【作者】 刘辉；

【导师】 陈骏；

【作者基本信息】 北京科技大学 ， 冶金工程， 2020， 博士

【摘要】 铅基钙钛矿铁电材料因其优异的压电、铁电、介电性能广泛的应用于机电器件;铅基钙钛矿反铁电材料因其大的电致应变,在换能器等方面具有重要的应用前景。铅基钙钛矿铁电材料准同型相界处极其优异的压电性能及反铁电材料的大电致应变起源一直是研究热点。本论文以铅基钙钛矿铁电、反铁电陶瓷为研究对象,基于原位高能同步辐射X射线衍射及全散射方法分析电场作用下相结构、晶格、电畴的响应及三者的耦合关系。结合宏观电学性能分析,探讨三者与宏观压电响应、电致应变的关联,阐述优异压电性及大电致应变的起源。首先,本论文研究了单斜相在电场作用下的行为,揭示了单斜极化旋转与压电性能的关联。在Pb(Mg1/3Nb2/3)O3-PbTi03中发现了电场诱导的单一单斜相,其单胞参数随电场作用呈现蝴蝶形,极化矢量在MA与MB之间可逆连续旋转,给出了单斜相中晶格应变与极化旋转强耦合作用的晶体结构证据。随后,通过研究不同体系中单斜相在弱电场作用下的行为及其宏观压电性能发现:压电响应与极化旋转高度相关,电场驱动敏感的极化旋转对应着高的压电性能:单斜相的压电响应来源于大的晶格应变,而不是铁电畴翻转。揭示了 MPB相共存体系可逆相转变的压电增强作用。在多个铅基钙钛矿MPB相共存体系发现了电场作用下可逆相转变,并且其压电性能与相转变是紧密关联的,电场驱动大的相含量变化对应着高的压电性能,相转变增进了电极化随电场的翻转。对PbTiO3-Bi(Ni1/2Hf1/2)O3四方相和MPB组分对比研究发现,电场诱导的可逆相变转使得MPB组分拥有灵活的相结构,同时也增强了铁电畴翻转和晶格应变。研究了相结构与铁电畴翻转的关联作用。在Pb(Zr0.54Ti0.47)O3研究发现,其长程平均结构为三方相,铁电畴定向度可达到饱和状态,在退电场过程中几乎无铁电畴翻转。但其短程局域结构为单斜相,电场驱动局域单斜极化旋转是这种异常的铁电畴翻转的起因。在MPB相共存PbTiO3-BiScO3研究发现,电场作用下表现出强取向分布的增强铁电畴翻转和涌现的相转变,二者具有非常强的协同交互作用;相场模拟说明这种协同作用促进了电极化定向,进而增强了压电性能。研究了 PbZrO3基钙钛矿反铁电陶瓷在电场作用下的长程、局域结构的演变。原位衍射研究表明反铁相和中间铁电相都表现为小的场致晶格应变和电畴翻转;反铁电铁电相转变过程大的电致应变起源于相变过程中大的晶格应变及中间相铁电相形成的强铁电畴织构。随后对不同组分的反铁电陶瓷研究表明其电场作用下的遍历行为取决于短程局域结构,而不是长程平均结构;基于衍射图谱计算的电致应变与宏观电致应变相近,但是通过对分布函数得到的局域电致应变偏小。基于电场作用下的短程、长程结构,电畴及晶格演变规律,及其的耦合交互作用的认识,构建的微观结构演变与宏观性能的关系,对今后铅基、无铅钙钛矿铁电反铁电材料性能的精准调控及新型高性能材料开发,设计提供一定的理论依据。更多还原

【Abstract】 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.更多还原