电场诱导PZST陶瓷反铁电-铁电相变

研究了ＰＺＳＴ陶瓷电场诱导反铁电－铁电相变。当外加电场大于相变临界参数ＥＡＦＥ－ＦＥ时,样品由反铁电态诱导为铁电态,并在宏观性能上产生突变：极化强度和纵向应变分别由零跃变到大约３０μＣ／ｃｍ＾２和０．３％,介电常数下降５０％。利用直流偏压原位Ｘ射线衍射表征为相变时晶格结构的变化,结果表明,伴随着相变的发生,晶格结构由反铁电四方相转变为铁电三方相。     

掺铌Pb(Zr,Sn,Ti)O3反铁电-铁电转换电场的研究

研究了掺铌PZST反铁电陶瓷中组份和温度对诱导反铁电－铁电相变转换电场的影响,测定了Pb0.99Nb0.02((Zr0.80Sn0.20)1-yTiy)0.98O3系中正向转换电场EF与组份y(Ti)的关系和电极化前后的反铁电／铁电相界。实验测量结果显示,某组份y(Ti)的反映电－铁电转换强度大小取决于该组份与铁电／铁电相界组份的差距。在Pb0.99Nb0.02((Zr0.80Sn0.20)1-yTiy)0.98O3系中随着试样温度升高,反向转换电场EB保持不变,正向转换电场EF和电滞△E降低。这一现象表明温度有助于降低反铁电－铁电相变的应能使得电场诱导反铁电－铁电相变容易进行,因此可以采用加热电极化方法来降低极化电场强度。     

PZT基陶瓷铁电－反铁电相界处各向异性的研究

本文研究了两个以ＰＺＴ瓷为基的系统：ＰＺＴ（Ｎｂ）和ＰＳＺＴ陶瓷在铁电－反铁电相界区域的压电和机电耦合等性能．结果表明，ＰＺＴ基陶瓷在该相界处具有高Ｋｔ和低Ｋｐ的性质．压电和机电耦合各向异性也比准同型相界要高，｜ｄ３３／ｄ３１｜＞５．５，Ｋｔ／Ｋｐ＞３．０．借助于电场诱导ＡＦ—Ｆ相变和反铁电双子晶格间的强耦合作用，对此现象作了较好解释．     

PZT基陶瓷铁电—反铁电相界处各向异性的研究

本文研究了两个以ＰＺＴ陶瓷为基的系统：ＰＺＴ（Ｎｂ）和ＰＳＺＴ陶瓷在铁电－反铁电相界区域的压电和机电耦合等性能。结果表明，ＰＺＴ基陶瓷在该相界处具有高Ｋｔ和低Ｋｐ的性质。压电和机电耦合各向异性也比准同型相界要高，│ｄ３３／ｄ３１│〉５．５，Ｋｔ／Ｋｐ〉３．０。借助于电场诱导ＡＦ→Ｆ相变和反铁电双子晶格间的强耦合作用，对此现象作了较好解释。     

PbZrO3晶体反铁电相至电场感应铁电相相变的研究

仔细研究了电场感应PbZrO3铁电相的晶体结构。在PbZrO3处于反铁电相时，各离子位移方向与极轴垂直。在外电场感应下，Pb离子沿极轴方向有相同方向0．17A的位移，从而使晶体呈现铁电相特征，发生反铁电-铁电相变。此铁电相称之为电场感应铁电相（EFI，Electric—Field—Induced）。通过结构对称性分析，确定EFI铁电相的对称性是C2mm（G2v），用极矢量Ps作为序参量来描述相变时对称性的变化是合适的。     

溶胶凝胶法制备掺铅钛酸钡纳米晶及其结构相变

采用溶胶－凝胶工艺制备了不同晶粒大小的、掺铅（５ｍｏｌ％）钛酸钡（ＢＰＴ）纳米晶．用ＴＥＭ、ＸＲＤ和ＤＳＣ研究了ＢＰＴ样品的晶粒大小、结构及其相变特性．结果表明,纳米晶ＢＰＴ随着晶粒尺寸的减小,由铁电四方相向顺电立方相过度,并且相变变得弥散．其顺电－铁电相变随着晶粒尺寸的减小而消失．另一方面,随着晶粒尺寸的增加,其铁电四方－铁电正交相交消失,即抑制了其正交相的形成．     

低相变场细电滞回线(Pb,La)(Zr,Sn,Ti)O_3反铁电陶瓷的研究

对远离反铁电-铁电准同型相界的(Pb,La)(Zr,Sn,Ti)O3反铁电组分进行Ba2+掺杂,制备出了细电滞回线、低相变电场的反铁电陶瓷,反铁电-铁电相变电场仅为1.5kV/mm,电场回滞减小到0.2kV/mm,并且极化强度和应变量随电场增大几乎呈线性变化,可通过调节电场大小得到不同的应变量,有利于开辟这类材料新的应用领域。     

非晶态铁电薄膜的铁电相转变

用ＡｒＦ脉冲激光在Ｐｔ／Ｔｉ／ＳｉＯ２／Ｓｉ衬底上合成了非晶态ＳｒＢｉ２Ｔａ２Ｏ９铁电薄膜,研究了铁电相转变。采用常规热退火、激光诱导和低温高压水热法使非晶态ＳＢＴ薄膜发生铁电相转变。     

脉冲电场诱导的相变研究

反铁电陶瓷材料在电场诱导下发生反铁电-铁电相变.为了研究快速电场诱导相变,诱导电场选择高压脉冲电源产生的脉冲电场.反铁电陶瓷选用Pb(Zr,Sn,Ti)O3相图中位于反铁电-铁电相界附近,正向相变电场小于40kV/cm的锆锡钛酸铅.脉冲电源输出波形为2.7 μs电压脉冲,测量陶瓷样品两端的电压波形与所通过的电流波形,作出正向半周期的"脉冲电滞回线".可以看到反铁电陶瓷在脉冲电场诱导下发生了相变.     

聚偏氟乙烯电极化的动力学相变和铁电性

对聚偏氟乙烯进行高温电极化处理以改善半晶聚合物的铁电性,研究了其铁电极化值随着极化电场的连续非线性变化,实现了结晶相中非铁电相向铁电相的转变.用动力学平衡方法模拟了聚偏氟乙烯样品的电场极化相变过程,结果表明:聚偏氟乙烯中结晶区域的有效极化电场约为50 MV/m,与铁电聚合物的矫顽电场吻合;非晶无定型区域的等效电场与实验的相变开启电场接近,并得到了理论与实验符合较好的结果,从而证明动力学平衡方法模拟聚偏氟乙烯铁电相变的可行性.     

A comprehensive review on the progress of lead zirconate-based antiferroelectric materials

Lead zirconate (PbZrO₃ or PZ)-based antiferroelectric (AFE) materials, as a group of important electronic materials, have attracted increasing attention for their potential applications in high energy storage capacitors, micro-actuators, pyroelectric security sensors, cooling devices, and pulsed power generators and so on, because of their novel external electric field-induced phase switching behavior between AFE state and ferroelectric (FE) state. The performances of AFE materials are strongly dependent on the phase transformation process, which are mainly determined by the constitutions and the external field. For AFE thin/thick films, the electrical properties are also strongly dependent on their thickness, crystal orientation and the characteristics of electrode materials. Accordingly, various strategies have been employed to tailor the phase transformation behavior of AFE materials in order to improve their performances. Due to their relatively poor electrical strength (low breakdown fields), most PZ-based orthorhombic AFE ceramics are broken down before a critical switching field can be applied. As a consequence, the electric-field-induced transition between AFE and FE phase of only those AFE bulk ceramics, with compositions within tetragonal region near the AFE/FE morphotropic phase boundary (MPB), can be realized experimentally at room temperature. AFE materials with such compositions include (Pb,A)ZrO₃ (A = Ba, Sr), (Pb_1−3/2xLa_x)(Zr_1−yTi_y)O₃ (PLZT x/(1−y)/y), (Pb_0.97La_0.02)(Zr,Sn,Ti)O₃ (PLZST) and Pb_0.99(Zr,Sn,Ti)_0.98Nb_0.02O₃ (PNZST). As compared to bulk ceramics, AFE thin and thick films always display better electric-field endurance ability. Consequently, room temperature electric-field-induced AFE–FE phase transition could be observed in the AFE thin/thick films with orthorhombic structures. Moreover, AFE films are more easily integrated with silicon technologies. Therefore, AFE thin/thick films have been a subject of numerous researches. This review serves to summarize the recent progress of PZ-based AFE materials, focusing on the external field (electric field, hydrostatic pressure and temperature) dependences of the AFE–FE phase transition, with a specific attention to the performances of AFE films for various potential applications, such as high energy storage, electric field induced strains, pyroelectric effect and electrocaloric effect.     

Electric response of Pb0.99[(Zr0.90Sn0.10)0.968Ti0.032]0.98Nb0.02O3 ceramics to the shock-wave-induced ferroelectric-to-antiferroelectric phase transition

Shock-wave-enforced ferroelectric (FE)-to-antiferroelectric (AFE) phase transition releases a large electrical polarization, having application in pulse power technology. In the present work, the depoling currents under shock wave compression were investigated in Pb_0.99[(Zr_0.90Sn_0.10)_0.968Ti_0.032]_0.98Nb_0.02O₃ (PZST) ceramics with composition close to the FE/AFE phase boundary. Shock wave was generated by gas-gun and propagated in a direction perpendicular to the remanent polarization. It was found that the shock pressure promoted the phase transition under the short-circuit condition. The shock pressure dependence of the released charge was associated with the evolution of FE-to-AFE phase transition. The onset of phase transition was about 0.40 GPa and complete transformation occurred at 1.23 GPa. However, the released charge decreased with increasing load resistance. The reason may be that the electric field suppresses the phase transition in uncompressed zone and/or shock induces conductivity in compressed zone. Results lay the foundation for application of PZST ceramics in shock-activated power supply.     

Effect of the orientation on the ferroelectric-antiferroelectric behavior of sol-gel deposited (Pb,Nb)(Zr,Sn,Ti)O3 thin films

The (Pb,Nb)(Zr,Sn,Ti)O₃ (PNZST) antiferroelectric thin films were prepared on two different substrates by sol-gel methods. Films derived on the LNO/Pt/Ti/SiO₂/Si substrates showed a strong (100) preferred orientation. The dependence of electrical properties derived on the Pt/Ti/SiO₂/Si and LNO/Pt/Ti/SiO₂/Si substrates have been studied, with the emphasis placed on field-induced phase switching from the antiferroectric to the ferroelectric state. The PNZST thin films deposition on two kinds of substrates show different phase transition behavior and associated properties such as antiferroelectric (AFE) to ferrroelectric (FE) switching field E_AFE-FE, FE to AFE switching field E_FE-AFE and the hysteresis ΔE=E_AFE-FE−E_FE-AFE.     

Influence of Composition and Pressure on the Electric Field-Induced Antiferroelectric to Ferroelectric Phase Transformation in Lanthanum Modified Lead Zirconate Titanate Ceramics

The electric field-induced phase transformation behavior in lanthanum-doped lead zirconate titanate ceramics was examined by polarization versus electrical field (P-E) measurements carried out from room temperature to 130degC and under hydrostatic pressures from 20 to 300 MPa. The samples with composition (Pb_1-xLa_x)(Zr_0.90Ti_0.10)_1-x/4O₃ [PLZT _x/90/10; x = 2,3,4 at%] were prepared by the standard solid-state reaction method. The analysis at room temperature under atmospheric pressure showed that the increase in the lanthanum content induces a transformation from the typical ferroelectric hysteresis, observed for PLZT 2,3/90/10, to double-hysteresis loops, typical of antiferroelectric phases, for PLZT 4/90/10 under a strong electric field. Hydrostatic pressure- induced and temperature-induced ferroelectric (FE) to antiferroelectric (AFE) phase transformations were examined. The measured hysteresis loops indicated that the FE-AFE phase transformation depends on both temperature and hydrostatic pressure for PLZT 3/90/10. This composition, which is in a ferroelectric state at room temperature under atmospheric pressure, can be transformed into the antiferroelectric phase by the application of a hydrostatic pressure of 100 MPa or by increasing the temperature to around 90degC. The PLZT 2/90/10 and 4/90/10 compositions displayed predominantly ferroelectric and antiferroelectric behavior, respectively, over the ranges of temperature and hydrostatic pressure examined in the present study.     

Direct current electric field adjustable phase transformation behavior in (Pb,La)(Zr,Ti)O3 antiferroelectric thick films

(Pb,La)(Zr,Ti)O₃ antiferroelectric 1.4 μm-thick films have been prepared on Pt (111)/Ti/SiO₂/Si(100) substrates by sol–gel process. The structures and dielectric properties of the antiferroelectric thick films were investigated. The films displayed pure perovskite structure with (100)-preferred orientation. The surface of the films was smooth, compact and uniform. The antiferroelectric (AFE) characterization have been demonstrated by P (polarization)-E (electric field) and C(capacitance)-V (DC bias) curves. The AFE–ferroelectric (FE) and FE-to-paraelectric (PE) phase transition were also investigated as coupling functions of temperature and direct current electric field. With the applied field increased, the temperature of AFE-to-FE phase transition decreased and the FE-to-PE phase shifted to high temperature. The AFE-to-FE phase transition was adjustable by direct current electric field. (Pb,La) (Zr,Ti) O₃ antiferroelectric films have broad application prospects in microelectromechanical systems because of the phase transition.     

Polarization-electric field relations of ferroelectric/antiferroelectric layered ceramics in Pb(Nb, Zr, Sn, Ti)O3 system

Ferroelectric/antiferroelectric bi-layer ceramics with different ferroelectric and antiferroelectric phase thickness ratio (FE/AFE thickness ratio) in Pb(Nb, Zr, Sn, Ti)O₃ system were prepared and characterized. With increasing the maximum external electric field from 0 to 40 kV/cm, polarization-electric field relation was always ferroelectric-like or underwent an antiferroelectric-ferroelectric transition, depending on the FE/AFE thickness ratio. All layered ceramics showed ferroelectric-like hysteresis loops with maximum external electric field of 40 kV/cm, and much higher remanent polarizations were attained than those of the ferroelectric/antiferroelectric heterostructures reported previously.     

The electric field-induced antiferroelectric to ferroelectric phase transition in some (Pb,La)Zr0.55Ti0.45O3 ceramics

Lanthanum substituted lead zirconate-titanate (PLZT) ceramics of composition 11.1/55/45 have been studied by measuring high electric field properties. Dc bias, dielectric and P-E hysteresis loop measurements have been employed to construct an E (electric field) versus T (temperature) phase diagram. At lower temperatures and small electric fields an antiferroelectric phase with tetragonal symmetry has been found. Applying high electric fields gives rise to a field-induced phase transition from the antiferroelectric to the ferroelectric state, however, without X-ray detectable change in crystal symmetry.     

Thermodynamics of phase transitions in liquids in external fields

We examine the conditions of phase equilibrium and transformations in a liquid located in an inhomogeneous external potential force field. If the force acting on the mass unit depends on the phase state, then a field-induced shift in phase equilibrium arises. As a result, at the phase interface at equal temperatures, the chemical potentials of the substance of phases do not coincide, although the full chemical potential is constant over the system. As well, one of the phases is located in a state which, in the absence of field, would be metastable. Such a field-induced phase equilibrium becomes impossible when one of the phases reaches the limiting state (spinodal). In this case, the system passes jumpwise into a new disperse state. We show that the above-mentioned features of phase equilibria in liquids and external fields manifest themselves in various physical systems and processes. These are electrical explosion of conductors, electrical explosion of micropoints on a cathode surface, and destruction of the surface of dielectrics by fast multicharged ions. Electric field also fosters the formation of nuclei of the competing phase in a supersaturated vapor and facilitates boiling of liquids on inhomogeneous heated surfaces. We discuss the possibility of achieving unusual states of substances, such as deeply supercooled hydrogen and ice at room temperature under the action of external fields.     

The interaction of multifold polar orderings in Ba-doped Sr0.7Ca0.3TiO3

A series of polycrystalline Sr_0.7?xCa_0.3Ba_xTiO₃ (SCBT) (0.0 ≤ x ≤ 0.25) samples were synthesized through solid-state reaction method, and their microstructural, anti-ferroelectric (AFE), ferroelectric (FE), dielectric, and phase transition properties were investigated. With the incorporation of Ba²⁺ at Sr²⁺ site, the AFE polar phase (x = 0.0) has been sharply changed, experiencing AFE state, enhanced FE state, cooperative FE state, and normal FE state, owing to the competition and coupling interactions of different polar orderings in SCBT system. Note that excellent FE behavior has been found in the cooperative FE state. In addition, the critical region has been proposed in the T ? x phase diagram.     

Large electric field-induced strain near AFE/FE phase boundary in (Pb0.97La0.02)(Zr, Sn, Ti)O3 system

(Pb_0.97La_0.02)(Zr, Sn, Ti)O₃ ceramics were prepared by conventional solid state reaction process, and the effects of Zr⁴⁺/Sn⁴⁺ and Zr⁴⁺/Ti⁴⁺ ratios on the crystal structure, dielectric, ferroelectric, and electric field-induced strain properties were systemically investigated. The XRD results showed, with the increase of Zr⁴⁺ and Ti⁴⁺ contents, the stability of the specimens became weakened and a transformation from AFE to FE phase was observed at x = 0.65 and y = 0.12, respectively. In addition, it was observed that the strain first increased with a maximum value in the composition near AFE/FE phase boundary, and then decreased with increasing Zr⁴⁺ and Ti⁴⁺ contents. Further, with the decrease of measuring frequency, the strain continuously increased because the reversal of the domain can be more sufficient. The maximum strain of 0.55 % is obtained in Pb_0.97La_0.02(Zr_0.63Sn_0.26Ti_0.11)O₃ AFE ceramics at 1 Hz measuring frequency which lays a foundation for preparing actuators with high properties.