Thermal behavior of Ni,Co and Fe succinates embedded in silica matrix

This paper presents the thermal behavior of Co, Ni and Fe succinates obtained by sol-gel synthesis using Co(II), Ni(II) and Fe(III) nitrates, 1,4-butanediol and tetraethyl orthosilicate as reactants. The thermal analysis revealed the formation of succinates at 413–453 K and their decomposition to ferrites at 503–623 K. The rate constants for the decomposition of succinates to ferrites, calculated using the isotherms at 473, 523, 573 and 623 K, were used to determine the activation energy of each ferrite (NiFe₂O₄, Ni_0.3Co_0.7Fe₂O₄, Ni_0.7Co_0.3Fe₂O₄ and CoFe₂O₄) embedded in the silica matrix. By increasing the Ni content in the mixed Ni–Co ferrites, the activation energy decreases from 13.530 to 1.944 kJ mol^?1. The formation and decomposition of succinate precursors and the formation of silica matrix were confirmed by FT-IR spectroscopy, while the formation of CoFe₂O₄ and NiFe₂O₄ single-phases embedded in the silica matrix was confirmed by X-ray diffraction analysis. The nanocrystallites size decreases from 31.7 (CoFe₂O₄) to 18.5 nm (NiFe₂O₄). The optical band gap of mixed Co–Ni ferrites was significantly higher than that corresponding to CoFe₂O₄. The photocatalytic activity of the samples was evaluated against Rhodamine B under visible light. All the samples have photocatalytic activities, the best performance being obtained in the case of Ni_0.7Co_0.3Fe₂O₄.

     

Interface charge transfer process in ZnO:Mn/ZnS nanocomposites

Journal of Nanoparticle Research - TiO2 photocatalysts co-doped with F and Fe were synthesized by a sol–gel method. Synergistic effects of F and Fe in the co-doped TiO2 were verified by NH3...     

EPR investigations of calcium phosphate glasses containing manganese ions

Glasses of the xMnO·(100−x)[yP₂O₅·CaO] systems, with y=1, 2, 3 and 0≤x≤50 mol% MnO were prepared and investigated by means of electron paramagnetic resonance (EPR). The local order in diamagnetic vitreous matrices could be revealed by the Mn²⁺ paramagnetic ions used in EPR experiments. In each systems corresponding to a particular value of y, the effect of increasing the MnO content in the samples was investigated. The structure of our glasses shows an evolution depending of MnO content from structural units involving Mn²⁺ ions in well defined vicinities, to structural units containing clustered manganese ions. The changes of the linewidth and the intensity of the resonance line centered at g_eff≈2.0 when the content of manganese ions are increasing revealed this evolution.     

EPR investigation of nanosized La0.67Ca0.33MnO3−δ manganites

We report an electron paramagnetic resonance (EPR) investigation of the spin dynamics in the paramagnetic regime of nanosized La_0.67Ca_0.33MnO_3?δ manganites. The temperature dependences of the EPR line width and integral intensity have been analyzed in terms of the bottlenecked spin relaxation and small polaron hopping scenarios. The exchange coupling integral between Mn³⁺ and Mn⁴⁺ ions and the polaron activation energy decrease with the reduction of grain size. A discussion is given concerning the factors which could explain the observed changes.     

Co<Superscript>2+</Superscript> Ions in ZnO powders as seen by Magnetic Resonance

This is a report of an X-band electronic paramagnetic resonance (EPR) study of Zn_1−x Co _x O (x = 1 and 3%) powders at various temperatures (10–200 K). EPR spectroscopy is a powerful tool to study the complex magnetic state and the Co ionic state, their local environment and interactions as well. These samples are interesting to study in order to understand how ‘Co doping’ produces ferromagnetism in ZnO₂, making it a promising ferromagnetic semiconductor at room temperature.     

Co doped ZnO semiconductor materials: structural,morphological and magnetic properties

Structural, morphological and magnetic properties of Zn_1−xCo_xO (x = 0.01 and 0.03) powdered materials are presented. XRD studies reveal a wurtzite-type structure, while the formation of a Co₃O₄ secondary phase was evidenced by Raman spectroscopy. A ferromagnetic behaviour with low Curie temperature was evidenced by Electron Paramagnetic Resonance (EPR) investigation. We suggest that the origin of the ferromagnetism in Zn_1−xCo_xO powders is probably due to the presence of the mixed cation valence of Co ions via a double-exchange mechanism rather than the real doping effect.     

The Influence of the Annealing Temperature on the Properties of Sn<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>Fe<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>O<Subscript>2</Subscript> Powders Evidenced by EMR Spectroscopy

Electron magnetic resonance (EMR) investigations of Sn_{1− x} Fe _x O₂ (x = 0.07) powders annealed at different temperatures are reported. EMR spectra show the presence of both the isolated paramagnetic Fe³⁺ ions incorporated into the SnO₂ lattice and a ferromagnetically ordered component. By increasing the annealing temperature, the EMR spectrum attributed to the ferromagnetically coupled Fe³⁺ ions diminishes probably due to the migration of Fe ions and the formation of the second phase. The presence of the second phase was evidenced by X-ray diffraction measurements.