SnO2(0.9)-Fe2O3(0.1)气敏材料的制备及气敏特性的研究

采用柠檬酸盐法制备SnO2(0.9)-Fe2O3(0.1)粉体材料.XRD结构分析表明,在750℃焙烧温度下制得的粉体材料中铁原子大部分进入SnO2晶格中,以SnO2(0.9)-Fe2O3(0.1)固溶体状态存在.采用750℃焙烧温度下制得的SnO2(0.9)-Fe2O3(0.1)固溶体为基体材料,制作旁热式气敏元件并考察其气敏特性.结果表明此类元件对乙醇、一氧化碳等还原性气体具有较高的灵敏度.同时元件长期稳定性良好,100天内元件阻值及灵敏度变化很小.     

Structural and morphological characterization of flux grown YTa7O19, Nd:YTa7O19, Nd:LaTa7O19 and NdTa7O19 crystals

YTa₇O₁₉ (YHT), Nd:YTa₇O₁₉ (Nd:YHT), Nd:LaTa₇O₁₉ (Nd:LHT) and NdTa₇O₁₉ (NHT) single crystals have been grown by spontaneous nucleation from high-temperature solutions using K₂Mo₃O₁₀-B₂O₃ as a flux and structurally characterized by X-ray diffraction techniques. The effect of the flux composition on the crystal morphology is discussed. The distribution of the Nd³⁺ ions in doped crystals has been investigated by electron microprobe analysis, evidencing non-uniform segregation coefficients. The Raman spectra of the investigated compounds are presented, and a reinterpretation of the fine structure present in the optical spectra is proposed in the light of the crystallographic information.     

Yttrium-doped effect on thermoelectric properties of La0.1Sr0.9TiO3 ceramics

Ceramic samples of La_0.1Y _x Sr_0.9–x TiO₃ with different yttrium concentration have been synthesized by conventional solid state reaction technique, and their thermoelectric properties have been investigated. X-ray diffraction characterization confirms that the main crystal structure is of perovskite, but with a small amount of second phase of Y₂Ti₂O₇ for samples with x = 0.05, 0.08, and 0.10. SEM images indicate all ceramic samples are dense and compact, and the largest grain size appears in sample with x = 0.03 and 0.05. Also the second phase can also be identified from the SEM images for x = 0.05, 0.08, and 0.10 samples. Electrical conductivity and Seebeck coefficient of samples have been measured in the temperature range between 300 and 1100 K. With increasing of yttrium concentration, electrical resistivity decreases, and reaches 0.8 mΩ cm for x = 0.10 sample at room temperature. The absolute Seebeck coefficients increase monotonically with increasing temperature in the whole temperature range. Sample with x = 0.03 exhibits the highest absolute Seebeck coefficient 219 μV K⁻¹ at 1059 K, as well as the maximum power factor 11 μW cm⁻¹ K⁻² at 624 K.     

La0.9Sr0.1Ga0.8Mg0.2O3-α的柠檬酸盐法制备和表征

采用柠檬酸盐法制备了La     

Synthesis of LiNi0.9Co0.1O2 cathode material for lithium secondary battery by a novel route

The cathode material, LiNi_0.9Co_0.1O₂ was prepared using a rheological phase reaction method with LiOH·H₂O, home-made Ni(OH)₂, and Co₂O₃ as starting materials. At first, the mixture of reactants and a proper amount of water reacted to form a rheological precursor. Then the dried precursor was heated at 730 °C in one step to yield the product. The effects of calcination time (between 0.5 and 10 h) on the structural, morphological and electrochemical properties were investigated. All obtained powders show a single phase with α-NaFeO₂ structure (R-3m space group). The sample prepared in 2.5 h delivers the largest initial discharge capacity of 218 mA h g^− 1 (3.0-4.35 V, 25 mA g^− 1) and still remains 192 mA h g^− 1 after 15 cycles. The method is simple, economical and effective and is promising for practical application.     

Detailed Physical Characterizations of Cu-rich and Ru-poor (Ru0.9Cu0.1)Sr2YCu2O7.9

The optimized nominal composition, (Ru_0.9Cu_0.1) Sr₂YCu₂O_7.9 sample, has been prepared through high-pressure and high-temperature solid-state densification method. The obtained material has been studied by X-ray (laboratory) diffraction powder technique, magnetization and detailed magneto-transport measurements. The title compound indicates bulk magneto-superconducting properties under field strengths of H=10, 100, 500 and 1000 Oe. It shows diamagnetic transition at T _d=54, 38, 20 and 8 K for H=10, 100, 500 and 1000 Oe, respectively, in the zero-field-cooled susceptibility measurements. The high-field (H=5 and 10 kOe) molar susceptibility measurements show sharp ferromagnetic transition at ∼150 K with reduced molar susceptibility values. The various field dependence of magnetization, M(H), isotherm curves recorded at constant temperatures (5, 10, 25, 50, 100 and 150 K) indicate ferromagnetic saturation, whereas the MH curves measured at 200 and 300 K conditions reveal the paramagnetic state of the compound. Though the sample showed onset transition temperature, T_c^onsetT_{\mathrm{c}}^{\mathrm{onset}}, at ∼34 K under different field strengths (H=0, 10, 30, 50, 70 and 90 kOe), no T_c^R=0T_{\mathrm{c}}^{R=0} is seen down to 2 K. Even under relatively low applied field (ΔH=10 kOe) the title compound shows large negative magnetoresistance (MR) of about 68% at 2 K and increases with increasing the field strength up to ΔH=90 kOe (MR=77% at 2 K). This value is amazing and probably higher than other 1212 type ruthenocuprates. The title compound which shows little negative MR (about 1%) in the high temperature regions (125–300 K) is not affected much by different field strengths. Among the different fixed temperature MR(H) isotherms, the MR(H) curve measured at 5 K shows maximum negative MR of about 47% at 90 kOe compared to other four (T=50, 100, 200 and 300 K) MR(H) curves.     

Upconversion and infrared luminescences in Er/Yb codoped Y2O3 and (Y0.9La0.1)2O3 transparent ceramics

Er³⁺ and Yb³⁺ codoped Y₂O₃ and (Y_0.9La_0.1)₂O₃ transparent ceramics were fabricated by the conventional ceramics processing with nanopowders. Compared to Er/Yb:Y₂O₃, Er/Yb:(Y_0.9La_0.1)₂O₃ ceramics had higher transmittance. Intense upconversion (UC) and infrared emission (1543 nm) were observed under excitation of 980 nm. According to three intensity parameters Ω₂, Ω₄, and Ω₆ fitted by the Judd-Ofelt theory, the spectroscopic quality parameters (X), radiative lifetimes (τ_rad), and emission cross-sections (α_em) were determined. Er/Yb:(Y_0.9La_0.1)₂O₃ ceramics owned broader peaks and longer lifetime (12.3 ms) at 1548 nm due to the glass-like structure of (Y_0.9La_0.1)₂O₃ ceramics. The results showed Y₂O₃ and Y_1.8La_0.2O₃ transparent ceramics are promising gain media for developing the solid-state 1.5 μm optical amplifiers and tunable UC lasers.     

Solid-state field-assisted silver diffusion in (TeO2)0.6(WO3)0.25(La2O3)0.05(Na2O)0.1 glass

Silver-doped layers have been produced in (TeO₂)_0.6(WO₃)_0.25(La₂O₃)_0.05(Na₂O)_0.1 (TWLN) glass by solid-state field-assisted diffusion. The silver concentration profile in the glass has been determined by secondary ion mass spectrometry (SIMS) and Rutherford backscattering spectrometry (RBS). The Matano-Boltzmann method applied to thermally activated diffusion indicates that the silver diffusion coefficient in the glass is a weak function of silver concentration. We carried out modeling of silver concentration profiles in the doped layer of the TWLN glass after solid-state field-assisted diffusion. Good agreement of the theoretical fit and experimental data suggests that the model chosen can be used to describe solid-state field-assisted diffusion of silver ions in TWLN glasses. Using RBS data, we have quantitatively estimated the surface density of silver atoms after field-assisted diffusion. Combining SIMS and RBS, we were able to assess the absolute silver concentration depth profile. Our results demonstrate that field-assisted diffusion, a simple and effective procedure for doping optical glasses, can be used to produce planar waveguide structures based on the tellurite glass studied here.     

热障涂层陶瓷层材料LnMgAl11O19(Ln=La,Nd)粉体的性能

用共沉淀法制备LaMgAl₁₁O₁₉粉体,证明了提高沉淀温度和pH值可使前驱粉体的性能明显提高。应用差热分析和X射线法研究了磁铅石相的生成温度和粉体的结晶度;使用Scherrer 公式并结合XRD谱计算了晶粒尺寸;用扫描电镜观察了各工艺参数的前驱粉体在1500℃时效5 h后的形貌;使用Malvern ZEN3600粒度仪和Manual measurement软件分析了粉体硬团聚的尺寸分布;用Nd₂O₃, Gd₂O₃, Sm₂O₃替代La₂O₃,研究了制备多种镁基六铝酸盐粉体的可行性。结果表明：在pH值为11.5、沉淀温度为60℃条件下制备的前驱粉体,其完全相变为纯LaMgAl₁₁O₁₉粉体的初始温度为1440℃,比在常温下沉淀的前驱粉体降低了150℃,磁铅石相的生成效率明显提高。在1500℃时效5 h的粉体其晶粒为纳米尺度。提高沉淀温度和pH值有利于减小晶粒尺寸和降低粉体的热导率。采用相同工艺参数可制备出纯NdMgAl₁₁O₁₉粉体,其晶粒尺寸略大于LaMgAl₁₁O₁₉粉体的尺寸。     

Microwave dielectric properties of LaMgAl11O19

The suitable choice of a substrate material is one of the aims to be fulfilled in high speed microwave technology. LaMgAl₁₁O₁₉ oxide ceramic material, which belongs to the magnetoplumbite family, has been reported earlier as a potential candidate for such applications. This material has been prepared by conventional solid-state ceramic route. The structure has been studied by X-ray diffraction and characterized at microwave frequencies. The effect of dopant and glass addition on the microwave dielectric properties of this material has also been investigated. LaMgAl₁₁O₁₉ has relatively low dielectric constant (ε_r=14), low dielectric loss or high quality factor (Q_u×f>28,000 GHz at 7 GHz) and small temperature variation of resonant frequency (τ_f=−12 ppm/°C) at room temperature (300 K). These properties make LaMgAl₁₁O₁₉ as a good substrate material and as a dielectric resonator to be used in microwave devices operating at relatively high frequencies.     

Effect of synthesis conditions on the nanopowder properties of Ce0.9Zr0.1O2

In this work, the synthesis of nanocrystalline Ce_0.9Zr_0.1O₂ powders via the gel-combustion method, using different fuels, and following either stoichiometric or non-stoichiometric pH-controlled routes is investigated. The objective is to evaluate the effect of synthesis conditions on the textural and morphological properties, and the crystal structure of the synthesized materials. The solids were characterized by nitrogen physisorption, Scanning Electron Microscopy (SEM), X-ray powder diffraction (XPD), and Carbon-Hydrogen-Nitrogen Elemental Analysis (CHN).All the powders exhibited nanometric crystallite size, fluorite-type structure and negligible carbon content. Synthesis conditions strongly affect the average crystallite size, the degree of agglomeration, the specific surface area and the pore volume. Our results indicate that, by controlling the synthesis conditions it is possible to obtain solids with custom-made morphological properties.     

Magnetic and transport properties of La0.3Ca0.7Mn0.9T0.1O3 (T = Cr, Fe, and W)

We have carried out structural, magnetic and magneto transport measurements of the electron-doped manganite La_0.3Ca_0.7MnO₃ substituted with 10% of Cr, Fe and W on the Mn site. The substitution by Cr, Fe and W suppresses the charge order transition present at 260 K in the parent compound. All the samples show a semiconducting behavior. Whereas the parent compound does not show any magneto resistance (MR) even in a field of 14 T, a maximum MR of 6% in 5 T at 25 K is observed for the Cr substituted sample that is attributed to a spin-cluster glass like states induced by Cr. The Fe and W substituted samples showed a MR of 1.5 and 3%, respectively which may be attributed to a smaller number of FM domains/spin-clusters and to an increase in anti-ferromagnetic interaction.     

Transmission electron microscopy study of multilayer p-n hetero-junction La0.9Sr0.1MnO3/SrNb0.05Ti0.95O3 thin films

We have fabricated multilayer p-n hetero-junction structure La_0.9Sr_0.1MnO₃/SrNb_0.05Ti_0.95O₃ colossal magneto-resistivity thin films. The observations of transmission electron microscopy showed that the interfacial structure between La_0.9Sr_0.1MnO₃ and SrNb_0.05Ti_0.95O₃ was of great epitaxy and atomic level smooth. There was a superstructure within La_0.9Sr_0.1MnO₃ thin films which was clarified in terms of the ordered partial substitution of La with Sr at center body of unit cell. Its chemical composition and distribution information investigated by electron energy loss spectrum and element mapping in the multilayer thin films were discussed.     

Thermomechanical processing and transport current density of Ag-sheathed (Tl,Cr)Sr2(Ca0.9,Pr0.1)Cu2O7 superconductor tapes

Powders with nominal composition (Tl,Cr_0.15)Sr₂(Ca_0.9,Pr_0.1)Cu₂O₇ (Tl-1212) and T_c90 K were used to fabricate Ag-sheathed superconducting tapes employing the powder-in-tube (PIT) method. The tapes were subjected to intermediate mechanical rolling or pressing. Conditions that enhance the transport critical current density (J_c) of the tapes were investigated. Optimum annealing temperature and period together with uniaxial pressing are necessary to increase J_c of the Tl-1212/Ag tapes. Annealing at 910 °C for 0.5–1 h enhanced the 1212 phase formation and improved intergranular connectivity between grains, as well as to provide healing for the fractured structure caused by deformation process. A relatively longer annealing time at higher temperature gave rise to secondary phases and resulted in the decrease of J_c. Mechanical uniaxial pressing greatly densified the tapes core and thus led to closer contact between grains. At liquid nitrogen temperature and zero field, J_c of the pressed tapes annealed at 910 °C for 1 h is 3060±127 A cm⁻². The initial drastic drop of J_c in low fields (<0.06 T) indicates the performance of the tapes is limited by weak links. No significant anisotropic transport properties were observed in applied magnetic field. This is due to the absence of texturing in the tapes as the grains are randomly oriented revealed through SEM micrographs.     

正极材料LiM0.9Ti0.1O2(M=Ni,Co)的合成及表征

利用溶胶-凝胶预处理固相方法合成了锂离子电池正极材料LiM0.9Ti0.1O2(M=Ni,Co),通过XRD对合成的材料进行结构分析,并将其组装成电池进行了电化学测试,对两种材料LiN0.9Ti0.1和LiCo0.9Ti0.1进行了比较.结果发现,LiCo0.9Ti0.1O2的结构和性能要好于LiNi0.9Ti0.1O2,根据实验结果对其原因进行了初步的分析.     

Enhancement of thermoelectric figure of merit by doping Dy in La0.1Sr0.9TiO3 ceramic

Ceramic samples of La_0.1Sr_0.9−xDy_xTiO₃ (x = 0.01, 0.03, 0.07, 0.10) have been prepared by the solid-state reaction method. Characterization from the powder X-ray diffraction indicates that their crystal structure changes from cubic to tetragonal phase. Their electrical and thermal transport properties are measured in the temperature range of 300-1100 K. n-Type thermoelectric is obtained with large Seebeck coefficient. The figure of merit is markedly improved, due to relatively lower electrical resistivity and thermal conductivity by Dy doping effect. A much lower electrical resistivity of 0.8 mΩ cm at room temperature is obtained in La_0.1Sr_0.8Dy_0.1TiO₃, and with a relatively lower thermal conductivity of 2.5 W/m K at 1075 K. The maximum figure of merit reaches ∼0.36 at 1045 K for La_0.1Sr_0.83Dy_0.07TiO₃, which is the largest value among n-type oxide thermoelectric ceramics.     

Mechanical and thermal properties of LaMgAl11O19

Lanthanum magnesium hexaaluminate (LaMgAl₁₁O₁₉) powders were synthesized successfully at 1300 °C for 4 h by solid-state reaction, and LaMgAl₁₁O₁₉ ceramic was prepared at 1700 °C for 6 h by pressureless sintering. Phase composition, microstructure, mechanical and thermophysical properties of LaMgAl₁₁O₁₉ ceramic were investigated. Results show that the flexural strength and fracture toughness of LaMgAl₁₁O₁₉ ceramic are 353.3 ± 12.5 MPa and 4.60 ± 0.46 MPa m^1/2. Young's Modulus and Poisson ratio is 295 GPa and 0.23, respectively. The linear thermal expansion coefficient of LaMgAl₁₁O₁₉ ceramic from 473 K to 1473 K is 9.17 × 10⁻⁶/K, and thermal conductivity at 1273 K is 2.55 W/m K.     

Synthesis and characterizations of Nd doped SrFe12O19 nanoparticles

This is the first report ever on Nd³⁺ doped M-type hexaferrite nanoparticles: SrNd_xFe_12−xO₁₉ (0 ≤ x ≤ 1) prepared by citrate precursor using the sol–gel technique followed by gel to crystallization. The influence of the Nd³⁺ substitution, Fe³⁺/Sr²⁺ molar ratio and the calcination temperature on the crystallization of ferrite phase have been examined using powder X-ray diffraction (XRD), scanning electron microscope (SEM), Fourier transform infrared spectroscopy (FTIR), inductance capacitance resistance meter bridge (LCR) and vibrating sample magnetometer (VSM). The structural analysis reveals that the Nd³⁺ ions rearrange themselves in the host lattice without disturbing the parent lattice and Fe³⁺/Sr²⁺ molar ratio less than 12 is more favorable to achieve single phase hexaferrite at calcination temperature 900 °C for 4 h. Mid-IR analysis confirms that Nd³⁺ occupies the octahedral site. Detailed studies of electrical properties of prepared materials have been investigated in the frequency range 100–1000 Hz at room temperature by LCR meter and two probe technique. The result shows that the electrical properties strongly depend upon the frequency of applied field and dopant concentration. The magnetic measurements showing a considerable improvement in coercivity with the substitution of Nd³⁺ on iron sites, while the unsubstituted hexaferrites have highest value of specific saturation magnetization.     

La2O3添加对MgAl2O4-CaAl4O7-CaAl12O19复合材料烧结行为的影响

为适应材料轻量化的发展需要,在1 400~1 600℃温度下开发了MgAl₂O₄-CaAl₄O₇-CaAl₁₂O₁₉（MA-CA₂-CA₆）复合材料,并考察了La₂O₃添加对该复合材料烧结行为、显微结构和力学性能的影响。结果表明,La₂O₃添加剂优先固溶到MA-CA₂-CA₆复合材料组成晶相CA₆中,促使CA₆相发生晶格畸变,有效抑制了CA₆晶粒沿基面的异常长大,其形貌由片状向等轴状趋势转变,促使MA-CA₂-CA₆复合材料制备过程中由于CA₆晶粒异常长大而导致的多孔网状显微结构得以有效消除,因此也极大地改善了Mg²⁺的扩散条件,在一定程度上间接促进了MA晶粒的发育,有效促进了MA-CA₂-CA₆复合材料的烧结。经1 200℃预烧、1 600℃保温2 h烧成后,当La₂O₃的添加量为4wt%时,MA-CA₂-CA₆复合材料试样的显气孔率由19.2%下降至6.1%,体积密度由2.78 g/cm³上升至3.18 g/cm³,制得了MA、CA₂、CA₆晶相呈现交织分布、显微结构致密、有利于其力学性能改善的La₂O₃/MA-CA₂-CA₆复合材料,经1 200℃预烧、-1 600℃保温2 h烧成后的4wt% La₂O₃添加试样,其冷态抗压强度由317 MPa增加到了501 MPa。     

Optical properties and laser performance of nearstoichiometric and non-stoichiometric Nd-doped LaMgAl11O19 single crystals

The optical properties and the laser performance of two kinds of LMA crystals are studied in detail. Up to four different Nd³⁺ sites are found and the multisite and disordered nature of the crystals and the resulting inhomogeneous broadening of the laser emission lines are explicitly taken into account to interpret the laser data.