New Soft Chemical Routes to Ferroelectric SrBi₂Ta₂O₉

Abstract

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 °C for 8 h show good dielectric and ferroelectric properties with a relative density of 96%, a dielectric constant ε‘ = 227, a remnant polarization Pr = 7.6 μC/cm2 at room temperature, and a maximum dielectric constant ε‘max = 950 at the Curie temperature TC = 330 °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 ε‘ of 235, a Pr of 3.7 μC/cm2 at room temperature, and an ε‘max of 850 at TC = 330 °C. The sol−gel-derived ceramics show superior dielectric and ferroelectric properties than the ceramics prepared by the solid-state reactions (ε‘max ≈ 500 and Pr = 4.5 μC/cm2), 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.