PMNT单晶电畴结构随组分与结构的变化

利用多种方法观察了弛豫型铁电单晶ＰＭＮＴ中电畴结构随组分与结构的演变过程与特征．观察发现,在ＰＭＮ－ＰＴ的三方相区内,随ＰＴ含量的增加,电畴结构表现出微畴一（亚微畴）－不规则宏畴一规则宏畴转变历程;在三方－四方相变中,非１８０°电畴发生７１°（或１０９°）宏畴－９０°宏畴的转化,同时电畴图像变得更为规则．根据不同组分ＰＭＮＴ电畴的显示特征,提出晶体的最大双折射率可以作为度量其弛豫性强弱的光学参数．观察到了电畴的分布不均匀与多级结构现象,前者与组分或结构的起伏有关,后者与多期式马氏体转变有关．本文还分析了偏光显微镜、ＤＩＣ、ＳＥＭ、ＳＥＡＭ等观察方法中电畴的成像特征．     

Pb(Mg1/3Nb2/3)O3-PbTiO3晶体组分对结构与性能的影响

用熔体Modified Brdgman法生长出尺寸直径40 mm长度80 mm的弛豫铁电单晶PMNT90/10,表明该方法不仅适合在准同型相界(MPB)附近生长PMNT单晶,也适合生长PT含量很低的PMNT单晶.在生长出的PMNT90/10晶体中,铁电相与顺电相两相共存,并呈现亚微畴结构特征.随着晶体组分由PMN组元变化到MPB组分附近,PMNT的电畴结构呈现微畴-亚微畴-不规则宏畴-规则宏畴演化系列,而介电弛豫特性则逐步弱化.PMNT固熔体的电学性能依赖于晶体组分,(001)切型PMNT90/10晶体的压电常数d33约80 pC/N,显著低于MPB附近组分,但其介电常数ε达到12600,明显高于后者.     

{110}cub切型Pb(Mg1/3Nb2/3)O3-PbTiO3单晶铁电相变的研究

测试了PMNT68／32{110}cub切型单晶的介电、压电性能和电滞回线，发现单晶铁电性能与所施加的极化电场及单晶中PbTiO3含量的变化密切相关。研究结果表明，相结构的变化是引起铁电性能变化的主要原因，即在＜110＞取向施加电场诱导出来的正交相是本征亚稳的，它的稳定性不仅取决于所施加的极化电场大小，而且与单晶中PbTiO3含量的变化密切相关。     

弛豫铁电单晶压差水听器有限元设计

分析了[001]切型PMNT弛豫铁电单晶各向异性的压电特性,利用有限元软件对PMNT弛豫铁电单晶压差水听器进行仿真计算,设计制作了压电三叠片压差水听器。仿真与测试结果表明:[001]切型PMNT弛豫铁电单晶可近似等效为横观各向同性材料,在轴对称结构压差水听器设计中具有一定的应用优势,压差水听器的测试结果与有限元仿真结果相符。     

掺杂对PMN-10PT铁电陶瓷介电性能的影响

铌镁酸铅与钛酸铅组成比为9:1(PMN-10PT)的固溶体陶瓷是典型的弛豫铁电体,其介电行为与偶极玻璃的介电行为极为相似.本文使用常用的Swartz两步法,研究了基体掺杂不同物质对PMN-10PT铁电陶瓷的介电性能的影响.经研究发现,当掺入Li₂O时,材料的峰值介电常数为28640,大于纯PMN-10PT,而频率色散和弥散相变的程度都变小.当掺杂CaO和Yb₂O₃时,材料的峰值介电常数下降,分别为19300和18850,它们的频率色散和弥散相变的程度都变大了.同时通过拉曼光谱研究了PMN-10PT陶瓷的B位离子有序度的变化.     

PMN-PT弛豫铁电单晶畴结构的压电响应力显微术研究

利用压电响应力显微术开展了PMN-PT弛豫铁电单晶铁电畴结构的三维极化取向成像、畴结构的不均匀性及极化状态稳定性机理的研究.揭示了纳米尺度畴结构的不均匀性源于纳米尺度极性微区的相互作用和无规场之间的共同调制,而单晶表面屏蔽电荷机制主要源于大气环境下水的溶解性吸附,该机制对PMN-PT单晶中畴状态的稳定性及材料最佳性能的发挥起着重要作用.     

Pb[(Zn1/3Nb2/3)0.91Ti0.09]O3压电单晶的弛豫反常

对用改进的Bridgman法生长的Pb[(Zn1/3Nb2/3)0.91Ti0.09]O3(PZNT91/9)单晶用Laue衍射法和XRD衍射曲线定向,取(001)晶片研究材料的电学性能.结果表明,材料的介电性能呈现出明显的频率色散现象,随着测试频率的升高,介电常数的峰值温度出现反常,峰的位置向低温方向移动.用扫描电子显微镜和正交偏光显微镜研究了PZNT91/9单晶的电畴结构,发现规则排列的带状畴与杂乱分布的细畴并存.X射线荧光分析结果表明,在PZNT91/9单晶中存在着由成分分凝引起的组分变化.成分分凝引起的组分波动和电畴结构的复杂性导致了材料性能的不均匀性,并与材料铁电相变的弥散性特征相关.     

近化学计量比LiNbO3晶体电畴结构观察和机理探讨

采用双坩埚提拉法(DCCZ)生长了各种不同成分的近化学计量比LiNbO3晶体,并用腐蚀法观察了其电畴结构.结果表明,化学成分对未经极化处理晶体的电畴结构起决定性作用,当Li2O含量处于49.4mol%附近时,晶体z面电畴呈现特殊的三次对称反畴;当晶体中Li2O含量为49.7mol%时,晶体为完全单畴.本文对其形成机理进行了探讨,认为在由顺电相向铁电相转变时,局部铁电畴的极性方向与该处沿z轴方向的温度梯度正负密切相关,z轴生长晶体时,由于相变发生所处位置离生长界面的距离受LiNbO3晶体计量比影响,所处温场固有温梯也随之不同,在此基础上解释了不同成分晶体的电畴结构形成原因.最后讨论了控制铁电畴结构的工艺措施.     

近化学计量比LiNbO3晶体电畴结构观察和机理探讨

采用双坩埚提拉法(DCCZ)生长了各种不同成分的近化学计量比LiNbO₃晶体, 并用腐蚀法观察了其电畴结构. 结果表明, 化学成分对未经极化处理晶体的电畴结构起决定性作用, 当Li₂O 含量处于49.4mol%附近时, 晶体z面电畴呈现特殊的三次对称反畴; 当晶体中Li₂O含量为49.7mol%时, 晶体为完全单畴. 本文对其形成机理进行了探讨, 认为在由顺电相向铁电相转变 时, 局部铁电畴的极性方向与该处沿z轴方向的温度梯度正负密切相关, z轴生长晶体时, 由于相变发生所处位置离生长界面的距离受LiNbO₃晶体计量比影响, 所处温场固有温梯也 随之不同, 在此基础上解释了不同成分晶体的电畴结构形成原因. 最后讨论了控制铁电畴结构的工艺措施.     

扫描探针显微镜研究弛豫铁电体电畴生长

本文研究了典型弛豫铁电陶瓷0．9PMN－0．1PT中的电畴生长过程．用扫描探针显微镜的轻敲模式和抬举模式对驰豫铁电陶瓷的表面形貌和电场力像进行了观察．结果表明,在施加不同针尖电压（0．05、0．5、1V）的情况下,能够诱导材料中纳米尺度极化微区通过沿＜111＞方向180°反转,从而形成亚微米尺度电畴．     

Mechanical and thermal transitions in morphotropic PZN-pT and PMN-PT single crystals and their implication for sound projectors

Isothermal compression experiments on multidomain [001] oriented and poled ferroelectric rhombohedral PZN-0.07PT and PMN-0.30PT single crystals revealed elastic instabilities corresponding to zero field ferroelectric-ferroelectric phase transition under mechanical compression. The application of an appropriate dc bias field doubled the stability range of the ferroelectric rhombohedral state under uniaxial compression for both crystals and maintained a linear elastic response. Young's modulus as derived from the quasistatic, zero field stress-strain linear response agreed well with that derived from small signal resonance for the ferroelectric rhombohedral FR state of both PZN-PT and PMN-PT. Elastic compliances s(E)33 as determined from high temperature resonance revealed a monotonically decreasing Young's modulus as a function of temperature in the ferroelectric rhombohedral state with a sudden stiffening near the ferroelectric rhombohedral (FR)-ferroelectric tetragonal (FT) transition. The reversible ferroelectric-ferroelectric transition of morphotropic PZN-PT and PMN-PT single crystals as accessed by mechanical compression is discussed in terms of strain calculations from Devonshire's theory, domain unfolding, and morphotropic phase boundary shift with mechanical stress. The mechanically-induced and thermally-induced ferroelectric-ferroelectric transition trajectories are discussed in terms of the Devonshire theory. Implications of these observations for sound projectors are discussed. A single crystal tonpilz projector fabricated into a 16-element array and a segmented cylinder transducer demonstrated the outstanding capabilities of single crystals to achieve compact, broadband, and high-source level projectors when compared to conventional lead zirconate-titanate PZT8 projectors.     

Electromechanical coupling properties of [001], [011] and [111] poled Pb(Mg1/3Nb2/3)O3-0.32PbTiO3 single crystals

The electric field induced “butterfly” curves and polarization loops, and the stress induced strain and polarization responses of [001], [011] and [111] oriented Pb(Mg_1/3Nb_2/3)O₃-0.32PbTiO₃ (PMN-0.32 PT) relaxor ferroelectric single crystals have been systematically investigated by experiment study. The focus is on the effect of constant compressive bias stress on the electromechanical coupling behavior along three crystallographic directions of PMN-0.32 PT single crystals. Dependence of the coercive field, remnant polarization, dielectric constant, and piezoelectric coefficient on the bias stress has been quantified for PMN-0.32 PT single crystals oriented in three different directions. Obtained results show that the large piezoelectric responses under zero compressive stress in [001] and [011] orientation are dominated by intrinsic crystal lattice while the engineered domain structure has a relatively minor effect. It is found that observed responses under stress cycle for [001] oriented crystals are due to polarization rotation and phase transformations. However, those for [011] and [111] oriented crystals are due to domain switching. The “butterfly” curves and polarization loops driven by electric field under different bias compression are described by two non-180° domain switching.     

Relations between single-domain and multidomain piezoelastic properties in single crystals

This paper presents a new method to compute the piezoelastic properties of multidomain single crystals from the single-domain constants. Based on a quasi static assumption, a PMN-chiPT multidomain is defined as a periodic medium with a lattice composed of layers of two domains in a twin structure. Such a structure is assumed to have charged domain walls that imply specific lattice media and boundary conditions. A numerical computation has been performed for a PMN-33PT single crystal in the rhombohedral phase. The effective elastic, piezoelectric, and dielectric constants of the macroscopic structure have been calculated, as well as the wave velocities in different configurations of domain patterns.     

Single crystal growth in PMN-PT and PMN-PZT

Single crystal growth of lead-based piezoelectric ceramics Pb(Mg_1/3Nb_2/3)_0.68Ti_0.32O₃ (PMN-32PT) and Pb(Mg_1/3Nb_2/3)_0.42(Ti_0.638Zr_0.362)_0.58O₃ (PMN-37PT-21PZ) ceramics via templated grain growth (TGG) was investigated. (001)- and (111)-oriented BaTiO₃ (BT) single crystals and (001)-oriented SrTiO₃ (ST) single crystals (of approximately 2.5 × 2.5 × 1 mm) were utilized as seeds for the growth experiments. The piezoelectric single crystals were produced in a process that involves at first hot pressing of single crystal in cold isostatically pressed ceramics followed by subsequent sintering of the samples. Growth of (001)-oriented single crystals with BT seeds was observed in both PMN-32PT and PMN-37PT-21PZ matrices. The measured growth lengths were up to 140 and 65 μm, respectively. The grown (001)-oriented single crystals grown were rectangular. The measured growth lengths of the pyramidal-shaped (111) BT single crystals were up to 1 mm, which is much larger than the growth lengths of the (001) single crystals. Experiments on (001) ST-seeded single crystals were not successful. No single crystal growth was observed due to the dissolution of the ST single crystals in the PMN-PZT matrix. The differences were explained by defect-chemical considerations.     

弛豫型铁电体PZNT制备与性能研究的进展

本文综述了近年来国际上弛豫型铁电体PZNT的制备与介电、压电及电致伸缩性能研究的进展．PZNT单晶体的制备方法以高温PbO熔剂法为主,其尺寸已达40mm．随PT含量的变化,PZNT的顺电一铁电相交由弥散性、混合型变为一级相变;其铁电-铁电相变可由组份或电场诱导,由介电性能表征．压电性能在MPB处及偏向三方相一侧达到最佳,＜001＞切向的三方相与四方相单晶可分别作为频带宽、分辨率高、且阻抗匹配好的新一代声阵列与单个器件传感器．＜001＞向的PZNT单晶具有巨大的电致伸缩应变,可望成为高性能的固体驱动器．     

弛豫型铁电体PZNT制备与性能研究的进展

本文综述了近年来国际上弛豫型铁电体PZNT的制备与介电、压电及电致伸缩性能研究的进展．PZNT单晶体的制备方法以高温PbO熔剂法为主,其尺寸已达40mm．随PT含量的变化,PZNT的顺电一铁电相交由弥散性、混合型变为一级相变;其铁电-铁电相变可由组份或电场诱导,由介电性能表征．压电性能在MPB处及偏向三方相一侧达到最佳,＜001＞切向的三方相与四方相单晶可分别作为频带宽、分辨率高、且阻抗匹配好的新一代声阵列与单个器件传感器．＜001＞向的PZNT单晶具有巨大的电致伸缩应变,可望成为高性能的固体驱动器．     

Dielectric and elastic properties of 0.70Pb(Mg1/3Nb2/3)O3–0.30PbTiO3 single crystal and their electric-field dependence

The dielectric and elastic properties of [001]_c-oriented 0.7Pb(Mg_1/3Nb_2/3)O₃–0.3PbTiO₃ (PMN–0.3PT) crystal were investigated as a function of poling field at 300 and 360 K, respectively. At 300 K, the dielectric constant and elastic compliance of rhombohedral PMN–0.3PT crystal change drastically at a critical field corresponding to an electric-induced ferroelectric phase transition. At 360 K, the PMN–0.3PT crystal is tetragonal, its dielectric constant and elastic compliance change drastically at two critical fields, which indicates an intermediate phase. Furthermore, much small dielectric loss factors and mechanical loss factors are observed in mono-domain state, which indicates that losses mainly come from domain wall contributions.     

The influence of defects on ferroelectric and pyroelectric properties of Pb(Mg1/3Nb2/3)O3-0.28PbTiO3 single crystals

Relaxor-based ferroelectric single crystals 0.72Pb(Mg_1/3Nb_2/3)O₃-0.28PbTiO₃ (PMN-0.28PT) were grown by a modified Bridgman technique. The direct current (dc) conductivity was investigated and corresponding conduction mechanisms were discussed. V^″Pb−VO defects are dominant from 245 °C to 650 °C. The ferroelectric properties of [1 1 1]-oriented PMN-0.28PT were systematically investigated, with the coercive field (E_c) of 5.2 kV cm⁻¹ and remnant polarization (P_r) of 37.8 μC cm⁻² at room temperature. Moreover, the dielectric and pyroelectric performances of PMN-0.28PT were measured and the integrated pyroelectric performances greatly enhanced after annealing in oxygen at 500 °C for 20 h. This is due to the decrease of oxygen vacancies in the single crystals when being annealed in the oxygen-rich atmosphere. These make [1 1 1]-oriented PMN-0.28PT crystals a promising candidate for infrared detectors and thermal imagers used at room temperature.     

Piezoelectric properties of niobium-doped 18PMN-41PZ-41PT ceramics

The effects of various amounts of excess niobium ions added to the 18PMN-41PZ-41PT three-component ceramics system on the crystal structure, microstructure, polarization versus electric field, strain versus electric field and piezoelectric properties, have been studied. It was found that addition of niobium ions to 18PMN-41PZ-41PT induced a change in the crystal structure from rhombohedral to tetragonal phase. The excessive niobium ions also formed a micro-second phase which existed in the grain boundary, which could refine and uniform the grain. The refined and uniformed microstructure was found to increase the remanent polarization, saturation strain, planar coupling coefficient, K _p, and mechanical quality factor, the best value of K _p being 69%.     

Toughening due to domain switching in single crystal ferroelectric materials

In this paper Mode I steady state crack growth in single crystal ferroelectric materials is investigated. Specifically, the fracture toughness enhancement due to domain switching near a steadily growing crack tip is analyzed. For this purpose, an incremental phenomenological constitutive law for single crystal ferroelectric materials is implemented within a finite element model to calculate the stress and remanent strain fields around the crack tip. Also, the ratio of the far field applied energy release rate to the crack tip energy release rate, i.e. the toughening, is calculated. The numerical computations are carried out for single crystal ferroelectric materials of tetragonal or rhombohedral structure with different switching hardening and irreversible remanent strain levels. Toughening levels for crack growth along different crystallographic directions and planes are obtained and compared. Results from numerical computations for the toughening anisotropy for both tetragonal and rhombohedral crystals are presented and discussed.