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掺镧钛酸钡陶瓷晶界的再氧化 总被引:8,自引:3,他引:5
掺La的BaTiO3陶瓷在H2和Ar(体积比1:99)的还原气氛下烧结后,在氧分压p(CO2)-260Pa的气氛(Ar和O2的混合气体)下进行氧化,测量了吸氧量不同时的复阻抗图谱,研究了再氧化过程中晶粒和晶界的吸附氧对电阻率的影响。结果表明:在还原气氛下烧结可以扩展有效施主掺杂浓度的范围,通过晶粒的异常生长.制备出高施主掺杂量(10%,摩尔分数)的半导性BaTiO3陶瓷。再氧化过程中,随氧化温度的升高(1017~1380℃),晶界吸附氧的量增大,晶界处的晶界势垒包括两部分:外部晶界吸收氧原子充当表面受主态;内部晶界在氧化过程中被氧化形成正离子空位(Ti空位)充当受主态.从而提高了受主态密度,导致样品的正温度系数电阻效应增强。 相似文献
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涂覆扩散型SrTiO3基陶瓷晶界叠加势垒模型 总被引:5,自引:0,他引:5
根据涂覆扩散型SrTiO3基陶瓷的晶界结构特点,势扩散分布与压敏电压的关系,提出了两晶粒之间的n-n‘-i-n’-n的物理模型以及晶界叠加势垒模型。以此模型推导晶势垒高度与扩散层深度的公式,对实验数据,晶界势垒高度及其在晶界的分布进行了模拟,其结果明确地说明了摭用层浓度增加,晶界势垒高度提高从而VlmA提高、并证明了叠加势垒模型比Schottky势垒模型更加合理。 相似文献
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n—型SrTiO_3半导瓷的压敏特性 总被引:1,自引:0,他引:1
采用一次烧成法研制成了具有压敏特性的n—型SrTiO_3晶界层电容器。n—型SrTiO_3半导瓷的压敏特性起因于氧化保温阶段晶粒表面的吸附氧、锶空位V_(sr)”(或V_(sr)')及掺杂的受主体Cu~+对Sr~(2+)位的不等价取代所组成的晶界内过剩负电荷。讨论了La_2O_3/CuO在0.5~2.5、氧化保温时间τO_2在10至25分钟时对SrTiO_3半导瓷的非线性系数a和V_(1mA/mm)的影响。 相似文献
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SrTiO3陶瓷晶界层电容器材料的晶界研究Ⅰ.晶界结构 总被引:1,自引:1,他引:1
利用高分辨电镜研究了低温一次烧结SrTiO_3陶瓷晶界层电容器材料的晶界结构,发现在西晶粒间存在着4种典型的晶界类型。通过构筑晶界形成的结构模型,揭示了两晶粒间晶界形成的特征,认为两晶粒间晶界相的形成既与两晶粒间的液相成份和杂质组成有关,亦与两晶粒的相对取向有关。此外,还与两次烧结SrTiO_3陶瓷晶界层电容器材料的晶界结构作了比较。 相似文献
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In和Nb共掺杂TiO2(INTO)陶瓷在100 kHz以下的巨大介电常数源于内部势垒层电容效应。根据这种电容效应,通过增加晶界对介电性能的贡献来降低其低频介电损耗。因此,将La掺杂到INTO陶瓷中,通过细化晶粒并增加晶界数量来降低陶瓷制备过程中的能耗。结果表明,La掺杂减小了INTO陶瓷的晶粒尺寸,增加了陶瓷中晶界的数量,并且陶瓷中析出LaNbTiO6二次相,在陶瓷晶粒之间形成高阻态的相界,降低陶瓷的低频介电损耗,优化了陶瓷介电常数的频率稳定性。 相似文献
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Varistor Performance of ZnO-Based Ceramics Related to Their Densification and Structural Development
Maria Cecilia S. Nobrega Walter A. Mannheimer 《Journal of the American Ceramic Society》1996,79(6):1504-1508
Electrical potential barriers are often observed in ZnO-based ceramics. Earlier studies on ZnO photoconduction have shown that the narrow regions, where the sintered grains have grown together, control the resistance of the entire sample. In those regions, the surface/volume ratio is sufficiently high for the acceptor concentration (which occurs because of adsorbed oxygen) to exceed the donor concentration inside the ZnO grains. More recent works have shown that Schottky barriers result from interface states because of the chemisorbed oxygen ion at the ZnO-ceramic grain boundaries. The work reported in this paper involves the relationship between the densification of the microstructure and the varistor performance of ZnO ceramics. The emphasis of densification percentage as an indicator of the degree of sintering shows the desirability of continuity across ZnO grain boundaries, without the presence of voids or films of second phases, in optimizing varistor behavior. The effect of oxygen partial pressure on the development of varistor microstructure and electrical properties, as well the kinetics of grain growth, during the sintering process have been determined and are discussed. 相似文献
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ZnO varistors with and without ZnO crystalline seeds have been prepared through conventional ceramic processing. Their electrical nonuniformity has been carefully examined using microcontact measurements of single grain boundaries, current-voltage ( I-V ) characteristics, and dielectric temperature spectra of bulk samples. Three types of grain boundaries with barrier heights of 0.2, 0.5, and 0.6 eV are identified in a ZnO varistor with the seeds, while only one with 0.4 eV barrier height has been found in a varistor without the seeds. Using a computerized electric circuit simulation, the influence of boundary thickness and grain size on I-V characteristics of varistor is investigated extensively. The simulated results show that currents passing across various grain boundaries are quite different. For a model varistor (1 × 1 × 1 mm3 ) with different grain size, a good agreement between measured data and simulated curves can be achieved. 相似文献
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为了研究ZnO压敏电阻组成中非化学配比氧化物对ZnO压敏电阻导电性能的影响,采用在不同氧分压条件下烧结样品以研究其烧结行为。结果表明:ZnO晶粒的电导率对数与氧分压对数成线性关系;斜率为-1/4;间隙Zn原子以一价电离Zni形式存在。由于CoO,MnO和NiO阳离子空位氧化物多偏析于晶界,晶界处氧的增加有利于降低压敏电阻漏电流,烧结时间从2h延长到8h,漏电流从5μA/cm^2降到3.6μA/cm^2。波谱分析表明:掺杂氧化物在晶界处都有偏析,ZnO晶粒中掺杂原子混溶比例不完全与掺杂阳离子半径相关。 相似文献
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《Journal of the European Ceramic Society》2014,34(8):1963-1970
The varistor effect in ZnO ceramics is triggered by the behavior of the grain boundaries. To understand this effect in detail we have electrically characterized individual grain boundaries. Here, we apply the micro four-point probe method to measure the electrical properties of individual grain boundaries in a polycrystalline ZnO varistor ceramic with a mean grain size of 10 μm. The investigation revealed a wide spread in electrical properties, like nonlinearty exponents from 10 to 150 and switching voltages from 2.3 V to 3.6 V. 相似文献
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Fe_2O_3掺杂对ZnO-Pr_6O_(11)系压敏电阻材料电学性能的影响 总被引:1,自引:1,他引:0
通过烧结法制备了Fe2O3掺杂的ZnO–Pr6O11压敏电阻材料,研究了Fe2O3掺杂量对ZnO–Pr6O11系压敏电阻材料电学性能的影响。实验表明:当Fe2O3掺杂量小于0.005%(摩尔分数,下同)时,ZnO–Pr6O11系压敏电阻材料的非线性系数和压敏电压随Fe2O3掺杂量增大而逐渐提高。当Fe2O3掺杂量为0.005%时,压敏电压达到最大值571V/mm,非线性系数达到最大值26。当Fe2O3掺杂量大于0.005%时,非线性系数和压敏电压均急剧下降。过量Fe2O3使ZnO压敏电阻材料非线性下降的主要原因是:Fe元素偏析在晶界处,提供额外载流子降低了晶界电阻率,同时晶界处PrFeO3相的堆积会破坏晶界结构,从而影响压敏电阻材料的电学性能。 相似文献
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Li‐Then Mei Hsing‐I Hsiang Wei‐Hung Hsu 《Journal of the American Ceramic Society》2014,97(12):3918-3925
Bi2O3 was added into nickel copper zinc niobium ferrite and treated with different thermal processes to change the grain‐boundary chemical composition. The relationship between the grain‐boundary composition and varistor properties were investigated using scanning electron microscopy, transmission electron microscopy, energy dispersion spectroscopy, and X‐ray photoelectric spectroscopy. The experimental results show that Bi2O3 reacts and diffuses into the spinel ferrite grain, forming bismuth iron compounds, causing the spinel ferrite chemical composition near grain boundary becomes iron deficient. The Fe deficiency spinel ferrite near the grain boundary then changes into p‐type conduction. The annealing process after sintering improves the bismuth oxide diffusion and chemical reaction near the grain boundary, which can increase the grain‐boundary resistivity. The n‐type semiconductive grain interior and p‐type spinel ferrite near the grain‐boundary combination can form a double Schottky barrier, leading the specimen to exhibit varistor properties. A multifunctional varistor‐magnetic material with a nonlinear coefficient of 10 and initial permeability of about 225 at 10 MHz can be successfully fabricated by sinteringNi0.2881Cu0.1825Zn0.4802Nb0.0096Fe2.0168O4 ferrites added with 5 mol% Bi2O3 sintered at 950°C, then annealed at 650°C for 1 h. 相似文献
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Electrical and hydrogen reduction enhances kinetics in doped zirconia and ceria: I. grain growth study
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The kinetics of mass transport is central to ceramic processing and device stability. In this work, the effect of electrical and hydrogen reduction on the grain growth behavior of doped zirconia and ceria has been investigated. Faster grain growth has been observed under reducing conditions in all cases. The results firmly establish that a depressed local oxygen potential can enhance cation kinetics in fluorite‐structured oxide ceramics. Meanwhile, a large electrical current can generate a sharp, spatially varied oxygen potential profile, creating a graded microstructure with a dramatic grain size transition across the length of the sample. 相似文献
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S.M. Gheno R.H.G.A. Kiminami M.R. Morelli P.I. Paulin Filho 《Journal of the European Ceramic Society》2010,30(2):549-554
The well known metal-oxide varistors (MOVs) are polycrystalline electronic ceramic materials whose electrical behavior is dominated by their grain boundaries. ZnO-based varistors are MOVs whose nonlinear properties are characterized by an electrical resistance that decreases as the applied voltage field increases. The objective of this work was to image the Schottky barriers in ZnO doped with 0.5 mol.% Cu and x wt.% G (G is a frit and x = 0, 1 and 5%). The frit is used to form a glassy insulating layer around grain boundaries. Samples were sintered at 850 °C and the microstructures were analyzed by atomic force microscopy (Nanoscope IIIa, VEECO Instruments). Electric force microscopy (EFM) experiments were conducted to map the electric field distribution on the surface of CuO–ZnO-based varistors. The formation of Schottky barriers was observed and their width measured. 相似文献
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Guo‐Zhong Zang Huan‐Huan Liu Jian‐Fei Lei Xiao‐Fei Wang Li‐Ben Li Jing‐Xiao Cao Guo‐Rong Li 《Journal of the American Ceramic Society》2015,98(7):2112-2116
SnO2–Zn2SnO4 composite ceramics with a colossal dielectric permittivity and varistor behavior are prepared by traditional ceramic processing. By increasing bias voltage from 0 to 10 V at a low frequency (~103 Hz) and at room temperature, the relative permittivity decreased rapidly from about 20 000 to several thousand, whereas the radius of the semicircle in the complex impedance decreased and the tail gradually disappeared. However, the peak height and the position of the imaginary part of the complex modulus in the spectra were independent of the applied DC voltage. The slope deduced from the bias voltage‐dependent straight lines of the double‐logarithmic imaginary permittivity spectra were constant with a value of ?0.63 at high frequencies and they decreased to ?1 at low frequencies. The results strongly indicate that a number of weekly trapped charges existed in the ceramic bulk. From the temperature‐dependent dielectric and electric modulus spectra, the trapped charge activation energy was about 0.32 eV, which may be associated with the oxygen vacancies. Based on the results, a modified equivalent circuit related to the colossal dielectric permittivity and varistor properties was proposed, in which a Warburg impedance was added in parallel with the resistance and capacitance. 相似文献