La1−xSrxMnO3 Research Articles

Magnetic pinning effects of epitaxial LaxSr1−xMnO3 nanostructured thin films on YBa2Cu3O7−δ layers

The present paper presents the effects of a nanostructured, ferromagnetic La1−xSrxMnO3(LSMO) thin film on the pinning characteristics of an epitaxial YBa2Cu3O7(YBCO) thin film deposited on top. Ordered arrays of LSMO grains were obtained upon growing the film on a terraced (001) SrTiO3 substrate. The analyses of magnetic measurements revealed the presence of a complex vortex pinning mechanism within the YBCO film. With respect to a reference single YBCO layer, an additional pinning potential was observed. Its temperature evolution suggests that a magnetic pinning mechanism is responsible for improved pinning characteristics in the high temperature and field region. Based on the morphology of the underlying LSMO buffer, a strong pinning force is expected to arise due to the anti-dot formations, where a high magnetization gradient exists.

Preparation of La<sub>1-<i>x</i></sub>Sr<sub><i>x</i></sub>MnO<sub>3</sub> Materials by High Temperature Solid Phase Method

La1-xSrxMnO3 (LSMO) (x=0.1, 0.2, 0.3, 0.4)powders were synthesized by high temperature solid phase method, and the crystal structure and morphology were characterized by XRD and SEM. Results indicated that the pure perovskite type LSMO could be obtained after sintered at the temperature of 1000°C for 6h. The average particle size of the powders decreases with the increasing concentration of Strontium.

Effects of crystallite size on magnetic properties of thermal-hydro decomposition prepared La1−xSrxMnO3 nanocrystalline powders

The effects of crystallite size (D) on the two magnetic parameters, saturation magnetization (MS) and coercivity (HC), of nanocrystalline powders of La1−xSrxMnO3 (LSMO) are investigated. LSMO samples with 0.0 ≤ x ≤ 0.5 are synthesized by a thermal-hydro decomposition method at different temperatures (TD) between 600 and 1000 °C, and are then characterized with XRD and VSM techniques at room temperature. The approximate crystallite sizes are in the range 11–45 nm, which increase with increasing TD but decrease with increasing x. Soft ferromagnetic behavior is found in all Sr-doped samples. The MS values for each Sr concentration (0.2 ≤ x ≤ 0.5) strongly depends on D, suggesting the presence of magnetically dead layers at the surface. The thickness of this magnetically dead layer (tm) is reduced by an increase in TD and x (only x ≤ 0.3), and shows the lowest value in the LS3M sample (x = 0.3) for all TD. The MS increase with increasing TD or D corresponds to a decrease in tm. From analysis of the case for a TD of 900 °C, the variation in MS is not only controlled by tm but also by the average ionic radius size in A-site (〈rA〉), and the size mismatch factor of the A-site cations (σ2). The enhancement in the MS value at 〈rA〉 ≤ 1.244 Å (x ≤ 0.3) can be explained by the continuous decrease in tm and the increase in x and 〈rA〉, including the variations in dMn–O and θMn–O–Mn in a direction to encourage FM coupling via double exchange interaction. Whereas the reduction in MS values for 〈rA〉 > 1.224 Å (x ≥ 0.4) is probably due to the higher tm and σ2. The HC values of all LSMO samples strongly vary with D. The single magnetic domain is present for all samples with D lower than 33 nm, while some LSMO samples with D higher than 40 nm contain multi domains. The range of D of 33–40 nm is the possible range in which domain wall formation begins.

LaCo0.6Ni0.4O3−δ as cathode contact material for intermediate temperature solid oxide fuel cells

LaCo0.6Ni0.4O3−δ (LCN64) was prepared through the polymeric steric entrapment precursor route with Polyvinyl alcohol (PVA) as the entrapment agent and was evaluated as a contact material between the metallic interconnect and the cathode in planar intermediate temperature solid oxide fuel cell stacks (IT-SOFC). The ratio of PVA to metal nitrates and the calcination temperature of the precursor were optimized for the process. The electrical conductivity and thermal expansion coefficient (TEC) of the synthesized LCN64 and its chemical compatibility with SUS 430 were also characterized. The results indicate that 1:4 is a proper ratio of PVA to metal nitrates for process control and safety management; and calcination of the precursor at temperatures above 650 °C leads to formation of single perovskite phase LCN64. The conductivity of fully sintered LCN64 is above 1150 S cm−1 in the temperature range between 100 °C and 800 °C, which is higher than those of conventional contact materials La1−xSrxMnO3 (LSM) and LaNiyFe1−yO3 (LNF). The average TEC is 17.22 × 10−6 K−1 at temperatures below 900 °C, which is higher than those of the metallic interconnect and cell components. Mn and Cr elements contained in SUS 430 migrated into the porous LCN64 layer at 800 °C without chemically forming resistive phases.

The influence of surface roughness in X-ray resonant magnetic reflectivity experiments

We present simulations of X-ray resonant magnetic reflectivity (XRMR) spectra of the surface magnetic dead layer in La1−x Sr x MnO3 (LSMO) films that take in account the effect of different forms of roughness that can be encountered experimentally. The results demonstrate a method to distinguish between surface (morphological) roughness, and two generic kinds of magnetic roughness at the buried interface between the surface dead layer and the fully magnetic bulk part of the film. We show that the XRMR technique can distinguish between different types of magnetic roughness at the dead layer/bulk interface only if the sample surface is nearly atomically flat (the morphological roughness is one unit cell or less). Furthermore, to distinguish between the two types of magnetic roughness, the simulations show that fitting of XRMR spectra out to very high incidence angles must be performed. In the specific case of LSMO films with a dead layer with average thickness of 4 unit cells, this corresponds to an incidence angle > 50∘.

Large-distance rf- and dc-sputtering of epitaxial La1 − xSrxMnO3 thin films

Studies on large-distance sputtering as an effective alternative to molecular beam epitaxy, pulsed laser deposition or off-axis sputtering for the deposition of epitaxial La1−xSrxMnO3 (LSMO) thin films, are reported. The focus of this study is on the quality of the samples and their structural and magnetic properties. The dependence of the characteristics of the LSMO films on the sputtering mode (rf, dc) and the sputtering parameters, in particular on the oxygen partial pressure is established and discussed. It is shown that large-distance sputtering can provide high quality LSMO thin films without the need for post-annealing.

Artificial construction of the layered Ruddlesden-Popper manganite La2Sr2Mn3O10 by reflection high energy electron diffraction monitored pulsed laser deposition.

Pulsed laser deposition has been used to artificially construct the n = 3 Ruddlesden–Popper structure La2Sr2Mn3O10 in epitaxial thin film form by sequentially layering La1–xSrxMnO3 and SrO unit cells aided by in situ reflection high energy electron diffraction monitoring. The interval deposition technique was used to promote two-dimensional SrO growth. X-ray diffraction and cross-sectional transmission electron microscopy indicated that the trilayer structure had been formed. A site ordering was found to differ from that expected thermodynamically, with the smaller Sr2+ predominantly on the R site due to kinetic trapping of the deposited cation sequence. A dependence of the out-of-plane lattice parameter on growth pressure was interpreted as changing the oxygen content of the films. Magnetic and transport measurements on fully oxygenated films indicated a frustrated magnetic ground state characterized as a spin glass-like magnetic phase with the glass temperature Tg ≈ 34 K. The magnetic frustration has a clear in-plane (ab) magnetic anisotropy, which is maintained up to temperatures of 150 K. Density functional theory calculations suggest competing antiferromagnetic and ferromagnetic long-range orders, which are proposed as the origin of the low-temperature glassy state.

Structures and Magnetism of La1–xSrxMnO3–(0.5+x)/2 (0.67 ≤ x ≤ 1) Phases

Topotactic reduction of La1–xSrxMnO3 (0.67 ≤ x ≤ 1) phases with sodium hydride yields a series of isoelectronic materials of composition La1–xSrxMnO3–(0.5+x)/2. Lanthanum rich members of the series...

Analysis on insulator–metal transition in yttrium doped LSMO from electron density distribution

Yttrium doped LSMO (La1 − x Sr x MnO3) was prepared using sol–gel technique and analysed for the insulator–metal transition from charge density variation in the unit cell with respect to different stoichiometric inclusion of yttrium. X-ray powder diffraction profiles of the samples were obtained and the well known Rietveld method and a versatile tool called maximum entropy method (MEM) were used for structural and profile refinement. The charge density in the unit cell was constructed using refined structure factors and was analysed. The charge ordering taking place in the insulator–metal transition was investigated and quantified. The insulator–metal transition was found to occur when 20% of La/Sr atoms were replaced by yttrium. The changes in the charge environment have also been analysed.

Development of a novel type of composite cathode material for proton-conducting solid oxide fuel cells

A high-performance solid oxide fuel cell La1−xSrxMnO3 (LSM) cathode/metallic interconnect contact material Ni1−xCoxO, added with the mixed ionic-electronic conducting Sm0.2Ce0.8O2−δ (SDC), was proposed as a novel composite cathode for proton-conducting solid oxide fuel cells (H-SOFCs) with BaZr0.1Ce0.7Y0.1Yb0.1O3−δ (BZCYYb) as the electrolyte. The X-ray diffraction (XRD) results indicated that the maximum doped ratio of Ni1−xCoxO was Ni0.7Co0.3O (NC3O), also shown that NC3O was chemically compatible with SDC at temperatures up to 1400 °C. The TEC of NC3O was also measured to check its thermal compatibility with other components. Laboratory-sized tri-layer cells of NiO–BZCYYb/BZCYYb/NC3O-SDC were fabricated and tested with humidified hydrogen (∼3% H2O) as fuel and static air as oxidant, respectively. A maximum power density of 204 mW cm−2 and a low interfacial polarization resistance Rp of 0.683 Ω cm2 were achieved at 700 °C. The results have indicated that the NC3O-SDC composite is a simple, stable and cost-effective cathode material for H-SOFCs.

Synthesis and characterization of La2NiO4-d coatings deposited by reactive magnetron sputtering using plasma emission monitoring

It is well known that the short life time and the high cost of each component of nowadays Solid Oxide Fuel Cells (SOFC) are induced by their high operating temperature. Many researches focus on the decrease of this operating temperature without reduction of the fuel cell performances (IT-SOFC). Regarding the cathode, one solution is to increase the electrocatalytic properties. Purely electronic conductor perovskite materials (for example LSM: La1-xSrxMnO3) are used in standard SOFC devices. A2MO4+d compounds, with K2NiF4 structure have recently been investigated as substitutes to LSM. Indeed, these materials are mixed ionic and electronic conductors (MIECs) that moreover exhibit rather high electrocatalytic properties. It is then possible to synthesize them as dense materials for SOFC cathodes. Among these materials, lanthanum nickelates La2NiO4+d exhibits convenient electrochemical characteristics. Its thermal expansion coefficient (TEC) is very close to that of the most commonly used electrolyte materials (13 10-6 K-1, 11.9 10-6 K-1 and 11.6 10-6 K-1 for La2NiO4+d, CeO2-Gd2O3 (CGO) and ZrO2-Y2O3 (YSZ) respectively). Its oxygen ionic conductivity and surface exchange coefficient are interesting and seem much better than those of La1-xSrxMnO3 (LSM) and La1-xSrxCo1-yFeyO3 (LSCF), the most commonly used cathodes.The deposition of La2NiO4 coatings by reactive magnetron sputtering has already successfully been performed under so called stable conditions in a laboratory vessel. In this study, we investigate the feasibility of La2NiO4+d coatings deposited by reactive magnetron sputtering under unstable conditions using Plasma Emission Monitoring (PEM).The chemical composition of the coatings was measured by Scanning Electron Microscopy coupled with Energy Dispersive Spectroscopy. The influence of the La/Ni ratio on the structure was checked by X-Ray Diffraction analyses.

Anisotropic Thermal and Chemical Expansion in Sr-Substituted LaMnO3+δ: Implications for Chemical Strain Relaxation

The anisotropic thermal and chemical expansion of rhombohedral (R3̅c) La1–xSrxMnO3+δ (x = 0.2, 0.3) was investigated by in situ high temperature X-ray diffraction of submicrometer size powders in pure oxygen and nitrogen (inert) atmospheres. The thermal expansion of the long axis c was found to be close to twice as high as the thermal expansion of the short axis a. The large thermal expansion of the c-axis is caused by rectification of the antiferrodistortive tilting and decompression of the MnO6/2 octahedra. The unit cell parameters were shown to be strongly dependent on the partial pressure of oxygen, which was attributed to chemical expansion/contraction due to reduction/oxidation of Mn. Anisotropic chemical expansion/contraction was more pronounced for the unit cell parameter a than for c, and the chemical expansion/contraction was inferred to reflect the size of the MnO6/2 octahedra. The onset of chemical expansion in nitrogen and contraction in oxygen atmosphere during heating was discussed in terms of a gradual transformation from a nonequilibrium to an equilibrium point defect population in La1–xSrxMnO3+δ. Possible implications of slow relaxation of chemically induced stresses at the nanoscale and in epitaxial thin films are addressed. Finally, a second order phase transition from the ferroelastic (R3̅c) to paraelastic state (Pm3̅m) is reported for La0.7Sr0.3MnO3+δ at 850 ± 25 °C. The temperature of the phase transition decreases with increasing Sr content in La1–xSrxMnO3+δ.

Ferroelectric and electrical characterization of multiferroic BiFeO3 at the single nanoparticle level

Ferroelectric BiFeO3 (BFO) nanoparticles deposited on epitaxial substrates of SrRuO3 (SRO) and La1−xSrxMnO3 (LSMO) were studied using band excitation piezoresponse spectroscopy (BEPS), piezoresponse force microscopy (PFM), and ferromagnetic resonance (FMR). BEPS confirms that the nanoparticles are ferroelectric in nature. Switching behavior of nanoparticle clusters were studied and showed evidence for inhomogeneous switching. The dimensionality of domains within nanoparticles was found to be fractal in nature, with a dimensionality constant of ∼1.4, on par with ferroelectric BFO thin-films under 100 nm in thickness. Ferromagnetic resonance studies indicate BFO nanoparticles only weakly affect the magnetic response of LSMO.

Comparison of Combustion and Solid-State Reaction Methods for the Fabrication of SOFC LSM Cathodes

This study investigates the crystal phase and microstructure of LSM (La1-xSrxMnO3) cathode material synthesized by solid state reaction method and combustion synthesis. It measures and compares their electrical properties. LSM is a lanthanum ferrite-based cathode material. It has an ABO3 perovskite structure; the A in this structure was substituted by Sr in this research to synthesize the LSM cathode powder. An electrolyte pellet was prepared using 8 mol% YSZ (yttria-stabilized zirconia) powder. The electrode was vapor deposited by screen printing. The crystal structure and morphology were measured by scanning electron microscopy (SEM) and X-ray diffraction (XRD) for the sintered samples collected. The complex impedance was measured in the temperature range 600–900°C in air (Computer Impedance Grain-Phase Analyzer). The electrical conductivity and polarization resistance of LSM were characterized systematically.

CeO2 Addition for Improving Electrochemical Behavior of La1-xSrxMnO3 Cathodes Sintered at High Temperature

This work evaluate the effects of CeO2 addition in La1-xSrxMnO3 (LSM) cathodes on the power density produced by cathode supported single cells co-sintered with YSZ electrolyte at high temperature (1350oC). Results show that regardless of La1-xSrxMnO3 composition, single cells containing CeO2-added LSM cathodes generate higher power density compared when no -added LSM cathodes are used. Highest power density was achieved using 6 mol% CeO2-added La0.7Sr0.3MnO3 cathode. Results suggests that both LSM composition and CeO2 addition are key factors in order to enhance the LSM and single cell performance after co-sintering with YSZ-electrolyte at 1350oC. In addition, both the maximum power density and the co-sintering temperature presented in this work correspond to the highest values as far reported without the need of a buffer layer between LSM-cathode and YSZ-electrolyte.

Synthesis and characterization of La1-xSr xMnO3±δ powders obtained by the polymeric precursor route

Polycrystalline strontium-doped lanthanum manganite (LSM) powders with 0.15, 0.22, and 0.30 mol % Sr were synthesized by the polymeric precursor route using a molar ratio of 3:1 citric acid and metal cations. The powders were characterized by Fourier transform infrared spectroscopy, thermal analysis, high-temperature X-ray diffraction to determine the crystalline perovskite phase and crystallite sizes, scanning electron microscopy for the morphological analysis, nitrogen adsorption to determine the specific surface area, and laser scattering to evaluate the particle size distribution. The LSM perovskite-type oxides containing intermediate 0.22 mol % Sr were found to exhibit a tendency to decrease in crystallite size and increase in specific surface area and, when calcined at 700-900 oC exhibited a pure phase of perovskite, had a crystallite size of about 17-20 nm and a specific surface area for 900 oC of 34.3 m2.g-1.

Nanofiber scaffold for cathode of solid oxidefuel cell

A high performance solid oxide fuel cell cathode using the yttria-stabilized zirconia (YSZ) nanofiber scaffold with the infiltrated La1−xSrxMnO3 (LSM) shows an enhanced catalytic activity toward oxygen reduction. Such a cathode offers a continuous path for charge transport and an increased number of triple-phase boundary sites.

Structural, Magnetic and Electrical Properties of the Slightly Doped Lanthanum Manganites

The temperature dependences of the transverse and longitudinal hypersound velocities at the frequencies (0.5-0.7) GHz were measured in the La1-xSrx MnO3 (x = 0.125; 0.15; 0.175) compositions. Structural phase transitions the position of which is confirmed by the electric resistance and magnetic measurements data for the same samples are observed. These results were analyzed within the model of the competing Jahn-Teller distortions and magnetic ordering. Anomalies in the behavior of the longitudinal hypersound velocities were related to the local Jahn-Teller distortions the suppression of which upon magnetic ordering is considered as a possible origin of a colossal magnetoresistance.

Solution Precursor Plasma Spray of Porous La1−xSrxMnO3 Perovskite Coatings for SOFC Cathode Application

The deposition of porous La1−xSrxMnO3 (LSM) perovskite cathode materials by conventional plasma spray has been a challenge because of the decomposition of perovskite materials to their suboxides at high temperature. In this paper, the solution precursor plasma spraying (SPPS) process, in which solution precursors of the desired resultant materials are fed into a direct current plasma jet by atomizing gas, was used to simultaneously synthesize LSM perovskite and deposit porous cathode coatings. The experimental results show that process parameters have a significant effect on the fabricated coatings. The perovskite coatings consist of porous agglomerates of small particles with rounded features and local denser regions referred to as thick flakes. The small particles and thick flakes were held together by the previously molten material. There are two kinds of pores in the fabricated coatings: large pores located between the agglomerates and fine pores inside the agglomerates. The porous LSM cathode coatings have 20–40 area % of desirable homogeneous pores determined by several processing parameters. X-ray diffraction of sintered coatings shows that no suboxides of La1−xSrxMnO3 perovskite appear. The results of this project indicate that the SPPS is a potential process to produce high quality cathodes for solid oxide fuel cell application.

Prediction of Surface Oxygen Vacancy Concentrations of (La1-xSrx)MnO3

Perovskite materials of the form ABO3 are an important family of compounds for use in solid oxide fuel cell (SOFC) cathodes. In particular, their surface properties play an essential role in their catalytic ability. This paper combines bulk defect models fit to experimental data with ab initio surface energies to predict surface vacancy concentrations in (La1-xSrx)MnO3. It is found that the surface vacancy concentration is ~106 times that of bulk under SOFC operating conditions. The enhanced concentration of surface vacancies may play a role in O2 dissociation, incorporation, and surface transport.