Crystal structure and spontaneous polarization of Bi4-xNdxTi3O12 studied by using neutron powder diffraction data

Abstract

Crystal structural parameters of Bi4-xNdxTi3O12 (BNT, x = 0.25, 0.5, 0.75 and 1.0) were determined by means of neutron powder diffraction and Rietveld analysis based on the monoclinic space group of B1a1. The a-axis has been found to shrink monotonically from 5.4475(8) to 5.4100(1) angstrom with x increasing from 0 to 0.75. The orthorhombicity defined as 2(a-b)/(a+b) decreased with increasing x because the b-axis lattice parameter remained almost constant. The c-axis increases monotonically up to x = 0.75. The spontaneous polarization, which is oriented along the a-axis (P-s//a), decreased from 35.4 to 28.3, 24.8 and 22.2 mu C cm(-2) with x increasing from 0 to 0.25, 0.5 and 0.75, respectively as calculated by using the refined structural parameters. Thus, the substitution of Nd for Bi has been found to cause a considerable structural relaxation. Bi3Nd1Ti3O12 showed a considerably small a-lattice parameter of 5.4004 (1) angstrom and a very small P-s value of only 7.5 mu C cm(-2) indicating that its structure is orthorhombic or close to tetragonal.