Nanostructured La0 Research Articles

Magnetocaloric effect of nanostructured La0.6Sr0.4CoO3

In this study, we investigate the magnetic and magnetocaloric properties of nanostructured La0.6Sr0.4CoO3 (LSC) samples synthesized under confinement conditions within porous templates. Using this method, we obtained de-agglomerated nanoparticles, which provide us with the feasibility of applying them in nanoparticle films that can be tailored to intricate geometries. We specifically explored the impact of pore size of the template on key parameters including saturation magnetization (MS), Curie temperature (TC), maximum entropy change (ΔS), and relative cooling power (RCP). Our findings reveal enhancements in those quantities, that are likely to be related with the nanostructure of the samples, indicating the potential of nanostructured LSC as an active material for magnetic refrigeration devices. Our alternative approach of synthesizing magnetocaloric materials under confinement conditions presents an exciting prospect for future research and development in the field.

Indentation creep characterization of plasma-sprayed nanostructured La2(Zr0.75Ce0.25)2O7 thermal barrier coatings

Nano-indentation technology can not only analyze the nano-hardness and elastic modulus, but also extract the creep properties. In the current study, the nanostructured La2(Zr0.75Ce0.25)2O7 (LCZ) coating were successfully constructed by atmospheric plasma spraying (APS). Furthermore, the indentation creep characterization of LCZ coating was systematically analyzed by nano-indentation. Results imply that power-law formula can well fit the curve relationship between indentation depth and time in the creep process of LCZ coating. The determined strain rate sensitivity of LCZ coating is 0.0134 ± 0.0045. The study provides support for further research on creep properties of nanostructured LCZ coating in the future.

Magnetoresistance and Magnetic Relaxation of La-Sr-Mn-O Films Grown on Si/SiO2 Substrate by Pulsed Injection MOCVD

The results of magnetoresistance (MR) and resistance relaxation of nanostructured La1−xSrxMnyO3 (LSMO) films with different film thicknesses (60–480 nm) grown on Si/SiO2 substrate by the pulsed-injection MOCVD technique are presented and compared with the reference manganite LSMO/Al2O3 films of the same thickness. The MR was investigated in permanent (up to 0.7 T) and pulsed (up to 10 T) magnetic fields in the temperature range of 80–300 K, and the resistance-relaxation processes were studied after the switch-off of the magnetic pulse with an amplitude of 10 T and a duration of 200 μs. It was found that the high-field MR values were comparable for all investigated films (~−40% at 10 T), whereas the memory effects differed depending on the film thickness and substrate used for the deposition. It was demonstrated that resistance relaxation to the initial state after removal of the magnetic field occurred in two time scales: fast’ (~300 μs) and slow (longer than 10 ms). The observed fast relaxation process was analyzed using the Kolmogorov–Avrami–Fatuzzo model, taking into account the reorientation of magnetic domains into their equilibrium state. The smallest remnant resistivity values were found for the LSMO films grown on SiO2/Si substrate in comparison to the LSMO/Al2O3 films. The testing of the LSMO/SiO2/Si-based magnetic sensors in an alternating magnetic field with a half-period of 22 μs demonstrated that these films could be used for the development of fast magnetic sensors operating at room temperature. For operation at cryogenic temperature, the LSMO/SiO2/Si films could be employed only for single-pulse measurements due to magnetic-memory effects.

Synthesis, characterization, and electrocatalytic behaviour of hydrothermally grown nanostructured La2 O3 and La2 O3 /K-complex.

Rare earth metals play a conspicuous role in magnetic resonance imaging (MRI) for detecting cancerous cells. The alkali metal potassium is a neurotransmitter in the sodium-potassium pump in biomedical sciences. This unique property of rare earth metals and potassium drew our attention to carry forward this study. Therefore, in this work, previously synthesized potassium (K) complexes formed by the reflux of 4-N,N-dimethylaminobenzoic acid (DBA) and potassium hydroxide in methanol, and named [(μ2-4-N,N-dimethylaminobenzoate-κO)(μ2-4-N,N-dimethylaminobenzoic acid-κO)(4-N,N-dimethylaminobenzoic acid-κO) potassium(I) coordination polymer)] were treated hydrothermally with La2 O3 nanomaterials to obtain a nanohybrid La2 O3 /K-complex. After that, the K-complex was analyzed using single-crystal X-ray diffraction and 1 H and 13 C NMR spectroscopy. In addition, the structural and morphological properties of the as-prepared nanostructured La2 O3 /K-complex were also characterized, which involved an investigation using X-ray diffraction (XRD)spectroscopy, Fourier transform infrared (FTIR) spectroscopy, atomic force spectroscopy (AFM), transmission electron microscopy (TEM), and energy dispersive X-ray (EDX) analysis. After this, the electrochemical redox behaviour of the synthesized nanohybrid material was studied using cyclic voltammetry (CV) and differential pulse voltammetry (DPV). Therefore, the results from these studies revealed that the as-prepared material was a La2 O3 /K-complex that has a promising future role in sensing various analytes, as it showed effective electrocatalytic behaviour.

CO2 reduction on a nanostructured La0.5Ba0.5CoO3 perovskite: Electrochemical characterization and DFT calculations

A La0.5Ba0.5CoO3 perovskite was evaluated as a catalyst for the electrochemical reduction of CO2. Nanocrystalline structures of La0.5Ba0.5CoO3 were synthesized using polycarbonate porous templates by microwave irradiation. Electrochemical characterization was carried out by linear sweep voltammetry, cyclic voltammetry and chronoamperometry. The electroreduction of CO2 produced HCOOH with a faradaic efficiency of 30% at − 0.9 V vs SHE as determined by ionic chromatography. The rotating ring-disc electrode configuration was used to further study the electroreduction processes. A faradaic efficiency of 85% at − 1.2 V vs SHE attributed to CO, was obtained from the disk and ring currents. In parallel, the adsorption process of CO2 and plausible reduction pathways to HCOOH and CO were studied by DFT calculation on the (001) and (110) orientations of the perovskite. The CO2 molecule strongly adsorbs at the oxygen surface sites through the C atom in a bent configuration, determining the *COOH species as the only possible intermediate. The formation and release of HCOOH becomes feasible under an applied potential of − 0.8 V and − 0.7 V vs SHE for the (001) and (110) orientations, respectively. On the other hand, the calculation showed that the release of CO is only feasible at the (001) surface plane for potentials below − 0.9 V vs SHE. The calculated applied potentials are in good agreement, both in trend and magnitude, with the experimental observations despite the model approximation of neglecting solvent effects.

Vacuum cold sprayed nanostructured La0.6Sr0.4Co0.2Fe0.8O3−δ as a high-performance cathode for porous metal-supported solid oxide fuel cells operating below 600 °C

Porous metal-supported solid oxide fuel cells (PMS-SOFCs) demonstrate potential to dramatically reduce their costs while simultaneously enhancing the durability of SOFCs. However, owing to the unsatisfactory performance improvement of PMS-SOFCs at low temperatures and available fabrication processes, their commercial applications are limited. In this study, exceptional performance of PMS-SOFCs for electricity generation at low temperatures (400–600 °C) with vacuum cold sprayed (VCS) nanostructured La0.6Sr0.4Co0.2Fe0.8O3−δ (LSCF) as the high-activity cathode, the plasma-sprayed Ce0.8Gd0.2O2−δ/La0.8Sr0.2Ga0.8Mg0.2O3−δ (GDC/LSGM) bilayer as the electrolyte, and a cermet consisting of the nickel–gadolinium-doped-ceria (Ni–GDC) composite as the anode. By carefully controlling the spray particle size, a nanostructured LSCF cathode is obtained, and the oxygen reduction reaction (ORR) is activated. Consequently, the microstructurally optimized cell exhibits remarkable peak power densities of >1 W/cm2 at 600 °C and >0.2 W/cm2 at 450 °C. Moreover, this nanostructured cathode maintains high activity over 1000 h at 550 °C due to the stable microstructure, strontium (Sr) surface segregation, and the exceptional stability of PMS-SOFCs. Our results demonstrate a simple route to dramatically improve the performance and stability of PMS-SOFCs operating at low temperatures by using a nanoscale cathode for activity toward the ORR.

The crystal and magnetic structure of nanostructured manganite La0.53Sr0.47MnO3 at high pressure

The crystal and magnetic structure of the nanostructured manganite La0.53Sr0.47MnO3 has been studied using the neutron diffraction method in the pressure range 0–5.5 GPa and the temperature range 15–300 K. At ambient pressure, the ferromagnetic ordering in the studied compound is formed below T ≈ 335 K. With an increase of the pressure above 2.1 GPa and cooling below T < 250 K, an A-type antiferromagnetic phase appears, which coexists with the initial ferromagnetic one. Further increase of the pressure leads to the growth of the volume fraction of the antiferromagnetic phase, while the ferromagnetic ordering is gradually suppressed. The structural origins of the pressure-induced magnetic phase separation in the nanostructured manganites are discussed.

Characterization and oxidation behaviour of nanostructured La2(Zr0.7Ce0.3)2O7/YSZ coatings prepared by calcined precursor precipitate plasma spraying

ABSTRACTIn this study, La2(Zr0.7Ce0.3)2O7 nanostructured coatings were applied by plasma spraying of the nanostructured agglomerates. Initial nanostructured precursor, precursors calcined at 400°C, 600°C and 900°C with La2(Zr0.7Ce0.3)2O7 compound were used to apply top coat layer of the coatings. XRD results and microstructural observations indicated that a uniform distribution of LC phase in LZ matrix was obtained in the coatings applied by the precursors calcined at 400°C, 600°C and 900°C. The coatings were composed of vertical cracks. The isothermal oxidation results showed that TGO layer in the coating applied by the precursor calcined at 600°C (coating 600D60) was composed of Al2O3 protective compound. While, TGO layer in the conventional YSZ coating contained both compounds of protective Al2O3 and Ni(Cr, Al)2O4 detrimental spinel. The coating 600D60 had better isothermal oxidation resistance compared to the conventional YSZ. But, its thermal cycling resistance was approximately equal to the conventional YSZ.

Evaluation of oxidation and thermal insulation capability of nanostructured La2(Zr0·7Ce0.3)2O7/YSZ functionally graded coatings

In the present work, nanostructured La2(Zr0·7Ce0.3)2O7/YSZ functionally graded coatings were prepared by applying the atmospheric plasma spraying process. The La2(Zr0·7Ce0.3)2O7 compound was synthesized via the calcination process to get a nanostructured precursor precipitate at 600 °C. Two types of nanostructured functionally graded coatings were applied on the Hastelloy X substrates coated with NiCrAlY and 8YSZ. The agglomerates of La2(Zr0·7Ce0.3)2O7 were then used to apply the type I coating. Type II coating was then applied by the plasma spraying of the heat-treated agglomerates of La2(Zr0·7Ce0.3)2O7. The results of the phase and microstructural analysis showed that a nano-composite microstructure comprising the main phases of lanthanum zirconate with the partial solubility of cerium cation (LZ) and the solid solution of cerium lanthanum zirconate (LC) was formed in both types of coatings. Type II coating was relatively denser; so, it could be considered as a dense nanostructured coating. The results of the oxidation tests also showed that only the type II coating had higher oxidation resistance, as compared to that of the conventional YSZ coating. Parabolic oxidation rate constant of this coating was equal to 0.114 μm2/h. On the other hand, the oxidation rate constant for the type I coating and conventional YSZ coating was measured to be 0.141 μm2/h and 0.147 μm2/h, respectively. In addition, the results of the thermal insulation capability test indicated that the thermal barrier capability of the type I coating was 59% higher than that of the conventional YSZ coating. However, under similar conditions, this percentage was 29% for the type II coating.

Influence of sintering temperature on the structural, electrical transport and magnetic behaviour of La0.7Sr0.3MnO3 prepared through co-precipitation technique

In this communication, report of nanostructured polycrystalline La0.7Sr0.3MnO3 (LSMO) prepared through a co-precipitation technique at 800 °C, 900 °C and 1000 °C is discussed in detail. The structural, electrical transport, magnetoresistance and magnetic properties of LSMO samples were found strongly dependent on the sintering temperature (TS). Structural properties were studied through XRD and SEM. The results of Rietveld refined XRD data show that all the samples are in tetragonal arrangement and having single-phase structure with space group I4/mcm (140). The average size of synthesized nanoparticles was found increasing (21.05 nm to 46.06 nm) with increase in sintering temperature. A significant increase in metal–insulator transition temperature (TMI) was observed at higher sintering temperatures. Higher sintering temperature results in the enhancement of resistivity. To understand the metallic part of resistivity (T < TMI) including upturn behavior, resistivity data with and without magnetic field were fitted using Kondo like spin-dependent scattering, electron–electron (e-e), electron–phonon (e-p) and electron-magnon (e-m) scattering. The decrement in magnetoresistance (MR) in the wide temperature range has been explained by spin-polarized tunnelling in this communication. Magnetic properties were examined through M−H measurements and found the highest value of magnetization for the sample sintered at 1000 °C.

Charge conduction mechanisms and MR behaviour of sol–gel-grown nanostructured La0.6Nd0.1Sr0.3MnO3 manganites

In this communication, structure and charge, conduction mechanisms have been understood for sol–gel-grown nanostructured La0.6Nd0.1Sr0.3MnO3 (LNSMO) manganites prepared at different process temperatures under air and oxygen environments. Obtained X-ray diffraction patterns of all the samples were analysed using Rietveld refinements and obtained structural lattice parameters have been discussed in correlation with resistivity behaviour of the samples. Observed low temperature resistivity upturn behaviour has been examined in the context of electron–electron scattering mechanism. Metallic and insulating/semiconducting behaviours of all the nanostructured LNSMO manganites have been understood by using various models and mechanisms. Magnetoresistance isotherms have also been theoretically fitted and separate grain and grain boundary contributions have been studied for LNSMO manganite samples. All obtained fitting parameters have been discussed in the context of role of applied magnetic field, process temperature and annealing environment.

Influence of Bi1.5Y0.5O3 Active Layer on the Performance of Nanostructured La0.8Sr0.2MnO3 Cathode

The efficiency of solid oxide fuel cell cathodes can be improved by microstructural optimization and using active layers, such as doped bismuth oxides. In this work, Bi1.5Y0.5O3 (BYO) films are prepared by spray-pyrolysis deposition at reduced temperatures on a Zr0.84Y0.16O1.92 (YSZ) electrolyte. The influence of the BYO film on the performance of an La0.8Sr0.2MnO3 (LSM) cathode prepared by traditional screen-printing and spray-pyrolysis is investigated. A complete structural, morphological, and electrochemical characterization is carried out by X-ray diffraction, electron microscopy, and impedance spectroscopy. The incorporation of BYO films decreases the Area Specific Resistance (ASR) of screen-printed cathodes from 6.4 to 2.2 Ω cm2 at 650 °C. However, further improvements are observed for the nanostructured electrodes prepared by spray-pyrolysis with ASRs of 0.55 and 1.15 Ω cm2 at 650 °C for cathodes with and without an active layer, respectively. These results demonstrate that microstructural control using optimized fabrication methods is desirable to obtain high-efficiency electrodes for solid oxide fuel cell (SOFC) applications.

Nanocrystalline construction in ultra-high temperature thermal barrier coatings using as-synthesized nanostructured La2(Zr0.75Ce0.25)2O7 feedstocks

Nanostructured rare earth zirconates are considered to be the most promising top materials for ultra-high temperature thermal barrier coatings. In this communication, the ultra-high temperature thermal barrier coatings using as-synthesized nanostructured La2(Zr0.75Ce0.25)2O7 feedstocks were deposited and the study is firstly focused on the nano-grains construction in nanostructured La2(Zr0.75Ce0.25)2O7 coatings with the aid of scanning electron microscopy (SEM) and transmission electron microscopy (TEM) analysis. Results show that the nano-grains in as-sprayed La2(Zr0.75Ce0.25)2O7 coatings comprise non-molten nanostructured feedstocks and columnar nanocrystalline with [222] preferential orientation in splats.

Nanomechanical characterization of nanostructured La2(Zr0.75Ce0.25)2O7 thermal barrier coatings by nanoindentation

Nanostructured rare-earth zirconates materials have a great potential in next generation ultra high temperature thermal barrier coatings. In this work, the nanostructured La2(Zr0.75Ce0.25)2O7 coatings were fabricated by atmospheric plasma spraying using as-prepared nanostructured La2(Zr0.75Ce0.25)2O7 spherical feedstocks and nanomechanical properties of coatings were characterized by nanoindentation in detail. Results indicate that the grain growth of nanostructured coating is not obvious compared with feedstocks. The elastic modulus and nano-hardness of coatings, which are sensitive to non-molten zones, are 116.483 ± 19.236 GPa and 5.715 ± 1.656 GPa, respectively. The elastic indentation work is 11.465 ± 0.750 nJ and the plastic indentation work is 23.981 ± 5.035 nJ. The parameter of energy dissipation during plastic deformation (microhardness dissipation parameter, MDP) is 0.672 ± 0.042, indicating that outstanding properties under wear conditions for nanostructured La2(Zr0.75Ce0.25)2O7 coatings.

Study of combined effect of partial Bi doping and particle size reduction on magnetism of La0.7Sr0.3MnO3

La0.7Sr0.3MnO3 has been subjected to simultaneous partial bismuth substitution and particle size reduction to understand the mechanism controlling the magnetic properties. Nanosized samples of 10% Bi doped La0.7Sr0.3MnO3 samples were prepared by high energy planetary ball milling. Compared to pristine La0.7Sr0.3MnO3, 10% Bi doping results in the reduction of saturated magnetic moment and Curie temperature. Using the ‘top-down approach’ through high energy planetary ball milling, particle size reduces from 250 nm for bulk to 26 nm for 48 h ball milled sample. Correspondingly, the magnetic properties show the direct influence of size reduction, as the observed magnetic moment shows drastic decrease as particle size reduces. It is interesting to note that 10% Bi doping in La0.7Sr0.3MnO3 plays important role in controlling the size with respect to milling time. In the present work, we discuss the magnetic properties of nanostructured La0.6Bi0.1Sr0.3MnO3 samples. The observed magnetization behaviour can be described using the core-shell model for nanoparticles.

Increase of Operating Temperature of Magnetic Field Sensors Based on La–Sr–Mn–O Films With Mn Excess

The results of Mn excess influence on the magnetoresistive properties of nanostructured La1– x Sr x MnyO3±δ films grown on polycrystalline Al2O3 substrates by pulsed-injection metal-organic chemical vapor deposition technique are presented. The electrical transport properties and magnetoresistance of these films were investigated in the temperature range of 77–363 K in pulsed magnetic fields up to 20 T. The results were analyzed from the perspective of using these films for magnetic field sensors operating at high temperatures. It was obtained that the increase of Mn/(La + Sr) ratio from 1.05 to 1.15 leads to the increase of metal–insulator transition temperature from 240 to 270 K. This behavior was associated with the presence of (La + Sr) vacancies, which act as self-dopants. At temperatures higher than 340 K, the highest magnetoresistance values were obtained for films with 15% Mn excess. These results allowed us to produce pulsed magnetic field sensors operating at ambient temperatures up to 90 °C.

La–Sr–Mn–Co–O Films for High Pulsed Magnetic Field Measurements at Cryogenic Temperatures

The magnetoresistance of nanostructured La1– x Sr x (Mn1– y Co y ) z $O_{3 \pm \delta}$ (La–Sr–Mn–Co–O) films with substitution of Co for Mn with amount of Co/(La + Sr) = 0.12 and different Mn excess Mn/(La + Sr) = 1.05, 1.07, and 1.11 was investigated at temperatures of 4–230 K in pulsed magnetic fields up to 60 T. It was found that the manganite–cobaltite films exhibit larger magnetoresistance in comparison with manganite films without Co doping. The largest magnetoresistance values and sensitivity to the magnetic field are obtained for La–Sr–Mn–Co–O films having Mn content close to the stoichiometric ratio for manganites: Mn/(La + Sr) = 1.05. It was found that magnetoresistance at high fields (20–60 T) has a minimum at (50–80 K) and increases with the decrease of temperature. The possibility to use these films for magnetic field measurements at cryogenic temperatures is demonstrated.

Hybrid graphene-manganite thin film structure for magnetoresistive sensor application

An increasing demand of magnetic field sensors with high sensitivity at room temperatures and spatial resolution at micro-nanoscales has resulted in numerous investigations of physical phenomena in advanced materials, and fabrication of novel magnetoresistive devices. In this study the novel magnetic field sensor based on combination of a single layer graphene (SLG) and thin nanostructured manganite La0.8Sr0.2MnO3 (LSMO) film—hybrid graphene-manganite (GM) structure, is proposed and fabricated. The hybrid GM structure employs the properties of two materials—SLG and LSMO—on the nanoscale level and results in the enhanced sensitivity to magnetic field of the hybrid sensor on the macroscopic level. Such result is achieved by designing the hybrid GM sensor in a Wheatstone half-bridge which enables to employ in the device operation two effects of nanomaterials—large Lorentz force induced positive magnetoresistance of graphene and colossal negative magnetoresistance of nanostructured manganite film, and significantly increase the sensitivity S of the hybrid GM sensor in comparison with the individual SLG and LSMO sensors: S = 5.5 mV T−1 for SLG, 14.5 mV T−1 for LSMO and 20 mV T−1 for hybrid GM at 0.5 T, when supply voltage was 1.249 V. The hybrid GM sensor operates in the range of (0.1–2.3) T and has lower sensitivity to temperature variations in comparison to the manganite sensor. Moreover, it can be applied for position sensing. The ability to control sensor’s characteristics by changing technological conditions of the fabrication of hybrid structure and tuning the nanostructure properties of manganite film is discussed.

Nanostructured La0.5Ba0.5CoO3 as cathode for solid oxide fuel cells

A simple method has been used to synthesize nanostructured La0.5Ba0.5CoO3 (LBCO) powders, by confining chemical precursors into the pores of polycarbonate filters. The proposed method allows us to obtain powders formed by crystallites of different sizes, it is scalable and does not involve the use of sophisticated deposition techniques. The area specific polarization resistance of symmetrical cells was studied to analyze the electrochemical behavior of the LBCO nanostructures as cathodes for Solid-Oxide Fuel Cells. We show that the performance is improved by reducing the size of the crystallites, obtaining area specific resistance values of 0.2 Wcm2 at 700C, comparable with newly developed cathodes using novel deposition techniques.

Bonding strength and thermal conductivity of novel nanostructured La2(Zr0.75Ce0.25)2O7/8YSZ coatings

The thermal protection coatings possessing functionality, reliability, and durability require appropriate bonding strength and low thermal conductivity. In this study, the novel nanostructured La2(Zr0.75Ce0.25)2O7/8YSZ (LCZ/8YSZ) coatings were deposited onto NiCoCrAlYCe coated nickel-based superalloy by atmospheric plasma spraying (APS) using the as-prepared nanostructured feedstocks. The microstructure, bonding strength, and thermal conductivity of nanostructured LCZ/8YSZ coatings were investigated. The results reveal that the microstructure of as-sprayed nanostructured LCZ/8YSZ coatings presents bi-modal distribution with some pores and microcracks. Furthermore, the microstructure of coatings is dense and the interface bonding of 8YSZ/bond coat and LCZ/8YSZ coatings is perfect. The bonding strength of nanostructured LCZ/8YSZ coatings is 25.1 MPa, which is lower than that of nanostructured 8YSZ coatings with the same thickness. The tensile failure mechanism is also analysed. The thermal conductivity of nanostructured LCZ/8YSZ coatings from 0.86 W·m−1·K−1 to 0.33 W·m−1·K−1 is obviously lower than that of nanostructured 8YSZ coatings from 1.24 W·m−1·K−1 to 0.40 W·m−1·K−1 in the temperature range from 30 °C to 1200 °C.