Combustion synthesis and characterization of BaTiO 3
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An important, somewhat novel procedure for the bulk synthesis of finely divided crystalline BaTiO3 powder has been studied and is applicable to the synthesis of other compounds in the BaO-TiO 2 system as well. An aqueous solution of Ba(NO 3 ) 2 , TiO(NO 3 ) 2 , and alanine is spray dried. A combustion reaction occurs when heating the product to 300 °C. The reaction converts the spray-dried mixture to BaTiO3. This BaTiO3 powder and its sinterability have been characterized by thermal analysis, XRD, SEM, dielectric, and particle size measurements. The powder resulting from the thermal runaway reaction is finely divided and sinters more readily than the conventionally prepared high purity BaTiO3.
I. INTRODUCTION The way materials are utilized for technological development is an important indicator of human progress and civilization. Contemporary microelectronic technology that is vital to daily life hinges on many metal oxide based ceramic materials that have appropriate electrical and magnetic properties. Ceramic materials are conventionally prepared by solid-state reactions between their compositional metal oxides and/or carbonates. For electronic application, solid-state reaction generally tends to produce less than optimum materials. This limits performance and miniaturization of electronic devices in many cases. As a result, new processing procedures that will generate high quality materials are of great technical importance. Possible higher costs of the processes may be justified by significantly improved devices. BaTiO3 is an important electronic ceramic widely used in the manufacture of thermistors, multilayer capacitors, and electro-optic devices. The traditional process for making BaTiO3 starts with weighing and ball milling TiO2 and BaCO 3 . This mixture is calcined at high temperature, around 1100 "C.1'2 The diffusion of atoms or ions between different phases is generally the ratelimiting step in solid-state reactions. Therefore, high temperatures and long reaction times are required. Another drawback in the traditional synthesis of BaTiO3 is that other compounds in the BaO-TiO 2 system, with a general formula BaxTiyOx + 2y, are likely to form during the diffusion process due to lengths of the typical diffusion paths. Usually repetitive calcination and grinding treatments are required to synthesize a single phase product. Ball milling also introduces oxides of Al, Si, or Zr as impurities that are usually detrimental to the quality of the materials. Therefore, BaTiO3 made by solid-state reaction tends to be coarse, impure, inhomogeneous, and multiphase powder, usually leading to less than optimal electric properties. While it is recognized that J. Mater. Res., Vol. 10, No. 4, Apr 1995
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some impurities at certain concentrations may actually be desirable for optimum performance, it is nevertheless advantageous to have a high purity starting material available for subsequent controlled doping. High purity, homogeneous, and ultrafine powder of BaTiO3 has
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