Effects of B-Site Donor Modification on the Crystal Structure and the Electrical Properties of Lead-Free 0.65BiFeO₃-0.35BaTiO₃ Ceramics

In the present work, lead-free piezoelectric ceramics 0.65Bi_1.05Fe_1−xTi_xO₃-0.35BaTi_1−yNb_yO₃, where x = y = 0, 0.01, 0.015, 0.02, and 0.025, abbreviated as BFT-BTNb, were successfully synthesized by a solid-state reaction method and an air quenching method. The effects of B-Site donor modifications (Nb⁵⁺ and Ti⁴⁺) on the crystal structure, the morphology and the electrical properties of the 0.65BF-0.35BT ceramics were studied. X-ray diffraction patterns showed the formation of a pure perovskite structure, without any secondary phases. Scanning electron microscope (SEM) micrographs revealed that the average grain size of the BF-BT ceramics decreased with the addition of B-Site donors. Improvements in the ferroelectric properties (P-E loops) and the electric field-induced strain properties (S-E loops) were obtained at the optimum composition of the BFT-BTN ceramics. In addition, the dynamic piezoelectric coefficient (d₃₃ ^*) was enhanced from 265 pm/V for (BFT-BTNb-0) to 360 pm/V for (BFT-BTNb-1) with high working temperature, T_m = 320 °C.