Low temperature synthesis of ultrafine strontium titanate (SrTiO 3 ) powders
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Ultrafine («0.4 lira) strontium titanate powder was synthesized using strontium nitrate and potassium titanyl oxalate as precursors. An aqueous (0.1 M) potassium titanyl oxalate solution was added dropwise to a (0.1 M) strontium nitrate solution with continuous stirring at room temperature to precipitate strontium titanyl oxalate (STO). The precipitate, after careful washing with distilled water several times, was air-dried and calcined at 550 °C/6 h to obtain homogeneous, spherical, stoichiometric powder of SrTiO3 «0.4 /um in size. The calcined powder was characterized using different techniques such as XRD, DTA/TG/DTG, SEM, and IR.
I. INTRODUCTION The low temperature synthesis of ultrafine ceramic powders1"3 is an area of considerable interest and technological significance. In particular, synthesis of polycrystalline electronic ceramic materials having high dielectric constants4'5 (e.g., BaTiO3 and SrTiO3) and their solid solutions at low temperature (T ^ 700 °C) is of immense importance for the cost-effective manufacture of multilayer capacitors, sensors, and other related devices.6"8 Four low-temperature methods have been reported for the preparation of SrTiO3 powders, namely (i) solgel or hydrolytic decomposition of Sr-Ti double alkoxide,9'10 (ii) hydrothermal synthesis,11'12 (iii) pechini or liquid-mix process,13 and (iv) chemical coprecipitation.14"16 Each method has certain advantages and disadvantages, and are summarized in Table I. In the chemical coprecipitation route, titanium tetrachloride (TiCLj) and strontium chloride solutions are most widely used as precursors to precipitate STO, which subsequently transforms to homogeneous SrTiO3 powder around T ^ 700 °C. The use of TiCl4 solution as the titanium source for the preparation of STO needs a quantitative estimation17 of Ti to aid in controlling the Sir: Ti ratio. Furthermore, a part of TiCU can get hydrolyzed while making the TiCl4 solution. Strontium chloride is quite soluble18 in aqueous oxalic acid and therefore an excess of 80-100 mole% of strontium is needed to achieve the required stoichiometry in the precipitated STO. It is known that chloride impurity ions are not completely eliminated by washing. To overcome these difficulties, we have developed a simple chemical method for the synthesis of STO using water soluble salts of Sr and Ti. By pyrolyzing STO in air at 550 °C/6 h, ultraline powder of strontium titanate (ST) is easily ^National Chemical Laboratory Communication No. 5162, Pune 411008, India. J. Mater. Res., Vol. 7, No. 2, Feb 1992 http://journals.cambridge.org
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obtained. It is carefully characterized using XRD (X-Ray Diffraction), DTA/TG/DTG, SEM (Scanning Electron Microcopy), and IR (Infra Red) techniques. These experimental results are presented in this communication. II. EXPERIMENTAL A (0.1 M) solution of potassium titanyl oxalate [K2TiO(C2O4)2] (Loba Chemie, 98.5%) was prepared in distilled water at room temperature (pH ss 3.1-3.3) and was kept in a separating funnel. Similarly, a (0.1 M) solution of stro
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