改性CaCu_3Ti_4O_(12)及相关陶瓷的结构与巨介电效应
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摘要
巨介电常数材料在电容器及电子元件小型化等方面有着重要的潜在应用。CaCu3Ti4O12是该类材料的典型代表,其巨介电常数具有温度和频率的稳定性,这一独特的介电性能,使其成为了电介质材料研究的热点之一。为了加深对CaCu3Ti4O12巨介电效应物理本质的理解,同时对其介电性能进行调制,系统研究了改性CaCu3Ti4O12及相关陶瓷的结构、微结构以及介电性能。
首先,采用固相反应法制备得到单相的Ca1-3x/2NdxCu3Ti4O12(x=0,0.1,0.2)陶瓷。利用宽温宽频分析仪,对样品进行了系统的介电性能测试。发现Ca1-3x/2NdxCu3Ti4O12(x=0,0.1,0.2)陶瓷存在低温与高温两个介电弛豫,低温介电弛豫属于样品的本征行为,且遵循Arrhenius定律,Cu+/Cu2+和Ti3+/Ti4+混价结构应该是形成该介电弛豫的根源。通过X射线光电子能谱测试,进一步证实了Ca1-3x/2NdxCu3Ti4O12 (x=0,0.1,0.2)陶瓷中Cu离子和Ti离子的变价情况。Nd元素在Ca位进行置换,使得样品中的混价结构发生了改变,从而达到调控其介电性能的效果。
进一步测试不同烧结温度下制备的Ca1-3x/2NdxCu3Ti4O12 (x=0,0.1,0.2)陶瓷的介电性能,发现在Nd元素置换量x=0.1的样品中,陶瓷介电性能对制备条件的敏感性得到了明显的控制。借助扫描电镜观察样品的微观形貌,发现x=0.1样品的微观形貌随烧结温度的改变而发生明显变化,而其介电性能却并未受到微结构变化的影响,始终保持稳定。结构分析表明,在x=0.1样品中,TiO6八面体的倾斜程度最小,Ti-O键长也相应最小,形成了更为紧凑的结构。这一结构特点应是其介电性能制备条件敏感性得到明显控制的原因。
采用固相反应法制备了SrCu3Ti4O12陶瓷,样品中存在少量的SrTiO3和CuO第二相。介电性能分析表明,SrCu3Ti4O12陶瓷在低温下存在一个明显的介电弛豫,该弛豫属于样品的本征行为。另外,将SrCu3Ti4012陶瓷与Ca1-3x/2NdxCu3Ti4012(x=0,0.1,0.2)陶瓷进行比较,发现SrCu3Ti4O12陶瓷的室温电导明显减小。
Giant dielectric constant materials show great potential in the applications for miniaturization of microelectronic devices. CaCu3Ti4O12 is one of the most typical giant dielectric materials. It indicates a giant dielectric constant which keeps temperature and frequency-independent. So far, intensive investigations have been focused on its giant dielectric characteristics. To investigate the origin of the giant dielectric response in CaCu3Ti4O12 and modify its dielectric characteristics, Nd-substituted CaCu3Ti4O12 and related ceramics were prepared and their structure, microstructure and dielectric characteristics were evaluated.
First, Ca1-3x/2NdxCu3Ti4O12 (x=0,0.1,0.2) ceramics were prepared by a solid state reaction process and single-phase structures were obtained for all the compositions. Dielectric characteristics of the present ceramics were evaluated in a broad range of temperature and frequency. Two significant dielectric relaxations were observed in the low and high temperature ranges. The low temperature dielectric relaxation following Arrhenius law, should be ascribed to the more intrinsic mechanisms where the mixed-valent structures of Cu+/Cu2+ and Ti3+/Ti4+ might play important roles. Dielectric characteristics of the present ceramics were modified through modifying the mixed-valent structures by Nd-substitution.
Dielectric characteristics of Ca1-3x/2NdxCu3Ti4O12 (x=0,0.1,0.2) ceramics sintered at various temperatures were also investigated. For samples with x=0.1, the processing dependence of dielectric characteristics was significant controlled. The samples with x=0.1 sintered at various temperatures maintained stable dielectric characteristics even though great changes took place in microstructures. Structure characteristics of the present ceramics were further investigated. Comparing with other compositions, TiO6 octahedron in the samples with x=0.1 tilted less. Correspondingly, Ti-O distance was the smallest. Such compact structure might be responsible for the controlled processing dependence of dielectric characteristics in such sample.
SrCu3Ti4O12 ceramics were prepared by a solid state reaction process, and the SrCu3Ti4O12 major phase combined with minor amount of SrTiO3 and CuO secondary phase were observed in the present ceramics. A significant dielectric relaxation was observed at low temperature which should originate from some intrinsic mechanism. Comparing with Ca1-3x/2NdxCu3Ti4O12(x=0,0.1,0.2) ceramics, the conductivity of SrCu3Ti4O12 ceramics at room temperature was significantly decreased.
首先,采用固相反应法制备得到单相的Ca1-3x/2NdxCu3Ti4O12(x=0,0.1,0.2)陶瓷。利用宽温宽频分析仪,对样品进行了系统的介电性能测试。发现Ca1-3x/2NdxCu3Ti4O12(x=0,0.1,0.2)陶瓷存在低温与高温两个介电弛豫,低温介电弛豫属于样品的本征行为,且遵循Arrhenius定律,Cu+/Cu2+和Ti3+/Ti4+混价结构应该是形成该介电弛豫的根源。通过X射线光电子能谱测试,进一步证实了Ca1-3x/2NdxCu3Ti4O12 (x=0,0.1,0.2)陶瓷中Cu离子和Ti离子的变价情况。Nd元素在Ca位进行置换,使得样品中的混价结构发生了改变,从而达到调控其介电性能的效果。
进一步测试不同烧结温度下制备的Ca1-3x/2NdxCu3Ti4O12 (x=0,0.1,0.2)陶瓷的介电性能,发现在Nd元素置换量x=0.1的样品中,陶瓷介电性能对制备条件的敏感性得到了明显的控制。借助扫描电镜观察样品的微观形貌,发现x=0.1样品的微观形貌随烧结温度的改变而发生明显变化,而其介电性能却并未受到微结构变化的影响,始终保持稳定。结构分析表明,在x=0.1样品中,TiO6八面体的倾斜程度最小,Ti-O键长也相应最小,形成了更为紧凑的结构。这一结构特点应是其介电性能制备条件敏感性得到明显控制的原因。
采用固相反应法制备了SrCu3Ti4O12陶瓷,样品中存在少量的SrTiO3和CuO第二相。介电性能分析表明,SrCu3Ti4O12陶瓷在低温下存在一个明显的介电弛豫,该弛豫属于样品的本征行为。另外,将SrCu3Ti4012陶瓷与Ca1-3x/2NdxCu3Ti4012(x=0,0.1,0.2)陶瓷进行比较,发现SrCu3Ti4O12陶瓷的室温电导明显减小。
Giant dielectric constant materials show great potential in the applications for miniaturization of microelectronic devices. CaCu3Ti4O12 is one of the most typical giant dielectric materials. It indicates a giant dielectric constant which keeps temperature and frequency-independent. So far, intensive investigations have been focused on its giant dielectric characteristics. To investigate the origin of the giant dielectric response in CaCu3Ti4O12 and modify its dielectric characteristics, Nd-substituted CaCu3Ti4O12 and related ceramics were prepared and their structure, microstructure and dielectric characteristics were evaluated.
First, Ca1-3x/2NdxCu3Ti4O12 (x=0,0.1,0.2) ceramics were prepared by a solid state reaction process and single-phase structures were obtained for all the compositions. Dielectric characteristics of the present ceramics were evaluated in a broad range of temperature and frequency. Two significant dielectric relaxations were observed in the low and high temperature ranges. The low temperature dielectric relaxation following Arrhenius law, should be ascribed to the more intrinsic mechanisms where the mixed-valent structures of Cu+/Cu2+ and Ti3+/Ti4+ might play important roles. Dielectric characteristics of the present ceramics were modified through modifying the mixed-valent structures by Nd-substitution.
Dielectric characteristics of Ca1-3x/2NdxCu3Ti4O12 (x=0,0.1,0.2) ceramics sintered at various temperatures were also investigated. For samples with x=0.1, the processing dependence of dielectric characteristics was significant controlled. The samples with x=0.1 sintered at various temperatures maintained stable dielectric characteristics even though great changes took place in microstructures. Structure characteristics of the present ceramics were further investigated. Comparing with other compositions, TiO6 octahedron in the samples with x=0.1 tilted less. Correspondingly, Ti-O distance was the smallest. Such compact structure might be responsible for the controlled processing dependence of dielectric characteristics in such sample.
SrCu3Ti4O12 ceramics were prepared by a solid state reaction process, and the SrCu3Ti4O12 major phase combined with minor amount of SrTiO3 and CuO secondary phase were observed in the present ceramics. A significant dielectric relaxation was observed at low temperature which should originate from some intrinsic mechanism. Comparing with Ca1-3x/2NdxCu3Ti4O12(x=0,0.1,0.2) ceramics, the conductivity of SrCu3Ti4O12 ceramics at room temperature was significantly decreased.
引文
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