【作者】 张磊；

【导师】 陈湘明；

【作者基本信息】 浙江大学 ， 材料科学与工程， 2008， 硕士

【摘要】 巨介电常数材料在电子元件小型/微型化以及高能量密度存储等方面有着巨大的应用前景。为探索巨介电常数材料新体系,本论文系统地研究了0.4Li_0.05Ni_0.95O/0.6SrTiO₃复相陶瓷与LuFeO₃陶瓷的结构与巨介电效应,得出了如下主要结论:通过固相烧结法获得了导电相和绝缘相共存的xLi_0.05Ni_0.95O/（1-x）SrTiO₃复相陶瓷。在xLi_0.05Ni_0.95O/（1-x）SrTiO₃的复相陶瓷的各个组分中,0.4Li_0.05Ni_0.95O/0.6SrTiO₃陶瓷的介电性能最为理想,具有较大的介电常数和相对较低的介电损耗。在0.4Li_0.05Ni_0.95O/0.6SrTiO₃陶瓷中存在低温下,中温下及高温下3个频率色散型介电弛豫。首先用Skanavi模型来解释0.4Li_0.05Ni_0.95O/0.6SrTiO₃中低温下介电弛豫,即由于空气中烧结的钙钛矿结构的陶瓷会有一定量的Ti⁴⁺转变成Ti³⁺,热激活过程可以让电子在之间Ti⁴⁺与Ti³⁺之间跃迁,从而在低温部分产生一个具有频率色散的弛豫峰;中温区的介电常数在氧气氛处理后被抑制,所以可以推断该温度区域的介电弛豫应当与点缺陷的作用密切相关,即空气环境下烧结过程中可能产生的氧空位引起的介电弛豫;最后高温的介电弛豫应当与晶界效应有关,既导电相之间的相互接近是造成介电常数增大的主要原因,导电颗粒Li_0.05Ni_0.95O和SrTiO₃基体在界面处形成异质结构而产生空间电荷区,空间电荷区阻碍了载流子在界面附近的迁移使其无法及时响应外电场的变化而出现介电弛豫。采用传统固相反应烧结法制得LuFeO₃致密陶瓷并进行了介电性能评价。LuFeO₃陶瓷中存在低温下巨介电常数台阶及高温下类弛豫铁电体行为两个频率色散型介电弛豫,且这两个介电弛豫均符合Arrhenius热激发定律。高温区介电弛豫可由氧气氛处理几乎完全消除,因而属于氧空位相关的缺陷有序诱导的非本征弛豫行为;而低温区巨介电常数台阶对氧气氛处理不敏感,基于LuFe₂O₄中低温巨介电效应起源于异价Fe离子有序导致的电子铁电性的推断,采用修正的德拜方程进行分析,得到LuFeO₃的低温弛豫的激活能,发现该激活能与LuFe₂O₄的低温弛豫激活能相差不大,所以作者推断低温的弛豫也是由于Fe²⁺与Fe³⁺电子跃迁,之后作者通过XPS分析给出了LuFeO₃中Fe²⁺与Fe³⁺的比例,提出异价Fe离子有序导致的电子铁电性为LuFeO₃低温介电行为的本征物理起源的最终结论。更多还原

【Abstract】 Giant dielectric constant materials have great potential in application of miniaturization of electronic devices and high density energy storage.In the present work,the structure and giant dielectric response have been systematically investigated in 0.4Li_0.05Ni_0.95O/0.6SrTiO₃ composite ceramics and LuFeO₃ ceramics.The following primary results and conclusions have been obtained.Novel high dielectric constant composite materials were prepared by incorporating the dispersed Li_0.05Ni_0.95O particles into SrTiO₃ matrix.A dielectric constant in the order of 10⁴ was obtained in the composite with 40mol%Li_0.05Ni_0.95O. In 0.4Li_0.05Ni_0.95O/0.6SrTiO₃ composites,the low-temperature dielectric relaxation ascribed to the e,lectron hoping between Ti³⁺and Ti⁴⁺because of the processing of thermal activation.The medi-temperature dielectric relaxations is significantly suppressed by the O₂-annealing,while the low and high-temperature dielectric relaxation is just affected slightly.Since there is no crystal structure change,the medi-temperature dielectric relaxations is deeply related with the oxygen vacancy. There a significant increasing for the dielectric constant in the high-temperature,as we know,the separated conducting particles approach to each other,which lead to the thinner of the small capacitors between two semi-conducting particles,and hence the higher effective dielectric constant of the composites.Hetero-structures formed in the interfaces of Li_0.05Ni_0.95O and SrTiO₃ during the sintering progress,which hindered the movements of oxygen vacancies near the interfaces,leading to a dielectric relaxation at high temperatures.The dielectric properties of dense LuFeO₃ ceramics prepared by solid state sintering process have also been characterized.An giant dielectric constant step is observed in LuFeO₃ ceramics,and there is a frequency-dependent critical temperature where the dielectric constant drops quickly when the sample is cooled down through there.A very high relaxor-like dielectric peak with strong frequency dispersion is also observed in the higher temperature range.The high-temperature dielectric relaxations is significantly suppressed by the O₂-annealing,while the low-temperature dielectric relaxation is just affected slightly.As the results,the dielectric constant peak is reduced significantly,and the dielectric constant step is extended and the magnitude is decreased.Since there is no crystal structure change,the only possible structural change is the reduced oxygen vacancy concentration and the subsequent reduction of Fe²⁺content to keep the electric compensation.These results confirm the relaxation peaks are observed on the curve of dielectric loss vs temperature.According to analysis of XPS,the estimated ratio of Fe²⁺:Fe³⁺is about 1:2.The presence of Fe²⁺ ions in the LuFeO₃ ceramics is compensated by the presence of oxygen vacancies. The mixed-valance structure of Fe²⁺/Fe³⁺offers the possibility of charge ordering,and subsequently offers the structure origin for the low-temperature relaxor-like dielectric behavior and the electronic ferroelectricity.The high-temperature dielectric relaxation is deeply related to the oxygen vacancies.更多还原