Processing and reduced sintering temperature of relaxor ferroelectric lead zinc niobate - lead nickel niobate/lead titanate ceramics for capacitor application

This dissertation investigates processing and property issues between relaxor ferroelectric Lead Zinc Niobate(PZN) and Lead Nickel Niobate(PNN), and the normal ferroelectric, Lead Titanate(PT). These materials were studied with regard to dielectric properties for potential usage in capacitor applications.;Compositions in the xPZN-(1-x)PNN binary system were prepared over a range of x = 0 to x = 0.94. The use of the mixed oxide processing technique resulted in substantial pyrochlore phase formation while use of the B-site precursor technique significantly reduced the pyrochlore phase. Peak dielectric constant was a maximum at x = 0.70, with a value of 8,800 at a T$rmsb c$ of 46$spcirc$C, following firing at 1125$spcirc$C/2 hours.;The addition of PT to the PZN-PNN system was performed to optimize dielectric properties. A composition was identified which possessed a room temperature dielectric constant of 12,000 (0.46PZN-0.46PNN-0.08PT). To further optimize dielectric properties, several processing variables were studied, including excess PbO additions to starting batches, firing configuration, powder purity and post-fire thermal annealing.;Thermal annealing was found to improve dielectric constant by 50% in the x = 0.65, x = 0.75 and 0.46PZN-0.46PNN-0.08PT systems. The x = 0.75 composition showed an increase in dielectric constant, despite the increased amount of pyrochlore phase present with increased annealing time. The other compositions showed negligible pyrochlore phase for all firing temperatures studied. The increase in K was due to increased grain development and decreased grain boundary phase.;A reduction in processing temperature from 1075 to 950$spcirc$C using lithium-based fluxing sintering aids was demonstrated in the 0.46PZN-0.46PNN-0.08PT composition, with an improvement in density to 96% with only a 1% Li$sp+$ concentration. Despite this large improvement, dielectric constant improved minimally. A systematic study comparing the effects of LiNO$sb3,$ Li$rmsb2COsb3$ and LiF on physical, structural and dielectric properties is presented.;Finally, an empirical relationship was derived showing the dependence of peak dielectric constant on the broadness of the dielectric constant vs. temperature plot in the paraelectric region. It is shown to be valid for all relaxors, regardless of composition, secondary phases or processing issues. It is concluded that the maximum dielectric constant obtainable in a relaxor ferroelectric system is primarily dependent on the extent of cation ordering.