New soft chemical routes to ferroelectric SrBi2Ta2O9

Ferroelectric ceramics of strontium bismuth tantalate, SrBi2Ta2O9 (SBT), have been synthesized in pure layer-structured perovskite phase by two new soft chemical techniques, namely, a sol-gel process and a coprecipitation method. The sol-gel process utilizes ethylene glycol as solvent while the coprecipitation technique makes use of a poly(ethylene glycol) 200 (PEG) and methanol mixture as solvent. The microstructure and properties of the ceramics have been studied and discussed. The sol-gel-derived ceramics sintered at 1200 degrees C for 8 h show good dielectric and ferroelectric properties with a relative density of 96%, a dielectric constant epsilon' = 227, a remnant polarization P-r = 7.6 mu C/cm(2) at room temperature, and a maximum dielectric constant epsilon'(max) = 950 at the Curie temperature T-C = 330 degrees C. In comparison, the SBT ceramics prepared using the coprecipitation method and sintered under the same conditions show a platelike microstructure with preferential grain orientation along the [0010] direction, a relative density of 85%, an epsilon' of 235, a P-r of 3.7 mu C/cm(2) at room temperature, and an epsilon'(max) of 850 at T-C = 330 degrees C. The sol-gel-derived ceramics show superior dielectric and ferroelectric properties than the ceramics prepared by the solid-state reactions (epsilon'(max) approximate to 500 and P-r = 4.5 mu C/cm(2)), which can be attributed to a denser and more homogeneous microstructure with a better distribution of grain orientations, thus reducing the preferential grain orientation along the nonpolar c-axis.