Domain structure of potassium-sodium niobate ceramics before and after poling

Domain structure and domain wall motion play important roles on the piezoelectric properties of ferroelectric ceramics. In this work, the domain structure of hot-pressed (K_0.50Na_0.50)NbO₃ (KNN) ceramics before and after poling were studied by observing the domain patterns with an acid-etching technique, and the extrinsic contribution to the piezoelectric properties were evaluated. It was found that the domain structure of the unpoled KNN ceramic was relatively complicated with many watermark, herringbone and zigzag patterns, while only a single set or few sets of parallel domain stripes were observed in the poled KNN ceramic, due to the domain reorientation and domain wall motion during the poling process. The average domain width changes from 200 (±10) nm before poling to 250 (±10) nm after poling. Domain configurations of "Herringbone-Zigzag-Watermark" and "Herringbone- Herringbone-Zigzag" types observed in the unpoled KNN ceramic were then further analyzed. The extrinsic contribution to the piezoelectric properties from the domain reorientation and irreversible domain wall motion in the hot-pressed KNN ceramic was found to be 71%, slightly higher than that of conventional sintered KNN ceramics ~68%.