Synthesis of fine Ca-doped BaTiO 3 powders by solid-state reaction method—Part I: Mechanical activation of starting materials Sung-Soo Ryu & Sang-Kyun Lee & Dang-Hyok Yoon Received: 26 May 2006 / Accepted: 30 January 2007 / Published online: 27 February 2007 # Springer Science + Business Media, LLC 2007 Abstract Fine (Ba 0.98 Ca 0.02 ) 1.002 TiO 3 powders for high capacitance multilayer ceramic capacitors (MLCCs) appli- cation were synthesized by solid state reaction method. The effects of mechanochemical activation using high energy milling and the starting materials properties on the reaction temperature and on the final powder properties were investigated. Previous heavy milling of BaCO 3 and the adoption of fine, anatase-rich TiO 2 phase were effective in decreasing the reaction temperature and in increasing the tetragonality (=c/a). BaCaTiO 3 powders with a tetragonality of 1.0097, an average particle size of 213±43 nm and a specific surface area of 6.30 m 2 /g were acquired after heat treatment at 985 °C for 2 h. MLCCs utilizing this developed powder showed superior dielectric and temper- ature characteristics to those with conventional, Ca-free BaTiO 3 powder. Keywords Powder-solid state reaction . Dielectric properties . BaTiO 3 . Capacitors 1 Introduction It has been recognized that multilayer ceramic capacitors (MLCCs) having X5R or X7R characteristics require a core-shell microstructure to attain the stable temperature dependency and voltage characteristics of dielectric con- stant (K)[1, 2]. The core-shell structure is comprised of a ferroelectric core region and a diffused paraelectric shell region which surrounds the core mainly with additive materials. On the other hand, fine BaTiO 3 powders of approximately 200 nm particle size with high tetragonality (=c/a) are required to manufacture very thin-layered MLCCs with large capacitance and small size to keep up with recent trends in consumer electronics such as miniaturization and multi-functionalization [3]. However, the reduction in particle size usually accompanies the decreases in K as well as tetragonality [4–6]. Most MLCCs are currently produced with nickel instead of expensive palladium inner electrodes for cost reasons, which requires sintering under reducing atmosphere. Nev- ertheless, sintering in a low oxygen pressure atmosphere generates problems such as low insulating resistance and poor reliability mainly due to the oxygen vacancies, although efforts have been made to overcome these draw- backs by doping transitional metal ions such as Co 3+ , Fe 3+ and Mn 3+ [7]. Sakabe et al. recently reported that 200 nm- sized BaTiO 3 powders produced by a hydrolysis method with high K, stable temperature dependence and with high reliability could be obtained by doping of a small amount of calcium [8]. Moreover, they explained that the high K of a sintered body using these powders came from the interfa- cial stress due to the role of the grain boundary without any core-shell formation. Since the formation of core-shell structure is increasingly difficult with fine powders due to the small core region, this finding is very interesting. J Electroceram (2007) 18:243–250 DOI 10.1007/s10832-007-9066-x S.-S. Ryu Korea Institute of Ceramic Engineering and Technology, Seoul 153-801, South Korea S.-K. Lee Samsung Electro-Mechanics Co., Suwon 442-743, South Korea D.-H. Yoon (*) School of Materials Science and Engineering, Yeungnam University, Gyeongsan 712-749, South Korea e-mail: dhyoon@ynu.ac.kr