Effects of Si and Ce on the microstructure and hydrogen storage property of Ti<Subscript>26.5</Subscript>Cr<Subscript>20</Subscript>V<Subscript>45</Subscript>Fe<Subscript>8.5</Subscript>Ce<Subscript>0.5</Subscript> alloy

In this paper, the effects of Si and Ce on the microstructure and hydrogen storage property of Ti_26.5Cr₂₀V₄₅Fe_8.5Ce_0.5 alloy were studied, respectively. First of all, effects of Si on the microstructure and hydrogen storage properties of Ti_26.5Cr₂₀(V₄₅Fe_8.5)_1−x Si _x Ce_0.5 (x = 0, 0.5, 1.0, 1.5 and 2.0 at%) alloys were studied by X-ray diffraction, scanning electron microscopy and P-C isotherm measurements. As the Si addition increases, the hydrogen absorption capacities of alloys decrease but the equilibrium pressure increases, due to the formation of Laves phase. Secondly, the effect of Ce on Ti_26.5Cr₂₀ (V₄₅Fe_8.5)_0.98Si₂ alloy was studied. It was found that Ce addition is an effective way to eliminate the effect of Si on the hydrogen storage properties of the alloy. Supported by the National Hi-Tech Research and Development Program of China (“863” Project) (Grant No. 2006AA05Z144)     

Moessbauer spectra of MnFe2-2x Al2xO4 （0 ≤x≤ 0.4） ferrites

The effect of non-magnetic Al³⁺ ion doping on the magnetic properties of MnFe_2−2x Al_2x O₄ (0≼x≼0.4) spinel ferrites was studied using M?ssbauer spectroscopy measurements at room temperature. From the M?ssbauer study, it is observed that the resolved hyperfine sextets are due to the distribution of Fe ions on the two sublattices of the spinel ferrites. The value of the isomer shift obtained from the fitting of the M?ssbauer spectra indicates that Fe ions are in +3 state. A paramagnetic doublet is observed at degree of inversion x=0.4, superimposed on the hyperfine sextets, indicating that the super-exchange interaction A–B decreases due to the dilution of sublattice by Al³⁺ ions. The hyperfine magnetic field decreases at both interstitial sites of tetrahedral (A) and octahedral (B) with the increase in Al concentration.     

Zn_(1-x)Co_xO Diluted Magnetic Semiconductor Bulk Prepared by Hot Pressing

Zn_1−x Co _x O diluted magnetic semiconductor bulks were prepared by hot pressing. Mixed powders of pure ZnO and CoO were compacted under pressure of 10 MPa at the temperature of 1 073 K. Then the samples were annealed in vacuum at the temperature from 673 K to 873 K for 10 h. The crystal structure and magnetic properties of Zn_1−x Co _x O bulks have been investigated by X-ray diffraction (XRD) and vibrating sample magnetometer (VSM). X-ray photoelectron spectroscopy (XPS) was used to study chemical valence of zinc and cobalt in the samples. The results showed that Zn_1−x Co _x O samples had c-axis oriented wurtzite symmetry, neither cobalt or cobalt oxide phase was found in the samples if x was less than 0.15. Zn and Co existed in Zn_0.9Co_0.1O sample in Zn²⁺ and Co²⁺ states. The results of VSM experiment proved the room temperature ferromagnetic properties (RTFP) of Co-doped ZnO samples. The saturation magnetization and the coercivity of Zn_0.9Co_0.1O sample, observed in the M-H curve, were about 0.20 emu/g and 200 Oe, respectively.     

Structure and infrared radiation property of Co<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>Zn<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Fe<Subscript>2</Subscript>O<Subscript>4</Subscript> ferrites by XAFS analysis

Co_1−x Zn _x Fe₂O₄ ferrites were prepared by solid state reaction. The microstructure and performance were studied by X-ray diffraction, X-ray absorption fine-structure analysis and IRE-2 infrared radiant test. It is found that infrared radiance show a nonlinear change with x, exhibiting the infrared radiance of this material improved and the average radiance in the 8–14 μm waveband reached 0.91. The Co³⁺ and Zn²⁺ ions are found to occupy both tetrahedral and octahedral sites, and correspondingly, the fraction of Fe³⁺ ions in B-site decreases nonlinearly in ferrites. The lattice parameters are found to concern with Zn²⁺, and the activation energy deduces from crystal strain and crystal vibrate increases with content Zn²⁺. The redistribution of the Co³⁺ and Zn²⁺ ions between tetrahedral and octahedral sites is related to the providing a selective tetrahedral and octahedral sites infrared radiance of Co_1−x Zn _x Fe₂O₄ ceramics with increasing x.     

Preparation and characterization of CeO<Subscript>2</Subscript>-TiO<Subscript>2</Subscript>/SnO<Subscript>2</Subscript>:Sb films deposited on glass substrates by R.F. sputtering

CeO2-TiO2 films and CeO2-TiO/SnO2：Sb （6 mol%） double films were deposited on glass substrates by radio-frequency magnetron sputtering （R.F. Sputtering）, using SnO2：Sb（6 mol%） target, and CeO2- TiO2 targets with different molar ratio of CeO2 to TiO2 （CeO2：TiO2-0：1.0; 0.1：0.9; 0.2：0.8; 0.3：0.7; 0.4：0.6; 0.5：0.5; 0.6：0.4; 0.7：0.3; 0.8：0.2; 0.9：0.1; 1.0：0）. The films are characterized by UV-visible transmission and infrared reflection spectra, scanning electron microscopy （SEM）, Raman spectroscopy, X-ray photoelectron spectroscopy （XPS） and X-ray diffraction （XRD）, respectively. The obtained results show that the amorphous phases composed of CeO2-TiO2 play an important role in absorbing UV, there are Ce^3-, Ce^4- and Ti^4- on the surface of the films; the glass substrates coated with CeO2-TiO2 （Ce/Ti=0.5：0.5; 0.6：0.4）/SnO2：Sb（6 mol%） double films show high absorbing UV（〉99）, high visible light transmission （75%） and good infrared reflection （〉70%）. The sheet resistance of the films is 30-50 Ω/□. The glass substrates coated with the double functional films can be used as window glass of buildings, automobile and so on.     

Synthesis and characterization of Nd doped M-type hexagonal barium ferrite ultrafine powders

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Thermal expansion properties and hygroscopicity of Y2?xSmxW3O12 (x = 0.0–0.4) compounds

A novel class of solid solutions of Y_2−x Sm _x W₃O₁₂ (x = 0.0−0.4) were synthesized and studied by means of powder X-ray diffraction. All samples crystallize in an orthorhombic space group Pnca. The lattice parameters a, b and c of Y_2−x Sm _x W₃O₁₂ increase with increasing Sm content. Since the compounds of this series hydrate at room temperature, thermogravimetric (TG) analysis was carried out. The result shows that the compound stores less water with increasing Sm content. The thermal expansion properties of Y_2−x Sm _x W₃O₁₂ (x = 0.1, 0.3 and 0.4) were investigated with high temperature X-ray diffraction. Negative thermal expansion coefficient α _I becomes less negative from −6.644×10⁻⁶ to −6.211×10⁻⁶°C⁻¹ when x changes from 0.1 to 0.4.     

Thermal stability and glass-forming ability of Y-Ce-Co-Al bulk metallic glasses

The thermal stability and glass-forming ability of Y_56-xCe_xCo₂₀Al₂₄ (x=15, 20, 25, 28, 38, 41, 44) bulk metallic glasses with a diameter of 5 mm were investigated by differential scanning calorimetry and X-ray diffraction. The results show that the thermal stability of the alloys decreases with the addition of Ce. It has the best glass-forming ability when x=25, whose calculated values can reach about 30 mm in diameter. The effect of Ce element could be explained on the view of Miedema's theory and electronegativity difference of amorphous alloys.     

Lower temperature synthesis of cerium-doped polycrystalline lutetium pyrosilicate powders by a novel sol-gel processing

A novel sol-gel processing was developed to synthesize polycrystalline cerium-doped lutetium pyrosilicate(Lu2Si2O7:Ce,LPS:Ce)powders under low temperature.It was found that the addition of propylene oxide(PPO)could promote the formation of Lu-O-Si bonds in precursor,which was beneficial to the formation of LPS phase.X-ray diffraction(XRD)patterns indicated that the single-phased LPS powder was well crystallized at 1050°C.Microstructure observation demonstrated that the synthetic LPS powder was composed of ellipsoidal grains with the mean size of 40 nm.The luminescent properties were characterized by photoluminescence(PL),X-ray excited luminescence(XEL)and vacuum ultraviolet(VUV)spectroscopy at room temperature.The synthetic LPS:Ce powder emitted a broad emission spectrum centered at about 380 nm,which should be ascribed to the 5d→4f transition of Ce3+.Decay time of the synthetic LPS:Ce powder was measured to be only 32 ns.     

Structure and Electric Conductivity of Ce-doped Bi<Subscript>2</Subscript>O<Subscript>3</Subscript> Electrolyte Synthesized by Reverse Titration Chemical Coprecipitation

Ce-doped Bi₂O₃ nanopowders were prepared by reverse titration chemical coprecipitation from Bi³⁺ and Ce⁴⁺ containing aqueous solution. Techniques of X-ray diffraction (XRD), transmission electron microscopic (TEM) and Fourier transform infrared spectroscopy (FTIR) were employed to characterize the as-synthesized materials. The XRD patterns indicated that the peaks can be easily indexed to β-Bi₂O₃ and no diffraction peaks of Ce or other impurity phases were detected in the prepared samples. The calculated average crystalline size decreased from 31.72 to 11.96 nm when the Ce content increased from 1 wt% to 10 wt%. The morphology changed from flake-like into the spherical-like with increase in Ce content. The electric conductivity of Ce-doped Bi₂O₃ electrolyte was also investigated by two probe DC method. Conductivity analysis exhibited that the rate of conductivity increased with increasing Ce²⁺ ratio, when the Ce concentration was up to 5 wt%, the as-synthesized Ce-doped Bi₂O₃ electrolyte showed the maximum value of conductivity(0.295 S·cm^–1).     

Impedance spectroscopy study on Mn1＋xFe2-2xTixO4 （0≤x≤0.5） ferrites

The complex impedance spectroscopy and surface morphology of Mn_1+x Fe_2−2x Ti _x O₄ (0⩽x⩽0.5) system, prepared using a conventional solid state reaction technique, were investigated. The impedance spectroscopy measurements were carried out at room temperature in the frequency range of 42–5 MHz. The electrical processes in the samples were modeled in the form of an equivalent circuit made up of a combination of two parallel RC circuits attributed to grain and grain boundaries. The DC conductivity obtained by extrapolation of AC data using impedance spectroscopy and four-probe method increases at 10% doping of Ti ions. The energy-dispersive X-ray (EDX) pattern confirmed the homogeneous mixing of the Mn, Fe, Ti and O atoms in pure and doped ferrite samples.     

Synthesis and coloring properties of Cd（S1-xSex） pigments by precipitate-hydrothermal method

Cd（S1-xSex） pigments （red to yellow） were synthesized by precipitate-hydrothermal method. The structure, morphology and hue of the powder were characterized by X-ray diffractometry （XRD）, scanning electron microscopy （SEM）, energy dispersive X-ray spectroscopy （EDAX） and CIE chromaticity. The optimum synthesis conditions were obtained and reaction mechanism was further analyzed as well. The results show that molar ratio of S to Se, pH value and hydrothermal reaction conditions have great effects on the hues of the pigments. Pigments with vivid hues are obtained under the conditions that pH value is about 13.0, hydrothermal reaction condition is at 140 ℃ for 4 h or at 160 ℃ for 6 h. The reaction mechanism is that Se^2- of Cd（S1-xSex） substitutes S^2- of CdS and then forms a continuous solid solution.     

Comparison of energy structure and spectral properties of Ce:LaAlO3 and Ce:Lu2(SiO4)O

Undoped LaAlO₃ and 1 at.% Ce:LaAlO₃ single crystals were grown by the Czochralski process. Absorption and fluorescence spectra were measured at room temperature. Detailed energy levels structure of Ce:LaAlO₃ was determined. In this paper, two viewpoints were provided. The first one is: the energy levels structure of Ce:LaAlO₃ is very similar to that of Ce:Lu₂(SiO₄)O which is a well-known scintillator. In the energy levels structure of Ce:LaAlO₃ and Ce:Lu₂(SiO₄)O, the lowest 5d energy level of Ce3+ is located below the bottom of the conduction band of host crystal and the other higher 5d energy levels of Ce³⁺ are located above the bottom of the conduction band of host crystal. The second one is: Ce:LaAlO₃ single crystal may not be suitable for scintillation application; by comparing the energy levels structures of Ce:LaAlO₃ and Ce:Lu₂(SiO₄)O, the large energy difference (1.13 eV) between the two lowest 5d energy levels of Ce³⁺ in LaAlO₃ is a crucial factor that causes the luminescence quenching.     

Structure and Electric Properties of （1-x）（Bi1/2Na1/2） TiO3-xBaTiO3 Systems

The structural, dielectric and piezoelectric properties of （1-x）（Bi1/2Na1/2） TiO3-xBaTiO3 ceramics were investigated for the compositional range, x=0.02, 0.04, 0.06, 0.08, 0.10. The samples were synthesized by a conventional solid-state reaction technique. All compositions show a single perovskite structure, and X-ray powder diffraction patterns can be indexed using a rhombohedral structure. Lattice constants and lattice distortion increase while the amount of BaTiO3 increases. The X-ray diffraction results show the morphotropic phase boundary （MPB） of （1-x）（Bi1/2Na12） TiO3-xBaTiO3 exists in near x=0.06-0.08. Temperature dependence of dielectric constant eT33/ε0 measurement reveals that all compositions experience one structural phase and two ferroelectric phases transition below 400℃： rhombohedral （or rhombohedral plus tetragonal） ferroelectric phase ←→ tetragonal antiferroelectric phase ←→ tetragonal paraelectric phase. Relaxor behaviors exist in the course of ferroelectric to antiferroelectric phase transition. Dielectric and piezoelectric properties are enhanced in the MPB range for （ 1-x）（Bi1/2Na1/2）TiO3-xBaTiO3.     

Effects of Substrate Temperatures on the Structure and UV-shielding Properties of TiO2-CeO2 Films Deposited on Glass by Radio-frequency Magnetron Sputtering

TiO2-CeO2 films were deposited on soda-lime glass substrates at varied substrate temperatures by rf magnetron sputtering using 40% molar TiO2-60% molar CeO2 ceramic target in Ar：O2=95：5 atmosphere.The structure,surface composition,UV-visible spectra of the films were measured by scanning electron microscopy and X-ray diffraction,and X-ray photoelectron spectroscopy,respectively.The experimental results show that the films are amorphous,there are only Ti^4＋ and Ce^4＋ on the surface of the films,the obtained TiO2-CeO2 films shou a good uniformity and high densification,and the films deposited on the glass can shield ultraviolet light without significant absorpition of visible light,the films deposited on substrates at room temperature and 220℃ absorb UV effectively.     

Effect of Lead Contents on the Properties of PMSZT Piezoelectric Ceramics

The effects of Pb content on crystallographic phase, microstructure, electric-properties of PMSZT piezoelectric ceramics were studied. The crystallographic phase and microstructure of the ceramics were examined by using X-ray diffraction （XRD） and scanning electron microscopy （SEM）. The experimental result shows that the samples consist of a mixture of tetragonal and rhombohedral phases in the range of lead contents x=0.95-1.06, grains grow up homogeneously and the minimum value of Curie temperature was obtained with x-=1.02. With Pb content x〈l.02 or x〉1.02, the Curie temperature moves towards a high temperature. A well-situated electric-properties of ET33/E0 （1660）, d33 （344pC/N）, Kp （0.684）, Qm （2350）,tan 3（0.0030） were obtained when lead content x=1.02.     

Novel wide band gap alloyed semiconductors, <Emphasis Type="Italic">x</Emphasis>(LiGaO<Subscript>2</Subscript>)<Subscript>1/2</Subscript>-(1−<Emphasis Type="Italic">x</Emphasis>)ZnO,and fabrication of their thin films

Oxide semiconductor alloys of x(LiGaO₂)_1/2-(1−x)ZnO were fabricated by the solid state reaction between β-LiGaO₂ and ZnO and rf-magnetron sputtering. For the solid state reaction, the wurtzite-type single phases were obtained in the composition range of x⩽0.38. The formation range of the alloys was wider than that of the (Mg_1−x Zn _x )O system, because the β-LiGaO₂ possesses a wurtzite-derived structure and approximately the same lattice constants with ZnO. The electrical resistivity and energy band gap of the 0.38(LiGaO₂)_1/2-0.62ZnO alloyed ceramic were 0.45 Ωcm and 3.7 eV, respectively, at room temperature. For the alloying by sputtering, the films consisting of the wurtzite-type single phase were obtained over the entire composition range of x(LiGaO₂)_1/2-(1−x)ZnO. The energy band gap was controllable in the range from 3.3 to 5.6 eV. For the as-deposited film fabricated using the 0.4(LiGaO₂)_1/2-0.6ZnO alloyed ceramic target, the energy band gap was 3.74 eV, and the electrical resistivity, carrier density and the Hall mobility at room temperature were 3.6 Ωcm, 3.4×10¹⁷ cm⁻³ and 5.6 cm² V⁻¹ s⁻¹, respectively.     

Microstructure refinement and magnetic properties enhancement of nanocrystalline Nd<Subscript>12.3</Subscript>Fe<Subscript>81.7</Subscript>B<Subscript>6.0</Subscript> ribbons by addition of Zr

Effects of Zr addition and annealing treatment on the formation, microstructure and magnetic properties of Nd_12.3Fe_81.7−x Zr _x B_6.0 (x=0−3.0) ribbons melt-spun and annealed have been systematically investigated by means of vibrating sample magnetometer (VSM), differential scanning calorimeter (DSC), X-ray diffraction (XRD), and high resolution scanning electron microscopy (HRSEM). Phase analysis reveals that Nd₂Fe₁₄B is single-phase material. It has been found that the intrinsic coercivity H _ci of the optimally processed Nd_12.3Fe_81.7−x Zr _x B_6.0 ribbons increases monotonically from 751.7 kA/m for x=0 to 1005.3 kA/m for x=3.0. The remanence polarization J _r and maximum energy product (BH)_max increase first with Zr addition, then slightly decrease with further increasing Zr content. Optimum magnetic properties with J _r=1.041 T, H _ci=887.5 kA/m and (BH)_max=175.2 kJ/m³ have been achieved for the ribbons with x=1.5. The significant improvement of magnetic properties originates from the finer grains of the ribbons by introducing Zr.     

Magnetism and Transport Properties of HfFe_6Ge_6-type Er_(1-x)Gd_xMn_6Ge_6(x=0.2-0.9) Compounds

Magnetic transitions and magnetotransport properties of polycrystalline Er_1−x Gd _x Mn₆Ge₆ (x=0.2−0.9) compounds were studied. The magnetic and resistivity properties were analyzed in an applied magnetic field up to 5 T. It is found that Er_1−x Gd _x Mn₆Ge₆ (x=0.2−0.9) compounds displays a transition from the antiferromagnetic state to the ferrimagnetic state for increasing Gd content. The Er_1−x Gd _x Mn₆Ge₆ with x=0.2 and 0.5 compounds order antiferromagnetically at 430 and 432 K, respectively. The Er_1−x Gd _x Mn₆Ge₆ with x=0.8 and 0.9 compounds order ferrimagnetically at 462 and 471 K, respectively. The Er_1−x Gd _x Mn₆Ge₆ compounds undergo the second transitions below 71 K. The magnetoresistance curves of the Er_0.1Gd_0.9Mn₆Ge₆ compound in a field of 5 T are presented and the magnetoresistance effects are related to the metamagnetic transitions.     

The Effect of Bi2O3 on the Structure and Microwave Dielectric Properties of Ba6-3xNd8＋2xTi18O54 System（x=2/3）

The structures and dielectric properties of Ba6-3xNd8＋2xTi18O54 system（x=2/3） doped with different contents of Bi2O3, whose final molecular formula is Ba6-3x（Nd1-yBiy）8＋2xTi18O54 were investigated. It is indicated that the dielectric constant increases greatly whereas Q value（f0=4 GHz） decreases with the increase of Bi2O3 content. However, the temperature coefficient could be controlled below 0±30×10^-6/℃ in the experiment. These phenomena are related to the appearance of a new phase, Bi4Ti3O12, which has high dielectric constant. Also, that Bi^3＋（0.13 nm） substitutes for Nd^3＋（0.099 5 nm） will increase the unit cell volume, which will lead to the enlargement of the octahedron B site occupied by Ti^4＋. So the spontaneous polarization of Ti^4＋ ions will be strengthened. Besides, Bi^3＋ will fill up some vacancies which Ba^2＋ or Nd^3＋ ions leave in two A1 sites and four A2 sites. More positive ions polarize, which also contributes to higher dielectric constant. The samples got with the optimium properties are sintered at 1 200 ℃ for 4 h, when y=0.25, ε≈110, Q≈5 400（f0=4 GHz）, TCC=-4.7×10^-6/℃; When y=0.3, ε≈120, Q≈5 000（f0=4 GHz）, TCC=-24×10^-6/℃.