A candidate for lead-free ultrahigh-temperature piezoelectrics: the excellent electro-mechanical properties of Aurivillius oxides, Ca1-5xLi2xNd2x□xBi2Nb2-2xScxWxO9-1.5x

Modified ultrahigh-temperature piezoelectric ceramics, Ca1-5xLi2xNd2x square xBi2Nb2-2xScxWxO9-1.5x (CBNO-LiNd-ScW-x, x = 0, 0.01, 0.02, 0.03, 0.04; square represented A-site vacancies), were synthesized by a traditional solid-state reaction process. XRD Rietveld refinement, TEM, HRTEM and Raman spectroscopy were used to characterize the crystal structures and domain structures of the prepared ceramics. The lithium/neodymium (Li/Nd) and scandium/tungsten (Sc/W) co-substitution as well as the existence of small amounts of A-site vacancies significantly enhanced the ferroelectric and electro-mechanical properties of the CBNO-LiNd-ScW-x ceramics. The Curie temperature (T-c) decreased from 941 degrees C to 832 degrees C as the x values increased in CBNO-LiNd-ScW-x, because of an enhancement in the cation disordering between the A site and the bismuth oxide layer. The CBNO-LiNd-ScW-0.01 ceramic with an ultrahigh Tc of 908 degrees C had a high piezoelectric activity (d(33)) of 20.6 pC N-1, a large field-induced strain (S-33) of 0.27 x 10(-3) and a high remnant polarization (P-r) of 6.1 mu C cm(-2), due to the perfect growth in the ferroelectric domains and the contribution from the reversal of the defect dipoles (V-Ca(II)-VO circle circle and Sc-Nb(II)-VO rectangle(circle circle)); interestingly, it still has a high d(33) of 19.5 pC N-1 after up to 800 degrees C thermal annealing. In addition, the CBNO-LiNd-ScW-0.01 ceramic had a relatively high resistivity of > 10(6) Omega cm at 600 degrees C and > 10(5) Omega cm at 700 degrees C.