CHANG Yiwen, REN Ruikang, YAO Zhongying, CUI Ge, REN Jiale, ZHANG Hongbo, KUANG Fenghua

(Ceramics Science Institute, China Building Materials Academy Co., Ltd., Beijing 100024, China)

Extended Abstract:[Significance] Dielectric properties of passive electronic components are highly connected with their capacitive properties. For a parallel plate capacitor, the capacitance increases as dielectric materials are inserted. Giant dielectric ceramics usually have dielectric contant over 10⁴, which are promising capacitive materials. Therefore, higher energy storage capability and higher energy density could be achieved, thus offering more powerful integrated circuit system and maintaining the developing rate defined by Moore's Law. Perovskite structured materials have been most widely and intensively studied, due to their outstanding dielectric properties. However, since the current perovskite structured materials have temperature sensitivity, the limited level of dielectric constant and even toxicity of those containing lead, it is necessary to further develop perovskite-like structure materials.[Progress] Three typical modules are introduced with representing materials. The conventional perovskite materials, such as BaTiO₃ (BTO), possess spontaneous polarization. As indicated in the Clausius-Mosotti equation, permittivity of material is directly propertion to its polarizability. However, the polarizability of BTO is highly temperature sensitive as their intrinsic Curie temperature limitation, corresponding to structure transforming. The polarizability is generated due to the offset of the central Ti ion with respect to the O ions. Therefore, it is necessary to extend the temperature window for tetrahedral structure so as to maintain high permittivity. In this article, representive research about achieving the aforementioned task will be introduced. Moreover, various other strategies, such as substitution with donor or acceptor ions and introduction of oxygen vacancy, to increase dielectric properties, will be elaborated. Perovskite-like structured CaCu₃Ti₄O₁₂(CCTO) is introduced due to its giant dielectric constant and achievable temperature stability. In this case, internal barrier layer capacitor (IBLC) will also be summarized. The IBLC model could be simply concluded as a combination of conductive grain and insulating grain boundary. It is started from the escaping of oxygen atom during heat treatment at high temperatures, causing loss of oxygen in grains and hence the reduction of Ti4⁺ and Cu2⁺ to to Ti³⁺ and Cu⁺ by obtaining electron. Meanwhile, a copper-rich phase is formed at grain boundary during cooling, since copper atom has strong affinity to oxygen. Therefore, the model to describe the effects of copper-rich phase on dielectric properties will be introduced. Then, the core-shell structure of CCTO family is presented. Lastly, the escape of oxygen from the material is discussed. Other ferroelectric materials with perovskite structure but low performance are also introduced, such as SrTiO₃ (STO), with cubic structure at room temperature. Although they have no spontaneous polarization, they could have high dielectric constant. They can be used to dope perovskite ceramics, thus generating spontaneous polarization and eventually resulting in colossal permittivity. Also, colossal permittivity could be achieved by making difference in conductivity through ion doping.[Conclusions and Prospects] Perovskite and perovskite-like structures giant dielectric constant materials have drawn strong attention, because of their high dielectric constant and possibility of doping. Theoretical models on spontaneous polarization, IBLCs and mixing effects are introduced, with typical ceramics, as BaTiO₃, CCTO and SrTiO₃. To be summarized, BTO has high element affinity and acceptable dielectric properties, but limited for applications owing to their temperature dependent permittivity. CCTO has shown giant dielectric constant, while the dielectric loss cannot be ignored. A mixture model could be achieved by incorporating with STO, since it could be employed to suppress the dielectric loss of CCTO ceramics.

Key words: giant dielectric ceramic; dielectric constant; spontaneous polarization; IBLC