The morphology and orientation of Mn5Si3 precipitates in an Mg-Sn-Mn-Si alloy

This paper reports a preliminary study of Mn₅Si₃ precipitates in an Mg-Sn-Mn-Si alloy. The transmission electron microscopy investigation reveals that the Mn₅Si₃ precipitates have a plate shape, approximately 50 nm in thickness and 200 nm in width. The orientation relationship (OR) between the precipitates and matrix is not unique, but all measured ORs obey the following relationship: g_{(1 0 − 1 0)Mn5Si3} // Δg₁ // Δg₂, where Δg₁ = g_{(2 − 1 − 1 0)Mn5Si3} − g_{(0 0 0 2)Mg}, Δg₂ = g_{(3 − 1 − 2 0)Mn5Si3} − g_{(0 0 0 2)Mg}. The precipitate morphology and their OR with the matrix are explained with a Δg parallelism rule, showing good agreement.     

Structural characterization, thermal, spectroscopic and magnetic studies of the (C3H12N2)0.75[Mn1.50Fe1.50(AsO4)F6] and (C3H12N2)0.75[Co1.50Fe1.50(AsO4)F6] compounds

The (C₃H₁₂N₂)_0.94[Mn_1.50Fe_1.50^III(AsO₄)F₆] and (C₃H₁₂N₂)_0.75[Co_1.50Fe_1.50^III(AsO₄)F₆] compounds 1 and 2 have been synthesized using mild hydrothermal conditions. These phases are isostructural with (C₃H₁₂N₂)_0.75[Fe_1.5^IIFe_1.5^III(AsO₄)F₆]. The compounds crystallize in the orthorhombic Imam space group. The unit cell parameters calculated by using the patterns matching routine of the FULPROOF program, starting from the cell parameters of the iron(II),(III) phase, are: a = 7.727(1) Å, b = 11.047(1) Å, c = 13.412(1) Å for 1 and a = 7.560(1) Å, b = 11.012(1) Å, c = 13.206(1) Å for 2, being Z = 8 in both compounds. The crystal structure consists of a three-dimensional framework constructed from edge-sharing [M^II(1)₂O₂F₈] (M = Mn, Co) dimeric octahedra linked to [Fe^III(2)O₂F₄] octahedra through the F(1) anions and to the [AsO₄] tetrahedra by the O(1) vertex. This network gives rise two kinds of chains, which are extended in perpendicular directions. Chain 1 is extended along the a-axis and chain 2 runs along the c-axis. These chains are linked by the F(1) and O(1) atoms and establish cavities delimited by eight or six polyhedra along the [1 0 0] and [0 0 1] directions, respectively. The propanediammonium cations are located inside these cavities. The thermal study indicates that the structures collapse with the calcination of the organic dication at 255 and 285 °C for 1 and 2, respectively. The Mössbauer spectra in the paramagnetic state indicate the existence of two crystallographically independent positions for the iron(III) cations and a small proportion of this cation in the positions of the divalent Mn(II) and Co(II) ones. The IR spectrum shows the protonated bands of the H₂N- groups of the propanediamine molecule and the characteristic bands of the [AsO₄]³⁻ arsenate oxoanions. In the diffuse reflectance spectra, it can be observed the bands characteristic of trivalent iron(III) cation and divalent Mn(II) and Co(II) ones in a distorted octahedral symmetry. The calculated Dq and B-Racah parameters for the cobalt(II) phase are 710 and 925 cm⁻¹, respectively. The ESR spectra of compound 1 maintain isotropic with variation in temperature, being g = 1.99. Magnetic measurements for both compounds indicate that the main magnetic interactions are antiferromagnetic in nature. However, at low temperatures small ferromagnetic components are detected, which are probably due to a spin decompensation of the two different metallic cations. The hysteresis loops give values of the remnant magnetization and coercive field of 84.5, 255 emu/mol and 0.01, 0.225 T for phases 1 and 2, respectively.     

Ion exchange and electrochemical evaluation of the microporous phosphate Li9Fe7(PO4)10

A new lithium iron(III) phosphate, Li₉Fe₇(PO₄)₁₀, has been synthesized and is currently under electrochemical evaluation as an anode material for rechargeable lithium-ion battery applications. The sample was prepared via the ion exchange reaction of Cs₅K₄Fe₇(PO₄)₁₀1 in the 1 M LiNO₃ solution under hydrothermal conditions at 200 °C. The fully Li⁺-exchanged sample Li₉Fe₇(PO₄)₁₀2 cannot yet be synthesized by conventional high-temperature, solid-state methods. The parent compound 1 is a member of the Cs_9−xK_xFe₇(PO₄)₁₀ series that was previously isolated from a high-temperature (750 °C) reaction employing the eutectic CsCl/KCl molten salt. The polycrystalline solid 1 was first prepared in a stoichiometric reaction via conventional solid-state method then followed by ion exchange giving rise to 2. Both compounds adopt three-dimensional structures that consist of orthogonally interconnected channels where electropositive ions reside. It has been demonstrated that the Cs_9−xK_xFe₇(PO₄)₁₀ series possesses versatile ion exchange capabilities with all the monovalent alkali metal and silver cations due to its facile pathways for ion transport. 1 and 2 were subject to electrochemical analysis and preliminary results suggest that the latter can be considered as an anode material. Electrochemical results indicate that Li₉Fe₇(PO₄)₁₀ is reduced below 1 V (vs. Li) to most likely form a Fe(0)/Li₃PO₄ composite material, which can subsequently be cycled reversibly at relatively low potential. An initial capacity of 250 mAh/g was measured, which is equivalent to the insertion of thirteen Li atoms per Li_9+xFe₇(PO₄)₁₀ (x = 13) during the charge/discharge process (Fe²⁺ + 2e → Fe⁰). Furthermore, 2 shows a lower reduction potential (0.9 V), by approximately 200 mV, and much better electrochemical reversibility than iron(III) phosphate, FePO₄, highlighting the value of improving the ionic conductivity of the sample.     

Parameterization of CuIn1−xGaxSe2 (x = 0, 0.5, and 1) energy bands

Parameterization of the electronic band structure of CuIn_1−xGa_xSe₂ (x = 0, 0.5, and 1) demonstrates that the energy dispersions of the three uppermost valence bands [E_j(k); j = v1, v2, and v3] are strongly anisotropic and non-parabolic even very close to the Γ-point valence-band maximum E_v1(0). Also the lowest conduction band E_c1(k) is anisotropic and non-parabolic for energies ~ 0.05 eV above the band-gap energy. Since the electrical conductivity depends directly on the energy dispersion, future electron and hole transport simulations of CuIn_1−xGa_xSe₂ need to go beyond the parabolic approximation of the bands. We therefore present a parameterization of the energy bands, the k-dependency of the effective electron and hole masses m_j(k), and also an average energy-dependent approximation of the masses m_j(E).     

Microwave assisted fast fabrication of Fe3O4-MWCNTs nanocomposites and their application as MRI contrast agents

Uniform Fe₃O₄ nanoparticles with diameters of 3-5 nm are successfully decorated onto the external walls of multiwall carbon nanotubes (MWCNTs) by in situ high-temperature decomposition of Fe(acac)₃ in polyol solution under the irradiation of microwave. With this method, reaction time of forming Fe₃O₄-MWCNTs nanocomposites has been significantly shortened to 15 min. The resulting Fe₃O₄-MWCNTs nanocomposites show superparamagnetic property at room temperature and can be remained as stable aqueous dispersion for 2 months. Longitudinal relaxivity (r₁) and transverse relaxivity (r₂) of the magnetic MWCNTs are 8.34 Fe mM⁻¹ S⁻¹ and 146 Fe mM⁻¹ S⁻¹ respectively. The much higher r₂ value and the obvious change in the gray scale of MR images confer the Fe₃O₄-MWCNTs nanocomposites as potential candidates for T₂-weighted MRI contrast agents.     

The effect of solution chemistry on the preparation of MgAl2O4 by hydrothermal-assisted sol-gel processing

Preparation of magnesium aluminate spinel powder by hydrothermal-assisted sol-gel processing from MgAl₂(OCH₂CH₂OR)₈, RCH₃ (1), CH₂CH₂OCH₃ (2), MgAl₂[OCH(CH₃)₂]₈ (3) and MgAl₂(O-^sBu)₈ (4) in toluene and parent alcohol has been investigated. Coordination status of aluminum atom in precursors was determined by ²⁷Al NMR and correlation between coordination number of aluminum and development of spinel phase in hydrothermal-assisted sol-gel processing has been studied. The gels obtained from hydrothermal-assisted hydrolysis of magnesium-aluminum alkoxides that contain six-coordinated aluminum atoms in solution (1 and 2) after calcination at 700 °C resulted in the formation of pure spinel phase, whereas in similar hydrolysis and calcination processes of precursors that contain four-coordinated aluminum (3 and 4) spinel phase forms along with some Al₂O₃ and MgO. Selected powders obtained from hydrothermal-assisted sol-gel processing were characterized by thermal analysis (TGA/DSC), X-ray powder diffraction (XRD) and scanning electron microscopy (SEM). Results indicate that the coordination status of aluminum in the precursor is very crucial for the formation of pure phase spinel. The morphology of prepared spinels was studied by SEM and the results showed that the solvent in hydrothermal-assisted sol-gel processing has a marked effect on the morphology of the resulting MgAl₂O₄. In hydrothermal-assisted sol-gel processing of aluminum-magnesium alkoxides in hydrophobic solvent, spherical particles are formed, while in the parent alcohol, non-spherical powders are formed.     

Effects of Fe2O3 doping on the microstructure and piezoelectric properties of 0.55Pb(Ni1/3Nb2/3)O3-0.45Pb(Zr0.3Ti0.7)O3 ceramics

0.55Pb(Ni_1/3Nb_2/3)O₃-0.45Pb(Zr_0.3Ti_0.7)O₃(PNN-PZT) ceramics with different concentration of xFe₂O₃ doping (where x = 0.0, 0.8, 1.2, 1.6 mol%) were synthesized by the conventional solid state sintering technique. X-ray diffraction analysis reveals that all specimens are a pure perovskite phase without pyrochlore phase. The density and grain size of Fe-doped ceramics tend to increase slightly with increasing concentration of Fe₂O₃. Comparing with the undoped ceramics, the piezoelectric, ferroelectric and dielectric properties of the Fe-doped PNN-PZT specimens are significantly improved. Properties of the piezoelectric constant as high as d₃₃ ~ 956 pC/N, the electromechanical coupling factor k_p ~ 0.74, and the dielectric constant ε_r ~ 6095 are achieved for the specimen with 1.2 mol% Fe₂O₃ doping sintered at 1200 °C for 2 h.     

Synthesis and electrochemical properties of Ti doped Li3 − xFe2 − xTix(PO4)3/C cathode materials

Li_3 − xFe_2 − xTi_x(PO₄)₃/C (x = 0-0.4) cathodes designed with Fe doped by Ti was studied. Both Li₃Fe₂(PO₄)₃/C (x = 0) and Li_2.8Fe_1.8Ti_0.2(PO₄)₃/C (x = 0.2) possess two plateau potentials of Fe³⁺/Fe²⁺ couple (around 2.8 V and 2.7 V vs. Li⁺/Li) upon discharge observed from galvanostatic charge/discharge and cyclic voltammetry. Li_2.8Fe_1.8Ti_0.2(PO₄)₃/C has higher reversibility and better capacity retention than that of the undoped Li₃Fe₂(PO₄)₃/C. A much higher specific capacity of 122.3 mAh/g was obtained at C/20 in the first cycle, approaching the theoretical capacity of 128 mAh/g, and a capacity of 100.1 mAh/g was held at C/2 after the 20th cycle.     

Dielectric and electric studies of the [N(CH3)4][N(C2H5)4]ZnCl4 compound at low temperature

The [N(CH₃)₄][N(C₂H₅)₄]ZnCl₄ compound was prepared and characterized by electrical technique. The temperature dependence of the dielectric permittivity shows that this compound is ferroelectric below T = 268 K. The two semi-circles observed in the complex impedance identify the presence of the grain interior and grain boundary contributions to the electrical response in the material. The equivalent circuit is modeled by a combination series of two parallel R_P–CPE circuits. The frequency dependent conductivity is interpreted in term of Jonscher's law. The modulus plots can be characterized by the empirical Kohlrausch–Williams–Watts (K.W.W.) function: ?(t) = exp [(−t/τ)^β]. The temperature dependence of the alternative current conductivity (σ_p), direct current conductivity (σ_dc) and the relaxation frequency (f_p) confirm the presence of the ferroelectric–paraelectric phase transition.     

Synthesis, structure and magnetic properties of a new iron phosphonate-oxalate with 3D framework: [Fe(O3PCH3)(C2O4)0.5(H2O)]

A new iron phosphonate-oxalate [Fe(O₃PCH₃)(C₂O₄)_0.5(H₂O)] (1), has been synthesized under hydrothermal condition. The single-crystal X-ray diffraction studies reveal that 1 consists of layers of vertex-linked FeO₆ octahedra and O₃PC tetrahedra, which are further connected by bis-chelate oxalate bridges, giving to a 3D structure with 10-membered channels. Crystal data: monoclinic, P2₁/n (no. 14), a = 4.851(2) Å, b = 16.803(7) Å, c = 7.941(4) Å, β = 107.516(6)°, V = 617.2(5) Å³, Z = 4, R₁ = 0.0337 and wR₂=0.0874 for 1251 reflections [I > 2σ(I)]. Mössbauer spectroscopy measurement confirms the existence of high-spin Fe(III) in 1. Magnetic studies show that 1 exhibits weak ferromagnetism with T_N = 30 K due to a weak spin canting.     

Transformation of Dion-Jacobson phase to Aurivillius phase: synthesis of (PbBiO2)MNb2O7 (M = La, Bi)

We describe transformations of the Dion-Jacobson (D-J) phases, KLaNb₂O₇ and RbBiNb₂O₇, to the Aurivillius (A) phases, (PbBiO₂)LaNb₂O₇ (1) and (PbBiO₂)BiNb₂O₇ (2), in a metathesis reaction with PbBiO₂Cl. Oxide 1 adopts centrosymmetric tetragonal structure (a = 3.905(1) Å, c = 25.66(1) Å), whereas oxide 2 crystallizes in a noncentrosymmetric orthorhombic (A2₁am) (a = 5.489(1) Å, b = 5.496(2) Å, c = 25.53(1) Å) structure. Oxide 2 shows a distinct SHG response towards 1064 nm laser radiation. The role of La³⁺ versus Bi³⁺ in the perovskite slabs for the occurrence of noncentrosymmetric structure/ferroic property in these materials is pointed out.     

Structural stability of ZnFe2O4 nanoparticles under different annealing conditions

We study the structural stability of surfactant coated ZnFe₂O₄ (ZF) nanoparticles of average particle size 10 nm annealed under different environments. The X-ray diffraction studies in oleic acid coated ZF (OC-ZF) show distinctly different phase transitions under different annealing conditions. The OC-ZF is reduced to α-Fe/ZnO phase under vacuum while it forms FeO/ZnO under argon whereas the ZnFe₂O₄ phase remains stable under air annealing. The simultaneous thermo gravimetric analysis (TGA), differential scanning calorimetry (DSC) coupled mass spectra (MS) in OC-ZF under argon atmosphere suggests that the residual carbon removes oxygen from the lattice to reduce the ZnFe₂O₄ phase into FeO/ZnO during argon annealing. Apart from CO and CO₂ gas evolution at high temperature under argon annealing, creation of oxygen vacancies due to the random removal of oxygen under vacuum annealing, leads to direct interaction between Fe–Fe and the formation of metal Fe. It appears that the residual carbon aids the reduction of ZF and the formation of α-Fe/ZnO during vacuum annealing. After annealing at 1000 °C in vacuum, the magnetization is increased abruptly from 13.8 to 106.5 emu g⁻¹. In sharp contrast, the air and argon annealed samples show a diminished magnetization of 1 emu g⁻¹. The field cooled (FC) and zero FC magnetization of vacuum and argon annealed samples exhibit superparamagnetic and spin-glass type behavior respectively. Our results offer possibilities to switch a magnetically inactive material to an active one.     

An easy fabrication of monodisperse oleic acid-coated Fe3O4 nanoparticles

An easy route is described for the synthesis of monodisperse oleic acid-coated Fe₃O₄ nanoparticles with uniform size and shape via a thermal decomposition of Fe(acac)₃ in the presence of oleic acid (OA). The prepared Fe₃O₄ samples are characterized by X-ray diffraction, transmission electron microscopy, Fourier transform infrared spectrometry, and vibrating sample magnetometer. The results show that the resulting OA-coated Fe₃O₄ nanoparticles have an average diameter of about 24 nm and an OA layer, around 3 nm in thickness. The magnetic saturation value of the prepared OA-coated Fe₃O₄ nanoparticles is determined to be 78.68 emu/g, indicating a well-established superparamagnetic property.     

Preparation and magnetic properties of SrFe12O19/Ni0.5Zn0.5Fe2O4 nanocomposite ferrite microfibers via sol–gel process

SrFe₁₂O₁₉/Ni_0.5Zn_0.5Fe₂O₄ nanocomposite ferrite microfibers with diameters of 1–2 μm have been prepared by the sol–gel process. The SrFe₁₂O₁₉/Ni_0.5Zn_0.5Fe₂O₄ nanocomposite ferrites are formed after the precursor calcined at 850 °C for 2 h, fabricating from nanosized particles with a uniform phase distribution. The ferrite grain size increases with the calcination temperature. The magnetic properties for the nanocomposite ferrite microfibers are mainly influenced by the chemical composition and grain size. The nanocomposite ferrite microfibers obtained at 900 °C show the enhanced specific saturation magnetization (M_sh) of 64.8 Am² kg⁻¹, coercivity (H_c) of 146.5 kA m⁻¹ and remanence (M_r) of 33.6 Am² kg⁻¹ owing to the exchange–coupling interaction. This exchange–coupling interaction in the SrFe₁₂O₁₉/Ni_0.5Zn_0.5Fe₂O₄ nanocomposite ferrite microfibers has been discussed.     

Synthesis and photocatalytic activity of cobalt oxide doped ZnFe2O4-Fe2O3-ZnO mixed oxides

Novel cobalt oxide doped ZnFe₂O₄-Fe₂O₃-ZnO mixed oxides with the Zn/Fe molar ratio of 1/2 were synthesized with a citric acid complex method. The effects of cobalt oxide and calcination temperature on phase composition and photocatalytic activity of the mixed oxides were investigated. X-ray diffraction (XRD) analysis revealed that there were mainly ZnFe₂O₄, α-Fe₂O₃, amorphous ZnO and Fe₂O₃ in the 6 mol% cobalt oxide doped products calcined at 500 °C. 5-10 mol% cobalt oxide doping could significantly enhance the formation of ZnFe₂O₄ and altered the phase composition of the mixed oxides. Experimental results showed that cobalt oxide doping could remarkably improve the photocatalytic activity of the mixed oxides for phenol degradation. The 6 mol% cobalt oxide doped mixed oxides calcined at 500 °C exhibited better photocatalytic activity as compared with other samples.     

Self-controlled growth of Fe3BO6 crystallites in shape of nanorods from iron-borate glass of small templates

Fe₃BO₆ can be an ideal compound for devising functional magnetic and dielectric properties in a single material for multiple applications such as electrodes, gas sensors, or medical tools. Useful to tailor such properties, here we report on a self-controlled Fe₃BO₆ growth in a specific shape of nanorods from a supercooled liquid precursor (an inorganic polymeric liquid or glass) of an initial composition (100 − x)B₂O₃ − xFe₂O₃, x = 40–50 mol%. B₂O₃ as a strong glass former co-bridges the Fe³⁺ ions in oxygen polygons primarily in a 2-D interconnected polymer network so that it dictates preferably a 1-D directional growth on the reaction Fe³⁺ species in form of a compound Fe₃BO₆, a favorable phase to nucleate and grow when annealing a precursor at 500–800 °C in ambient air. Distinct nanorods with a diameter ∼200 nm and 40–100 μm length have been formed on 10–15 min annealing a sample in microwave at moderate temperature 550 °C. A bonded surface B₂O₃ layer (15–25 nm thickness) has grown on the Fe₃BO₆ of the nanorods in situ in a specific structure. XPS bands in the Fe³⁺, B³⁺ and O²⁻ species confer this model structure. A local BO₃ → BO₄ conversion has incurred in the boroxol (B₃O_4.5)_n, n → ∞, rings in the surface layer, showing three distinct IR bands at 1035, 1215 and 1425 cm⁻¹.     

Preparation of Fe3O4/PVA nanofibers via combining in-situ composite with electrospinning

A novel approach, combining in-situ composite method with electrospinning, was used to prepare high magnetic Fe₃O₄/poly(vinyl alcohol) (PVA) composite nanofibers. Fe₃O₄ magnetic fluids were synthesized by chemical co-precipitation method in the presence of 6 wt.% PVA aqueous solution. PVA was used as stabilizer and polymeric matrix. The resulting Fe₃O₄/PVA composite nanofibers were characterized with field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM) and X-ray diffractometer (XRD), respectively. These composite fibers showed a uniform and continuous morphology, with the Fe₃O₄ nanoparticles embedded in the fibers. Magnetization test confirmed that the composite fiber showed a high saturated magnetization (M_s = 2.42 emµ·g^-1) although only 4 wt.% content.     

Ferric oxide and ZnFe2O4 nanotubes derived from nano ZnO/FeOx core/shell structures

The ZnO/FeO_x core/shell nanorods were prepared with ZnO nanorods as templates, on which ferric oxide was deposited by thermal decomposition of Fe(acac)₃ in solution. The thickness of the ferric oxide shell could be precisely controlled by the concentration of Fe(acac)₃. The amorphous ferric oxide nanotubes were fabricated by wet-etching the ZnO core nanorods in HAc solution and polycrystalline ZnFe₂O₄ nanotubes were prepared by annealing the core/shell ZnO/FeO_x nanocomposites in air. The obtained ZnFe₂O₄ nanotubes showed paramagnetism at room temperature.