Effect of doping on the luminescence properties of Li2B4O7

In this work, we have investigated the influence of doping agents on the luminescence properties of multiply doped Li₂B₄O₇ and the temperature lag between TSL materials and the heating element. The results of thermoluminescence studies show that the Ag doping leads to the appearance of a new glow curve peak at 165 °C and the increasing sensitivity of Li₂B₄O₇:Cu,Ag,P is correlated with copper and phosphate concentrations. Under the excitation at 245 nm the emission spectra show maxima at 365 and 450 nm in the ceramic, crystal and glass. The low energy shift in the latter system might be related to the local structural distortion in the glass around Cu⁺ ions.     

纯Cr2O3包覆Li4Ti5O12微球的制备及其储锂性能研究

The pure Cr₂O₃ coated Li₄Ti₅O₁₂ microspheres were prepared by a facile and cheap solutionbased method with basic chromium(III) nitrate solution (pH=11.9). And their Li-storage properties were investigated as anode materials for lithium rechargeable batteries. The pure Cr₂O₃ works as an adhesive interface to strengthen the connections between Li₄Ti₅O₁₂ particles, providing more electric conduction channels, and reduce the inter-particle resistance. Moreover, LixCr₂O₃, formed by the lithiation of Cr₂O₃, can further stabilize Li₇Ti₅O₁₂ with high electric conductivity on the surface of particles. While in the acid chromium solution (pH=3.2) modification, besides Cr₂O₃, Li₂CrO₄ and TiO₂ phases were also found in the final product. Li₂CrO₄ is toxic and the presence of TiO₂ is not welcome to improve the electrochemical performance of Li₄Ti₅O₁₂ microspheres. The reversible capacity of 1% Cr₂O₃-coated sample with the basic chromium solution modification was 180 mAh/g at 0.1 C, and 134 mAh/g at 10 C. Moreover, it was even as high as 127 mAh/g at 5 C after 600 cycles. At-20℃, its reversible specific capacity was still as high as 118 mAh/g.     

Electrical properties of pure and Li2O-doped CuO/Fe2O3 system precalcined at different temperatures

The electrical properties of pure and Li₂O-doped CuO/Fe₂O₃ solids were investigated. Pure and variously doped solids were subjected to thermal treatment at 1073–1273 K and the amount of dopant was varied between 0.84 to 3.36 mol%. The effect of precalcination temperature and amount of Li₂O added on the electrical conductivity σ, activation energy E_a and dielectric constant * were studied. The variation of ′ and ″ as a function of frequency for pure and variously doped solids precalcined at different temperatures was also investigated. The results obtained were discussed.     

Chemical quenching of positronium in Fe2O3/Al2O3 catalysts

Fe₂O₃/Al₂O₃ catalysts were prepared by solid state reaction method using α-Fe₂O₃ and γ-Al₂O₃ nano powders. The microstructure and surface properties of the catalyst were studied using positron lifetime and coincidence Doppler broadening annihilation radiation measurements. The positron lifetime spectrum shows four components. The two long lifetimes τ₃ and τ₄ are attributed to positronium annihilation in two types of pores distributed inside Al₂O₃ grain and between the grains, respectively. With increasing Fe₂O₃ content from 3 wt% to 40 wt%, the lifetime τ₃ keeps nearly unchanged, while the longest lifetime τ₄ shows decrease from 96 ns to 64 ns. Its intensity decreases drastically from 24% to less than 8%. The Doppler broadening S parameter shows also a continuous decrease. Further analysis of the Doppler broadening spectra reveals a decrease in the p-Ps intensity with increasing Fe₂O₃ content, which rules out the possibility of spin-conversion of positronium. Therefore the decrease of τ₄ is most probably due to the chemical quenching reaction of positronium with Fe ions on the surface of the large pores.     

Silane treatment of Fe3O4 and its effect on the magnetic and wear properties of Fe3O4/epoxy nanocomposites

In this study, the effect of silane treatment of Fe₃O₄ on the magnetic and wear properties of Fe₃O₄/epoxy nanocomposites was investigated. Fe₃O₄ nanopowders were prepared by coprecipitation of iron(II) chloride tetrahydrate with iron(III) chloride hexahydrate, and the surfaces of Fe₃O₄ were modified with 3-aminopropyltriethoxysilane. The magnetic properties of the powders were measured on unmodified and surface-modified Fe₃O₄/epoxy nanocomposites using SQUID magnetometer. Wear tests were performed on unmodified and surface-modified Fe₃O₄/epoxy nanocomposites under the same conditions (sliding speed: 0.18 m/s, load: 20 N).The results showed that the saturation magnetization (M_s) of surface-modified Fe₃O₄/epoxy nanocomposites was approximately 110% greater than that of unmodified Fe₃O₄/epoxy nanocomposites. This showed that the specific wear rate of surface-modified Fe₃O₄/epoxy nanocomposites was lower than that of unmodified Fe₃O₄/epoxy nanocomposites. The decrease in wear rate and the increase in magnetic properties of surface-modified Fe₃O₄/epoxy nanocomposites occurred due to the improved dispersion of Fe₃O₄ into the epoxy matrix.     

Synthesis and characterization of thermoluminescent Li2B4O7 nanophosphor

Lithium borate (Li₂B₄O₇) is a low Z_eff, tissue equivalent material that is commonly used for medical dosimetry using the thermoluminescence (TL) technique. Nanocrystals of lithium borate were synthesized by the combustion method for the first time in the laboratory. TL characteristics of the synthesized material were studied and compared with those of commercially available microcrystalline Li₂B₄O₇. The optimum pre-irradiation annealing condition was found to be 300 °C for 10 min and that of post-irradiation annealing was 300 °C for 30 min. The synthesized Li₂B₄O₇ nanophosphor has very poor sensitivity for low doses of gamma up to 10¹ Gy whereas from 10¹ to 4.5×10² Gy this phosphor exhibits a linear response and then from 4.5×10² to 10³ Gy it shows supralinearity. Thermoluminescence properties of Li₂B₄O₇ nanophosphor doped with Cu has also been investigated in this paper. It shows low fading and a linear response over a wide range of gamma radiation from 1×10² to 5×10³ Gy. Therefore the synthesized lithium borate nanophosphor doped with Cu may be used for high dose measurements of gamma radiations.     

Comparison of magnetic properties in LixCoO2 and its decomposition products LiCo2O4 and Co3O4

Thermal stability of cathode material in the charged state is an important aspect for the safety of rechargeable batteries. It is well known that layered Li_xCoO₂ decomposes to a mixture of LiCoO₂ and Co₃O₄ at elevated temperatures. However, not many experimental evidences exist on intermediate phases those may form during the decomposition. Using magnetic measurements we show that it is possible to distinguish between the spinels LiCo₂O₄ and Co₃O₄ and thereby follow the decomposition of Li_xCoO₂. We characterize the magnetic behavior of thermally aged Li_xCoO₂ (x = 0.98, 0.76, 0.55) with increasing annealing time. Our results reveal the appearance of magnetic ordering in the thermally degraded products. The detailed analysis illustrates that the formation of Co₃O₄ is preceded by the formation of a meta stable LiCo₂O₄ phase.     

Biosynthesis and magnetic properties of mesoporous Fe3O4 composites

Magnetic Fe₃O₄ materials with mesoporous structure are synthesized by co-precipitation method using yeast cells as a template. The X-ray diffraction (XRD) pattern indicates that the as-synthesized mesoporous hybrid Fe₃O₄ is well crystallized. The Barrett-Joyner-Halenda (BJH) models reveal the existence of mesostructure in the dried sample which has a specific surface area of 96.31 m²/g and a pore size distribution of 8-14 nm. Transmission electron microscopy (TEM) measurements confirm the wormhole-like structure of the resulting samples. The composition and chemical bonds of the Fe₃O₄/cells composites are studied by Fourier transform infrared (FT-IR) spectroscopy. Preliminary magnetic properties of the mesoporous hybrid Fe₃O₄ are characterized by a vibrating sample magnetometer (VSM). The magnetic Fe₃O₄/cells composites with mesoporous structure have potential applications in biomedical areas, such as drug delivery.     

Large nonlinear optical properties of Fe2O3 nanoparticles

Nonlinear optical properties of Fe₂O₃ nanoparticles were investigated by the signal-beam Z-scan technique with Ar⁺ and Ne–He lasers. The largest reported effective nonlinear coefficient, n₂=−8.07×10⁻⁷ cm²/W, was obtained. It is demonstrated that the nonlinear optical response originals from quantum confinement effect.     

Synthesis and properties of Au-Fe3O4 and Ag-Fe3O4 heterodimeric nanoparticles

Monodisperse Au-Fe 3 O 4 heterodimeric nanoparticles (NPs) were prepared by injecting precursors into a hot reaction solution.The size of Au and Fe 3 O 4 particles can be controlled by changing the injection temperature.UV-Vis spectra show that the surface plasma resonance band of Au-Fe 3 O 4 heterodimeric NPs was evidently red-shifted compared with the resonance band of Au NPs of similar size.The as-prepared heterodimeric Au-Fe 3 O 4 NPs exhibited superparamagnetic properties at room temperature.The Ag-Fe 3 O 4 heterodimeric NPs were also prepared by this synthetic method simply using AgNO 3 as precursor instead of HAuCl 4.It is indicated that the reported method can be readily extended to the synthesis of other noble metal conjugated heterodimeric NPs.     

Fabrication, characterization and photoelectrochemical properties of Fe2O3 modified TiO2 nanotube arrays

TiO₂ nanotube (NT) arrays modified by Fe₂O₃ with high sensibility in the visible spectrum were first prepared by annealing anodic titania NTs pre-loaded with Fe(OH)₃ which was uniformly clung to the titania NTs using sequential chemical bath deposition (S-CBD). The photoelectrochemical performances of the as-prepared composite nanotubes were determined by measuring the photo-generated currents and voltages under illumination of UV-vis light. The titania NTs modified by Fe₂O₃ showed higher photopotential and photocurrent values than those of unmodified titania NTs. The enhanced photoelectrochemical behaviors can be attributed to the modified Fe₂O₃ which increases the probability of charge-carrier separation and extends the range of the TiO₂ photoresponse from ultraviolet (UV) to visible region due to the low band gap of 2.2 eV of Fe₂O₃.     

Emission features of Ho ion in Nb2O5, Ta2O5 and La2O3 mixed Li2O-ZrO2-SiO2 glasses

Li₂O-ZrO₂-SiO₂: Ho³⁺ glasses mixed with three interesting d-block elemental oxides, viz., Nb₂O₅, Ta₂O₅ and La₂O₃, were prepared. Optical absorption and photoluminescence spectra of these glasses have been recorded at room temperature. The luminescence spectra of Nb₂O₅ and Ta₂O₅ mixed Li₂O-ZrO₂-SiO₂ glasses (free of Ho³⁺ ions) have also exhibited broad emission band in the blue region. This band is attributed to radiative recombination of self-trapped excitons (STEs) localized on substitutionally positioned octahedral Ta⁵⁺ and Nb⁵⁺ ions in the glass network. The Judd-Ofelt theory was successfully applied to characterize Ho³⁺ spectra of all the three glasses. From this theory various radiative properties, like transition probability A, branching ratio β_r and the radiative lifetime τ_r, for ⁵S₂ emission levels in the spectra of these glasses have been evaluated. The radiative lifetime for ⁵S₂ level of Ho³⁺ ions has also been measured and quantum efficiencies were estimated. Among the three glasses studied the La₂O₃ mixed glass exhibited the highest quantum efficiency. The reasons for such higher value have been discussed based on the relationship between the structural modifications taking place around the Ho³⁺ ions.     

Influence of postdeposition annealing on structural properties and electrical characteristics of thin Tm2O3 and Tm2Ti2O7 dielectrics

We describe the structural properties and electrical characteristics of thin thulium oxide (Tm₂O₃) and thulium titanium oxide (Tm₂Ti₂O₇) as gate dielectrics deposited on silicon substrates through reactive sputtering. The structural and morphological features of these films were explored by X-ray diffraction, X-ray photoelectron spectroscopy, secondary ion mass spectrometry, and atomic force microscopy, measurements. It is found that the Tm₂Ti₂O₇ film annealed at 800 °C exhibited a thinner capacitance equivalent thickness of 19.8 Å, a lower interface trap density of 8.37 × 10¹¹ eV⁻¹ cm⁻², and a smaller hysteresis voltage of ∼4 mV than the other conditions. We attribute this behavior to the Ti incorporated into the Tm₂O₃ film improving the interfacial layer and the surface roughness. This film also shows negligible degrees of charge trapping at high electric field stress.     

Characterization and catalytic performance of pure and Li2O-doped CuO/CeO2 catalysts

Pure and Li₂O-doped CuO/CeO₂ catalysts calcined at 500 °C were prepared by impregnation method. The catalysts are characterized by DTA, TG-DTG, XRD, IR, TEM, nitrogen adsorption at −196 °C and the catalytic decomposition of hydrogen peroxide at 30 °C.The effects of molar ratio, heat treatment time and the doping on the structural, surface and catalytic properties of nanocrystalline Cu/Ce-mixed oxides system have been studied. It was found that the catalytic activity of ceria-supported copper oxide catalysts increased by increasing both the heat treatment time and dopant content. However, the pure Cu/Ce-mixed oxide solids containing 10 wt.% CuO exhibited the best performance. The characterization results indicated that the higher surface area, the formation of solid solution between copper and cerium oxides, and the high dispersion of copper species on the ceria were responsible for the high catalytic activity of the CuO/CeO₂ catalysts.     

Effect of sintering temperature and the particle size on the structural and magnetic properties of nanocrystalline Li0.5Fe2.5O4

Sintering temperature and particle size dependent structural and magnetic properties of lithium ferrite (Li_0.5Fe_2.5O₄) were synthesized and sintered at four different temperatures ranging from 875 to 1475 K in the step of 200 K. The sample sintered at 875 K was also treated for four different sintering times ranging from 4 to 16 h. Samples sintered at 1475 K have the cubic spinel structure with a small amount of α-Fe₂O₃ (hematite) and γ-Fe₂O₃ (maghemite). The samples sintered at≤1275 K do not show hematite and maghemite phases and the crystals form the single phase spinel structure with the cation ordering on octahedral sites. Particle size of lithium ferrite is in the range of 13-45 nm, and is depend on the sintering temperature and sintering time. The saturation magnetization increased from 45 to 76 emu/g and coercivity decreases from 151 to 139 Oe with an increase in particle size. Magnetization temperature curve recorded in ZFC and FC modes in an external magnetic field of 100 Oe. Typical blocking effects are observed below about 244 K. The dielectric constant increases with an increase in sintering temperature and particle size.     

A novel UV-emitting phosphor: Li6CaB3O8.5:Pb

Pure Li₆CaB₃O_8.5 and Li₆Ca_1−xPb_xB₃O_8.5 (0.005≤x≤0.04) materials were prepared by a solution combustion synthesis method. The phase of synthesized materials was determined using the powder XRD and FTIR. The synthesized materials were investigated using spectrofluorometer at room temperature. The emission and excitation bands of the synthesized phosphors were observed at 307 and 268 nm, respectively. The dependence of the emission intensity on the Pb²⁺ concentration for the Li₆Ca_1−xPb_xB₃O_8.5 (0.005≤x≤0.04) was studied and observed that the optimum concentration of Pb²⁺ in phosphor is 0.01 mol. The Stokes shift of the synthesized phosphor was calculated to be 4740 cm^-1.     

Green synthesis and characterization of superparamagnetic Fe3O4 nanoparticles

In this paper, we have first demonstrated a facile and green synthetic approach for preparing superparamagnetic Fe₃O₄ nanoparticles using α-d-glucose as the reducing agent and gluconic acid (the oxidative product of glucose) as stabilizer and dispersant. The X-ray powder diffraction (XRD), X-ray photoelectron spectrometry (XPS), and selected area electron diffraction (SAED) results showed that the inverse spinel structure pure phase polycrystalline Fe₃O₄ was obtained. The scanning electron microscopy (SEM) and transmission electron microscopy (TEM) results exhibited that Fe₃O₄ nanoparticles were roughly spherical shape and its average size was about 12.5 nm. The high-resolution TEM (HRTEM) result proved that the nanoparticles were structurally uniform with a lattice fringe spacing about 0.25 nm, which corresponded well with the values of 0.253 nm of the (3 1 1) lattice plane of the inverse spinel Fe₃O₄ obtained from the JCPDS database. The superconducting quantum interference device (SQUID) results revealed that the blocking temperature (T_b) was 190 K, and that the magnetic hysteresis loop at 300 K showed a saturation magnetization of 60.5 emu/g, and the absence of coercivity and remanence indicated that the as-synthesized Fe₃O₄ nanoparticles had superparamagnetic properties. Fourier transform infrared spectroscopy (FT-IR) spectrum displayed that the characteristic band of Fe-O at 569 cm⁻¹ was indicative of Fe₃O₄. This method might provide a new, mild, green, and economical concept for the synthesis of other nanomaterials.     

Subsolidus phase relation in the Bi_2O_3–Fe_2O_3–La_2O_3 system

Bismuth-containing semiconductor material is a hot topic in photocatalysts because of its effective absorption under the visible light.In this paper,we expect to explore a new bismuth-based photocatalyst by studying the subsolidus phase relations of the Bi2O3–Fe2O3–La2O3system.The X-ray diffraction data shows that in this ternary system the ternary compound does not exist,while seven binary compounds(including one solid solution series Bi1 xLaxO1.5with 0.167≤x≤0.339)are obtained and eight compatibility triangles are determined.     

Synthesis and magnetic properties of hard magnetic (CoFe2O4)-soft magnetic (Fe3O4) nano-composite ceramics by SPS technology

CoFe₂O₄/Fe₃O₄ nano-composite ceramics were synthesized by Spark Plasma Sintering. The X-ray diffraction patterns show that all samples are composed of CoFe₂O₄ and Fe₃O₄ phases when the sintering temperature is below 900 °C. It is found that the magnetic properties strongly depend on the sintering temperature. The two-step hysteresis loops for samples sintered below 500 °C are observed, but when sintering temperature reaches 500 °C, the step disappears, which indicates that the CoFe₂O₄ and Fe₃O₄ are well exchange coupled. As the sintering temperature increases from 500 to 800 °C, the results of X-ray diffractometer indicate the constriction of crystalline regions due to the ion diffusion at the interfaces of CoFe₂O₄/Fe₃O₄ phases, which have great impact on the magnetic properties.     

Ab initio prediction on ferrotoroidic and electronic properties of olivine Li4MnFeCoNiP4O16

First-principles calculations predict that olivine Li4MnFeCoNiP4O16 has a large toroidal moment and ferrimagnetic configuration with a magnetic moment of 1.99μB per formula unit. Density functional theory plus U (DFT+U) shows an indirect band gap of 0.65 eV in this hypothetical material. The band gap is not simply related to the electronic conductivity when it is used as cathode material in rechargeable Li-ion batteries. Based on the orbital-resolved density of states for the transition-metal ions in the hypothetical material, Co, Ni and Mn are in the high-spin configuration while Fe is in the low-spin configuration, which leads to a large resulting toroidal moment deriving from the Co and Ni ions. The spin configuration of the transition-metal ions in the system breaks the space-and time-inversion symmetry and leads to the magnetoelectric property simultaneously. The ferrotoroidic domain, the fourth form of ferroic, is observed in this new material, as in the case of LiCoPO4 reported recently.