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本文用差热分析和X射线衍射等方法研究了BaO-Na2O-B2O3三元系的两个截面:BaB2O4-Na2B2O4和BaB2O4-Na2O赝二元系的相平衡关系。BaB2O4-Na2B2O4属共晶体系,其共晶温度为826±3℃。在BaB2O4-Na2O体系中发现一个新化合物BaB2O4·Na2O,该化合物在846±3℃同成分熔化。BaB2O4·Na2O对BaB2O4和Na2O均为共晶体系,其共晶温度分别为755±3℃和573±3℃。并根据所得的结果,分别以15mol%Na2O和13mol%Na2B2O4为助熔剂,用提拉法培养出2×4×6mm3和2×4×8mm3的低温相BaB2O4单晶体。
关键词: 相似文献
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本文用X射线衍射、热处理及差热分析等方法测定了SrNb2O6-NaNbO3-LiNbO3赝三元系的室温截面及相应的SrNb2O6-NaNbO3,SrNb2O6-LiNbO3和NaNbO3-LiNbO3等三个赝二元系相图;粗略地研究了Sr0.42Na0.16NbO3-LiNbO3系的纵截面;含5mol%LiNbO3及10mol%LiNbO3的SrNb2O6-NaNbO3的纵截面。确定了室温Sr2Na(NbO3)5(以下略为S2N)相为四方钨青铜结构。其点阵常数为a=12.36?,c=3.906?.LiNbO3在S2N相内的溶解度可达~10mol%,当LiNbO3含量超过5mol%时,S2N相畸变为S2N′相。S2N′相为正交晶系。实验确定室温S2N(S2N′)相系亚稳相。在900-1100℃长时间退火即分解为SrNb2O6和以NaNbO3为基的固溶体的混合物。
关键词: 相似文献
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本文用X射线和差热分析方法对BaO-Li2O-B2O3三元系中的两个截面:BaB2O4-Li2B2O4和BaB2O4-Li2O作了研究。在BaB2O4-Li2B2O4赝二元系中发现了一个新的化合物4BaB2O4·Li2B2O4。化合物在930±3℃由包晶反应形成,并与Li2B2O4形成共晶反应。共晶温度为797±3℃,共晶点组分为79mol%Li2B2O4。在BaB2O4-Li2O截面中也存在化合物4BaB2O4·Li2B2O4,其包晶反应温度从930±3℃随Li2O含量增加下降到908±3℃。在组分60mol%Li2O处形成另一个新的化合物2BaB2O4·3Li2O。该化合物在630±3℃也是由包晶反应形成,并与Li2O和Li2CO3分别形成共晶反应,共晶温度分别为400±3℃和612±3℃。在BaB2O4-Li2B2O4和BaB2O4-Li2O体系中都没有观察到固溶体。用计算机程序分别对化合物4BaB2O4·Li2B2O4和2BaB2O4·3Li2O的X射线粉末衍射图案进行了指标化,其结果:4BaB2O4·Li2B2O4的空间群为Pmma,a=13.033?,b=14.630?,c=4.247?,每个单胞包含两个化合式单位;2BaB2O4·3Li2O的空间群为Pmmm,a=4.814?,b=9.897?,c=11.523?,每个单胞也含有两个化合式单位。
关键词: 相似文献
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采用溶胶-凝胶(sol-gel)工艺制备0.1 mol% Er3+掺杂Al2O3体系和SiO2-Al2O3复合体系粉末. 实验结果表明:5 mol%的SiO2复合加入Al2O3抑制γ→θ和θ→α相转变. 掺0.1 mol%Er3+:Al2O3体系粉末,900℃烧结,在1.47—1.63μm波段内光致发光(PL)谱为中心波长1.53 μm、半高宽56 nm的单一宽峰,1000—1200℃烧结,劈裂为多峰PL谱. 掺0.1 mol%Er3+:SiO2-Al2O3复合体系粉末,在高达1200℃烧结,仍保持中心波长1.53 μm的单一宽峰PL谱,由于—OH更完全的脱除,PL强度较900℃烧结Al2O3体系,SiO2-Al2O3复合体系均提高1个数量级.
关键词:
2-Al2O3复合体系')" href="#">SiO2-Al2O3复合体系
掺铒
溶胶-凝胶工艺
光致发光 相似文献
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用高温熔融法制备了Bi离子掺杂浓度为1mol%的GeO-B2O3-Na2O (GBNB),GeO2-Al2O3-Na2O(GANB),GeO2-Al2O3-BaO(GABB)和GeO2-Al2O3-Y2O3(GAYB)玻璃.测定了样品玻璃的差热曲线、吸收、发射光谱及荧光衰减曲线.实验发现GBNB,GANB,GAYB,GABB的吸收边带逐步发生红移.由于这些吸收边带是由Bi3+的6s2电子到Bi5+ 6s0空轨道的跃迁引起.因此推断GBNB,GANB,GAYB,GABB玻璃中Bi5+离子的含量逐步增加.在GABB,GAYB,GANB三个样品中观察到发光中心约1220nm超宽带荧光发射.荧光强度从GABB,GAYB,GANB逐步减弱,荧光半高宽和荧光寿命逐步变小.这些超宽带的荧光归属为Bi5+离子的发光所致.从吸收与荧光光谱的变化,推断在GeO2-Al2O3玻璃中引入BaO,Y2O3组分有利于Bi5+离子的形成.讨论了BaO,Y2O3化学组分对Bi离子在玻璃中的价态影响的内在机理.
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5+离子')" href="#">Bi5+离子
超宽带发光
吸收带
荧光寿命 相似文献
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从理论上证明了介电松弛过程在介电谱上等效于电子松弛过程,认为室温下105Hz处特征损耗峰起源于耗尽层处本征缺陷所形成的电子陷阱.在-130—20℃范围内测量了三种配方ZnO陶瓷的介电频谱,发现ZnO压敏陶瓷室温下105Hz处的特征损耗峰在低温下分裂为两个特征峰,认为它们起源于耗尽层中的本征缺陷(锌填隙或/和氧空位)的电子松弛过程.发现ZnO-Bi2O3二元系陶瓷特征峰仅仅由锌填隙引起,而ZnO-Bi2关键词:
ZnO压敏陶瓷
本征缺陷
介电谱
热处理 相似文献
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Guo-Zhong Zang Feng-Zi Zhou Jing-Xiao Cao Xiao-Fei Wang Zhao-Wu Wang Li-Ben Li Guo-Rong Li 《Current Applied Physics》2014,14(12):1682-1686
Cr2O3 doped SnO2–Zn2SnO4 composite ceramics were prepared by traditional ceramic processing and the varistor, dielectric properties were investigated. With increasing Cr2O3 content, the breakdown electrical field EB increases from 11 to 92 V/mm and the relative dielectric constant εr measured at 1 kHz, 50 °C decreases from 11,028 to 3412, respectively. The barrier height ?B about 0.8–0.84 eV and the decreasing of SnO2 grain size suggest that the varistor behavior with high εr is originated from SnO2–SnO2 or SnO2–Zn2SnO4 grain boundary. In the dielectric spectra lower than 1 kHz, a dielectric peak is presented and depressed with increasing bias voltage. Similarly, at high temperature, the dielectric constant also presents a dielectric peak in the temperature spectra and the peak becomes faint with increasing frequency. The exhibition of the dielectric peak is thought to be attributed to the conduction of grain boundary since it is accompanied by the sharp increase of dielectric loss. In addition, a dielectric relaxation with the activation energy about 0.4–0.5 eV was observed in the temperature range of 20–100 °C. Based on the results, the formation mechanism of Schottky barriers at grain boundaries and the varistor behavior with high dielectric constant are well understood. 相似文献
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《Current Applied Physics》2015,15(11):1332-1336
A CaBi4Ti4O15 (CBTO) ceramic in which the Bi2O3 concentration was controlled from 0 to 10 wt% was fabricated using a solid-state reaction method. Structural analysis by field-emission scanning electron microscopy (FE-SEM) and X-ray diffraction (XRD) indicated differences in the preferred grain orientation and size of the plate-like grains according to the Bi2O3 concentration. The orientation of plate-like grains was also found to vary with the Bi2O3 concentration. There was no noticeable change trend of dielectric properties with different Bi2O3 concentrations. Relatively low dielectric constants (about 135) were exhibited by the CBTO ceramic with 1 wt% Bi2O3 and CBTO ceramic with 10 wt% Bi2O3 only, and similar values (about 150) were exhibited by the other ceramics. The dielectric loss exhibited a low value in the range of 0.01–0.09 for all samples (frequency range of 1–100 kHz). Regarding the ratio changes of the piezoelectric coefficient (d33) and the ratio of a-axis orientation of plate-like grains, the trends of these two values were shown to be similar. These results suggest that the addition of Bi2O3 greatly influences the microstructure of CBTO ceramics, including the grain size and orientation of plate-like grains. In particular, the change in the preferred grain orientation is closely related to the change in the piezoelectric properties. 相似文献
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X.X. Wang X.G. Tang K.W. Kwok H.L.W. Chan C.L. Choy 《Applied Physics A: Materials Science & Processing》2005,80(5):1071-1075
(Bi1/2Na1/2)TiO3 ceramics (BNT) with 0–6 mol% of excess Bi2O3 are prepared by conventional solid-state sintering. The electrical properties of the samples are examined. The addition of excess Bi2O3 reduces the leakage current of BNT ceramics significantly, thus facilitating the poling process, and improves their piezoelectric properties slightly for certain amounts of added Bi2O3. BNT ceramics have very high dielectric constants and dissipation factors at low frequency and high temperature due to their high conductivity. Adding excess Bi2O3 to BNT ceramics affects their dielectric behavior and phase transition temperatures. Grain growth is suppressed by adding Bi2O3 and no second phase is observed for BNT ceramics with up to 6 mol% of excess Bi2O3 added. 相似文献
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Structural and electric properties of Bi2Zn2/3Nb4/3O7 thin films prepared by pulsed laser deposition
Xiaohua Zhang Wei Ren Peng Shi Xiaoqing Wu Xiaofeng Chen Xi Yao 《Applied Physics A: Materials Science & Processing》2014,114(3):793-800
Bi2Zn2/3Nb4/3O7 thin films were deposited on Pt/TiO2/SiO2/Si(100) substrates under an oxygen pressure of 10 Pa by pulsed laser deposition. The substrate temperature varied from 500 °C to 750 °C. Effects of substrate temperature on the crystallinity, microstructure, and electric properties of Bi2Zn2/3Nb4/3O7 thin films have been systematically investigated. Bi2Zn2/3Nb4/3O7 thin films are amorphous in nature at a substrate temperature of 500 °C. With increase of substrate temperature to 550 °C, thin films begin to crystallize. At higher temperature of 750 °C, Bi2O3 phase can be detected in thin films. However, the crystallized thin films exhibit a cubic pyrochlore structure, not a monoclinic zirconolite structure, which is probably attributed by the composition deviation from the stoichiometric ratio. The resultant Bi2Zn2/3Nb4/3O7 thin films exhibit the character with high dielectric constant and low loss tangent. The dielectric constant gradually increases with the substrate temperature and reaches a maximum at 700 °C. The dielectric constant and loss tangent of the thin films deposited at 700 °C are 152 and 0.002 at 10 kHz, respectively. With further increase of substrate temperature to 750 °C, the dielectric constant decreases to 128. However, the tunability of the resultant thin films disappears, and the temperature coefficients are positive, which implies a more ordered structure in thin films. 相似文献
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The ferroelectric Bi2GeO5 crystalline phase is synthesized by heat treatment of 1Bi2O3-1GeO2-xFe2O3 and 1Bi2O3-1GeO2-yCr2O3 glasses. The obtained glass ceramics and initial glasses are studied using X-ray diffraction analysis and optical spectroscopy. The dielectric characteristics are measured, and the Curie temperature is determined. The effect of chromium and iron ions on the absorption spectra and dielectric properties of glasses and glass ceramics is determined. 相似文献
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In the multiferroic materials, the dielectric and magnetic properties are closely correlated through the coupling interaction between the ferroelectric and magnetic order. We attempted to determine the magnetoelectric coupling coefficient from the temperature dependences of the dielectric permittivity for multiferroic Bi5Ti3FeO15. Multiferroic ceramics Bi5Ti3FeO15 belong to materials of the Aurivillius-type structure. Multiferroic ceramics Bi5Ti3FeO15 was synthesized via sintering the Bi2O3 and Fe2O3 mixture and TiO2 oxides. The precursor material was ground in a high-energy attritorial mill for 5 hours. This material was obtained by a solid-state reaction process at T = 1313 K. We investigated the temperature dependences of the dielectric permittivity for the different frequencies. From the dielectric measurements, we determined the temperature of phase transition of the ferroelectric-to-paraelectric type at about 1013 K. Based on dielectric measurements and theoretical considerations, the values of the magnetoelectric coupling coefficient were specified. 相似文献
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Thanatep Phatungthane Gobwute Rujijanagul Kamonpan Pengpat Sukum Eitssayeam Tawee Tunkasiri Luiz F. Cotica Ruyan Guo Amar S. Bhalla 《Current Applied Physics》2014,14(12):1819-1824
In this work, ((1−x)Ba(Fe1/2Ta1/2)O3-xBa(Zn1/3Ta2/3)O3), ((1−x)BFT-xBZT) ceramics with x = 0.00–0.12 were synthesized by the solid–state reaction method. X-ray diffraction data revealed that both the powders and ceramics were of a pure-phase cubic perovskite structure. All ceramics showed large dielectric constants. For the x = 0.12 sample, a very high dielectric constant (>20,600) was observed. A lowering in the dielectric loss compared to pure BFT ceramics was observed with the BZT addition. The impedance measurements indicated that BZT has a strong effect on the bulk grain and grain boundary resistance of BFT ceramics. These results are in agreement with the measured dielectric properties. Based on dielectric and impedance results, (1−x)BFT-xBZT ceramics could be of great interest for high performance dielectric materials applications due their giant dielectric constant behavior. 相似文献