MSnO3(M=Ca,Sr,Ba)的溶胶-凝胶法合成及性能

采用溶胶-凝胶法制备了钙钛矿结构的MSnO3(M=Ca,Sr,Ba)晶体.将其作为锂离子电池负极材料的活性物质,利用恒电流电池测试仪研究其电化学性能.结果表明CaSnO3、SrSnO3和BaSnO3的首次放电容量分别为894.3 mAh/g、703.8 mAh/g和673.6 mAh/g,首次充电容量分别为418.3 mAh/g、257.8 mAh/g和224.8 mAh/g,不可逆容量损失分别达53.2%、63.3%和66.6%.     

氧电极催化剂La0.6Ca0.4CoO3的合成及性能

用溶胶.凝胶法合成了氧电极催化剂La0.6Ca0.4CoO3,通过热重(TG)分析确定了干凝胶的焙烧温度.利用X射线衍射、电化学测试等研究了pH值、柠檬酸用量对催化剂性能的影响.制备La0.6Cao.4C003的最佳工艺条件是:pH=3.0,n(柠檬酸):n(M)=2:1(M为总金属离子).焙烧条件为:700 ℃,2 h.     

溶胶-凝胶法SrInxTi1-xO3薄膜的制备及表征

以Sr(OOCCH3)2·H2O,In(NO3)3·41/2H2O及Ti(OC4H9)4为原料,用溶胶-凝胶工艺制备了SrInx-Ti1-xO3(SITO)薄膜.SITO凝胶薄膜经过575~725℃/60 min退火形成立方钙钛矿结构.用XRD、SEM对薄膜结构和形貌表征.霍尔测定表明In-STO薄膜属于空穴导电的p-...     

溶胶-凝胶法制备纳米LaMnO_3的电催化活性

采用表面活性剂聚乙二醇-2000辅助溶胶-凝胶法,制备锌-空气电池催化剂锰酸镧(LaMnO_3)。通过热重-差示扫描量热(TG-DSC)法、XRD、傅里叶变换红外光谱(FTIR)、透射电子显微镜(TEM)和极化曲线,研究催化剂LaMnO_3的结构和电催化活性。较优的制备工艺为:初始pH值为6.5,表面活性剂与金属离子物质的量比为0.018∶1.000,在700℃下煅烧3 h。制备的LaMnO_3为钙钛矿结构,晶体成型温度在450℃左右、晶粒尺寸处于纳米级别,具有良好的氧还原电催化活性。以LaMnO_3为催化剂的电极在电位为-600 mV(vs.Hg/HgO)时的输出电流密度为0.165 A/cm~2。     

溶胶-凝胶法制备的Li_(1.15)V_3O_8的电化学性能

以Li2CO3和NH4VO3为原料,分别采用柠檬酸和酒石酸为螯合剂,通过溶胶-凝胶法制备了正极材料Li1.15V3O8。用红外光谱、TG-DTG、XRD和SEM等方法对前驱体和产物进行分析,并进行了电化学性能测试。用酒石酸制备的Li1.15V3O8,首次放电比容量比用柠檬酸制备的高,且循环性能较好,以0.14 mA在1.8～3.9 V充放电的首次放电比容量为190.17 mAh/g,在第32次和第47次循环时达到210.99 mAh/g,循环过程中容量折线上升。     

溶胶-凝胶法制备Nb掺杂TiO_2的电化学性能

溶胶-凝胶法制备不同晶型的铌(Nb)掺杂二氧化钛(TiO_2),并对电化学性能进行研究。550℃烧结的锐钛矿相Nb掺杂TiO_2具有良好的电化学性能,循环(1~3 V)50次后,仍有190 mAh/g的比容量。600~700℃烧结的样品为锐钛矿/金红石混合相,随着温度的升高,金红石相的含量逐渐增加,电化学性能逐渐变差。     

溶胶-凝胶法合成正极材料LiFePO4

以Fe3 盐为铁源,采用溶胶-凝胶法制备了锂离子电池正极材料LiFePO4,用XRD、SEM、恒流充放电和交流阻抗方法研究了样品的结构、形貌和电化学性能。样品0.1C首次放电容量达到131 mAh/g,经10次循环后,容量保持率为96%。采用溶胶-凝胶法合成的LiFePO4,抑制了循环过程中电化学反应阻抗的增加。     

焙烧温度对溶胶-凝胶法制备磷酸钒锂的性能

以柠檬酸为螯合剂和C源,采用溶胶-凝胶法合成了Li3V2(PO4)3。通过交流阻抗、恒电流充放电及XRD等进行测试和表征。结果表明,焙烧温度对材料电化学性能影响较大。700℃合成的样品综合电化学性能较好,首次放电比容量为105.6 mAh/g,循环10次后比容量保持在99.0%,并且晶体结构发育完整,粒度分布均匀。     

表面活性剂对溶胶-凝胶法合成Li3V2(PO4)3的影响

讨论了表面活性剂OP-10对溶胶-凝胶法合成正极材料单斜晶型Li3V2(PO4)3的影响.表面活性剂可降低微粒的表面张力,提高前驱体的Zeta(ζ)电位,防止原生粒子团聚,提高溶胶的稳定性.加入5%OP-10制备的样品以0.2 C在3.0～4.3 V循环,首次放电比容量为123.1 mAh/g,第30次循环的容量衰减率...     

溶胶凝胶-燃烧法合成La0.7Sr0.3MnO3阴极材料及其性能

低温合成钙钛矿单相La0.7Sr0.3MnO3粉体,以降低粒度、提高活性,已成为本领域研究的一个新方向。采用溶胶凝胶-燃烧法合成La0.7Sr0.3MnO3粉体,讨论了溶胶体系pH值和柠檬酸用量对燃烧程度及相组成的影响。利用络合理论,计算了溶胶体系的pH值对于络合物的影响。实验结果表明,当pH<3时,溶胶凝胶体系稳定存在;而当pH达到3有白色沉淀出现。燃烧完全程度随着pH值的增加和柠檬酸用量的减少而提高。晶相合成程度以柠檬酸/硝酸盐比值(j)=0.5时最为完全,随着j提高,生成微量第二相。1300℃烧结试样以j=1.5最为致密,电导率峰值达150S/cm。综合考虑相组成和性能两因素,运用此法制备La0.7Sr0.3MnO3粉体时,j以1.5为宜。     

Liquid source chemical vapor deposition of high-dielectric-constant (Ba,Sr)TiO3 films

High-dielectric-constant (Ba, Sr)TiO₃ [BST] films were deposited by the liquid source chemical vapor deposition (CVD) method. The system consisted of a single-wafer, low-pressure thermal CVD reactor, a vaporizer for liquid source materials, and a shower-type gas nozzle head, giving stable BST film deposition on a 6-in. diam. substrate with uniform thickness and uniform chemical composition ratio. The source materials employed were Ba(DPM)₂, Sr(DPM)₂, and TiO(DPM)₂ dissolved in tetrahydrofuran (THF), resulting in conformal step coverage of BST films at lowered substrate temperatures, where DPM denotes dipivaloylmethanate. Moreover, the two-step deposition technique was developed to restart protrusions formed on BST film surfaces at low temperatures, where the BST films consisted of a buffer layer and a main layer; the buffer layer was a layer about 60 Å thick of CVD-BST film annealed in N₂. Thus, the two-step CVD deposition of BST films on Pt and Ru electrodes achieved an equivalent SiO₂ thickness of t_eq ∼ 0.5 nm, a leakage current of J_L ∼ 1.0 × 10⁻⁸ A/cm² (at +1.1 V), and a dielectric loss of tan δ ∼ 0.01 at a total film thickness of 250 Å, along with conformal coverage of 80% for a trench with an aspect ratio of 0.65. Then, for BST films deposited on patterned electrodes 0.24 μm wide, 0.60 μm deep, and 0.15 μm high (each spaced by 0.14 μm), the capacitance was demonstrated to be increased without significant deterioration of the leakage current: the capacitance was increased in comparison with that for films on flat electrodes, by a factor corresponding to the increase in surface area due to sidewalls of storage-node-like pattern features. This capacitance increase reflects the most characteristic advantage of CVD, an excellent step coverage on microscopic pattern features. These electrical properties satisfy the specifications for capacitors for Gb-scale dynamic random access memories (DRAMs), giving a storage capacitance of more than 25 fF/cell for a stacked capacitor having a storage node 0.2 to 0.3 μm high. © 1998 Scripta Technica, Electr Eng Jpn, 125(1): 47–54, 1998     

MOCVD of (Ba,Sr)TiO3: Nucleation and Growth

(Ba_0.7Sr_0.3)TiO₃ and SrTiO₃ thin films were deposited on Pt electrodes in a planetary multi-wafer MOCVD reactor. The nucleation behavior and the size of the stable nuclei were investigated by different SPM techniques. Characteristic differences were observed for different deposition temperatures, i.e. a homogeneous nucleation of small BST grains on the larger Pt grains at 565°C and a dominating nucleation at the grain boundaries at 655°C. The micro structural evolution after further film growth was investigated by HRTEM and revealed randomly oriented grains (typical inplane size 10–20 nm) with a high density of twins at 565°C and (100)-oriented defect free grains of only slightly increased size at 655°C. For SrTiO₃ the inplane grain size was increased, however, the (100) texture was less perfect. As the electrical properties like permittivity and also leakage current depend on film thickness the final discussions of the electrical properties are based on thickness series (5 nm–100 nm films) and evaluated within the phenomenological dead layer model.     

Structure of Ferroelectric (Ba,Sr)TiO3 Thin Films for Tunable Microwave Devices

Ferroelectric (Ba,Sr)TiO₃ films have been deposited on (001) MgO single crystals by a pulsed laser deposition with oxygen background while heating the substrates. Deposited BST films exhibit epitaxial growth along (001), which are confirmed by x-ray diffraction measurement. Structure of (Ba,Sr)TiO₃ along in-plane and surface normal direction have been investigated and found to have a tetragonal distortion depend on the deposition conditions, such as oxygen pressure. Lattice parameter decreases with increasing oxygen pressure, and tetragonallity (c/a) changes from 1.005 to 0.997 as oxygen pressure increase. Interestingly, energy gap measured by FTIR decreases with decreasing oxygen pressure until it reach a certain oxygen pressure, then increases again with increasing oxygen pressure. Furthermore, microwave properties of devices measured by a HP 8510C vector network analyzer from 0.045–20 GHz suggest that the least distorted films exhibit a larger dielectric constant changes with dc bias field.     

Preparation and electrical properties of Ni/(Ba,Sr)TiO3 PTC composite with low resistivity

Ni/ (Ba,Sr)TiO₃ PTC composite of low resistivity was fabricated by a solid state route. A mildly reducing sintering atmosphere was employed to avoid the oxidation of nickel. Metallic nickel is the main chemical state after sintering in the mildly reducing sintering atmosphere. With the increase in nickel amount, the room-temperature resistivity declines and the PTC effect worsens. The quantum mechanical tunneling effect at the Ni–(Ba_,Sr)TiO₃ interface is presumably the prime factor in the deterioration of the PTC effect. PbO–B₂O₃–ZnO–SiO₂ glass was added to modify the interface between nickel and (Ba,Sr)TiO₃ ceramics. The intergranular phase introduced by the glass has an amorphous structure and exists at the interfaces and triple junctions of (Ba,Sr)TiO₃ grains and nickel grains. No obvious diffusion occurs at the interface between crystalline (Ba,Sr)TiO₃ grain and the intergranular phase. Also the added-glass improves the distribution of metal phase. The proper glass addition screens interfacial electron tunneling effect and improves the composite electrical properties. An abundance of the intergranular phase due to excess glass will, however, result in high room-temperature resistivity. The influences of nickel amount and glass amount on the microstructure evolution and electrical properties were analyzed.     

Optimum Reflection-Type Phase Shifter Using (Ba,Sr)TiO3 Thin Film

In this paper, in order to obtain a large differential phase shift with a little change in applied voltage, a ferroelectric reflective load circuit has been designed on top of barium strontium titanate (Ba,Sr)TiO₃ [BST] thin film. The design of the ferroelectric reflection-type phase shifter is based on a reflection theory of terminating circuit, which has a reflection-type analogue phase shifter with two ports terminated in symmetric phase-controllable reflective networks. To achieve large amounts of phase shift in low bias-voltage range, the effects of change of capacitance and transmission line connected with two coupled ports of a 3-dB 90° branch-line hybrid coupler have been investigated. A large phase shift with a small capacitance change in the parallel terminating circuit has been demonstrated in the paper.     

Growth of (Ba,Sr)TiO 3 Thin Films by MOCVD: Stoichiometry Effects

(Ba x Sr 1 m x )TiO 3 thin films were deposited in a planetary multi-wafer MOCVD reactor combined with a liquid delivery system using 0.35 molar solutions of Ba(thd) 2 and Sr(thd) 2 and a 0.4 molar solution of Ti(O-i-Pr) 2 (thd) 2 . The film growth on Pt-(111) was investigated within a wide parameter field, e.g., the deposition temperature was varied between 560C and 650C, which yields films with microstructures ranging from randomly oriented polycrystalline to perfectly (100)-textured columnar structures. Special emphasis is given to film stoichiometry: starting with (Ba 0.7 Sr 0.3 )TiO 3 the Group-II/Ti content was varied from 0.9 to 1.1 and the Ba content was reduced to the limit of pure SrTiO 3 films. The electrical properties of MIM structures were investigated after deposition of Pt top electrodes. The nominal thickness of the films was varied between 5 and 100 nm and permittivity and leakage current both are shown to depend strongly on the film thickness. These dependencies on the film thickness are analyzed within the phenomenological dead layer model. The dependence of the electrical properties on stoichiometry are discussed in detail.     

Dielectric,ferroelectric, and piezoelectric properties of lead-free Ba0.95Ca0.05Ti1-xZrxO3 ceramics

Abstract

Ba_0.95Ca_0.05Ti_1-xZr_xO₃ (BCTZO) ceramics were prepared by a solid state reaction method. The samples were characterized by X-ray diffraction (XRD), Scanning electron microscopy (SEM) and X-ray absorption near edge structure (XANES). The ceramics exhibit a pure perovskite structure. The average grain size gradually decreases with increasing Zr concentration. XANES results indicate that the intensities of pre-edge peaks dropped with increasing Zr concentration. The BCTZO ceramic of x?=?0.05 has the optimum electrical properties with the maximum dielectric constant (ε'_m), remanent polarization (2P_r), coercive electric field (2E_c) and piezoelectric charge constant (d₃₃) of 7,244, 12.54 (μC/cm²), 5.29 (kV/cm) and 288 (pC/N), respectively.     

Chemical Processing and Properties of (Sr,Ca) 2 (Nb,Ta) 2 O 7 Thin Films

Ca-doped Sr 2 (Nb,Ta) 2 O 7 thin films have been synthesized by the chemical solution deposition. Homogeneous and stable (Sr,Ca) 2 (Nb,Ta) 2 O 7 precursor solutions were prepared by optimizing the reaction of starting metal alkoxides in ethanol with a key additive of 2-ethoxyethanol. The improvement of ferroelectric properties of the Sr 2 (Nb,Ta) 2 O 7 based films were achieved through the Ca substitution into Sr 2 (Nb 0.3 Ta 0.7 ) 2 O 7 as well as the optimization of heating conditions. The crystallization temperature of the layered perovskite (Sr 0.9 Ca 0.1 ) 2 (Nb 0.3 Ta 0.7 ) 2 O 7 thin films on Pt/Ir/Ti/SiO 2 /Si substrates was found to be above 750C. (Sr 0.9 Ca 0.1 ) 2 (Nb 0.3 Ta 0.7 ) 2 O 7 thin films crystallized at 750C exhibited P r of 0.51 w C/cm 2 and E c of 69 kV/cm.     

Calculation of the intrinsic dead layers thicknesses from Au/Ba0.5Sr0.5TiO3/Pt thin film capacitors

Ferroelectric Ba_0.5Sr_0.5TiO₃ (BST) films were prepared on Pt/Ti/SiO₂/Si substrates by the sol-gel process. The films were spin-coated at 2000 rpm for 30 secs and then pyrolysed for 5 mins at the temperature of 350^∘C. This coating procedure was repeated for 3, 4, 5 and 6 times to obtain BST films with different thicknesses. After coating the films with the desired repetition times, the films were finally annealed in a conventional furnace at temperatures ranging from 600^∘C to 800^∘C with a 50^∘C interval in between. The films obtained with an annealing procedure of 750^∘C were polycrystalline with the presence of an impurity BaCO₃ phase. The capacitance and leakage current were measured and used to extract information on the metal-BST interface. With the series capacitance model and modified Schottky emission equation, the thickness of the dead layers for Au/BST and Pt/BST interfaces were calculated to be less than 6 nm and 5 nm, respectively.