Achieving Large Switchable Polarization and Enhanced Piezoelectric Response in BiFeO₃-PbTiO₃ Solid Solution Ceramics

Perovskite materials based on BiFeO3-PbTiO3 (BFPT) solid solutions are promising for various applications thanks to the extremely large spontaneous polarization (P-s) and existence of multiferroic morphotropic phase boundary. For applications in piezoelectric and memory devices, complete switching of P-s is needed, which is hard to achieve practically. In this work, a simple modified mixed-oxide reaction method is developed allowing to prepare Dy- and Sm-modified BFPT ceramics with significantly improved properties. The MPB compositions demonstrate well-saturated ferroelectric hysteresis loops with large switchable remanent polarization of 60 mu C cm(-2) and enhanced piezoelectric properties with a large-signal piezoelectric coefficient d(33)* = 214 pm V-1 and a direct piezoelectric coefficient d(33) = 128 pC N-1, which is one and a half times larger than the best d(33) value reported for the BFPT ceramics so far. The Curie temperature reaches 539 degrees C, suggesting a potential for high-temperature applications. The domain structure is studied by piezoresponse force microscopy. It is found that the enhanced dielectric/piezoelectric properties are mainly due to polarization rotation/extension (intrinsic) mechanism, while the extrinsic contributions of the interphase and domain walls are virtually absent. The strategies for improvement of properties of BFPT and related materials are proposed.