Boosting the High Performance of BiFeO-BaTiO Lead-Free Piezoelectric Ceramics: One-Step Preparation and Reaction Mechanisms.

One of the notorious problems in BiFeO-based piezoelectric ceramics is how to limit the formation of BiFeO and BiFeO impurities to achieve excellent piezoelectric performance. In this study, a one-step preparation technology, namely, excluding PVA, calcining, and sintering are completed in one step, instead of three steps in the ordinary sintering method, is developed to prepare BiFeO-BaTiO (BF-BT) ceramics. The significance of this one-step method is that the thermodynamically unstable region of BiFeO is successfully avoided based on the Gibbs free energy of BiFeO, BiFeO, and BiFeO. Benefiting from preventing the formation of BiFeO and BiFeO impurities, the resultant ceramics show dense structures, macroscopic stripe domains, and a small number of island domains and display saturated - curves, sharp - characteristics, butterfly-shape - loops, and good piezoelectric properties ( = 174-199 pC/N; = 494-513 °C). By analyzing X-ray diffraction patterns of BF-BT (0 ≤ ≤ 1) powders at different calcination temperatures (), the different reaction mechanisms between 750 °C ≤ ≤ 900 °C and 950 °C ≤ ≤ 1000 °C are revealed. When 750 °C ≤ ≤ 900 °C, Bi diffuses into FeO particles to form BiFeO and BiFeO and then reacts with BaTiO; in this temperature range, the formed BiFeO is hard to eliminate. At 950 °C ≤ ≤ 1000 °C, Bi and Fe ions simultaneously diffuse into BaTiO to form BF-BT, which is beneficial to preventing the formation of BiFeO and the improvement of performance.