用共沉淀-熔盐法和溶胶-凝胶法合成的 BaFe8(Ti0.5Mn0.5)4O19铁氧体纳米粒子

采用共沉淀-熔盐法和溶胶-凝胶法合成了BaFe8(Ti0.5Mn0.5)4O19铁氧体纳米粒子.借助XRD、TEM和VSM等分析手段研究了不同制备方法对铁氧体纳米粒子的粒径、形貌及磁性能的影响.结果表明,采用溶胶-凝胶法合成的BaFe8(Ti0.5Mn0.5)4O19纳米晶粒径比共沉淀-熔盐法的均匀,对于相同的焙烧温度,矫顽力比共沉淀-熔盐法的低得多.     

(La0.5Na0.5)xBa1-xFe12O19纳米铁氧体粉末的微波吸收特性

利用柠檬酸溶胶-凝胶自蔓延燃烧法合成掺杂稀土元素镧的M型六角铁氧体(La0.5Na0.5)xBa1-xFe12O19 (x=0.0,0.1,0.3,0.5)纳米粉末,铁氧体的晶型通过X射线衍射得到证实,研究了镧含量对铁氧体的复介电常数、复磁导率的影响.实验结果表明,添加适量的稀土镧能显著地改善铁氧体的吸波性能,掺杂量为x=0.3的样品微波性能最佳.     

FePO_4包覆的LiMn_(1.5)Ni_(0.5)O_4/Li_(3.9)Na_(0.1)Ti_5O_(12)全电池性能

分别采用溶胶凝胶法和高温固相法合成了Fe PO4包覆的Li Mn1.5Ni0.5O4正极材料和Li3.9Na0.1Ti5O12负极材料,并组装了Li Mn1.5Ni0.5O4/Li3.9Na0.1Ti5O12(LMNO/LNTO)全电池,采用充放电测试、循环伏安(CV)和电化学阻抗(EIS)研究了Fe PO4包覆对Li Mn1.5Ni0.5O4/Li4Ti5O12全电池电化学性能的影响。结果表明,Fe PO4的包覆抑制了Li Mn1.5Ni0.5O4高温合成时Mn3+的产生,有利于锂离子的可逆脱嵌。Fe PO4包覆的Li Mn1.5Ni0.5O4/Li3.9Na0.1Ti5O12(FP-LMNO/LNTO)比LMNO/LTO全电池具有更高的放电容量、循环性能、库仑效率和能量密度。FP-LMNO/LNTO全电池更适合作为动力锂离子电池。     

锂离子电池正极材料LiNi_(0.5)Mn_(0.5)O_2的研究进展

综述了Li Ni0.5Mn0.5O2的研究进展。对固相合成法、共沉淀法、溶胶-凝胶法、冷冻干燥法和离子交换法等制备方法进行了介绍;提出了目前Li Ni0.5Mn0.5O2正极材料存在的一些问题,同时对Li Ni0.5Mn0.5O2正极材料发展前景进行了展望。     

镍锌铁氧体／二氧化硅纳米复合材料的制备及表征

用溶胶-凝胶法制备了Ni0.5Zn0.5Fe2O4/SiO2纳米复合粉末，采用TG-DTA、XRD、TEM等测试手段分析了其结构和形貌，用矢量网络分析仪测量了其在2-18GHz频带上的电磁参数，结果表明，反应生成镍锌铁氧体和非晶态二氧化硅的复合材料，颗粒形貌为球形链状；Ni0.5Zn0.5Fe2O4/SiO2纳米复合中铁氧体的摩尔百分含量为20%，热处理温度为1000℃时磁损耗值较大，吸波性能较好。     

溶胶凝胶法制备锂离子电池正极材料LiNi_(1/3)Mn_(1/3)Co_(1/3)O_2的研究

综述了溶胶凝胶法制备锂离子电池三元正极材料Li Ni1/3Mn1/3Co1/3O2的研究,讨论了三元材料的结构特性,着重从添加有机络合剂、掺杂、包覆改性以及模板辅助等方面探讨对Li Ni1/3Mn1/3Co1/3O2材料电化学性能的影响,并分析三元材料目前存在的问题和未来应用的前景。     

FePO_4包覆改善LiNi_(0.5)Mn_(1.5)O_4正极材料高温循环性能

采用喷雾干燥法制备Li Ni0.5Mn1.5O4正极材料,通过沉淀法在Li Ni0.5Mn1.5O4正极材料表面包覆Fe PO4以改善Li Ni0.5Mn1.5O4材料的高温循环性能。制备了质量分数1%Fe PO4、3%Fe PO4、5%Fe PO4三种不同包覆比例的Li Ni0.5Mn1.5O4/Fe PO4材料,电化学测试结果显示质量分数1%Fe PO4包覆效果最好。X射线衍射光谱法(XRD)数据表明,Fe PO4表面包覆处理并没有影响Li Ni0.5Mn1.5O4的晶型,材料仍为尖晶石结构。电化学性能测试表明,质量分数1%Fe PO4包覆材料的高温下循环稳定性得到显著的提升,其充放电100次后比容量为120 m Ah/g,为初始比容量的96.7%,远高于未包覆材料的89.99%的容量保持率。扫描电子显微镜法(SEM)观察显示,质量分数1%Fe PO4包覆的材料中Li Ni0.5Mn1.5O4颗粒被Fe PO4均匀包覆。ICP数据表明,Fe PO4的包覆减少了Li Ni0.5Mn1.5O4材料在高温循环时锰元素和镍元素的溶解,从而提高材料的循环稳定性。     

TiO2包覆LiNi0.5Mn0.5O2的结构和电化学性能研究

通过溶胶-凝胶法在LiNi0.5Mn0.5O2表面包覆一层TiO2,采用X射线衍射(XRD),扫描电镜(SEM),恒电流充放电和电化学阻抗谱(EIS)对材料的结构、形貌及电化学性能进行了研究。实验结果表明,经过包覆后,有效地抑制了电解液对正极材料的侵蚀,包覆量为1.0%(质量分数)的放电容量略有提高,循环性能也得到明显改善。因此TiO2包覆是改善LiNi0.5Mn0.5O2材料的电化学性能的有效方法。     

LiNi_(0.5)Mn_(1.5)O_4在不同电解液中的电化学性能

利用溶胶凝胶法合成4.7 V高电压正极材料LiNi0.5Mn1.5O4,运用X射线衍射(XRD)和扫描电子显微镜(SEM)对其结构与形貌进行表征,并测试了其在1 mol/L LiPF6/(EC+DEC)、1 mol/L LiPF6/(EC+DEC+DMC)、1 mol/L LiPF6/(EC+EMC)三种电解液中的充放电性能。研究发现,不同成分的电解液显著影响LiNi0.5Mn1.5O4材料的电化学性能,其中在1 mol/L LiPF6/(EC+EMC)电解液中,材料具有相对好的循环性能,其最大放电比容量为92.4 mAh/g,50周循环后,比容量衰减为68.4 mAh/g,容量保持率为74%。循环伏安曲线(CV)结果表明,在4.7 V附近出现两对强氧化还原峰分别对应于Ni2+/Ni3+和Ni3+/Ni4+,在4.0 V出现的弱氧化还原峰则对应于Mn3+/Mn4+。相比于4.0 V低电压,在4.7 V高电压下LiNi0.5Mn1.5O4电极的SEI膜电阻增大而锂离子的脱嵌更容易进行。     

Mg掺杂对LiNi_(0.5)Mn_(0.5)O_2电化学性能的影响

通过溶胶-凝胶法合成正极材料LiNi0.5Mn0.5O2,为了提高材料LiNi0.5Mn0.5O2的高倍率放电性能,采用Mg进行掺杂。通过X射线衍射(XRD),扫描电镜(SEM),恒电流充放电对材料的结构和形貌及电化学性能进行了研究。结果表明少量Mg的掺杂未影响到LiNi0.5Mn0.5O2的晶体结构,但改善了其电化学性能,其中,当Mg的掺杂量为5%(摩尔分数)时,材料具有更好的电化学性能,4 C放电时,首次放电比容量达到118 m Ah/g,且循环性能良好。     

Na0.5K0.5NbO3 Film Microwave Varactors

Na_0.5K_0.5NbO₃ (NKN) and Pb(Zr_0.53Ti_0.47)O₃ (PZT) films have been grown by rf-magnetron sputtering and pulsed laser deposition techniques, correspondingly, on sapphire (Al₂O₃-0112, r-cut), quartz (Y+36°-cut) and YAlO₃ + 1% Nd (Nd:YAlO₃-001) single crystal substrates with Interdigital Capacitor (IDC) of Coplanar Waveguide (CPW) structure. Photolithography and metal lift-off technique was used for processing of the tunable microwave capacitor. Microwave network analyzer with G-S-G Picoprobe and probe station performed microwave measurement with external DC bias. NKN film interdigital capacitors on Nd:YAlO₃ show superior performance in the microwave range from 1 to 40 GHz. Within this range, the voltage tunability (40 V, 200 kV/cm) was about 29%, loss tangent ～ 0.13, K-factor from 152% @10 GHz to 46% @40 GHz, voltage independent C _p was about 230 fF, tan δ _p changes from 0.14 @10 GHz to 0.36 @40 GHz, real and imaginary part of interconnect impedance increases with frequency from 0.13 Ω @10 GHz to 0.50 Ω @40 GHz and from 1.9 Ω @10 GHz to 5.9 Ω @40 GHz respectively.     

Impedance spectroscopy studies of K0.5Bi0.5TiO3

Lead free Potassium bismuth Titanate K_0.5Bi_0.5TiO₃ (KBT) was prepared by high temperature solid state reaction method in a closed crucible with excess KBT powder around the samples. A room temperature study of XRD confirms, single phase formation with tetragonal structure .Grain and grain boundary conduction is observed from complex impedance spectrum at high temperatures (425°C) by the appearance of two semicircular arcs. The Cole-Cole plots of impedance spectrum consisted of a Circular arc followed by a semicircular spur indicate that the dielectric phenomenon of KBT is due to conductive grain boundaries. The temperature variation of grain resistance and grain boundary resistance is observed with the activation energies. The presence of non-Debye type multiple relaxations has been confirmed by complex modulus analysis. The dielectric data obtained from impedance measurements, indicates broad dielectric peaks around 380°C. The ferroelectric nature confirmed from hysteresis plot. The DC Conductivity results indicate activation energy 0.54 eV below 400°C and 0.85 eV above 400°C. The AC conductivity values and electric modulus values are computed from the impedance data. The activation energies of AC conductivity have observed to decrease with decrease in frequencies.     

Effect of La3+ substitution on microwave dielectric properties of (Pb0.5Ca0.5)(Fe0.5Nb0.5)O3 ceramics

Microwave dielectric properties of the [(Pb_0.5Ca_0.5)_1?x La_2x/3](Fe_0.5Nb_0.5)O₃ and [(Pb_0.5Ca_0.5)_1?x La _x ](Fe_0.5Nb_0.5)O₃ ceramics were investigated as a function of La³⁺ content $ {\left( {0.0 \leqslant \times \leqslant 0.2} \right)} $ . A single perovskite phase was detected in [(Pb_0.5Ca_0.5)_1?x La_2x/3](Fe_0.5Nb_0.5)O₃, while Pb₃Nb₄O₁₃ were detected as a secondary phase in [(Pb_0.5Ca_0.5)_1?x La _x ](Fe_0.5Nb_0.5)O₃ beyond x?=?0.05 due to the excess of unbalanced charge. The amount of Pb₃Nb₄O₁₃ was proportional to the unbalanced charge. Qf value of [(Pb_0.5Ca_0.5)_1?x La_2x/3](Fe_0.5Nb_0.5)O₃ decreased remarkably with La³⁺ substitution due to the increase of oxygen vacancy. For [(Pb_0.5Ca_0.5)_1?x La _x ](Fe_0.5Nb_0.5)O₃ ceramics, dielectric constant and Qf value increased with La³⁺ content up to x?=?0.03 due to an increase of density and grain size. Temperature coefficient of resonant frequency (TCF) was depended on B-site bond valence in single perovskite phase.     

层状结构LiMn0.5Ni0.5O2材料的合成及性能

廉价正极材料的研究开发及应用是目前锂离子电池进一步发展和推广应用的关键.采用高温固相合成LiMn0.5Ni0.5O2材料,用XRD对合成材料结构进行表征,并用恒电流法进行电化学性能测试,在此基础上对材料进行Al掺杂改性.实验结果表明,合成材料经微量掺杂后具有较好的电化学循环性能,可作为锂离子电池的替代正极材料。     

非计量比Mn_(1.25)Fe_xP_(0.5)Si_(0.5)系列化合物的结构及磁性

用机械合金化和固相烧结的方法制备了Mn_(1.25)Fe_xP_(0.5)Si_(0.5)(x=0.6,0.63,0.65,0.67,0.7,0.75)系列化合物,研究了其结构及磁性。结果表明,该系列化合物的主相均为Fe2P型六角结构,空间群为P-62m;并且随着Fe含量的增加,热滞先减小后增大,居里温度先升高后降低。当Fe的含量为0.65时,热滞最小为1 K,且居里温度最高275 K。当Fe含量为0.63时,化合物的磁熵变最大,在1.5 T的外磁场下的最大磁熵变为10.0 J/kg·K。     

0.5Li2MnO3-LiNi0.5Mn0.5O2的电化学行为及结构稳定性研究

对低温燃烧法合成的富锂锰基正极材料0.5Li2MnO3-LiNi0.5Mn0.5O2的充放电性能、充放电循环过程中Mn离子的价态变化、电化学阻抗变化以及正极材料的结构变化进行了系统的研究。研究结果表明,在开头的若干次充放电循环中,富锂锰基正极材料0.5Li2MnO3-LiNi0.5Mn0.5O2的放电比容量随循环次数的增加而增加,经过若干次循环后可以达到一个相当高的水平,其循环性能良好。以0.1 C在2.5～4.6 V之间充放电,放电比容量可达244 mAh/g,第50次循环,仍保有233 mAh/g。充放电过程中晶格中的Mn4+离子部分转变为Mn3+并参与电化学反应,这是造成放电比容量随循环次数增加而增加的原因,而显微结构和晶体结构保持稳定及电化学阻抗的降低是材料具有良好循环性能的原因。     

回火处理对0.5Li2MnO3-LiNi0.5Mn0.5O2性能的影响

以LiNO3、Ni(NO3)2·6H2O、Mn(NO3)2和尿素为原料,用低温燃烧法合成正极材料0.5Li2 MnO3-LiNi0.5Mn0.5O2,研究回火处理对产物结构、形貌和电化学性能的影响.回火处理提高了产物的结晶度和电化学性能.回火处理的最佳条件为:在850℃下回火20h.在此条件下合成的0.5Li2MnO3...     

LiNi_(0.5)Mn_(0.5)O_2正极材料的电化学性能研究

采用共沉淀法制备LiNi_(0.5)Mn_(0.5)O_2正极材料。并用X射线衍射(XRD),扫描电镜(SEM)对材料结构及形貌进行分析。讨论了不同保温时间对LiNi_(0.5)Mn_(0.5)O_2正极材料的影响,及不同电压下LiNi_(0.5)Mn_(0.5)O_2正极材料的电化学性能。结果表明,保温时间为16 h制备的正极材料电化学性能最优,在0.5 C倍率下,100次后容量保持率为99.02%;材料分别在2.75~4.2 V,2.75~4.3 V,2.75~4.35 V,2.75~4.4 V,2.75~4.5 V,2.75~4.6 V下进行充放电时,首次放电比容量分别135.6、143.6、154.1、165.5、177.9、184.1 m Ah/g。充放电电压越高,循环性能越差。     

Epitaxial Ba0.5Sr0.5TiO3 thin films for microwave phase shifters

Abstract

A tunable phase shifter was fabricated with epitaxial Ba_0.5Sr_0.5TiO₃ (BST) thin film and gold coplanar waveguide. BST thin film of the thickness ～0.5 μm was deposited by laser ablation on the MgO(OOl) single crystalline substrate. Gold electrode of the thickness ～2 μm was prepared by the sequence of thermal evaporation, electroplating, and wet etching. Epitaxial quality of the BST thin film was confirmed by X-ray diffraction. The microwave performance of phase shifter was measured at room temperature in the frequency range of 8–12 GHz, and with applied bias voltage of up to 30 V. Effect of Mn dopant in the epitaxial films was also considered.     

Dielectric characteristic of nanocrystalline Na0.5K0.5NbO3 ceramic green body

Dielectric spectroscopy was applied to porous nanocrystalline Na_0.5K_0.5NbO₃ (NKN) ceramic green body, wherein influences of percolation effect and water adsorption at pore surface of the ceramic green body on dielectric response were examined over wide temperature (150 to 450?K) and frequency (100?Hz to 1?MHz) ranges. Dielectric permittivity of the ceramic green body is about 2–3 orders of magnitude higher than that of pure NKN powder or NKN ceramic. Furthermore, the high dielectric permittivity and high humidity sensitivity of the ceramic green body can appear again with aging a period of time in air. The data from this investigation make potential applications for NKN as a giant dielectric material or a humidity sensing material.