High temperature Aurivillius piezoelectrics: the effect of (Li, Ln) modification on the structure and properties of (Li, Ln)0.06(Na, Bi)0.44Bi2Nb2O9 (Ln = Ce, Nd, La and Y)

High temperature Aurivillius piezoelectrics, (Li, Ln)(0.06)(Na, Bi)(0.44)Bi2Nb2O9 (NBN-LiLn), with Li and Ln (Ce, Nd, La and Y) co-substitution at the A site, were prepared using a solid-state reaction process. Taking cation disordering between A site and the (Bi2O2)(2+) layers into consideration, the crystal structure of (Li, Nd)(0.06)(Na, Bi)(0.44)Bi2Nb2O9 (NBN-LiNd) was refined by using the Rietveld method with powder X-ray diffraction, which was confirmed to be a two-layer Aurivillius oxide with an orthorhombic space group, A2(1)am [a = 5.48666(9) angstrom, b = 5.46046(8) angstrom, c = 24.9122(4) angstrom and Z = 4], at room temperature. LiNd substitution induced a decrease in cation disorder and an increase in orthorhombic distortion. The ferroelectric to paraelectric phase transition temperature (T-c) of the NBN-LiLn (Ln = Ce, Nd, La and Y) ceramics ranged from 751 to 842 degrees C and the T-c increased as the radii of the Ln(3+) (Ce3+, Nd3+, La3+ and Y3+) was decreased. The NBN-LiCe and NBN-LiNd had a d(33) of 31 and 29 pC N-1, respectively, which is much higher than the reported d(33) values of other Aurivillius ceramics with a high T-c (T-c > 650 degrees C, d(33) < 20 pC N-1). With increasing annealing temperature, a significant degradation in d(33) was observed for NBN-LiCe, while no drop in d(33) was observed up to 650 degrees C for NBN-LiNd. The inhomogeneous domain structures determined the dissimilar piezoelectric behaviors of NBN-LiCe and NBN-LiNd.