Study Of Medium Temperature Sintering Of X9r Batio₃-based Ceramics

As electronic information terminal equipments are applied into the high temperature environment of extreme heat, MLCCs adapting to the hash working condition, become urgent need now. BaTiO₃ has an excellent performance of dielectric properties, and BaTiO3-based dielectric ceramic capacitors with wide-raged working temperature, is the research direction of the ceramic capacitors. Barium titanate is a kind of important ferroelectric phase crystal materials, however purifed-BaTiO₃ has abnormal dielectric constants at Curie peak around 130℃, which makes dielectric properties worse sharply and restricts the application in the high temperature.Through proper-doping and control of preparing technology, BaTiO3-based dielectric material can be obtained with a fine dielectric properties. The effect of initial size of medium and sintering-temperature to BaTiO3-based dielectric ceramics is discussed especially in the paper. According to the T-C curve and SEM morphology of dielectric ceramic sample, the role of powder size and sintering steps to BaTiO3-based dielectric ceramic is analysed deeply, and a kind of dielectric ceramic meeting the specification of EIA X9R is prepared.The dielectric property of ceramic is greatly influenced by the initial size of medium size, and different particle sizes of powder is prepared by different milling-balls and variant milling time in the paper. In the experiments, it is showed that the dielectric properties of the system is greatly influenced by the initial powder size . With the decrease of powder size, the surface energy of particle is enhanced and the amount of surface atoms will also be increased, which will be active due to inadequate atom and high surface energy.Under the condition of invariable sintering temperature,the growth of BaTiO₃ grain can be more effectively restricted with smaller specific surface area and smaller powder size ,and fine-grain effect can be produced.More shell-core grain can be formed with the doping elements distributing into BaTiO₃ particles greatly, and the volume of ferroelectric phase core is increased while the volume of shell decreased. The dielectric property of doping BaTiO₃ is enhanced with the Curie peak flat and a slowing rate of dielectric constant. At the same time, the ratio of core to shell is increased with the decrease of BaTiO₃ grain size, and the crystal phase of BaTiO3 is changed from tetragonal phase to the artifact cubic. Because the increase of inner-stress mismatch between the shell and core, the Curie Point is shifted to higher temperature.The physical and electrical properties of ceramics are greatly influenced by sintering process, and the growth of grain,density of holes,the distribution of doping elements and the crystal phase are affected by the sintering temperature, which also determine the final dielectric properties. The dielectric ceramic meeting EIA X9R specification, were made through the controlling of sintering temperature and keeping time. The main performance indexes are as follows:ε25oC>1820,tanδ≈1.6%,△ε\ε≤±15% (-55℃～200℃).