Synthesis of Aurivillius Ceramics by the Polymerized Complex Method
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Synthesis of Aurivillius Ceramics by the Polymerized Complex Method Brian S. Luisi and Scott T. Misture1 New York State College of Ceramics at Alfred University 2 Pine Street, Alfred, N.Y. 14802 USA 1 Corresponding author. Electronic mail: [email protected] Abstract Aurivillius phases of the type Bi2Sr2Nb2TiO12 and Bi1.6Pb0.4Sr2Nb2Ti1-xAlxO12 (0.0 ≤ x ≤ 0.8) were synthesized by the polymerized complex method involving an organometallic precursor. The effect of raising the pH of the solution was investigated through the addition of ammonium hydroxide. Infrared spectroscopy was taken at various points in the reaction to generate a mechanism. The IR data showed the formation of an ester as well as an amide with the addition of ammonium hydroxide. Pure Bi2Sr2Nb2TiO12 was formed after heat treatment for 5 hours at 900°C for the unaltered solution and 5 hours at 700°C when the solution pH was raised to 9.00. A solubility limit of aluminum was determined for Bi1.6Pb0.4Sr2Nb2Ti1-xAlxO12 when x ≥ 0.4. Conductivity measurements at 1123 K of Bi1.6Pb0.4Sr2Nb2Ti1-xAlxO12 range from 4.76 x 10-3 S•cm-1 at x = 0.8 to 1.74 x 10-4 S•cm-1 at x = 0.1. Introduction Perovskite structures have been the source of recent interest as potential electrolyte materials in solid oxide fuel cells. This is due to their oxygen conducting behavior. In particular, Aurivillius phases have shown promise as oxygen conducting electrolytes at reduced temperatures [1-5]. Aurivillius phases are composed of perovskite layers with the composition (An-1BnO3n+1)2- separated by sheets of (Bi2O2)2+ [1-4]. The general formula for the Aurivillius phase is Bi2An-1BnO3n+3 where n denotes the number of perovskite layers, A is a large electropositive cation such as Ba, Sr, Ca, Bi or Pb and B is a small cation such as Ti, Nb, Ta, Mo, W, or Fe [1-4]. Aurivillius structures with n =1 to n=4 layers have been synthesized and tested [1-5]. Doping these phases with aliovalent cations will introduce oxygen vacancies thus theoretically increasing the ionic conductivity [1-5]. Preliminary processing of mixed cation oxides has generally proceeded by solidstate synthesis with some research involved with developing wet chemical methods [6,7]. Solid-state synthesis is a time consuming process that does not easily generate homogenous, phase pure compounds but has enjoyed popularity due to its relative simplicity. Somewhere between two and four days of heat treatment time is usually necessary in order to achieve phase purity in the systems of interest [8]. Nevertheless, some researchers continue to process Aurivillius phases by the solid-state route [9]. Wet chemical methods provide a means of reducing heat treatment time. Wet chemical synthesis naturally lends itself to highly pure, homogenous products. The lengthy processing requirement of the solid-state method is also eliminated with total firing times of two hours having been reported [7]. Potential drawbacks have been the complexity of the initial reactions. Many variables such as temperature, pH,
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