Revealing the core-shell interactions of a giant strain relaxor ferroelectric 0.75Bi1/2Na1/2TiO3-0.25SrTiO3

Morphotropic Relaxor Boundary Construction Highly Boosts the Piezoelectric Properties of Bi-Based Lead-Free Thin Films

To achieve large electrostrain and low hysteresis, we further optimized a morphotropic phase boundary (MPB) by modulating its local polar symmetries. The construction of a morphotropic relaxor boundary (MRB) in thin films can be achieved by suitable introduction of Bi(Fe_0.95Mn_0.03Ti_0.02)O₃ into (Bi_0.5Na_0.5)TiO₃-SrTiO₃ to form a solid solution. The designed thin film achieves surprising piezoelectric properties with an inverse piezoelectric coefficient of 179.7 pm V^-1 and negligible hysteresis. The composition of two relaxors with different local polar symmetries (tetragonal nanoregions and rhombohedral nanoregions), namely, an MRB, and the coexistence of multiscale domain structures can greatly weaken the anisotropy of polarization, degrade the energy barrier, attenuate the discontinuity of polarization, and achieve a large electrostrain and low hysteresis. The domain dynamics of the PNRs under the action of an external excitation field are analyzed to clarify the enhancement mechanism. This construction of MRBs is feasible for producing lead-free piezoelectric films with high-voltage electrical properties and low hysteresis, and various experimental design and theoretical references are provided.

Macroscopic and local approaches of phase transition in sol-gel synthesized (Bi0.5Na0.5)TiO3-SrTiO3 thin films

High-quality (1 - x)(Bi0.5Na0.5)TiO3-xSrTiO3 lead-free piezoelectric thin films (x = 0, 0.1, and 0.25) on Pt(111)/Ti/SiO2/Si(100) substrates were prepared by a sol-gel method. The microstructures of the thin films as a function of SrTiO3 doping level and temperature were investigated by X-ray diffraction and Raman spectroscopy. Their temperature- and frequency-dependent piezoelectric properties were studied on the nanoscale using switching spectroscopy piezoresponse force microscopy (SS-PFM). A rhombohedral ferroelectric to pseudocubic relaxor phase transition was observed when either ST content or temperature increased. The significant frequency dependence of both ferroelectric and piezoelectric properties was also disclosed by analyzing polarization hysteresis loops on the macroscopic scale and local switching dynamics at various frequencies. It was determined that the short-range order clusters came out through the long-range ferroelectric order, thus the nanoscale approaches are consistent with macroscopic data at elevated temperatures and various frequency ranges.