Study Of Barium Titante Based Ceramic Materials With Low Frequency Thermal Stability

Multilayer ceramic capacitors (MLCC) are important fundamental components used in electronic and information technology field, X7R type MLCC which have thermal stability in low frequency are now widely used. As more and more electronic terminal equipments are used in high temperature environments and extreme conditions, X8R type MLCC which can work under high temperature are in urgent need. X8R ceramic materials which have thermal stability in low frequency become a research hotspot.Barium titanate (BaTiO₃, BT)-based ceramic materials are important materials used for MLCC production. Most of the ceramic capacitors with thermal stability and high reliability are currently made of BaTiO₃-based ceramic materials. However, for pure BaTiO₃, there exists a Curie peak near 125℃, where the dielectric constant is abnormal, so the temperature characteristics of pure BaTiO₃ can not meet the X8R specifications. In order to obtain BaTiO₃-based ceramic materials that can meet the X8R specifications, appropriate doping agents and process conditions are needed.In the background of applications of MLCC materials, doping agents in BaTiO₃-based ceramics were studied in this paper, which aims to obtain lead-free X8R ceramic materials with good dielectric properties.The effects of Nb₂O₅-Co₂O₃, Nd₂O₃ and CeO₂ on the dielectric properties of BaTiO₃-based ceramics were fist studied and the doping mechanism was analyzed. Appropriate constants of the dopants were determined and X7R ceramic materials with good dielectric properties were obtained.When Nb⁵⁺:Co³⁺ =3:2, the doping contents of Nd₂O₃ and CeO₂ were 6mol% and 4mol%, BaTiO₃-based ceramic samples which were sintered at 1280℃could meet the X7R specifications. The dielectric constant of the ceramic samples was 3200 at room temperature and the temperature coefficient of capacitance was less than 10% when temperature was in the range from -55℃to +150℃. When the doping contents of Nd₂O₃ and CeO₂ were both 6mol%, ceramic samples which were sintered at 1280℃could also satisfy the X7R specifications, and the dielectric constant was 3400 at room temperature. On this basis, the effects of Bi₄Ti₃O₁₂ and Bi₄(Ti, Sn)₃O₁₂ on the dielectric properties of BaTiO₃-based ceramics were studied. It was found that Bi₄Ti₃O₁₂ and Bi₄(Ti, Sn)₃O₁₂ not only improved the temperature characteristics of BaTiO₃-based ceramics, but also significantly reduced the sintering temperature of the system.With appropriate doping constants of Bi₄Ti₃O₁₂ and Bi₄(Ti, Sn)₃O₁₂, X8R type BaTiO₃-based ceramics were achieved when the process conditions were appropriate. Bi₄Ti₃O₁₂-doped ceramic samples(doping constants was 1mol%) sintered at 1200℃could meet the X8R specifications, the dielectric constant was about 2040 at room temperature. Bi₄(Ti, Sn)₃O₁₂-doped ceramic samples(doping constants was 1mol%) sintered at 1180℃and 1200℃could also meet the X8R specifications, dielectric constants were about 1950 (sintered at 1180℃) and 2020 (sintered at 1200℃) at room temperature. The Bi₄(Ti, Sn)₃O₁₂-doped ceramic samples have better temperature characteristics than BIT-doped ceramic samples.