亚锰酸盐La0.7-xYxCa0.3MnO3的电磁特性和磁电阻效应

研究了用固相反应法制备亚锰酸盐多晶样品La0.7-xYxCa0.3MnO3,并研究了Y的不同掺杂(x=0.1,0.2)对样品的晶体结构、电磁特性和磁电阻效应的影响.实验结果表明,随着温度的降低,x=0.1样品的R-T曲线没有出现峰值,而x=0.2样品出现了峰值,显示了复杂的输运特性.两种样品的磁电阻Rm都随着温度的降低而升高,但都没有出现峰值.x=0.2的样品在较宽的温区内,磁电阻效应都很显著,而且Y掺杂由x=0.1提高至x=0.2,磁电阻效应增强.     

亚锰酸盐La0.7—xYcCa0.3MnO3的电磁特性和磁电阻效应

研究了用固相反应法制备亚锰酸盐多晶样品La0.7-xYcCa0.3MnO3，并研究了Y的不同掺杂（x=0.1,0.2），对样品的晶体结构，电磁特性和磁电阻效应的影响。实验结果表明，随着温度的降低，X＝0．1样品的R－T曲线没有出现峰值，而x=0.2样品出现了峰值，显示了复杂的输运特性，而种样品的磁电阻Rm都随着温度的降低而升高，但都没有出现出值。X＝0．2的样品在较宽的温区内，磁电阻效应都很显著，而且Y掺杂由x=0.1提高至x=0.2，磁电阻效应增强。     

La位Y掺杂对亚锰酸盐La0.7 Sr0.3 MnO3低场磁电阻影响

针对钙钛矿亚锰酸盐在较低磁场下的磁电阻效应,采用固相反应法制备了亚锰酸盐多晶样品La_(0.7-x)Y_xSr_(0.3)MnO_3(x=0, 0.1, 0.2),测量了两个样品(x=0, 0.2)的X射线衍射谱及3个样品(x=0, 0.1, 0.2)在未加磁场和加0.25 T磁场的电阻-温度(R-T)曲线和磁电阻-温度(MR-T)曲线,分析了La位Y掺杂对样品低场磁电阻效应的影响。实验结果表明,样品La_(0.7)Sr_(0.3)MnO_3的晶体结构由立方结构向四方结构畸变,样品La_(0.5)Y_(0.2)Sr_(0.3)MnO_3为立方结构。随着La位Y掺杂量从x=0增加到x=0.2,晶格常数减小。在实验温区内,3个样品的R-T曲线没有出现金属-绝缘体转变峰,呈现出金属电阻温度特性。在相同的温度下,3个样品在加磁场时的电阻比未加磁场时的电阻要小,表现为负磁电阻。3个样品的MR-T曲线没有出现峰值温度T_P,磁电阻的大小随温度的降低而增加。在0.25 T磁场下,3个样品在实验温区都具有明显的低场磁电阻效应。为钙钛矿亚锰酸盐在磁电子学领域的应用研究提供了重要参考。     

亚锰酸盐La0.7-xCexCa0.3MnO3的磁电阻效应

用固相反应法制备亚锰酸盐La0.7-xCexCa0.3MnO3系列多晶样品(量分数x＝0,0.05,0.10,0.15,0.20),并在零磁场和0.3T磁场下研究了电阻和磁电阻与温度(77～300K)的关系.结果发现随x的增加,样品的巨磁电阻效应减弱,磁电阻峰有所扩宽,磁电阻峰值出现的温度比无掺杂相对提高了约14K.     

Mn位Cr掺杂对亚锰酸盐La0.7Ca0.3MnO3低场磁电阻影响

为了研究钙钛矿亚锰酸盐在较低磁场下的磁电阻效应,采用固相反应法制备了亚锰酸盐多晶样品La_(0. 7)Ca_(0. 3)Mn_(1-x)Cr_xO_3(x=0,0. 1),测量了两个样品在未加磁场和加0. 25 T磁场的电阻-温度曲线及磁电阻-温度曲线,分析了Mn位Cr掺杂对样品低场磁电阻效应的影响。实验结果表明,随着Cr掺杂量从x=0增加到x=0. 1,样品的金属-绝缘体转变温度逐渐向低温推移,磁电阻峰值温度由T_P≈220 K下降到T_P≈190 K。在0. 25 T磁场下,样品在液氮温区具有较明显的磁电阻效应。     

亚锰酸盐La0.7-xCexCa0.3MnO3的磁电阻效应

用固相反应法制备亚锰酸盐La0.7-xCexCa0.3MnO3系列多晶样品(量分数x＝0，0．05，0．10，0．15，0．20)，并在零磁场和0．3T磁场下研究了电阻和磁电阻与温度(77-300K)的关系．结果发现：随x的增加，样品的巨磁电阻效应减弱，磁电阻峰有所扩宽，磁电阻峰值出现的温度比无掺杂相对提高了约14K．     

Cu掺杂对 Fe/Si多层膜的层间耦合和负磁电阻效应的影响

研究了Cu掺杂对Fe/Si多层膜的层间耦合和负磁电阻效应的影响。在用磁控溅射方法制备的Fe/Si多层膜中,发现在Si的标称厚度tSi =1.9nm附近存在一较强的反铁磁耦合（AFM）峰和与之相对应的负磁电阻峰,在Si层中掺入6％的Cu后,发现反铁磁耦合峰的饱和场显著降低,峰宽变窄,峰位略向较厚方向移动。掺杂后磁电阻峰的宽和峰位变化与AFM峰相似,而磁电阻峰值则略有下降,在液氮温度T＝77K下,掺杂前后具有负磁电阻效应的多层膜样品阻率都降低,而磁电阻效应和饱和场均增大,实验结果表明,用磁控溅射方法制备的Fe/Si多层的层间耦合机制和磁电阻效应的机制与磁性金属／非磁金属多层膜的层间耦合及磁电阻效应的机制是一致的。     

中温固体电解质Ce_(0.8)Gd_(0.2-x)Y_xO_(2-δ)(x=0,0.05,0.10)的制备与性能研究

用溶胶-凝胶法合成了固体电解质Ce0.8Gd0.2-xYxO2-δ(x=0,0.05,0.10).用X射线衍射谱、拉曼光谱分析了样品的微观结构,用交流复阻抗谱研究了样品的电学性能.结果表明:800℃焙烧的所有样品均为具有氧缺位的单相立方萤石结构,晶胞参数随钇(Y)掺杂量增加而减小.钇掺杂量x=0.05的样品Ce0.8Gd0.15Y0.05O2-δ的电导率最高,导电活化能最小,(σ700℃=5.58×10-3S·cm-1,Eα=0.92 eV),高于未掺杂Y的Ce0.8Gd0.2O2-δ样品的电导率(σ700℃=5.38×10-3S·cm-1Eα=1.09 eV).说明适量双掺杂Y提高了Ce0.8Gd0.2-xYxO2-δ的电导率并且降低了其活化能.     

Sr离子含量的减少对于La0.60Sr0.25Na0.15Mn3材料性能的影响

利用溶胶-凝胶法(sol-gel)制备了稀土锰氧化物多晶样品La0.60Sr0.25-xNa0.15MnO3发现随着Sr离子含量的减少,样品在室温附近庞磁电阻效应有了明显的改善.在1.8 T的磁场下,对于x=0.05的样品,其CMR值在240～320 K的温区范围内均保持在5.3%(±0.2%),温度稳定性有显著改善.     

Sr离子含量的减少对于La0.60Sr0.25Na0.15MnO3材料性能的影响

利用溶胶-凝胶法（sol-gel）制备了稀土锰氧化物多晶样品La0.60Sr0.25-xNa0.15MnO3,发现随着Sr离子含量的减少,样品在室温附近庞磁电阻效应有了明显的改善。在1.8 T的磁场下,对于x=0.05的样品,其CMR值在240~320 K的温区范围内均保持在5.3%（±0.2%）,温度稳定性有显著改善。     

Ba3La2Ti2Ta2O15: A new microwave dielectric of A5B4O15-type cation-deficient perovskites

The synthesis, structure and properties of a new A5B4O15-type cation-deficient perovskite Ba3La2Ti2Ta2O15 were discribed. The compound was prepared by the conventional solid-state reaction route. The phase and structure of the ceramics were characterized by X-ray diffraction （XRD）, scanning electron microscopy （SEM）. The results reveal that the compound is successfully synthesized. The compound crystallizes in the trigonal system with unit cell parameter a=5.6730（2） A, c=11.6511（2） A, V=324.93（1） A^3 and Z=1. The microwave dielectric properties of the ceramic are studied using a network analyzer, and it shows a high dielectric constant of 45.1, a high quality factors with Q×fof21 029 GHz, and a positive τf of 5.3 ppm℃^-1.     

低介Ba(Al0.98Co0.02)2Si2O8-Ba5Si8O21基LTCC微波介质陶瓷的研究

采用传统固相反应法,按摩尔比合成0.7Ba(Al_0.98Co_0.02)₂Si₂O₈?0.3Ba₅Si₈O₂₁(BACS-BS)基陶瓷,分析Li₂O-B₂O₃(1wt%)(L-B)烧结助剂对其烧结特性、相组成和微波介电性能的影响,探讨0.7BACS-0.3BS+1wt%(L-B)陶瓷理论与实验介电常数(ε_r)的差异。结果表明:添加1wt%(L-B)烧结助剂能有效降低0.7BACS-0.3BS基陶瓷的烧结温度(950 ℃),但严重影响其微波介电性能;在950℃烧结的0.7Ba(Al_0.98Co_0.02)₂Si₂O₈-0.3Ba₅Si₈O₂₁+1wt%(Li₂O-B₂O₃)陶瓷具有较好的微波介电性能,其ε_r=7.56, Q×f=13 976 GHz, τ_f=?6.32 ppm/℃;0.7BACS-0.3BS+1wt%(L-B)复合陶瓷与Ag电极有很好的化学相容性,这为其在LTCC技术的应用奠定了良好的基础。     

Electrical conductivity of （Na3AlF6-40%K3AlF6）-AlF3-Al2O3 melts

The effects of contents of AlF3 and Al2O3, and temperature on electrical conductivity of （Na3AlF6-40%K3AlF6）- AlF3-Al2O3 were studied by continuously varying cell censtant （CVCC） technique. The results show that the conductivities of melts increase with the increase of temperature, but by different extents. Every increasing 10 ℃ results in an increase of 1.85 × 10^-2, 1.86× 10^-2, 1.89 × 10^-2 and 2.20 × 10^-2 S/cm in conductivity for the （Na3AlF6-40%K3AlF6）-AlF3 melts containing 0%, 20%, 24%, and 30% AlF3, respectively. An increase of every 10 ℃ in temperature results an increase about 1.89× 10^-2, 1.94 × 10^-2, 1.95 × 10^-2, 1.99× 10^-2 and 2.10× 10^-2 S/cm for （Na3AlF6-40%K3AlF6）-AlF3-Al2O3 melts containing 0%, 1%, 2%, 3% and 4% Al2O3, respectively. The activation energy of conductance was calculated based on Arrhenius equation. Every increasing 1% of AlF3 results in a decrease of 0.019 and 0.020 S/cm in conductivity for （Na3AlF6-40%K3AlF6）-AlF3 melts at 900 and 1 000 ℃, respectively. Every increase of 1% Al2O3 results in a decrease of 0.07 S/cm in conductivity for （Na3AlF6-40%K3AlF6）-AlF3-Al2O3 melts. The activation energy of conductance increases with the increase in content of AlF3 and Al2O3.     

Preparation and electrical-magnetic properties of Co0.6Cu0.16Ni0.24Fe2O4/MWCNTs composites

Co0.6Cu0.16Ni0.24Fe2O4/multi-walled carbon nanotube nanocomposites (CCNF/MWCNTs) were synthesized by solution filling method.The phase structure,thermal stability,morphology and electrical-magnetic properties of the samples were characterized by means of modern testing technology.The effect of iron concentration,filling time,sintering temperature on their electrical and magnetic performance was discussed.The results indicated that conductivity was related to the content of MWCNTs,while the magnetism correlated with the volume fraction of the filled CCNF in the composites.When the optimal condition satisfied the filling time of 18 h,ferric concentration of 0.25 mol L-1 and sintering temperature of 350°C,the prepared composite had the best magnetic loss performance,and its minimum reflection loss reached-22.47 dB on 9.76 GHz,the available bandwidth was beyond 2.0 GHz.Hence,the obtained composite can be used as advancing absorption and shielding material due to its favorable microwave absorbing property.     

Ca0.9Ce0.1Ti0.8Al0.2SiO5在水热作用下的化学稳定性

通过固相法合成掺铈榍石固溶体(Ca0.9 Ce0.1Ti0.8Al0.2SiO5),采用PCT粉末浸泡试验法,借助X射线衍射(XRD)、扫描电镜(SEM)、电感耦合等离子体发射光谱(ICP-OES)等分析测试手段,研究掺铈榍石固溶体在热液作用下的稳定性.实验结果表明,掺铈榍石固化体在不同条件下(温度150～ 200℃,0.476～1.554 MPa,pH值5～9),都具有良好的稳定性.随着浸泡时间的增加,各元素的归一化浸出率逐渐降低并保持在较低水平.     

Synthesis and characterization of Mg3(PO4)2-coated Li1.05Ni1/3Mn1/3Co1/3O2 cathode material for Li-ion battery

Mg₃(PO₄)₂-coated Li_1.05Ni_1/3Mn_1/3Co_1/3O₂ cathode materials were synthesized via co-precipitation method. The morphology, structure, electrochemical performance and thermal stability were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), cyclic voltammetry(CV), electrochemical impedance spectroscopy(EIS), charge/discharge cycling and differential scanning calorimeter (DSC). SEM analysis shows that Mg₃(PO₄)₂-coating changes the morphologies of their particles and increases the grains size. XRD and CV results show that Mg₃(PO₄)₂-coating powder is homogeneous and has better layered structure than the bare one. Mg₃(PO₄)₂-coating improved high rate discharge capacity and cycle-life performance. The reason why the cycling performance of Mg₃(PO₄)₂-coated sample at 55 °C was better than that of room temperature was the increasing of lithium-ion diffusion rate and charge transfer rate with temperature rising. Mg₃(PO₄)₂-coating improved the cathode thermal stability, and the result was consistent with thermal abuse tests using Li-ion cells: the Mg₃(PO₄)₂ coated Li_1.05Ni_1/3Mn_1/3Co_1/3O₂ cathode did not exhibit thermal runaway with smoke and explosion, in contrast to the cells containing the bare Li_1.05Ni_1/3Mn_1/3Co_1/3O₂. Funded by the National Natural Science Foundation of China (No. 20273047)     

Modification of LiCo1/3Ni1/3Mn1/3O2 cathode material by CeO2-coating

LiCo_1/3Ni_1/3Mn_1/3O₂ was coated by a layer of 1.0 wt% CeO₂ via sol-gel method. The bared and coated LiMn_1/3Co_1/3Ni_1/3O₂ was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), cyclic voltammogram (CV) and galvanotactic charge-discharge test. The results show that the coating layer has no effect on the crystal structure, only coating on the surface; the 1.0 wt% CeO₂-coated LiCo_1/3Ni_1/3Mn_1/3O₂ exhibits better discharge capacity and cycling performance than the bared LiCo_1/3Ni_1/3Mn_1/3O₂. The discharge capacity of 1.0 wt% CeO₂-coated cathode is 182.5 mAh·g⁻¹ at a current density of 20 mA·g⁻¹, in contrast to 165.8 mAh·g⁻¹of the bared sample. The discharge capacity retention of 1.0 wt% CeO₂-coated sample after 12 cycles reaches 93.2%, in comparison with 86.6% of the bared sample. CV results show that the CeO₂ coating could suppress phase transitions and prevent the surface of cathode material from direct contact with the electrolyte, thus enhance the electrochemical performance of the coated material.     

Electrolysis expansion performance of semigraphitic cathode in [K3AlF6/Na3AlF6]-AlF3-Al2O3 bath system

The electrolysis expansion of semigraphitic cathode in [K₃AlF₆/Na₃AlF₆]-AlF₃-Al₂O₃ bath system was tested by self-made modified Rapoport apparatus. A mathematical model was introduced to discuss the effects of α _CR (cryolite ratio) and β _KR (elpasolite content divided by the total amount of elpasolite and sodium cryolite) on performance of cathode electrolysis expansion. The results show that K and Na (potassium and sodium) penetrate into the cathode together and have an obvious influence on the performance of cathode electrolysis expansion. The electrolysis expansion and K/Na penetration rate increase with the increase of α _CR. When α _CR=1.9 and β _KR=0.5, the electrolysis expansion is the highest, which is 3.95%; and when α _CR=1.4 and β _KR=0.1, the electrolysis expansion is the lowest, which is 1.28%. But the effect of β _KR is correlative with α _CR. When α _CR=1.6 and 1.9, with the increase of β _KR, the electrolysis expansion and K/Na penetration rate increase. However, when α _CR=1.4, the electrolysis expansion and K/Na penetration rate firstly increase and then decrease with the increase of β _KR. Foundation item: Project (2005CB623703) supported by the Major State Basic Research and Development Program of China; Project (2008AA030502) supported by the National High-Tech Research and Development Program of China     

Characteristics of LiCoO2, LiMn2O4 and LiNi0.45Co0.1Mn0.45O2 as cathodes of lithium ion batteries

LiNi_0.45Co_0.10Mn_0.45O₂ was synthesized from Li₂CO₃ and a triple oxide of nickel, cobalt and manganese at 950 °C in air. The structures and characteristics of LiNi_0.45Co_0.10Mn_0.45O₂, LiCoO₂ and LiMn₂O₄ were investigated by XRD, SEM and electrochemical measurements. The results show that LiNi_0.45Co_0.10Mn_0.45O₂ has a layered structure with hexagonal lattice. The commercial LiCoO₂ has sphere-like appearance and smooth surfaces, while the LiMn₂O₄ and LiNi_0.45Co_0.10Mn_0.45O₂ consist of cornered and uneven particles. LiNi_0.45Co_0.10Mn_0.45O₂ has a large discharge capacity of 140.9 mA · h/g in practical lithium ion battery, which is 33.4% and 2.8% above that of LiMn₂O₄ and LiCoO₂, respectively. LiCoO₂ and LiMn₂O₄ have higher discharge voltage and better rate-capability than LiNi_0.45Co_0.10Mn_0.45O₂. All the three cathodes have excellent cycling performance with capacity retention of above 89.3% at the 250th cycle. Batteries with LiMn₂O₄ or LiNi_0.45Co_0.10Mn_0.45O₂ cathodes show better safety performance under abusive conditions than those with LiCoO₂ cathodes. Foundation item: Project(50302016) supported by the National Natural Science Foundation of China; Project(2005037698) supported by the Postdoctoral Science Foundation of China     

Molar heat capacities of La2Mo2O9 and La1.9Sr0.1MO209-δ

The molar heat capacities of La2Mo209 and La1.9Sr0.1MO209-δ were obtained using the differential scanning calorimetry （DSC） technique in a temperature range from 298 to 1473 K. The DSC curve of La2Mo209 showed an endothermal peak around 834 K corresponding to a first-order monoclinic-cubic phase transition, and the enthalpy change accompanying this phase transition is 5.99 kJ/mol. No evident endothermal peak existed in the DSC curve of La1.9Sr0.1MO209-δ, but a broad thermal anomaly existed in its heat capacity curve at around 832 K. In addition, the heat capacity values of La2Mo209 and La1.9Sr0.1MO209-δ began to decrease at 1196 and 1330 K, respectively. The non-transitional heat capacity values of La2Mo209 and La1.9Sr0.1MO209-δ were formulated using multiple regression analysis in two temperature ranges.