Structure,chemical stability and electrical conductivity of perovskite La0.6Sr0.4M0.3Fe0.7O3−δ (M = Co,Ti) oxides

The perovskite La_0.6Sr_0.4M_0.3Fe_0.7O_3?δ (M = Co, Ti) powders have been synthesized by the citrate gel method. The structural and chemical stability of the La_0.6Sr_0.4M_0.3Fe_0.7O_3?δ (M = Co, Ti) oxides were studied by X-ray diffraction (XRD), differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) techniques. The electrical conductivities of the sintered La_0.6Sr_0.4M_0.3Fe_0.7O_3?δ (M = Co, Ti) ceramics were measured. The results demonstrate the chemical stability in H₂/helium (He) atmosphere of the La_0.6Sr_0.4Ti_0.3Fe_0.7O_3?δ oxide is improved significantly compared to that of the La_0.6Sr_0.4Co_0.3Fe_0.7O_3?δ oxide. The incorporation of Ti^3+/4+ ions in the perovskite structure can significantly stabilize the neighboring oxygen octahedral due to the stronger bonding strength, leading to the enhanced structural and chemical stability of the La_0.6Sr_0.4Ti_0.3Fe_0.7O_3?δ. In addition, the perovskite La_0.6Sr_0.4M_0.3Fe_0.7O_3?δ (M = Co, Ti) oxides possess much higher chemical stability in CO₂/He atmosphere than that of Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3?δ oxide, in which the perovskite structure is destroyed completely in a flowing CO₂-containing atmosphere.     

Magnetoimpedance effect in semiconducting La0.4Sr0.6MnO3

In the present work, it was found that for La_0.4Sr_0.6MnO₃, the dc resistance decreases with increasing temperature, from 77 to 280 K. Different from the case of metallic La_0.65Sr_0.35MnO₃, the ac impedance of the semiconducting La_0.4Sr_0.6MnO₃ at room temperature decreases with increasing frequency, from 100 kHz to 12 MHz. The magnetoimpedance effect was observed in La_0.4Sr_0.6MnO₃ at room temperature. The value of impedance ratio (Z(0)−Z(H))/Z(0) at H=0.8 kOe reaches 5% at a frequency of 500 kHz.     

Green synthesis of lanthanum oxide nanoparticles using Moringa oleifera leaves extract and its biological activities

Phytosynthesis is a reliable way to produce metal nanoparticles without affecting the environment. Plant extracts act as reducing agent and favors nanoparticle synthesis. Recently, potential drugs were developed in nanotechnology platforms by the green synthesis approach. In this study, the leaves extract of ‘Moringa Oleifera’ (M. oleifera) used as a reducing agent for the synthesis of Lanthanum oxide nanoparticles (La₂O₃ NPs). The X-ray diffraction (XRD) confirmed the formation of body-centered cubic structure of La₂O₃ NPs. The optical behavior of La₂O₃ NPs was analyzed by UV–Vis spectrum. The bandgap energy of the La₂O₃ NPs was found to be 4.31 eV using Tauc’s plot. The morphology and purity of La₂O₃ NPs was analyzed by using Field Emission Scanning Electron Microscope (FESEM) and Energy Dispersive X-ray (EDX) spectrum. High Resolution Transmission Electron Microscope (HR-TEM) analysis reveals the morphology, lattice spacing, and selected area electron diffraction (SAED) pattern of the La₂O₃ NPs. The XPS analysis of the La₂O₃ NPs reveals the binding energy of La (3d_5/2 and 3d_3/2) and O 1s at 835.5, 852.3, and 536 eV respectively. The total antioxidant activity (TOA) of La₂O₃ NPs was found to be 75.32% at 500 µg/mL with the standard drug of vitamin C. The anti-inflammatory activity of the La₂O₃NPs was found to be 94.15% at 500 µg/mL using the bovine serum albumin denaturation (BSA) technique. The inhibitory activity of La₂O₃ NPs against α-amylase was found to be 79.99% at 500 µg/mL. In summary, the pure, highly stable and good biocompatible, greener approach based M. oleifera assisted La₂O₃ was synthesized for radical scavenging, α-amylase and BSA denaturation inhibition activities which can play a key role in the future biomedical and nano-biotechnological applications.     

Significant improvement of the oxygen permeation flux of tubular Ba0.5Sr0.5Co0.8Fe0.2O3 − δ membranes covered by a thin La0.6Sr0.4Ti0.3Fe0.7O3 − δ layer

We present a new method to improve the oxygen flux properties and stability of Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3 − δ tube membrane using a thin layer of La_0.6Sr_0.4Ti_0.3Fe_0.7O_3 − δ as protective coatings. The first relevant result is that the La_0.6Sr_0.4Ti_0.3Fe_0.7O_3 − δ protective layer had an extraordinary positive effect on improving the oxygen permeation flux of the tubular Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3 − δ membranes. La_0.6Sr_0.4Ti_0.3Fe_0.7O_3 − δ-coated Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3 − δ tubular membrane showed the highest oxygen permeability with the flux reaching ~ 3 ml cm⁻² min⁻¹ (oxygen purity > 99%) at 950 °C in static atmospheric pressure through a 1.0 mm thick membrane.     

Ba<Subscript>1−x</Subscript>La<Subscript>x</Subscript>Fe<Subscript>12</Subscript>O<Subscript>19</Subscript> (x = 0.0, 0.2, 0.4, 0.6) hollow microspheres: material parameters,magnetic and microwave absorbing properties

Ba_1?xLa_xFe₁₂O₁₉ (x = 0.0, 0.2, 0.4, 0.6) hollow ceramic microspheres (HCMs) have been prepared by combining self-reactive quenching method with heat treatment. Their material parameters, magnetic and microwave absorbing properties were investigated. It was observed that after doping of lanthanum, the material parameters showed a little change except hexagonal crystal disappearing. And the magnetic properties of HCMs were decided by lanthanum content and material parameters. With the lathanum increases from 0.0 to 0.6, the saturation magnetization (Ms) values initially increased, and then decreased sharply to a minimum value, and increased again, moreover, the coercive force (Hc) values were reduced first, and then increased, and decrease to a minimum value. Absorbing properties tests indicate that after La³⁺-doped, at 2 mm thickness, the effective absorbing band (<?10 dB) was reduced to 4.7, 5 and 4.4 GHz, respectively, the minimum reflectance would decrease in low substituted level (x ≤ 0.4) and increase in high level (x = 0.6), and the frequency shifts to low frequency with the increasing of doping content. In 1.5–3 mm range, with the increasing of thickness, the absorption peak of Ba_1?xLa_xFe₁₂O₁₉ (x = 0.2, 0.4, 0.6) HCMs shifts to low frequency and the absorption intensity increases, the effective absorbing band can up to 10, 8.1 and 8 GHz, respectively.     

Ferroic metal-oxide films grown by polymer assisted deposition

Polymer assisted deposition is a versatile technique to grow simple and complex metal-oxide thin films. In this paper we report the structural and electrical properties of ferroic materials, namely La_0.67M_0.33MnO₃ (M = Sr and Ca) and Ba_1 − xSr_xTiO₃ (x = 0.3, 0.5, and 0.7) prepared using this process. The films were prepared on single crystalline LaAlO₃ substrates. The films were highly c-axis oriented and epitaxial in nature. The ferromagnetic La_0.67Sr_0.33MnO₃ and La_0.67Ca_0.33MnO₃ films show intrinsic transport properties with maximum magnetoresistance values (at applied field of 5 T) of − 50% and − 88%, respectively. The highest dielectric constant (∼ 1010) and tunability (∼ 69%) of Ba_1 − xSr_xTiO₃ film occurs at x = 0.3 for films, which is at the phase boundary of tetragonal and cubic.     

Field Effects in Thin Films of Manganites Using a Planar Field Effect Configuration

Modulation of the metal-insulator phase transition of perovskite manganite oxides is achieved by a static electric field. The field is applied using a planar field-effect configuration, which was formed on a monolayer film. In such a field-effect configuration, La_1−x A _x MnO₃ film is used as the channel and substrate acts as the gate. Both divalence-doped (La_0.7Ba_0.3MnO₃, Pr_0.7Sr_0.3MnO₃), and tetravalence-doped (La_0.7Ce_0.3MnO₃) systems demonstrate significant field effects. The field modulations are found being nonlinear and polarity dependent on the applied bias. The results obtained in La_0.7Ce_0.3MnO₃ indicates that electron doped manganites have similar features as those found in hole doped manganites. The observed field effects were discussed with the percolative phase separation picture.     

Theoretical Investigation of Magnetocaloric Effect in La0.6Ca0.2Ba$_{0.15}\square _{0.05}$MnO3 Manganite

In this paper, the prediction of the magnetocaloric properties has been investigated in the La_0.6Ca_0.2Ba\(_{\mathrm {0.15}}\square _{\mathrm {0.05}}\)MnO₃ system near the ferromagnetic-paramagnetic phase transition as a function of temperature. The data indicate that the La_0.6Ca_0.2Ba\(_{\mathrm {0.15}}\square _{\mathrm {0.05}}\)MnO₃ system has potential application for magnetic refrigerants in an extended high-temperature range. In addition, the magnetic entropy change distribution is quite uniform, which is desirable for an Ericsson cycle magnetic refrigerator.     

Synthesis of La0.5A0.5MnO3 (A = Sr, Ba) by a hydrothermal method at low temperature

A mild hydrothermal method has been adopted to prepare La_0.5Sr_0.5MnO₃ and La_0.5Ba_0.5MnO₃, which is of interest for a number of possible applications. The results from X-ray diffraction (XRD) indicate that in the present work the temperature of 200 and 240 °C are sufficient to prepare phase pure La_0.5Sr_0.5MnO₃ and La_0.5Ba_0.5MnO₃ crystals. At 200 °C, La_0.5Sr_0.5MnO₃ nanowires are obtained. The average width and length of the nanowires are 40 nm and 4 μm, respectively. At 240 °C, La_0.5Ba_0.5MnO₃ powders obtained have a cubic structure with the average size of 3-5 μm.     

Electrochemical performance of La2NiO4+δ-La0.6Sr0.4Co0.2Fe0.8O3−δ composite cathodes for intermediate temperature solid oxide fuel cells

The composite cathodes La₂NiO_4+δ-La_0.6Sr_0.4Co_0.2Fe_0.8O_3−δ were prepared for intermediate temperature solid oxide fuel cells. La₂NiO_4+δ and La_0.6Sr_0.4Co_0.2Fe_0.8O_3−δ powders were synthesized successfully by glycine-nitrate process. The effect of composition on the electrochemical performance of the composite electrodes was studied by AC impedance spectroscopy and the optimal calcination temperature was determined when the electrode showed the minimum area specific resistance. The addition of La_0.6Sr_0.4Co_0.2Fe_0.8O_3−δ to La₂NiO_4+δ electrode decreased the area specific resistance remarkably. The composite electrode with 30 wt% La_0.6Sr_0.4Co_0.2Fe_0.8O_3−δ calcined at 1150 °C exhibited the lowest area specific resistance of 0.125 Ω cm², about 60% of the area specific resistance of La₂NiO_4+δ electrode at 700 °C in air. The composite electrode with 30 wt% La_0.6Sr_0.4Co_0.2Fe_0.8O_3−δ can be a promising cathode material through the evaluation of electrical conductivity and thermal expansion behavior.     

Electrical conductivity of LaxSr2−xFe1−yRuyO4±δ

Materials of the K₂NiF₄ structure type have been prepared and the electrical conductivity in air determined for a number of compositions in the La_xSr_2−xFe_1−yRu_yO_4±δ solid solution series including three with Ru substituted for Fe on the B site: La_0.2Sr_1.8Fe_0.6Ru_0.4O_4±δ, La_0.4Sr_1.6Fe_0.7Ru_0.3O_4±δ, and La_0.6Sr_1.4Fe_0.8Ru_0.2O_4±δ. Overall the total conductivity values measured were lower than expected for the Ru-doped materials, with a peak conductivity of ≈2 S cm⁻¹ at 700 °C. In the undoped La_xSr_2−xFeO_4±δ materials, a significant jump in conductivity was observed between the x = 0.7 and 0.8 compositions and was related to the bonding in the materials and the Fe³⁺/Fe⁴⁺ redox behaviour. In all materials, the conduction behaviour was found to follow a semi-conducting trend.     

Combined platinum/perovskite catalyst for an efficient nanostructured air electrode

This work shows the stepwise improvement of air electrodes by the right combination of catalysts. In all electrodes carbon nanotubes serve as carbon support. The electrodes are produced by ultrasonic mixing of the carbon nanotubes and the catalysts. Their catalytic activity towards oxygen reduction in alkaline solution is evaluated by polarisation curves and electrochemical impedance spectroscopy. In a first step La_1?xSr_xMnO₃ perovskites are investigated, as well as La_0.65Sr_0.35MnO₃ and La_0.6Sr_0.4CoO₃ are compared. It is found that La_0.65Sr_0.35MnO₃ and La_0.6Sr_0.4CoO₃ have a positive impact on different parts of the current–potential curve. In a second step the influence of small amounts of platinum as an additional catalyst besides the perovskite is analyzed with the result that platinum lowers significantly the activation polarisation. Finally, the optimum composition of the electrode is found by using the synergetic effect of platinum, La_0.65Sr_0.35MnO₃ and La_0.6Sr_0.4CoO₃.     

Electrochemical performance of (La,Sr)(Co,Fe)O3−δ–(Ce,Sm)O2−θ–CuO composite cathodes for intermediate temperature solid oxide fuel cells

La_0.6Sr_0.4Co_0.2Fe_0.8O_3?δ–Ce_0.8Sm_0.2O_2?θ–CuO composite cathodes were studied for the potential application in intermediate temperature solid oxide fuel cells. Ce_0.8Sm_0.2O_2?θ electrolyte with porous Ce_0.8Sm_0.2O_2?θ interlayer was successfully prepared by one-step sintering process. The effect of interlayer between cathode and electrolyte and CuO on the electrochemical performance of the composite cathodes was investigated by AC impedance spectroscopy. The application of interlayer decreased the area specific resistance of La_0.6Sr_0.4Co_0.2Fe_0.8O_3?δ–Ce_0.8Sm_0.2O_2?θ cathode. The addition of CuO to La_0.6Sr_0.4Co_0.2Fe_0.8O_3?δ reduced the phase formation temperature of La_0.6Sr_0.4Co_0.2Fe_0.8O_3?δ by 150 °C and the addition of CuO to La_0.6Sr_0.4Co_0.2Fe_0.8O_3?δ–Ce_0.8Sm_0.2O_2?θ cathode reduced the optimal calcination temperature of the cathode to 800 °C. The composite cathode with 2 mol% CuO calcined at 800 °C exhibited the lowest area specific resistance of 0.05 Ω cm² at 700 °C in air, which was reduced by 67% compared with that of La_0.6Sr_0.4Co_0.2Fe_0.8O_3?δ–Ce_0.8Sm_0.2O_2?θ cathode. The studies of the corresponding single cell performance, thermal expansion and thermal cycling behaviors further indicated that the composite cathode with 2 mol% CuO could be a promising cathode material.     

Appearance of Griffiths Phase in La0.7−x Pr x Ba0.3MnO3 (0 ≤x≤ 0.2)

Polycrystalline La_0.7?x Pr _x Ba_0.3MnO₃ (0 ≤x≤ 0.2) samples were prepared using solid-state reaction and checked by X-ray diffraction. Magnetization measurements versus temperature and applied magnetic field were used to investigate their magnetic properties. For samples with x= 0.2, the Griffiths phase is observed when the inverse of susceptibility (1/ χ vs. T) is analyzed.     

Microstructure and NO decomposition behavior of sol-gel derived (La0.8Sr0.2)0.95MnO3/yttria-stabilized zirconia nanocomposite thin film

(La_0.8Sr_0.2)_0.95MnO₃ and (La_0.8Sr_0.2)_0.95MnO₃/YSZ gel films were deposited by a spin-coating technique on scandium-doped zirconia (ScSZ) substrate using the precursor solution prepared from La(Oi-C₃H₇)₃, Sr(Oi-C₃H₇)₂, Mn(Oi-C₃H₇)₂ and 2-methoxyethanol. By heat-treating the gel films, the membrane reactors, (La_0.8Sr_0.2)_0.95MnO₃|ScSZ|Pt and (La_0.8Sr_0.2)_0.95MnO₃/YSZ|ScSZ|Pt were fabricated. It was found that the pre-firing temperature affected the microstructure evolution of (La_0.8Sr_0.2)_0.95MnO₃ and (La_0.8Sr_0.2)_0.95MnO₃/YSZ thin films. Pre-firing at low temperature resulted in high porosity and large grain size of the thin films. NO decomposition characteristics of the obtained membrane reactors were investigated at 600 °C in reactant gas, 1000 ppm of NO and 2% of oxygen. By applying a direct current to the membrane reactors, NO can be decomposed at the (La_0.8Sr_0.2)_0.95MnO₃ and (La_0.8Sr_0.2)_0.95MnO₃/YSZ composite cathode. By incorporating YSZ into (La_0.8Sr_0.2)_0.95MnO₃, the required consuming power to decompose NO could be reduced.     

Magnetic entropy change in the monovalent doping La<Subscript>0.7</Subscript>Ba<Subscript>0.2</Subscript>M<Subscript>0.1</Subscript>MnO<Subscript>3</Subscript> (M = Na,Ag, K) manganites

Structural, magnetic, and magnetocaloric properties of monovalent doped La_0.7Ba_0.2M_0.1MnO₃ (M = Na, Ag, K) powder samples, synthesized using the solid state reaction at high temperature, have been experimentally investigated. The Rietveld refinement of the X-ray powder diffraction shows that all our synthesized samples are single phase and crystallize in the distorted rhombohedral system with space group. Lattice parameters and the unit cell volume increases with increasing average A-site ionic radius 〈r _A〉. The Mn–O–Mn bond angle decreases with increasing 〈r _A〉, ranging from 168.32° (M = Na) to 165.91° (M = K). All our studied samples undergo a paramagnetic–ferromagnetic transition. The Curie temperature T _C, shifts slightly to a lower temperature with increasing 〈r _A〉, which is consistent with large cationic disorder. Magnetic entropy change, , deduced from isothermal magnetization curves, reaches 3.04, 3.14, and 3.01 J/kg K for M = Na, Ag, and K, respectively, in a magnetic applied field change of 5T. Large relative cooling power (RCP) value of 337.9 J/kg is obtained for La_0.7Ba_0.2K_0.1MnO₃ sample, at a field change of 5T. This relatively large value associated to a Curie temperature of 311.5 K makes the present compound a promising candidate for the magnetic refrigerators around room temperature.     

Phase formation mechanism and kinetics in solid-state synthesis of undoped and calcium-doped lanthanum manganite

LaMnO_3+δ and La_0.7Ca_0.3MnO₃ were synthesized from La₂O₃(La(OH)₃), CaCO₃ and MnO₂ powder mixture with solid-state reaction technique. X-ray diffraction and thermal analysis were employed in the present study on the process of synthesizing of the two compound powders. The kinetic study on solid-state reaction between La₂O₃ and MnO₂ in the powder mixture was isothermally carried out for LaMnO_3+δ formation. The result showed that the reaction process was controlled by three-dimensional solid-ionic diffusion. Both Jander and Ginstling-Brounstein model can be used to describe the reaction kinetics satisfactorily. The relevant apparent activation energy values obtained were as great as 205 ± 11 and 189 ± 8 kJ/mol. The reaction process of La_0.7Ca_0.3MnO₃ preparation from La₂O₃, SrCO₃ and MnO₂ powder mixture was also studied using X-ray diffraction and thermal analysis. The result indicated that the following steps composed the overall reaction: the decomposition of the reactant; the formation of La_1−xCa_xMnO_3+δ; La₂O₃ and Mn₃O₄ reacted with La_1−xCa_xMnO₃ to form final La_0.7Ca_0.3MnO₃ phase. The latest step was the most time-consuming one among others in the overall reaction.     

Preparation and properties of thick LaMnO3-based films

Thick (50 ±10 μm) La_1-xSr_xMnO₃ (x = 0.2, 0.4) and La_0.7Ca_0.3Mn0₃ films were prepared by screen printing, and their electrical properties were studied. The films were found to be close in magnetoresistance and resistivity to bulk materials     

Ferroelectric and pyroelectric properties of (Na0.5Bi0.5)TiO3-BaTiO3 based trilayered thin films

Trilayered Bi_3.25La_0.75Ti₃O₁₂ (25 nm)/(Na_0.5Bi_0.5)_0.94Ba_0.06TiO₃ (300 nm)/Bi_3.25La_0.75Ti₃O₁₂ (25 nm) and Pb(Zr_0.4Ti_0.6)O₃ (25 nm)/(Na_0.5Bi_0.5)_0.94Ba_0.06TiO₃ (300 nm)/Pb(Zr_0.4Ti_0.6)O₃ (25 nm) thin films without undesirable phases have been deposited on Pt/Ti/SiO₂/Si substrates. It was found that the Bi_3.25La_0.75Ti₃O₁₂ and Pb(Zr_0.4Ti_0.6)O₃ layers are very effective to inhibit the charge transport in the trilayered films. Much better insulating properties than those of (Na_0.5Bi_0.5)_0.94Ba_0.06TiO₃ films have been achieved in the trilayered films. The trilayered films show good dielectric, ferroelectric and pyroelectric properties. Remnant polarizations 2P_r of 16 µC/cm² and 34 µC/cm², pyroelectric coefficients of 4.8 × 10^− 4 C m^− 2 K^− 1 and 7.0 × 10^− 4 C m^− 2 K^− 1 have been obtained for the Bi_3.25La_0.75Ti₃O₁₂/(Na_0.5Bi_0.5)_0.94Ba_0.06TiO₃/Bi_3.25La_0.75Ti₃O₁₂ and Pb(Zr_0.4Ti_0.6)O₃/(Na_0.5Bi_0.5)_0.94Ba_0.06TiO₃/Pb(Zr_0.4Ti_0.6)O₃ thin films, respectively. The trilayered films are promising candidates for sensor and actuator applications.     

Synthesis and magnetocaloric properties of La0.85K0.15MnO3 nanoparticles

In this paper, La_0.85K_0.15MnO₃ nanoparticles were successfully synthesized at relatively low calcinated temperature from a polyaminocarboxylate complex precursor with diethylenetriaminepentaacetic acid (H₅DTPA) as ligand, and the magnetocaloric properties were investigated. The phase transformation, chemical composition, and microstructure of La_0.85K_0.15MnO₃ nanoparticles were characterized by X-ray diffraction (XRD), thermogravimetric (TG), differential scanning calorimetry (DSC), transmission electron microscopy (TEM) and electron diffraction (ED). The results revealed that La_0.85K_0.15MnO₃ nanoparticles calcined at temperatures within the range of 600–1000 °C are of pure single-phase rhombohedral structure and the grain sizes were precisely controlled by varing the calcined temperature. The relationship between magnetocaloric properties and the calcined temperature of La_1?xK_xMnO₃ nanoparticles was also investigated systematically. From the magnetic measurements as function of temperature and magnetic applied field, we have discovered that the Curie temperature T_C is 274.5 K and is independent of the calcined temperature. From the measurements and calculation of isothermal magnetization at different temperatures, the maximum magneticentropy changes close to T_C (274 K) of the samples calcined at 600 °C, 800 °C and 1000 °C are 2.02, 3.06 and 3.56/kg K at H = 2T, respectively. Also La_0.85K_0.15MnO₃ nanoparticle displays a second-order phase transition. These results suggest that this material is a candidate for use as an active for magnetic refrigerent around the room temperature.