Study On Mechanism Of BaTiO₃-based Ceramics With Thermal Stability Sintered At Medium Temperature And Pilot Production

Multilayer ceramic capacitors (MLCC) are important fundamental components of electronic information technology. To meet the requirements of electronic system, MLCC are developing towards wide temperature, large capacitance and low cost. BaTiO3based ferroelectric ceramics are one of the important materials of MLCC. The preparation of temperature-stable ceramics sintered at medium temperature were researched in this dissertation, of which the principles and micromechanism was researched by modern methods such as XRD, SEM on the basis of crystal structure.1、The effects of Nb2O5, CoCO3, MgO, CeO2, Bi2O3to the dielectric properties of the system was discussed too. A X8R system with the following parameters was gained:ε>2500at1KHz, tanδ≤1.5%,|△ε/ε|<15%in the region of-55～150℃.2、The Pb(Tio.55Sno.45)O3additives can shift the Curie temperature of BaTiO3to150℃. Pb2+substitutes for A-site and Sn4+substitutes for B-site in ABO3structure, causing the constituent phase transition diffusion, so the Curie temperature was shifted to higher temperature. Pb(Ti0.55Sn0.45)O3and BaTiO3can form partial solid solution, and core-shell structure was observed, so the temperature characteristics of the capacitance of the system was improved. When2wt%Pb(Tio.55Sno.45)O3was added,the sample showed super dielectric properties that the dielectric constant was>1750at25℃, dielectric loss was lower than2.0%and TCC was≤±10%from-55℃to200℃.Therefore the materials satisfied EIA X9R specifications.3、When the mixed materials were milling, the smaller milling balls and the longer milling time resulted in smaller particle size of the materials and bigger specific surface area,and the growth of BaTiO3grain 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 BaTiO3particles greatly, and the volume of ferroelectric phase core is increased while the volume of shell decreased. The dielectric property of doping BaTiO3is enhanced with the Curie peak flat and a slowing rate of dielectric constant. 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.4、In order to environmental protection, Bi0.sNao.sTiO3,(BNT) was doped to substitute for Pb(Ti0.55Sn0.45)O3.BTBNT has higher Curie temperature (170℃)which was generated by calcining the mixture of BaTiO3and BNT. As additives,Nb2O5can accommodate the temperature coefficient of capacitance (TCC)cures of the ceramics based on BTBNT.Nb5+mainly enters the Ti-sites as a donor and the secondary phases are identified as Ti-rich phases.the existence of the secondary phases can flatting the TCC.Suitable Nb2O5-doped BTBNT ceramic material is able to satisfy the EIA X9R specification with a dielectric constant of1660and a dielectric loss of0.0194, AC/C25℃≤15%. At last, the influence of milling time and sintering temperature on the dielectric properties of BTBNT ceramics was investigated.