Journal of Alloys and Compounds 505 (2010) 568–572 Contents lists available at ScienceDirect Journal of Alloys and Compounds journal homepage: www.elsevier.com/locate/jallcom Synthesis and characterization of BaTiO 3 nanoparticles in oxygen atmosphere S. Fuentes a,f,∗ , R.A. Zárate b , E. Chávez b , P. Mu ˜ noz c,f , M. Ayala c , R. Espinoza-González d , P. Leyton e a Departamento de Química y Farmacia, Facultad de Ciencias, Universidad Católica del Norte, Casilla 1280, Antofagasta, Chile b Departamento de Física, Facultad de Ciencias, Universidad Católica del Norte, Casilla 1280, Antofagasta, Chile c Departamento de Química, Facultad de Ciencias, Universidad Católica del Norte, Casilla 1280, Antofagasta, Chile d Departamento de Ciencia de los Materiales, Facultad de Ciencias Físicas y Matemáticas, Universidad de Chile, Av. Tupper 2069, Santiago, Chile e Laboratorio de Fotofísica y Espectroscopia Molecular, Instituto de Química, Pontificia Universidad Católica de Valparaíso, Av. Brasil 2950, Valparaíso, Chile f Center for the Development of Nanoscience and Nanotechnology, CEDENNA, Santiago, Chile article info Article history: Received 12 January 2010 Received in revised form 10 June 2010 Accepted 11 June 2010 Available online 23 June 2010 Keywords: Sol–gel process Nanostructures Barium compounds Ferroelectric materials abstract A new synthesis route to obtain high-purity barium titanate, BaTiO 3 , using the sol–gel-hydrothermal reaction of TiCl 4 and a BaCl 2 solution in an oxygen atmosphere has been developed. The synthesized BaTiO 3 nanoparticles are nearly spherical. Their grain sizes are determined by the reaction temperature, reaching values as low as 50 nm when the particles are synthesized at 200 ◦ C; interestingly even those particles with the smallest grain sizes displayed a ferroelectric behavior as characterized by a polarization hysteresis loop. The microstructure and composition of the as-synthesized samples were investigated by X-ray diffraction (XRD), high-resolution TEM (HRTEM), Raman spectroscopy, atomic force microscopy (AFM) and energy-dispersive X-ray spectroscopy (EDS). © 2010 Elsevier B.V. All rights reserved. 1. Introduction Barium titanate (BT) has been one of the best known and widely used materials for electric ceramics due to its excellent dielec- tric, piezoelectric, pyroelectric and ferroelectric properties [1–6]. BaTiO 3 is mainly used in multilayer ceramic capacitors (MLCCs), sensors and actuators, electro-optic devices, thermistors, integral capacitors in printed circuit boards (PCBs), temperature–humidity gas sensors, memory applications, etc. However, it is difficult to develop a dielectric layer of less than 10 m with large capaci- tance, which is a major requirement for MLCC miniaturization and electronic/microelectronic devices [7]. Therefore, in order to get further compactness is strongly needed to synthesize BT powders with particle sizes smaller than 100 nm and with high dielectric constant. The controllable preparation of crystalline BT particles and thin films has been extensively investigated since BT dielectric and ferroelectric properties strongly depend on its microstructure (crystallinity and grain size) [8–10]. Indeed, it is known that the improved BT microstructure has a direct impact on the increas- ∗ Corresponding author at: Departamento de Química y Farmacia, Facultad de Ciencias, Universidad Católica del Norte, Av. Angamos 0610, Casilla 1280, Antofa- gasta, Chile. Tel.: +56 55 355517; fax: +56 55 355521. E-mail address: sfuentes@ucn.cl (S. Fuentes). ing of electronic devices performance. The traditional preparation methods of perovskite-type powders are performed by solid- state reactions at high temperatures, usually higher than 1000 ◦ C, and under specific pressure and pH conditions [11,12]. Several techniques are available for synthesizing fine BT powders; these include sol–gel [13,14], microwave [15], hydrothermal methods [16–18], and sputtering [19]. In recent years some new meth- ods have been introduced to make porous BaTiO 3 too. These methods include the development of soft-chemistry routes to produce nanoparticles or specially shaped materials, such as one- dimensional nanowires [20,21], sonochemical methods to prepare size-tunable BT crystals [22], and the introduction of biosynthe- sis methods to prepare BaTiO3 nanopowders [23]. Among these synthetic methods, hydrothermal or chemical reaction methods are of great interest, because they are safe and environmentally friendly. The syntheses are performed at moderate temperatures, i.e. ∼200 ◦ C, and they are effective for creating novel architectures or hierarchical structures based on nanocrystals [24]. To the best of our knowledge, the influence of the atmosphere in the use of hydrothermal methods to prepare BT has not been yet reported in the literature. In this paper we report a new route to direct synthesize nanocrystalline BaTiO 3 powder using TiCl 4 and BaCl 2 as starting materials. The route used is a sol–gel-hydrothermal method under oxygen atmosphere, which has allowed us to obtain tetragonal BT and particle sizes of less than 100 nm. 0925-8388/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.jallcom.2010.06.074