Lanthanum Strontium Manganese Oxide Research Articles

Reaction Joining of Aluminum‐Doped Lanthanum Strontium Manganese Oxide to Yttria‐Stabilized Tetragonal Zirconia for Gas Sensor Applications

Aluminum‐doped lanthanum strontium manganese oxide (LSAM) has been investigated as an electrically conductive ceramic material. LSAM formulations with varying amounts of aluminum were synthesized using standard ceramic processing followed by pressure‐less sintering in air. Electrical conductivity of LSAM was measured as a function of aluminum content and temperature. Optimum LSAM formulations were joined to yttria‐stabilized tetragonal zirconia (YTZP) using a high‐temperature deformation process. Electron microscopy, X‐ray diffraction, and Raman spectroscopy were used to evaluate the joint interface. Joining was attributed to the formation of a reaction layer of strontium zirconate. Joining of LSAM to oxygen‐ion conducting YTZP has implications in using this approach as interconnect for variety of high‐temperature applications, including fuel cells and gas sensors.

The Orientation Distributions of Lines, Surfaces, and Interfaces around Three‐Phase Boundaries in Solid Oxide Fuel Cell Cathodes

Three‐dimensional electron backscatter diffraction was used to measure the crystallographic distribution of the electrochemically relevant triple phase boundary lines and surfaces near them in SOFC cathodes made up of a porous mixture of yttria‐stabilized zirconia and lanthanum strontium manganese oxide, both before and after mild electrochemical loading. All distributions were observed to be nearly isotropic, but non‐random textures above the detection threshold were observed. The distributions differ between the two cells, as do the phase fractions and the electrochemical history. The different distributions are interpreted as evidence that steady‐state distributions vary locally with phase fractions or that they evolve during the initial operation of the fuel cell. The rates at which triple lines, pore surfaces, and interface boundaries in the porous mixture approach a steady‐state value appear to decrease with the average amount of mass transport required to reorient that specific feature. This work provides initial insights into the crystallography of interfaces in a multiphase ceramic material.

Microstructural analysis of interfaces in a ferromagnetic-multiferroic epitaxial heterostructure

We report a study on multiferroic bismuth ferrite (BiFeO3, BFO)-ferromagnetic lanthanum strontium manganese oxide (La0.7Sr0.3MnO3, LSMO) epitaxial interfaces by scanning transmission electron microscopy-energy dispersive spectroscopy (STEM-EDS) and energy-filtered transmission electron microscopy (EFTEM). Epitaxial (001) oriented LSMO/BFO heterostructures were fabricated on a (001) strontium titanate (SrTiO3, STO) substrate using pulsed laser deposition (PLD). Different cooling conditions to room temperature (rapid or slow) were used to investigate the effect of fabrication conditions on the structural quality of the interfaces. The combined analysis of bright field transmission electron microscopy imaging, STEM-EDS and EFTEM data reveals that the LSMO-BFO heterostructure interface is free from any defects but the phases are chemically interdiffused over a length scale of ∼4 nm.

Chromium transport by solid state diffusion on solid oxide fuel cell cathode

Iron–chromium ferritic stainless steel is widely used in solid oxide fuel cell (SOFC) components. At 650–800 °C, stainless steels form a protective chromia oxide scale. This low conductivity catalytic compound can degrade SOFC cathode performance. The migration of Cr species onto the cathode occurs through vapor transport and/or solid state diffusion, and electrochemical reactions may affect the migration. It is important to understand the relative Cr transport and reaction rates to evaluate the most viable commercially available cathode material. This study characterizes the migration of Cr species through solid state diffusion and vapor deposition. Chromia blocks and chromia-forming stainless steel interconnects were held in contact with LSM (Lanthanum Strontium Manganese Oxide), LSCF (Lanthanum Strontium Cobalt Ferrite) and LNF (Lanthanum Nickel Ferrite) perovskite pellets in Cr-saturated air at 700 °C for 300 h. XRD (X-ray Diffraction), SEM (Scanning Electron Microscope), EDS (Energy Dispersive X-ray Spectroscopy) and Ion Milling by FIB (Focused Ion Beam) were used to detect Cr on and within the perovskite pellets. Cr transport and reaction on LSCF is the most severe, followed by LSM. Cr transport is observed on LNF, but without noticeable reaction.

Effect of various coal contaminants on the performance of solid oxide fuel cells: Part I. Accelerated testing

The contaminants that are potentially present in the coal-derived gas stream and their thermochemical nature are discussed. Accelerated testing was carried out on Ni–YSZ/YSZ/LSM solid oxide fuel cells (YSZ: yttria stabilized zirconia and LSM: lanthanum strontium manganese oxide) for eight main kind of contaminants: CH 3 Cl, HCl, As, P, Zn, Hg, Cd and Sb at the temperature range of 750–850 °C. The As and P species, at 10 and 35 ppm, respectively, resulted in severe power density degradation at temperatures 800 °C and below. SEM and EDX analysis indicated that As attacked the Ni region of the anode surface and the Ni current collector, caused the break of the current collector and the eventual cell failure at 800 °C. The phosphorous containing species were found in the bulk of the anode, they were segregated and formed “grain boundary” like phases separating large Ni patches. These species are presumably nickel phosphide/phosphate and zirconia phosphate, which could break the Ni network for electron transport and inhibit the YSZ network for oxygen ion transport. The presence of 40 ppm CH 3 Cl and 5 ppm Cd only affected the cell power density at above 800 °C and Cd caused significant performance loss. Whereas the presence of 9 ppm Zn, 7 ppm Hg and 8 ppm Sb only degraded the cell power density by less than 1% during the 100 h test in the temperature range of 750–850 °C.

Joining of highly aluminum-doped lanthanum strontium manganese oxide with tetragonal zirconia by plastic deformation

Aluminum-doped lanthanum strontium manganese oxide, La 0.77Sr 0.20Al 0.9Mn 0.1O 3 (LSAM), was joined to stabilized tetragonal zirconia polymorph YTZP (ZrO 2) 0.97(Y 2O 3) 0.03 by a uniaxial stress (3–6 MPa) and high-temperature (1250–1350 °C) bonding method that initiates grain-boundary sliding between the ceramic components. The flow stress of LSAM was larger than that of La 0. 8Sr 0.2Mn 0. 3 under the same test conditions. Electron microscopy confirmed that intergranular penetration occurred at the joining plane, leading to effective bonding between the two dissimilar ceramics. Raman spectral maps of the joining planes obtained with 2-D Raman microscopy demonstrated the absence of any new phases at the interface.

Chromium vaporization of bare and of coated iron–chromium alloys at 1073 K

Suppression of chromium vaporization from oxidation scales formed on ferritic stainless steel, when used on the cathode side of Solid Oxide Fuel Cells (SOFC), is a most important issue, since gaseous chromium species cause deposition of chromium oxide on electrolyte or electrode materials. This phenomenon leads to deterioration of the cell performance. The chromium vaporization rates of bare and of coated iron–chromium alloys were measured at 1073 K. The effect of ceramic coating layers, deposited by low-cost aerosol spraying or by dip coating, was evaluated and the morphology of the coating layer was observed. Lanthanum strontium manganese oxide (LSM: La 0.65Sr 0.3MnO 3), lanthanum strontium cobalt iron oxide (LSCF: La 0.6Sr 0.4Co 0.8Fe 0.2O 3) and manganese cobalt oxide (MCO: MnCo 2O 4) coatings, formed from submicron powders, decreased chromium vaporization by a factor of as much as 21–40 at 1073 K. Manganese cobalt oxide and lanthanum strontium chromium oxide (La 0.7Sr 0.3CrO 3) coating, formed from powders prepared by a glycine nitrate combustion synthesis, reduced chromium vaporization by factors of only 2–3 because the coating layers were porous.

Nanolithography made from water-based spin-coatable LSMO resist

A dual functional and water soluble spin-coatable lanthanum strontium manganeseoxide (LSMO) resist has been developed that consists of lanthanum nitrate,strontium nitrate, manganese nitrate, polyvinyl alcohol and water. Energeticnitrates plus polyvinyl alcohol fuel promote autoignition and produce nanopatterns(<60 nm) upon mild electronbeam exposure (<2 mC cm−2). The formation of cubic perovskite LSMO has been confirmed by micro-IR spectroscopy,elemental analysis, x-ray diffraction and transmission electron microscopy. The patternedLSMO film can be developed using nontoxic and environmentally friendly purewater, and the resist can fabricate active magnetic patterns directly by electronbeam exposure. The spin-coatable LSMO resist can be fabricated into eitherpositive or negative patterns easily by varying the electron doses. It can changefrom negative resist to positive resist and then finally negative resist with theincrease of electron dose. The positive and negative dual functional mechanism ofspin-coatable LSMO resist is reported. A resist with simultaneous positive andnegative capabilities patterning will benefit the direct writing technology of anelectron beam. The active magnetic characteristics and high refractive index of thematerial are useful for the direct fabrication of magnetic and optical devices.

Flame assisted vapour deposition of cathode for solid oxide fuel cells. 1. Microstructure control from processing parameters

The flame assisted vapour deposition (FAVD) technique has been used to deposit porous lanthanum strontium manganese oxide (LSM) to produce the cathode for a solid oxide fuel cell (SOFC). FAVD combines flame synthesis and vapour deposition methods where the liquid precursor undergoes a combustion process into a vapour phase, and then deposits as an oxide film on a substrate. The work has shown that the microstructures of deposited films may be dense or porous depending on processing parameters such as the deposition temperature, the concentration of the fuel and the distance between the spray nozzle and the substrate. A mechanism for the effects of these processing parameters interpreted as ‘the combustion zone’ has been proposed. This mechanism is used to explain the physical properties of films which were characterised using SEM and XRD. The FAVD technique is shown to be an efficient way in which SOFCs’ cathode film can be fabricated with tailoring of the desired phases and microstructure.

Flame assisted vapour deposition of cathode for solid oxide fuel cells. 2. Modelling of processing parameters

Flame assisted vapour deposition (FAVD) has been used to deposit porous lanthanum strontium manganese oxide (LSM) films for solid oxide fuel cell (SOFC) cathodes. The variation of microstructure of the deposited films with the processing parameters has been described in Part 1 of this paper. In parallel with the experiments, complementary modelling work of the turbulent flame was carried out using the finite volume CFD package FLUENT*. This was the first attempt in FAVD process modelling. The effects of varying experimental parameters such as the ratio of alcohol to water and the concentration of the precursor solution, have been investigated. The temperature distributions obtained from the modelling are consistent with the experimental results. The highest combustion temperature predicted from the model indicates the complete combustion process which yields powdery film in Part 1. Hence, the results in this paper confirm the trends for the experimental work.

Comparison of Anode and Electrolyte Support Configuration of Single-Chamber SOFC

The single-chamber solid oxide fuel cell (SOFC) has recently received considerable attention. This type of fuel cell operates in the mixed reactant gas and therefore does not require separation of the fuel and oxidant gases. In this paper we report the anode- and electrolyte-supported configurations of the single chamber SOFC that we have studied. The system based on typical fuel cell composition has been examined: yttrium stabilized zirconia (YSZ) as an electrolyte, nickel/YSZ cermet as an anode, lanthanum strontium manganese oxide (LSM) as a cathode. The cells were prepared by tape-casting and screen-printing techniques. The cathode processing parameters have been correlated with fuel cell performance. The results of the single chamber were compared with conventional SOFCs tested in our laboratory.

Liquid Compounds for CVD of Alkaline Earth Metals

AbstractThe first room-temperature liquid compounds useful for the CVD of alkaline earth metalcontaining oxides were prepared by reacting metal (Mg, Ca, Sr, and Ba) beta-diketonates with novel polyamine ligands. The compounds are monomeric and can be completely flash-vaporized without leaving any non-volatile residue detectable at the parts-per-million level. A stable, solvent-free liquid mixture was formed by mixing new liquid barium, strontium and titanium compounds. CVD experiments using direct liquid injection of this liquid mixture deposited films of barium strontium titanate. This approach should also be applicable to the deposition of many other multicomponent oxides containing alkaline earth metals: ferroelectrics (strontium bismuth tantalate), metallic conductors (strontium vanadium oxide, lanthanum strontium cobalt oxide), phosphors (calcium tungstate), non-linear optical materials (beta-barium borate), magnetic oxides (barium ferrite), colossal magnetoresistive materials (lanthanum strontium manganese oxide), high Tc superconductors (yttrium barium copper oxide, bismuth calcium strontium copper oxide) and microwave dielectrics (barium magnesium tantalate).

Fabrication of cathode for solid oxide fuel cells using flame assisted vapour deposition technique

Thick films of lanthanum strontium manganese oxide, La 1 − x Sr x MnO 3 (LSM), cathode material for solid oxide fuel cells, was deposited using the flame assisted vapour deposition method, a simple and cost-effective technique. The surface morphology and microstructure of porous cathode films were analysed using scanning electron microscopy. X-ray diffraction indicated the presence of a desirable lanthanum strontium manganese oxide phase at the deposition temperature of 710 °C. The interfacial resistance between the electrode and electrolyte was measured by an AC impedance method. The interfacial electrical resistance was measured to be comparable with existing literature. In addition, the effect of deposition temperatures on the film's microstructure was discussed.

Preparation of oxide film by the oxidation plating method

Oxide coating on a ceramic substrate using a new method was attempted with a view to applying the method to the direct preparation of an oxide air electrode, La 1−xSr x MnO 3, in solid oxide fuel cells. As a first step, the oxide of manganese which is a component of an oxide electrode was plated on a yttria stabilized zirconia substrate by oxidizing the manganese hydroxide using hydrogen peroxide as an oxidant. The film was firmly affixed to the substrate even before heat treatment, and SEM observation showed that it was relatively dense. Also an attempt to deposit lanthanum strontium manganese oxide was made using this new method.