共查询到16条相似文献,搜索用时 62 毫秒
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根据弛豫铁电材料在相变区域的介电弥散行为和玻璃化 液体材料在过冷状态下黏度与温度的行为所共同满足的Vogel-Fulcher 函数关系, 分析了施主替代钛酸钡系列陶瓷的缺陷补偿原理, 通过引入玻璃化液体的构型熵概念, 研究了弛豫铁电材料中钛阳离子缺陷作用势的温度关系, 得到了如下结论: 施主掺杂含量的增加导致了无序度的增加, 钛离子缺陷浓度的增大和平均极性区域尺寸的减小; 在构型熵满足Vogel-Fulcher 函数关系的条件下, 温度越低, 钛离子缺陷作用的范围越大, 极化区域也越大. 缺陷作用的范围随温度的变化导致了弛豫铁电材料的弥散性. 温度下降到一定程度, 冻结效应发生, 介电弥散现象消失. 相似文献
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运用极限的概率模型和Ngai的耦合概念,导出了聚合物介电弛豫的KohlrauschWilliamsWatts(KWW)方程(t)=exp[-(tτ)β],证明了弛豫的能量势垒为Ngai的活化能量E.由β的温度关系推出了适用于聚合物的WilliamsLandelFerry方程和过冷液体的VogelTammannFulcher方程,特别是提出了由聚合物的β(T)可导出弛豫时间的温度函数.认为KWW行为由单个衰减单元产生,幂律行为由局部区域内多个衰减单元的协同衰减造成.将活化能量E引入热刺激电流公式,得到了可通过改变升温速率测量β(T)的公式.
关键词:
介电弛豫
聚合物
极限概率模型
KWW方程 相似文献
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弛豫铁电体铁电相变的介电弛豫性涉及外来离子掺杂或原有离子的有序排列, 需要深入理解和有效统一的表征. 针对高浓度施主掺杂在晶粒中产生金属离子缺位, 降低居里温度并引起钛酸钡基铁电材料扩散相变的现象, 分析了高斯型的杂质分布、居里温度分布和金属离子缺位分布的等效对应关系, 得出了在介电常数峰值温区金属离子缺位浓度随温度降低而作用增大的结论, 认为金属离子缺位引起的单极电荷在电场作用下的跳跃运动有可能引起介电弥散和介电损耗. 提出了用‘弛豫度’表征铁电弛豫程度. 相似文献
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基于一定浓度的杂质会在钛酸钡型铁电体中导致键能与配位数的高斯型分布原理,利用键能与配位数起伏模型导出了介电峰温与测量频率的关系.当键能和配位数的相对起伏接近时,其关系呈现出一般弛豫铁电体所普遍具有的Vogel-Fulcher函数形式,且冻结温度仅与键能的相对起伏和激活能有关.并由此解释了低掺杂浓度下杂质均匀分布导致弥散性的机理和超过临界浓度时的弛豫铁电性的机理.同时提出,杂质替代对畴的形成和生长所产生的强烈抑制作用及微畴化是实现键能起伏与配位数起伏一致的来源. 相似文献
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介电弥散和介电隔离率的温度非线性关系是弛豫铁电体的主要特征. 通过对掺杂成分以线性梯度递减的核壳结构进行热力学函数分析, 认为核壳结构能够在低温区保持较高的介电常数, 但不能导致介电隔离率与温度的非线性关系. 通过对不同浓度掺杂的铁电体扩散相变的比较, 认为掺杂浓度会影响晶粒掺杂成分的不均匀性, 在较宽的分布条件下会导致介电隔离率与温度的非线性关系. 因而在介电常数的峰值温度区域, 顺电相与铁电相的晶粒共存. 温度变化会影响两相比例及铁电畴的变化, 从而导致弛豫铁电体的介电弥散性. 核壳结构会增大介电弥散性. 铁电陶瓷的掺杂物种类、掺杂物浓度和烧结温度均会影响核壳结构的成分不均匀性和介电弥散性. 相似文献
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Monte Carlo simulation on dielectric relaxation and dipole cluster state in relaxor ferroelectrics
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The Ginzburg--Landau theory on ferroelectrics with random field induced by dipole defects is studied by using Monte Carlo simulation, in order to investigate the dipole configuration and the dielectric relaxation of relaxor ferroelectrics. With the increase of random field, the dipole configuration evolves from the long-range ferroelectric order into the coexistence of short-range dipole-clusters and less polarized matrix. The dipole-cluster phase above the transition temperature and superparaelectric fluctuations far below this temperature are identified for the relaxor ferroelectrics. We investigate the frequency dispersion and the time-domain spectrum of the dielectric relaxation, demonstrating the Vogel--Fulcher relationship and the multi-peaked time-domain distribution of the dielectric relaxation. 相似文献
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S. Kamba D. Nuzhnyy O. Tkáč B. Malič M. Kosec J. Petzelt 《Phase Transitions》2013,86(11-12):1005-1012
Polar phonons in infrared spectra of (Pb0.88La0.08 0.04)(Zr0.65Ti0.35)O3 ceramics and thin films exhibit similar behaviour. Each phonon allowed in perfect cubic lattice is split not only below the Burns temperature T B = 620 K, where it can be explained with breaking of cubic symmetry in polar nanoclusters, but also above T B. We explain it with two chemical species at both A and B perovskite sites. The E component of the soft mode remains heavily damped at all temperatures and its frequency near 35 cm?1 is almost temperature-independent. The A1 component of the soft mode remarkably hardens below T* ≈ 500 K from 50 to 85 cm?1 and moreover a new mode activates in IR spectra below 300 K at frequencies between A1 and E soft modes. Based on comparison with other relaxors, we conclude that such behaviour is general for all relaxor ferroelectrics with perovskite structure. 相似文献
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The local structure of Ba(Ti0.70,Sn0.30)O3 (BSnT) was investigated using micro Raman spectroscopy from 80 to 500 K, which indicated three local phase sequences. The dielectric spectroscopy studies illustrated freezing of polar nano‐regions (PNR) below 95 K, merger of frequency dispersion at 220 K, and the origin of polar nano‐regions at 482 K. The temperature evolution of Raman spectra, basically integrated intensity, indicates non‐ergodic relaxor phase below 100 K, mature ergodic phase between 100 and 200 K, and the existence of ergodic polar clusters until 450 K, and above paraelectric phase. The observation of local phase sequences by Raman spectra are in agreement with dielectric spectroscopy anomalies. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
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Ceramic KBiScNbO6 compound was synthesized for the first time. X‐ray diffraction analysis revealed that at room temperature the samples consist of a mixture of the perovskite and pyrochlore phases. The dominant phase is the perovskite one. This phase can be described as distorted pseudocubic Pm3m structure with unit‐cell parameter ac = 4.069 Å. Rhombohedral distortion leading the polar R3m phase is assumed to be one of possible structural distortions. Dielectric measurements of the compound under study demonstrated anomalies associated with relaxor ferroelectric behavior (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
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J. Kroupa V. Bovtun D. Nuzhnyy M. Savinov P. Vanek S. Kamba 《Phase Transitions》2013,86(11-12):1059-1064
We investigated the grain size effect on the high temperature behaviour of PMN-35PT ceramics around the tetragonal–cubic phase transition using second harmonic generation (SHG) and dielectric spectroscopy. Our data revealed coexistence of the first-order ferroelectric phase transition and relaxor behaviour in the coarse grain (grain size ~4 µm) µ_PMN-35PT. The phase transition is hindered and relaxor features prevail in the fine grain (grain size ~150 nm) n_PMN-35PT ceramics. Effect of the grain-size reduction on the SHG and dielectric response could be attributed to stabilisation of intermediate domain configurations between the frozen polar nanoclusters and large ferroelectric domains and to the enhanced stability of polar nanoclusters in the fine grain ceramics. 相似文献
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用改进的溶胶凝胶(sol-gel)法逐层制备钛酸锶钡(Ba0.6Sr0.4TiO3, BST)薄膜,研究中间热处理(preheating,PT)对薄膜结构及介电性能的影响.X射线衍射(XRD)表明,BST薄膜主要沿(110)方向生长,对应立方钙钛矿结构,PT使晶化增强.X射线光电子能谱(XPS)表明,PT促使表面非钙钛矿结构向钙钛矿结构转变.原子力显微镜(AFM)和介电性能测试表明,随着PT频次的增加,薄膜形貌改善,表面粗糙度降低,介电调谐
关键词:
中间热处理
高调谐
溶胶凝胶法
钛酸锶钡 相似文献