Synthesis,Characterization, Magnetic Properties,and Applications of La0.85Ce0.15FeO3 Perovskite in Heavy Metal Pb2+ Removal

Journal of Superconductivity and Novel Magnetism - Perovskite La0.85Ce0.15FeO3 was synthesized with crystallite size 23 nm by flash combustion technique. The obtained sample was...     

Local Valence and Hole-Doping Effect on Magnetic Properties in Double Perovskite La2NiMnO6

Local valence and Ca-doping effect in polycrystalline La₂NiMnO₆ have been investigated by using X-ray diffraction, X-ray absorption spectroscopy, Raman spectrum, and magnetometry. The refinement of X-ray diffraction data shows that all the samples are crystallized in pure double perovskite phase. The refined Ni(Mn)–O bond lengths and X-ray absorption spectroscopy provide evidences that the oxidation state of Ni and Mn ions in bulk La₂NiMnO₆ has the Ni²⁺ and Mn⁴⁺ configuration and the decrease of average A-site valence caused by Ca doping is compensated by the increase of Ni valence, while Mn keeps unchanged. As the Ca-doping content increases, the peak shapes of Raman spectroscopy exhibit an increase in the linewidth and decrease in the intensity, respectively, which reveals the increase the disorder of Ni–O bond length and the decrease of Ni/Mn ordering degree. Both the paramagnetic–ferromagnetic transition temperature and the saturation magnetization exhibit decrease with the increase of Ca-doping content, which are attributed to the decrease of Ni–O–Mn bond angle and the increase of Ni/Mn antisite disorder, respectively. All those behaviors can be ascribed to the valence state change of Ni ion caused by hole doping.     

Electric and Structural Properties of the New Ba2TiZrO6 Ferroelectric Complex Perovskite

We report the synthesis, structural characterization, morphologic and ferroelectric behavior of the Ba₂TiZrO₆ complex perovskite. The samples of Ba₂TiZrO₆ were synthesized through the standard solid-state reaction method. Rietveld analysis of X-ray diffraction patterns reveals that this material crystallizes in a rhombohedral structure, space group R-3 (#148), with cell parameter a=5.8038(7) Å. Images of Scanning Electron Microscopy show the micrometric granular character of samples with 1.0 μm grain size. Results of semi-quantitative Energy Dispersive X-ray analysis are 97.5 % in agreement with the nominal stoichiometry of Ba₂TiZrO₆. Curves of polarization as a function of the applied electric field reveal that the Ba₂TiZrO₆ double perovskite behaves as a ferroelectric material at room temperature.     

Magnetic and Transport Properties of Bilayered Perovskite Sr3Ir2O7

We report magnetic and transport properties of polycrystalline samples of bilayered perovskite Sr₃Ir₂O₇, which is synthesized by using high pressure technique. Magnetic susceptibility shows weak ferromagnetism below 290K with small size of remanent moment (10^–3B/Ir). Resistivity shows insulating behavior below 290K. We discuss the magnetism and conductivity in Sr₃Ir₂O₇ comparing with those of Sr₃Ru₂O₇, which has a quite similar crystal structure to Sr₃Ir₂O₇, from the view point of rotation angle of MO₆ (M=Ir, Ru) octahedra.     

Magnetic and Electrotransport Properties of the Anion-Deficient Manganites with Perovskite Structure

The chemical phase content and microstructure as well as magnetic and magnetotransport properties for the doped anion-deficient La³⁺_1-xSr²⁺_xMn³⁺O^2–_3-x/2 orthomanganites have been experimentally studied. The high-quality anion-deficient ceramic with controlled chemical phase content and microstructure has been obtained from the parent stoichiometric one at the 800 C in vacuum. The average grain size is ~5 m. It is established that the samples in the region of 0 x 0.125 are O-orthorhombic perovskites whereas in the 0.175 x 0.30—rhombohedric. As doping level increases along with the oxygen vacancies number the samples in ground state undergo a transition from the antiferromagnet A-type (x=0) through the inhomogeneous magnetic state (0 < x 0.175 to the cluster spin glass one (0.175 < x 0.30. The temperature of magnetic moment freezing is ~ 45 K. All the samples are semiconductors and show considerable magnetoresistance over a wide temperature range with peak for x = 0.175 only. Fitting of the electrical resistivity to T^–1 and T^–1/4 realized. The concentration dependences of the activation energy, spontaneous magnetization, coercivity as well as magnetic transition temperatures for the anion-deficient La³⁺_1-xSr²⁺_xMn³⁺O^2–_3-x/2 ortomanganites have been established. Obtained experimental results are interpreted in terms of the oxygen vacancies, isotropic superexchange Mn³⁺-O–Mn³⁺ interactions and phase separation models.     

Structural Evolution and Magnetic Properties of Underfluorinated C2F

A series of layered inclusion compounds based on fluorinated graphite C₂F _x (x≤1) was obtained by a room temperature synthesis. Inclusion compounds (intercalates) of fluorinated graphite matrix were n-hexane and dichloromethane, i.e., organic guest molecules that differ in size and symmetry. The changes in C₂F _x stoichiometry are shown to have a decisive effect on magnetic properties of produced complexes. The spin concentration decreases with the increase of fluorine content in fluorocarbon matrix. All samples have groups of correlated spins; at the temperatures 1.75–5 K nonlinear magnetization is observed, indicating a high-spin state. Application of the Langevin formula shows that the clusters consist of 10–20 interacting spins.     

Structural and Magnetic Properties of Ln2CoMnO6(Ln=Dy and La) Produced by Combustion Synthesis

In this article, the structural and magnetic properties of the Ln₂MnCoO₆ (Ln=La and Dy) produced by the combustion method are reported. The samples were characterized by X-ray diffraction (XRD) with Rietveld refinement, and their magnetic properties by studying the dependence of the magnetization with the magnetic field and temperature. XRD analysis reveals that the La₂MnCoO₆ (LCM) consists of a mixture of crystalline orthorhombic, monoclinic, and rhombohedral phases. This mixture might be originated by the mixing of valence states of the Co⁺²/Mn⁺⁴ and Co⁺³/Mn⁺³. Dy₂CoMnO₆ (DCM) presents a mixed composition of hexagonal and orthorhombic structures with the transition metal atoms in mixed valences. Magnetic measurements show that the magnetic transition temperature T _C decreases from 150 K to 85 K when the La ions are replaced by Dy. We also observe that the magnetic order changes from a ferromagnetic to a ferrimagnetic when La is replaced by Dy.     

Influence of Ag-doping in La0.5Sr0.5CoO3 on Its Structural and Magnetic Properties

The structural and magnetic properties of the mixed valent cobaltites La_0.5Sr_0.5?x Ag _x CoO₃ (0≤x≤0.15) with perovskite structure have been investigated. X-ray diffraction (XRD) analysis using Rietveld refinement shows that all our samples crystallize in the orthorhombic structure with $R\overline{3}c$ space group. Although the unit cell volume remains almost constant, the Co–O bond length and the Co–O–Co bond angle are sensitive to the Ag addition. All our studied samples undergo a paramagnetic-ferromagnetic transition with decreasing temperature. The zero field cooled (ZFC) and field cooled (FC) magnetization curves at 50 mT of La_0.5Sr_0.5CoO₃ (x=0) sample exhibits thermomagnetic irreversibility indicating frustration and competition of both antiferromagnetic and ferromagnetic interactions. It is suggested that Co³⁺ ions are in the intermediate spin state but Co⁴⁺ ions stay in a mixture of intermediate and high spin states. Ag addition leads to dramatic changes in magnetic properties. An interesting result has been obtained for La_0.5Sr_0.4Ag_0.1CoO₃, where the ZFC and FC curves coincide. For La_0.5Sr_0.35Ag_0.15CoO₃ (x=0.15) sample, the observed thermomagnetic irreversibility is much higher than that observed in x=0 sample. Hysteresis loops were recorded for x=0, 0.05, 0.1, and 0.15. The coercitive field is found to increase with Ag content reaching 0.26 T for x=0.15 whereas the remanent magnetization decreases.     

Structural and Magnetic Properties of MnO-P2O5-PbO Glasses

1.IntroductionStructuralpropertiesofvitreoussystemswerefre-quentlystudiedbymeansoftheEPRofMn2+ionsusedasparamagneticprobes.Mallyoxideglassessuchasborate[l~4],alkalisilicatel5],aluminasilicate,phosphate[61andtelluritel7'8]!andalsochalcogenidel9]andhalideglassesl1o)111wereinvestigated.Informationsconcerningthestructuraldetailsofthevitreousmatrixrevealedbythepa-ramagneticionsdistributionondifferentstructuralunitsbuildingthenetworkandtheircoordinationwereobtained.Themagneticbehavioursofmanganese…     

Effect of Air Annealing on the Structural and Magnetic Properties of LaMnO3 Perovskite Produced by Reactive Spark Plasma Sintering Route

Perovskite-type lanthanum manganite (LaMnO₃) was synthesized from Mn₂O₃ and La₂O₃ precursor powders using the Spark Plasma Sintering technique (SPS). The in situ reaction proceeds in a few minutes at 1000 °C under 50 MPa with a very high heating rate of 100 °C/min. The Rietveld refinement of the X-ray powder diffraction shows that LaMnO₃ sample crystallizes in a perovskite structure of O′-type orthorhombic symmetry with Pbnm space group. After annealing at 1000 °C in air for 10 hrs, the symmetry changes to rhombohedral with R-3c space group. For the as prepared sample, two critical temperature points in the temperature dependence of the ZFC and FC magnetization occurring at 125 K and 145 K are observed. They are suggested to be related to A-type antiferromagnetic Néel temperature and ferromagnetic short range order, respectively. The ferromagnetic component in the annealed sample increases indicating the expected variation in the concentration of Mn³⁺ and Mn⁴⁺ ions, which was attributed to the oxygen stoichiometry effects.     

Structural and Catalytic Properties of Co-doped Perovskite Oxide on Coal Combustion

In this paper, the structural and catalytic properties of co-doped perovskite oxide La_0.8Ce_0.2Mn_1?xCo_xO₃ are investigated. First, coal combustion catalysts of mesoporous perovskite-type La_0.8Ce_0.2Mn_1?xCo_xO₃ were prepared by using sol–gel method. The resulting powder was characterised by scanning electron microscopy (SEM), X-ray diffraction (XRD), Brunauer–Emmett–Teller’s test (BET), and thermogravimetric analysis (TGA). Then, the results showed that after partially substituting La with Ce and substituting Mn with Co in LaMnO₃, Ce occupied parts of the La site and Co occupied parts of the Mn site. As the substitution rate of Co increased, the pore diameter significantly decreased, and the specific surface area increased first and then decreased. Thirdly, thermogravimetric measurements and coal combustion constructed single-reaction model in the presence of the La_0.8Ce_0.2Mn_1?xCo_xO₃ catalysis indicated that the presence of catalysts reduced the reaction initiation temperature (T_eo), the maximum mass loss velocity temperature (T_max), and the completion temperature of the main pyrolysis (T_f). The addition of 5 % La_0.8Ce_0.2Mn_0.9Co_0.1O₃ to coal caused the reaction initiation temperature (T_eo) to decrease by 34 °C compared with coal alone. Lastly, a distributed activation energy model of 5 % La_0.8Ce_0.2Mn_0.9Co_0.1O₃ obtained an activation energy distribution curve. Results indicated that the activation energy of samples at the primary pyrolysis stage did not present a single peak value but mainly accumulated at 140–160 kJ, which could replace the mean activation energy of pyrolysis reaction. At the same time, frequency factor was not constant but presented a certain degree of linear correlation with activation energy, thereby indicating the presence of more than a single-reaction pyrolysis mechanism.     

Structural, Magnetic, and Magnetocaloric Properties of La0.5M0.1Sr0.4MnO3 (M=Bi, Eu, Gd, and Dy) Perovskite Manganites

Structural, magnetic, and magnetocaloric properties of La_0.5M_0.1Sr_0.4MnO₃ (M=Bi, Eu, Gd, and Dy) powder samples, synthesized using the solid-state reaction at high temperature, have been experimentally investigated. X-ray diffraction analysis using the Rietveld refinement show that La_0.5Bi_0.1Sr_0.4MnO₃ sample is single phase and crystallizes in the rhombohedral system with $R\overline{3}c$ space group whereas a mixture of orthorhombic (Pbnm) and rhombohedral ( $R\overline{3}c$ ) phases is observed for M=Eu, Gd, and Dy compounds. The Curie temperature, T _C , shifts to lower temperature with decreasing the average A-site ionic radius 〈r _A 〉, which is consistent with large cationic disorder. Arrott plots show that all our samples exhibit a second order magnetic phase transition. From the measured magnetization data of La_0.5M_0.1Sr_0.4MnO₃ (M=Bi, Eu, Gd, and Dy) samples as a function of magnetic applied field, the associated magnetic entropy change |ΔS _M | has been determined. In the vicinity of T _C , |ΔS _M | reached, in a magnetic applied field of 1 T, maximum values of 0.98 J/kg?K, 1.01 J/kg?K, 0.81 J/kg?K, and 0.77 J/kg?K for M=Bi, Eu, Gd, and Dy, respectively.     

Effect of Vacuum and O2 Annealing Treatments on Structural and Magnetic Properties of La0.5Ca0.5MnO3 Thin Films

La_0.5Ca_0.5MnO₃ films with a nominal thickness of 80 nm were epitaxially grown on (001) SrTiO₃ and SrLaAlO₄ substrates by the pulsed laser deposition technique. The magnetic moment of the films was observed to depend strongly on the oxygen stoichiometry, tuned by heat treatments in vacuum and O₂ environments. A distinctly larger out-of-plane lattice parameter was measured for the vacuum-annealed films due to transformation of some Mn⁴⁺ ions to Mn³⁺. Both the variations in the magnetic moment and out-of-plane lattice parameter during vacuum annealing can be recovered by subsequent heat treatments in O₂ environment. In this study, it is shown that the enhancement of the magnetic moment via O₂ annealing is considerably less prominent than the respective improvement obtained by the application of compressive epitaxial strain.     

La0.68Pb0.32FeO3纳米材料在低工作温度条件下对CO气体的气敏性研究

采用sol-gel法制备了具有正交钙钛矿结构的La0.68Pb0.32FeO3和LaFeO3纳米粉体.用该粉体制成气敏元件,并测试了该粉体材料在CO气体中的气敏特性,测试结果表明：与LaFeO3相比,La0.68Pb0.32FeO3具有更小的粒径、较大的电导值、对CO气体具有更好的气敏性能,特别是工作温度大大降低.与空气中相比,在CO气体中,材料La0.68Pb0.32FeO3的导电激活能增大.     

Structural and Magnetic Properties of Various Ferromagnetic Nanotubes

The structural and magnetic properties of ferromagnetic nanotubes fabricated by a low cost electrodeposition method are investigated. The fabrication of various elemental ferromagnetic materials are described, such as Fe, Co, and Ni, and ferromagnetic alloys, such as NiFe, CoPt, CoFeB, and CoCrPt nanotube arrays, in aluminum oxide templates and polycarbonate membranes with different diameters, wall thicknesses, and lengths. The structural, magnetic, and magnetization reversal properties of these nanotubes are investigated as a function of the geometrical parameters. The angular dependence of the coercivity indicates a transition from the curling to the coherent mode for the ferromagnetic nanotubes. The results show that nanotube fabrication allows the outer and inner diameter, length, and thickness of the nanotubes to be tuned systematically. The magnetization processes of ferromagnetic nanotubes are influenced by the wall thickness.     

Synthesis of Perovskite Pr1.1MnO3.15 and Phase Evolution and Magnetic Properties

Pr_1.1MnO_3.15 precursor was synthesized by solid-state reaction at low temperatures using Pr(NO₃)₃?6H₂O, MnSO₄?H₂O, and Na₂C₂O₄ as raw materials. Pr_1.1MnO_3.15 was obtained by calcining a precursor, 1.1/2Pr₂(C₂O₄)₃–MnC₂O₄?5.3H₂O, over 1,000 ^°C in air. The precursor and its calcined products were characterized by thermogravimetry and differential scanning calorimetry, X-ray powder diffraction, scanning electron microscopy, and vibrating sample magnetometer. A high-crystallized Pr_1.1MnO_3.15 with an orthorhombic structure was obtained when the precursor was calcined over 1,000 ^°C in air for 2 h. Magnetic characterization indicated that orthorhombic Pr_1.1MnO_3.15 behaved with weak magnetic properties. The thermal transformation of the precursor from ambient temperature to 1,050 ^°C in air presented four steps: the dehydration of 5.3 crystal waters; the reaction of MnC₂O₄ with 0.75O₂ into 1/2Mn₂O₃ and the two CO₂ molecules; the reaction of 1.1/2Pr₂(C₂O₄)₃ with 0.825O₂ into 1.1/2Pr₂O₂CO₃ and of 2.75CO₂ molecules; and the reaction of 1.1/2Pr₂O₂CO₃ with 1/2Mn₂O₃ into Pr_1.1MnO_3.15 and 0.55CO₂     

Structural, Dielectric, Ferroelectric and Magnetic Properties of Bi0.80A0.20FeO3 (A=Pr,Y) Multiferroics

Here we studied the effect of homovalent Pr³⁺ and Y³⁺ substitution on the crystal structure, dielectric, electronic polarization and magnetic properties of the BiFeO₃ multiferroic ceramic. The samples were synthesized by the conventional solid-state reaction method. Pure phase formation of Pr doped BiFeO₃ (BFO) has been obtained, while Y³⁺ doped BFO has shown a few impurity peaks. It has shown that the crystal structure of the compounds is described within the space group R3c. Pr³⁺ modified BFO has shown an anomaly in the ε _r vs. T plot around and a Néel temperature ‘T _N’～370 ^°C. P–E hysteresis loops have shown higher value of remnant polarization for Pr³⁺ modified BFO. Magnetic properties of ceramics are determined by the ionic radius of the substituting element. Experimental results propose that the increase in the radius of A-site ion leads to effective suppression of the spiral spin structure of BiFeO₃, resulting in the appearance of net magnetization.