Search Results (16)

In this study, silica-encapsulated gadolinium was doped in lanthanum strontium manganite nanoparticles (NPs) with different concentrations using the citrate–gel auto-combustion method. We focused on tuning the Curie temperature and enhancing the specific absorption rate (SAR) of silica-coated gadolinium-doped lanthanum strontium manganite NPs to make them suitable for self-controlled magnetic hyperthermia. The samples were characterized by using transmission electron microscopy (TEM), X-ray diffraction, Fourier transform infrared spectroscopy (FTIR), and magnetic measurements to examine the structural, optical, and magnetic properties of the manganite NPs. While our results exhibit a successful doping of gadolinium in lanthanum strontium manganite NPs, we further prepared magnetic core NPs with sizes between 20 and 50 nm. The Curie temperature of the NPs declined with increasing gadolinium doping, making them promising materials for hyperthermia applications. The Curie temperature was measured using the magnetization (M-T) curve. Magnetic heating was carried out in an external applied AC magnetic field. Our present work proved the availability of regulating the Curie temperature of gadolinium-doped lanthanum strontium manganite NPs, which makes them promising candidates for self-controlled magnetic hyperthermia applications. Full article

The progressive research trends in the development of low-cost, commercially competitive solid oxide fuel cells with reduced operating temperatures are closely linked to the search for new functional materials as well as technologies to improve the properties of established materials traditionally used in high-temperature devices. Significant efforts are being made to improve air electrodes, which significantly contribute to the degradation of cell performance due to low oxygen reduction reaction kinetics at reduced temperatures. The present review summarizes the basic information on the methods to improve the electrochemical performance of conventional air electrodes with perovskite structure, such as lanthanum strontium manganite (LSM) and lanthanum strontium cobaltite ferrite (LSCF), to make them suitable for application in second generation electrochemical cells operating at medium and low temperatures. In addition, the information presented in this review may serve as a background for further implementation of developed electrode modification technologies involving novel, recently investigated electrode materials. Full article

In this study, Strontium (Sr)-doped perovskite lanthanum manganite (La_1−xSr_xMnO₃) nanoparticles were prepared by the sol–gel method and used as electrode materials of supercapacitors. Microstructures, morphologies, and electrochemical properties of the samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), a transmission electron microscope (TEM), Brunauer–Emmett–Teller (BET) surface area measurements, cyclic voltammetry (CV), and galvanostatic charge/discharge (GCD) cycling. Investigations demonstrated that the La_0.85Sr_0.15MnO₃ nanoparticles had a maximum specific capacitance of 185.5 F/g at a current density of 0.5 A/g and a low charge transfer resistance (0.38 Ω) in 3 M KOH aqueous electrolyte solutions. La_0.85Sr_0.15MnO₃ electrode yields the highest capacitance behavior because of the larger specific surface area, lower charge transfer resistance, and higher concentration of oxygen vacancy. This result demonstrates that Sr doping significantly improved the electrochemical properties of the LaMnO₃ system. The anion-intercalation mechanism was examined by a charge–discharge process. This provides a promising electrode material for supercapacitors. Full article

The results of colossal magnetoresistance (CMR) properties of La_1-xSr_xMn_yO₃ (LSMO) films grown by the pulsed injection MOCVD technique onto an Al₂O₃ substrate are presented. The grown films with different Sr (0.05 ≤ x ≤ 0.3) and Mn excess (y > 1) concentrations were nanostructured with vertically aligned column-shaped crystallites spread perpendicular to the film plane. It was found that microstructure, resistivity, and magnetoresistive properties of the films strongly depend on the strontium and manganese concentration. All films (including low Sr content) exhibit a metal–insulator transition typical for manganites at a certain temperature, T_m. The T_m vs. Sr content dependence for films with a constant Mn amount has maxima that shift to lower Sr values with the increase in Mn excess in the films. Moreover, the higher the Mn excess concentration in the films, the higher the T_m value obtained. The highest T_m values (270 K) were observed for nanostructured LSMO films with x = 0.17–0.18 and y = 1.15, while the highest low-field magnetoresistance (0.8% at 50 mT) at room temperature (290 K) was achieved for x = 0.3 and y = 1.15. The obtained low-field MR values were relatively high in comparison to those published in the literature results for lanthanum manganite films prepared without additional insulating oxide phases. It can be caused by high Curie temperature (383 K), high saturation magnetization at room temperature (870 emu/cm³), and relatively thin grain boundaries. The obtained results allow to fabricate CMR sensors for low magnetic field measurement at room temperature. Full article

Magnetic hyperthermia (MHT) is a therapy that uses the heat generated by a magnetic material for cancer treatment. Magnetite nanoparticles are the most used materials in MHT. However, magnetite has a high Curie temperature (Tc~580 °C), and its use may generate local superheating. To overcome this problem, strontium-doped lanthanum manganite could replace magnetite because it shows a Tc near the ideal range (42–45 °C). In this study, we developed a smart composite formed by an F18 bioactive glass matrix with different amounts of Lanthanum-Strontium Manganite (LSM) powder (5, 10, 20, and 30 wt.% LSM). The effect of LSM addition was analyzed in terms of sinterability, magnetic properties, heating ability under a magnetic field, and in vitro bioactivity. The saturation magnetization (M_s) and remanent magnetization (M_r) increased by the LSM content, the confinement of LSM particles within the bioactive glass matrix also caused an increase in Tc. Calorimetry evaluation revealed a temperature increase from 5 °C (composition LSM5) to 15 °C (LSM30). The specific absorption rates were also calculated. Bioactivity measurements demonstrated HCA formation on the surface of all the composites in up to 15 days. The best material reached 40 °C, demonstrating the proof of concept sought in this research. Therefore, these composites have great potential for bone cancer therapy and should be further explored. Full article

The high efficiency of solid oxide fuel cells with La_0.8Sr_0.2MnO_3−δ (LSM) cathodes working in the range of 800–1000 °C, rapidly decreases below 800 °C. The goal of this study is to improve the properties of LSM cathodes working in the range of 500–800 °C by the addition of YFe_0.5Co_0.5O₃ (YFC). Monophasic YFC is synthesized and sintered at 950 °C. Composite cathodes are prepared on Ce_0.8Sm_0.2O_1.9 electrolyte disks using pastes containing YFC and LSM powders mixed in 0:1, 1:19, and 1:1 weight ratios denoted LSM, LSM1, and LSM1, respectively. X-ray diffraction patterns of tested composites reveal the presence of pure perovskite phases in samples sintered at 950 °C and the presence of Sr₄Fe₄O₁₁, YMnO₃, and La_0.775Sr_0.225MnO_3.047 phases in samples sintered at 1100 °C. Electrochemical impedance spectroscopy reveals that polarization resistance increases from LSM1, by LSM, to LSM2. Differences in polarization resistance increase with decreasing operating temperatures because activation energy rises in the same order and equals to 1.33, 1.34, and 1.58 eV for LSM1, LSM, and LSM2, respectively. The lower polarization resistance of LSM1 electrodes is caused by the lower resistance associated with the charge transfer process. Full article

In this report, lanthanum strontium manganite at different Sr²⁺ ion concentrations, as well as Gd³⁺ or Sm³⁺ ion substituted La_0.5−YM_YSr_0.5MnO₃ (M = Gd and Sm, y = 0.2), have been purposefully tailored using a sol gel auto-combustion approach. XRD profiles confirmed the formation of a monoclinic perovskite phase. FE-SEM analysis displayed a spherical-like structure of the La_0.8Sr_0.2MnO₃ and La_0.3Gd_0.2Sr_0.2MnO₃ samples. The particle size of the LSM samples was found to decrease with increased Sr²⁺ ion concentration. For the first time, different LSM concentrations were inspected for their cytotoxic activity against CACO-2 (intestinal carcinoma cells) and HepG-2 (human hepatocellular carcinoma cells). The cell viability for CACO-2 and HepG-2 was assayed and seen to decrease depending on the Sr²⁺ ion concentration. Half maximal inhibitory concentration IC₅₀ of CACO-2 cell and HepG-2 cell inhibition was connected with Sr²⁺ ion ratio. Low IC₅₀ was noticable at low Sr²⁺ ion content. Such results were correlated to the particle size and the morphology. Indeed, the IC₅₀ of CACO-2 cell inhibition by LSM at a strontium content of 0.2 was 5.63 ± 0.42 µg/mL, and the value increased with increased Sr²⁺ ion concentration by up to 0.8 to be = 25 ± 2.7 µg/mL. Meanwhile, the IC₅₀ of HepG-2 cell inhibition by LSM at a strontium content of 0.2 was 6.73 ± 0.4 µg/mL, and the value increased with increased Sr²⁺ ion concentration by up to 0.8 to be 31± 3.1 µg/mL. All LSM samples at different conditions were tested as antimicrobial agents towards fungi, Gram positive bacteria, and Gram negative bacteria. For instance, all LSM samples were found to be active towards Gram negative bacteria Escherichia coli, whereas some samples have presumed antimicrobial effect towards Gram negative bacteria Proteus vulgaris. Such results confirmed that LSM samples possessed cytotoxicity against CACO-2 and HepG-2 cells, and they could be considered to play a substantial role in pharmaceutical and therapeutic applications. Full article

The objective of this paper is to manufacture free-standing solid oxide cells (SOCs) through the atmospheric plasma spray process (APS), without the aid of a metallic support nor the need for a post-process heating treatment. A five-layered cell was fabricated. Fused and crushed yttria-stabilized zirconia (YSZ) powder in the 5–22 μm particle size range was used in order to achieve a dense electrolyte layer, yet still permitting satisfactory ionic diffusivity. Nickel oxide (NiO) powder that was obtained by in-house flame spray (FS) oxidation of pure nickel (Ni) powder was mixed and sprayed with the original Ni-YSZ feedstock, so as to increase the porosity content in the supporting electrode. Two transition layers were sprayed, the first between the support electrode and the electrolyte (25% (Ni/NiO)–75% YSZ) and the second at the electrolyte and the end electrode interface (50% YSZ–50% lanthanum strontium manganite (LSM)). The purpose of intercalation of these transition layers was to facilitate the ionic motion and also to eliminate thermal expansion mismatches. All the as-sprayed layers were separately tested by an in-house developed acetone permeability comparative test (APCT). Electrodes with adequate porosity (25–30%) were obtained. Concerning electrolytes, relatively thick (150–200 µm) layers derived from fused and crushed YSZ were found to be impermeable to acetone, while thinner YSZ counterparts of less than 100 µm showed a low degree of permeability, which was attributed mostly to existent microcracks and insufficient interparticle cohesion, rather than to interconnected porosity. Full article

Laser additive manufacturing (LAM) of a multi-material multi-layer structure was investigated using femtosecond fiber lasers. A thin layer of yttria-stabilized zirconia (YSZ) and a Ni–YSZ layer were additively manufactured to form the electrolyte and anode support of a solid oxide fuel cell (SOFC). A lanthanum strontium manganite (LSM) layer was then added to form a basic three layer cell. This single step process eliminates the need for binders and post treatment. Parameters including laser power, scan speed, scan pattern, and hatching space were systematically evaluated to obtain optimal density and porosity. This is the first report to build a complete and functional fuel cell by using the LAM approach. Full article

A nickel-ceria-yttria stabilized zirconia (Ni-CYSZ) cermet material was synthesized and tested as the anode for the direct oxidation of methane in a solid oxide fuel cell (SOFC) with YSZ as the electrolyte and strontium-doped lanthanum manganite (LSM) as the cathode. Initially, the electrochemical behavior was investigated under several load demands in wet (3% H₂O) CH₄ at 850 °C during 144 h using I-V curves, impedance spectra, and potentiostatic measurements. Long-term tests were subsequently conducted under 180 mA·cm^–2 in wet CH₄ for 236 h and dry CH₄ for 526 h at 850 °C in order to assess the cell stability. Material analysis was carried out by SEM-EDS after operation was complete. Similar cell performance was observed with wet (3% H₂O) and dry CH₄, and this indicates that the presence of water is not relevant under the applied load demand. Impedance spectra of the cell showed that at least three processes govern the direct electrochemical oxidation of methane on the Ni-CYSZ anode and these are related to charge transfer at high frequency, the adsorption/desorption of charged species at medium frequency and the non-charge transfer processes at low frequency. The cell was operated for more than 900 h in CH₄ and 806 h under load demand, with a low degradation rate of ~0.2 mV·h^–1 observed during this period. The low degradation in performance was mainly caused by the increase in charge transfer resistance, which can be attributed to carbon deposition on the anode causing a reduction in the number of active centers. Carbon deposits were detected mostly on the surface of Ni particles but not near the anode/electrolyte interface or the cerium surface. Therefore, the incorporation of cerium in the anode structure could improve the cell lifetime by reducing carbon formation. Full article

The oxygen surface kinetics of Sr₂Fe_1.5Mo_0.5O_6−δ was determined using the ¹⁶O₂/¹⁸O₂ isotope exchange method with gas phase analysis at 600–800 °C. The heterogeneous exchange rates (r_H) and the oxygen diffusion coefficients (D) were calculated by processing the concentration dependences of the ¹⁸O fraction using Ezin’s model. The rates of oxygen dissociative adsorption (r_a) and incorporation (r_i) were calculated based on a model using the three exchange type rates. It has been established that the rates r_a and r_i were comparable in this temperature range. Assumptions were made about the effect of the chemical composition of the surface on the rate of oxygen adsorption. It was found that the oxygen exchange coefficient (k) of Sr₂Fe_1.5Mo_0.5O_6−δ is comparable to that of La_0.6Sr_0.4MnO_3±δ oxide. High values of the oxygen diffusion coefficient were found for Sr₂Fe_1.5Mo_0.5O_6−δ. The values were comparable to those of the double cobaltite praseodymium-barium and exceed by more than an order those of lanthanum-strontium manganite. Full article

Fabricating lanthanum strontium manganite (LSM) ceramics with certain shapes is important for the design and construction of high-temperature energy conversion and storage devices. Here, we describe a low-cost and environmentally friendly method for fabricating LSM ceramics via agar gel casting and high temperature sintering. This new approach uses temperature tuning to fabricate LSM gel bodies, not only by manufacturing in the secondary process but also by remolding and recycling during the gel casting process. The effect of the sintering temperature on the properties of LSM ceramics was investigated as well. As a result, the porosity and compressive strength of LSM ceramics sintered at 1000 °C are ~60% and 5.6 MPa, respectively. When the sintering temperature increases to 1200 °C, the porosity decreases to ~28%, whereas the compressive strength increases to 25 MPa, which is able to meet the requirement of cathode-supported SOFCs (solid oxide fuel cells). Full article

Chemical doping via insertion of ions into the lattice of a host material is a key strategy to flexibly manipulate functionalities of materials. In this work, we present a novel case study on the topotactic insertion of fluoride ions into oxygen-deficient ferromagnetic thin films of La_0.74Sr_0.26MnO_3−δ (LSMO) epitaxially grown onto single-crystal SrTiO₃ (STO) substrates. The effect of fluorination on the film structure, composition, and magnetic properties is compared with the case of oxygen-deficient and fully-oxidized LSMO films. Although incorporation of F⁻ anions does not significantly alter the volume of the LSMO unit cell, a strong impact on the magnetic characteristics, including a remarkable suppression of Curie temperature and saturation magnetization accompanied by an increase in magnetic coercivity, was found. The change in magnetic properties can be ascribed to the disruption of the ferromagnetic exchange interactions along Mn-anion-Mn chains driven by F⁻ doping into the LSMO lattice. Our results indicate that F⁻ doping is a powerful means to effectively modify the magnetic functional properties of perovskite manganites. Full article

Mechanical damage is a major factor limiting the long-term stability of solid oxide fuel cells (SOFCs). Here, the mechanical stability of planar SOFCs consisting of Ni-YSZ anode/YSZ electrolyte/LSM-YSZ cathode (Ni=Nickel, YSZ=yttria-stabilized zirconia, LSM=lanthanum strontium manganite) is analyzed by a structural mechanics model with composition dependent mechanical properties. Influencing factors considered include: the Ni and LSM volume fractions, the thicknesses of anode, cathode and electrolyte layers, and the cell types of anode-, cathode-, and electrolyte-supported designs. It is found that (i) the anode failure probability increases with the Ni content. However, SOFCs remain mechanically safe if the Ni volume fraction is below 65%. (ii) An LSM volume fraction of over 40% is required to maintain the mechanical integrity of cathode. (iii) For an anode-supported cell with a 20 μm thick electrolyte, the anode thickness should be more than 0.5 mm to be mechanically stable. (iv) The anode-supported cell is found to be mechanically safer than that of the electrolyte-supported cell. Full article

We report on a novel method to fabricate composition gradient, epitaxial La1−_xSr_xMnO₃ thin films with the objective to alleviate biaxial film strain. In this work, epitaxial, composition gradient La1−_xSr_xMnO₃, and pure LaMnO3 and La_0.67Sr_0.33MnO₃ thin films were deposited by radio frequency (RF) magnetron sputtering. The crystalline and epitaxy of all films were first studied by symmetric θ–2θ X-ray diffraction (XRD) and low angle XRD experiments. Detailed microstructural characterization across the film thickness was conducted by high-resolution transmission electron microscopy and electron diffraction. Four compositional gradient domains were observed in the La1−_xSr_xMnO₃ film ranging from LaMnO3 rich to La_0.67Sr_0.33MnO₃ at the surface. A continuous reduction in the lattice parameter was observed accompanied by a significant reduction in the out-of-plane strain in the film. Fabrication of the composition gradient La1−_xSr_xMnO₃ thin film was found to be a powerful method to relieve biaxial strain under critical thickness. Besides, the coexistence of domains with a composition variance is opening up various new possibilities of designing new nanoscale structures with unusual cross coupled properties. Full article