MnO3 Materials Research Articles

Room temperature properties of microstructure and resistivity of alkaline earth – doped on lanthanide manganite

Microstructure of material has a strong relation with resistivity property. Here we report our interesting sample of La0.7(Sr1-xBax)0.3MnO3 (x = 0, 0.3, 0.6, and 0.9) material that has been synthesized by using sol-gel method successfully. All pattern of X-ray diffractometer (XRD) on the successful samples show that all samples are single phase confirmed without significant crystal disorder. The XRD pattern refinement yield that all samples formed R-3c space group with a rhombohedral structure. Although the substitution of Ba2+ to Sr2+ ions have significant difference in atomic radius; it does not change the crystal structure. However, the alkaline earth – doped on lanthanide manganite causes a change in lattice parameters which is followed by shifted of average crystal size, bond length, cell unit volume and bond angle at Mn-O-Mn. The microstructure results by means of scanning electron microscope (SEM) characterization shows that substitution of Ba2+ ions decrease the grain size and yield agglomeration. The relation on the microscopic result resistively confirmed by cryogenic magnetometer characterization in the concentration x = 0 has minimum resistivity of 1.28.10-3 Ωm and the maximum resistivity in the concentration x = 0.9 is 1.85.10-1 Ωm. The Ba2+ doped into Sr2+ in lanthanum manganite may cause a wider resistivity range.

Green synthesis of CaxLa1-xMnO3 with modulation of mesoporous and vacancies for efficient low concentration phosphate adsorption

Phosphate concentrations in eutrophic surface waters are usually low, and efficient removal of low concentration phosphate remains a challenge. In this study, Ca-doped LaMnO3 synthesized at doping ratios, designated as CaxLa1-xMnO3 (x = 0, 0.2, 0.4, 0.7), were compared. It was found that, the adsorption capacity of Ca0.4La0.6MnO3 material reached 63.01 mg/g at pH = 5, increased by 63.6% over the undoped LaMnO3 perovskite. For long-term adsorption, Ca0.4La0.6MnO3 could constantly adsorb phosphate to avoid phosphate accumulation (<0.05 mg/L). This proves that Ca0.4La0.6MnO3 has the ability to control dynamic water eutrophication. Characterization and density functional theory results confirmed that CaxLa1-xMnO3 can increase the content of mesopores and oxygen vacancies, providing additional active sites. This reduces the adsorption energy of the La site, promotes electron transfer, and increases its affinity. It provides a new method for removing low-concentration phosphates.

Magnetic properties and ferrimagnetic structures of Mn self-doped perovskite solid solutions (Ho1−xMnx)MnO3

A high-pressure synthesis method was employed to prepare (Ho1-xMnx)MnO3 solid solutions with x = 0.2 and 0.3 (at about 6 GPa and 1,670 K) and magnetic properties and structures were investigated by magnetic, dielectric and neutron diffraction measurements. Both samples crystallize in the GdFeO3-type Pnma perovskite structure, and both samples show magnetization reversal behavior below the compensation temperature of about 35 K (at H = 100 Oe). The magnetization reversal phenomena are originated from a ferrimagnetic (FiM) structure which takes place below TC = 76 K (x = 0.2) and 102 K (x = 0.3) and is built from ferromagnetic (FM) ordering of Mn3+ and Mn4+ cations at the B site which are antiferromagnetically (AFM) coupled with Ho3+ and Mn2+ cations at the A site. The magnetic moment of Ho3+ cations increases significantly with deceasing temperature, and it overcomes the saturated magnetic moment of Mn3+ and Mn4+ cations at the B site. Field-induced first-order transitions were found in both compounds below about 35 K. Neutron diffraction measurements on the x = 0.2 sample found a collinear FiM structure between 76 K and 40 K, and the development of spin canting at the A site below 40 K. The coexistence of Ho3+ and Mn2+ at the A-site gives rise to additional short-range magnetic ordering of Ho3+ and to strain effects along the a-direction which are stronger than in (R1−xMnx)MnO3 materials with heavier and smaller rare-earths cations.

Effects of the sintering temperature on the La0.63Gd0.37MnO3 structure and magnetic properties

La0.63Gd0.37MnO3 material was synthesized using the Pechini-modified-sol–gel method at different sintering temperatures 600, 650, 750, 800, and 900 °C. After characterizing the samples structurally and magnetically, we report a direct relation between the crystallite size, particles agglomeration level, and material performance in field-cooling/zero-field-cooling magnetization modes, in addition to an inverse relation between the existence of Griffith phase and the samples’ magneto-caloric performance. The material sintered at 800 °C presents the maximum isothermal entropy change among others that is 7.57 J kg−1 K−1 at 7 T, in addition to a good performance shown at higher temperatures, making it a promising candidate for different cooling applications.

Magnetocaloric effect and electrical properties of (0.95)La0.45Nd0.25Sr0.3MnO3/(0.05)CuO composites

In this work, the structural, magnetic and magnetocaloric properties of 0.95La0.45Nd0.25Sr0.3MnO3/0.05CuO composites materials were investigated. The samples have been synthesized by solid-state reaction route. The XRD patterns of composites powders show the presence of both perovskite La0.45Nd0.25Sr0.3MnO3 and monoclinic Tenorite CuO materials. The microstructural characterization performed using Scanning Electron Microscope shows that copper oxide nanostructure is located in the grains boundaries after pressing. According to the isothermal magnetization measurements around the Curie temperature, the maximum isothermal magnetic entropy change is calculated to be 4.128 J/(Kg.K) at 5 T for the pellet with an interesting enhancement compared to the powder sample 2.7 J/(Kg.K). The relative cooling power is about 212.8 J Kg−1. Resistivity measurements under different magnetic fields were performed in order to investigate the magnetoresistance properties. The obtained magnetocaloric properties show that 0.95La0.45Nd0.25Sr0.3MnO3/0.05CuO composite was an attractive candidate material for magnetic refrigeration application. About magnetoresistance properties the (% MR) is found to be 32.78% around 320 K under a magnetic field of 5 T.

Application of Large Specific Surface Area Perovskite Oxygen Reduction Catalyst with Three-Dimensional Macropores in Aluminum Air Battery

Perovskite-type catalytic materials have received wide attention as high-performance, low-cost alternatives to precious metal catalysts on the market at present. For a typical perovskite oxide (ABO3), the perovskite material with unsubstituted A and B sites is rarely used as an oxygen reduction catalyst alone due to its limited activity. Secondly, due to the high calcination temperature, the perovskite material usually has a small specific surface area. In this paper, the partial substitution of the A site element is carried out to improve the activity and stability of perovskite oxide, combining with the template method to increase the specific surface area of the perovskite La0.7Sr0.3MnO3 (LSMO) material. The physicochemical properties of the synthesized materials were characterized by SEM, EDS, XRD and BET. The catalytic activity of LSMO as an oxygen reduction reaction (ORR) catalyst was measured by a rotating disk test system. After that, the catalyst material was applied to a flexible aluminum air battery and its discharge behavior and flexibility was studied and tested. The results show that LSMO prepared with SiO2 template has a higher specific surface area (61.5486 m2/g) and pore volume (0.267392 cm3/g), and it also shows higher electrocatalytic activity in the electrochemical test system. When it is used in aluminum-air batteries, the activity of 3D porous LSMO is significantly better than that of sheet and bulk LSMO. The aluminum air battery assembled by LSMO prepared by the template method has a higher discharge voltage (up to 1.46 V) at a constant current. In addition, discharged performance degradation of template-based LSMO was obviously slowed down in the large current density, and the discharge voltage can be improved by 8.2% and 24.5%, respectively, compared with the template-free method and sol-gel method. The specific capacity and energy density of the battery were up to 1048.6 mA h/g and 1020.6 mW h/g, respectively. The battery does not damage its inherent structure within a certain range of deformation, and the output voltage is maintained above 1.38 V. Once released, the voltage can be immediately restored to over 99% of the initial value. This design not only provides a new direction for the future development of variable power supplies, but also provides a new solution for powering wearable electronic devices in the future market.

Structural and transport properties of composite of La0.8Sr0.2MnO3 and BaTiO3 materials

We studied the effect of BaTiO3 phase on the structural, vibrational, and electrical properties of La0.8Sr0.2MnO3. The parent samples of La0.8Sr0.2MnO3, BaTiO3 and their composite (0.85) La0.8Sr0.2MnO3 + (0.15) BaTiO3 were synthesized by solid-state reaction route. Structural study using X-ray diffraction (XRD) for La0.8Sr0.2MnO3 phase revealed a rhombohedrally distorted (space group R3c) structure, while BaTiO3 compound was found to have crystallized in tetragonal structure (space group P4mm). The XRD results were verified using Rietveld refinement. The composite sample (0.85) La0.8Sr0.2MnO3 + (0.15) BaTiO3 display the presence of both of La0.8Sr0.2MnO3 and BaTiO3 phases. The addition of insulating BaTiO3 phase in the ferromagnetic metallic phase of La0.8Sr0.2MnO3 which exhibits well-characterized metal-to-insulator transition in the vicinity of 350 K enhances the resistivity and shifts the metal–insulator transition temperature TMI towards lower temperature. Further, with the application of magnetic field, resistivity of the composite sample is found to decrease and TMI in composite sample is observed to shift towards higher temperature. The magnetoresistance (MR) of composite sample (0.85) La0.8Sr0.2MnO3 + (0.15) BaTiO3 decreases monotonously in 200–300 K regime under magnetic field of 8 T. The analysis of electrical resistivity data in the metallic region (T TMI) is well described using Small polaron hopping (SPH) and Mott's variable range hopping (VRH) models.

Enhanced magnetocaloric effect in Eu-doped La0.7Ca0.3MnO3 compounds

Orthorhombic La0.7-xEuxCa0.3MnO3 samples (x = 0.04–0.12) with apparent density of ρ = 3.9–4.1 g/cm3 prepared by solid-state reactions have been studied. The analysis of temperature-dependent magnetization for an applied field H = 500 Oe indicated a decrease of the Curie temperature (TC) from about 225 K for x = 0.04 through 189 K for x = 0.08–146 K for x = 0.12. The magnetocaloric (MC) study upon analyzing M(H, T) data has revealed that the magnetic entropy change around TC reaches the maximum (|ΔSmax|), which is dependent on both x and H. For an applied field interval of ΔH = 60 kOe, |ΔSmax| values are about 5.88, 4.93, and 4.71 J/kg⋅K for x = 0.04, 0.08, and 0.12, respectively. Though |ΔSmax| decreases with increasing x, relative cooling power (RCP) increases remarkably from 383 J/kg for x = 0.04 to about 428 J/kg for x = 0.08 and 0.12. This is related to the widening of the ferromagnetic-paramagnetic transition region when x increases. Particularly, if combining two compounds with x = 0.04 and 0.08 (or 0.12) as refrigerant blocks for MC applications, a cooling device can work in a large temperature range of 145–270 K, corresponding to RCP ≈ 640 J/kg for H = 60 kOe. M(H) analyses around TC have proved x = 0.04 exhibiting the mixture of first- and second-order phase transitions while x = 0.08 and 0.12 exhibit a second-order nature. The obtained results show potential applications of Eu-doped La0.7Ca0.3MnO3 materials for magnetic refrigeration below room temperature.

Correlation between B value deviation and sintering temperature of perovskite solid solution materials

AbstractThe effects of different sintering temperatures on the system of Ba0.5Sr0.5TiO3–La0.8Ca0.2MnO3 (BST‐LCM) material were investigated by means of scanning electron microscopy, X‐ray, resistance‐temperature measurements, and X‐ray photoelectron spectroscopy. X‐ray diffraction and X‐ray photoelectron spectroscopy confirm that BST‐LCM is completely miscible and BST is the main phase, which under the premise of following the theory of small polaron conduction, titanium ions interact with manganese ions, which affects the electrical properties of the system of BST‐LCM material. For the electrical properties of related, the LCM content is inversely proportional to the activation energy. Through the linear fitting of the experimental data, the empirical formula between the sintering temperature B value and the content of solid solution is obtained, and the approximate B value within a certain range can be preliminarily calculated.

Enhanced Bifunctional Catalytic Activity of Manganese Oxide/Perovskite Hierarchical Core-Shell Materials by Adjusting the Interface for Metal-Air Batteries.

LaMnO3 perovskite is one of the most promising catalysts for oxygen reduction reaction (ORR) in metal-air batteries and can be compared to Pt/C. However, the low catalytic activity toward oxygen evolution reaction (OER) limits its practical application in rechargeable metal-air batteries. In this work, the MnO2/La0.7Sr0.3MnO3 hierarchical core-shell composite materials with a special interface structure have been designed via the selective dissolution method. The core of La0.7Sr0.3MnO3 particles is wrapped by the porous and loose MnO2 nanoparticles. The as-prepared MnO2/La0.7Sr0.3MnO3 materials have excellent catalytic activity toward ORR/OER and are used as bifunctional oxygen electrocatalysts for metal-air batteries. Based on results of transmission electron microscopy, X-ray photoelectron spectroscopy, valence-band spectroscopy, and O2 temperature-programmed desorption analysis, we conclude that the bifunctional catalytic activity of the MnO2/La0.7Sr0.3MnO3 materials can be effectively promoted due to the specific interface structure between the La1-xSrxMnO3 core and the MnO2 shell. This can be attributed to three aspects: (a) the electronic conductivity, which is beneficial for providing the faster charge-transfer paths and kinetics at the oxide/solution interface than that of the MnO2 sample; (b) the enhancement of oxygen adsorption capacity due to surface defects (oxygen vacancies) and chemical adsorption, which is helpful to improve the reaction kinetics during the process of oxygen catalysis; and (c) the tuning of oxygen adsorption ability via the moderate Mn-O bond strength, which may be conducive to getting for obtain an enhanced Mn-O bond strength on the surfaces for ORR and a weakened Mn-O bond in the lattice for OER.

Structure and microstructure of La0.8Ca0.05Ag0.15MnO3 material synthesized by sol-gel method

The La0.8Ca0.05Ag0.15MnO3 material was prepared by the sol-gel method, sintered at 800°C for 24 hours. The material is derived from the La0.8Ca0.2MnO3 material substituted by 15% Ag on the Ca-site. The substitution changed the lattice parameters, Mn-O bond length, and Mn-O-Mn bond angle. These can affect the transport of electrons from the material. The XRD data were analyzed using Rietveld refinement technique and show the material has a rhombohedral structure with the lattice parameters a, b, and c are 5.494, 5.494, and 13.33, respectively. The SEM data with SE mode show La0.8Ca0.2MnO3 material substituted by 15% Ag seen the existence of agglomeration and porous. Furthermore, the material has a high homogeneity, this is seen in SEM data with BSE mode. The EDX results show that the silver has been successfully substituted into the La0.8Ca0.2MnO3 matrix with the value at% for each element contained in the material close to value at% calculation.

Effects of Ag doping on the microstructural, morphological, and magnetic properties of a perovskite material, (La1-xAgx)0.8Ca0.2MnO3

In this study, perovskite (La1-xAgx)0.8Ca0.2MnO3 material was synthesized using the solgel method with different Ag doping levels (x = 0.0.3 and 0.1). The precursors, La2O3, AgN3, Ca(NO3)2.4H2O, and Mn(NO3)2.4H2O were combined stoichiometrically and sintered at 900°C for 24 h. Energy dispersive X-ray spectroscopy was used to confirm the purity of each sample. Rietveld refinement of the X-ray diffraction pattern showed that the samples had a single phase and orthorhombic structure with the Pnma space group. Scanning electron microscopy revealed density, porosity, and granular morphology that affected the characteristics of the sample. The magnetic hysteresis curves indicate that the material was paramagnetic and material with x = 0.1 has a higher magnetic susceptibility than with x = 0.03.

Influence of silver (Ag) doping on a crystal structure of La0.7Ag0.1Ca0.2MnO3 and La0.65Ag0.15Ca0.2MnO3 manganites synthesized by sol-gel method

Perovskite manganite material has been extensively investigated because it has many attractive properties. In this paper, crystal structure of La0.7Ag0.1Ca0.2MnO3 (LACMO1) and La0.65Ag0.15Ca0.2MnO3 (LACMO15) materials will be reported. LACMO1 and LACMO15 materials were synthesized by sol-gel method with sintering temperature 900°C for 24h. Structural properties of LACMO1 and LACMO15 materials were characterized using X-Ray Diffractometer (XRD). The characterized results show a crystal structure transition from orthorhombic (Pnma spacegroup) to rhombohedral ( space group) along with increasing the concentration of Ag doping. The crystal structure transition show there is a distortion of the material structure caused by Ag-doping. Increasing the concentration of Ag doping may affect the tolerance factor (t) that used to measure the degree of distortion of a perovskite.

The effect of Ag-doping (x = 0 and 0.05) on structural and morphological La0.8-xAgxCa0.2MnO3 material synthesized by sol-gel method

In this paper, we will report the Ag-doping effect on the structure and morphology of La08Ca02MnO3 (LCMO) and La075Ag005Ca02MnO3 (LACMO) materials. LCMO and LACMO materials were synthesized via the sol-gel method and sintered at 900 °C for 24h. The structure of the materials was characterized using X-Ray Diffractometer (XRD) and found that both materials are in the orthorhombic structure (Pnma space group). Scanning Electron Microscopy (SEM) was used to observe the morphology of the material and obtained the homogeneity of the materials. With Ag doping, the grain size of the material will decrease. The results of Electron Dispersive Spectroscopy (EDS) confirm the composition of both materials.

Structural, magnetic, magnetocaloric and impedance spectroscopy analysis of Pr0.8Sr0.2MnO3 manganite prepared by modified solid-state route

Orthorhombic Pr0.8Sr0.2MnO3 sample is prepared by solid-state reaction method and quenched in water. The occurrence of a second-order phase transition is confirmed by Arrott plots. The critical exponents determined using different models are in good agreement with the 3D-Ising model. The magnetocaloric results have shown an important maximum of the magnetic entropy change and relative cooling power evaluated at 2.14 J kg−1 K−1 and 101.52 J kg−1 under a field change of 2T. The DC conductance measurements revealed that this compound exhibited a semiconductor to metallic behavior at TSM=400 K. Moreover, the AC results are described by the Jonscher power law. Concerning the electrical and dielectric properties, they disclosed the behavior-dependency of both temperature and frequency. As for the complex impedance measurements, they showed that the conduction mechanism was governed by grain boundaries. The dielectric results demonstrated important values of the real part of the permittivity, and the Pr0.8Sr0.2MnO3 material can be used for capacitor manufacturing.

Effect of Low Doped Calcium on the Magnetic Properties of La0.7Ba0.297Ca0.003MnO3 for Magnetocaloric Application

Effect of low doped calcium concentration to the magnetic properties of La0.7Ba0.3MnO3 material has been reported in this paper. This compound was chosen because it has high potential to be applied in electronic devices. The most intensive research in the last decade is about magnetocaloric effect (MCE). Magnetic refrigeration will replace Freon R12 that is used in conventional refrigeration with magnetic material which has MCE properties. It is due to conventional refrigeration produce chlorofluorocarbons (CFC) and hydrochlorofluorocarbons (HCFCs) gases which causes ozone depletion. The magnetic measurement was performed by using Vibrating Sample Magnetometer in the range of temperature between 300-400 K under external magnetic field until 20 kOe. By using derivative of magnetization as a function of temperature of the material’s result, Curie temperature (Tc ) of the material is 332.7 K. By using equation (5) for calculating magnetic field dependence of magnetization at various temperature result, magnetic entropy change value (ΔSM ) of the material can be obtained. The ΔSM of the material is -2.928 Jkg-1K-1. The material has highest magnetic entropy change value around its Tc . It is due to there is strong lattice spin coupling around its Tc and would be weak at below and above its Tc .

The effect incorporation of Ni=0.05 at Mn site on microwave absorption properties of La0.67Sr0.33MnO3 material

Nowadays we need material that can reduce electromagnetic interference (EMI). Doped LaMnO3 has electromagnetic properties which makes it possible for this material to be used for microwave absorption material. In this study the Ni doped (Ni=0.05) La0.67Sr0.33MnO3 was fabricated by sol-gel method and characterized by X-Ray Diffraction (XRD), Scanning Electron Microscopy-Electron Energy Dispersive Spectroscopy (SEM-EDS), and Vector Network Analyzer (VNA). The XRD result showed that the material was single phase and the crystal structure of the material was rhombohedral with space group R-3c. The lattice parameter of sample decreased after incorporation of Ni. The influence incorporation of Ni into LSMO on microwave absorption performance was investigated. The microwave absorption performance was improved after Ni doping. The maximum reflection loss was -6.29 dB at 11.47 GHz.

Evolution of Hot Polaron States with a Nanosecond Lifetime in a Manganite Perovskite

Understanding and controlling the relaxation process of optically excited charge carriers in solids with strong correlations is of great interest in the quest for new strategies to exploit solar energy. Usually, optically excited electrons in a solid thermalize rapidly on a femtosecond to picosecond timescale due to interactions with other electrons and phonons. New mechanisms to slow down thermalization will thus be of great significance for efficient light energy conversion, e.g., in photovoltaic devices. Ultrafast optical pump–probe experiments in the manganite Pr0.65Ca0.35MnO3, a photovoltaic, thermoelectric, and electrocatalytic material with strong polaronic correlations, reveal an ultraslow recombination dynamics on a nanosecond‐time scale. The nature of long living excitations is further elucidated by photovoltaic measurements, showing the presence of photodiffusion of excited electron–hole polaron pairs. Theoretical considerations suggest that the excited charge carriers are trapped in a hot polaron state. Escape from this state is possible via a slow dipole‐forbidden recombination process or via rare thermal fluctuations toward a conical intersection followed by a radiation‐less decay. The strong correlation between the excited polaron and the octahedral dynamics of its environment appears to be substantial for stabilizing the hot polaron.

Study of La0.67Sr0.33MnO3 Structure and Resistivity Synthesized by Using Sol Gel Method

In this study a colossal magnetoresistance La0.67Sr0.33MnO3 material was synthesized by using a sol gel method with different treatment heating process. First sample calcined at 850°C for 10 hours and pelletized, labelled as LSMO1, while another sample calcined at 850°C for 10 hours, pelletized, and sintered at 1200°C for 2 hours, labelled as LSMO2. The aim of this study was to learn a structure and resistivity of this material. The XRD results showed that both samples were single phase with no peak of impurity and formed a rhombohedral structure with space group R-3c. And the result showed that LSMO1 has smaller crystallite size than LSMO2. Result of resistivity measurement showed that LSMO1 has insulator behavior with resistivity several order of magnitude bigger than LSMO2. While LSMO2 had the peak of resistivity that showed a metal-insulator transition.

Correlating melting and collapse of charge ordering with magnetic transitions in La0.5-xPrxCa0.5MnO3

The magnetic properties of polycrystalline La0.5-xPrxCa0.5MnO3 material are investigated at different temperatures. The existence of magnetically diverse phases associated with various relaxation modes and their modulation with temperature and doping is analyzed. La0.5Ca0.5MnO3 exhibited field induced melting and collapse of charge ordered antiferromagnetic (CO-AFM) phase into ferromagnetic (FM) state. This phenomenon results in lowering of Neel’s temperature (TN) along with changes in the slope of magnetic moment with temperature. Using normalized M(T) curves, the variation and interplay of charge ordered temperature (TCO), Curie temperature (TC) and TN is conferred. The coexistence of two magnetic modes is explained as major ingredient for the magnetic transitions as well as metal to insulator transition (MIT); where melting and collapse of charge ordering is conversed as basic feature in these Praseodymium (Pr) doped La0.5Ca0.5MnO3 materials.