Crystal Structure and Enhanced Piezoelectric Properties of Scandium and Bismuth‐Excess Modified Aurivillius Oxides, Na0.5–xBi2.5+xNb2–xScxO9

Aurivillius piezoelectrics, Bi–Sc modified Na0.5–xBi2.5+xNb2–xScxO9 (x = 0.05 and 0.1) and Na‐deficient and Bi‐enriched Na0.5–xBi2.5+xNb2O9 (x = 0.05, 0.1, and 0.2), were prepared by using a solid‐state reaction process. The Rietveld refinement verified that Sc3+ and excess Bi3+ were incorporated into the layered perovskite structure and that they occupied the B and A sites, respectively. The Na0.45Bi2.55Nb1.95Sc0.05O9 [0.05(BiSc)‐modified] crystallized in the orthorhombic space group A21am [a = 5.49853(9) Å, b = 5.45976(9) Å, c = 24.98351(29) Å, and V = 750.021(20) Å3; Z = 4] at room temperature. The A‐site Bi3+ donor substitution induced no obvious increase in the Curie point (Tc), but a further Sc3+ modification at the B site gave rise to a significant increase in Tc. The movements of non‐180° domains contributed to the piezoelectric activities of the Bi‐excess polycrystalline materials, whereas the excellent piezoelectric properties of the Bi–Sc‐modified polycrystalline materials mostly originated from intrinsic lattice contributions, which are due to their single‐180°‐domain‐wall structures. The Na0.45Bi2.55Nb1.95Sc0.05O9 [0.05(BiSc)‐modified] polycrystalline materials have a high Tc of 811 °C and a high piezoelectric activity (d33) of 28 pC/N; interestingly, its d33 was very stable against temperature.