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 electrooptical 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., 0.9BaTiO(3)-0.1BiScO(3), 0.8BaTiO(3)-0.2Bi(Mg1/2Ti1/2)O-3, 0.8BaTiO(3)-0.2Bi(Mg2/3Nb1/3)O-3, 0.5BaTiO(3)-0.5Pb(Mg1/3Nb2/3)O-3, 0.4BaTiO(3)-0.6Pb(Zn1/3Nb2/3)O-3, 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.