8Cu0·2O3-δ, respectively. Ln0.5Sr0.5Fe0.8Cu0.2O3-δ is shown to be a promising cathode material for IT-SOFCs.

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

    NASA Astrophysics Data System (ADS)

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

    2015-02-01

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

  15. Effect of (Ca0.8Sr0.2)0.6La0.267TiO3 on Phase, Microstructure, and Microwave Dielectric Properties of Mg0.95Zn0.05TiO3 Synthesized by Polymeric Precursor Method

    NASA Astrophysics Data System (ADS)

    Naeem, Abdul; Ullah, Asad; Mahmood, Tahira; Iqbal, Yaseen; Mahmood, Asad; Hamayun, Muhammad

    2016-08-01

    A number of compounds in the (1 - x)Mg0.95Zn0.05TiO3- x(Ca0.8Sr0.2)0.6 La0.267TiO3 ( x = 0 to 0.25) composition series have been obtained via a polymeric precursor route to investigate the effect of increasing (Ca0.8Sr0.2)0.6La0.267TiO3 proportion on the phase, microstructure, and microwave dielectric properties of the sintered ceramics. Composite powders having nanometric particles were obtained by calcining the precursors at 700°C. Refinement results revealed that these samples comprised a mixture of Mg0.95Zn0.05TiO3 and (Ca0.8Sr0.2)0.6La0.267TiO3 ceramics. A combination of optimum microwave dielectric properties, i.e., dielectric constant of 25.17, quality factor of 58,754 GHz, and temperature coefficient of resonant frequency of -5.8 ppm/°C, was achieved for the x = 0.2 composition sintered at 1200°C.

  16. Effect of (Ca0.8Sr0.2)0.6La0.267TiO3 on Phase, Microstructure, and Microwave Dielectric Properties of Mg0.95Zn0.05TiO3 Synthesized by Polymeric Precursor Method

    NASA Astrophysics Data System (ADS)

    Naeem, Abdul; Ullah, Asad; Mahmood, Tahira; Iqbal, Yaseen; Mahmood, Asad; Hamayun, Muhammad

    2016-05-01

    A number of compounds in the (1 - x)Mg0.95Zn0.05TiO3-x(Ca0.8Sr0.2)0.6 La0.267TiO3 (x = 0 to 0.25) composition series have been obtained via a polymeric precursor route to investigate the effect of increasing (Ca0.8Sr0.2)0.6La0.267TiO3 proportion on the phase, microstructure, and microwave dielectric properties of the sintered ceramics. Composite powders having nanometric particles were obtained by calcining the precursors at 700°C. Refinement results revealed that these samples comprised a mixture of Mg0.95Zn0.05TiO3 and (Ca0.8Sr0.2)0.6La0.267TiO3 ceramics. A combination of optimum microwave dielectric properties, i.e., dielectric constant of 25.17, quality factor of 58,754 GHz, and temperature coefficient of resonant frequency of -5.8 ppm/°C, was achieved for the x = 0.2 composition sintered at 1200°C.

  17. THERMAL AND ELECTRICAL PROPERTIES OF Ba0.5Sr0.5CoxFe1-x-yNiyO3-δ (x = 0.4, 0 ≤ y ≤ 0.25) AS CATHODE MATERIAL FOR IT-SOFCs

    NASA Astrophysics Data System (ADS)

    Burnwal, Suman Kumar; Kistaiah, P.

    2015-03-01

    Ba0.5Sr0.5CoxFe1-x-yNiyO3-δ (BSCFNi; x = 0.4, 0 ≤ y ≤ 0.25) were studied in relation to their potential use as intermediate temperature solid oxide fuel cell (IT-SOFC) cathode. An emphasis is made on the effect of Ni-doping on crystal structure, thermal expansion coefficient (TEC) and dc electrical conductivity. A cubic perovskite structure was observed in the X-ray diffraction (XRD) measurement. The TEC of BSCFNi obtained for 0 ≤ y ≤ 0.25, varies in the range of (12.38-18.81) × 10-6 K-1, measured in the temperature range of 30°C to 800°C. The electrical conductivity which is a major defect of Ba0.5Sr0.5CoxFe1-xO3-δ (BSCF) was improved by Ni-doping. The compound with y = 0.20 and 0.25 demonstrated a conductivity of σ = 62.59 S-cm-1 and 72.64 S-cm-1 at 400°C and 77.01 S-cm-1 and 89.68 S-cm-1 at 500°C.

  18. Effect of anode firing on the performance of lanthanum and nickel co-doped SrTiO3 (La0.2Sr0.8Ti0.9Ni0.1O3-δ) anode of solid oxide fuel cell

    NASA Astrophysics Data System (ADS)

    Park, Byung Hyun; Choi, Gyeong Man

    2015-10-01

    Perovskite oxides have potential for use as alternative anode materials in solid oxide fuel cells (SOFCs) due to stability in anode atmosphere; donor-doped SrTiO3 (e.g., La0.2Sr0.8TiO3-δ) is a good candidate for this purpose. Electro-catalytic nanoparticles can be produced in oxide anodes by the ex-solution method, e.g., by incorporating Ni into a perovskite oxide in air, then reducing the oxide in H2 atmosphere. In this study, we varied the temperature (1100, 1250 °C) and atmosphere (air, H2) of La0.2Sr0.8Ti0.9Ni0.1O3-δ (LSTN) anode firing to control the degree of Ni ex-solution and microstructure. LSTN fired at 1250 °C in H2 showed the best anodic performance for scandia-stabilized zirconia (ScSZ) electrolyte-supported cells in H2 and CH4 fuels due to the favorable microstructure and Ni ex-solution.

  19. Performance of Gd0.2Ce0.8O1.9 infiltrated La0.2Sr0.8TiO3 nanofiber scaffolds as anodes for solid oxide fuel cells: Redox stability and effects of electrolytes

    NASA Astrophysics Data System (ADS)

    Fan, Liquan; Xiong, Yueping; Wang, Yuwei; Kishimoto, Haruo; Yamaji, Katsuhiko; Horita, Teruhisa

    2015-10-01

    Nanofiber-based La0.2Sr0.8TiO3-Gd0.2Ce0.8O1.9 (LST-GDC) composite anodes show good electrochemical performance and microstructure stability when subjected to reduction and oxidation (redox) cycling. With the increasing amount of GDC, the polarization resistance of LST-GDC composite anode gradually decreases. The porous LST nanofiber scaffold in the composite anode buffers the volume change caused by the transition between Ce4+ and Ce3+, which improves the LST-GDC electrode redox stability. A comparative study of the electrochemical performance of the composite anode has been conducted with 1 mol%CeO2-10 mol%Sc2O3-89 mol%ZrO2 (ScSZ), 8 mol% yttria stabilized zirconia (YSZ) and La0.8Sr0.2Ga0.8Mg0.2O3-δ (LSGM) electrolytes to evaluate the effects of electrolytes with different oxygen ion conductivity on anode interfacial polarization resistance. Among the three electrolytes, the LST-GDC composite anode with LSGM as the electrolyte shows the best electrochemical performance due to the electrolyte high O2- conductivity.

  20. Microstructures and Microwave Dielectric Properties of Low-Temperature Fired Ca0.8Sr0.2TiO3-Li0.5Sm0.5TiO3 Ceramics with Bi2O3-2B2O3 Addition

    NASA Astrophysics Data System (ADS)

    Yuan, Changlai; Chen, Guohua; Yang, Tao; Liu, Fei; Zhou, Changrong; Yang, Yun

    2015-01-01

    The microstructures and microwave dielectric properties of xCa0.8Sr0.2TiO3-(1- x) Li0.5Sm0.5TiO3 ( x = 0.25, 0.28, 0.3, 0.35 and 0.4) ceramics with about 20 wt.% Bi2O3-2B2O3 (BB) addition were investigated. All the composite ceramics prepared using the conventional mixed oxide route consisted of a primarily orthorhombic perovskite xCa0.8Sr0.2TiO3-(1- x)Li0.5Sm0.5TiO3 solid-solution phase and minor secondary phases ascribed to LiBO2 and BiB3O6. It was found that the addition of 20 wt.% Bi2O3-2B2O3 in xCa0.8Sr0.2TiO3-(1- x) Li0.5Sm0.5TiO3 (CSLST x) phases decreased the optimal sintering temperature range to 1025-1050°C. In the optimal sintering temperature range, the highest values of bulk density ( ρ), dielectric constant ( ɛ r) and the product ( Q. f) of quality factor ( Q) and frequency ( f) for the ceramics were obtained. With x increasing from 0.25 to 0.40, ɛ r increased from 94.9 to 116.6 and τ f from -14.76 ppm/°C to 100.2 ppm/°C, while Q. f value slightly increased from 1725 GHz to 1745 GHz and then decreased from 1745 GHz to 1541 GHz. For the 100 CSLST x-20BBO ceramics sintered at 1025°C, a near-zero τ f ceramic with ɛ r of 100 and Q. f value of 1737 GHz was obtained at x = 0.28.

  1. Frequency-dependent impedance spectroscopy on the 0.925(Bi0.5Na0.40K0.10)TiO3-0.075(Ba0.70Sr0.30)TiO3 ceramic

    NASA Astrophysics Data System (ADS)

    Ullah, Amir; Rahman, Muneeb-ur; Iqbal, Muhammad Javid; Ahn, Chang Won; Kim, Ill Won; Ullah, Aman

    2016-06-01

    The electrical properties of the 0.925(Bi0.5(Na0.40K0.10)TiO3-0.075(Ba0.70Sr0.30)TiO3 (0.925BNKT-0.075BST) ceramic were investigated by using AC impedance spectroscopy over a wide range of frequencies (10 -2 ~ 105 Hz). The X-ray diffraction patterns confirmed the formation of a single-phase compound. A single semicircular arc in the impedance spectrum indicates that the main contribution of the bulk resistance ( R b ) were due to grain effects, with Rb decreasing with increasing temperature. The conductivity of the ceramics increased with increasing temperature, and the activation energy resulting from the DC conductivity was 0.86 eV. The ceramic displayed a typical negative temperature coefficient of resistance (NTCR) behavior, like that of a semiconductor.

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

    NASA Astrophysics Data System (ADS)

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

    2015-02-01

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

  3. X-ray absorption and magnetic circular dichroism of LaCoO3 , La0.7Ce0.3CoO3 , and La0.7Sr0.3CoO3 films: Evidence for cobalt-valence-dependent magnetism

    NASA Astrophysics Data System (ADS)

    Merz, M.; Nagel, P.; Pinta, C.; Samartsev, A.; v. Löhneysen, H.; Wissinger, M.; Uebe, S.; Assmann, A.; Fuchs, D.; Schuppler, S.

    2010-11-01

    Epitaxial thin films of undoped LaCoO3 , of electron-doped La0.7Ce0.3CoO3 , and of hole-doped La0.7Sr0.3CoO3 exhibit ferromagnetic order with a transition temperature TC≈84K , 23 K, and 194 K, respectively. The spin-state structure for these compounds was studied by soft x-ray magnetic circular dichroism and by near-edge x-ray absorption fine structure at the CoL2,3 and OK edges. It turns out that superexchange between Co3+ high-spin and Co3+ low-spin states is responsible for the ferromagnetism in LaCoO3 . For La0.7Ce0.3CoO3 the Co3+ ions are in a low-spin state and the spin and orbital moments are predominantly determined by a Co2+ high-spin configuration. A spin blockade naturally explains the low transition temperature and the insulating characteristics of La0.7Ce0.3CoO3 . For La0.7Sr0.3CoO3 , on the other hand, the magnetic moments in the epitaxial films originate from high-spin Co3+ and high-spin Co4+ states. Ferromagnetism is induced by t2g double exchange between the two high-spin configurations. For all systems, a strong magnetic anisotropy is observed, with the magnetic moments essentially oriented within the film plane.

  4. High-performance solid oxide fuel cells based on a thin La0.8Sr0.2Ga0.8Mg0.2O3-δ electrolyte membrane supported by a nickel-based anode of unique architecture

    NASA Astrophysics Data System (ADS)

    Sun, Haibin; Chen, Yu; Chen, Fanglin; Zhang, Yujun; Liu, Meilin

    2016-01-01

    Solid oxide fuel cells (SOFCs) based on a thin La0.8Sr0.2Ga0.8Mg0.2O3-δ (LSGM) electrolyte membrane supported by a nickel-based anode often suffers from undesirable reaction/diffusion between the Ni anode and the LSGM during high-temperature co-firing. In this study, a high performance intermediate-temperature SOFC is fabricated by depositing thin LSGM electrolyte membranes on a LSGM backbone of unique architecture coated with nano-sized Ni and Gd0.1Ce0.9O2-δ (GDC) particles via a combination of freeze-drying tape-casting, slurry drop-coating, and solution infiltration. The thickness of the dense LSGM electrolyte membranes is ∼30 μm while the undesirable reaction/diffusion between Ni and LSGM are effectively hindered because of the relatively low firing temperature, as confirmed by XRD analysis. Single cells show peak power densities of 1.61 W cm-2 at 700 °C and 0.52 W cm-2 at 600 °C using 3 vol% humidified H2 as fuel and ambient air as oxidant. The cell performance is very stable for 115 h at a constant current density of 0.303 A cm-2 at 600 °C.

  5. Coupling of Jahn-Teller and tilting distortions in high temperature structural phase transition of the Ca0.2Sr0.6Nd0.2Mn1-xCrxO3; 0 ≤ x ≤ 0.2 perovskites

    NASA Astrophysics Data System (ADS)

    Tan, Teck-Yee; Zhou, Qingdi; Kennedy, Brendan J.; Gu, Qinfen; Kimpton, Justin A.

    2012-04-01

    The manganite perovskites Ca0.2Sr0.6Nd0.2Mn1-xCrxO3, 0 ≤ x ≤ 0.2, have been synthesized by solid state methods, and their room temperature structures determined using synchrotron X-ray powder diffraction. At room temperature, the oxides have a tetragonal structure in space group I4/mcm. Whereas the BO6 groups in the x = 0 sample are noticeably distorted those in the x = 0.2 sample are more regular as a consequence of the progressive removal of the Jahn-Teller type distortion. High temperature diffraction measurements of the x = 0, 0.1 and 0.2 samples reveal that Cr doping has little effect on the transition to the cubic Pm3¯m structure that occurs around 450 °C. Cr doping does however significantly alter the spontaneous strains in the oxides as a consequence of the cooperative Jahn-Teller distortion.

  6. Decrease in electrical resistance of surface oxide of iron-chromium-aluminium alloy by La0.6Sr0.4Co0.2Fe0.8O3 coating and heat treatment for the application of metal-supported solid oxide fuel cells

    NASA Astrophysics Data System (ADS)

    Pham, Hung-Cuong; Taniguchi, Shunsuke; Inoue, Yuko; Chou, Jyh-Tyng; Izumi, Toru; Matsuoka, Koji; Sasaki, Kazunari

    2015-11-01

    We have investigated the property of a Fe-Cr-Al-type stainless steel as a porous alloy substrate for metal-supported solid oxide fuel cells (SOFCs) especially on the cathode side. We found that the microstructure and electrical resistance of the surface oxide layer of the alloy changes depending on the heat-treatment conditions. A relatively low electrical resistance was obtained when the porous alloy substrate was coated with La0.6Sr0.4Co0.2Fe0.8O3 (LSCF) and heat treated at 700-800 °C in air. The morphology of the surface oxide layer observed by high-resolution transmission electron microscopy was a columnar structure of γ-Al2O3 polycrystal and Sr3Al2O6 growing outward in the same direction. In contrast, the surface oxide layer of the alloy showed a high electrical resistance when the uncoated porous alloy substrate was heat treated. The morphology of the surface oxide layer in that case was a columnar structure consisting of only γ-Al2O3 growing outward in various directions.

  7. A cobalt-free Sm0.5Sr0.5Fe0.8Cu0.2O3-δ-Ce0.8Sm0.2O2-δ composite cathode for proton-conducting solid oxide fuel cells

    NASA Astrophysics Data System (ADS)

    Ling, Yihan; Yu, Jia; lin, Bin; Zhang, Xiaozhen; Zhao, Ling; Liu, Xingqin

    2011-03-01

    A cobalt-free composite Sm0.5Sr0.5Fe0.8Cu0.2O3-δ-Ce0.8Sm0.2O2-δ (SSFCu-SDC) is investigated as a cathode for proton-conducting solid oxide fuel cells (H-SOFCs) in intermediate temperature range, with BaZr0.1Ce0.7Y0.1Yb0.1O3-δ (BZCYYb) as the electrolyte. The XRD results show that SSFCu is chemically compatible with SDC at temperatures up to 1100 °C. The quad-layer single cells of NiO-BZCYYb/NiO-BZCYYb/BZCYYb/SSFCu-SDC are operated from 500 to 700 °C with humidified hydrogen (∼3% H2O) as fuel and the static air as oxidant. It shows an excellent power density of 505 mW cm-2 at 700 °C. Moreover, a low electrode polarization resistance of 0.138 Ω cm2 is achieved at 700 °C. Preliminary results demonstrate that the cobalt-free SSFCu-SDC composite is a promising cathode material for H-SOFCs.

  8. Anode-supported single-chamber solid oxide fuel cell based on cobalt-free composite cathode of Nd0.5Sr0.5Fe0.8Cu0.2O3-δ-Sm0.2Ce0.8O1.9 at intermediate temperatures

    NASA Astrophysics Data System (ADS)

    Yin, Jie-Wei; Zhang, Chunming; Yin, Yi-Mei; Shi, Huangang; Lin, Ye; Lu, Jun; Ma, Zi-Feng

    2015-07-01

    As a candidate of cathode material of single-chamber solid oxide fuel cell (SC-SOFC), cobalt-free mixed ionic electronic conductor (MIEC) Nd0.5Sr0.5Fe0.8Cu0.2O3-δ (NSFCu) is synthesized by sol-gel method with ethylene diamine tetraacetic acid and citric acid as co-complexing agents. The XRD shows NSFCu is stable after CO2 treatment and chemical compatible with SDC at high temperatures. CO2-TPD (CO2-temperature programmed desorption) demonstrates both CO2 adsorption and desorption phenomenon on NSFCu surface. However, the polarization resistances (Rp) of NSFCu and SDC (10:4 in weight) composite electrodes showed no decay in 5% CO2. Single cell using N2-O2-CH4 mixed gas (CH4 to O2 ratio = 1.5) as fuel shows maximum power density of 635 mW cm-2 at 700 °C. These results suggest that NSFCu-SDC is a promising composite cathode material for application in single-chamber solid oxide fuel cell.

  9. Studies on the percolation limit of Ce0.9Gd0.1O1.95 in La0.6Sr0.4Co0.2Fe0.8O3-δ-Ce0.9Gd0.1O1.95 nanocomposites for solid oxide fuel cells application

    NASA Astrophysics Data System (ADS)

    Jamale, Atul P.; Jadhav, S. T.; Dubal, S. U.; Bhosale, C. H.; Jadhav, L. D.

    2015-10-01

    A large difference in thermal expansion coefficient of electrode and electrolyte leads to imperfect electrode/electrolyte interface and hence significant polarization losses in solid oxide fuel cells. To overcome the difficulties associated with electrode and electrode/electrolyte interface, there is need to fabricate the composite cathode. Thus the present paper deals with study of La0.6Sr0.4Co0.2Fe0.8O3-δ(LSCF)-Ce0.9Gd0.1O1.95(GDC) nanocomposite with different fractions of GDC obtained by physical mixing of combustion synthesized nanopowders. No secondary phases were observed upon sintering at 1100 °C for 2 h affirming the chemical compatibility between LSCF and GDC. The composites with relatively high GDC% have higher density as a consequence of rapid grain growth and less conductivity. The nanocomposite with 50% of GDC showed electric conductivity of 30 Scm-1 at 500 °C and low area specific resistance of 106 Ω cm2 with 10 μs relaxation time at 200 °C.

  10. Liquid plasma sprayed nano-network La0.4Sr0.6Co0.2Fe0.8O3/Ce0.8Gd0.2O2 composite as a high-performance cathode for intermediate-temperature solid oxide fuel cells

    NASA Astrophysics Data System (ADS)

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

    2016-09-01

    Here, we investigate the feasibility of using a liquid plasma spray process as a novel method for the cost-effective fabrication of a nanonetwork of La0.4Sr0.6Co0.2Fe0.8O3-δ (LSCF) and Ce0.8Gd0.2O2-δ (GDC) composite as a high-performance cathode for intermediate-temperature solid oxide fuel cells. A suspension containing well-dispersed nanosized GDC particles in an LSCF precursor solution is designed as the feedstock. The effects of GDC concentration in the suspension on the phase composition, microstructure, and electrochemical performance of the resulting cathode are studied. When the GDC concentration increases to 15 g L-1, the nanosized GDC particles distribute uniformly and continuously on the LSCF backbone to form a porous network structure. The electrochemical studies further indicate that the cathode polarization decreased with the increase in GDC concentration from 0 g L-1 to 15 g L-1, whereas a further increase in the GDC concentration increases the cathode polarization instead. At 600 and 750 °C, the cathode prepared using 15 g L-1 GDC concentration exhibits an impressive area-specific polarization resistance (Rp) of 0.1 Ω cm2 and 0.009 Ω cm2, respectively. Finally, the Rp of the optimal cathode almost does not change after the isothermal dwelling at 650 °C for 350 h.

  11. A top-down strategy for the synthesis of mesoporous Ba0.5Sr0.5Co0.8Fe0.2O3-δ as a cathode precursor for buffer layer-free deposition on stabilized zirconia electrolyte with a superior electrochemical performance

    NASA Astrophysics Data System (ADS)

    Su, Chao; Xu, Xiaomin; Chen, Yubo; Liu, Yu; Tadé, Moses O.; Shao, Zongping

    2015-01-01

    We develop a facile and effective top-down method for the fabrication of mesoporous Ba0.5Sr0.5Co0.8Fe0.2O3-δ (BSCF) oxide with a high specific surface area (∼25 m2 g-1). The original BSCF is first synthesized by the simple EDTA-citric acid complexing method, and then treated in H2O2 to obtain the mesoporous BSCF. The structure and morphology of as-prepared BSCF power is systematically characterized by N2 adsorption/desorption isotherms, XRD, TEM, SEM and ICP techniques. A possible mechanism for the creation of mesoporous BSCF is proposed, in which Ba2+ and Sr2+ dissolve selectively from partial BSCF particles during the catalytic decomposition of H2O2. The electrochemical properties are investigated by the EIS and I-V test in the symmetrical cell and integrated single cell configurations, respectively. The interfacial reaction between BSCF electrode and YSZ electrolyte was suppressed successfully by using the BSCF with high specific surface area to decrease the sintering temperature (800 °C), thus the electrode exhibits high oxygen reduction reaction activity. The solid oxide fuel cell (SOFC) achieves an exciting peak power density of ∼1800 mW cm-2 at 800 °C, signifying the mesoporous BSCF, together with the preparation method, has a good application prospect in the development of SOFCs.

  12. Composition range and electrical properties of the morphotropic phase boundary in Bi0.5(Na0.80K0.20)0.5TiO3-(Ba0.7Sr0.3)TiO3 system

    NASA Astrophysics Data System (ADS)

    Jaita, Pharatree; Watcharapasorn, Anucha; Jiansirisomboon, Sukanda

    2013-07-01

    The lead-free piezoelectric ceramic binary system of (1- x)Bi0.5(Na0.80K0.20)0.5TiO3- x(Ba0.7Sr0.3)TiO3 or (1- x) BNKT- xBST (with x ranging from 0.05 to 0.15 mol fraction) near the morphotropic phase boundary (MPB) has been investigated. The ceramics were synthesized by a conventional mixed-oxide method and sintered at 1125°C for 2 h. All BNKT-BST samples had relative density higher than 98% of their theoretical values. X-ray diffraction patterns showed that all compositions had a pure perovskite structure and BST effectively diffused into the BNKT lattice during sintering to form a solid solution. Crystal structure changed from rhombohedral-rich phase to tetragonal-rich phase with increasing BST content. Because of such MPB-like behavior, the highest dielectric ( T c = 325°C, ɛ r = 1827, tan δ = 0.0823) and piezoelectric performances ( d 33 = 225 pC/N) were obtained in the BNKT-0.11BST sample.

  13. Effect of the annealing temperature on the structural and magnetic behaviors of 0.875La0.6Ca0.4MnO3/0.125La0.6Sr0.4MnO3 composition

    NASA Astrophysics Data System (ADS)

    Gharsallah, H.; Bejar, M.; Dhahri, E.; Hlil, E. K.; Sajieddine, M.

    2016-03-01

    The polycrystalline compounds of La0.6Ca0.4MnO3 (S0C1) and La0.6Sr0.4MnO3 (S1C0) were prepared using the citric-gel method. With the resultant nanoparticle powders having crystallite size of 22.51 nm from S0C1 and 27.39 nm from S1C0, the 0.875(S0C1)0.125(S1C0) composition was sintered at different temperatures: SC. 4-1 (at 700 °C), SC. 4-2 (at 900 °C), SC. 4-3 (at 1100 °C) and SC. 4-4 (at 1300 °C). XRD data were analyzed by Rietveld refinement technique. The two S0C1 and S1C0 mother compounds were found to crystallize in the rhombohedral and orthorhombic structure, respectively. The compounds sintered at 700 °C (SC. 4-1) and 900 °C (SC. 4-2) were found to present the two rhombohedral and orthorhombic phases corresponding to the mother compounds, which indicates that no interfacial reaction occurs. However, when augmenting the sintering temperature, the formation of the 0.875(S0C1)0.125(S1C0) new phase was observed. These observations were confirmed from the magnetization study, which revealed that the SC. 4-1 and SC. 4-2 compounds present two magnetic transitions temperature corresponding to the two mother compounds. For higher sintering temperature (1100 and 1300 °C), we have noted the presence of a new magnetic transition corresponding to the composition 0.875(S0C1)0.125(S1C0) compound. The variation of the M(T) curves were discussed in terms of the orthorhombic distortion σ2(Mn-O).

  14. Promoted electrochemical performance of intermediate temperature solid oxide fuel cells with Pd0.95Mn0.05O-infiltrated (La0.8Sr0.2)0.95MnO3-δ-Y0.16Zr0.84O2 composite cathodes

    NASA Astrophysics Data System (ADS)

    Wang, Ao; Pu, Jian; Yan, Dong; Duan, Nan-Qi; Tan, Yuan; Jia, Lichao; Chi, Bo; Li, Jian

    2016-01-01

    Pd0.95Mn0.05O-infiltrated (La0.8Sr0.2)0.95MnO3-δ-8 mol.% Y2O3 stabilized ZrO2 (LSM-YSZ) cathode is used to large size (11 × 11 × 0.1 cm) Ni-YSZ anode-supported planar cells for the first time and electrochemically evaluated in the intermediate temperature range from 650 to 800 °C with H2 as the fuel and air as the oxidant. The initial open circuit voltage (OCV) of the cell is 1.15 V, and the achieved maximum power density increases from 328 to 734 mW cm-2 with the increase of testing temperatures from 600 to 800 °C, which is almost 2.6 times higher than that of the cell with conventional LSM-YSZ cathode. After each thermal cycle between 750 and 300 °C, the OCV remains almost unchanged and the cell voltage decreases less than 0.007 V, indicating that the cell is capable of thermal cycling. The cell voltage at 310 mA cm-2 and 750 °C declines linearly with testing time at a rate of 2.6 × 10-4 V h-1 for the growth of the infiltrated Pd0.95Mn0.05O size, resulting in reduction of the total surface area of the particles. The mechanism of performance degradation of the cell with Pd0.95Mn0.05O-infiltrated LSM-YSZ composites cathode is discussed in detail.

  15. Microstructural properties, electrical behavior and low field magnetoresistance of (1-x)La0.67Sr0.33MnO3 (LSMO)+(x)Ni0.5Zn0.5Fe2O4 (NZFO) composites

    NASA Astrophysics Data System (ADS)

    Dar, Mashkoor Ahmad; Varshney, Dinesh

    2015-12-01

    The composites with composition of (1-x)La0.67Sr0.33MnO3 (LSMO)+(x)Ni0.5Zn0.5Fe2O4 (NZFO) with x=0.0 (S1), 0.04 (S2), 0.07 (S3), 0.10 (S4), 0.30 (S5) and 1.0 (S6) were synthesized by solid-state reaction route. Structural study using Rietveld refinement of X-ray diffraction (XRD) pattern indicates a rhombohedrally-distorted structure (space group R3c) for LSMO phase while to that NZFO compound crystallizes in cubic structure (space group Fd3m). XRD patterns and microstructural analysis show that LSMO and NZFO phase exists independently in Ni0.5Zn0.5Fe2O4 doped composites. The transport properties of the compositions x=0.0, x=0.04, and x=0.07 showed that NZFO phase improves the resistivity and shifts the metal-insulator transition temperature TMI towards lower temperature. The magnetoresistance (MR) of composite samples with x=0.04 and x=0.07 decreases monotonously from 200 to 300 K in a magnetic field of 8 T. At lower temperatures (~5 K), a sharp drop of negative MR at low fields (H<1 T) has been observed followed by a slower varying MR at a comparatively high-field regime (H>1 T) where MR is almost linear with applied magnetic field. Temperature dependence of resistivity for composites samples with x=0.04 and x=0.07 has been best fitted by small Polaron hopping (SPH) and variable range hopping models (VRH).

  16. Magnetic field, frequency and temperature dependence of complex conductance of ultrathin La1.65Sr0.45CuO4/La2CuO4 films and the organic superconductors κ-(BEDT-TTF)2Cu[N(CN)2]Br

    DOE PAGESBeta

    V. A. Gasparov; Bozovic, I.; He, Xi; Dubuis, G.; Pavuna, D.; Kushch, N. D.; Yagubskii, E. B.; Schlueter, J. A.

    2015-09-01

    In this study, we used atomic-layer molecular beam epitaxy (ALL-MBE) to synthesize bilayer films of a cuprate metal (La1.65Sr0.45CuO4) and a cuprate insulator (La2CuO4), in which interface superconductivity occurs in a layer that is just one-half unit cell thick. We have studied the magnetic field and temperature dependence of the complex sheet conductance, σ(ω), of these films, and compared them to κκ-(BEDT-TTF)2Cu[N(CN)2]Br single crystals. The magnetic field H was applied both parallel and perpendicular to the 2D conducting layers. Experiments have been carried out at frequencies between 23 kHz and 50 MHz using either two-coil mutual inductance technique, or themore » LC resonators with spiral or rectangular coils. The real and the imaginary parts of the mutual-inductance M(T,ω) between the coil and the sample were measured and converted to complex conductivity. For H perpendicular to the conducting layers, we observed almost identical behavior in both films and κ-Br single crystals: (i) the transition onset in the inductive response, Lk–1(T) occurs at a temperature lower by 2 K than in Re σ(T), (ii) this shift is almost constant with magnetic field up to 8 T; (iii) the vortex diffusion constant D(T) is exponential due to pinning of vortex cores. These results can be described by the extended dynamic theory of the Berezinski–Kosterlitz–Thouless (BKT) transition and dynamics of bound vortex–antivortex pairs with short separation lengths.« less

  17. Control of VO•• ˜ TiT i ' dipole pairs as well as M gTi ″ defects on dielectric properties of Mg doped (Pb0.35Sr0.65)TiO3 thin film

    NASA Astrophysics Data System (ADS)

    Hu, Tao; Wang, Zongrong; Ma, Ning; Du, Piyi

    2016-01-01

    Mg doped (Pb0.35Sr0.65)TiO3 (PST) thin films were fabricated on indium tin oxide /glass substrates by the sol-gel technique. The formation of the PST phase and control of the magnesium doping on the microstructure, defect states, and dielectric properties of the thin film were investigated by means of XRD, SEM, AFM, XPS, and impedance analysis. Results showed that the oxygen vacancies and the associated Ti3+ ions formed as VO•• ˜ TiT i ' dipole pairs, and the dipole pairs were aligned opposite to the direction of the intrinsic dipole moments in the PST thin film. The amount of dipole pairs was strongly affected by the formed M gTi ″ in the thin film. The minimum amount of the dipole pairs appeared in the PST thin film with Mg doping content of 6% in molar ratio. The thin film with Mg doping content of 6% showed high permittivity due to low offset from VO•• ˜ TiT i ' dipole pairs and low dielectric loss due to low defect electrons generated in the thin film simultaneously. The formed M gTi ″ in the oxygen octahedral contributed lower response of the dipole moments to external electric field and resulted in lower tunability of the PST thin film with increasing Mg doping content. Controlled by the substitution of Mg2+ ions for Ti4+ ions and the induced VO•• ˜ TiT i ' dipole pairs, the optimal figure of merit was obtained in the PST thin film with Mg doping content of 6% with which the thin film possessed the smallest dielectric loss and still high tunability simultaneously.

  18. Temperature- and field-dependent critical currents in [(Bi,Pb)2Sr2Ca2Cu3Ox]0.07(La0.7Sr0.3MnO3)0.03 thick films grown on LaAlO3 substrates

    NASA Astrophysics Data System (ADS)

    Paredes, Omar; Morán, Oswaldo; Baca, Eval

    2013-01-01

    La0.7Sr0.3MnO3 (LSMO) nanoparticles were embedded in (Bi,Pb)2Sr2Ca2Cu3Ox (Bi2223) thick films, which were grown by simple melting-quenching-annealing (MQA) method on (001)-oriented LaAlO3 (LAO) substrates. The nominal composition of the composite-like hybrid system was (Bi2223)1-x(LSMO)x with x = 0.03. The constituent elements, Bi2223 and LSMO, were prepared separately by standard solid state reaction and Pechini's method, respectively. The analysis of the X-ray diffraction patterns suggested a polycrystalline growth mode of the thick films on the LAO substrates. From electric transport measurements, the superconducting onset temperature and the superconducting critical temperature (ρ = 0) ended up being 105 and 62 K, respectively. The flux pinning energy U was determined using the Anderson-Kim model. The value of U was compared with those obtained for similar samples with concentrations x = 0.01 and x = 0.05. Current-voltage characteristics were recorded at different temperatures in order to analyze the behavior of the superconducting current (Ic) of the films. A dramatic drop of Ic was observed at ˜20 K. This seems to be linked to the presence of flux creep acting as dissipation factors attributed to LSMO nanoparticles. Isothermal magnetization loops recorded at T < Tc and T > Tc showed clear diamagnetic and ferromagnetic signals, which verify the multifunctional character of the system. Based on the isothermal M(H)-loops recorded at 5, 20, and 40 K and taking Kim's model into account, the dependence of superconducting current density (Jc), and the volume pinning force (Fp) on the magnetic field were calculated. The dependence Jc(B) at 5 K showed an exponential-type behavior, which is described by an empirical equation. This empirical equation considers the maximum value of Fp, which may be scaled with the Kramer's expression for Fp. From this scaling procedure, diverse exponents, associated with different pinning mechanisms, were determined. The drastic fall

  19. Structural, magnetic, and superconducting properties of pulsed-laser-deposition-grown La1.85 Sr0.15 CuO4 / La2/3 Ca1/3 MnO3 superlattices on (001)-oriented LaSrAlO4 substrates

    DOE PAGESBeta

    Das, S.; Sen, K.; Marozau, I.; Uribe-Laverde, M. A.; Biskup, N.; Varela, M.; Khaydukov, Y.; Soltwedel, O.; Keller, T.; Döbeli, M.; et al

    2014-03-12

    Epimore » taxial La1.85 Sr0.15 CuO4 / La2/3 Ca1/3 MnO3 (LSCO/LCMO) superlattices (SL) on (001)- oriented LaSrAlO4 substrates have been grown with pulsed laser deposition (PLD) technique. Their structural, magnetic and superconducting properties have been determined with in-situ reflection high energy electron diffraction (RHEED), x-ray diffraction, specular neutron reflectometry, scanning transmission electron microscopy (STEM), electric transport, and magnetization measurements. We find that despite the large mismatch between the in-plane lattice parameters of LSCO (a = 0.3779 nm) and LCMO (a = 0.387 nm) these superlattices can be grown epitaxially and with a high crystalline quality. While the first LSCO layer remains clamped to the LSAO substrate, a sizeable strain relaxation occurs already in the first LCMO layer. The following LSCO and LCMO layers adopt a nearly balanced state in which the tensile and compressive strain effects yield alternating in-plane lattice parameters with an almost constant average value. No major defects are observed in the LSCO layers, while a significant number of vertical antiphase boundaries are found in the LCMO layers. The LSCO layers remain superconducting with a relatively high superconducting onset temperature of Tconset ≈ 36 K. The macroscopic superconducting response is also evident in the magnetization data due to a weak diamagnetic signal below 10 K for H ∥ ab and a sizeable paramagnetic shift for H ∥ c that can be explained in terms of a vortex-pinning-induced flux compression. The LCMO layers maintain a strongly ferromagnetic state with a Curie temperature of TCurie ≈ 190 K and a large low-temperature saturation moment of about 3.5 (1) μB. These results suggest that the LSCO/LCMO superlattices can be used to study the interaction between the antagonistic ferromagnetic and superconducting orders and, in combination with previous studies on YBCO/LCMO superlattices, may allow one to identify the relevant

  20. Magnetic structure of La0.7Sr0.3MnO3/La0.7Sr0.3FeO3 superlattices

    SciTech Connect

    Arenholz, E.; van der Laan, G.; Yang, F.; Kemik, N.; Biegalski, M.D.; Christen, H.M.; Takamura, Y.

    2009-01-10

    Using x-ray magnetic dichroism we characterize the magnetic order in La{sub 0.7}Sr{sub 0.3}MnO{sub 3} (LSMO)/La{sub 0.7}Sr{sub 0.3}FeO{sub 3} (LSFO) superlattices with 6 unit cell thick sublayers. The LSMO layers exhibit a reduced Curie temperature compared to the bulk while antiferromagnetic order in the LSFO layers persists up to the bulk Neel temperature. Moreover, we find that aligning the LSMO magnetization by a magnetic field within the (001) surface plane leads to a reorientation of the Fe moments as well maintaining a perpendicular orientation of Fe and Mn moments. This perpendicular alignment is due to the frustrated exchange coupling at the LSMO/LSFO interface.

  1. Anisotropic dispersion of charge stripe fluctuations in La1.75Sr0.25NiO4

    NASA Astrophysics Data System (ADS)

    Tranquada, John; Zhong, Ruidan; Gu, Genda; Reznik, Dmitry; Winn, Barry

    2015-03-01

    It has recently been demonstrated that charge stripe fluctuations can be detected in La2-xSrxNiO4 by inelastic neutron scattering at temperatures close to the charge-ordering transition. The next step is to characterize the dispersion of these excitations. To do this, we have studied a crystal with x = 0 . 25 using the HYSPEC instrument at the Spallation Neutron Source. The clearest picture has been obtained at a temperature of 160 K, where spin order is absent while the charge order is weak but finite. The effective observation window is limited to E < 8 meV, as acoustic phonons dispersing from neighboring Bragg peaks obscure the weak signal of interest at higher energies. Measuring about the charge-order peak at wave vector (4.4,3,0), where a* = 1 . 159 Å-1, we observe a dispersion with a velocity of ~ 20 meV-Å along the stripe-modulation direction, but no clear dispersion in the orthogonal direction. The detected velocity has the scale of lattice, rather than purely electronic, excitations. Work at BNL supported by Office of Basic Energy Sciences, US DOE, under Contract No. DE-AC02-98CH10886.

  2. Oscillatory Magnetoresistance in Nanopatterned Superconducting La1.84Sr0.16CuO4 Films

    SciTech Connect

    Sochnikov, I.; Bozovic, I.; Shaulov, A.; Yeshurun, Y.; Logvenov, G.

    2010-09-21

    A superconducting La{sub 1.84}Sr{sub 0.16}CuO{sub 4} film patterned into a network of 100 x 100 nm{sup 2} noninteracting square loops exhibits large magnetoresistance oscillations superimposed on a background which increases monotonically with the applied magnetic field. Neither the oscillations amplitude nor its temperature dependence can be explained by the Little-Parks effect. Conversely, a good quantitative agreement is obtained with a recently proposed model ascribing the oscillations to the interaction between thermally excited moving vortices and the oscillating persistent currents induced in the loops. Extension of this model, allowing for direct interaction of the vortices and antivortices magnetic moment with the applied field, accounts quantitatively for the monotonic background as well. Analysis of the background indicates that in the patterned film both vortices and antivortices are present at comparable densities. This finding is consistent with the occurrence of Berezinskii-Kosterlitz-Thouless transition in La{sub 1.84}Sr{sub 0.16}CuO{sub 4} films.

  3. Temperature-dependent emissivity property in La0.7Sr0.3MnO3 films

    NASA Astrophysics Data System (ADS)

    Fan, Desong; Li, Qiang; Dai, Ping

    2016-04-01

    Thermochromic films have been deposited by magnetron sputtering technique on different substrates. The crystallinity and surface morphology of the films have been characterized. Characterization result shows that the films are of perovskite structure. Composition analysis is performed and the result indicated that the element composition of the film can be close to its stoichiometric ratio. Temperature-dependent reflectivity and emissivity are studied. Reflectivity spectra show a downward trend with increasing temperature. Emissivity of the film is large at high temperature and it decreases sharply upon cooling. The emissivity increment at 123-373 K can approach 0.43 at 1.4 Pa sputtering pressure environment, which is attractive for thermal control application in spacecraft.

  4. Preparation of the Second Shipment of Spent Nuclear Fuel from the Ustav Jaderneho Vyzkumu Rez (UJV Rez), a.s., Czech Republic to the Russian Federation for Reprocessing - 13478

    SciTech Connect

    Trtilek, Radek; Podlaha, Josef

    2013-07-01

    After more than 50 years of operation of the LVR-15 research reactor operated by the UJV Rez, a. s. (formerly Nuclear Research Institute - NRI), a large amount of the spent nuclear fuel (SNF) of Russian origin has been accumulated. In 2005 UJV Rez, a. s. jointed the Russian Research Reactor Fuel Return (RRRFR) program under the United States (US) - Russian Global Threat Reduction Initiative (GTRI) and started the process of SNF shipment from the LVR-15 research reactor back to the Russian Federation (RF). In 2007 the first shipment of SNF was realized. In 2011, preparation of the second shipment of spent fuel from the Czech Republic started. The experience obtained from the first shipment will be widely used, but some differences must be taken into the account. The second shipment will be realized in 2013 and will conclude the return transport of all, both fresh and spent, high-enriched nuclear fuel from the Czech Republic to the Russian Federation. After the shipment is completed, there will be only low-enriched nuclear fuel on the territory of the Czech Republic, containing maximum of 20% of U-235, which is the conventionally recognized limit between the low- and high-enriched nuclear materials. The experience (technical, organizational, administrative, logistic) obtained from the each SNF shipment as from the Czech Republic as from other countries using the Russian type research reactors are evaluated and projected onto preparation of next shipment of high enriched nuclear fuel back to the Russian Federation. The results shown all shipments provided by the UJV Rez, a. s. in the frame of the GTRI Program have been performed successfully and safely. It is expected the experience and results will be applied to preparation and completing of the Chinese Miniature Neutron Source Reactors (MNSR) Spent Nuclear Fuel Repatriation in the near future. (authors)

  5. Self-assembled monolayers and chemical derivatization of Ba 0.5Sr 0.5TiO 3 thin films: Applications in phase shifter devices

    NASA Astrophysics Data System (ADS)

    Morales-Cruz, Angel L.; Keuls, Fred W. Van; Miranda, Félix A.; Cabrera, Carlos R.

    2005-11-01

    Thin films of barium strontium titanate (Ba 1- xSr x TiO 3 (BSTO)) have been used in coupled microstrip phase shifters (CMPS) for possible insertion in satellite and wireless communication platforms primarily because of their high dielectric constant, low loss, large tunability, and good structural stability. In an attempt to improve the figure of merit K (phase shift °/dB of loss) of phase shifters, modification of the metal/BSTO interface of these devices has been done through surface modification of the BSTO layer using a self-assembled monolayer approach. The impact of this nanotechnology promises to reduce RF losses by improving the quality of the metal/BSTO interface. In this study, compounds such as 3-mercaptopropyltrimethoxysilane (MPS), 16-mercaptohexadecanois acid (MHDA) and 3-mercaptopropionic acid (MPA) were used to form the self-assembled monolayers on the BSTO surface. As a result of the previous modification, chemical derivatization of the self-assembled monolayers was done in order to increase the chain length. Chemical derivatization was done using 3-aminopropyltrimethoxysilane (APS) and 16-mercaptohexadecanoic acid. Surface chemical analysis was done to reveal the composition of the derivatization via X-ray photoelectron spectroscopy (XPS) and Fourier Transform Infrared (FT-IR). Low and high frequencies measurements of phase shifters were done in order measure the performance of these devices for insertion in antennas. X-ray photoelectron spectroscopy characterization of modified BSTO thin films with MPS showed a binding energy peak at 162.9 eV, indicative of a possible S sbnd O interaction: sulfur of the mercapto compound, MPS, used to modify the surface with the oxygen site of the BSTO thin film. This interaction is at higher binding energies compared with the thiolate interaction. This behavior is observed with the other mercapto compounds such as: MHDA and MPA. An FT-IR analysis present a band at 780 cm -1, which is characteristic of an O sbnd S sbnd C stretching and reveals the modification of the BSTO thin film by the coupling of the O of the BSTO with the S of the mercapto compound. All the modification using mercapto compounds is through sulfur to the BSTO thin film. MHDA SAM on BSTO thin film was chemically derivatized using APS shown by XPS and FT-IR. The SAMs modified phase shifters showed an improvement in performance with respect to those phase shifters fabricated with standard methods.

  6. Magnetic-field-driven superconductor-insulator transition in stripe-ordered La1.48Nd0.4Sr0.12CuO4

    NASA Astrophysics Data System (ADS)

    Baity, Paul; Shi, Zhenzhong; Popović, Dragana; Sasagawa, T.

    2015-03-01

    The effects of the magnetic field (H) in underdoped cuprates, the nature of the H-driven superconductor-insulator transition (SIT), and the interplay with charge ordering are some of the key questions in high-temperature superconductivity. A recent study of the H-driven SIT in highly underdoped (Tc ~ 4 K) La2-xSrxCuO4 (LSCO) revealed an intermediate phase, with two quantum critical points separating the superconductor and the insulator. While charge distribution in highly underdoped LSCO seems to be inhomogeneous, its sister compound La2-xNd0.4SrxCuO4 (LNSCO) with x = 0 . 12 is known to have a charge-stripe order already in H = 0 at low enough temperatures (T). In order to address the above issues, we carry out detailed measurements of the in-plane and out-of-plane magnetoresistance with different H orientations and over a wide range of T on LNSCO single crystals with x = 0 . 12 and Tc ~ 4 K. The results will provide insight into the universality of the H-driven SIT in cuprates with different types or, at least, varying degrees of charge order. Supported by NSF DMR-1307075 and NHMFL via NSF DMR-1157490 and the State of Florida.

  7. Hyperthermia mediated by dextran-coated La0.7Sr0.3MnO3 nanoparticles: in vivo studies

    PubMed Central

    Haghniaz, Reihaneh; Umrani, Rinku D; Paknikar, Kishore M

    2016-01-01

    Purpose The aim of this study was to evaluate radiofrequency-induced dextran-coated lanthanum strontium manganese oxide nanoparticles-mediated hyperthermia to be used for tumor regression in mice. Materials and methods Nanoparticles were injected intra-tumorally in melanoma-bearing C57BL/6J mice and were subjected to radiofrequency treatment. Results Hyperthermia treatment significantly inhibited tumor growth (~84%), increased survival (~50%), and reduced tumor proliferation in mice. Histopathological examination demonstrated immense cell death in treated tumors. DNA fragmentation, increased terminal deoxynucleotidyl transferase-dUTP nick end labeling signal, and elevated levels of caspase-3 and caspase-6 suggested apoptotic cell death. Enhanced catalase activity suggested reactive oxygen species-mediated cell death. Enhanced expression of heat shock proteins 70 and 90 in treated tumors suggested the possible development of “antitumor immunity”. Conclusion The dextran-coated lanthanum strontium manganese oxide-mediated hyperthermia can be used for the treatment of cancer. PMID:27175076

  8. Strain engineering to control the magnetic and magnetotransport properties of La0.67Sr0.33MnO3 thin films

    SciTech Connect

    Yang, F.; Kemik, N.; Biegalski, M.D.; Christen, H.M.; Arenholz, E.; Takamura, Y.

    2010-06-15

    This work studies the control of the magnetic and magnetotransport properties of La{sub 0.67}Sr{sub 0.33}MnO{sub 3} thin films through strain engineering. The strain state is characterized by the tetragonal distortion (c/a ratio), which can be varied continuously between a compressive strain of 1.005 to a tensile strain of 0.952 by changing the type of substrate, the growth rate, and the presence of an underlying La{sub 0.67}Sr{sub 0.33}FeO{sub 3} buffer layer. Increasing tensile tetragonal distortion of the La{sub 0.67}Sr{sub 0.33}MnO{sub 3} thin film decreases the saturation magnetization, changes the temperature dependence of the resistivity and magnetoresistance, and increases the resistivity by several orders of magnitude.

  9. Exchange current model for (La0.8Sr0.2)0.95MnO3 (LSM) porous cathode for solid oxide fuel cells

    NASA Astrophysics Data System (ADS)

    Miyoshi, Kota; Miyamae, Takuma; Iwai, Hiroshi; Saito, Motohiro; Kishimoto, Masashi; Yoshida, Hideo

    2016-05-01

    In this paper, we propose an empirical formula for i0,TPB, the exchange current density per unit triple-phase boundary (TPB) length, for porous lanthanum strontium manganite (LSM) cathodes of solid oxide fuel cells (SOFCs); the evaluation of i0,TPB is of crucial importance in numerical simulations of electrodes based on reconstructed microstructures obtained by a dual beam focused ion beam scanning electron microscopy (FIB-SEM) and tomography techniques. To derive a widely applicable empirical formula for i0,TPB, electrochemical measurements of porous LSM cathodes are conducted under various oxygen partial pressures (0.05-0.25 atm) and temperatures (800-950 °C). By comparing the derived formula with that derived from a thin and dense patterned LSM electrode used in previous studies, it is found that at an air temperature of 800 °C, i0,TPB derived from a porous LSM cathode is approximately 40% smaller than that for the patterned electrode. This can be attributed to the fact that the electrochemical reaction in thin and dense electrodes can occur not only at the TPBs but also at the LSM surface owing to the non-negligible ionic conductivity of LSM. The derived formula is also applied to a three-dimensional numerical simulation to confirm its validity.

  10. Low-energy dispersion of dynamic charge stripes in La1.75Sr0.25NiO4 observed with inelastic neutron scattering

    NASA Astrophysics Data System (ADS)

    Zhong, Ruidan; Tranquada, John; Gu, Genda; Reznik, Dmitry; Winn, Barry

    The dynamic stripe correlations have been the subject of intense research, owing to the possible links with high-Tc superconductivity. In light of a recently published, direct observation of charge-stripe fluctuations in La2-xSrxNiO4 using inelastic neutron scattering, we did a follow-up neutron experiment on a x=0.25 sample to characterize the low-energy dispersion of these dynamic charge stripes using the HYSPEC instrument at the Spallation Neutron Source. The scattering signals are collected in the vicinity of a charge-order peak with a large wave vector (4.4, 3, 0), where dynamic spin-stripe correlations are negligible. Mapping the low-energy charge-stripe fluctuations in a wide temperature range, we observe a finite dispersion along the stripe-modulation direction at T >=160K where the charge stripes become disordered, while the steep dispersion in the orthogonal direction is not resolved. Work at BNL supported by Office of Basic Energy Sciences, US DOE, under Contract No. DE-SC00112704.

  11. Preparation and characterization of Sr0.5Ba0.5Nb2O6 glass-ceramic on piezoelectric properties

    NASA Astrophysics Data System (ADS)

    Shan, Jiang; Xuan-Ming, Wang; Jia-Yu, Li; Yong, Zhang; Tao, Zheng; Jing-Wen, Lv

    2016-03-01

    We studied the influence of heat treatment time on the optical, thermal, electrical, and mechanical properties of strontium barium niobate (Sr1-xBaxNb2O6 hereafter SBN) piezoelectric glass-ceramics with tungsten bronze-type structure, which have good piezoelectric properties and are important lead-free piezoelectric materials. We found that the best heat treatment time is 4 h. The properties of the prepared materials are better than that of SBN ceramics and the glass-ceramic growth is faster than the SBN crystal when the heat treatment time of the SBN piezoelectric glass-ceramic is controlled, reducing the preparation costs greatly.

  12. Large transport Jc in Cu-sheathed Sr0.6K0.4Fe2As2 superconducting tape conductors

    PubMed Central

    Lin, He; Yao, Chao; Zhang, Haitao; Zhang, Xianping; Zhang, Qianjun; Dong, Chiheng; Wang, Dongliang; Ma, Yanwei

    2015-01-01

    Copper sheath is the first choice for manufacturing high-Tc superconducting wires and tapes because of its high electrical and thermal conductivities, low-cost and good mechanical properties. However, Cu can easily react with superconducting cores, such as BSCCO, MgB2 and pnictides, and therefore drastically decrease the transport Jc. Here, we report the fabrication of Cu-sheathed Sr1−xKxFe2As2 tapes with superior Jc performance using a simple hot pressing method that is capable of eliminating the lengthy high-temperature sintering. We obtained high-quality Sr1−xKxFe2As2 tapes with processing at 800 oC for 30 minutes and measured high Tc and sharp transition. By this rapid fabrication, Cu sheath does not give rise to apparent reaction layer, and only slightly diffuses into Sr-122 core. As a consequence, we achieved high transport Jc of 3.1 × 104 A/cm2 in 10 T and 2.7 × 104 A/cm2 in 14 T at 4.2 K. The in-field Jc performance is by far the highest reported for Cu-sheathed high-Tc conductors. More importantly, Cu-sheathed Sr-122 tapes also showed a high Je value of 1.0 × 104 A/cm2 in 10 T at 4.2 K, which has reached the widely accepted practical level for applications. These results demonstrate that Cu is a very promising sheath for the practical application of pnictide conductors. PMID:26122741

  13. Large transport Jc in Cu-sheathed Sr0.6K0.4Fe2As2 superconducting tape conductors

    NASA Astrophysics Data System (ADS)

    Lin, He; Yao, Chao; Zhang, Haitao; Zhang, Xianping; Zhang, Qianjun; Dong, Chiheng; Wang, Dongliang; Ma, Yanwei

    2015-06-01

    Copper sheath is the first choice for manufacturing high-Tc superconducting wires and tapes because of its high electrical and thermal conductivities, low-cost and good mechanical properties. However, Cu can easily react with superconducting cores, such as BSCCO, MgB2 and pnictides, and therefore drastically decrease the transport Jc. Here, we report the fabrication of Cu-sheathed Sr1-xKxFe2As2 tapes with superior Jc performance using a simple hot pressing method that is capable of eliminating the lengthy high-temperature sintering. We obtained high-quality Sr1-xKxFe2As2 tapes with processing at 800 oC for 30 minutes and measured high Tc and sharp transition. By this rapid fabrication, Cu sheath does not give rise to apparent reaction layer, and only slightly diffuses into Sr-122 core. As a consequence, we achieved high transport Jc of 3.1 × 104 A/cm2 in 10 T and 2.7 × 104 A/cm2 in 14 T at 4.2 K. The in-field Jc performance is by far the highest reported for Cu-sheathed high-Tc conductors. More importantly, Cu-sheathed Sr-122 tapes also showed a high Je value of 1.0 × 104 A/cm2 in 10 T at 4.2 K, which has reached the widely accepted practical level for applications. These results demonstrate that Cu is a very promising sheath for the practical application of pnictide conductors.

  14. Superconductivity in La1.56Sr0.44CuO4/La2CuO4 Superlattices

    SciTech Connect

    Bozovic I.; Suter, A.; Morenzoni, E.; Prokscha, T.; Luetkens, H.; Wojek, B.M.; Logvenov, G.; Gozar, A.

    2011-12-01

    Superlattices of the repeated structure La{sub 1.56}Sr{sub 0.44}CuO{sub 4}/La{sub 2}CuO{sub 4} (LSCO-LCO), where none of the constituents is superconducting, show a superconducting transition of T{prime}{sub c} 25 K. In order to elucidate the nature of the superconducting state we have performed a low-energy {mu}SR study. By applying a magnetic field parallel (Meissner state) and perpendicular (vortex state) to the film planes, we could show that superconductivity is sheet like, resulting in a very anisotropic superconducting state. This result is consistent with a simple charge-transfer model, which takes into account the layered structure and the difference in the chemical potential between LCO and LSCO, as well as Sr interdiffusion. Using a pancake-vortex model we could estimate a strict upper limit of the London penetration depth to 380 nm in these superlattices. The temperature dependence of the muon depolarization rate in field cooling experiments is very similar to what is observed in intercalated BSCCO and suggests that vortex-vortex interaction is dominated by electromagnetic coupling but negligible Josephson interaction.

  15. Congruent Sr0.61Ba0.39Nb2O6 doubly doped with Ce and Cr: Photo- and thermoluminescence investigations

    NASA Astrophysics Data System (ADS)

    Kislova, I. L.; Gao, M.; Kapphan, S. E.; Pankrath, R.; Kutsenko, A. B.; Vikhnin, V. S.

    Congruent Sr-x Ba1-xNb2O6 (SBN, x=0.61) doped with Ce or Cr ions exhibits enhanced photorefractive properties and new spectral features like increased red sensitivity. Here special emphasis is placed on the luminescence features of doubly doped Ce+Cr SBN crystals. The luminescence excitation and emission spectra combined with the absorption of the impurities allow to draw conclusions about the origin of the charge carriers und their recombination. The well separated thermo-luminescence peaks detected and their spectral line shape in emission point to specific recombination processes following the thermal liberation of light-induced electron trapping centers: Nb4+ polarons and VIS-centers created at low temperature under light irradiation. The thermal activation energy for the hopping motion of Nb4+ polarons and of VIS-centers are estimated to be 0.18+/-0.02 eV and 0.30+/-0.05 eV respectively. Possible excitation and recombination mechanisms in SBN:Ce+Cr are discussed.

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

    SciTech Connect

    Matsuda, Masaaki; Fernandez-Baca, Jaime A; Fujita, M.; Yamada, K.; Tranquada, John M.

    2011-01-01

    Inelastic neutron scattering experiments have been performed on lightly doped La{sub 1.975}Sr{sub 0.025}CuO{sub 4}, 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 E{sub cross}, 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 E{sub cross}. Our experimental results suggest that the magnetic excitations rising from the pair of (diagonally) incommensurate wave vectors merge at E{sub cross} into isotropic excitations.

  17. Reversible Control of Magnetism in La0.67 Sr0.33 MnO3 through Chemically-Induced Oxygen Migration

    NASA Astrophysics Data System (ADS)

    Grutter, Alexander; Gilbert, Dustin; Maranville, Brian; Borchers, Julie; Kirby, Brian; Arenholz, Elke; Alaan, Urusa; Suzuki, Yuri; Liu, Kai

    There has been a surge of interest in controlling magnetism through oxygen migration for applications in hybrid ionic/magnetoelectric device architectures. With a rich magnetic and electronic phase diagram, the colossal magnetoresistive perovskite (La,Sr)MnO3 (LSMO) is an ideal candidate for achieving large modulations in magnetic properties with small changes in oxygen content. We demonstrate reversible control of magnetism in LSMO films through interfacial oxygen migration. Gd metal capping layers deposited onto LSMO leach oxygen from the film to form porous Gd2O3. X-ray absorption and polarized neutron reflectometry measurements show Mn valence alterations consistent with high oxygen vacancy concentrations, resulting in suppressed magnetization and increased coercive fields. Oxygen migration is observed both at the interface and also throughout the majority of a 40 nm thick film, suggesting extensive oxygen vacancy diffusion. After Gd-capped LSMO is exposed to atmospheric oxygen for a prolonged period of time, oxygen diffuses through the Gd2O3 layer and the magnetization of the LSMO returns to the uncapped value. These findings showcase perovskite heterostructures as ideal candidates for developing functional interfaces through chemically-induced oxygen migration.

  18. Surface Tuning of La0.5Sr0.5CoO3 Perovskite Catalysts by Acetic Acid for NOx Storage and Reduction.

    PubMed

    Peng, Yue; Si, Wenzhe; Luo, Jinming; Su, Wenkang; Chang, Huazhen; Li, Junhua; Hao, Jiming; Crittenden, John

    2016-06-21

    Selective dissolution of perovskite A site (A of ABO3 structure) was performed on the La1 - xSrxCoO3 catalysts for the NOx storage and reduction (NSR) reaction. The surface area of the catalysts were enhanced using dilute HNO3 impregnation to dissolve Sr. Inactive SrCO3 was removed effectively within 6 h, and the catalyst preserved the perovskite framework after 24 h of treatment. The tuned catalysts exhibited higher NSR performance (both NOx storage and NO-to-NO2 oxidation) under lean-burn and fuel-rich cycles at 250 °C. Large amounts of NOx adsorption were due to the increase of nitrate/nitrite species bonding to the A site and the growth of newly formed monodentate nitrate species. Nitrate species were stored stably on the partial exposed Sr(2+) cations. These exposed Sr(2+) cations played an important role on the NOx reduction by C3H6. High NO-to-NO2 oxidation ability was due to the generation of oxygen defects and Co(2+)-Co(3+) redox couples, which resulted from B-site exsolution induced by A-site dissolution. Hence, our method is facile to modify the surface structures of perovskite catalysts and provides a new strategy to obtain highly active catalysts for the NSR reaction. PMID:27233105

  19. Layed Perovskite PRBA0.5SR0.5CO205 as High Performance Cathode for Solid Oxide Fuels Using Photon Conducting Electrolyte

    SciTech Connect

    Brinkman, K.

    2010-05-05

    The layered perovskite PrBa{sub 0.5}Sr{sub 0.5}Co{sub 2}O{sub 5+{delta}} (PBSC) was investigated as a cathode material for a solid oxide fuel cell using a proton-conducting electrolyte based on BaCe{sub 0.7}Y{sub 0.2}Zr{sub 0.1}O{sub 3-{delta}} (BCYZ). The sintering conditions for the PBSC-BCYZ composite cathode were optimized resulting in the lowest area-specific resistance and apparent activation energy obtained with the cathode sintered at 1200 C for 2h. The maximum power densities of the PBSC-BCYZ/BZCY/NiO-BCYZ cell were 0.179, 0.274, 0.395, and 0.522 Wcm{sup -2} at 550, 600, 650, and 700 C, respectively with a 15{micro}m thick electrolyte. A relatively low cell interfacial polarization resistance of 0.132 {Omega}cm{sup 2} at 700 C indicated that the PBSC-BCYZ could be a good cathode candidate for intermediate temperature SOFCs with proton-conducting electrolyte.

  20. Neutron Diffraction Study of Parasitic Nd-Moment Order in the Checkerboard-Type Phase Nd1.3Sr0.7NiO4

    DOE PAGESBeta

    Kobayashi, Riki; Yoshizawa, Hideki; Matsuda, Masaaki; Kajimoto, Ryoichi; Ishizaka, Kyoko; Tokura, Yoshinori

    2015-05-25

    In this paper, the Nd-moment order in the layered nickelate Nd2-xSrxNiO4 (x = 0.7) has been investigated by performing a neutron diffraction experiment using a single crystal sample. First, the checkerboard (CB)-type charge order was confirmed by observing the temperature dependence of the nuclear superlattice peak at Q=(5,0,0) between 1.9 and 300 K, which indicates that the transition temperature of the CB-type charge order is above 300 K. Magnetic superlattice peaks with the propagation vector k=(1-ε,0,1) appear below 67 K, and the value of ε was determined to be 0.455 in good agreement with previous studies. The intensity of themore » magnetic superlattice peaks appearing below 67 K shows a sharp increase below ≈20 K. This behavior indicates that the Nd moments freeze under the influence of the Ni ordering. The CB-type antiferromagnetic (AFM) Ni order in the NiO2 layers is stacked antiferromagnetically in the c-axis direction, while the Nd moments in the Nd/SrO2 layers are coupled antiferromagnetically with the Ni moments. Finally, the Nd moments are parallel to the c-axis, while the Ni moments are canted towards the c-axis direction from the basal ab-plane at low temperatures where the Nd moments are well ordered.« less