Electron spin resonance linewidths of Fe3+ in magnesium oxide

Electron spin resonance linewidths of Fe³⁺ in single crystal MgO at 9 GHz were examined experimentally and theoretically for a range of Fe³⁺ concentration. In contrast to the behaviour expected from dipolar broadening the experimental derivative peak-to-peak linewidth for the 1/2 ↔ −1/2 transition, about 0.6 mT at 77 K and a polar angle of 0°, was independent of concentration from 140 to 8500 ppm. The calculated dipolar linewidths greatly exceeded those observed and values of the ratio of moments M ₄ ^1/4 /M ₂ ^1/2 derived from the experimental data lay between 1.33 and 1.48. Optical examination, coupled with heat-treatment experiments, confirmed that the predominant valency state present was Fe³⁺. The data suggested that Fe³⁺ entered the lattice substitutionally, occupying magnesium sites, and that the linewidths were determined by exchange narrowing over the whole concentration range examined.     

Preparation,electrical and photoelectrochemical properties of magnesium doped iron oxide sintered discs

Sintered discs of magnesium substituted iron oxides have been prepared by gel routes or classical solid state reaction techniques and their crystallographic, electrical, and photoelectrochemical properties examined. The discs, sintered between 1200 and 1400°C for 20 hours, contain both α-Fe₂O₃ and a spinel phase. The electrical properties of the discs have been correlated with spinel concentration, the electrical resistivity decreasing with increasing spinel content. The materials were found to be consistently n-type by Seebeck voltage measurements. Photoelectrochemical measurements in aqueous solution showed however that the sintered disc electrodes exhibit photocathodic currents that are characteristic of p-type semiconductors. Evidence is presented which suggests that inhomogeneities in the near surface region of the discs are responsible for the observed photoelectrochemical properties.     

Spin-lattice relaxation in gadolinium-doped calcium tungstate

The spin-lattice relaxation of the S-state ion Gd³⁺ in a calcium tungstate host lattice has been examined at 37.5 GHz over the temperature range 1.5 to 30 K. The gadolinium concentrations in the doped single crystals used were about 50 ppm. Single exponential recovery was observed and the spin-lattice relaxation time (T ₁) varied from about 14 msec at 1.5 K to 0.03 msec at 30 K, measured with =90° and =8°. It was found that T ₁ varied with temperature (T) as T ₁ T ^–1 below 8 K and as T ₁ T ^–3 between 8 and 30 K. The experimental data was fitted by the expressions T ₁ ^–1 =35 T+0.5 T ³ and T ₁ ^–1 =35T+0.1 T ^3.6 for crystals of nominal gadolinium concentrations 0.005 wt % and 0.05 wt % respectively. The difference between the observed dependence and the T ^–5 variation predicted in the Raman region for an S-state ion in a perfect lattice is attributed to defects. Measurements in the -plane at 4.2 K showed that T ₁ was anisotropic with a maximum value at =25° about three times greater than the minimum value obtained at =55°. The angular positions at which these features occur show a remarkable coincidence with the acoustic axes of symmetry of the crystal, which have recently been determined by ultrasonic methods.     

A new approach to the synthesis of nanostructured Fe3Al alloy and aluminum doped iron oxide material

Aluminum doped iron oxide nanostructured material with hematite phase has been produced by the heat-treatment process of an amorphous precursor under air atmosphere. The nano sized precursor was synthesized by using a co-precipitation method. The heat-treated product of the precursor under reduction atmosphere was Fe₃Al alloy with particle sizes around 200 nm. Powder X-ray diffraction pattern and Fourier transform infrared spectroscopy confirmed the formation of the products. That is, the intermetallic alloy, Fe₃Al has really produced via a wet chemical route for first time. Magnetic measurements indicated that all the samples are soft magnets with different magnetization.     

Electron spin resonance linewidths of Cr3+ in magnesium oxide

Electron spin resonance linewidths of Cr³⁺ in single crystal MgO at 9 GHz and 35 GHz were examined experimentally and theoretically for a range of Cr³⁺ concentrations. In contrast to the behaviour expected from dipolar broadening the experimental peak-to-peak linewidth for the 1/2 to–1/2 transition, which had a value of about 0.5 mT at 293 K, was independent of both polar angle and concentration over the range from 800 p.p.m. Cr to 15 100 p.p.m. Cr. The calculated dipolar linewidths exceeded those observed by factors of over one hundred; the ratio of momentsM ₄ ^1/2 /M ₂ ^1/2 derived from the experimental data lay between 1.33 and 1.39 and the lineshapes were markedly Lorentzian. The data suggested that Cr³⁺ entered the lattice substitutionally, occupying magnesium sites, that the linewidths were determined by exchange narrowing over the whole concentration range examined and that the exchange energy, whose values lay between 4 GHz and 100 GHz, varied linearly with concentration.     

EPR study of Gd3+ doped lead oxide based glasses

The electron paramagnetic resonance (EPR) spectra of Gd³⁺ ions in lead germanate and lead phosphate glasses are analyzed as a function of Gd content and host composition in the temperature range between 4.2 and 300 K. The investigated samples were (40 – x)PbO·60GeO₂·xGd₂O₃ (x = 0.25, 0.5, 1, 2, 3, 4 mol%) and 97.5Pb(PO₃)₂·2.5Gd(PO₃)₃ glasses, prepared by conventional melting technique. From comparison of spectra on different samples—some of which partially crystallized—no evidence emerges of the existence of distinct types of Gd³⁺ coordination environments. The analysis of the line-broadening by increasing the Gd³⁺ content evidences that the line width of the EPR signal components is proportional to the concentration of rare earth ions, suggesting that clustering effects are negligible, at least up to 4 mol% Gd₂O₃.     

过渡金属离子掺杂对TiO2纳米尺寸及其相结构的影响

利用酸催化的溶胶-凝胶法合成了一系列不同掺杂量的Fe3 /TiO2、Cr3 /TiO2纳米复合微粒.用XRD和TEM研究了Fe3 、Cr3 的掺杂对TiO2纳米粒子尺寸和相结构的影响.结果表明:掺杂离子不同,对TiO2纳米粒子尺寸和相结构的影响不同.在所研究的掺杂量范围内(x:0.0000～0.1000),TiO2纳米粒子的粒径随Cr3 掺杂量的增加呈减小的趋势,但幅度不大;而Fe3 的掺杂则会引起TiO2粒子的团聚和晶粒的长大;由XRD分析可知:在掺杂量范围内,不会发生Fe2O3、Cr2O3等相的偏析,但Fe3 的掺杂引起了TiO2在低温条件下由锐钛矿向金红石的相转变.通过UV-Vis光谱的研究发现:Fe3 、Cr3 的加入,可以使TiO2对光的吸收拓展到可见区,同时随着掺杂量的增加,对可见光的吸收强度显著增强.     

Deciphering the potentiodynamic polarization curves of iron aluminides Fe3Al and Fe3Al + Cr

The potentiodynamic polarization curves of Fe₃Al and Fe₃Al + Cr intermetallics obtained in aerated pH 4 H₂SO₄ acidic solution have been theoretically analyzed. The role of chromium in minimizing the hydrogen embrittlement (HE) of the intermetallic Fe₃Al (resulting in its poor ductility) has been addressed based on the analysis. In the case of the chromium-alloyed iron aluminide, calculations indicate that hydrogen liberation does not occur on the surface due to the shift of the corrosion mixed potential to a value nobler than the electrode potential for the hydrogen evolution reaction. This shift occurs due to the induction of passivity on alloying with Cr resulting in the formation of a passive film. The minimization of HE of iron aluminides on alloying with Cr can thus be understood.     

Elastic constants of the iron oxide doped yttria-stabilized zirconia

Ultrasonic compressional and shear wave velocity measurements have been made on the (ZrO₂)_1−A (Y₂O₃)_A−X (Fe₂O₃) _X system at 5 MHz. The amounts of Fe₂O₃ dopant ranging from 0 up to 10 mol% were mixed with the ceramic matrix. In this paper the ultrasonic compressional and shear wave velocity measurements made on this system at room temperature are discussed. The elastic moduli, Poisson's ratio and density are found to be sensitive to the additions of the Fe₂O₃ dopant and they show an anomalous behaviour. A qualitative explanation of the compositional dependence of the elastic moduli and Poisson's ratio is given in terms of changes in packing density, bond strength, co-ordination number and cross-link density.     

Size-dependent ultrafast magnetization dynamics in iron oxide (Fe3O4) nanocrystals

Optically induced ultrafast demagnetization and its recovery in superparamagnetic colloidal iron oxide (Fe3O4) nanocrystals have been investigated via time-resolved Faraday rotation measurements. Optical excitation with near-infrared laser pulse resulted in ultrafast demagnetization in approximately 100 fs via the destruction of ferrimagnetic ordering. The degree of demagnetization increased with the excitation density, and the complete demagnetization reached at approximately 10% excitation density. The magnetization recovered on two time scales, several picoseconds and hundreds of picoseconds, which can be associated with the initial reestablishment of the ferrimagnetic ordering and the electronic relaxation back to the ground state, respectively. The amplitude of the slower recovery component increased with the size of the nanocrystals, suggesting the size-dependent ferrimagnetic ordering throughout the volume of the nanocrystal.     

Optical spectroscopy of La3Ga5SiO14 disordered crystals doped with Fe3+ ions

The circular dichroism, absorption and luminescence spectra of langasite (La₃Ga₅SiO₁₄) doped with iron ions (Fe) are investigated at temperatures T of 300 and 8 K. Analysis of the data obtained reveals the Fe ions are trivalent. The Fe³⁺ impurity ions substitute Ga³⁺ ions and occupy 3f tetrahedral sites. Luminescence from the ⁴T₁ excited state of the dopant was detected at 8 K.     

Sonochemical assisted synthesis and spectroscopic characterization of Fe3+ doped ZnO diluted magnetic semiconductor

Fe³⁺ doped ZnO nanopowder has been synthesized by sonochemical assistance and characterized by different spectroscopic techniques. The structure, surface morphologies and optical properties were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), photoluminescence spectrometer (PL) and ultraviolet–visible spectrophotometer. XRD reveals that Fe³⁺ ions enter into ZnO lattices without any secondary phases. SEM micrographs of prepared sample show that surface is rough and stone like structure with different sizes. PL studies of Fe³⁺ doped ZnO nanopowder exhibits ultraviolet and blue emission bands. Magnetometric measurements (vibrating sample magnetometer) indicate ferromagnetic behavior at room temperature. This observation is further confirmed by the EPR spectrum of Fe³⁺ doped ZnO at room temperature.     

Growth,optical and electro-optical characterisations of potassium hydrogen phthalate crystals doped with Fe3+ and Cr3+ ions

Potassium hydrogen crystals have good electro-optic properties that are in order of urea crystal. Trivalent ions doped KAP crystals KAP:M⁺³ (M = Fe³⁺, Cr³⁺) ions were grown using solution growth technique. Optical and electro-optical characterisations on the coefficient r₅₁ were carried out. The refractive matching offered by the KAP:M⁺³ crystals was investigated. One of the factors causing the observed enhancement in the electro-optics properties is the ligand interactions due the presence of trivalent ions in KAP lattice.     

Study on luminescent properties of Eu3+ doped new type yttrium tungsten oxide nanophosphors

In this paper, a novel nanophosphor, Y10W2O21:Eu, was synthesized through co-precipitation which is a simple and low-costing method. The structure and morphology of the nanocrystal samples were characterized by using XRD and FE-SEM. The emission spectra, excitation spectra and fluorescence decay curves were measured. J-O parameters, quantum efficiencies of Eu3+ 5D0 energy level, color coordinates and Huang-Rhys factor of Y10W2O21:Eu nanophosphors were calculated. The results indicate that EU3+ 5D0-7F2 red luminescence at 610 nm can be effectively excited by 394 nm near-UV light and 464 nm blue light in Y10W2O21 host, which is similar to the familiar Eu3+ doped tungstate phosphors (e.g., Gd2(WO4)3:Eu, CaWO4:Eu). Besides, compared with the other types of tungstate phosphors, a less expensive tungsten was used, which can effectively reduce cost. Therefore, the Y10W2O21:Eu red nanophosphors may have a potential application for white LED.     

Ni doped Fe3O4 magnetic nanoparticles

In this work, the effect of nickel doping on the structural and magnetic properties of Fe3O4 nanoparticles is analysed. Ni(x)Fe(3-x)O4 nanoparticles (x = 0, 0.04, 0.06 and 0.11) were obtained by chemical co-precipitation method, starting from a mixture of FeCl2 x 4H2O and Ni(AcO)2 x 4H2O salts. The analysis of the structure and composition of the synthesized nanoparticles confirms their nanometer size (main sizes around 10 nm) and the inclusion of the Ni atoms in the characteristic spinel structure of the magnetite Fe3O4 phase. In order to characterize in detail the structure of the samples, X-ray absorption (XANES) measurements were performed on the Ni and Fe K-edges. The results indicate the oxidation of the Ni atoms to the 2+ state and the location of the Ni2+ cations in the Fe2+ octahedral sites. With respect to the magnetic properties, the samples display the characteristic superparamagnetic behaviour, with anhysteretic magnetic response at room temperature. The estimated magnetic moment confirms the partial substitution of the Fe2+ cations by Ni2+ atoms in the octahedral sites of the spinel structure.