Search Results (38)

Novel high-entropy perovskite oxide powders were synthesized using a sol-gel process. The B-site contained five cations: chromium, cobalt, iron, manganese, and nickel. The B-site cations were present on an equiatomic basis. The A-site cation was lanthanum, with calcium doping. The amount of A-site doping varied from 0 to 30 at%, yielding a composition of La_1−xCa_x(Co_0.2Cr_0.2Fe_0.2Mn_0.2Ni_0.2)O_3−δ. The resulting perovskite powders were pressurelessly sintered in air at 1400 °C for 2 h. Sintered densities were measured, and the grain structure was imaged via scanning electron microscopy to investigate the effect of doping. Samples were cut and polished, and their resistance was measured at varying temperatures in air to obtain the electrical conductivity and the mechanism that governs it. Plots of electrical conductivity as a function of composition and temperature indicate that the increased configurational entropy of the perovskite materials has a demonstrable effect. Full article

The search for effective and reliable methods of photosensitization of oxide-based semiconductor materials is of great significance for their use in photocatalytic reactions of hydrogen production and environmental remediation under natural sunlight. The present study is focused on partial substitution of titanium with manganese in the structure of layered perovskite-like titanate Na₂La₂Ti₃O₁₀, which was employed to yield a series of photocatalytically active materials, Na₂La₂Mn_xTi_3−xO₁₀ (x = 0.002–1.0), as well as their protonated forms H₂La₂Mn_xTi_3−xO₁₀ and nanosheets. It was established that the manganese cations Mn⁴⁺ are embedded in the middle sublayer of oxygen octahedra in the perovskite slabs La₂Mn_xTi_3−xO₁₀²⁻ and that the maximum achievable manganese content x in the products is ≈0.9. The partial cationic substitution in the perovskite sublattice led to a pronounced contraction of the optical band gap from 3.20 to 1.35 eV (depending on x) and, therefore, allowed the corresponding photocatalysts to utilize not only ultraviolet, but also visible and near-infrared light with wavelengths up to ≈920 nm. The materials obtained were tested as photocatalysts of hydrogen evolution from aqueous methanol, and the greatest activity in this reaction was demonstrated by the samples with low manganese contents (x = 0.002–0.01). However, the materials with greater substitution degrees may be of high interest for use in other photocatalytic processes and, especially, in thermophotocatalysis due to their improved ability to absorb the near-infrared part of solar radiation. Full article

The most commonly used optical oxygen sensing materials are phosphorescent molecules and functionalized nanocrystals. Many exploration studies on oxygen sensing have been carried out using the fluorescence or phosphorescence of semiconductor nanomaterials. Lead halide perovskite nanocrystals, a new type of ionic semiconductor, have excellent optical properties, making them suitable for use in optoelectronic devices. They also show promising applications in analytical sensing and biological imaging, especially manganese-doped perovskite nanocrystals for optical oxygen sensing. As a class of materials with diverse sources, copper iodide cluster semiconductors have rich structural and excellent luminescent properties, and have attracted attention in recent years. These materials have adjustable optical properties and sensitive stimulus response properties, showing great potential for optical sensing applications. This review paper provides a brief introduction to traditional oxygen sensing using organic molecules and introduces research on oxygen sensing using novel luminescent semiconductor materials, perovskite metal halides and copper iodide hybrid materials in recent years. It focuses on the mechanism and application of these materials for oxygen sensing and evaluates the future development direction of these materials for oxygen sensing. Full article

In this paper, the synthesis, characterization, and investigation of electrocatalytic properties of perovskites of general formula PrMn_0.5M_0.5O₃ (M = Cr, Fe, Co, Ni) are presented. The synthesis was conducted by the solution combustion method using glycine as a fuel. The perovskite with the formula PrMn_0.5Fe_0.5O₃ was also synthesized by the sol–gel combustion method with citric acid as fuel. The obtained perovskites were investigated by X-ray powder diffraction (XRPD), scanning electron microscopy (SEM) with energy dispersive X-ray spectroscopy (EDX), infrared spectroscopy, and cyclic voltammetry. The XRPD patterns showed that the compounds are pure and isostructural within the series. The unit cell parameters of the compounds were determined within the Pnma space group, and several crystallochemical parameters were calculated and discussed. The recorded SEM images of the perovskites revealed a porous morphology, while the EDX analysis confirmed the 2:1:1 atomic percentage ratio of Pr:Mn:M. Within this investigation, the electrocatalytic properties of the obtained perovskites towards oxidation of OH⁻ ions and H₂O₂ oxidation in phosphate buffer were studied by cyclic voltammetry, using a paraffin-impregnated graphite electrode (PIGE) modified with microcrystals of the investigated perovskites. PrMn_0.5Fe_0.5O₃ showed high electrocatalytic activity for OH⁻ oxidation, while both PrMn_0.5Fe_0.5O₃ and PrMn_0.5Co_0.5O₃ exhibited significant efficiency for H₂O₂ oxidation, with a distinct oxidation peak with a peak potential of 0.6 V. Full article

Hole-doped manganese oxides exhibit a gigantic negative magnetoresistance, referred to as colossal magnetoresistance (CMR), owing to the interplay between double-exchange (DE) ferromagnetic metal and charge-ordered antiferromagnetic insulator/semiconductor phases. Magnetoresistive manganites display a sharp resistivity drop at the metal–insulator transition temperature (T^MI). CMR effects in perovskite manganites, specifically La_0.67Ca_0.33MnO₃ (La-Ca-Mn-O or LCMO), have been extensively investigated. This review paper provides a comprehensive introduction to the crystallographic structure, as well as the electronic and magnetic properties, of LCMO films. Furthermore, we delve into a detailed discussion of the effects of epitaxial strain induced by different substrates on LCMO films. Additionally, we review the early findings and diverse applications of LCMO thin films. Finally, we outline potential challenges and prospects for achieving superior LCMO film properties. Full article

In this work, a series of Ba_xMn_0.7Cu_0.3O₃ samples (x: 1, 0.9, 0.8, and 0.7, BxMC) was synthesized, characterized, and used as catalysts for CO oxidation reaction. All formulations were active for CO oxidation in the tested conditions. A correlation between the electrical conductivity, obtained by impedance spectroscopy, and the reducibility of the samples, obtained by H₂-TPR, was observed. The Ba_0.8Mn_0.7Cu_0.3O₃ composition (B0.8MC) showed the best catalytic performance (comparable to that of the 1% Pt/Al₂O₃ reference sample) during tests conducted under conditions similar to those found in the exhaust gases of current gasoline engines. The characterization data suggest the simultaneous presence of a high Mn(IV)/Mn(III) surface ratio, oxygen vacancies, and reduced copper species, these two latter being key properties for ensuring a high CO conversion percentage as both are active sites for CO oxidation. The reaction temperature and the reactant atmosphere composition seem to be the most important factors for achieving a good catalytic performance, as they strongly determine the location and stability of the reduced copper species. Full article

Formaldehyde (HCHO) is identified as the most toxic chemical among 45 organic compounds found in industrial wastewater, posing significant harm to both the environment and human health. In this study, a novel approach utilizing the Lanthanum-manganese complex oxide (LaMnO₃)/peroxymonosulfate (PMS) system was proposed for the effective removal of HCHO from wastewater. Perovskite-Type LaMnO₃ was prepared by sol-gel method. The chemical compositions and morphology of LaMnO₃ samples were analyzed through thermogravimetric analysis (TG), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and transmission electron microscopy (TEM). The effects of LaMnO₃ dosage, PMS concentration, HCHO concentration, and initial pH on the HCHO removal rate were investigated. When the concentration of HCHO is less than 1.086 mg/mL (5 mL), the dosage of LaMnO₃ is 0.06 g, and n(PMS)/n(HCHO) = 2.5, the removal rate of HCHO is more than 96% in the range of pH = 5–13 at 25 °C for 10 min. Compared with single-component MnO₂, the perovskite structure of LaMnO₃ is beneficial to the catalytic degradation of HCHO by PMS. It is an efficient Fenton-like oxidation process for treating wastewater containing HCHO. The LaMnO₃ promoted the formation of SO₄•⁻ and HO•, which sequentially oxidized HCHO to HCOOH and CO₂. Full article

Mixed oxides featuring perovskite-type structures (ABO₃) offer promising catalytic properties for applications focused on the control of atmospheric pollution. In this work, a series of Ba_xMnO₃ (x = 1, 0.9, 0.8 and 0.7) samples have been synthesized, characterized and tested as catalysts for CO oxidation reaction in conditions close to that found in the exhausts of last-generation automotive internal combustion engines. All samples were observed to be active as catalysts for CO oxidation during CO-TPRe tests, with Ba_0.7MnO₃ (B0.7M) being the most active one, as it presents the highest amount of oxygen vacancies (which act as active sites for CO oxidation) and Mn (IV), which features the highest levels of reducibility and the best redox properties. B0.7M has also showcased a high stability during reactions at 300 °C, even though a slightly lower CO conversion is achieved during the second consecutive reaction cycle. This performance appears to be related to the decrease in the Mn (IV)/Mn (III) ratio. Full article

The achievement of size uniformity and monodispersity in perovskite quantum dots (QDs) requires the implementation of precise temperature control and the establishment of optimal reaction conditions. Nevertheless, the accurate control of a range of reaction variables represents a considerable challenge. This study addresses the aforementioned challenge by employing manganese (Mn) doping to achieve size uniformity in CsPbBr₃ perovskite QDs without the necessity for the precise control of the reaction conditions. By optimizing the Mn:Pb ratio, it is possible to successfully dope CsPbBr₃ QDs with the appropriate concentrations of Mn²⁺ and achieve a uniform size distribution. The spectroscopic measurements on single QDs indicate that the appropriate Mn²⁺ concentrations can result in a narrower spectral linewidth, a longer photoluminescence (PL) lifetime, and a reduced biexciton Auger recombination rate, thus positively affecting the PL properties. This study not only simplifies the size control of perovskite QDs but also demonstrates the potential of Mn-doped CsPbBr₃ QDs for narrow-linewidth light-emitting diode applications. Full article

In this work, evidence of isothermal magnetic entropy change ($∆S_M$) over a broad temperature region is presented in a series of La_1.4Sr_1.6Mn_2−xNb_xO₇ Ruddlesden–Popper compounds with niobium modification (Nb) (0.0 ≤ x ≤ 0.15) at the manganese (Mn) site. The ceramic samples were obtained through a solid-state sintering method in optimized conditions. All compounds predominantly possessed Ruddlesden–Popper phase while a few additional reflections were resolved in Nb-doped compounds which indicates the separation of structural phases. These peaks are assigned to a separate layered perovskite and single perovskite with tetragonal symmetry and hexagonal symmetry, respectively. The microstructure of the pure sample reveals uniform grain morphology but in Nb-doped specimens chiefly three types of grains were found. It was assumed that the inter-connected large particles were of R-P phase which is dominant in both parent and x = 0.05 compounds, while the hexagonal and polygonal morphology of grains in higher concentrations of dopants directly corroborates with the symmetry of single perovskite and additional layered perovskite phases, respectively. The parent compound exhibits a single $∆S_M$ curve, whereas all Nb-substituted samples display bifurcated $∆S_M$ curves. This indicated two transition regions with multiple magnetic components, attributed to distinct structural phases. The highest ${∆S}_M$ values obtained for components corresponding to the R-P phase are 2.32 Jkg⁻¹k⁻¹, 0.75 Jkg⁻¹k⁻¹, 0.58 Jkg⁻¹k⁻¹ and 0.43 Jkg⁻¹k⁻¹ and for the second component located around room temperature are 0.0 Jkg⁻¹k⁻¹, 0.2 Jkg⁻¹k⁻¹, 0.28 Jkg⁻¹k⁻¹ and 0.35 Jkg⁻¹k⁻¹ for x = 0.0, 0.05, 0.10 and 0.15 compositions, respectively, at 2.5 T. Due to the collective participation of both components the $∆S_M$ was expanded through a broad temperature range upon Nb doping. Full article

The dielectric properties of non-stoichiometric SrMnO₃ (SMO) thin films grown by molecular beam epitaxy were systematically investigated. Especially, the effects of cation stoichiometry-induced diverse types and densities of defects on the dielectric properties of SMO films were revealed. Two anomalous dielectric relaxation behaviors were observed at different temperatures in both Sr-rich and Mn-rich samples. High-temperature dielectric relaxation, resulting from a short-range Mn-related Jahn–Teller (JT) polaron hopping motion, was reinforced by an enhancement of JT polaron density in the Sr-rich film, which contained abundant SrO Ruddlesden–Popper (R-P) stacking faults. However, an excessive number of disordered Sr vacancy clusters in Mn-rich thin film suppressed the hopping path of JT polarons and enormously weakened this dielectric relaxation. Thus, The Sr-rich film demonstrated a higher dielectric constant and dielectric loss than the Mn-rich film. In addition, low-temperature dielectric relaxation may be attributed to the polarization/charge glass state. Full article

Lead halide perovskites have been widely used in optoelectronic devices due to their excellent properties; however, the toxicity of lead and the poor stability of these perovskites hinder their further application. Herein, we report a zero-dimensional (0D) lead-free organic manganese (II) bromide hybrid compound of (TBA)₂MnBr₄ (TBA⁺ = tetrabutylammonium cation) single crystals (SCs) with great environmental stability. The (TBA)₂MnBr₄ SCs show a strong green emission peak at 518 nm with a high photoluminescence quantum yield (PLQY) of 84.98% at room temperature, which is attributed to the d-d transition of single Mn²⁺ ions, as also confirmed through density functional calculation. A green light-emitting diode was produced based on (TBA)₂MnBr₄ SCs, which exhibited CIE coordinates (0.17, 0.69) close to those of standard green. A photodetector fabricated by the (TBA)₂MnBr₄ SCs shows an obvious photo response with a rapid millisecond rise/decay response time (at 365 nm). Our findings promote the research of Mn(II)-based organic–inorganic hybrid materials and pave the way by using these materials for future high-performance optoelectronic devices. Full article

In recent years, metal-halide hybrid materials have attracted considerable attention because materials, such as lead-iodide perovskites, can have excellent properties as photovoltaics, light-emitting devices, and photodetectors. These materials can be obtained in different dimensionalities (1D, 2D, and 3D), which directly affects their properties. In this article, we built 0D, 1D, and 2D manganese halide materials with 3-aminopyridine (3AP) or 4-ethylpyridine (4EtP). Two isomorphic complexes with 3AP and manganese chloride ([MnCl₂(3AP)₄]) or manganese bromide ([MnBr₂(3AP)₄]) were obtained with the amino group in 3AP assisting in the formation of 0D structures via hydrogen bonding. By modifying the reaction conditions, 3AP can also be used to build a 2D coordination polymer with manganese chloride ([MnCl₃3AP]⁻ [3APH]⁺). Unlike 3AP, 4EtP does not provide the opportunity for hydrogen bonding, leading to the formation of two additional isomorphic compounds built of individual 1D chains with manganese chloride ({MnCl₃(4EtP)₂}_n) and manganese bromide ({MnBr₂(4EtP)₂}_n). In the visible region, the 0D and 1D manganese halide compounds have similar photoluminescence properties; however, 0D and 1D have different near-IR emissions. In conclusion, hydrogen-bonding groups can play a role in the formation of discrete manganese-halide units, 1D halide chains, or 2D polymeric sheets. Full article

In this study, we analyzed the role of a series of BaMn_1−xNi_xO₃ (x = 0, 0.2, and 0.4) mixed oxide catalysts, synthesized using the sol–gel method, in NO_x-assisted diesel soot oxidation. ICP-OES, XRD, XPS, and H₂-TPR techniques were used for characterization and Temperature-Programmed Reaction experiments (NO_x-TPR and Soot-NO_x-TPR), and isothermal reactions at 450 °C (for the most active sample) were carried out to determine the catalytic activity. All samples catalyzed NO and soot oxidation at temperatures below 400 °C, presenting nickel-containing catalysts with the highest soot conversion and selectivity to CO₂. However, the nickel content did not significantly modify the catalytic performance, and in order to improve it, two catalysts (5 wt % in Ni) were synthesized via the hydrothermal method (BMN2H) and the impregnation of nickel on a BaMnO₃ perovskite as support (M5). The two samples presented higher activity for NO and soot oxidation than BMN2E (obtained via the sol–gel method) as they presented more nickel on the surface (as determined via XPS). BMN2H was more active than M5 as it presented (i) more surface oxygen vacancies, which are active sites for oxidation reactions; (ii) improved redox properties; and (iii) a lower average crystal size for nickel (as NiO). As a consequence of these properties, BMN2H featured a high soot oxidation rate at 450 °C, which hindered the accumulation of soot during the reaction and, thus, the deactivation of the catalyst. Full article

Perovskite SCR catalysts have become a hot research topic in the field of de-NO_x catalyst development. This article selects LaMnO₃ with high performance as the research object, modifies the catalyst by doping some iron elements instead of manganese elements, and applies density functional theory to study its reaction mechanism, providing theoretical reference for further research on perovskite. Research has found that several main reactants such as NH₃, NO, and O₂ can form stable adsorption at the active site, with NO more inclined to adsorb at the nitrogen atom end at the active site. The oxidation of O₂ molecules after adsorption is greater than that of the active site. The adsorption capacity of the Mn active site of the catalyst before modification on the above molecules is weaker than that of the Fe active site introduced after modification. Under both anaerobic and aerobic conditions in the SCR reaction process, NH₃ molecules are first adsorbed at the active site, and then influenced by lattice oxygen under anaerobic conditions. Under aerobic conditions, they are gradually dehydrogenated and produce NH₂ and NH radicals. These two radicals react with NO molecules to form intermediate products in the form of NH₂NO and NHNO molecules. Due to the instability of the intermediate products, they ultimately decompose into N₂ and H₂O molecules. The introduction of Fe active sites can increase the generation of NH₂ and NH radicals during the reaction process and simplify the reaction process between NH₂ radicals and NO molecules, which will be conducive to the completion of the reaction. Full article