Origins Of High Piezoelectricity In Lead-based Perovskites Revealed By In-situ High-energy X-ray

Lead-based perovskite ferroelectrics have been widely used as electromechanical devices due to their excellent piezoelectric,ferroelectric and dielectric properties.Lead-based perovskite antiferroelectrics have important potential application for transducers due to their large electrostrain.The origins of high piezoelectricity at morphotropic phase boundary(MPB)and large electrostrain in antiferroelectrics have attracted considerable attention.In this thesis,the lead-based perovskite ferroelectric and antiferroelectric ceramics were selected as the research subject.The electric-field-induced structure,domain switching,lattice evolution and their interaction were analyzed by employing in-situ high-energy X-ray diffraction/total scattering technology.Simultaneously,combined with the measurements of macroscopic properties,the correlation between these evolutions and the high piezoelectric response and large electrostrain was explored.Firstly,the behavior of monoclinic was studied under electric field,and the correlation between monoclinic polarization rotation and high piezoelectric response was revealed.In Pb(Mg1/3Nb2/3)O3-PbTiO3,electric-field-induced single monoclinic phase was observed.Under driven of bipolar electric field,the lattices of monoclinic structure exhibit reproducibly switching and flexible capacity and its polarization continuously and reversibly rotates between monoclinic Ma and MB regions,resulting in a butterfly shape.The direct structural evidence reveals the strong coupling role between lattice strain and polarization rotation.Subsequently,the behavior of monoclinic in several piezoelectric systems was studied under applied a weak electric field.It is found that,the piezoelectric property depends critically on the sensitivity of the polarization rotation.A strong tendency of electric-field-driven polarization rotation generates the peak piezoelectric performance,which is mainly attributed to intrinsic lattice strain and little to extrinsic domain wall motion.The role of reversible phase transformation for piezoelectric enhancement of MPB was revealed.Electric-field-driven reversible phase transformation was observed in various lead-based perovskite piezoelectric systems at the MPB and their piezoelectric performance are highly related to the tendency of electric-field-driven phase transformation.A strong tendency of phase transformation driven by an electric field generates peak piezoelectric response.Phase-field modeling reveals that the polarization alignment and the piezoelectric response can be much enhanced by the electric-field-driven phase transformation.A comparative study on the MPB and T phase composition of PbTiO3-Bi(Ni1/2Hf1/2)O3 revealed that electric-field-driven phase transformation enables the structures of coexisting phases to change easily,and can enhance the domain switching and lattice strain.The interaction of phase structure and domain switching was studied.In Pb(Zr0.54Ti0.47)O3,its long range average structure is rhombohedral and a saturated domain alignment and negligible domain switching was observed.But the in-situ total scattering measurements revealed that its short range local structure is monoclinic.The polarization in local monoclinic can rotate with electric field,and gives rise to such unique domain switching behavior.The phase coexisted MPB composition of PbTiO3-BiScO3 displays orientation-dependent emerging phase transformation and enhanced the domain switching.They exhibit strong synergistic interactions.Owing to this strong synergistic interaction,increasingly populated polarization variants aligned with the applied electric field,and thus enhances the piezoelectric performance at MPB.The structural evolution of PbZrO3-based antiferroelectrics during the electric-field-induced antiferroelectric-ferroelectric state transformation was studied.It was found that both antiferroelectric and ferroelectric phase exhibit negligible electric-field-induced domain reorientation and lattice strain.The large macroscopic electrostrain stems from intrinsic structural change associated large lattice strain and strong domain texture in intermediate ferroelectric phase at the phase transition.The results of in-situ total scattering experiments indicate that the electric-field-induced behavior of antiferroelectrics is determined by local structure.The electrostrain estimated from diffraction patterns is close to the macroscopic measured one,but the local strains are much lower.Based on the evolution of short,long range-structure,domain switching,lattice,and these interactions revealed by in-situ high-energy X-ray,the constitutive relationships between microstructure and properties is established.It will provide a theory foundation for the optimization and design of perovskite-type piezoelectric/ferroelectric materials.