The domain configuration of lead-free (K0.48Na0.52)(Nb0.96Sb0.04)O3-Bi0.50(Na0.82K0.18)0.50ZrO3 ceramics with rhombohedral-tetragonal morphotropic phase boundary, accounting for the high piezoelectric property and good thermal stability, were systematically studied. Short domain segments (before poling) and long domain stripes with wedge-shaped or furcated ends (after poling) were found to be typical domain configurations. The reduced elastic energy, lattice distortion, and internal stress, due to the coexistence of rhombohedral and tetragonal phases, result in much easier domain reorientation and domain wall motion, responsible for the high piezoelectric properties, being on the order of 460 pC/N, in which the extrinsic contribution from irreversible domain switching was estimated to be around 50% of the total piezoelectricity. Minor piezoelectric property variations (<6% over a temperature range from -50 to 100 °C) were observed as a function of temperature, showing a good thermal stability. In addition, nanodomains (50 ± 2 nm) were found to be assembled into domain stripes after poling, believed to benefit the high piezoelectric properties but not causing much thermal instability due to the small quantity.

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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 (K0.50Na0.50)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%.

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