High Temperature Mlcc Ceramic Material Composition And Process

Because of high dielectric constant and stable temperature coefficient of capacitance (TCC) (-55℃～125℃,ΔC/C_25℃≤±15%), X8R based on BT (BaTiO₃) modificated by doping is widely studied and used, however, TCC of X8R ceramic material fail to keep stable TCC when the temperature is higher than 150℃. Today, MLCC is popluar used in the automobile electronic device, aviation and space flight, petroleum drilling and other devices. The work environment of the devices is so terrific. It becomes the global professionals who involes investigate key point that studying and developing the high temperature MLCC ceramic materials.Curie temperature of BT (BaTiO₃) is about 130℃. It is very difficult for BT to satisfy the high temperature MLCCs specification: high temperature MLCCs specification:△C/C25℃less than±15% over the temperature range from 130 to 200℃. As result, new material systems which satisfy high temperature MLCCs specification should be investigated. Sodium bismuth titanate, Pb-free pioelectronic cercamic materials modificated by doping is investigated in the dissertation. Temperature coefficients of capacitance meet the requirement for high temperature MLCCs specification:△C/C_25℃ less than±15% over the temperature range from -55 to 200℃.1. Ceramic materials doped by ion, sodium bismuth titanate system and BNCT system have been studied.Three alkaline-earth metal elements ion doped the Sodium bismuth titanate system. Doped by Ca²⁺ leads to improve of ceramic materials dielectric constant in normal temperature, decrease of dielectric loss, improve TCC characteristic. Dielectric loss and dieletric constant are both descend when Mg²⁺ doped into the sodium bismuth titanate system, but TCC is big. Transform temperature is ascend while sodium bismuth titanate system is doped by Sr²⁺. Compare the result, doped by Ca²⁺ would make the dielectric temperature curve flatness.Transform temperarture of BNCT system is improve though doped by Mn²⁺, Ba²⁺. TCC curve low temperature area is declined, while high termperature area is raise. Compare to Mn²⁺, Ba²⁺ makes the decline seriously, fail to meet△C/C_25℃≤±15%.2. Nonstoichiometry has been investigated.Nostoichiometry on sodium bismuth titanate system has been studied, with the develop of content of Ba,Bi, transform temperature grows. TCC cruve in low temperature area ascend, dielectric in normal temperature decline, however, TCC cruve in high temperature area decend when Ti content ascend, dielectric in normal temperature grow.Growing the content of Ba,Bi in sodium bismuth titanate-Ca system leads to TCC cruve in high temperature raise, TCC cruve in high temperature area decend when Ti content ascend. Dieletric loss desend if the content of Bi,Ti grow, however, it asend if content of Ba increase.3. Sodium bismuth titanate-Ca system doped by assist-sintering materials has been studied.Several assist-sintering materials, ZnO,CuO,CuBi₂O₄,Ca-B-Si(CBS), have been investigated. Study show that: doped by the last two materials above would satisfy the specification,△C/C_25℃≤±15%, increase the dielectric in normal temperature at the same time. But doped by ZnO,CuO would deteriorate the dielectric property, increase the dielectric loss.4. Craft influents the dielectric property and micostructure of sodium bismuth titanate-Ca system ceramic hugely.With the increase of second ball milling time, grain become smaller, TCC cruve get flatness, dielectric constant and dielectric loss decrease, and then not change a lot. After fore-sintering, dielectric loss of sodium bismuth titanate-Ca system desend, TCC cruve become smooth. Method of synthesize play an important role in influence the dielectric property, extro-doped CaCO₃ would make the dielectric temperature curve smooth more efficiently.