Study On The Giant Dielectric Properties Of CaCu₃Ti₄O₁₂

The perovskite-like material CaCu3Ti4O12(CCTO) has a giant dielectric constant (-10,000) at low frequencies and the dielectric constant remains almost independent of temperature (100-400K). Such kinds of properties make CCTO a promising candidate for the fabrication of microelectronic devices.As a potential material for microelectronic devices, CCTO has a relatively high dielectric loss, which is disadvantageous for the application. In Chapter 2, in order to look for the approach to optimize the CCTO-based dielectric materials, we synthesized La doped CCTO and studied the dielectric properties. In our results, it was found that La doped CCTO samples still remained high dielectric constant and the dielectric loss was decreased sharply with the La-doping. For example, the dielectric loss value at 1 kHz was decreased from-0.1 to-0.015 by the La-doping from x=0 to x=0.2. It was noted that the CCTO samples with different La doping concentration were sintered under different temperatures to obtain similar grain sizes.In Chapter 3, CCTO ceramic samples sintered at different temperatures were studied by the measurements of internal friction, microstructures and dielectric properties. The temperature dependence of internal friction was characterized by a weak peak at 125-140 K and another or two broad peaks at 200-240 K, depending on the sintering temperature. The mechanical loss peaks were ascribed to the subgrain boundary relaxation and the grain boundary one, respectively, with the aid of the scanning electron microscopy. The detailed dielectric properties, which were controlled by the grain/subgrain boundaries, were shown to be in conformable with the double-barrier-layer-capacitor model. The complex electric modulus analysis revealed unambiguously each contribution to the dielectric constant from the subgrain interiors, subgrain boundaries and grain boundaries, depending on the frequency and temperature. Our result clarified how the dielectric properties, including the dielectric relaxation times, changed with increasing the sintering temperature. It was concluded that grain boundaries mostly played the key role for the giant dielectric constant in CCTO ceramics.The extraordinary dielectric properties make CCTO as a potential capacitor material for dynamic random access memory (DRAM). As we know, thin films offer a unique advantage over bulk materials for the device applications. In Chapter 4, we used chemical solution deposition (CSD) method to prepare CCTO thin films on SrTiO3 substrates without any buffer layer and highly-oriented CCTO thin films were obtained. This work demonstrates that the CSD technique has more advantages for fabricating complex oxide films such as CCTO. Meanwhile, the successful growth of CCTO films on SrTiO3 substrates provides an effective way to develop the related all-perovskite heterostructures for future applications.