Ferroelectric Domains and Grain Engineering in SrBi2Ta2O9

Abstract

Aurivillius phase oxide ferroelectrics have attracted great interest as a lead-free replacement of PZT, especially for high-temperature applications. In this work, we report the growth of high-quality SrBi2Ta2O9 (SBT) single crystals by self-flux solution method. According to X-ray topography, the crystals with sizes up to 7 × 5 × 0.05 mm3 show perfect (001)-orientation with the edges directed along [110] axes. Anisotropy, crystalline orientation, growth mechanism, and their effect on the electrical properties are discussed. The domain structure of the single crystals is investigated by X-ray diffraction and piezoresponse force microscopy. Both ferroelectric 180° domains and ferroelastic 90° domains (twins) are revealed at room temperature. We observed coexisting domains of two types forming a well-known “herringbone” structure with mostly flat 90° walls. These high-quality crystals were used as templates for fabricating textured SBT ceramics via templated grain growth (TGG) technique. The SBT templates (5 wt.%) with dimensions ~40 × 40 × 8 μm3 were embedded in a fine-grained SBT powder matrix containing 3 wt.% of Bi2O3 excess that were partially aligned by uniaxial pressing. The influence of the pressing and sintering conditions on texture development was evaluated using scanning electron microscopy and X-ray diffraction analysis. It was found that the ceramics develop a bimodal microstructure with notable concentration of large (longer than 90 μm) aligned grains with c-axis oriented parallel to the pressing direction. The mechanism controlling the texture development and grain growth in SBT ceramics and its influence on the piezoelectric properties are discussed.