Ferroelectric phases and relaxor states in the novel lead-free (1 − x) Bi1/2K1/2TiO3 − x BiScO3 system (0 ≤ x ≤ 0.3)
The novel lead-free Bi-based ferroelectric system with perovskite structure (1 − x) Bi1/2K1/2TiO3 − x BiScO3, chemically designed to show a ferroelectric morphotropic phase boundary (MPB) and high piezoelectric response, was synthesized by the conventional solid-state reaction method for compositions with 0 ≤ x ≤ 0.3. X-ray diffraction analysis shows that the samples possess perovskite-type structure for x < 0.3 and reveals a phase evolution in the symmetry from tetragonal for x < 0.1 to pseudocubic for 0.1 ≤ x ≤ 0.3. Electrical and piezoelectric properties of ceramic samples were systematically investigated, and results indicate that a ferroelectric MPB is not formed, but instead a transition from conventional ferroelectric to relaxor ferroelectric behavior occurs when increasing the (Bi, Sc) content between 5 and 10%. The origin of this unexpected effect, and its implications in the design of novel lead-free piezoelectric materials are discussed.