Studies Of Compositional Modification And Novel Process For Non-reducible BaTiO₃-based Dielectrics

Ceramic multilayer capacitors (MLCC) are one of the most important electronic components at the surface mounting of electronic circuits. A substantial cost saving can be achieved by utilizing base metal (Ni or Cu) electrode as internal metallization in MLCC over the more expensive precious metals such as Pd or Ag/Pd. The base-metal-electrode capacitors (BME-MLCC) need to be fired in reducing atmosphere, since the Ni (or Cu) metal is subjective to oxidation during sintering in air. This inevitably results in requirements for high performance non-reducible dielectrics for BME-MLCC. As a result, BaTiO₃-based non-reducible dielectrics, which can be co-fired with BME, have become one of the most attracting fields in both industry and academia.Nowadays, much attention has been paid to MLCC satisfying EIA X8R specification (-55 to 150℃,ΔC=±15% or less, tan δ_25℃≤0.025) for automotive applications, which work under harsh conditions. However, it is very difficult for BaTiO₃-based dielectrics to satisfy the R characteristic (ΔC/C=± 15% or less) when the temperature is higher than 130℃, since the Curie point (T_C) of pure BaTiO₃ is about 125℃. Accordingly, how to shift T_C to higher temperatures has become a key issue in research of BaTiO₃-based X8R materials. Besides, ultrafine starting materials have become the basis of the mass production of MLCC, which inevitably leads to high requirements for particle size, purity, and uniformity of additives. Some technologies have been developed in order to achieve downsizing and uniform distribution of additives. However, most of these techniques suffer from complex equipments, complicated processing procedures and expensive raw materials.In this thesis, the basic modification mechanisms of BaTiO₃ have been analyzed. Then novel materials and process are explored and investigated for non-reducible dielectrics.The main results are as follows:1. The effects of rare earth elements on the microstructure and dielectric properties of BaTiO₃-Mg-R (R=rare earth elementals La, Pr, Ce, Nd, Sm, Gd, Dy, Ho, Er, Yb) system are investigated in detail. The mechanisms governing average grain size and the formation of core-shell structure are discussed in terms of the solubilities of the rare earth elements. Pyrochlore-type R₂Ti₂O₇ is found to be helpful to form core-shell structure. In the cases of Dy³⁺, Ho³⁺, Er³⁺, Yb³⁺-substituted samples with...