La 0.5 Sr 0.5 TiO 3 nanopowders prepared by the hydrothermal method Thanin Putjuso a , Santi Maensiri b , Sitchai Hunpratub c , Ekaphan Swatsitang c, * a School of General Education, Faculty of Liberal Arts, Rajamangala University of Rattanakosin Wang Klai Kangwon Campus, 77110, Thailand b School of Physics, Institute of Science, Suranaree University of Technology, Nakhon Ratchasima 30000, Thailand c Department of Physics, Faculty of Science, Khon Kaen University, Khon Kaen 40002, Thailand 1. Introduction Lanthanum strontium titanate ((La,Sr)TiO 3 ) has attracted considerable attention due to its fascinating fundamental physical properties such as the potential use of dilute magnetic oxide based on La 0.5 Sr 0.5 TiO 3 useful for ferrofluids, magnetic recording and biomedical applications. In particular, La 1Àx Sr x TiO 3 (x = 0.5, 0.6, 0.7 and 0.8) have been studied as materials with possible application as an alternative anode for solid fuel cells (SOFCs). It was found that La 0.5 Sr 0.5 TiO 3 demonstrated good ionic conductivity and could be used as a basic phase for producing composite anodes for SOFCs [1]. Subsequent study has shown that the microstructure of La 0.5 Sr 0.5 TiO 3 could be improved by using Al–(La,Sr)TiO 3+d [2]. Moreover, the material showed a low polarization resistance and good catalytic properties. In a study of perovskite oxides with a general formula of La 0.4 Sr 0.6 Ti 1Àx Mn x O 3Àd (x = 0, 0.2, 0.4 and 0.6), Fu et al. [3] reported that the materials were thermally and chemically compatible with yttria-stabilized zirconia and could be used as anodes in electrolyte-supported cells. In addition, Wongsaprom et al. [4] demonstrated the existence of ferromag- netism in Co–La 0.5 Sr 0.5 TiO 3 and they indicated that the undoped samples were diamagnetic, whereas the Co-doped sample showed ferromagnetism at room temperature. Generally, the multicomponent oxide systems, i.e., (Pb,Sr)TiO 3 , (Ba,Ca)TiO 3 , (Pb,La)TiO 3 and (La,Sr)TiO 3 perovskites, are usually fabricated by a conventional solid state reaction [5], thermal decomposition [6], molten salt [7], polymerized complex [8], co- precipitation [9], and sol–gel [10]. Alternatively, a more attractive method is the hydrothermal method, due to the simplicity of its preparation process at low temperature, without high tempera- ture calcination. It is also a CO 2 free process and more energy can be saved than in all the methods mentioned above. In previous study, Wang et al. [11] successfully synthesized a single-crystal SrTiO 3 of dendritic nanostructure by a hydrothermal method at a temperature as low as 200 8C with 0.1–0.7 M KOH and Qiu et al. [12] also synthesized a Pb(Zr 0.52 Ti 0.48 )O 3 nanostructure by the same method at 200 8C with 1.2 M KOH. However, no research on the preparation of (La,Sr)TiO 3 by the hydrothermal method has been reported yet. In this paper, we report the preparation of La 0.5 Sr 0.5 TiO 3 nanopowders by the hydrothermal method. The influences of the KOH concentration, reaction time and temperature on the phase formation of the product were investigated. 2. Experiment In this study, the La 0.5 Sr 0.5 TiO 3 nanopowders were synthesized by the hydrothermal method. Lanthanum chloride hydrate (98.5% purity, Fluka), strontium chloride hexahydrate (99% purity, Fluka) and titanium diisopropoxide bis(acetyl acetonate 75 wt% in isopropanol, Aldrich) were used as the starting materials. Initially, lanthanum chloride hydrate and strontium chloride hexahydrate were dissolved in de-ionized water under vigorous magnetic stirring for 10 min until a clear solution was obtained. Titanium Materials Research Bulletin 47 (2012) 2270–2276 A R T I C L E I N F O Article history: Received 4 October 2011 Received in revised form 15 March 2012 Accepted 23 May 2012 Available online 1 June 2012 Keywords: A. Inorganic compounds B. Chemical synthesis C. Electron microscopy C. X-ray diffraction D. Microstructure A B S T R A C T La 0.5 Sr 0.5 TiO 3 nanopowders were prepared by the hydrothermal method. The influence of processing parameters, including KOH concentration, reaction temperature and reaction time on the obtained products were studied. The structure and morphology of the obtained products were characterized by X- ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The XRD results show that pure phase La 0.5 Sr 0.5 TiO 3 nanopowders can be successfully synthesized with 2 M KOH concentration at a low temperature of 220 8C for 24 h. In addition, the product has a plate-like shape with particle sizes in the range of 25–100 nm as estimated by TEM. ß 2012 Elsevier Ltd. All rights reserved. * Corresponding author. Tel.: +66 43 203166; fax: +66 43 202374. E-mail address: ekaphan@kku.ac.th (E. Swatsitang). Contents lists available at SciVerse ScienceDirect Materials Research Bulletin jo u rn al h om ep age: ww w.els evier.c o m/lo c ate/mat res b u 0025-5408/$ – see front matter ß 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.materresbull.2012.05.043