Effect of lanthanum and tungsten co-substitution on the structure and properties of new Aurivillius oxides Na0.5La0.5Bi2Nb2-xWxO9

New Aurivillius ferroelectrics Na0.5La0.5Bi2Nb2-xWxO9 (NLBN-W, x = 0, 0.01, 0.02, 0.03, and 0.05) by lanthanum (La3+) and tungsten (W6+) co-substitution were prepared by using a solid-state reaction process. The crystal structure of Na0.5La0.5Bi2Nb1.98W0.02O9 (NLBN-W-0.02) was refined by the Rietveld method with powder X-ray diffraction at room temperature and it was confirmed to be a two-layer Aurivillius oxide with an orthorhombic space group A2(1)am (a = 5.48754(8) angstrom, b = 5.47967(9) angstrom and c = 24.8523(4) angstrom). The ferroelectric to paraelectric phase transition temperature (T-c) of NLBN-W-0.02 is around 501 degrees C, with prominent relaxation behavior. The NLBN-W-0.02 ceramics have a high piezoelectric coefficient (d(33) = 31 pC N-1) and large remnant polarization (P-r = 15.1 mu C cm(-2)). The decrease in P-r for the NLBN-W-0.02 ceramics after 10(7) switching cycles at 40 and 120 degrees C is only 2 and 9%, respectively.