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The structural, magnetic and electrical properties of (LaNd)SrMnTi O perovskites (0 ≤ x ≤ 0.30) prepared by the usual ceramic procedure were investigated. Structural Rietveld refinements of the X-ray powder diffraction revealed that for x = 0 the compound crystallizes in a rhombohedral (R $\bar {{3}}$c) perovskite structure, while for x = 0.10, 0.20 and 0.30 the structure becomes orthorhombic (Pbnm). The field-cooled, zero-field-cooled and M( H) measurements lead to conclude that the samples with x≥0.10 behave like spin-glass systems. The temperature dependence of the resistivity exhibits two transitions at two temperatures T and T, with the same width for the two peaks. T results from the competition between double-exchange and super-exchange mechanisms inside the grain (intrinsic effects) whereas T arises due to the grain boundary effects (extrinsic effect). The resistivity of this system seems to be related to the competition between antiferromagnetic insulating (AFI) phases, ferromagnetic insulating (FMI) phases and ferromagnetic metal (FMM) phases, which is induced by Nd doping effect. [ABSTRACT FROM AUTHOR]

The effects of non-magnetic Ti substitution on the structural, electrical and magnetic properties of LaBaMnTiO (0≤ x≤0.1) are investigated and compared to those existing in LaBaMnCrO (magnetic Cr). The structural refinement by the Rietveld method revealed that Ti-doped samples crystallize in the cubic lattice with space group $\mathrm{Pm}\bar{3}\mathrm{m}$, while samples with Cr crystallize in the hexagonal setting of the rhombohedral $\mathrm{R}\bar{3}\mathrm{C}$ space group for identical contents of dopant. The most relevant structural features are an increase of the lattice parameters, of the cell volume and of the inter-ionic distances with increasing Ti doping level. Both series of samples show a decrease of the paramagnetic-ferromagnetic transition temperature when the amount of chromium or titanium increases. Transport measurements show that when increasing the metal doping, the resistivity increases whereas the metallic behavior of the parent compound LaBaMnO is destroyed. For a substitution higher than 5 at.% of Ti and 10 at.% of Cr, the samples exhibit a semiconducting behavior in the whole range of temperature, for which the electronic transport can be explained by variable range hopping and/or small polaron hopping models. [ABSTRACT FROM AUTHOR]

The transport properties and conduction mechanism in LaSrMnFeCrO (0≤ x≤0.3) have been investigated. The undoped samples show metal-semiconductor transition with a peak of resistivity at a temperature T, whereas for all doped compounds the semiconducting behavior persists in the whole temperature range. The insertion of Cr and Fe ions leads to the increase of resistivity because the simultaneous substitution of Fe and Cr for Mn reduces the number of available hopping sites for the Mn e electron and suppresses the double-exchange mechanism. It was found that the transport mechanism for substituted samples is dominated by the variable range hopping of small polarons between localized states in a model where the various parameters estimated from Mott's relation obey the variable range hopping (VRH) mechanism. [ABSTRACT FROM AUTHOR]

This work proposes the synthesis, characterization and investigation of the stabilization capabilities of chitosan doped with magnetic nanoparticles. Nanoparticles of Fe, Co, Co(II,III) oxide, Ni and Ni/Ag mixture in 2-propanol were synthesized by chemical liquid deposition and the incorporation on the polymeric matrix was performed by solvated metal atom dispersion. Colloids and nanoparticles supported on chitosan were characterized by ultraviolet, Fourier-transform infrared, thermogravimetric analysis, electron diffraction X-ray and magnetic behaviour; transmission and field electronic scanning electron microscopy. The particle size distribution of colloids ranges from 6 to 50 nm with low particle stability due to flocculation after 120 days. The nanoparticles supported on chitosan had a particle size distribution of approximately between 10 and 80 nm, with low particle distribution; however, these particles do not flocculate because the matrix increases the stabilization of nanoparticles. All compounds present superparamagnetic behaviour at low temperature. [ABSTRACT FROM AUTHOR]

Great differences in crystallographic phases, magnetic properties, and catalytic activity were detected in lanthanum cobaltite and cobaltite modified with the insertion of 10 wt.% of Mn. Atomic absorption spectroscopy, BET area measurements, XRD analysis, TPR, and FT-IR suggest that the total insertion of manganese in the LaCoO3 structure is successful. Thermal stability is reached for LaCo0.90Mn0.10O3 up to 973 K without loss of the perovskite structure. The magnetic properties of the as-grown compounds are maintained after a first reduction process up to 723–773 K, while presence of segregated phases is observed after reduction at 973 K. The catalytic activity evaluated in the total combustion of acetyl acetate shows a decrease in the ignition temperature, i.e. an increase in the catalytic activity for the LaCo0.90Mn0.10O3 perovskite. A significant enhancement in the catalytic activity expressed as intrinsic activity, mol m−2 h−1, with the manganese substitution was found. [ABSTRACT FROM AUTHOR]