Synthesis and investigation of electromechanical property of lead-free BiFeO₃-BaTiO₃ quenched ceramics

Lead-free bulk ceramics 0.67Bi(1.03)Fe(1-x)Nb(x)O(3)-0.33BaTiO(3) (BFNbBT with x = 0.00, 0.01, 0.02 and 0.03) were fabricated via a solid-state reaction method and then quenched in the air from its sintering temperature. The XRD analysis shows a morphotropic phase boundary between rhombohedral and tetragonal phases for the un-doped BFBT ceramics. Therefore, a high static piezoelectric coefficient (d(33) approximate to 268 pC/N) with a large remnant polarization (P-r approximate to 20 mu C/cm(2)) and the highest Curie temperature (T-C approximate to 510 degrees C) were obtained. However, with Nb doping, a compositionally driven phase transformation occurred from rhombohedral and tetragonal mixed phase to pseudo-cubic phase. Because of the Nb doping, the grain size suddenly decreased, as a result, the long-range ferroelectric phase was converted into a short-range relaxor phase. Hence, a high dynamic piezoelectric constant (d(33)* approximate to 353 pm/V) was achieved at the crossover boundary between the normal and relaxor ferroelectric phases. In the current investigated results, the microstructure and crystal structure properties show a strong correlation with dielectric, ferroelectric and piezoelectric properties.