Low-temperature synthesis and processing of electronic materials in the BaO-TiO₂ system

Abstract

The BaO-TiO₂ system contains several technologically important electronic materials. BaTiO₃, a ceramic with high dielectric constant, is useful for the manufacture of multilayer ceramic capacitors, thermistors and electro-optic components. Titania rich compounds in this system (such as BaTi₄O₉ and Ba₂Ti₉O₂₀) are suitable for the manufacture of miniaturized microwave resonators. Conventional processing of these ceramics relies on the solid-state reactions between readily available raw materials (typically TiO₂ and BaCO₃) and tends to produce coarse, impure, inhomogeneous and multiphase powders. Low temperature, wet chemical routes offer an exciting possibility for the synthesis of high purity, homogeneous, ultrafine and multicomponent powders from which electronic components with tailored and predictable properties could be prepared. A review of new and emerging techniques for the low temperature, wet chemical synthesis of barium titanates is presented. Salient features of several of these processes based on the use of alkoxides, acetates, citrates, chlorides, hydroxides and oxalates of barium and titanium, and combinations thereof, are described. The reaction pathways for the formation of barium titanates are discussed. A comparative summary of the powder characteristics and electrical properties of the barium titanates obtained by different techniques is presented along with a brief discussion of the economic viability of these processes.