Effect of doped strontium on catalytic properties of La1‒xSrxMnO3 for rhodamine B degradation

A series of La_1‒xSr_xMnO₃ samples were prepared by sol–gel method and used to degrade rhodamine B (RhB) in water. All samples were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), N₂ adsorption–desorption, temperature-programmed reduction of H₂ (H₂-TPR) and temperature-programmed desorption of O₂ (O₂-TPD). The results show that the degradation of RhB is highly dependent on the initial pH value of solution. Sr doping enhances the degradation ability of LaMnO₃ for RhB in the time range of 0–40 min under a strong acidic environment, but all samples exhibit similar degradation rate from 40 to 60 min. In La_0.7Sr_0.3MnO₃–RhB reaction system, there are two different degradation pathways, including N-de-ethylation, chromophore cleavage, ring-opening and mineralization. La_1‒xSr_xMnO₃ (x ≤ 0.3) has the perovskite structure of La–Mn oxides, while La_0.6Sr_0.4MnO₃ exhibits a Sr_0.4MnLa_0.6O_2.98 perovskite phase. Sr doping leads to distortion of rhombohedral crystal structure and increases the relative content of Mn⁴⁺. The perovskite structure is stable in strong acidic environment during RhB degradation, but the relative content of Mn⁴⁺ and Mn³⁺ on the material surface changes. Sr doped LaMnO₃ achieves specific surface area of 58.8 m²/g and total pore volume of 0.152 cm³/g. Furthermore, Sr²⁺ doping improves redox properties of La–Mn oxides, and the presence of defects makes oxygen diffusion easier compared with the undoped samples.     

Influence of the substitution of Sm, Gd, and Dy for La in La0.7Sr0.3MnO3 on its magnetic and electric properties and strengthening effect on room-temperature CMR

A series of La0.7-xSmxSr0.3MnO3, La0.7-xGdxSr0.3MnO3, and La0.7-xDyxSr0.3MnO3 （x=0.00, 0.10, 0.20, 0.30） samples were prepared by the solid-state reaction method. The influence of the substitution of Sm, Gd, and Dy for La on the magnetic and electric properties and on the magnetoresistance （MR） was studied through measurements of M-T curves and p-T curves. The results showed that： lattice distortion induced by substitution of Sm, Gd, and Dy for La and extra magnetism of substitution had great influence on the magnetic and electric properties of pcrovskite manganites; substitution of magnetic rare earth element for La was an effective way to change Curie temperature and to strengthen MR in perovskite manganites; and appropriate substitution proportion would generate large MR near room temperature.     

Optical and magnetic properties of perovskite materials: Ba0.3La0.7Ti0.3Fe0.7O3 and Ba0.1La0.9Ti0.1Fe0.9O3

Structural, optical and magnetic properties are reported for new synthesized perovskite materials. Ba_0.3La_0.7Ti_0.3Fe_0.7O₃ and Ba_0.1La_0.9Ti_0.1Fe_0.9O₃ compositions were prepared via solid state reaction. X-ray analysis confirms that both compositions show feature of perovskite structure. Rietveld refinement method was used to confirm the phase formation and investigate the structure and space group. The study demonstrates the formation of orthorhombic structure with Pnma space group for Ba_0.3La_0.7Ti_0.3Fe_0.7O₃ while the composition Ba_0.1La_0.9Ti_0.1Fe_0.9O₃ structure adopts Pbnm symmetry. UV–vis spectroscopy measurements show very broad and intense UV–visible light absorption, the estimated band gap ranges between 2.07 and 2.15 eV. Magnetic measurements were carried out for the compositions Ba_0.3La_0.7Ti_0.3Fe_0.7O₃ and Ba_0.1La_0.9Ti_0.1Fe_0.9O₃. The hysteresis loops of both samples at 300 and 10 K show a strong ferromagnetic behavior. The temperature dependent magnetization at 0.05 T under field-cooled (FC) and zero field cooled (ZFC) modes shows magnetic frustration or spin glass-like behavior.     

A-site defects in LaSrMnO_3 perovskite-based catalyst promoting NO_x storage and reduction for lean-burn exhausts

Herein,we report the high De-NO_x performance of the A-site defective perovskite-based Pd/La_(0.5)Sr_(0.3)MnO_3 catalyst.The formation of the defective perovskite structure can be proved by both the increased Mn~(4+)/Mn~(3+) ratio and serious lattice contraction due to cationic nonstoichiometry.It promotes the Sr doping into perovskite lattice and reduces the formation of the SrCO_3 phase.Our results demonstrate that below 300℃ the A-site defective perovskite can be more efficiently regenerated than the SrCO_3 phase as NO_x storage sites due to the latter's stronger basicity,and also exhibits the higher NO oxidation ability than the A-site stoichiometric and excessive catalysts.Both factors promote the lowtemperature De-NO_x activity of the Pd/La_(0.5)Sr_(0.3)MnO_3 catalyst through improving its NO_x trapping efficiency.Nevertheless,above 300℃,the NO_x reduction becomes the determinant of the De-NO_x activity of the perovskite-based catalysts.A-site defects can weaken the interactions between perovskite and Pd,inducing activation of Pd sites by in-situ transformation from PdO to metallic Pd in the alternative leanburn/fuel-rich atmospheric alternations,which boosts the De-NO_x activity of the Pd/La_(0.5)Sr_(0.3)MnO_3 catalyst.The Pd/L_(0.5)Sr_(0.3)MnO_3 catalyst exhibits the high sulfur tolerance as well.These findings provide insight into optimizing the structural properties and catalytic activities of the perovskite-based catalysts via tuning formulation,and have potential to be applied for various related catalyst systems.     

Magnetoelectric,Raman, and XPS Properties of Pb0.7Sr0.3[(Fe2/3Ce1/3)0.012Ti0.988]O3 and Pb0.7Sr0.3[(Fe2/3La1/3)0.012Ti0.988]O3 Nanoparticles

The Pb_0.7Sr_0.3[(Fe_2/3Ce_1/3)_0.012Ti_0.988]O₃ (PSFCT) and Pb_0.7Sr_0.3[(Fe_2/3La_1/3)_0.012Ti_0.988]O₃ nanoparticles were prepared by chemical synthesis route using polyvinyl alcohol as surfactant. X-ray diffraction pattern has been used to analyze the phase structure and average particles size. The phase structure is also confirmed by Raman spectra. The chemical states of Pb²⁺, Sr²⁺, Fe³⁺; Ti⁴⁺, Ce³⁺, La³⁺, and oxygen ions have been analyzed by X-ray photoelectron spectroscopy. The magnetoelectric coupling effect is confirmed by magnetic phase transition near ferroelectric phase-transition temperature. The magnetoelectric effect is also confirmed by measuring the value of magnetoelectric coefficient (α _E) as the function of applied dc magnetizing field under the influence of ac magnetic field of 10 Oe and frequencies of 847 and 997 Hz. The higher value of α _E is observed in PSFCT sample.     

Structural,magnetic and electrical characterization of the La0.7Ca0.3Co1–xMnxO3（x=0,0.7 and 1） compounds prepared by a simple method

Structural, magnetic and electrical properties of the La0.7Ca0.3Co1–xMnxO3（x=0, 0.7 and 1） samples prepared by a simple method were systematically studied and it was found that the crystal structure was transformed from rhombohedral for La0.7Ca0.3CoO3（LCCO） and La0.7Ca0.3Co0.3Mn0.7O3（LCCMO） samples to orthorhombic for La0.7Ca0.3MnO3（LCMO） sample. The AC magnetic susceptibility measurements showed that LCCO sample underwent a transition from paramagnetic（PM） to ferromagnetic（FM） phase at Curie temperature, TC~155 K and below Curie temperature, the glassy ferromagnetism nature was observed. In LCCMO sample,clear evidence of spin glass（SG） state was observed at low temperature. PM-FM phase transition at about TC~260 K and long range FM order at low temperatures were observed in LCMO sample. Both the LCCO and LCCMO samples exhibited insulating behavior in the whole range of measuring temperature whereas the LCMO sample underwent a clear metal-insulator（MI） transition at about TMI~263 K, corresponding to Curie temperature. Metallic region of ρ（T） curve of the LCMO sample was fitted to the model of electron-electron and electron-magnon scattering. The charge carrier transport behavior in all the samples was compared based on polaronic models.     

Influence of composition and sintering temperature on density of structure defects, phase transitions, and properties of magneto-resistive strontium-doped ceramic of manganate-lanthanum perovskites

Ceramic samples of La³ _1?x Sr²⁺ _x MnO^2? ₃ (x = 0, 0.1, 0.15, 0.2, 0.3, 0.4), sintered at different temperatures (1150, 1200, 1350, and 1500 °C) are investigated by means of methods of x-ray diffraction analysis and resistive and magnetic analysis. It is established that the perovskite structure parameter (a) and degree of its rhombohedric $(R\bar 3c)$ distortion (α) both decrease with increasing content of Sr²⁺ in La _1?x Sr _x MnO _3±δ (x = 0–0.4). The metal-semiconductor (T_ms) and ferromagnetic-paramagnetic (T_c) phase transition temperatures and magnetoresistive peak temperature (T_p) all increase, while the activation energy (E_a) decreases. The density of defects in the lattice which contains anion (V^(a)) and cation (in A and B positions) vacancies, average valency of manganese (ω), and tolerance factor (t) also increase. It is shown that with Sr²⁺ doping, charge compensation is achieved by two mechanisms, first, the Mn³⁺ → Mn⁴⁺ transition (～80%), and second, the formation of V^(a) vacancies (～20%), with the contribution of the second mechanism increasing with increasing sintering temperature. With increasing x the magnetoresistive effect decreases at T_p and the lowfield tunneling magnetoresistive effect increases slightly. It is established that the concentration dependence of the intracrystaline peak magnetoresistive effect at T_p is opposite to the concentration dependence of the intercrystalline magnetoresistive effect in the semiconductor region for T ? T_p.     

Transport and Magneto-Transport Properties of Ru Doped Ln0.67Sr0.33MnO3 (Ln?=?La, Pr, and Nd)

The effect of Mn site doping by small amount Ru (5?%) on the transport and magneto-transport properties of the Ln_0.67Sr_0.33Mn_1?x Ru _x O₃ (where Ln?=?La, Pr, and Nd, x?=?0, 0.05) has been studied. Polycrystalline samples were synthesized by the conventional solid state reaction method. The samples of Pr_0.67Sr_0.33Mn_1?x Ru _x O₃ and Nd_0.67Sr_0.33Mn_1?x Ru _x O₃ have shown single phase with orthorhombic structure as well as La_0.67Sr_0.33Mn_1?x Ru _x O₃ has rhombohedral are revealed from XRD measurement. The temperature dependence of the resistivity is measured from 5 to 400?K. La_0.67Sr_0.33Mn_0.95Ru_0.05O₃ shows the metal?Cinsulator (M?CI) transition at 379?K while Pr_0.67Sr_0.33Mn_0.95Ru_0.05O₃ and Nd_0.67Sr_0.33Mn_0.95Ru_0.05O₃ have shown M?CI transition at 294 and 249?K, respectively. The magnetoresistance (MR) was measured with an applied magnetic field of 1, 3 and 5?T. Though the M?CI transition temperature decreases marginally, MR up to 70?% has been observed.     

Characterization of A-site excessive perovskite La0.7-xSmx＋0.02Ca0.3CrO3-δ

La0.7-xSmx+0.02Ca0.3CrO3-δ(0≤x≤0.4) powders with A-site excessive perovskite structure were synthesized by auto-ignition process and characterized. X-ray diffraction (XRD) patterns of samples after sintering at 1400℃ for 4 h were indexed as tetragonal structure. The relative densities were all above 96% although decreased slightly with the increasing content of samarium, indicating that the excessive A-site element was helpful to enhance their sinterability. Conductivities of the specimens in air increased with increasing content of samar-ium. The conductivity of La0.6Sm0.12Ca0.3CrO3-δ was 33.6 S/cm in air at 700 ℃ which was about 1.7 times as high as that of La0.7Ca0.3CrO3-δ (20.1 S/cm). Average thermal expansion coefficients (TECS) of the specimens increased from 11.06×10-6 to 12.72×10-6 K-1 when x in-creased from 0 to 0.4, and they were close to that of Y doped ZrO2 (YSZ). La0.7-xSmx+0.02Ca0.3CrO<3-δ>(0.1≤x≤0.3) were good choices for in-termediate temperature solid oxide fuel cells (IT-SOFCs) interconnect materials.     

Microwave electromagnetic and absorbing properties of Dy3+doped MnZn ferrites

Dy3+ doped Mn-Zn ferrites Mn0.3Zn0.7Fe2-xDyxO4(x=0,0.01,0.02,0.03,0.04)were prepared by the conventional solid-state reaction.The crystal structure,surface morphology and electromagnetic properties of the calcined samples were characterized by X-ray diffraction analysis(XRD),scanning electron microscopy(SEM) and network analyzer(Agilent 8722ET).All the XRD patterns showed the single phase of the spinel-type ferrite without other intermediate when x≤0.03.The average crystallite size was about 44?56 nm.The mi...     

Impact of La3+ substitution on electrical,magnetic, dielectric and optical properties of Ni0.7Cu0.1Zn0.2LaxFe2–xO4 (0 < x < 0.035) system

The oxalate co-precipitation method was used to synthesize the La³⁺ substituted Ni–Cu–Zn (La–NCZ) nanoferrites having chemical composition Ni_0.7Cu_0.1Zn_0.2La_xFe_2–xO₄ (x = 0, 0.015, 0.025 and 0.035). DC resistivity study of nanoferrites shows both the conducting and semiconducting behaviour. The room temperature DC electrical resistivity of Ni–Cu–Zn (NCZ) nanoferrites decreases, whereas Curie temperature increases with increasing La³⁺ content. In the temperature range of 30–170 °C nanoferrites show p-type semiconducting behavior except x = 0.015; thereafter, they show n-type behaviour. The frequency dispersive initial permeability (μ_i) associated with its real and imaginary (μ′ and μ") parts are attributed to the domain wall movement and magnetic spin resonant. The μ_i, μ′ and μ" of La–NCZ nanoferrites are higher than those of pure NCZ nanoferrite. Dielectric constant (ε′), dielectric loss (ε″) and AC resistivity (ρ_AC) of La–NCZ nanoferrites show normal dielectric behaviour. It is found that ε′ of NCZ nanoferrites decreases with the increasing content of La³⁺ ions. The bandgap energy of La–NCZ nanoferrites is achieved in the range 1.36–1.70 eV confirming the semiconducting nature of materials.     

Conductivity and electric properties of La1-xSrxMnO3-δ nanopowders

La_0.8Sr_0.2MnO_3−δ was synthesized by the Pechini's method. The XRD pattern and TEM indicate the formation of the perovskite without the presence of secondary phases. It was found that La_0.8Sr_0.2MnO_3−δ sample prepared at 1000 °C in air atmospheres, contains about 13.11% of the manganese as Mn⁴⁺ and 86.89% of the manganese as Mn³⁺. The electric measurements were carried out for La_0.8Sr_0.2MnO_3–δ nanoceramics by using impedance spectroscopy methods and found to be 0.1 S/cm at 250 °C similar to the typical value of La_0.8Sr_0.2MnO_3-δ materials. Its dependence on reciprocal temperature shows quite complicated mechanism of conduction.     

Monodisperse micro-spherical Sr2–zMg1+yYzAl22–xO36:xMn4+ red phosphors

With narrow red photoluminescence (PL) bands, tetravalent Mn⁴⁺ doped phosphors show promising prospect in commercial application to effectively expand color gamut of phosphor converted LED displays. Here, we report a type of Sr_2–zMg_1+yY_zAl_22–xO₃₆:xMn⁴⁺ phosphors with regular cage-like micro-spherical morphologies. The micron size spherical precursors were synthesized with a propylene oxide (PO) driven fast sol–gel method. The cage -like spherical morphology is beneficial to efficiently trapping much incident light to enhance the PL of the phosphors. Being calcined at 1300 ^°C, Sr₂MgAl_21.978O₃₆:0.022Mn⁴⁺ only exhibits the internal quantum efficiency (IQE) of 24.91%. With the Mg²⁺-Mn⁴⁺ codoping and Y³⁺/Sr²⁺ substituting strategies, to fulfill charge balance and produce John-Teller distortion, IQE of Sr_2–zMg_1+yY_zAl_22–xO₃₆:xMn⁴⁺ can be further improved up to 36.45%. The CIE color coordinates of Sr_2–zMg_1+yY_zAl_22–xO₃₆:xMn⁴⁺ under near ultraviolet excitation can be stably fixed to (0.723, 0.227) at deep red region. It thus finds a potential application as pc-LED display with much broader color gamut than that of the NTSC standard. Therefore, Sr_2–zMg_1+yY_zAl_22–xO₃₆:xMn⁴⁺ micron size spheres can be employed as promising red phosphors for high performance LED displays.     

Effects of manganese substitution on magnetic and magnetostrictive properties of Tb0.5Dy0.5(Fe1-xMnx)1.92/epoxy composites with spherical single-crystal particles

Spherical Tb_0.5Dy_0.5(Fe_1-xMn_x)_1.92(x=0,0.05,0.10 and 0.15) single-crystal particles were prepared.The magnetic anisotropy of the alloy decreases as x increases from 0 to 0.15.Subsequently,we prepared giant magnetostrictive composites with these spherical Tb_0.5Dy_0.5(Fe_1-xMn_x)_1.92 single-crystal particles.As a consequence,well <111>-orie nted Tb_0.5Dy_0.5(Fe_1...     

Structural and electrical properties of La2-xSrxMo2O9-δ

Sr-doped La2Mo2O9 were prepared by solid state reaction and characterized by XRD,impedance spectroscopy and HebbWagner polarization method.XRD patterns of the samples indicated that the solubility limit of Sr2+ in La2-xSrxMo2O9-δ was in the range of 7 mol.% to 7.5 mol.%,i.e.,the maximum stoichiometric coefficient x in La2-xSrxMo2O9-δ was larger than 0.14 and less than 0.15.The cubic lattice parameter of La2-xSrxMo2O9-δ(0相似文献   

Extraordinary Transport Behaviors of La0.67Sr0.33Mn1-xCrxO3（0.00≤x ≤0.30）

M-T curves, ρ-T curves and MR-T curves of La0.67Sr0.33Mn1-xCrxO3（0.00≤ x ≤0.30） were studied. Experimental results indicate that the substitution of Cr on Mn sites is impotent in driving Tc, but with an increase of Cr content, there appear two peaks in resistivity and MR response, thus the temperature range of CMR response is significantly broadened. The extraordinary transport behavior and the abnormal CMR effect could be the results of coexistence and competition of Mn^3 ＋ -O-Mn^4 ＋ and Mn^3＋ -O-Cr^3 ＋ channels.     

Fabrication of La_(1-x)Ca_xFeO_3 perovskite-type oxides with macro-mesoporous structure via a dual-template method for highly efficient soot combustion

A series of three-dimensionally ordered macro-mesoporous(3DOMM) La_(1-x)Ca_xFeO_3(x=0-0.3)perovskite-type oxides were designed and successfully fabricated for the first time via a dual-template method.In which,PMMA and Brij-56 were employed as the hard template and soft template,respectively.It is found that 3 DOMM La_(1-x)Ca_xFeO_3 exhibits abundant wormlike mesoporous channels about 3 nm in diameter on macroporous skeleton walls.The excellent catalytic activity of soot combustion benefits from not only the well-designed hierarchical porous structure of catalyst,but also the redox electron pair of Fe~(3+)/Fe~(4+) induced by the doping of low-valent alkaline earth metal Ca to A-site of LaFeO_3.3DOMM La_(0.8)Ca_(0.2)FeO_3 exhibits superior catalytic performance for soot combustion,which shows T_(50) of396℃.It is 189℃lower than that without catalyst.A combination of structure and composition in the design of catalyst can be widely extended to other catalytic systems.     

Mechanical properties,thermophysical properties and electronic structure of Yb3+ or Ce4+-doped La2Zr2O7-based TBCs

First-principles calculations based on density functional theory were performed to investigate the cohesive energies, elastic modulus, Debye temperatures, thermal conductivities and density of states of La_2−xYb_xZr₂O₇, La₂Zr_2−xCe_xO₇ and La_2−xYb_xZr_2−xCe_xO₇ (x = 0.00, 0.25, 0.50, 0.75, 1.00) ceramics. The results show that doping Yb³⁺ or Ce⁴⁺ into La₂Zr₂O₇ reduces its elastic modulus, thermal conductivity and Debye temperature. Compared with La_2−xYb_xZr₂O₇ (x ≠ 0.00), La₂Zr_2−xCe_xO₇ compounds have better ductility and lower Debye temperature. The Debye temperature values of La₂Zr_2−xCe_xO₇ (x ≠ 0.00) compounds are in the range of 485.0–511.5 K. Among all components, the fluorite-type La_2−xYb_xZr_2−xCe_xO₇ (x = 0.75, 1.00) compounds exhibit better mechanical and thermophysical properties, and their thermal conductivity values are only 1.213–1.246 W/(m∙K) (1073 K), which are 14.5%–16.7% lower than that of the pure La₂Zr₂O₇. Thus, our findings open an entirely new avenue for TBCs.     

Phase structure and electrochemical properties of non-stoichiometric La0.7Ce0.3(Ni3.65Cu0.75Mn0.35Al0.15(Fe0.43B0.57)0.10)x hydrogen storage alloys

Phase structure and electrochemical characteristics of Co-free La0.7Ce0.3(Ni3.65Cu0.75Mn0.35Al0.15(Fe0.43B0.57)0.10)x (0.90≤x≤1.10) al-loys were investigated. When x was 0.90, the alloy was composed of LaNi5, La3Ni13B2 and Ce2Ni7 phases. The Ce2Ni7 phase disappeared, and the abundant of La3Ni13B2 phase decreased when x increased to 0.95. When x was 1.00 or higher the alloys consisted of LaNi5 phase. The lat-tice parameter a and the cell volume V of the LaNi5 phase decreased, and the c/a ratio of the LaNi5 phase increased with x value increasing. Maximum discharge capacity of the alloy electrodes first increased and then decreased with x value increasing from 0.90 to 1.10, and the highest value was obtained when x was 1.00. High-rate dischargeability at the discharge current density of 1200 mA/g increased from 50.7% (x= 0.90) to 64.1% (x=1.10). Both the charge-transfer reaction at the electrode/electrolyte interface and the hydrogen diffusion in the alloy were responsible for the high-rate dischargeability. Cycling capacity retention rate at 100th cycle (S100) gradually increased from 77.3% (x= 0.90) to 84.6% (x=1.10), which resulted from the increase in Ni content and the c/a ratio of the LaNi5 phase with x value increasing.     

Structure and luminescence properties of color-tunable phosphor Sr2La3(SiO4)3F:Tb3+,Sm3+

A series of single-phase and color-tunable phosphors Sr₂La₃(SiO₄)₃F:0.15Tb³⁺,xSm³⁺(SLSOF:0.15Tb³⁺,xSm³⁺) was prepared using solid-state route.The X-ray diffraction(XRD) was used to characterize the phase of the as-prepared samples.The synthesized phosphors have apatite-type structure without other impurities.Sm³⁺ and Tb³⁺ ions substitute La³⁺ into the lattice and form a single...