LaMnO3 Systems Research Articles

Effects of Calcium Substitution for La on the Electrochemical Performance of LaMnO3 Nanoparticles

AbstractWith the advantages of short charging and discharging times, high power density, and long cycle life, supercapacitors are regarded as one of the most promising energy storage devices and have garnered massive attention in the field of energy storage. This paper prepared La1−xCaxMnO3 (x=0, 0.05, 0.1, 0.15, and 0.2) nanoparticles by the sol‐gel method. The microstructure, morphology, and electrochemical performance of the samples were characterized. The results depict that La0.85Ca0.15MnO3 has a low charge transfer resistance (0.19 Ω) and a large specific surface area (38.79 m2 g−1). The maximum specific capacitance of the La0.85Ca0.15MnO3 sample reached 248 F/g at a current density of 0.5 A/g, which is ascribable to its large specific surface area and high oxygen vacancy concentration. The anion‐intercalation mechanism was investigated by the charging and discharging process. The above results depict that Ca‐doping significantly enhances the electrochemical performance of LaMnO3 system.

Enhancement in the Electrochemical Performance of Strontium (Sr)-Doped LaMnO3 as Supercapacitor Materials

In this study, Strontium (Sr)-doped perovskite lanthanum manganite (La1−xSrxMnO3) 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 La0.85Sr0.15MnO3 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. La0.85Sr0.15MnO3 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.

Photo-induced optical anisotropy and coherent oscillations in a quasi-two-dimensional two-orbital model for LaMnO3

Ultrafast transient optical conductivity of spin-orbital ordered LaMnO3 was investigated theoretically. A quasi-two-dimensional Hubbard Hamiltonian based on a four-site Mn cluster was established to simulate the LaMnO3 system. The time evolution of the transient optical conductivity was numerically calculated. Intensity oscillations of the optical conductivity were observed, which were interpreted as the result of the quantum interference between phonon-coupled orbiton excited states. Also, the photo-induced anisotropy was observed, which revealed the broken orbital symmetry of the optical excited state.

Interfacial reactions of Ba2YCu3O6+z with coated conductor buffer layer, LaMnO3

Abstract Chemical interactions between the Ba2YCu3O6+x superconductor and the LaMnO3 buffer layers employed in coated conductors have been investigated experimentally by determining the phases formed in the Ba2YCu3O6+x–LaMnO3 system. The Ba2YCu3O6+x–LaMnO3 join within the BaO–(Y2O3–La2O3)–MnO2–CuOx multi-component system is non-binary. At 810 °C (pO2 = 100 Pa) and at 950 °C in purified air, four phases are consistently present along the join, namely, Ba2−x(La1+x−yYy)Cu3O6+z, Ba(Y2−xLax)CuO5, (La1−xYx)MnO3, (La,Y)Mn2O5. The crystal chemistry and crystallography of Ba(Y2−xLax)CuO5 and (La1−xYx)Mn2O5 were studied using the X-ray Rietveld refinement technique. The Y-rich and La-rich solid solution limits for Ba(Y2−xLax)CuO5 are Ba(Y1.8La0.2)CuO5 and Ba(Y0.1La1.9)CuO5, respectively. The structure of Ba(Y1.8La0.2)CuO5 is Pnma (No. 62), a = 12.2161(5) A, b = 5.6690(2) A, c = 7.1468(3) A, V = 494.94(4) A3, and Dx = 6.29 g cm−3. YMn2O5 and LaMn2O5 do not form solid solution at 810 °C (pO2 = 100 Pa) or at 950 °C (in air). The structure of YMn2O5 was confirmed to be Pbam (No. 55), a = 7.27832(14) A, b = 8.46707(14) A, c = 5.66495(10) A, and V = 349.108(14) A3. A reference X-ray pattern was prepared for YMn2O5.

Correlation between structure, dielectric, and ferroelectric properties in BiFeO3–LaMnO3 solid solution thin films

Chemical solution processed BiFeO3 thin films usually show high leakage currents and poor ferroelectric properties. The optimizations of processing conditions and doping with appropriate elements have been among the most promising strategies to enhance the overall properties of BiFeO3 thin films. However, detailed studies on the effects of doping elements on the structure and through it on the properties are still lacking. In this work we investigate the interplay between structure and dielectric-electric-ferroelectric properties of BiFeO3–LaMnO3 [Bi1−xLaxFe1−xMnxO3 (0≤x≤0.1)] solid solution thin films grown on Pt-terminated silicon substrates. The BiFeO3–LaMnO3 system is shown to undergo a structural transition from monoclinic to orthorhombic-tetragonal with various degrees of orthorhombic distortion. All LMO-containing films show a Debye-like dielectric relaxation with the activation energy of 0.90 eV. Both dielectric relaxation and leakage current mechanisms were interpreted in terms of ionized oxygen vacancy hopping. On the basis of comparative studies on individual doping with La and Mn it is shown that Mn is responsible for the dielectric anomaly and structural transition whereas La alone seems to stabilize the perovskite structure. A correlation between the degree of orthorhombic distortion, leakage current, and polarization properties was also found, with a minimum of leakage current and fairly high polarization at the highest distortion.

Optimization of Ethylene Production via Catalytic Partial Oxidation of Ethane on Pt–LaMnO3 Catalyst

A novel catalyst formulation (Pt–LaMnO3) was recently developed and disclosed for ethylene production via the catalytic partial oxidation of ethane at short contact time. In this paper we report results of the extensive experimental campaign performed on the Pt–LaMnO3 system for the tuning and optimization of process parameters, which, in turn, shed light on the effect of the main variables controlling overall performance. The novel catalytic system under optimized operating conditions was capable of performances better than state-of-the art systems, with ethylene yields exceeding 65% while preserving selectivities above 80% under self-sustained operation, by adding H2 as a sacrificial fuel in a simple reactor configuration, thus suggesting to reconsider the economical viability of ethylene production by ethane CPO at short contact time.

Characteristics of permittivity and permeability spectra in range of 2–18 GHz microwave frequency for La1-xSrxMn1-yByO3 (B=Fe, Co, Ni)

Doped LaMnO3 has unusual electromagnetic properties, which makes it possible for this material to be used for absorbing microwave. LaMnO3 systems doped by Sr at site A and Fe or Co, Ni at site B were prepared by sol-gel as an microwave absorption material and their permittivity and permeability spectra were measured by microwave vector network analyzer in the frequency range of 2-18 GHz. A novel phenomenon is discovered that the complex permittivity, complex permeability and electromagnetic loss tangent have suddenly a step change at a certain frequency and the step-change frequency is relevant to content of Sr and Fe or Co, Ni. The samples show mainly dielectric loss when microwave frequency is smaller than the step-change frequency, and mainly magnetic loss when larger than that frequency. It is indicated that anti-ferromagnetic clusters in the material can absorb energy quantum of microwave electromagnetic field to change into ferromagnetic clusters because they can overcome higher energy barrier when the frequency of incident microwave reaches a certain value.

The structure and conductivity of LaMn1−zCrzO3 and (La, A)1−yMn1−zCrzO3 (A=Sr, Ca) as air cathodes in solid oxide fuel cells

Doped LaMnO3 systems are used as cathodes in solid oxide fuel cells, mainly due to their high electronic conductivity, thermal matching to the electrolyte material and good catalytic activity towards oxygen reduction. Lanthanum deficient LaMnO3 has been shown to have a higher electronic conductivity than stoichiometric LaMnO3, however, the material has been found to sinter more readily causing a reduction in the efficiency of the cathode. This paper discusses the effect of imparting non-stoichiometry to the LaMnO3 system with the incorporation of a B site dopant, Cr. The paper examines the effect on the conductivity and phase present with increased Cr content, and shows that Cr in LaMn1−zCrzO3, up to z=0.15, does not produce an unacceptably large decrease in the electronic conductivity, especially for a Ca doped, A site deficient system. Thus, a B site doped system is considered as a possible candidate for solid oxide fuel cell cathode systems.