Application of Rare Earth Oxides in MLCC

Ceramic powder is the core raw material of MLCC, accounting for 20% to 45% of its total cost. Especially for high-capacity MLCC, strict requirements are imposed on the purity, particle size, particle distribution and morphology of the ceramic powder, leading to a relatively higher cost ratio of ceramic powder. MLCC is an electronic ceramic powder material formed by adding modified additives to barium titanate powder, which can be directly used as the dielectric in MLCC.

Rare earth oxides are important doping components in MLCC dielectric powder. Although they account for less than 1% of MLCC raw materials, they play a crucial role in adjusting ceramic properties and effectively improving the reliability of MLCC, making them indispensable in the development of ceramic powder for high-end MLCC.

Barium titanate is one of the main raw materials for manufacturing MLCC, with excellent piezoelectric, ferroelectric and dielectric properties. However, pure barium titanate has a large capacitance temperature coefficient, high sintering temperature and high dielectric loss, which makes it unsuitable for direct use in ceramic capacitors.

Studies have shown that the dielectric properties of barium titanate are closely related to its crystal structure. Doping can regulate the crystal structure of barium titanate, thereby improving its dielectric properties. This is mainly because fine-grained barium titanate forms a core-shell structure after doping, which is important for improving the temperature characteristics of capacitance. Doping rare earth elements into the barium titanate structure is one of the ways to improve the sintering behavior and reliability of MLCC.

Research on rare earth ion-doped barium titanate can be traced back to the early 1960s. The addition of rare earth oxides reduces oxygen mobility, enhances the dielectric temperature stability and voltage resistance of dielectric ceramics, and improves product performance and reliability. Commonly added rare earth oxides include yttrium oxide (Y₂O₃), dysprosium oxide (Dy₂O₃), holmium oxide (Ho₂O₃), etc. The ionic radius of rare earth elements has a vital impact on the Curie peak position of barium titanate-based ceramics.

Doping rare earth elements with different radii will change the lattice parameters of crystals with core-shell structure, thereby altering the internal stress of crystals. Doping with rare earth ions with larger radii causes the crystals to form a pseudo-cubic phase and generates residual stress inside the crystals; while the introduction of rare earth ions with smaller radii results in lower internal stress and inhibits phase transition of the core-shell structure.