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.     

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.     

An effect of microstructure on the interface resistance between a perovskite-type oxide electrode and yttria-stabilized zirconia

The electrode characteristics of perovskite-type oxides, La_0.6Sr_0.4CoO₃ and La_0.6Sr_0.4MnO₃, on ceria-based oxide and stabilized zirconia were analysed by the a.c. impedance method. The ionic conductivities of the electrolyte and electrode conductivities from the a.c. impedance analysis agreed with those obtained from the current interruption and d.c. four-probe methods. Two semicircles from the charge transfer and diffusion processes appeared as the electrode resistance. The relative contribution of these two processes to the overall electrode resistance strongly depended on the microstructure of the electrode. The electrode microstructure could be controlled by the dispersion medium used for the electrode slurry. The La_0.6Sr_0.4MnO₃ electrode coated with n-butyl acetate slurry exhibited the smallest electrode resistance.     

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.     

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.     

Influence of Ag-doping in La0.5Sr0.5CoO3 on Its Structural and Magnetic Properties

The structural and magnetic properties of the mixed valent cobaltites La_0.5Sr_0.5?x Ag _x CoO₃ (0≤x≤0.15) with perovskite structure have been investigated. X-ray diffraction (XRD) analysis using Rietveld refinement shows that all our samples crystallize in the orthorhombic structure with $R\overline{3}c$ space group. Although the unit cell volume remains almost constant, the Co–O bond length and the Co–O–Co bond angle are sensitive to the Ag addition. All our studied samples undergo a paramagnetic-ferromagnetic transition with decreasing temperature. The zero field cooled (ZFC) and field cooled (FC) magnetization curves at 50 mT of La_0.5Sr_0.5CoO₃ (x=0) sample exhibits thermomagnetic irreversibility indicating frustration and competition of both antiferromagnetic and ferromagnetic interactions. It is suggested that Co³⁺ ions are in the intermediate spin state but Co⁴⁺ ions stay in a mixture of intermediate and high spin states. Ag addition leads to dramatic changes in magnetic properties. An interesting result has been obtained for La_0.5Sr_0.4Ag_0.1CoO₃, where the ZFC and FC curves coincide. For La_0.5Sr_0.35Ag_0.15CoO₃ (x=0.15) sample, the observed thermomagnetic irreversibility is much higher than that observed in x=0 sample. Hysteresis loops were recorded for x=0, 0.05, 0.1, and 0.15. The coercitive field is found to increase with Ag content reaching 0.26 T for x=0.15 whereas the remanent magnetization decreases.     

Surface characterization and catalytic properties of La1−x -Sr x CoO3

The surface chemical states of the perovskite-type compounds, strontium doped lanthanum cobalt oxides (La_1?x Sr _x CoO₃), have been investigated using X-ray photoelectron spectroscopy (XPS). Catalytic oxidations of both methane and CO have also been investigated using flow methods. The chemical composition of the surface of La_1?x Sr _x CoO₃ was very different from that in the bulk, which was measured by X-ray fluorescence spectroscopy (XRFS). The catalytic activity of La_1?x Sr _x CoO₃ increased with an increase in the quantity of cobalt atoms on the surface.     

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.     

Synthesis of LSMO at low temperature by novel hydroxide precursor technique

A novel technique of mixing individual hydroxide is employed to prepare La_0.65Sr_0.35MnO₃ (LSMO) at low temperature. Freshly prepared lanthanum and manganese hydroxides are mixed thoroughly with strontium hydroxide in stoichiometric ratio and heated at different temperatures ranging from 100 to 500 °C for 6 h. At 500 °C, formation of La_0.65Sr_0.35MnO₃ was confirmed by the X-ray diffraction studies (XRD). This is the lowest temperature so far reported in the literature. The particle size and morphology were investigated by scanning electron microscopy (SEM).     

Theoretical Study on the Spin-State Transition of Electron-Doped Sr2−x La x CoO4 Compounds

The spin-state transition is an interesting and unresolved problem in layered perovskite Sr_2?x La _x CoO₄ under doping. The unrestricted Hartree-Fock approximation on a realistic multiband lattice model has been applied to study the various spin states of electron-doped Sr_2?x La _x CoO₄ compounds. In the doping range 0.0≤x≤0.9, various spin states in an enlarged double cell are investigated and four of them are the ground states at different doping concentration. The magnetic ground state of the doped system takes a low-spin–intermediate-spin ferromagnetically ordered state for x<0.26, a high-spin–intermediate-spin ferromagnetically ordered state for 0.26≤x<0.47, an intermediate-spin state for 0.47≤x<0.65, and followed by an high-spin antiferromagnetically ordered state for 0.65≤x≤0.9. The densities of states of all magnetic ground states are computed and their electronic and magnetic properties are discussed.     

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.     

A four-way catalytic system for control of emissions from diesel engine

The pollution caused by diesel-fuelled vehicles has become a subject of global concern. Presently, various separate technologies such as diesel oxidation catalyst, diesel particulate filter, selective catalytic reduction and ammonia selective catalytic reduction are used to control these pollutants. The four-way catalytic (FWC) system integrates all the separate control systems into a single compact unit. FWC technique using a combination of oxidation–reduction catalysts under various strategies has been investigated to simultaneously remove CO, HC, PM and NOx emitted from diesel engines. An oxidation catalyst (La_0.6K_0.4CoO₃) was prepared by two different methods (sol–gel and co-precipitation). The reduction catalysts: Ag/Al₂O₃ and Cu-ZSM5 were synthesized by impregnation and ion-exchange method, respectively. The FWC was characterized by N₂-sorption, X-ray diffraction, Fourier transform spectroscopy and scanning electron microscopy. The catalytic activities of FWC containing double-layer of catalysts were evaluated in a fixed-bed-tubular-reactor. The highest catalytic activity resulted by the two-layered system of La_0.6K_0.4CoO₃ (sol–gel)?+?Cu-ZSM5 showing 100% NO conversion to N₂ at 415°C, maximum-temperature of soot-combustion at 410°C, complete C₃H₈ conversion at 450°C and 100% CO conversion at 388°C. Maximum NO conversion was maintained up to 427°C; conversion started decreasing with further increase in temperature and 75.4% conversion remained up to 450°C. The performance of double-layered-catalytic-system was as follows: La_0.6K_0.4CoO₃(sol–gel)?+?Cu-ZSM5?>?La_0.6K_0.4CoO₃(sol–gel)?+?Ag/Al₂O₃?>?La_0.6K_0.4CoO₃(co-ppt)?+?Ag/Al₂O₃?>?La_0.6K_0.4CoO₃(co-ppt)?+?Cu-ZSM5.     

Effect of FeOx loaded on CoOx/Al2O3 catalyst for the formation of thin-walled carbon nanotubes

Effects of FeO_x loaded on CoO_x/Al₂O₃ catalyst on the yield and morphology of the produced carbon nanotubes were studied. The findings showed that the addition of a small amount of FeO_x on the CoO_x/Al₂O₃ catalyst provoked the formation of carbon nanotubes with a thin wall structure. The results also revealed that an increase in FeO_x content decreased the yield of carbon nanotubes. An optimized weight ratio of CoO_x to FeO_x was found to be 8:2 (w/w) whereby the catalyst of this composition grew carbon nanotubes with a thin wall structure and not of diminutive carbon yield.     

RF magnetron sputtering ferroelectric PbZr0.52Ti0.48O3 thin films with (001) preferred orientation on colossal magneto-resistive layers

Deposition by RF magnetron sputtering of PbZr_0.52Ti_0.48O₃ (PZT) ferroelectric thin films on two types of colossal magneto-resistive (CMR) oxide electrodes, La_0.67Sr_0.33MnO₃ (LSMO) and La_0.67Ca_0.33MnO₃ (LCMO), is demonstrated in this work. The multiferroic heterostructure is grown on a STO substrate, which causes a 〈001〉 preferred orientation to develop. Ferroelectric, retention of polarisation and local piezoelectric properties were measured for assessing the success of the integration from the ferroelectric point of view. Remnant polarisation P_r and coercive field E_c were found to be ∼ 40 μC/cm² and ∼ 100 kV/cm, respectively. Films presented good retention of polarisation and piezoresponse loops. These results show that ferroelectric layers with good functionality can be grown on CMR oxide films, and open the possibility of designing a piezoelectrically driven spin valve memory cell device based on this heterostructure.     

Observation of Higher Suppression of Superconducting Transition Temperature in YBa2Cu3O7??? /La0.5Sr0.5CoO3 as?Compared?to?YBa2Cu3O7??? /La0.7Sr0.3MnO3 Bilayers

We report the experimental investigations of the suppression of superconductivity due to the pair breaking effect induced by ferromagnetic layer in YBa₂Cu₃O_7??? /La_0.5Sr_0.5CoO₃ and YBa₂Cu₃O_7??? /La_0.7Sr_0.3MnO₃ bi-layers fabricated by pulsed laser deposition. The current dependent electrical transport studies in the bilayers exhibit a significant reduction in the superconducting transition temperature in accord to I ^2/3 law as compared to single YBa₂Cu₃O_7??? layer, and moreover the superconducting transition temperature in YBa₂Cu₃O_7??? /La_0.7Sr_0.3MnO₃ bilayer is surprisingly found to be much larger than the YBa₂Cu₃O_7??? /La_0.5Sr_0.5CoO₃. It appears that the current driven from a low spin polarization (?11%) material like La_0.5Sr_0.5CoO₃ can also suppress the superconductivity to a larger extent. This indicates that the degree of spin polarization of the ferromagnetic electrode is not the only criteria to determine the suppression of superconductivity by pair breaking effect in superconductor/ferromagnet hybrid structures; rather the transparency of the interface for the spin polarization, the formation of vortex state due to the stray field of ferromagnetic layer and the ferromagnetic domain patterns might play significant roles to determine such effect.     

Structures and properties of La1−x,Sr x CoO3−y,prepared by freeze drying

Several samples of La_1–x Sr _x CoO_3–y (x = 1, 0.8, 0.5, 0.2) were prepared by calcining freezedried, stoichiometric mixtures of nitrates at different temperatures and for different lengths of time. Selected samples were characterized by powder X-ray diffraction, conductivity measurements, Brunauer-Emmett-Teller surface area measurement, and by electrochemical cyclic voltammetry in alkaline solutions and alkaline solutions containing methanol. The structures of each composition were complex and varied with composition and preparation conditions. There is evidence for non-stoichiometry caused by oxygen anion vacancies. For La_0.5Sr_0.5CoO_3–y the electrochemical activity towards the oxidation of methanol is a maximum at the fully formed cubic perovskite. The oxidation currents at La_0.8Sr_0.2CoO_3–y and La_0.2Sr_0.8CoO_3–y go through maxima at more distorted structures.     

Magnetic and Electrical Properties Induced by the Substitution of Divalent by Monovalent in the La<Subscript>0.6</Subscript>Ca<Subscript>0.4</Subscript>MnO<Subscript>3</Subscript> Compound

The La_0.6Ca_0.4?x Ag _x MnO₃ samples with x = 0 and 0.10 were prepared by sol–gel methods. Structural and electrical measurements were performed to examine the effect of the silver substitution in the calcium sites on the physical properties. Magnetization versus temperature studies have shown that all samples exhibit a magnetic transition from ferromagnetic to paramagnetic phase when temperature is increased. The second transition in the resistivity in the La_0.6Ca_0.4MnO₃ compound can be attributed to an abnormality characteristic of charge ordering (CO) effect. The electrical resistivity was described by a phenomenological percolation model. Ten percent of Ag substitution in the Ca site exhibits a magnetoresistance value about 75 % near room temperature at the applied magnetic field of 8 T.     

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.     

Peculiarities in the electrical and magnetic properties of cobalt perovskites Ln1−xMxCoO3 (Ln3+: La3+, M2+: Ca2+, Sr2+, Ba2+; Ln3+: Nd3+, M2+: Sr2+)

We refer here to the electrical and magnetic properties of the Ln_1−xM_xCoO₃ systems (Ln³⁺: La³⁺, M²⁺: Ca²⁺, Sr²⁺, Ba²⁺; Ln³⁺: Nd³⁺, M²⁺: Sr²⁺), paying special attention to those ferromagnetic compounds that display M–I transitions as temperature rises: La_1−xM_xCoO₃ (M²⁺: Ca²⁺, Sr²⁺, Ba²⁺) in the compositional interval x=0.2–0.3, and Nd_1−xSr_xCoO₃, with x=0.40. The magneto-transport properties of such materials are peculiar and interesting: they show diodic behavior and large relaxation effects — these latter being specially important in the Nd compound — they display magnetoresistive effects specially at the M–I transition temperatures, and they age with time. All these results are discussed on the basis of the inhomogeneous electronic structure of these doped cobalt perovskites and taking into account the influence of the lanthanide ion on their magnetic and electrical properties.     

Griffiths Phase and Disorder in Perovskite Manganite Oxides La1?xCaxMnO3 and La0.7Sr0.3MnO3

Polycrystalline samples La_1−x Ca _x MnO₃ (x=0.17, 0.15, 0.10) and La_0.7Sr_0.3MnO₃ were prepared in order to investigate the Griffiths-like features induced by disorder compared with their counterpart single crystals. The magnetization data exhibit the traditional transition from ferromagnetic phase to paramagnetic phase. From the temperature dependence of inverse susceptibility, it can be testified that the Griffiths-like features still exist in as-prepared Ca doped samples, while non-Griffiths-like features exist in La_0.7Sr_0.3MnO₃. All these samples, however, exhibit the large effective spins resulting from formation of the short-order ferromagnetic clusters. The O K-edge X-ray absorption spectra indicate the Jahn–Teller (J-T) distortions are definitely present due to the J-T ion Mn³⁺, which indicate that static J-T distortion is not a sufficient condition for the existence of Griffiths phase in Sr-doped system. And, the size of J-T distortion is a little larger in polycrystalline La_0.7Sr_0.3MnO₃ than that in polycrystalline samples La_1−x Ca _x MnO₃ (x=0.17, 0.15, 0.10), revealed by X-ray diffraction parameters and extended X-ray fine structure absorption data of Mn K-edge. It also testifies that the disorder in La_0.7Sr_0.3MnO₃ caused by both chemical doping and J-T distortions is lower than that in polycrystalline samples La_1−x Ca _x MnO₃, which may be the reason of non-Griffiths-like phase existing in La_0.7Sr_0.3MnO₃ samples.