The Phase Transformation Of Dy Doped BiFeO₃Ceramics From Ferroelectric To Paraelectric

Lead zirconate titanate (PZT) has a great application in many aspects like sensors and actuators. However, because of the dangers of lead on the environment, its application has been limited. Researching lead-free materials to replace lead-based materials becomes a hotspot in recent years. BiFeO3(BFO) is well known due to the high Curie temperature of810℃and ferromagnetic transition temperature of370℃, expected to be applied above room temperature. Nevertheless, pure BiFeO3material has many drawbacks which restrict its application like the large leakage current, the small polarization and the weak magnetoelectric coupling coefficient. Here, we dope BiFeO3ceramics with rare earth element Dy to research (1) the lattice structural change, the evolvement of (2) samples’electric properties and (3) Cure temperature with different Dy concentration. Meanwhile, we expect a morphotropic phase boundary (MPB) with a sharp increase in electrical properties at a certain Dy concentration. The piezoelectric performance of BiFeO3and Bio.92Dyo.osFe03at high temperatures are also studied. The results demonstrate the potential application of BiFeO3family as a substitute for lead-based materials in the future.Insulated Bi1-xDyxFeO3(x=0-0.2) ceramics are prepared after studying the influence of sintering temperature and time on properties of samples. Then the phase structure evolution of Bi1-xDyxFeO3is studied. Bi1-xDyxFeO3(x=0-0.08) shows rhombohedral R3c phase at room temperature. There are both ferroelectric phase and PZT-like anti-polar orthorhombic phase in Bi1-xDyxFeO3(x=0.11-0.17). Finally, Bi1-xDyxFeO3(x=0.2) transforms to non-polar orthorhombic phase according to structural and electric measurements. Temperature also plays an important role in the phase transition. With rhombohedral structure at room temperature, Bi0.92Dy0.08Fe03allows the coexistence of rhombohedral phase and orthorhombic phase at250-650℃.The dielectric curve (εr-F) of Bi1-xDyxFeO3shows that the relative dielectric constant at x<0.1is about80at1kHz. Then the constant increases sharply, emerging a strong and wide peak in εr-F curve at x=0.1-0.2. The maximum(-180) appears at x=0.17. This phenomenon is ascribed to the transition from rhombohedral phase to orthorhombic phase.Compared with pure BiFeO3ceramic, Bi1-xDyxFeO3ceramics show higher piezoelectric and ferroelectric properties with ferroelectric polarization of27μC/cm2and piezoelectric d33of35pC/N at x=0.08, which is near the MPB.The pizeoelectric properties in poled Bi1-xDyxFeO3at various temperatures show the existence of ferroelectric phase below700℃. Especially, obvious dielectric resonances observed in Bi0.92Dy0.08FeO3indicate that the sample may be applied at high temperature.