Preparation And Study Of High-temperature Stable Mlcc Ceramic

Multilayer ceramic capacitors (MLCCs) have been widely used in electronic equipments, attributed to compact structure, small size, high specific volume, low dielectric loss and low cost. Harsh environments, such as underground exploration, aerospace and military, require MLCCs to extend their working temperature, at the same time maintain good electrical properties. For example, the working temperature for oil exploring and gas reserves must be raised above 200℃. Therefore, developments of high-temperature capacitors are of great importance.Currently, BaTiO3 (BT) is one of the most important materials for MLCC products because of its high dielectric constant, but the low Curie temperature limits its applications in high-temperature capacitors. Bi0.5Na0.5TiO3 (BNT), which has a high Curie temperature of 320℃and the same perovskite structure with BT, has attracted much attention. However, it is difficult to be practical used due to polarization problems. The solid solution of BT and BNT (BNBT), which has advantages of BT and BNT, is hopeful to to become a new material for high-temperature stable MLCC products. According to the characteristics of these materials, the dielectric properties of the systems affected by the dopings and sintering processes were deeply studied. The systems were on the base of BNBCT,BNBT-La-Nb and BNCT-Mn materials. The main results are as follows:1. Three sintering aids (Boron- silicate, CuV2O6, CuBi2O4) were doped to BNBCT ceramics and the sintering temperature was reduced to 1120℃. After that, the effects of rare-earth elements doping on the dielectric properties of low-temperature sintered BNBCT ceramics were studied. Finally, high-temperatiure capacitor materials which meet the X9R specification in a wide temperature range from -55℃to 250℃were achieved.2. The effects of major components and CaCO3 on the microstructure and dielectric properties of BNBT-La-Nb and BNCT-Mn system were investigated. Moreover, the addition of Fe2O3 on the sintering mechanism and dielectric properties of BNCT-Mn system were investigated. 3. The effects of ball milling time and doping methods on the microstructure and dielectric properties of multi-layer ceramic capacitors are investigated in detail. The results revealed that a longer milling time would bring to a lower dielectric loss. The temperature characteristic of capacitance for La outside-doped BNBT-La-Nb system was greatly improved, compared with La inside-doped system.