An inexpensive and efficient method for the synthesis of BTO and STO at temperatures lower than 200 °C Elsy Bacha a, ⁎, Philippe Deniard b , Mireille Richard-Plouet b , Luc Brohan b , Hartmut W. Gundel a a Institut de Recherche en Electrotechnique et Electronique de Nantes Atlantique, E.A. 1770, Université de Nantes, 2 rue de la Houssinière, 44322, Nantes, France b Institut des Matériaux Jean Rouxel, Université de Nantes, CNRS, UMR 6502, Université de Nantes, 2 rue de la Houssinière, 44322, Nantes, France abstract article info Available online 1 January 2011 Keywords: BaTiO 3 (BTO) SrTiO 3 (STO) Solvothermal synthesis Aqueous solution Ferroelectric powder (tetragonal phase) Rietveld refinement Acid treatment During the past decade the reduction in size of functional architectures has been a dominating trend in many fields of science and technology. The search for electronic materials that can be cheaply solution-processed into nanopowders, while simultaneously providing quality device characteristics, represents a major challenge for material scientists. Solvothermal process is used in order to obtain fine nanoparticles of BaTiO 3 and SrTiO 3 at low temperatures by using an inorganic, ionic precursor. Rietveld refinement proves the presence of a mixture of 65% tetragonal and 35% cubic nanoparticles in the barium titanate powder with an average size of 73 nm and 67 nm, respectively. FTIR shows that an acid treatment allows the elimination of carbonate impurities. © 2010 Published by Elsevier B.V. 1. Introduction Ferroelectric nonlinear behavior has been used since many years for different electronic and optical applications. Perovskite materials like BaTiO 3 (BTO) and SrTiO 3 (STO) display a wide range of interesting properties that make these materials one of the today's most studied ferroelectric ceramic thin films. Used as a capacitor material, applications in non-volatile memories, tunable filters, electronically steering antennas, and many other microelectronic devices are possible. The conventional solid-state route [1,2] normally requires high sintering temperatures (T N 1300 °C) for synthesizing BTO and STO powders. During calcinations, several secondary phases like BaCO 3 (BCO) and SrCO 3 (SCO) may be formed, which is a further major drawback of this route. More recently, many research works have been performed on new methods such as solvothermal [3–6] and sol– gel [7–9] processes. Sol–gel synthesis, however, requires sintering at temperatures above 650 °C in order to crystallize the gel obtained from organic reagents, whereas the solvothermal process is attractive because it is environmentally benign, a low temperature (b 200 °C), one-step process, and may involve inexpensive starting materials. In this study, we investigated the solvothermal process in order to synthesize crystallized nanoparticles of BaTiO 3 and SrTiO 3 at 175 °C. Rietveld refinement of the XRD pattern was employed in order to evaluate the tetragonal to cubic BTO proportion (detected by Raman spectroscopy) together with the crystallite size. Carbonate species, introduced by the reaction of atmospheric CO 2 with the base reactants, were eliminated by washing with acid. Finally, the samples were examined by SEM and TEM. 2. Experimental techniques 2.1. Powder synthesis The STO or BTO nanopowders were synthesized in a beaker by adding TiOCl 2 1,4HCl·7H 2 O respectively to Sr(OH) 2 ·8H 2 O or Ba(OH) 2 ·8H 2 O. The mixture was transferred to a Teflon-lined autoclave (capacity: 50 mL) and heated to 448 K during 72 h. The material was washed with distilled water (100 mL), filtered in order to eliminate the barium or strontium chloride and finally dried in air at 343 K. 2.2. Acid treatment A controlled acid wash treatment of the 0.1 mol L -1 BTO or STO suspensions, using 0.1 mol L -1 hydrochloric acid with a flow of 0.02 mL/min, is performed. The pH evolution permits determination of the carbonate amount in the suspension. 2.3. Characterization methods SEM characterization is obtained by using a JEOL 6400F with a tungsten cathode field emission gun operating at 10 keV. XRD data were collected on a Siemens D5000 and a Bruker D8 diffractometer in a Bragg–Brentano geometry with respectively Cu K α and CuK a1 radiation. Rietveld refinement was done with the JANA2006 [10] code using the fundamental parameter approach [11–13]. This procedure Thin Solid Films 519 (2011) 5816–5819 ⁎ Corresponding author. E-mail address: m.gooley@elsevier.com (E. Bacha). 0040-6090/$ – see front matter © 2010 Published by Elsevier B.V. doi:10.1016/j.tsf.2010.12.190 Contents lists available at ScienceDirect Thin Solid Films journal homepage: www.elsevier.com/locate/tsf