Li_xCoO_2(0≤x≤1)结构稳定性和力学性质的第一性原理计算

采用基于密度泛函的第一性原理,从电子层次计算研究了锂离子电池正极材料Li_xCoO_2(0≤x≤1)的晶体结构、电子结构和力学性质。结果表明:Li_xCoO_2在脱锂过程中晶体结构会发生转变,当x=0.5时由六方结构R ■ m晶型转变为单斜结构P2/m晶型,当完全脱锂(x=0)时又转变为六方结构P ■ m1晶型。随着Li原子的脱出,Li_xCoO_2导带被部分填充,价带被完全填充,金属性质和电子导电性增强,并出现自旋极化。Li_xCoO_2中Co—O键为含有部分离子性特征的共价键,随着Li原子的脱出,Co—O键的离子性特征减弱,共价性特征增强。随着Li原子的脱出,Li_xCoO_2的体积模量(B)、剪切模量(G)和弹性模量(E)均呈现逐渐减小的趋势,而Poisson比和各向异性指数逐渐增大。G/B值变化趋势表明,LiCoO_2呈脆性,脱锂过程中向韧性转变。     

(ZrO2)n(1≤n≤5)团簇的结构及其光谱特征

应用密度泛函理论方法计算了各种可能的(ZrO2)n(1≤n≤5)团簇结构,同时模拟了对应团簇结构的红外光谱.氧化锆团簇中,锆氧原子间最大程度的交互连接是最稳定的结构.团簇的红外光谱表明:600～700 cm-1附近的峰对应着氧化锆团簇的Zr-O-Zr-O四元环振动,800 cm-1附近的峰对应着氧化锆团簇的Zr-O-Zr-O-Zr-O六元环振动,大于900 cm-1的峰对应着氧化锆团簇的自由氧原子的Zr-O振动.实验分析与理论计算结果表明:500 cm-1附近较强的特征振动峰对应着四方氧化锆的特征振动.     

Influence of TiO2 doping on thermo-optical properties of pyrochlore Sm2(Zr1–xTix)2O7 (0≤x≤0.15) ceramics

Sm₂(Zr_1–xTi_x)₂O₇ (0≤x≤0.15) ceramics have been fabricated by pressureless-sintering method at 1973 K for 10 h in air. The influence of TiO₂ doping on microstructure and thermo-optical properties of Sm₂(Zr_1–xTi_x)₂O₇ ceramics is investigated by X-ray diffraction, scanning electron microscopy and Fourier transform infrared spectroscopy measurements. The partial substitution of Ti⁴⁺ for Zr⁴⁺ results in a significant increase in emissivity at low wavelengths contrasted with undoped Sm₂Zr₂O₇. Sm₂(Zr_0.85Ti_0.15)₂O₇ ceramic exhibits a high emissivity of above 0.70 at 1073 K in a wavelength range of 3–16 µm, where the highest value at this temperature is more than 0.90 especially in the wavelength range of 9–14 µm. FT-IR spectra and optical absorption spectra unveil the mechanisms of enhanced emissivity in Sm₂(Zr_1–xTi_x)₂O₇ (0.05≤x≤0.15) ceramics in the intermediate infrared range, especially at the wavelengths of 3–8 µm, due to Ti⁴⁺ ion substitution for Zr⁴⁺ ion.     

Sintering behavior,phase evolution and microwave dielectric properties of thermally stable Li2O-3MgO-mTiO2 ceramics (1≤m≤6)

Li₂O-3MgO-mTiO₂ (1≤m≤6) ceramics were prepared by the solid state reaction method. X-ray diffraction, energy dispersive spectrometer and scanning electron microscopy techniques were used to investigate the phase composition and crystal structure. With increasing m values, the phase structures of ceramics changed as: (Li₂Mg₃TiO₆, m=1)→(Li₂Mg₃Ti₄O₁₂ and Mg₂TiO₄, m=2,3)→(Li₂Mg₃Ti₄O₁₂, m=4)→(Li₂Mg₃Ti₄O₁₂, MgTiO₃ and Li₂MgTi₃O₈, m=5)→(Li₂Mg₃Ti₄O₁₂, MgTiO₃, Li₂MgTi₃O₈ and MgTi₂O₅, m=6). The optimized sintering temperature was lowered from 1275 °C to 1050 °C. When m=5, Li₂O-3MgO-5TiO₂ ceramics showed good microwave dielectric properties at a wide sintering temperature range of 1000–1200 °C, and the best microwave dielectric properties of Q×f=71,726 GHz, ε_r=21.9 and τ_f=−20.9 ppm/°C were obtained at a relatively low sintering temperature of 1050 °C.     

Electrochemical performance of NixCo1-xMoO4 (0 ≤ x ≤ 1) nanowire anodes for lithium-ion batteries

Ni _x Co_1-x MoO₄ (0 ≤ x ≤ 1) nanowire electrodes for lithium-ion rechargeable batteries have been synthesized via a hydrothermal method, followed by thermal post-annealing at 500°C for 2 h. The chemical composition of the nanowires was varied, and their morphological features and crystalline structures were characterized using field-emission scanning electron microscopy and X-ray powder diffraction. The reversible capacity of NiMoO₄ and Ni_0.75Co_0.25MoO₄ nanowire electrodes was larger (≈520 mA h/g after 20 cycles at a rate of 196 mA/g) than that of the other nanowires. This enhanced electrochemical performance of Ni _x Co_1-x MoO₄ nanowires with high Ni content was ascribed to their larger surface area and efficient electron transport path facilitated by their one-dimensional nanostructure.     

Studies on NO2 gas sensing properties of sprayed Co1−xMnxFe2O4 (0≤x≤0.5) spinel ferrite thin films

The Co_1−xMn_xFe₂O₄ (0≤x≤0.5) spinel ferrite thin films were deposited on quartz substrates by chemical spray pyrolysis technique. The effect of Mn substitution on to the structural, electrical, dielectric and NO₂ gas sensing properties of cobalt ferrite thin films was studied. The X-ray diffraction analysis reveals that deposited films exhibit spinel cubic crystal structure. The lattice constant increases with the increase in Mn²⁺ content. The decrease in resistivity with increase in temperature suggests that the films have a semiconducting nature. The room temperature dielectric properties such as dielectric constant (ε′), loss tangent (tanδ), dielectric loss (ε′′) and AC conductivity have been studied in the frequency range 20 Hz–1 MHz. The film shows the highest sensor response at moderately low (150 °C) operating temperature. The effect of operating temperature, gas concentration, film selectivity and substitution of Mn on to gas response is carefully studied. The manganese substituted cobalt ferrite films are extremely selective towards NO₂ with a 20 times gas response compared with other gases. The gas response achieved nearly 92% of its initial value after 150 days, indicating good stability of the films.     

Depolarization temperature and piezoelectric properties of (Bi1/2Na1/2)TiO3–(Bi1/2Li1/2)TiO3–(Bi1/2K1/2)TiO3 lead-free piezoelectric ceramics

The phase transition temperature and piezoelectric properties of x(Bi_1/2Na_1/2)TiO₃–y(Bi_1/2Li_1/2)TiO₃–z(Bi_1/2K_1/2)TiO₃ [x + y + z = 1] (abbreviated as BNLKT100y–100z) ceramics were investigated. BNLKT100y–100z ceramics were prepared by conventional ceramic fabrication. The depolarization temperature T_d was determined by the temperature dependence of the dielectric and piezoelectric properties. This study focuses on the effect of Li¹⁺ and K¹⁺ ions on T_d and the piezoelectric properties of BNT ceramics. BNLKT100y–100z (y = 0–0.08) has a morphotropic phase boundary (MPB) between rhombohedral and tetragonal phases at z = 0.18–0.20, and high piezoelectric properties were obtained at the MPB composition. The piezoelectric constant d₃₃ increased with increasing y; however, T_d decreased above y = 0.06. The d₃₃ and T_d values of BNLKT4-20 and BNLKT8-20 were 176 pC/N and 171 °C, and 190 pC/N and 115 °C, respectively.     

低温燃烧合成制备NixZn1-xFe2O4(O.3≤x≤0.8) 铁氧体粉末与特性

本报告以低温燃烧法合成NixZn1-xFe2O4铁氧体粉末,整个燃烧合成在低温下进行.所得铁氧体粉末以X光粉末绕射法进行结构分析,并以穿透式电子显微镜进行粉末颗粒大小与形状之鉴定,再以振动样品测磁仪进行磁性质之量测.实验结果显示以低温燃烧合成法所制备之NixZn1-xFe2O4铁氧体粉末为立方晶结构,但在x=0.3～0.4之间时有γ-Fe2O3相出现,而在x=0.7～0.8之间有Ni结晶出现.磁性质方面,在x=0.4时饱和磁化量最高达81.2 emu/g,矫顽磁力达117.02 Oe.而在x=0.7时可得最大矫顽磁力142.5 Oe,此时饱和磁化量约为56 emu/g.以穿透式电子显微镜分析铁氧体颗粒大小约在10～30 nm之间,显示此方法可快速并且在低温下合成NixZn1-xFe2O4铁氧体粉末.     

6 1/2井眼下4 1/2套管固井技术及应用

6?井眼下4?套管井的固井是一个新领域,给固井工艺提出了一些问题。为了解决问题,对固井难点进行分析,对低密度水泥浆体系、防漏压稳工艺、提高顶替效率等方面进行研究,形成了一套6?井眼下4?套管的固井技术,投入现场应用后,固井质量良好。     

Thermoelectric properties of copper-deficient Cu2-xSe (0.05 ≤ x ≤ 0.25) binary compounds

Recently, many novel superionic thermoelectric materials have been discovered along the concept of “phonon-liquid electron-crystal” (PLEC). Among them, Cu_2-xSe-based liquid-like materials are typical examples. In this study, a series of copper-deficient Cu_2-xSe (0.05 ≤ x ≤ 0.25) materials were synthesized and used to study the role of Cu vacancies on the electrical and thermal transport properties. The X-ray photoelectron spectroscopy (XPS) measurements suggest that the valence states of Cu and Se are independent on the Cu/Se atomic ratio. With increasing the content of Cu vacancies, the hole concentration is monotonously increased, leading to the improved electrical conductivity and reduced Seebeck coefficient. Based on the single parabolic band model analysis, it is found that changing the content of Cu vacancies does not obviously modify the material's electronic band structure and effective mass. Due to the presence of highly mobile Cu ions inside the crystal structure, the lattice thermal conductivities of all Cu_2-xSe (0.05 ≤ x ≤ 0.25) materials are very low with values around 0.39 W m⁻¹ K⁻¹ at 500 K. Because of the significantly reduced Seebeck coefficient and increased electronic thermal conductivity, the thermoelectric figure of merit zTs are decreased when increasing x from 0.05 to 0.25. At 750 K, a maximum zT of 0.46 is obtained in Cu_1.95Se among all Cu_2-xSe (0.05 ≤ x ≤ 0.25) materials.     

Ca3–xMgxYb2Ge3O12(0≤x≤3)石榴石的A位Rattling效应与微波介电性能

微波介质陶瓷是5G/6G通讯技术的关键基础材料，具有高品质因数(Q×f)、低介电常数(ε_r)以及近零谐振频率温度系数(τ_f)的材料已逐渐成为研究与开发的重点。通过固相反应法制备了系列Ca_3–xMg_xYb₂Ge₃O₁₂ (0≤x≤3)石榴石陶瓷。当0≤x≤2时，样品为正石榴石结构，相对介电常数ε_r逐渐从10.3增加至11.8，品质因数Q×f值逐渐从98 000 GHz降低到78 000 GHz，谐振频率温度系数τ_f在(-40～-56)×10^–6/℃之间波动。当22+进入A位，ε_r迅速增大(～13.5),Q×f值显著降低(～19 800 GHz)，τ_f值则从负急剧转变为正(+70.5×10^–6/℃)，可归之于A位Mg²⁺的Rattling效应以...     

Design and characterization of novel manganite perovskites Ba1-xBixTi1-xMnxO3 (0≤x≤0.2)

Polycrystalline manganite powders of Ba_1-xBi_xTi_1-xMn_xO₃ (x = 0, x = 0.1 and x = 0.2) were synthesized by the conventional solid-state reaction process. Their crystal structure, morphological, optical, dielectric and electrical properties were investigated. X-ray diffraction of the prepared samples was made at room temperature and confirmed the formation of a perovskite phase. Structural refinement, using the Rietveld method, revealed a tetragonal P4mm phase of pure BTO and a tetragonal P4/mmm phase with the presence of vacancies for both doped samples (x = 0.1 and x = 0.2). Scanning electron microscopy indicated that the perovskite samples had a grain size smaller than 1 μm. From UV–vis–NIR spectra, we found that the band gap reduces from 3.29 eV to 1.48 eV with the increase of Bi and Mn amounts, resulting in a shift of the absorption wavelength region toward the visible range. Dielectric analysis was conducted in a wide range of temperatures at different frequencies. Phase transitions were identified from thermal dielectric results, showing that the samples exhibited a non-relaxor behavior. The structural transformation from tetragonal to cubic structure corresponding to the transition from ferroelectric phase to paraelectric phase was observed in the dielectric properties investigation. The complex impedance spectroscopy indicated the presence of grain and grain boundary effects in the conduction mechanism. Electrical analysis showed that doping with Bi and Mn enhanced the DC conductivity. Furthermore, the DC conductivity temperature dependence confirmed that the studied samples present a semiconductor behavior. The activation energies of grain and grain boundaries depended on the amount of incorporated Bi and Mn. The activation energy of grain varied between 0.54 and 0.87 eV suggesting that the DC electrical conductivity is governed by ionized oxygen vacancies. The activation energy of grain boundaries varied between 0.85 and 0.58 eV.     

厚壁容器1 1/4Cr-1/2Mo钢的焊接

本文简要地介绍了SA387Gr11C12钢焊接工艺试验,通过两种焊接方法的比较,说明双丝窄间隙自动焊是厚壁容器的最佳工艺。     

Bi1/2Na1/2TiO3无铅压电陶瓷的研究进展

近年来,随着环境保护和人类社会可持续发展的需求,作为环境友好的铁电压电陶瓷典型代表的Bi1／2Na1／2TiO3(BNT)基无铅压电陶瓷,已成为世界发达国家致力研发的热点材料之一。本文结合目前有关BNT基无铅压电陶瓷的报道,探讨了BNT压电瓷的压电机理及其相变过程,着重介绍了BNT压电陶瓷制备工艺以及改性研究和目前的应用,并对BNT基无铅压电陶瓷未来的发展趋势作了展望。     

锂离子电池正极材料LiNi1/2Co1/6Mn1/3O2的制备与性能

采用Co2+浓度递增的金属离子混合溶液分次共沉淀方法制备Ni1/2Co1/6Mn1/3(OH)2,以其为前驱体,通过高温固相反应得到具有Co含量梯度的层状LiNi1/2Co1/6Mn1/3O2,探讨了焙烧温度及Co含量梯度对材料的结构和电化学性能的影响. 通过X射线衍射、扫描电镜、热重分析及恒电流充放电测试对合成的样品进行了表征. 结果表明,700℃合成产物即具有类LiNiO2的六方层状结构,800和850℃合成产物阳离子排列有序度高,层状结构显著. 材料结晶度好,粒度均匀,粒径在亚微米级. 合成温度800℃的梯度材料具有最佳的电化学性能, 2.5~4.2 V, 0.1 C倍率充放电50次后,梯度材料的容量仍保持在171.2 mA×h/g. 相同的焙烧温度,梯度材料比均匀材料的电化学性能更加优异.     

Li[Ni1/2Mn1/2]O2的制备及电化学性能研究

介绍了一种采用前驱体碳酸盐共沉淀法制备锂离子电池正极材料Li[Ni1/2Mn1/2]O2的工艺路线。通过对样品进行X射线衍射(XRD)测试,可知产品具有类似钴酸锂的层状结构。通过对产品进行扫描电镜(SEM)观察可以看出,产品具有规则的球形形貌,且粒径在5~10μm;电化学测试表明,材料的首次放电比容量大于170 mA.h/g,循环20次后容量保持率大于98%。     

0.7Li2MnO3-0.3LiNi1/2Mn1/2O2的共沉淀制备及电化学性能

本文通过共沉淀法合成了0.7Li2MnO3-0.3LiNi1/2Mn1/2O2这种正极材料,并对这种材料的结构、相组成和微观形貌进行了表征,并且进行了电化学性能测试。结果表明这种电极材料在循环测试中比容量能达到100mAh.g-1,后续循环稳定性较好。     

Li1-xTixFePO4(O≤x≤0.02)制备表征及电化学性能研究

采用固相工艺制备了具有锂位掺杂的磷酸铁锂正极材料Li1-xTixFePO4(0≤x≤0.02),并将该材料与相同条件下制备的LiFePO4/C材料进行晶体结构、表面形貌、容量性能以及倍率性能比较.通过比较发现,Li1-xTixFePO4和LiFePOJC均具有橄榄石结构,且粒径大小均在2～4 μn.电化学性能测试结果表明,Li1-xTixFePO4比LiFePO4/C具有更加优异的容量性能和倍率性能.     

La(Mg1/2Ti1/2)O3–La2/3TiO3 microwave dielectric ceramics

Structure and microwave dielectric properties were studied in the (1−x)La(Mg_1/2Ti_1/2)O₃–xLa_2/3TiO₃ system. Ceramics with this composition in the 0⩽x⩽0.5 range were processed from powders obtained by a citrate-based chemical route. Structure of these perovskite solid solutions changed from orthorhombic for x=0.1 and 0.3 to pseudocubic for x=0.5. Microwave and radio frequency measurements revealed increase in permittivity and temperature coefficient of the resonant frequency τ_f with increasing of La_2/3TiO₃ content. Close to zero τ_f value was found near to x=0.5 composition of (1−x)La(Mg_1/2Ti_1/2)O₃–x La_2/3TiO₃.