Abstract:
The polymerized complex method was utilized to synthesize n=3 Aurivillius compounds based on the parent phase Bi_{2}Sr_{2}Nb_{2}TiO_{12}. Results show that this is a viable option to replace solid-state synthesis of these materials because of the good homogeneity of powders and the substantially shorter processing times. The Aurivillius materials studied cannot be prepared to high density without the assistance of hot pressing. Compounds substituting transition metals (Fe, Cr, Co) for titanium remained phase pure up to 50 atom% (dependent on the valance and cation size as expected). Samples prepared substituting lead for bismuth were clearly phase pure up to 15 atom%, and in the 15-50 atom% substitution range XRD patterns indicate that a lead oxide or bismuth oxide impurity phase may be present; however, these impurity phases were not visible in the SEM. Transition metal substitutions did not increase the electrical conductivity of the material, and lead substitutions in high concentration decreased the conductivity. The substitutions did not affect the shape of Cole-Cole impedance plots. An anomalous diffraction behavior was observed in the lead substituted series. Peaks mixed indices peaks having c-axis character broadened as the lead concentration increased. This could correspond to a crystallite size or stain effect; however, attempts to separate the two using XRD analysis were unsuccessful. The charge carrier was studied under four different atmospheres, ranging from pure oxygen to 500ppm of oxygen. The data indicated that the parent phase Bi_{2}Sr_{2}Nb_{2}TiO_{12} is an electronic conductor. Results for the transition metal substituted sample Bi_{2}Sr_{2}Nb_{2}Ti_{0.8}Fe_{0.2}O_{12} indicate the sample is an ionic conductor. The stability of the Aurivillius phase under reducing conditions at 1050°C was determined: at a PO_{2} of 10-3 atm a bismuth oxide impurity phase (if present) decomposes and the Aurivillius phase is stable for 30 hours. At a PO_{2} of 10-8atm the Aurivillius phase starts to break down after just 10hrs. At a PO_{2} of 10-12atm the Aurivillius phase completely breaks down after 10 hours.
