Abstract CaCu 3 Ti 4 O 12 (CCTO) electroceramic possesses unusual giant dielectric permittivity up to e = 10 4 at low frequency range and room temperature. CCTO dielectric properties strongly depend on its microstructure therefore it is essential to pay attention to the processing techniques which impact grain size and microstructure. In this work, direct and hybrid microwave solid state synthesis was specifically designed and used for the synthesis of CCTO. The microwave process was also compared to the conventional process which involves usual infrared heating. The structural (XRD) and microstructural (SEM) characterizations indicate that microwave synthesis is particularly efficient to get rapidly pure CCTO powder. The fully automated 915 MHz single-mode microwave cavity used for hybrid synthesis allows a perfect control of the temperature distribution and heating rate. Therefore hybrid microwave synthesis leads to a fine, mono-disperse and practically pure CCTO powder in the range of 300 – 500 nm. The advantages of the hybrid microwave heating method are discussed and compared to the conventional and direct microwave heating processes. From the powders synthesized by the different routes, dense compacts were sintered in air at 1050 °C in a conventional furnace. Microstructural characterizations reveal abnormal grain growth during sintering which levels dielectric properties. All exhibit a giant dielectric constant e > 10 3 at room temperature which decreases drastically to e = 90 at 10 K. Those properties are discussed according to the well-established Internal Barrier Layer Capacitor (IBLC) model.

中文翻译：

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CaCu 3 Ti 4 O 12 陶瓷的直接和混合微波固态合成：微观结构和介电性能

摘要 CaCu 3 Ti 4 O 12 (CCTO) 电瓷在低频范围和室温下具有高达e = 10 4 的异常巨介电常数。CCTO 介电性能在很大程度上取决于其微观结构，因此必须注意影响晶粒尺寸和微观结构的加工技术。在这项工作中，直接和混合微波固态合成被专门设计并用于合成 CCTO。微波工艺还与涉及常用红外线加热的常规工艺进行了比较。结构 (XRD) 和微观结构 (SEM) 表征表明，微波合成对于快速获得纯 CCTO 粉末特别有效。用于混合合成的全自动 915 MHz 单模微波腔可以完美控制温度分布和加热速率。因此，混合微波合成可产生 300 – 500 nm 范围内的精细、单分散且几乎纯的 CCTO 粉末。讨论了混合微波加热方法的优点，并将其与传统和直接微波加热过程进行了比较。从通过不同途径合成的粉末，在空气中在 1050 °C 的常规炉中烧结致密的压块。微观结构特征揭示了烧结过程中异常的晶粒生长，这会降低介电性能。所有在室温下都表现出巨大的介电常数 e > 10 3，在 10 K 时急剧下降至 e = 90。