Development And Structural Mechanism Of High-Performance Lead-based Perovskite-type Ferroelectric And Piezoelectric Ceramics

Lead-based perovskite-type ferroelectric and piezoelectric ceramics are essential functional materials of various electromechanical devices such as sensors,ultrasonic transducers,and displacement actuators,playing a critical role in biomedical,aerospace,and ocean detection fields.With the rapid development of modern science and technology,there is an urgent need to develop new materials with higher piezoelectric and electromechanical properties to meet the application requirements of various high-end devices.This thesis focuses on the polarization configuration of ferroelectric materials.The relationship between the long-range average structure and piezoelectric response of binary relaxor ferroelectric ceramics was investigated using in-situ electric field high-energy synchrotron X-ray diffraction techniques.On this basis,several new systems with high piezoelectric properties were developed by designing local polarization configuration,and the effect of local polarization distribution and domain configuration on piezoelectric properties was analyzed using aberration-corrected transmission electron microscopy.The hardening mechanism of defect polarization in this thesis were explored.Finally,a new system with both high piezoelectric and electromechanical properties was designed by regulating domain configuration and defect polarization,and the origin of excellent comprehensive performance were also revealed.The binary relaxor ferroelectric systems of Pb(Ni1/3Nb2/3)O3-PbTiO3(PNN-PT)and Pb(In1/2Nb1/2)O3-PbTiO3(PIN-PT)exhibit excellent piezoelectric and dielectric properties near the morphotropic phase boundary.In-situ high-energy synchrotron experiments confirm that the long-range average structure of PNN-PT is a single monoclinic phase.The presence of monoclinic and large intrinsic lattice strain induces high piezoelectric properties.The structure of PIN-PT is consisted of tetragonal and monoclinic phases,and it undergoes a reversible phase transition from tetragonal to monoclinic phase,enhancing the contribution of intrinsic lattice strain and external domain switching,thus promoting a high piezoelectric response.Based on the study of binary ferroelectric systems,a ternary Pb(Ni1/3Nb2/3)O3Pb(Sc1/2Nb1/2)O3-PbTiO3 system was designed(d33=804 pC/N).The average structure is a pseudocubic phase featuring small structural distortion,which exhibits a large lattice strain.Heterogeneous domains are also observed by transmission electron microscopy.The small structural distortion and heterogeneous domain configuration reduce the polarization anisotropy,and promote polarization rotation and lattice strain,leading to high piezoelectric properties.To further improve d33,multiple high-performance systems were designed by introducing B-site ions with different radii and valence states to increase chemical disorder and decrease local polarization anisotropy.These systems include Pb(Ni1/3Nb2/3)O3-Pb(In1/2Nb1/2)O3PbTiO3,Pb(Ni1/3Nb2/3)O3-Pb(Sc1/2Nb1/2)O3-Pb(Zr0.1Ti0.9)O3,and Pb(Ni1/3Nb2/3)O3Pb(In1/2Nb1/2)O3-Pb(Zr0.05Ti0.95)O3,with d33 values of 920 pC/N,930 pC/N,and 990 pC/N,respectively.The results indicate that the quasi-isotropic polarization distribution formed by correlated local multiple polar symmetries facilitates continuous polarization rotation,leading to a large field-induced lattice strain and significantly enhanced piezoelectric properties.Different low-valence ions with different valence states were quantitatively doped in Pb(Zr,Ti)O3 ceramics,and local defect polarization was designed in different structures to investigate the effect on the mechanical quality factor(Qm).It is found that Qm is related to the valence state of the accepter ions,the defect concentration and the pinning effect of defect polarization.The stronger the pinning effect,the better the Qm.Among various ions,In3+ can achieve the best hardening effect,while Mn2+can achieve the best d33 and Qm performance.Based on the above research,MnCO3 was introduced to regulate the domain configuration and local defect polarization in Pb(Ni1/3Nb2/3)O3-Pb(In1/2Nb1/2)O3PbTiO3,and excellent comprehensive performance was obtained(d33=545 pC/N,Qm=574).The doping of Mn2+increases the phase transition temperature(Tm=137℃)and changes the domain configuration.The high sensitivity of a small number of nanoscale domains maintains the d33 at a high level,while the most largesized layered domains increase the potential barrier for domain switching,thereby enhancing the Qm.The change of domain configuration and the design of defect polarization jointly induce high comprehensive performance.In this thesis,multiple systems with high piezoelectric and electromechanical performance were designed by regulating the long-range and local polarization configuration,providing new candidate materials for high-end devices.The mechanism of piezoelectric and electromechanical properties is deeply studied,and the relationship between micro structure and macro properties is established,which will provide a reference for designing new piezoelectric materials in the future.