Abnormal phase transition and polarization mismatch phenomena in BaTiO3-based relaxor ferroelectrics

Relaxor ferroelectrics have been extensively studied due to their outstanding dielectric, piezoelectric, energy storage, and electro-optical properties. Although various theories were proposed to elaborate on the relaxation phenomena, polar nanoregions formed by disruption of the long-range-order structures are considered to play a key role in relaxor ferroelectrics. Generally, relaxor ferroelectrics are formed by aliovalent substitution or isovalent substitution in normal ferroelectrics, or further combinations of solid solutions. Herein, one category of BaTiO3-based relaxor ferroelectrics with abnormal phase transition and polarization mismatch phenomena is focused. Characteristic parameters of such BaTiO3-based relaxor ferroelectrics, including the Curie temperature, polarization, and lattice parameter, show a typical “U”-shaped variation with compositions. The studied BaTiO3-based relaxor ferroelectrics are mostly solid solutions of A -site coupling and B -site coupling ferroelectrics, exhibiting polarization mismatch in certain compositions [e.g., 0.9BaTiO3–0.1BiScO3, 0.8BaTiO3–0.2Bi( Mg 1 ∕ 2 Ti 1 ∕ 2 ) O3, 0.8BaTiO3–0.2Bi( Mg 2 ∕ 3 Nb 1 ∕ 3 ) O3, 0.5BaTiO3–0.5Pb( Mg 1 ∕ 3 Nb 2 ∕ 3 ) O3, 0.4BaTiO3–0.6Pb( Zn 1 ∕ 3 Nb 2 ∕ 3 ) O3, etc.]. Of particular interest is that excellent electrical properties can be achieved in the studied relaxor ferroelectrics. Therefore, polarization mismatch theory can also provide guidance for the design of new high-performance lead-free relaxor ferroelectrics.