Fabrication of BaTiO 3 thin films through ink-jet printing of TiO 2 sol and soluble Ba salts Yeoh Cheow Keat ⁎ , Srimala Sreekantan, Sabar Derita Hutagalung, Zainal Arifin Ahmad School of Materials and Mineral Resources Engineering, Engineering Campus, Universiti Sains Malaysia, Malaysia Received 13 June 2006; accepted 15 February 2007 Available online 28 February 2007 Abstract BaTiO 3 thin films were prepared by ink-jet printing aqueous solutions of TiO 2 sol and soluble Ba salts. Higher pH values (pH N 13) as well as higher than stoichiometric Ba (Ba:Ti=1.1:1) salt additions were required to compensate for the different aqueous solubilities of the Ba and the Ti. Impedance spectroscopy of the samples shows the thin film samples to have similar activation energy with bulk samples prepared through low temperature aqueous synthesis. The relative permittivity of the thin films (∼ 280) was lower than the bulk pellets (∼ 2750) which was attributed to the lower temperature heat treatment for the thin films. © 2007 Elsevier B.V. All rights reserved. Keywords: Sol–gel preparation; Dielectrics; Thin films 1. Introduction Ink-jet printing is a low cost alternative for producing microcircuits [1], metallization of solar cells [2], or the fabrication of small structures [3,4]. Advantages include low cost, direct patterning, low wastage and close composition control [5]. BaTiO 3 films have been printed on a commercial ink-jet printer using suspensions of the bulk powders [6]. In ink- jet printing ceramic thin films, solutions with very fine or no suspended solids are needed, therefore researchers have used very fine suspensions of ceramic particles [7] and ink-jet systems custom built for delivering these suspensions [5]. However, with the emergence of printers that deliver increasingly finer droplets [8,9], it becomes more difficult to have finer particle suspen- sions. Therefore, several researchers have begun utilizing chemical solutions, sols or colloids as their ceramic inks [10,11]. The low temperature aqueous method holds great promise for ink-jet printing because of the lower processing temperatures and the atmospheric pressure operating conditions. Low temperature aqueous synthesis usually starts from the prepara- tion of a TiO 2 sol prepared from the hydrolysis and subsequent peptization of the titanium alkoxides. Barium ions in the form of soluble salts are then added to the peptized solution. The potential-pH diagram [12] shows the Ti species to be soluble in aqueous solutions at pH b 3, while Ba ions are soluble over a wide range of pH b 13. The differences in solubility cause the leaching of Ba ions from BaTiO 3 particles suspended in aqueous solutions leaving a TiO 2 skin on the particles [13,14]. Increasing the pH value of the solution to pH 13 causes the precipitation of BaTiO 3 since it is the only stable phase under these conditions [15]. Thin films of BaTiO 3 should be relatively easy to process through ink-jet printing because at low pH levels, the solution is essentially precipitate-free. Increasing the pH of the deposited solution films can be achieved by simultaneously printing out an alkaline NH 4 OH solution, thereby avoiding precipitate forma- tion that would clog the nozzle of the ink-jet printer. In this paper, the dielectric properties of thin films fabricated through ink-jet printing are characterized and compared to the dielectric properties of bulk pellets precipitated from the same solution. 2. Materials and methods 0.4 M titania sol was prepared via the hydrolysis of Ti (C 4 H 9 O) (Fluka) and peptization using HNO 3 (Fluka). Appro- priate amounts of 0.4 M BaCl 2 ·2H 2 O (Fluka) solution were Materials Letters 61 (2007) 4536 – 4539 www.elsevier.com/locate/matlet ⁎ Corresponding author. Tel.: +60 4 593 7788; fax: +60 4 594 1011. E-mail address: yck5@yahoo.com (Yeoh Cheow Keat). 0167-577X/$ - see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.matlet.2007.02.046