Manganese Perovskite Oxides Research Articles

Nanofibrous La0.95K0.05MnO3 perovskite with improved photoelectrical properties for photocatalytic degradation of antibiotics

Potassium doped lanthanum manganese perovskite oxides, La1−xKxMnO3, with nanofibrous structure, are prepared and used for Photo-Fenton degradation of antibiotics, including ciprofloxacin (CIP), tetracycline (TC), and sulfathiazole (ST). Effects of K doping on the textural structure, optical property, band gap and surface chemistry of LaMnO3 are investigated, showing that La0.95K0.05MnO3 (LKMO-5) has the optimal properties. The photoelectric measurements, including photoluminescence (PL), photocurrent response (PCR) and electrochemical impedance spectroscopy (EIS), also suggest that the LKMO-5 has the best electron–hole separation efficiency, the most amounts of irradiated electrons and the lowest impedance. Photocatalytic tests indicate that LKMO-5 not only shows the best activity for CIP degradation, but also exhibits good stability in the reaction, with negligible activity loss within four cycles. Mechanism investigations, explored by the radical trapping experiments and with the reference of band positions, indicate that superoxide radical ions (·O2−) and holes (h+) are the major reactive species of the reaction.

Molten salt-directed synthesis of strontium manganese perovskite oxide: an active electrocatalyst for the oxygen reduction reaction and oxygen evolution reaction

We report a molten-salt pathway for the synthesis of strontium manganese perovskite oxide (SMO), its phase transition with the variation of temperature and demonstrate the intrinsic catalytic behaviour of different phases towards the ORR and OER.

The role of modified manganese perovskite oxide for selective oxidative dehydrogenation of ethane: Not only selective H2 combustion but also ethane activation

To break through the thermodynamic reaction limitation of ethane dehydrogenation to ethylene, the oxidative dehydrogenation in the presence of O2 and chemical looping oxidative dehydrogenation has been investigated with the oxygen storage oxide compound. LaMnO3 perovskite catalysts with large specific surface areas were prepared using citric acid-nitrate combustion. The oxygen vacancies and M4+ contents in the catalysts were improved by doping LaMnO3 as the active sites. The experimental results show that the catalyst not only promotes ethane dehydrogenation through selective hydrogen combustion but also promotes ethane conversion through activation of CH. The catalyst exhibits good stability in oxidative dehydrogenation reaction.

The Role of Modified Manganese Perovskite Oxide for Selective Oxidative Dehydrogenation of Ethane: Not Only Selective H2 Combustion But Also Ethane Activation

The Role of Modified Manganese Perovskite Oxide for Selective Oxidative Dehydrogenation of Ethane: Not Only Selective H2 Combustion But Also Ethane Activation

The Role of Modified Manganese Perovskite Oxide for Selective Oxidative Dehydrogenation of Ethane: Not Only Selective H2 Combustion But Also Ethane Activation

The Role of Modified Manganese Perovskite Oxide for Selective Oxidative Dehydrogenation of Ethane: Not Only Selective H2 Combustion But Also Ethane Activation

Structure–Activity Relationship in Manganese Perovskite Oxide Nanocrystals from Molten Salts for Efficient Oxygen Reduction Reaction Electrocatalysis

We report a synthesis pathway in molten salts toward ligand-free nanoparticles of the layered perovskite La0.5Sr1.5MnO4 (l-LSMO) and of the pseudocubic perovskite La0.7Sr0.3MnO3 (pc-LSMO). These pa...

Catalytic Oxidation of VOCs over SmMnO3 Perovskites: Catalyst Synthesis, Change Mechanism of Active Species, and Degradation Path of Toluene.

Highly active samarium manganese perovskite oxides were successfully prepared by employing self-molten-polymerization, coprecipitation, sol-gel, and impregnation methods. The physicochemical properties of perovskite oxides were investigated by XRD, N2 adsorption-desorption, XPS, and H2-TPR. Their catalytic performances were compared via the catalytic oxidation of toluene. The perovskite prepared by self-molten-polymerization possessed the highest catalytic capacity, which can be ascribed to its higher oxygen adspecies concentration (Olatt/Oads = 0.53), higher surface Mn4+/Mn3+ ratio (Mn4+/Mn3+ = 0.95), and best low-temperature reducibility (H2 consumption = 0.27; below 350 °C). The most active catalyst also exhibited good cycling and long-term stability for toluene oxidation. After a multistep cycle reaction and a long-term reaction of 42 h, the toluene conversion maintained above 99.9% at 270 °C. Mechanistic study hinted that lattice oxygen was involved in toluene oxidation. The oxidation reaction was dependent on the synergism of lattice oxygen, adsorbed oxygen, and oxygen vacancies. The degradation pathway of toluene, researched by diffuse reflectance infrared Fourier transform spectroscopy and online mass spectrometry technologies, demonstrated that a series of organic byproducts existed at a relatively low temperature. This work provides an efficient and practical method for selecting highly active catalysts and for exploring the catalytic mechanism for the removal of atmospheric environmental pollution.

Highly active Co-doped LaMnO 3 perovskite oxide and N-doped carbon nanotube hybrid bi-functional catalyst for rechargeable zinc–air batteries

Abstract Herein, non-precious cobalt doped lanthanum manganese perovskite oxide nanoparticles are used as a growth substrate for nitrogen-doped carbon nanotubes to form efficient and durable hybrid bi-functional catalyst (LMCO/NCNT). LMCO/NCNT demonstrates significantly enhanced onset and half-wave oxygen reduction reaction (ORR) potentials (− 0.11 and − 0.24 V vs. SCE, respectively), and oxygen evolution reaction (OER) current density (27 mA cm − 2 at 0.9 V vs. SCE). Likewise, practical rechargeable zinc–air battery testing using atmospheric air reveals superior discharge voltages obtained with LMCO/NCNT, particularly at current densities higher than 30 mA cm − 2 , and significantly lower charge voltages at all current densities tested, compared to state-of-art commercial platinum on carbon catalyst. In addition, very stable charge and discharge voltages of 2.2 and 1.0 V, respectively, are obtained over 60 cycles. The excellent performance and durability of the hybrid catalyst are attributed to very uniformly distributed LMCO nanoparticles on the surface of NCNT resulting in enhanced surface area and material utilization.

Charge Disproportionation and Magnetoresistivity in a Double Perovskite with Alternate Fe4+(d4) and Mn4+(d3) Layers

AbstractAn oxygen‐stoichiometric, B‐site‐ordered perovskite Ca2Fe1.1Mn0.9O6 (CFMO) with alternate stacking of Fe and Mn layers was obtained through topochemical oxidation of the corresponding brownmillerite phase under high pressure in the presence of KClO4. The structure crystallizes in the P21/m space group with a doubling of the cell along all three crystallographic axes. Mössbauer spectroscopy, susceptibility, and resistivity measurements suggest ferromagnetic interactions between Fe4+(d4) and Mn4+(d3) along [001] through a double‐exchange mechanism, a situation similar to half‐doped manganese perovskite oxides. Upon cooling, CFMO exhibits a ferrimagnetic transition below Tc = 90 K, likely accompanied by a charge disproportionation of the iron site, 2Fe4+ → Fe3+ + Fe5+. A reasonably good magnetoresistivity of 27 % was observed below Tc.

Lattice parameters and orthorhombic distortion of CaMnO3

CaMnO3is a parent compound for numerous multicomponent manganese perovskite oxides. Its crystallographic data are of primary importance in the science and technology of functional CaMnO3-based materials. In the present study, data were collected for a CaMnO3sample at 302 K. The crystal structure refinement yields accurate absolute values of lattice parameters,a=5.281 59(4) Å,b=7.457 30(4) Å, andc=5.267 48(4) Å, leading to orthorhombic distortion of (c/a, √2c/b)=(0.997 33,0.998 95). The orthorhombic distortion of the CaMnO3structure is discussed on the basis of comparison of our unit-cell size with data already published. At a graphical representation of the distortion, it is observed that there is a considerable scatter of the distortion values among the literature data but, interestingly, a considerable fraction of experimental results (including the present one) for stoichiometric samples are grouped around the distortion (c/a, √2c/b)=(0.9973,0.9990), which lies close to a maximum in the extent of orthorhombicity. The influence of off-stoichiometry on the orthorhombic distortion is discussed on the basis of available experimental data. Simulations, employing a mean-field approach for low temperatures, predict an increase in cell volume and structural distortions with the concentration of oxygen vacancies when the additional electrons are localized on the manganese. A simple model of delocalization produced the opposite effect, which is expected to combine with lattice vibrations to recover the cubic phase at high temperatures.

Synthesis and Properties of Monoclinic and Cubic Forms of the A-Site-Ordered (BiMn3)Mn4O12 Perovskite

We have obtained two new A-site-ordered manganese perovskite oxides with the common chemical formula of (BiMn3)Mn4O12±δ with regard to their metal composition. The two phases were prepared through high-pressure synthesis under identical conditions except for the oxygen-to-metal ratio in the precursor mixture. Accordingly, they were found to differ from each other in the oxygen content. The less-oxidized phase possesses a monoclinic crystal structure and shows two magnetic transitions, at 28 and 59 K, whereas the more-strongly-oxidized and hence denser phase with a cubic crystal structure lacks the higher-temperature transition. Thus, the present work has demonstrated an attractive but not-yet-utilized possibility to tailor the properties of (A′A′′3)B4O12±δ-type cation-ordered perovskite oxides by means of oxygen-content control.

Three oxidation states and atomic-scale p–n junctions in manganese perovskite oxide from hydrothermal systems

Perovskite oxides have provided magical structural models for superconducting and colossal magnetoresistance, and the search for nano-scale and/or atomic-scale devices with particular property by specific preparations in the same systems has been extensively conducted. We present here the three oxidation states of manganese (Mn3+, Mn4+, Mn5+) in the perovskite oxide, La0.66Ca0.29K0.05MnO3, which most interestingly shows the rectifying effect as atomic-scale p–n junctions (namely FY-Junctions) of single crystals and films. The family of cubic perovskite oxides were synthesised by the so-called hydrothermal disproportionation reaction of MnO2 under the condition of strong alkali media. The new concept of the atomic-scale p–n junctions, based on the ideal rectification characteristic of the p–n junctions in the single crystal, basically originates from the structural linkages of [Mn3+–O–Mn4+–O–Mn5+], where Mn3+ \( {\left( {{\text{t}}^{{\text{3}}}_{{{\text{2g}}}} {\text{e}}^{1}_{{\text{g}}} } \right)} \) and Mn5+ \( {\left( {{\text{t}}^{{\text{2}}}_{{{\text{2g}}}} {\text{e}}^{{\text{0}}}_{{\text{g}}} } \right)} \) in octahedral symmetry serve as a donor and an acceptor, respectively, corresponding to the localized Mn4+ \( {\left( {{\text{t}}^{{\text{3}}}_{{{\text{2g}}}} {\text{e}}^{{\text{0}}}_{{\text{g}}} } \right)} \).

Relationship between the synthesis parameters and the morphology of manganite nanoparticle-assembled nanostructures

Nanoparticles assembled into nanostructures (NAN) of manganese perovskite oxides for different compositions and diameters have been synthesized following a template-assisted method. We discuss the relationship among geometrical, structural and nanostructural parameters observed when synthesizing LaMnO 3, La 0.66Sr 0.33MnO 3, La 0.66Ca 0.33MnO 3 and La 0.325Pr 0.300Ca 0.375MnO 3 manganite based complex oxides. For all the studied compounds, the structures are composed of an assembly of small (some few tens of nanometers) grains. They form nanotubes above some threshold diameter of the template, and nanowires below it. Here we focus on the correlation between grain size and the diameter at which the tube to wire crossover occurs. The threshold for this tube to wall crossover seems to depend on the specific compound. We present evidence from TEM observations that allow a rationalization of several phenomena in the synthesis process.

Charge ordering, stripes and phase separation in manganese perovskite oxides: An STM/STS study

A microscopic characterisation of the phase transitions associated with colossal magnetoresistance (CMR) in manganese perovskite oxides is a very important ingredient in the quest of understanding its underlying mechanism. Scanning tunneling microscopy (STM) is most suitable to investigate some of their reported hallmarks, including charge ordering, lattice distortions, and electronic phase separation. Here we investigate Bi 1− x Ca x MnO 3 (BCMO) with x = 0.76. At this composition, BCMO develops an insulating charge-ordered phase upon cooling, whose study as a function of temperature will allow identifying atomic scale characteristics of the metal-insulator phase transition (MIT). We observe distinct atomic scale phases at temperatures above and below the MIT, with very different electronic and structural characteristics. Combining STM micrographs and current–voltage tunneling characteristics, we find that charge ordering correlates both with the local conduction state (metallic or insulating) and the local structural order. Furthermore, STM shows coexistence of these phases as expected for a first order phase transition.

Fabrication Of La0.7Sr0.3MnO3/La0.5Sr0.5CoO3/La0.7Sr0.3MnO3 Heterostructures for Spin Valve Applications

ABSTRACTEpitaxial growth of oxide heterostructures, which may be utilized in spin valve applications, has been demonstrated. The heterostructures consist of two ferromagnetic layers separated by a nonmagnetic metallic interlayer. The ferromagnetic material used is the manganese perovskite oxide, La0.7Sr0.3MnO3, while the metallic oxide interlayer is La0.5Sr0.5CoO3. X-ray diffraction spectra demonstrate the high structural quality of the heterostructures. The magnetization of the heterostructure as a function of magnetic field measured at room temperature yields a double hysteresis loop that is characteristic of this type of spin valve structure. The behavior of this double hysteresis loop is also examined as a function of the metallic interlayer thickness.

Density-functional studies of the electronic structure of the perovskite oxides: La1−xCaxMnO3

Using density-functional methods, we study the electronic structures of the lanthanum-based ‘‘double-exchange’’ perovskite magnets. Antiferromagnetic insulating solutions are obtained for both the end members, LaMnO3 and CaMnO3, within the local density approximation (LDA), with the Jahn-Teller (JT) distortion of the oxygen octrahedron taken into account. The JT distortion splits off the Mn(3d)eg bands producing an energy gap within the LDA, with the bands derived from the (z2−1) orbital, pointed along the long basal-plane Mn—O bond, occupied and the (x2−y2) bands empty. The on-site Coulomb repulsion and the intra-site exchange terms are found to be, respectively, U≂8–10 eV and J≂0.9 eV, from the ‘‘constrained’’ density-functional theory. The large value of U as compared to the bandwidth indicates that the manganese perovskite oxides are strongly correlated systems.