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81.
Transport of ionic species in the melt and their partitioning at the solid–liquid interface during growth of lithium niobate was studied under the influence of intrinsic and external electric fields. A Mn-doped lithium niobate (Mn:LiNbO3) single crystal was grown via the micro-pulling-down (μ-PD) method with electric current injection at the interface. Mn ions were accumulated or depleted at the interface, depending on the sign of the injected current. The electric current injection induced an interface electric field as well as a Coulomb force between the interface and Mn ions. The electric field modified the transportation of Mn ions and their partitioning into the crystal, while the Coulomb force led to adsorption or rejection of Mn ions at the interface in addition to Mn concentration change due to the electric field. Effect of the Coulomb force was often observed to be larger on Mn concentration at the interface than that of the induced electric field, and dominated the redistribution of Mn in the solid. It has been experimentally and analytically shown that Mn concentration partitioned into the crystal can be obtained by multiplying Mn concentration at the interface by a field-modified partition coefficient, kE0, instead of the conventional equilibrium partition coefficient, k0. 相似文献
82.
A facile route to prepare lithium niobate (LiNbO3) powders was proposed by an alternative solid‐state method. Stoichiometric Li2C2O4 and ammonium niobium oxalate were mixed with small amounts of water and then dried at room temperature. It was demonstrated that Li[NbO(C2O4)2]·n H2O intermediate was produced by an ion‐exchange reaction. Pure LiNbO3 powders were successfully synthesized by heating the intermediate at 500, 600 and 700 °C for 3 h. X‐ray diffraction (XRD), scanning electron microscopy (SEM), Fourier‐transform infrared (FTIR) spectroscopy, UV‐Vis diffuse reflectance (UV‐Vis) spectroscopy and thermogravimetric (TG) analysis were used to characterize the precursor compound and as‐prepared samples. XRD results reveal that all the products are identified as hexagonal structure with high relative crystallinity (>87%). The particle size is found to be about 40 nm for the mixture calcined at 500 °C according to XRD data, which is in good agreement with SEM data. The as‐prepared LiNbO3 powders by this method are high quality according to FTIR spectra. (Li0.996Nb0.005)Nb0.999O3 phase was formed when the calcination temperature was raised to 800 °C. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
83.
Preparation and Structure of LnNb7O19 (Ln = La, Ce) Two new ternary compounds, LaNb7O19 and CeNb7O19, could be prepared and characterized. At temperatures about 900°C already decomposition of both compounds will be initiated, but at lower temperatures (800°C) no reaction between the binary components occured. Single crystals could be obtained by chemical transport reactions (T2 → T1; T2 = 800°C; T1 = 780°C). Chlorine for mineralization or as transport agent is absolutely indispensable for preparation. Single crystal investigations on LaNb7O19 (R = 4.4%; Rw = 4.19%) result in the trigonal space group P3. The cell dimensions are a = 6.2531(2) A; c = 20.0685(10) Å; Z = 2. The structure can be described as to be build up by layers of 8-coordinated La and 6-coordinated Nb, alternating with layers of edge-sharing pentagonal NbO7-bipyramids. Corresponding to the unusual sequence of layers the structure of LnNb7O19 (Ln = La,Ce) is the first example of a trigonal member of a family of structures, which has been described in detail by Jahnberg. The most examples are represented by tantalates, but only a few niobates related to these structures are known. 相似文献
84.
M. P. F. Graça M. G. Ferreira da Silva M. A. Valente 《Journal of Sol-Gel Science and Technology》2007,42(1):1-8
The glass composition 88SiO2-6Li2O-6Nb2O5 (mole %) was successfully prepared by the sol-gel technique. The dried and translucent gel was heat-treated at temperatures
between 500°C and 800°C. Lithium niobate crystallites, an important ferroelectric material, were detected in the gel derived
glass-ceramics treated above 650°C. In the samples treated at 700 and 800°C the Li2Si2O5 crystalline phase is present. The 800°C treated sample also presents the Li3NbO4 phase.
The structure and morphology of the samples were studied by X-ray powder diffraction (XRD), Raman spectroscopy and scanning
electron microscopy (SEM). The SEM revealed that all the samples, heat-treated above 650°C, present crystallites embedded
in the glass matrix. The particles detected in the 600°C treated sample are essentially amorphous, or with an incipient structure.
The temperature dependence of the dc electrical conductivity (σ
dc
) shows two regions with different activation energies. The conductivity behaviour of the sample is mainly due to the mobile
ion number. The ac conductivity (σ
ac
), measured at 1 kHz decreases with the rise of the treatment temperature due to the increase of the LiNbO3 crystallites amount.
The electrical behavior of the glass and glass-ceramics reflects the important role carried out by the treatment temperature
in the gel-glass structure. 相似文献
85.
铌酸锂晶体的缺陷及其控制 总被引:1,自引:0,他引:1
针对铌酸锂晶体中的缺陷研究,本文总结了国内外学者提出的不同晶体缺陷模型及各自的特点,并介绍了我们提出的铌位依赖、锂位敏感模型.在分析晶体缺陷研究的基础上提出了对铌酸锂晶体进行缺陷控制的意义及理论依据,指出缺陷控制的主要任务是保护锂格位.本文还简要概括了铌酸锂晶体缺陷控制的主要手段,并建议从反映铌酸锂晶体性能的角度来研究缺陷结构. 相似文献
86.
87.
88.
用化学共沉淀法制备了镧和锌掺杂的铌酸铋纳米颗粒,表征了制备样品的微观结构和光催化降解性能。结果表明制备的样品对RhB表现出良好的可见光催化降解活性,且光催化效果受各种因素的影响。其中,Bi_(0.96)La_(0.04)NbO_4用量为0.15 g时,对pH=4、50 m L浓度为5 mg·L-1 RhB溶液的光催化效果最佳。光催化机理研究表明催化剂在可见光照射下产生的电子空穴对Rh B的降解起主要作用。该催化剂的制备方法简单、光催化性能稳定,5次循环后的活性仍大于95%。 相似文献
89.
90.