Effect Of Anion Doped CCTO Ceramics On Composition,structure And Properties

The structure of Ca Cu₃Ti₄O₁₂（hereinafter referred to as CCTO）ceramics is perovskite ABO₃type.It is widely concerned because it can maintain a stable high dielectric constant in a wide temperature range.The characteristic of high dielectric constant makes CCTO have great potential in high-density storage and capacitor applications.Therefore,more and more researchers are devoted to the research of CCTO.In this thesis,anion doped CCTO was synthesized by solid phase method,and samples were sintered mainly by air quenching cooling method.The influence of anion doped CCTO ceramics on the composition,structure and properties was systematically analyzed.The results show that:1、The effects of F element on the composition,structure and dielectric properties of CCTO ceramics were studied.Doped Mg F₂had no second phase and changed the microstructure.Within a certain frequency and temperature range,the dielectric property was stable and the loss was reduced.This is because the introduction of Mg F₂enhanced the density,and increased the activation energy of the grain boundary,improved the barrier height of the grain boundary to reduce the oxygen vacancy.The second phase Ca Ti O₃appeared when the Ca F₂doping amount was large,which was due to the reaction of excessive Ca²⁺,Ti⁴⁺and O^2-during the sintering process.The dielectric loss was optimized,and the dielectric loss of 10%doped Ca F₂was significantly reduced to 0.051,which is because the high grain boundary resistance reduced the response between the sample and the electrode,and the increase of the activation energy of the grain boundary increased the height of the grain boundary barrier.In addition,compared with furnace cooling and air quenching,it is found that air quenching can better optimize the dielectric properties.2、The effects of Br on the composition,structure and properties of CCTO ceramics were studied.Doping Cu Br₂produced the second phase Cu O,which is because the excess Cu²⁺reacted with O^2-at high temperature.Compared with pure CCTO,the average grain size decreased.The introduction of Cu Br₂significantly improved the frequency and temperature stability of the dielectric constant,and the dielectric loss decreased significantly.This phenomenon was due to the increase of the density of the sample and the increase of the grain boundary resistance.Doping Cu Br₂also increased the grain boundary and grain activation energy.The introduction of Ca Br₂produced the second phase Ca Ti O₃and reduced the grain size.The improvement of dielectric loss was attributed to the increase of grain boundary resistance and activation energy.Compared with furnace cooling and air quenching with Br element doping,air quenching had higher dielectric stability and lower dielectric loss.3、The influence of co doped F and Br on the dielectric properties was studied.It is found that the temperature and frequency stability of dielectric constant and dielectric loss were improved by adjusting the doping amount of Mg F₂and Cu Br₂.Among them,doping 4%Cu Br₂on the basis of 8%Mg F₂was the most effective way to reduce the loss.At 40°C,the dielectric loss was only 0.024,indicating that co doped anions changed the grain boundary characteristics and effectively improved the dielectric properties.