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

Abstract

Lead-free relaxor ferroelectrics that feature a core-shell microstructure provide an excellent electromechanical response. They even have the potential to replace the environmentally hazardous lead-zirconia-titanate (PZT) in large strain actuation applications. Although the dielectric properties of core-shell ceramics have been extensively investigated, their piezoelectric properties are not yet well understood. To unravel the interfacial core-shell interaction, we studied the relaxation behaviour of field-induced ferroelectric domains in 0.75Bi1/2Na1/2TiO3-0.25SrTiO3 (BNT-25ST), as a typical core-shell bulk material, using a piezoresponse force microscope. We found that after poling, lateral domains emerged at the core-shell interface and propagated to the shell region. Phase field simulations showed that the increased electrical potential beneath the core is responsible for the in-plane domain evolution. Our results imply that the field-induced domains act as pivotal points at the coherent heterophase core-shell interface, reinforcing the phase transition in the non-polar shell and thus promoting the giant strain.

Chemical heterogeneity and approaches to its control in BiFeO3–BaTiO3 lead-free ferroelectrics

“…Elastic interactions between the shell and the core give rise to predominantly reversible ferroelectric switching behaviour. It was reported by Liu et al 91 that the strain and polarisation mismatch can also induce lateral domain nucleation at the interface of the core and shell in 0.75Bi 0.5 Na 0.5 TiO 3 -0.25SrTiO 3 ceramics. The occurrence of both inter-granular and intra-granular stresses could play an important role in the electro-mechanical fatigue behaviours of these core-shell structured materials, in addition to their influence on the polarisation-and strain-electric field relationships.…”

“…Recently, this type of microstructure has been reported in other Bi-based ferroelectrics. 66,91,67,92 In the case of 0.75Bi 0.5 Na 0.5 TiO 3 -0.25SrTiO 3 , a large unipolar strain output of 0.3% at 4 kV mm -1 was attributed to the effects of reversible electric field-driven phase transformations in the shell region. On the other hand, to our knowledge core-shell microstructures have not been reported previously in BiFeO 3 -BaTiO 3 ceramics.…”

Designing properties of (Na1/2Bix)TiO3-based materials through A-site non-stoichiometry

“…[13][14][15] A core-shell microstructure favored the development of a reversible high electrostrain at reduced electric field. 16 Despite the amount of work performed on the core-shell microstructure, other works on NBT-ST or related materials presented no evidence of a core-shell structure, [17][18][19][20][21][22][23][24][25][26][27][28][29][30][31][32][33] or it was proposed that no core-shell structure forms. 34,35 The electrical properties of the NBT-ST compounds also differ, despite similar synthesis parameters.…”

Large strain under low driving field in lead‐free relaxor/ferroelectric composite ceramics

“…It is well‐known that pure NBT–25ST is a typical core‐shell bulk material . The large strain response at low driving electric field of NBT–25ST ceramic is due to an electric‐field‐induced phase transition of the core and shell, ie, intergrain composite effect .…”