Effect of Nd substitution on the microstructure and electrical properties of Bi7Ti4NbO21 piezoceramics

Neodymium (Nd) doped intergrowth bismuth layer-structured ferroelectric compounds Bi7−xNdxTi4NbO21 (x = 0, 0.5, 0.75, 1.0, 1.25, 1.5, 1.75 and 2.0) were synthesized through a solid-state method. The influence of the Nd3+ substitution of Bi3+ on the lattice, microstructure and electrical properties of these compounds were investigated. The X-ray diffraction and Raman scattering analyses demonstrate that a phase transition from orthorhombic to pseudo-tetragonal occurs in these compounds, relying on substitution proportions and sites of Nd3+ for Bi3+. With the increasing Nd3+ dopants, the growth of plate-like grains along the a–b plane and a secondary intergranular metallic Bi phase were retarded which resulted in the increases of sintering temperature, density and electrical resistance of the doped ceramics. The resultant ceramic with x = 1.25 possesses a piezoelectric coefficient d33 up to 16.3 pC/N with a Curie temperature TC above 750 °C were obtained for the compound.