Design Of Automatic Measurement System And Research Of CaCu₃Ti₄O₁₂ Dielectric Properties

Due to giant-dielectric constant, temperature stability, and one-step synthesized under normal conditions etc., CaCu3Ti4O12become the focus of giant dielectric materials. However, as the complexity of the interface problems and limitations of research methods, origin of giant dielectric constant of CaCu3Ti4O12is still controversial. In this paper, we summarized the common equivalent circuits of dielectric materials. Based on the circuits, we simulated the frequency-spectrum and temperature-spectrum. According to the new phenomena of ceramic interface and effects of relaxation recent observed in CaCu3Ti4O12, we used impedance spectroscopy, dielectric temperature spectrum and the "capacitance-voltage method" and other measurement methods to research dielectric properties of the defect and deep level traps and contributions to CaCu3Ti4O12ceramic dielectric constant. We try to build interface energy band model to make theoretical explanation of the dielectric properties of CaCu3Ti4O12. This paper made a more systematic study of giant dielectric constant of CaCu3Ti4O12from defect, deep level traps and other new initial point which provides new clues to the origin of the dielectric properties of CaCu3Ti4O12.The main contents and conclusions include:Firstly, we set up the Automatic Measurement System of dielectric. The system is composed of WK-6500B impedance analyzer, Lakeshore332temperature controller and Janis closed cycle cryogenic refrigeration system. Impedance analyzer, temperature controller connected to a computer using the USB-488card. Based on LabVIEW, we designed software to control instruments, and data collected and processed automated. The system can automatically achieve data acquisition and real-time display curve of Z-T, Z-ω,C-V. By software processing, the system eliminates the impact of distributed parameters of wire in the higher frequencies, so that the data are true and reliable.Secondly, as the equivalent circuit is a common method of dielectric, this paper summarizes the basic and common equivalent circuit of dielectric materials. From the frequency-spectrum and temperature-spectrum, we made a in-depth and systemic study which was the foundation of temperature Spectral Properties of CCTO.Finally, we study the characteristics of the temperature spectral and capacitance-voltage CaCu3Ti4O12prepared in different atmosphere. The results suggest that the three platforms of the dielectric temperature spectra are from the grain, grain boundary and the oxygen vacancy trap in grain boundary. The activation energy of the grain is related with the sintering atmosphere, variable-range-hopping conductivity and polaron caused by the oxygen vacancy is the main origins of the conductivity and capacitance of the grains. The activation energy of oxygen vacancy traps is about0.46eV, which is nearly independent of sintering atmosphere. Because of the presence of oxygen vacancy trap, capacitance will increase as voltage.