球形Ta2O5/Nb2O5制备方法的研究

研究了用氨沉淀氟钽(或铌)酸溶液制备球形Ta2O5/Na2O5工艺.通过实验探讨了沉淀条件、溶液浓度、沉淀时间、焙烧温度等工艺参数的最佳组合.结果表明,用氨沉淀氟钽(或铌)酸溶液制备球形的Ta2O5/Nb2O5,必须首先得到不规则的Ta(OH)5/Nb(OH)5.要得到不规则Ta(OH)5/Nb(OH)5,反应时搅拌强度要大,搅拌速率应控制在800～1 200 r/min,反应结束后继续搅拌10～20 min,终点pH值控制为8.5;氟钽(或铌)酸溶液浓度为60～80 g/L沉淀10 min,浓度为120～140 g/L沉淀15 min,之后可得到不规则Ta(OH)5/Nb(OH)5.再在800～850℃,焙烧6 h可得到球形Ta2O5/Nb2O5.     

磁控反应溅射制备的Ta2O5薄膜的光学与介电性能

采用直流磁控反应溅射技术，在不同的Ar/O2比条件下制备了系列Ta2O5薄膜样品，采用紫外．可见光透射光谱和椭偏光谱测试分析技术，研究了Ta2O5薄膜在可见光范围内的透射率、折射率和消光系数；同时还采用HP 4192A阻抗分析仪测试分析了样品在500Hz～13MHz频段的介电谱，结果表明在300～700nm的可见光波长范围内，氧化钽薄膜的消光系数k→0，折射率＞2．0，透射率大约80％。500Hz下的低频介电常数5的典型值为20.1。损耗角正切tgδ为19.9。     

去除Ta2O5/Nb2O5中杂质S的工艺研究

从理论和实际应用方面,研究了去除Ta2O5/Nb2O5中杂质S的方法.通过对制取高纯Ta2O5和Nb2O5的中间产品高纯Ta(OH)5/Nb(OH)3进行过氧化处理,改变Ta,Nb,S等元素在物料中的存在方式,增大了含S杂质的溶解性,降低了物料对含S离子的吸附能力及硫酸盐的分解温度,通过洗涤、焙烧达到有效去除产品中杂质元素S的目的.该方法可在不影响Ta2O5/Nb2O5产品质量的情况下,使杂质S降低到0.0001%以下.     

Surface morphology and dielectric properties of alkoxy-derived Sr2Ta2O7 and Sr2Ta, Nb2O7 thin films

Sr₂Ta₂O₇ and Sr₂(Ta, Nb)₂O₇ thin films were prepared from molecular structure-controled alkoxide solutions. The Sr₂Ta₂O₇ thin films initiated to crystallize at around 650 °C and showed random orientation. The surface topography developed was dependent on the solutions. In the thin films prepared from the ethanolic solution, grains formed at low temperatures. However, many small pores still remained and no grains were observed in the thin films prepared from the methoxyethanolic solution. In contrast, the 800 °C-annealed Sr₂(Ta, Nb)₂O₇ thin films showed the (0 k 0) orientation as in Sr₂Nb₂O₇ thin films. The dielectric constants and loss factors of the 750 °C-annealed Sr₂Ta₂O₇ and Sr₂(Ta_0.7Nb_0.3)₂O₇ thin films were around 90 and less than 0.05 at 100 kHz, respectively.     

还原氧化钽和氧化铌制备电容器用粉末的方法评述

评述了氧化铌、氧化钽的两步镁还原、镁蒸气还原、在CaCl2-NaCl熔融盐里钙还原和在CaCl2-NaCl熔融盐里钠还原的方法.两步镁还原氧化铌、氧化钽的工艺路线长.采用镁蒸气还原能够得到性能好的钽粉,但是还原时间长,还原装置复杂,希望能找到一种有效的设备.用CaCl2-NaCl熔融盐里钙还原氧化铌、氧化钽.还原温度高,得到的金属粉末比表面积小,工艺不够成熟.在CaCl-KCI-NaCl熔盐里金属Na还原Ta2O5、Nb2O5,反应时间短,还原温度范围广,能够得到高纯度高比表面积的钽、铌粉末.     

金属有机物分解法制备SrBi2Ta2O9铁电薄膜的开关特性

用金属有机物分解（MOD）以及sol-gel方法制备了SiBi2Ta2O9（STB）铁电薄膜。经测量在750℃晶化的SBT薄膜具有很好的铁电性能。通过对SBT样品极化反转过程进行测试,得出了外加电压（0．5－5V）与SBT薄膜的开关时间（100－600ms）及极化反转电荷的关系。并研究了不同气氛不退火对SBT铁电薄膜形状特性的影响。     

Third-order nonlinear optical properties of sol-gel-derived V(2)O(5), Nb(2)O(5), and Ta(2)O(5) thin films

The third-order nonlinear optical properties of sol-gel-derived V(2)O(5), Nb(2)O(5), and Ta(2)O(5) thin films have been investigated by the third-harmonic-generation method, and the effect of the metal-oxygen bond length on the third-order nonlinear optical susceptibility χ((3)) has been examined. The χ((3)) values of V(2)O(5), Nb(2)O(5), and Ta(2)O(5) thin films were 1.1 × 10(-11), 1.3 × 10(-12), and 6.1 × 10(-13) esu, respectively, which corresponds to an increase in the average bond length I(b) of the order of V-O (I(b) = 0.183 nm), Nb-O (I(b) = 0.200 nm), and Ta-O (I(b) = 0.204 nm). The current and previous results indicate that χ((3)) of these transition metal oxides with the empty d orbitals is dominated mainly by the metal-oxygen bond length rather than the valence of the metal cation. It is predicted on the basis of Lines' model that transition metal oxides with the shortest I(b) exhibit the highest χ((3)), whereas nontransition metal oxides with the longest I(b) exhibit the highest χ((3)).     

Electrical properties of Li2O-La2O3-SiO2 electrode glasses after Ta2O5 doping and Ta implantation

Electrical conductivities, , of the Li₂O-La₂O₃-SiO₂ glasses were investigated as functions of Ta₂O₅ doping and Ta ion-implantation. A linear relationship between logarithm and the inverse of the sample temperature, T, was found in 2 to 4 mol% Ta₂O5 doped Li₂O-La₂O₃-SiO₂ glasses. The conductivity increases as Ta₂O₅ content increases at sample temperatures above 100°C. Fluences of 50 keV Ta ions per cm² from 5 × 10¹⁶ to 2 × 10¹⁷ were implanted into 0% and 2% Ta₂O₅ containing Li₂O-La₂O₃-SiO₂ glass samples. The activation energy of the conductivity was deduced from the relation between log and 1/T. It was found in implanted samples that the conductivity increased, but the activation energy and T _k–100 decreased, where T _k–100 is the sample temperature when the conductivity reaches 100 × 10^–1 S/cm. However, the Ta₂O₅ containing implanted samples show higher conductivities, lower activation energies and lower T _k–100. X-ray photoelectron spectroscopy (XPS) was used to study the structural modification introduced by implantation. Bridging oxygen (BO) and non-bridging oxygen (NBO), were observed in all samples. The changes in relative concentrations of BO and NBO before and after implantation clearly indicate the structure modification which results in the increase of the conductivity. It was clearly demonstrated in this study that both doping Ta₂O₅ and implanting Ta ions enhance the conductivity of Li₂O-La₂O₃-SiO₂ electrode glasses.     

Ta2O5薄膜的结构和电学性能研究

采用紫外光诱导热丝CVD沉积技术制备Ta2O5薄膜和Al/Ta2O2/SiMOS电容。利用XRD，AFM测试分析方法研究了紫外光源功率对Ta2O5薄膜结构的影响；通过C-V和，I-V测试对Ta2O5薄膜的介电常数，击穿场强和漏电流等电学性能进行了研究，结果表明：紫外光源的功率越大，Ta2O5薄膜的结晶性越好，介电常数越大，最大值为29，但紫外光功率对击穿场强和漏电流没有明显改善。     

Electrical properties of Ta2O5 films deposited on ZnO

High dielectric constant (high-k) Ta₂O₅films have been deposited on ZnO/p-Si substrate by microwave plasma at 150°C. Structure and composition of the ZnO/p-Si films have been investigated by X-ray diffraction (XRD), atomic force microscopy (AFM), scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS) for chemical composition. The electrical properties of the Ta₂O₅/ZnO/p-Si metal insulator semiconductor (MIS) structures were studied using high frequency capacitance-voltage (C-V), conductance-voltage (G-V) and current-voltage (I-V) characteristics. Charged trapping properties have been studied by measuring the gate voltage shift due to trapped charge generation under Fowler-Nordheim (F-N) constant current stressing.     

Enhanced dielectric properties of modified Ta2O5 thin films

 Tantalum oxide (Ta₂O₅) is a promising high dielectric constant material for the DRAM applications because of its ease of integration compared to other complex oxide dielectrics. The dielectric constant and thermal stability characteristics of bulk Ta₂O₅ samples were reported to enhance significantly through small substitutions of Al₂O₃. However, this improvement in the dielectric constant of (1-x)Ta₂O₅-xAl₂O₃ is not clearly understood. The present research attempts to explain the higher dielectric constant of (1-x)Ta₂O₅-xAl₂O₃ by fabricating thin films with enhanced dielectric properties. A higher dielectric constant of 42.8 was obtained for 0.9Ta₂O₅–0.1Al₂O₃ thin films compared to that reported for pure Ta₂O₅ (25–30). This increase was shown to be closely related to a-axis orientation. Pure Ta₂O₅ thin films with similar a-axis orientation also exhibited a high dielectric constant of 51.7, thus confirming the orientation effect. The leakage current properties and the reliability characteristics were also found to be improved with Al₂O₃ addition. Received: 24 November 1998 / Reviewed and accepted: 7 December 1998     

Dielectric and impedance properties of LiCa2Nb5O15 ceramics

Polycrystalline sample of LiCa₂Nb₅O₁₅ was prepared by a high-temperature solid-state reaction technique. Structural and microstructural characterizations were performed by X-ray diffraction (XRD) and scanning electron microscope (SEM). X-ray studies reveal that the material has orthorhombic structure at room temperature. Electrical properties of the material have been studied using a complex impedance spectroscopy (CIS) technique in a wide temperature (31–500 °C) and frequency (10²–10⁶ Hz) ranges. The complex impedance plots reveal the main contribution of bulk effects in it. The bulk resistance, evaluated from complex impedance spectrum, has been observed to decrease with rise in temperature showing a typical negative temperature coefficient of resistance (NTCR) behavior. Variation of dc conductivity (bulk) with temperature demonstrates that the compound exhibits Arrhenius type of electrical conductivity.     

Microstructure and electrical properties of Nb2O5 doped titanium dioxide

The present work attempts to investigate the sintering characteristics, grain boundary morphology and electric conductivity of Nb₂O₅ doped TiO₂ semiconductor ceramics. X-ray diffraction results showed evidence of a second phase beside the rutile TiO₂ when Nb₂O₅ exceeds 0.7 mol%. SEM images showed that Nb₂O₅ doping can lowers the sintering temperature of TiO₂, although not significantly. Lattice images of the grain boundary morphology obtained by high resolution transmission electron microscopy revealed defects introduced from the doping. Grain boundaries vary from amorphous to a faceted structure. Finally, electrical conductivity measurements showed that the grain boundary resistance is greatly reduced at high temperature.     

Residual stress in Ta2O5-SiO2 composite thin-film rugate filters prepared by radio frequency ion-beam sputtering

Ta-Si oxide composite thin-film rugate filters were prepared by radio frequency ion-beam sputtering and their residual stress and substrate deflections were measured. The residual stress and substrate deflection of these composite film rugate filters were less than that of notch filters made from a series of discrete quarter-wave layers with alternate high and low indices because of the smooth modulation of composition and no interface structure of the rugate filter.     

Nb2CTx MXene Derived Polymorphic Nb2O5

Previously, heat treatment was the only feasible route for tuning the crystal phases of niobium pentoxide (Nb₂O₅). With the use of Nb₂CT_x MXene precursors, the first case of phase tuning of Nb₂O₅ in the low-temperature hydrothermal synthesis using sulfuric acid regulating agents is presented. By varying the amount of the agent, four pure-phase Nb₂O₅ crystals and mixed phases in-between are obtained. The required amount is found to be related to the H-covered surface energy calculated based on density functional theory. Overall, MXene-derived B-phase Nb₂O₅ is of particular interest due to its exceptionally high capacities as lithium-ion battery anodes, which are three times higher than the routine synthesized one. Oxygen vacancies induced by crystallographic shear would be responsible for the extraordinary performance. The proposed phase tuning strategy encourages the prudent synthesis of difficult-to-obtain crystal phases.     

阳极氧化法制备非晶Ta2O5及绝缘性能研究

利用阳极氧化法制备Ta2O5绝缘介质薄膜。扫描电子显微镜（SEM）、能谱分析（EDS）和X射线衍射仪（XRD）研究表明Ta2O5绝缘介质薄膜表面平整,致密,呈非晶态。电击穿场强测试系统研究利用Ta-Ta2O5-Al复合薄膜制备FED器件（MIM结构）的绝缘性,表明薄膜具有较高的耐击穿场强,约为2.3MV/cm,分析Ta2O5的导通机理,主要为肖特基效应和F-N效应。     

Characterization and dielectric properties of Ba5NdZnM9O30 (M=Nb, Ta) ceramics

Ba₅NdZnM₉O₃₀ (M=Nb, Ta) ceramics were prepared by the conventional high temperature solid state reaction route. The sintered samples were characterized by X-ray diffraction and scanning electron microscopy methods. They belong to paraelectric phases of filled tetragonal tungsten bronze structure at room temperature and have high dielectric constants of 282 and 85, combined with low dielectric losses of 0.0048 and 0.0081 at 1 MHz for Nb- and Ta-based ceramics, respectively.     

Electrical properties of SnO2·CuO·Ta2O5 varistor system

The CuO and Ta₂O₅-doped SnO₂ system was obtained by conventional ceramics processing. The ceramic phases of samples was analyzed by X-ray diffraction (XRD) and the microstructure by means of scanning electron microscopy (SEM). The electrical field of a single phase of CuO and Ta₂O₅-doped SnO₂ system was studied as a function of current density behavior and compared with the CoO and Ta₂O₅-doped SnO₂ system. A high nonlinear coefficient α=37.9 was obtained. To illustrate the grain–boundary barrier formation of CuO and Ta₂O₅-doped SnO₂-based varistors, a modified defect barrier model is introduced.     

Structural and optical properties of BaTi2O5 thin films prepared by pulsed laser deposition at different substrate temperatures

BaTi₂O₅ thin films were prepared on MgO (1 0 0) substrates by pulsed laser deposition. The effect of substrate temperature (T_sub) on the structural and optical properties of the films, such as crystal phase, preferred orientation, crystallinity, surface morphology, optical transmittance and bandgap energy, was investigated. The preferred orientation of the films changed form (7 1 0) to (0 2 0) depending on T_sub, and the b-axis oriented BaTi₂O₅ thin film could be obtained at T_sub = 973–1023 K. The surface morphology of the films was different with changing T_sub, which showed a dense surface with an elongated granular texture at T_sub = 973–1023 K. The crystallinity and surface roughness increased at the elevated substrate temperatures. The as-deposited BaTi₂O₅ thin films were highly transparent with an optical transmittance of ～70%. The bandgap energy was found to decrease with increasing substrate temperature, from 3.76 eV for T_sub = 923 K to 3.56 eV for T_sub = 1023 K.