Enhanced Shrinkage of Lanthanum Strontium Manganite (La0.90Sr0.10MnO3+δ) Resulting from Thermal and Oxygen Partial Pressure Cycling (original) (raw)
Related papers
Journal of the American Ceramic Society, 2007
Exposure of (La 0.90 Sr 0.10 ) 0.98 MnO 31d (LSM-10) to repeated oxygen partial pressure cycles (air/10 ppm O 2 ) resulted in enhanced densification rates, similar to behavior shown previously due to thermal cycling. Shrinkage rates in the temperature range 7001-10001C were orders of magnitude higher than Makipirtti-Meng model estimations based on stepwise isothermal dilatometry results at a high temperature. A maximum in enhanced shrinkage due to oxygen partial pressure cycling occurred at 9001C. Shrinkage was the 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 are reestablished, whereas the latter condition does not lead to excess vacancy concentrations.
Low-Temperature Densification of Lanthanum Strontium Manganite (La 1−x Sr x MnO 3+δ ), x =0.0-0.20
Journal of the American Ceramic Society, 2009
Intermediate-stage sintering of lanthanum strontium manganite (LSM, where Sr 5 0.00, 0.05, 0.10, 0.15, and 0.20) was shown in dilatometry studies to be accelerated when subjected to alternating flows of air and nitrogen. The extent of rate enhancement decreased with increased Sr content, and decreased with increased temperature, which coincides with diminished oxygen nonstoichiometry. Shrinkage rates were further shown to be sensitive to the difference in oxygen content in the alternating gas flows. Baseline air sintering rates were measured using stepwise isothermal dilatometry, from which kinetic parameters were calculated using the Makipirtti-Meng model. Activation energies for sintering in air were determined to be 255726, 258728, 308732, 373737, and 417741 kJ/mol for Sr 5 0.0, 0.05, 0.10, 0.15, and 0.20, respectively. A diffusion-based model is proposed that is consistent with trends in accelerated shrinkage versus temperature. Transient cation vacancy gradients, which lead to higher cation mobility, were calculated from established oxygen diffusivities and oxygen nonstoichiometry as a function of temperature and time. A potential application of this approach is the processing of LSM-based cathode-side contact pastes in solid oxide fuel cells. (2) Sintering Studies Porous samples of LSM-0, LSM-5, LSM-10, LSM-15, and LSM-20 were subjected to repeated cycles of air exposure for P. Clem-contributing editor
Oxygen transport in nanostructured lanthanum manganites
Physical Chemistry Chemical Physics, 2013
Methods and models describing oxygen diffusion and desorption in oxides have been developed for slightly defective and well crystallised bulky materials. Does nanostructuring change the mechanism of oxygen mobility? In such a case, models should be properly checked and adapted to take into account new material properties. In order to do so, temperature programmed oxygen desorption and thermogravimetric analysis, either in isothermal or ramp mode, have been used to investigate some nanostructured La 1-x A x MnO 3±δ samples (A=Sr and Ce, 20-60 nm particle size) with perovskite-like structure. The experimental data have been elaborated by means of different models to define a set of kinetic parameters able to describe oxygen release properties and oxygen diffusion through the bulk. Different rate-determining steps have been identified, depending on the temperature range and oxygen depletion of the material. In particular, oxygen diffusion shows rate-limiting at low temperature and with low defect concentration, whereas oxygen recombination at the surface seems to be the rate-controlling step at high *
Influence of Pellet Compaction Pressure on the Physical Properties of La0.7Ba0.3MnO3 Manganite
2017
Perovskite manganite La0.7Ba0.3MnO3, synthesized by ionic coordination reaction method (ICR) was compacted into pellets under different compaction pressures (Pc) and sintered at a temperature of 1150°C for 10h under a flow of O2. X-ray diffraction (XRD) data reveal that the samples can present simultaneously two phases a rhombohedral structure with space group R3c and an orthorhombic structure with space group Pnma. Scanning electron microscopy (SEM) images show that, for this sintering temperature, the particle size and shape can be modified depending on the compaction pressure (Pc). Magnetization measurements show that the saturation magnetization and Curie temperature increase with Pc. The enhancement of the ferromagnetic properties of perovskite manganites La0.7Ba0.3MnO3 as a function of the compaction pressure is explained by an increase in the rhombohedral/orthorhombic structure ratio caused by this effect.
Thermodynamic properties of doped lanthanum manganites
Materials Research Bulletin, 1994
The thermodynamic properties of the perovskite compounds La[sub 0.8]Sr[sub 0.2]MnO[sub 3] (LSM), La[sub 0.9]Na[sub 0.1]MnO[sub 3] (LNM), and LaMnO[sub 3] (LM) were studied by use of the solid electrolyte galvanic cell method at 1,000 C, 1,050 C, and 1,100 C. Two samples of each compound were investigated as well as decomposed samples of LSM and LNM. The cell assembly was constructed by means of eight small stabilized zirconia tubes and a common Ni/NiO reference electrode. The equilibrium partial pressures of the samples were calculated form the measured EMF values. The results reveal that the equilibrium pO[sub 2] of LM appears to be one or two orders of magnitude lower than that of LSM and LNM, respectively, which means that LM is more stable than the doped perovskites. The variation in the standard free energy with temperature for the perovskite decomposition reaction was calculated from the pO[sub 2] equilibrium values, i.e. [Delta]G[degree]d (LSM) = 140.86 [minus] 0.05199T kJ/mole and [Delta]G[degree]d (LNM) = 106.06 [minus] 0.02572T kJ/mole. On the basis of the above equations, the reaction enthalpy and entropy changes were calculated. Perovskite oxides have received considerable attention in recent years for their use as cathodes in solid oxide fuel cells.
Journal of Solid State Chemistry, 2000
We present the oxygen deficiency effects on the structural, magnetic, and electrical properties in La 0.7Sr 0.3MnO 3- δ□ δ solution where □ is a vacancy and 0≤ δ≤0.15. Polycrystalline samples La 0.7Sr 0.3MnO 3- δ□ δ were synthesized by a new method. In this series of manganites the Mn 3+ content is systematically increased due to the increase in the nonstoichiometry δ. X-ray diffraction analysis shows a phase transition from a rhombohedral to an orthorhombic system at 0.075≤ δ≤0.1. The material is ferromagnetic for 0≤ δ≤0.1 and antiferromagnetic for 0.125≤ δ≤0.15. The Curie temperature TC and saturation magnetization Ms decrease with increasing δ. Resistivity measurements as a function of temperature show a remarkable behavior for the La 0.7Sr 0.3MnO 2.9 compound; it is ferromagnetic metallic for 115≤ T≤180 K and becomes ferromagnetic insulator below 115 K, where a charge ordering seems to appear. The difference in the hopping energies in our samples can be related to the existence of two crystallographic structures, one orthorhombic and the other rhombohedral.
Journal of Solid State Chemistry, 2000
We present the oxygen de5ciency e4ects on the structural, magnetic, and electrical properties in La 0.7 Sr 0.3 MnO 3؊ ) solution where ) is a vacancy and 04 40.15. Polycrystalline samples La 0.7 Sr 0.3 MnO 3؊ ) were synthesized by a new method. In this series of manganites the Mn 3؉ content is systematically increased due to the increase in the nonstoichiometry . X-ray di4raction analysis shows a phase transition from a rhombohedral to an orthorhombic system at 0.0754 40.1. The material is ferromagnetic for 04 40.1 and antiferromagnetic for 0.1254 40.15. The Curie temperature T C and saturation magnetization M s decrease with increasing . Resistivity measurements as a function of temperature show a remarkable behavior for the La 0.7 Sr 0.3 MnO 2.9 compound; it is ferromagnetic metallic for 1154T4180 K and becomes ferromagnetic insulator below 115 K, where a charge ordering seems to appear. The di4erence in the hopping energies in our samples can be related to the existence of two crystallographic structures, one orthorhombic and the other rhombohedral.
Physical Review B, 2003
The pressure dependence of the resistivity and structure of La 0.60 Y 0.07 Ca 0.33 MnO 3 has been explored in the pressure range from 1 atm to ϳ7 GPa. The metal to insulator transition temperature (T MI ) was found to reach a maximum and the resistivity achieves a minimum at ϳ3.8 GPa. Beyond this pressure, T MI is reduced with a concomitant increase in the resistivity. Structural measurements at room temperature show that at low pressure ͑below 2 GPa͒ the Mn-O bond lengths are compressed. Between ϳ2 and ϳ4 GPa, a pressure-induced enhancement of the Jahn-Teller ͑JT͒ distortion occurs in parallel with an increase in Mn-O1-Mn bond angle to ϳ180°. Above ϳ4 GPa, the Mn-O1-Mn bond angle is reduced, while the JT distortion appears to remain unchanged. The resistivity above T MI is well modeled by variable range hopping. The pressure dependence of the localization length follows the behavior of T MI .
Pressure-Induced Magnetic Transition in Manganite (La0.75Ca0.25MnO3
Physical Review Letters, 2009
Low temperature Mn K-edge x-ray magnetic circular dichroism and x-ray diffraction measurements were carried out to investigate the stability of the ferromagnetic ground state in manganite La 0:75 Ca 0:25 MnO 3 under nearly uniform compression using diamond anvil cells. The magnetic dichroism signal gradually decreases with pressure and disappears at 23 GPa, and meanwhile a uniaxial compression of MnO 6 octahedra along the b axis is observed to continuously increase with pressure and become anomalously large at 23.5 GPa. These changes are attributed to a ferromagnetic-antiferromagnetic transition that is associated with orbital ordering at high pressure.
The properties of half-metallic manganite thin films depend on the composition and structure in the atomic scale, and consequently, their potential functional behavior can only be based on fine structure characterization. By combining advanced transmission electron microscopy, electron energy loss spectroscopy, density functional theory calculations, and multislice image simulations, we obtained evidence of a 7 nm-thick interface layer in La 0.7 Sr 0.3 MnO 3 (LSMO) thin films, compatible with the formation of wellknown dead layers in manganites, with an elongated out-of-plane lattice parameter and structural and electronic properties well distinguished from the bulk of the film. We observed, for the first time, a structural shift of Mn ions coupled with oxygen vacancies and a reduced Mn valence state within such layer. Understanding the correlation between oxygen vacancies, the Mn oxidation state, and Mn-ion displacements is a prerequisite to engineer the magnetotransport properties of LSMO thin films.