The microstructure and ferroelectric property of Nd-doped multiferroic ceramics Bi0.85Nd0.15FeO3

The microstructures of Bi0.85Nd0.15FeO3 ceramics were investigated by using transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), selected area electron diffraction (SAED), convergent-beam electron diffraction (CBED) and X-ray energy dispersive spectrometry (EDS). The superstructure phase related to 1/4(hh0)p and 1/4(00 l)p diffraction spots were observed in the samples. It is found that the superstructure phase can co-exist with R3c phase in a single grain. The bright and dark field images accompanied with SAED patterns provided evidences of the superstructure phase dispersed into the matrix with R3c symmetry and evolution of the domain. The ferroelectric domain wall was observed according to the displacement of Fe3+ ions respect to Bi3+ sub-lattice in the ferroelectric R3c phase based on HRTEM observations. The space group Pnam of the superstructure was identified by combining SAED and CBED techniques. EDS measurement revealed that the concentration of Nd in the Pnam phase is higher than that in R3c phase. This might mean that the transition from R3c to Pnam structure is due to the inhomogeneous distribution of the Nd concentration and the weakened stereochemical activity of Bi3+ lone electron pair, arisen from the increase in Nd content.