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حرية الوصول المقاله
1 - The effect of MgO doping on the structural, magnetic, and magnetotransport properties of La0.8Sr0.2MnO3 manganite
Mahin Eshraghi Parviz Kameli Hadi SalamatiAbstractThe effect of MgO doping on the structural, magnetic, and magnetotransport properties of La0.8Sr0.2MnO3 (LSMO)/x MgO has been investigated. All samples were prepared by a solid-state reaction method. Alternating current susceptibility measurements for LSMO/x MgO أکثرAbstractThe effect of MgO doping on the structural, magnetic, and magnetotransport properties of La0.8Sr0.2MnO3 (LSMO)/x MgO has been investigated. All samples were prepared by a solid-state reaction method. Alternating current susceptibility measurements for LSMO/x MgO samples show that the Curie transition temperature (Tc) and magnetization decrease with the increase of MgO concentration. The rate of the decrease of Tc at higher doping level is very fast. Also, samples with low doping level (x ≤ 2) show insulator-metal transition, but the transition temperature decreases and resistivity increases with the amount of MgO. It is observed that there is no insulator-metal transition at higher MgO doping level (x ≥ 3). Also, the results show that the value of low-field magnetoresistance decreases with the increase of MgO doping level. It seems that due to the higher sintering temperature and almost the same ionic radii of Mg2+ and Mn3+, Mg2+ mostly replaced Mn3+ and weakened the double-exchange interaction, and consequently, Tc and magnetoresistance decrease and resistivity increases with MgO doping. تفاصيل المقالة -
حرية الوصول المقاله
2 - Magnetoresistance temperature dependence of LSMO and LBMO perovskite manganites
Z. Jafari Razi S. A. Sebt A. KhajehnezhadAbstractLa0.7Sr0.3MnO3 (LSMO) and La0.7Ba0.3MnO3 (LBMO) Polycrystalline manganite nanoparticles were prepared by combustion method using glycine fuel. The ignition process was done at 360 °C and 330 °C for LSMO and LBMO, respectively. Both of the samples have rhombohedr أکثرAbstractLa0.7Sr0.3MnO3 (LSMO) and La0.7Ba0.3MnO3 (LBMO) Polycrystalline manganite nanoparticles were prepared by combustion method using glycine fuel. The ignition process was done at 360 °C and 330 °C for LSMO and LBMO, respectively. Both of the samples have rhombohedral structure using XRD analysis. The reduction is observed in electrical resistivity when external magnetic field is applied during the decrease in temperature from 300 to 89 °K, which is due to the tunneling between particles. The magnetoresistance (MR) of samples was measured in this range of temperature in both the presence and absence of a magnetic field of about 10 kG. The colossal role of a kind of extrinsic MR which is 19% and 22% for LSMO and LBMO, respectively, has been investigated in this research. The metal–insulator transition temperature of 200 °K is recorded for LBMO. تفاصيل المقالة -
حرية الوصول المقاله
3 - Effect of Sr substitution on structural, redox and catalytic properties of nano-particles La1-xSrxMn0.5Co0.5O3 (x = 0.0, 0.1, 0.2, 0.3, 0.4, 0.5) as a catalyst for CO oxidation
Marzieh Lotfi Ahmad Gholizadeh Azim MalekzadehStructural features of La(1-x)SrxMn0.5Co0.5O3 (x = 0.0, 0.1, 0.2, 0.3, 0.4, and 0.5) nano-particles were investigated using X-ray powder diffraction and FT-IR spectroscopy. The characterization of compounds by X-ray powder diffraction and using Fullprof program show a c أکثرStructural features of La(1-x)SrxMn0.5Co0.5O3 (x = 0.0, 0.1, 0.2, 0.3, 0.4, and 0.5) nano-particles were investigated using X-ray powder diffraction and FT-IR spectroscopy. The characterization of compounds by X-ray powder diffraction and using Fullprof program show a cubic structure (Pm3m space group) for x = 0.0 and a rhombohedra structure (R-3c space group) for the Sr substituted La(1-x)SrxMn0.5Co0.5O3 samples. Crystallite size and unit cell parameters decrease with Sr substitution. The electrical conductivity of the samples in oxidizing (air) and reducing atmosphere (6%CO in nitrogen) and also band gap of the samples has been investigated to interpret the performance of samples. Results show that their behavior increases non-uniformly with increase in Sr substitution. An increase of Sr substitution up to 0.5 increases the performance of the samples and an optimal catalytic activity in the low-temperature conversion of CO to CO2. It is mainly attributed to a decrease of the crystallite size. تفاصيل المقالة -
حرية الوصول المقاله
4 - X-ray peak broadening analysis in LaMnO3+δ nano-particles with rhombohedral crystal structure
Ahmad GholizadehIn this work, structural and magnetic properties of LaMnO3+δ compound prepared by citrate precursor method and annealed in presence of oxygen are investigated. The structural characterization of LaMnO3+δ by X-ray powder diffraction and using X’pert pac أکثرIn this work, structural and magnetic properties of LaMnO3+δ compound prepared by citrate precursor method and annealed in presence of oxygen are investigated. The structural characterization of LaMnO3+δ by X-ray powder diffraction and using X’pert package and Fullprof program is evidence for a rhombohedral structure (R-3c space group) confirmed by FTIR measurement. The magnetic measurements show a super-paramagnetic behavior of LaMnO3+δ due to low values of coercive field and romance magnetization and also high value of saturation magnetization. In addition, a comparative study of the crystallite size of the compounds obtained from powder XRD is reported. The Williamson-Hall analysis, size-strain plot and Halder-Wagner methods were used to study the individual contributions of crystallite sizes and lattice micro-strain on isotropic line broadening of all the reflection peaks of the LaMnO3+δ compound. The results show the Halder-Wagner method is more accurate, with all data points touching the fitting line better than the other methods. The crystallite sizes estimated from XRD (30.86 nm) and particle size estimated from TEM method (36 nm) and also the magnetic core size (33.6 nm) estimated from magnetic measurement agree well, while a little difference reflects a spherical shape of the nanoparticles. تفاصيل المقالة
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