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.     

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 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.     

Fabrication of (La1−x Gd x )2/3Sr1/3MnO3 Manganite Perovskite Nanorods by Sonication-Assisted Coprecipation

(La_1?x Gd _x )_2/3Sr_1/3MnO₃ manganite perovskite nanorods were synthesized by sonication-assisted coprecipitation. Lower sintering temperatures were required for all the samples to crystallize. The fully crystallize samples of (La_0.5Gd_0.5)_2/3Sr_1/3MnO₃ and (La_0.4Gd_0.6)_2/3Sr_1/3MnO₃ show the formation of nanorods upon their synthesis with an average length and width of 160 nm and 20 nm, respectively. The structural, electrical, and magnetic transport properties were investigated.     

Doping effects on the physicochemical and electrochemical properties of lanthanum manganite

The structural, thermal, electrical, and electrochemical properties of La_0.7Ca_0.3Mn_1-x(Co,Ni)_xO₃ and La_0.6Sr_0.4Mn_1-x(Co,Ni)_xO₃ (x = 0, 0.02, 0.05, 0.1) electrode materials were studied. Doping of the cubic perovskites with Co or Ni increases the fraction of Mn4+ ions, up to 49% in La_0.7Ca_0.1O₃ and 57% in La_0.6Sr_0.4Mn_0.95Co_0.05O₃. The 300-K conductivity of La_0.7Ca_0.3Mn_1-xNi_xO₃ passes through a maximum atx = 0.05, while that of La_0.6Sr_0.4Mn_1-xCo_xO₃ decreases steadily with increasingx. In the range 300–1100 K, the conductivity of the Ca-containing manganites exhibits semiconducting behavior, whereas that of the Sr-containing materials shows metallic behavior. No phase transformations were detected in this temperature range. In the four systems, the thermal-expansion coefficients are virtually independent ofx. In both undoped and doped electrode materials, the resistance parameterp/d of electrode layers on solid-electrolyte substrates shows semiconducting behavior at temperatures from 300 to 1100 K and oxygen partial pressures from 102 to 105 Pa. With increasing oxygen partial pressure or electrode-layer thickness (d = 15–100 mg/cm2),p/d decreases. The optimal electrode-layer thickness is found to be about 50 mg/cm2. The introduction of Co or Ni into the electrode materials decreases the polarization resistance of the electrode layer in gas/electrode/electrolyte systems. Compositions ensuring the lowest polarization resistance were found.     

Synthesis and characterization of perovskite type of La1-xBaxMnO3 nanoparticles with investigation of biological activity

The enhanced biological activity of perovskite type La_1-xBa_xMnO₃ (x = 0.2, 0.3, 0.4) nanoparticle was studied based on antioxidant, antimicrobial, anti-biofilm, bacterial viability inhibition, and DNA cleavage studies. The nanoparticles were prepared by Sol-gel technique and they were analyzed on structure and morphological by XRD and SEM. La_0.6Ba_0.4MnO₃ showed the highest DPPH free radical scavenging activity and iron chelating activity as 67.23% and 46.54%, respectively. All tested lanthanum nanoparticles showed good chemical nuclease activity. C. tropicalis was the most affected species by lanthanum nanoparticles and MIC values were 4 µg/mL, 8 µg/mL, and 16 µg/mL for La_0.7Ba_0.4MnO₃, La_0.6Ba_0.4MnO₃, and La_0.8Ba_0.2MnO₃, respectively. La_0.7Ba_0.4MnO₃ exhibited the highest percentage of biofilm inhibition against P. aeruginosa and S. aureus as 99.78% and 98.38%, respectively. Cell viability assay demonstrated that La_0.7Ba_0.4MnO₃, La_0.6Ba_0.4MnO₃, and La_0.8Ba_0.2MnO₃ showed %100 cell viability inhibition after 30 and 60 min treatment.     

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.     

Electronic conduction in La-based perovskite-type oxides

Abstract

A systematic study of La-based perovskite-type oxides from the viewpoint of their electronic conduction properties was performed. LaCo_0.5Ni_0.5O_3±δ was found to be a promising candidate as a replacement for standard metals used in oxide electrodes and wiring that are operated at temperatures up to 1173 K in air because of its high electrical conductivity and stability at high temperatures. LaCo_0.5Ni_0.5O_3±δ exhibits a high conductivity of 1.9 × 10³ S cm^?1 at room temperature (R.T.) because of a high carrier concentration n of 2.2 × 10²² cm^?3 and a small effective mass m? of 0.10 m_e. Notably, LaCo_0.5Ni_0.5O_3±δ exhibits this high electrical conductivity from R.T. to 1173 K, and little change in the oxygen content occurs under these conditions. LaCo_0.5Ni_0.5O_3±δ is the most suitable for the fabrication of oxide electrodes and wiring, though La_1?xSr_xCoO_3±δ and La_1?xSr_xMnO_3±δ also exhibit high electronic conductivity at R.T., with maximum electrical conductivities of 4.4 × 10³ S cm^?1 for La_0.5Sr_0.5CoO_3±δ and 1.5 × 10³ S cm^?1 for La_0.6Sr_0.4MnO_3±δ because oxygen release occurs in La_1?xSr_xCoO_3±δ as elevating temperature and the electrical conductivity of La_0.6Sr_0.4MnO_3±δ slightly decreases at temperatures above 400 K.     

Effect of high temperature post-annealing of La0.7Sr0.3MnO3 films deposited by radio frequency magnetron sputtering on SiO2/Si substrates heated at low temperature

La_0.7Sr_0.3MnO₃ thin films were deposited on SiO₂/Si substrates by RF magnetron sputtering under different oxygen gas flow rates with a sputtering power of 100 W. During deposition, the substrate was heated at 623 K. To investigate post-annealing effects, the as-deposited La_0.7Sr_0.3MnO₃ thin films were thermal-treated at 973 K for 1 h. The effects of oxygen gas flow rate and post-annealing treatment on the physical properties of the films were systematically studied. X-ray diffraction results show that the growth orientation and crystallinity of the films were greatly affected by the oxygen gas flow rate and substrate heating during deposition. The sheet resistance of the films gradually decreased with increasing oxygen gas flow rate, while the post-annealed films showed the opposite behavior. The temperature coefficient of resistance at 300 K of La_0.7Sr_0.3MnO₃ thin films deposited at an oxygen gas flow rate of 40 sccm decreased from − 2.40%/K to − 1.73%/K after post annealing. The crystalline state of the La_0.7Sr_0.3MnO₃ thin films also affected its electrical properties.     

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.     

A La0.6Sr0.4CoO3−δ-based electrode with high durability for intermediate temperature solid oxide fuel cells

A highly stable electrode based on La_0.6Sr_0.4Co_3−δ (LSC) was developed for intermediate temperature solid oxide fuel cells (IT-SOFCs). The electrode was prepared by impregnating LSC into a porous samaria-doped ceria (SDC, Sm_0.2Ce_0.8O_1.9) frame, which was deposited to an SDC electrolyte using screen-printing and co-firing techniques. The electrochemical properties of the composite electrode were investigated by impedance spectroscopy. High stability upon thermal cycle was demonstrated for this composite electrode although LSC and SDC have significant difference in thermal expansion. After 20 times of 500-800 °C thermal cycles and 10 times of room-temperature-to-800 °C thermal cycles, no increase in area specific resistance (ASR) was observed for such electrodes. In addition, improved performance was achieved with the impregnated composite electrode when compared with a conventional composite electrode prepared with a screen-printing technique.     

Powder prepared by spray pyrolysis as an electrode material for solid oxide fuel cells

A variety of spray pyrolysis (SP) techniques have been developed to directly produce ceramic powders from solutions. Examples that are discussed include the following powders: (La_0.8Sr_0.2)_0.9MnO₃-YSZ (La(Sr)MnO₃-YSZ), La_0.6Sr_0.4CoO₃ (La(Sr)CoO₃), (CeO₂)_0.8(SmO_1.5)_0.2-NiO (SDC-NiO) and La_0.9Sr_0.1Ga_0.8Mg_0.2O₃-NiO (LSGM-NiO). For all these powders, spherical, non-agglomerated, submicrometer particles were obtained from aqueous solution of metal salts into a furnace using an ultrasonic atomizer at 1.7 MHz. After SP some of the particles exhibit a hollow-shell morphology. Subsequent calcination at 1000°C yielded crystalline particles. The electrical performance of Ni-SDC/LSGM/La(Sr)CoO₃ fuel cells operating at 800°C, prepared from the powders obtained by SP, is reported.     

Effects of Co and Fe addition on the properties of lanthanum strontium manganite

The effects of Co and Fe dopants with the amount of 20 and 40 mol% on the properties of La_0.84Sr_0.16MnO₃ were investigated. All compositions were prepared by conventional mixed oxide process and sintered at 1450 °C. The structure of undoped and Co-doped compositions was found to be monoclinic. In addition, the second phase was observed in these sintered compositions. The conductivity of doped materials decreased as compared to that of La_0.84Sr_0.16MnO₃. The SEM microstructure showed the decrease of grain size as Co content increased. The thermal expansion coefficient (TEC) tended to increase as Co content increased. In contrast, the monoclinic and orthorhombic structures were found in 20 and 40 mol% Fe-doped La_0.84Sr_0.16MnO₃. The amount of second phase in sintered composition depends on the amount of Fe content. The conductivity at 1000 °C decreased, but the grain size increased as Fe content increased. The thermal expansion coefficient slightly changed with Fe addition.     

Properties and performance of La1.6Sr0.4NiO4+δ-Ce0.8Sm0.2O1.9 composite cathodes for intermediate temperature solid oxide fuel cells

La_1.6Sr_0.4NiO_4+δ-Ce_0.8Sm_0.2O_1.9 composite cathodes were prepared successfully using combustion synthesis method for intermediate temperature solid oxide fuel cells. The chemical compatibility, thermal expansion behavior, electrical conductivity and electrode performance were studied. The X-ray diffraction of La_1.6Sr_0.4NiO_4+δ-Ce_0.8Sm_0.2O_1.9 composite result proved a slight reaction between La_1.6Sr_0.4NiO_4+δ and Ce_0.8Sm_0.2O_1.9. Both the thermal expansion coefficient and the electrical conductivity of La_1.6Sr_0.4NiO_4+δ-Ce_0.8Sm_0.2O_1.9 decreased with increasing Ce_0.8Sm_0.2O_1.9 content. AC impedance spectroscopy measurements indicated that the addition of 30 wt% Ce_0.8Sm_0.2O_1.9 to La_1.6Sr_0.4NiO_4+δ exhibited the lowest polarization resistance (0.238 Ωcm²) at 800 °C in air, which was only one fourth of the La_1.6Sr_0.4NiO_4+δ electrode measured at the same temperature.     

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.     

Effect of bottom electrodes on dielectric properties of high frequency Ba0.5Sr0.5TiO3 parallel plate varactor

Three types of Ba_0.5Sr_0.5TiO₃ (BST) thin film parallel plate varactor with different bottom electrodes were fabricated. The bottom electrodes of three types of varactor were perovskite conducting oxide La_0.7Sr_0.3MnO₃ (LSMO), Pt and Au, respectively. Dielectric properties of the BST thin films were characterized in the frequency range from 10 MHz to 15 GHz. The microstructure of the BST thin films was investigated by X-ray diffraction and scanning electron microscope. The microstructural analysis shows that the BST thin films grown on LSMO and Pt bottom electrodes are polycrystalline textured with columnar grains. Dielectric measurement indicates that the BST thin film grown on LSMO bottom electrode has a maximum dielectric constant and a little higher loss tangent.     

Positive Giant Magnetoresistance in La0.67Sr0.33MnO3/Alq3/Co Organic Spin-Valves

We report a positive spin valve effect—low resistance for parallel electrodes configuration—in organic spin valves fabricated by vacuum thermal evaporation using half-metal perovskite manganites La_0.67Sr_0.33MnO₃ as the bottom electrode, cobalt as the top electrode, and tris(8-hydroxyquinoline) aluminum (Alq₃) as the organic semiconductor spacer. A positive giant magnetoresistance (GMR) of ～12% has been observed at 100 K. The origination mechanism of negative and positive GMR in organic spin valves has been discussed in detail.     

Electronic conduction in La-based perovskite-type oxides

A systematic study of La-based perovskite-type oxides from the viewpoint of their electronic conduction properties was performed. LaCo_0.5Ni_0.5O_3±δ was found to be a promising candidate as a replacement for standard metals used in oxide electrodes and wiring that are operated at temperatures up to 1173 K in air because of its high electrical conductivity and stability at high temperatures. LaCo_0.5Ni_0.5O_3±δ exhibits a high conductivity of 1.9 × 10³ S cm⁻¹ at room temperature (R.T.) because of a high carrier concentration n of 2.2 × 10²² cm⁻³ and a small effective mass m∗ of 0.10 m_e. Notably, LaCo_0.5Ni_0.5O_3±δ exhibits this high electrical conductivity from R.T. to 1173 K, and little change in the oxygen content occurs under these conditions. LaCo_0.5Ni_0.5O_3±δ is the most suitable for the fabrication of oxide electrodes and wiring, though La_1−xSr_xCoO_3±δ and La_1−xSr_xMnO_3±δ also exhibit high electronic conductivity at R.T., with maximum electrical conductivities of 4.4 × 10³ S cm⁻¹ for La_0.5Sr_0.5CoO_3±δ and 1.5 × 10³ S cm⁻¹ for La_0.6Sr_0.4MnO_3±δ because oxygen release occurs in La_1−xSr_xCoO_3±δ as elevating temperature and the electrical conductivity of La_0.6Sr_0.4MnO_3±δ slightly decreases at temperatures above 400 K.     

A new route to synthesize La1?xSrxMnO3

Self-Propagating High-temperature Synthesis (SHS) was used to producecomplex oxides (La_1–x Sr _x MnO₃ with x = 0, 0.1 and 0.2), which are used as the cathode in solid oxide fuel cells (SOFCs). Thermodynamic predications and experiments show that La_1–x Sr _x MnO₃ can be prepared via SHS under moderate conditions from a mixture of La₂O₃ + SrO₂ + Mn, using either gaseous oxygen or solid NaClO₄ as the oxidant. Partial melting at the high combustion temperature increased product homogeneity. The electrical conductivity of the product was 180 S·cm^–1 at 1000°C in air, matching that of sample made by other synthesis processes. SHS enables a more economical production of La_1–x Sr _x MnO₃ than existing commercial processes.     

Symmetry breaking and electrical conductivity of La0.7Sr0.3Cr0.4Mn0.6O3−δ perovskite as SOFC anode material

This work is focused on nanocrystalline solid oxide fuel cell synthesis and characterization (SOFC) anodes of La_0.7Sr_0.3Cr_0.4Mn_0.6O_3−δ (perovskite-type) with Nickel. Perovskite-type oxide chemical reactivity, nucleation kinetics and phase composition related with La_0.7Sr_0.3Cr_0.4Mn_0.6O_3−δ–NiO to La_0.7Sr_0.3Cr_0.4Mn_0.6O_3−δ–Ni transformation have been analyzed. SOFC anode powders were obtained by sol–gel synthesis, using polyvinyl alcohol as an organic precursor to get a porous cermet electrode after sintering at 1365 °C and oxide reduction by hydrogen at 800 °C/1050 °C for 8 h in a horizontal tubular reactor furnace under 10% H₂/N₂ atmosphere. Composite powders were compressed into 10-mm diameter discs with 25–75 wt% Ni.