Search Results (19)

Lanthanum strontium manganate (La_1−xSr_xMnO₃) is considered a highly promising material for the development of intelligent thermal control coatings due to its exceptional properties. Recent studies on this material have primarily utilized solid-state synthesis as the main preparation method. Research efforts have predominantly focused on investigating the effects of material composition, heat treatment processes, and other factors on the properties of the synthesized material. There has been a limited amount of research investigating the influence of chemical precipitation process parameters on the properties of the synthesized La_1−xSr_xMnO₃ material. In this study, the intelligent thermal control coating material La_0.8Sr_0.2MnO₃ was synthesized using the chemical precipitation method. The effects of varying precipitant concentrations on the properties of the synthesized material were investigated. When the precipitant concentration is 12 wt.% or 15 wt.%, the synthesized powder agglomerates predominantly form three-dimensional blocky structures after sintering. At lower concentrations such as 6 wt.% and 9 wt.%, the powder agglomerates predominantly form two-dimensional sheet-like structures after sintering. At precipitant concentrations of 6 wt.% and 9 wt.%, the strontium content in the synthesized powder becomes significantly lower than the designed theoretical value. When the precipitant concentration is relatively high, localized manganese aggregation occurs in the synthesized lanthanum strontium manganate material. The temperature dependence of the emittance test result indicates that the emissivity variation of La_0.8Sr_0.2MnO₃ material synthesized using 12 wt.% ammonia solution as precipitant reaches 0.428 from 173 K to 373 K, demonstrating excellent emissivity modulation performance. Full article

This study comparatively evaluates the performance of ABO₃ perovskite materials (A = La, Ca, Sr; B = Mn, Fe) as oxygen carriers in three-step Chemical Looping Hydrogen (CLH) technology, focusing on redox behavior, oxygen transport capacity, hydrogen production, and selectivity under controlled pulse-mode conditions. The redox behavior of the materials is analyzed in relation to their defect chemistry. Perovskites such as (La_1−xCa_x)MnO₃, (La_1−xSr_x)MnO₃, and (La_0.6Ca_0.4)(Mn_1−xFe_x)O₃ were synthesized via wet chemical methods and tested in chemical looping cycles. Doping A-site cations with Ca or Sr enhanced oxygen delivery capacity by more than 100% upon reduction with CH₄ when dopant content (x) increased from 0 to 0.5. However, H₂ selectivity decreased from 52% to 2.5% for (La_1−xCa_x)MnO₃ and from 46% to 14% for (La_1−xSr_x)MnO₃ under the same conditions. In contrast, substituting Mn with Fe significantly improved hydrogen production, particularly in LaFeO₃, which exhibited the highest hydrogen selectivity and yield. At 1000 °C, LaFeO₃ produced nearly 10 mmol H₂ g⁻¹, with 80% generated during the reduction step at 99.9% selectivity and the remaining 20% during the water-splitting step at 100% selectivity. These results are linked to the extent of B-site cation reduction reactions (i) B⁴⁺ → B³⁺, which facilitates complete fuel oxidation and (ii) B³⁺ → B²⁺, which leads to partial fuel oxidation. The reverse of (ii) also contributes to H₂ production during water splitting. Additionally, the study assesses the materials’ microstructure and stability over prolonged cycles. The findings highlight Fe-based perovskites, particularly LaFeO₃, as promising candidates for CLH applications, emphasizing the need for structural and compositional optimization to enhance hydrogen production efficiency. Full article

The increasing use of natural gas as an efficient, reliable, affordable, and cleaner energy source, compared with other fossil fuels, has brought the catalytic CH₄ complete oxidation reaction into the spotlight as a simple and economic way to control the amount of unconverted methane escaping into the atmosphere. CH₄ emissions are a major contributor to the ‘greenhouse effect’, and therefore, they need to be effectively reduced. Catalytic CH₄ oxidation is a promising method that can be used for this purpose. Detailed studies of the activity, oxidative thermal aging, and the time-on-stream (TOS) stability of pristine La_1−xSr_xMnO₃ perovskites (LS_XM; X = % substitution of La with Sr = 0, 30, 50 and 70%) and iridium-loaded Ir/La_1−xSr_xMnO₃ (Ir/LS_XM) perovskite catalysts were conducted in a temperature range of 400–970 °C to achieve complete methane oxidation under excess oxygen (lean) conditions. The effect of X on the properties of the perovskites, and thus, their catalytic performance during heating/cooling cycles, was studied using samples that were subjected to various pretreatment conditions in order to gain an in-depth understanding of the structure–activity/stability correlations. Large (up to ca. 300 °C in terms of T₅₀) inverted volcano-type differences in catalytic activity were found as a function of X, with the most active catalysts being those where X = 0%, and the least active were those where X = 50%. Inverse hysteresis phenomena (steady-state rate multiplicities) were revealed in heating/cooling cycles under reaction conditions, the occurrence of which was found to depend strongly on the employed catalyst pre-treatment (pre-reduction or pre-oxidation), while their shape and the loop amplitude were found to depend on X and the presence of Ir. All findings were consistently interpreted, which involved a two-term mechanistic model that utilized the synergy of Eley–Rideal and Mars–van Krevelen kinetics. Full article

The catalytic oxidation of CO is probably the most investigated reaction in the literature, for decades, because of its extended environmental and fundamental importance. In this paper, the oxidation of CO on La_1−xSr_xMnO₃ perovskites (LSMx), either unloaded or loaded with dispersed Ir nanoparticles (Ir/LSMx), was studied in the temperature range 100–450 °C under excess O₂ conditions (1% CO + 5% O₂). The perovskites, of the type La_1−xSr_xMnO₃ (x = 0.0, 0.3, 0.5 and 0.7), were prepared by the coprecipitation method. The physicochemical and structural properties of both the LSMx and the homologous Ir/LSMx catalysts were evaluated by various techniques (XRD, N₂ sorption–desorption by BET-BJH, H₂-TPR and H₂-Chem), in order to better understand the structure–activity–stability correlations. The effect of preoxidation/prereduction/aging of the catalysts on their activity and stability was also investigated. Results revealed that both LSMx and Ir/LSMx are effective for CO oxidation, with the latter being superior to the former. In both series of materials, increasing the substitution of La by Sr in the composition of the perovskite resulted to a gradual suppression of their CO oxidation activity when these were prereduced; the opposite was true for preoxidized samples. Inverse hysteresis phenomena in activity were observed during heating/cooling cycles on the prereduced Ir/LSMx catalysts with the loop amplitude narrowing with increasing Sr-content in LSMx. Oxidative thermal sintering experiments at high temperatures revealed excellent antisintering behavior of Ir nanoparticles supported on LSMx, resulting from perovskite’s favorable antisintering properties of high oxygen storage capacity and surface oxygen vacancies. Full article

A measurement system based on the colossal magnetoresistance CMR-B-scalar sensor was developed for the measurement of short-duration high-amplitude magnetic fields. The system consists of a magnetic field sensor made from thin nanostructured manganite film with minimized memory effect, and a magnetic field recording module. The memory effect of the La_1−xSr_x(Mn_1−yCo_y)_zO₃ manganite films doped with different amounts of Co and Mn was investigated by measuring the magnetoresistance (MR) and resistance relaxation in pulsed magnetic fields up to 20 T in the temperature range of 80–365 K. It was found that for low-temperature applications, films doped with Co (LSMCO) are preferable due to the minimized magnetic memory effect at these temperatures, compared with LSMO films without Co. For applications at temperatures higher than room temperature, nanostructured manganite LSMO films with increased Mn content above the stoichiometric level have to be used. These films do not exhibit magnetic memory effects and have higher MR values. To avoid parasitic signal due to electromotive forces appearing in the transmission line of the sensor during measurement of short-pulsed magnetic fields, a bipolar-pulsed voltage supply for the sensor was used. For signal recording, a measurement module consisting of a pulsed voltage generator with a frequency up to 12.5 MHz, a 16-bit ADC with a sampling rate of 25 MHz, and a microprocessor was proposed. The circuit of the measurement module was shielded against low- and high-frequency electromagnetic noise, and the recorded signal was transmitted to a personal computer using a fiber optic link. The system was tested using magnetic field generators, generating magnetic fields with pulse durations ranging from 3 to 20 μs. The developed magnetic field measurement system can be used for the measurement of high-pulsed magnetic fields with pulse durations in the order of microseconds in different fields of science and industry. Full article

The electrocatalytic activity characterization of the oxygen reduction reaction (ORR) is commonly characterized using a rotating disk electrode (RDE) with linear sweep voltammetry (LSV) or cyclic voltammetry (CV) measurements. Despite the wide application of this method in the literature, its reproducibility and comparability are rarely mentioned in articles. LSV and CV are sensitive to experimental conditions, thus the reproducibility is a significant concern. In this article, the perovskite oxides La_1−xSr_xMnO₃ (LSMO_x, x = 0, 0.1, 0.2, 0.3, 0.4, 0.5) are chosen for the case study to measure their electroactivity using the RDE method. The main elements that influence the reproducibility of the experiment are presented and the corresponding explanations as well as the means for ensuring the reproducibility are given. Through the case study of LSMO_x with variations in x and calcination temperatures, the values for the kinetic current of ORR on different catalysts are compared. It is found that doping ratios above 0.1 are associated with higher ORR electroactivity, with around a 50 mV difference in ORR onset potential between x > 0.1 and x = 0.1, which is in accordance with the results of reported works, whereas there is no significant difference when x = 0.2–0.5. Calcination temperature has little influence on the electroactivity of LSMO_x, resulting in only a slight advantage at lower calcination temperatures, with an ORR onset potential that is around 10 mV more positive. Full article

A perovskite La_1−xSr_xMnO₃ cathode thin film for an oxygen ion conducting solid oxide fuel cell was prepared using a low power (8.8 kW) liquid solution plasma spray method. Usually, a 30–50 kW Ar plasma torch with temperature higher than all the melting points of solid precursors is essential to synthesis oxides thin film. However, using the liquid precursors as the feeding materials, the required power can be reduced and save a lot of thermal budget. The precursors are water solutions of lanthanum nitrate hexahydrate, manganese(II) nitrate tetrahydrate, and strontium nitrate. The atomic percentage of La in the plasma sprayed La_1−xSr_xMnO₃ cathode film is lower than that of La in the feeding precursor into the torch, which is due to the low boiling temperature of La(NO₃)₃ precursor. The oxygen stoichiometry of La_1−xSr_xMnO_3−δ deduced from the valence state of Mn measured by X-ray absorption spectroscopy shows an oxygen deficit structure. The measured low resistivity of 0.07–0.09 Ωcm at room temperature for this La_1−xSr_xMnO_3−δ is essential for oxygen ion transport in the cathode thin film of a solid-state fuel cell. 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

High-entropy perovskite oxides have already been studied in various fields owing to their high-entropy-induced properties. Partial substitution of an element by a lower valence element usually improves the oxygen permeability of perovskite oxides, but high substitution amounts may lead to structural instability. In this work, pure high-entropy perovskites Pr_$1-x$Sr_x(Cr,Mn,Fe,Co,Ni)O_$3-\delta$ with high amounts Sr up to $x=0.5$ were synthesized via a sol–gel method. Several characterization methods prove that the solubility of Sr increases with higher temperatures of the heating treatment. The ceramic with $x=0.5$ shows a transition from semi-conductive to metallic behavior when the temperature reaches 873 K. Its oxygen flux is comparable to the low-entropy counterpart La_0.6Sr_0.4Co_0.5Fe_0.5O_$3-\delta$. A stable run of ca. 46.2 h was documented for oxygen permeation under an air/CO₂ gradient. 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

Perovskite oxides, being transition metal oxides, show promise as bifunctional catalysts being able to catalyze both oxygen evolution reactions (OER) and oxygen reduction reactions (ORR). These two reactions play a crucial role in energy storage and energy conversion devices. An important feature of perovskite catalyst is their ability to be tuned, as tuning can positively affect both reactivity and stability. In this study, Density Functional Theory (DFT) has been utilized to calculate both the equilibrium phase stability and the overpotentials (reactivity performance indicator of the catalysts) of La_1−xSr_xMnO₃ (LSM) structures with different stoichiometry by introducing Mn and O vacancies for both the OER/ORR reactions. The electronic structures reveal that combined Mn and O vacancies can lead to higher catalytic activity for both OER and ORR due to the optimum filling of antibonding orbital electrons. Moreover, both O p-band centers and equilibrium phase stability plots show that LSM structures can be stable at normal OER/ORR operating conditions in an alkali medium. Full article

Ventilation air methane (VAM) is the main cause of greenhouse gas emissions in coal mining. Catalytic flow reverse reactor (CFRR) is widely used in VAM to mitigate methane emissions. In this study, palladium (Pd) and La_1−xSr_xMnO₃ were used as catalysts in a CFRR. Different types of catalysts were prepared by loading La_0.8Sr_0.2MnO₃, La_0.9Sr_0.1MnO₃, and 0.1%Pd-La_0.9Sr_0.1MnO₃ on a cordierite honeycomb reactor coated with γ-Al₂O₃ to compare their performances. In addition, this study compared the performance of the three catalysts in an 800 °C reactor based on different methane inlet concentrations, inlet speeds, and conversion times. The results showed: (1) 0.1% addition of Pd increased methane conversion. (2) La_0.8Sr_0.2MnO₃ had higher efficiency at lower methane inlet concentrations, whereas La_0.9Sr_0.1MnO₃ was more efficient at higher methane concentrations. This study demonstrates that a higher Sr loading is worth implementing only when the methane concentration of VAM is lower than 0.6%. (3) To achieve a higher methane conversion efficiency, the inlet velocity of methane should also be considered. Full article

Benefitting from exceptional energy storage performance, dielectric-based capacitors are playing increasingly important roles in advanced electronics and high-power electrical systems. Nevertheless, a series of unresolved structural puzzles represent obstacles to further improving the energy storage performance. Compared with ferroelectrics and linear dielectrics, antiferroelectric materials have unique advantages in unlocking these puzzles due to the inherent coupling of structural transitions with the energy storage process. In this review, we summarize the most recent studies about in-situ structural phase transitions in PbZrO₃-based and NaNbO₃-based systems. In the context of the ultrahigh energy storage density of SrTiO₃-based capacitors, we highlight the necessity of extending the concept of antiferroelectric-to-ferroelectric (AFE-to-FE) transition to broader antiferrodistortive-to-ferrodistortive (AFD-to-FD) transition for materials that are simultaneously ferroelastic. Combining discussion of the factors driving ferroelectricity, electric-field-driven metal-to-insulator transition in a (La_1−xSr_x)MnO₃ electrode is emphasized to determine the role of ionic migration in improving the storage performance. We believe that this review, aiming at depicting a clearer structure–property relationship, will be of benefit for researchers who wish to carry out cutting-edge structure and energy storage exploration. Full article

Phase composition, crystal structure, and selected physicochemical properties of the high entropy Ln(Co,Cr,Fe,Mn,Ni)O_3−δ (Ln = La, Pr, Gd, Nd, Sm) perovskites, as well as the possibility of Sr doping in Ln_1−xSr_x(Co,Cr,Fe,Mn,Ni)O_3−δ series, are reported is this work. With the use of the Pechini method, all undoped compositions are successfully synthesized. The samples exhibit distorted, orthorhombic or rhombohedral crystal structure, and a linear correlation is observed between the ionic radius of Ln and the value of the quasi-cubic perovskite lattice constant. The oxides show moderate thermal expansion, with a lack of visible contribution from the chemical expansion effect. Temperature-dependent values of the total electrical conductivity are reported, and the observed behavior appears distinctive from that of non-high entropy transition metal-based perovskites, beyond the expectations based on the rule-of-mixtures. In terms of formation of solid solutions in Sr-doped Ln_1−xSr_x(Co,Cr,Fe,Mn,Ni)O_3−δ materials, the results indicate a strong influence of the Ln radius, and while for La-based series the Sr solubility limit is at the level of x_max = 0.3, for the smaller Pr it is equal to just 0.1. In the case of Nd-, Sm- and Gd-based materials, even for the x_Sr = 0.1, the formation of secondary phases is observed on the SEM + EDS images. Full article

Electric noise spectroscopy is a non-destructive and a very sensitive method for studying the dynamic behaviors of the charge carriers and the kinetic processes in several condensed matter systems, with no limitation on operating temperatures. This technique has been extensively used to investigate several perovskite compounds, manganese oxides (La_1−xSr_xMnO₃, La_0.7Ba_0.3MnO₃, and Pr_0.7Ca_0.3MnO₃), and a double perovskite (Sr₂FeMoO₆), whose properties have recently attracted great attention. In this work are reported the results from a detailed electrical transport and noise characterizations for each of the above cited materials, and they are interpreted in terms of specific physical models, evidencing peculiar properties, such as quantum interference effects and charge density waves. Full article