【作者】 倪磊；

【导师】 陈湘明；

【作者基本信息】 浙江大学 ， 材料学， 2009， 博士

【摘要】 巨介电常数陶瓷材料由于在大容量电容器及电子元件小型化/微型化等方面的潜在应用,而受到了广泛关注。本论文系统地研究了CaCu₃Ti₄O₁₂陶瓷的介电弛豫和巨介电效应的起源,同时探讨了其结构性能调控。首先,借助宽温宽频介电分析仪、X射线光电子能谱（XPS）及超声损失谱等手段,对CaCu₃Ti₄O₁₂陶瓷的介电异常行为进行了深入的研究,探索了其介电弛豫及巨介电常数平台的物理机制与结构根源。CaCu₃Ti₄O₁₂陶瓷存在高温与低温两个类Debye介电弛豫,它们均为遵循Arrhenius定律的热激活过程。氧气氛热处理可显著减弱高温介电弛豫,而低温介电弛豫则几乎不受氧气氛热处理影响。这说明高温介电弛豫起源于缺陷结构,而低温介电弛豫应起源于更本征的因素。Cu²⁺/Cu⁺与Ti³⁺/Ti⁴⁺混价结构可能是低温介电弛豫的主要根源。而CaCu₃Ti₄O₁₂陶瓷中的巨介电常数平台正是低温与高温介电弛豫相互竞争平衡的结果,因此,可通过对低温和高温介电弛豫的调控,增宽或缩短其巨介电常数平台,进而改善其介电性能。用非变价元素取代Cu和Ti,研究其对CaCu₃Ti₄O₁₂陶瓷介电性能的影响规律,对于深入理解CaCu₃Ti₄O₁₂陶瓷巨介电效应的起源并追求其性能调控有着重要的意义。通过Zn置换Cu,采用固相反应法得到了Ca(Cu_1-xZn_x)₃Ti₄O₁₂（x=0,0.05,0.1）陶瓷。随着Zn置换量的增加,Ca(Cu_1-xZn_x)₃Ti₄O₁₂陶瓷的巨介电常数台阶增高。XPS结果显示,Zn置换导致了CaCu₃Ti₄O₁₂陶瓷中Ti³⁺离子的含量显著增加。这意味Ti³⁺/Ti⁴⁺混价结构增强,进而增强了CaCu₃Ti₄O₁₂陶瓷的巨介电效应。Mg置换Cu对CaCu₃Ti₄O₁₂陶瓷巨介电效应的影响规律与Ca(Cu_1-xZn_x)₃Ti₄O₁₂陶瓷的结果类似。即Mg置换Cu导致了CaCu₃Ti₄O₁₂陶瓷中Ti³⁺离子的含量显著增加。这意味Ti³⁺/Ti⁴⁺混价结构的增强,因而增强了CaCu₃Ti₄O₁₂陶瓷的巨介电效应。而当用非变价的Sn置换易变价的Ti时,随着Sn含量的增加,CaCu₃(Ti_1-xSn_x)₄O₁₂（x=0,0.05,0.1）陶瓷的介电常数降低。Ti³⁺离子含量的减少与相应混价结构的减弱是其巨介电效应下降的主要原因。以上非变价元素置换的研究结果进一步验证了晶粒内部由于Ti与Cu变价而形成的混价结构(特别是Ti³⁺/Ti⁴⁺)是导致CaCu₃Ti₄O₁₂陶瓷产生巨介电效应的主要根源。采用低损耗的SrTiO₃对CaCu₃Ti₄O₁₂陶瓷进行改性,得到（1-x）CaCu₃Ti₄O₁₂-xSrTiO₃（x=0.2,0.4,0.6,0.8）复相陶瓷。其介电常数随着x的增加而逐渐减小,这一趋势符合Lichtenecker的对数法则。介电损耗随着x的增大先增加后逐渐减小,当x=0.8时,介电损耗从x=0的0.16减小至0.06。但是介电常数的温度稳定性会随着SrTiO₃的增加而下降。更多还原

【Abstract】 CaCu₃Ti₄O₁₂ giant dielectric constant material has attracted much attention because of its great importance in device miniaturization and the potential application for high-capacity capacitors.In the present thesis,the origin of dielectric relaxation and the giant dielectric response for CaCu₃Ti₄O₁₂ ceramics were systematically investigated,and the modification of dielectric properties was also carried out.In order to explore the physical mechanism and structural origin for the unusual dielectric responses in CaCu₃Ti₄O₁₂ ceramics,the dielectric relaxations at low and high temperatures as well as the giant dielectric constant step were investigated by using broadband dielectric spectrometer,X-ray photoelectron spectroscopy and ultrasonic attenuation measurements.The Debye-like dielectric relaxations in low and high temperature ranges were both thermal activated process.The high-temperatrue dielectric relaxation could be suppressed by O₂-annealing which was suggested to the results of defects,while the low-temperature dielectric relaxation was not affected by O₂-annealing which was induced by mixed-valent structure of Cu⁺/Cu²⁺ and Ti³⁺/Ti⁴⁺. Moreover,the giant dielectric constant step was resulted from the competing balance of the low and high temperature relaxations and the giant dielectric constant step could be modified by optimizing the competing balance between the two dielectric relaxations.Determining the effect of invariable-valent element substitution for the variable-valent element（Cu or Ti） on the dielectric properties should be helpful in deepening the understanding of the giant dielectric response in CaCu₃Ti₄O₁₂ ceramics. The effects of Zn-substitution on the giant dielectric response in CaCu₃Ti₄O₁₂ ceramics were investigated,and Ca(Cu_1-xZn_x)₃Ti₄O₁₂（x=0,0.05,0.1） ceramics were obtained by solid-state reaction.As the content of Zn-substitution increased,the dielectric constant increased together with the obvious increase of Ti³⁺ content.The enhanced giant dielectric response should be primarily caused by the increase of Ti³⁺ ions and the modification of such mixed-valent structure.Investigation of Mg-substitution for Cu was also performed to confirm the results in the Zn-substituted system.As supposed,the giant dielectric response was significantly enhanced by Mg-substitution.The results of X-ray photoelectron spectroscopy analysis confirmed again that the enhanced giant dielectric response primarily originated from the corresponding modification of mixed-valent structure caused by the obvious increase of Ti³⁺ content.The enhanced dielectric response caused by the increase of Ti³⁺ content in the Mg or Zn substituted systems indicated that the variable-valent Ti element should be the primary factor affecting the giant dielectric constant in CaCu₃Ti₄O₁₂ ceramics. Therefore,the effects of invariable-valent Sn substitution for Ti on the dielectric properties were investigated.The dielectric constant of CaCu₃(Ti_1-xSn_x)₄O₁₂（x=0, 0.05,0.1） ceramics decreased with increasing Sn substitution content.The decrease of Ti³⁺ content should be the dominating factor for the depressed dielectric properties.Modification of dielectric properties for CaCu₃Ti₄O₁₂ ceramics by introducing low loss SrTiO₃ phase was investigated.The dielectric constant of （1-x）CaCu₃Ti₄O₁₂-xSrTiO₃（x=0.2,0.4,0.6,0.8） composite ceramics decreased with increasing SrTiO₃ content,which fitted well with Lichtenecker’s logarithmic law.As x increasing,the dielectric loss increased first,and then rapidly decreased.The dielectric loss was 0.06 for x=0.8 which was much smaller than that for x=0 （tanδ=0.16）.The temperature dependence of dielectric constant enhanced with increasing content of SrTiO₃.更多还原