Normal ferroelectric to ferroelectric relaxor conversion in fluorinated polymers and the relaxor dynamics

To elucidate the molecular origin of the polarization dynamics in the ferroelectric relaxor poly(vinylidene fluoride—trifluoroethylene-chlorofluoroethylene) (P(VDF-TrFE-CFE)) terpolymer, a broadband dielectric study was carried out in the frequency range from 0.01 Hz to 10 MHz and temperatures from −150°C to 120°C for the terpolymer and a normal ferroelectric P(VDF-TrFE) copolymer. The relaxation processes were also studied using dynamic mechanical analysis. It was shown that in the terpolymer, which was completely converted to a ferroelectric relaxor, there is no sign of the relaxation process associated with the ferroelectric-paraelectric transition which occurs in the P(VDF-TrFE) copolymer. In the copolymer, three additional relaxation processes have been observed. It was found that the relaxation process β_a, which was commonly believed to be associated with the glass transition in the amorphous phase, in fact, contains significant contribution from chain segment motions such as domain boundary motions in the crystalline region. In the temperature range studied, the terpolymer exhibits the latter three relaxation processes with the one (termed β_r) near the temperature range of β_a significantly enhanced. This is consistent with the observation that in conversion from the normal ferroelectric to a ferroelectric relaxor, the macro-polar domains are replaced by nano-polar-clusters and the boundary motions as well as the reorientation of these nano-clusters generate the high dielectric response. The experimental data also reveal a broad relaxation time distribution related for the β_r process whose distribution width increases with reduced temperature, reflecting the molecular level heterogeneity in the crystalline phase due to the random introduction of the CFE monomer in the otherwise ordered macro-polar domains. The random interaction among the nano-clusters as well as the presence of the random fields produces ferroelectric relaxor behavior in the terpolymer.     

铅基弛豫铁电单晶体的生长技术

铅基弛豫铁电单晶体由于其优异的压电性能在机电换能领域具有广泛的应用前景.介绍了铅基弛豫铁电单晶体生长技术的研究进展,比较了不同生长技术的优缺点,指出了目前晶体生长中出现的问题,并展望了其研究方向.     

From normal ferroelectric transition to relaxor behavior in Aurivillius ferroelectric ceramics

The influence of the barium concentration on the dielectric response of Sr_1?x Ba _x Bi₂Nb₂O₉ system, with x = 0, 15, 30, 50, 70, 85, 100 at.%, has been studied. The barium concentration dependence of T _m, as well as the temperature of the corresponding maximum for the real part of the dielectric permittivity, has suggested a cation site mixing among atomic positions, which has been supported by the structural analysis. A transition from normal ferroelectric–paraelectric phase transition to a relaxor behavior has been observed in the studied samples, when the barium concentration has increased. The relaxor behavior has been discussed.     

Thermal expansion measurements in the relaxor ferroelectric PIN-PT system

Thermal expansion was measured for the ceramic compositions (1 − x)Pb(In_0.5Nb_0.5)O₃-(x)PbTiO₃ (x = 0.0, 0.1, 0.2 and 0.3) prepared via the wolframite method. The deviation from the straight line below Burns temperature for all the compositions was due to the dynamic polarization fluctuations. Burns temperature was determined and found to increase with increasing PT concentration. The local polarization was calculated from the thermal expansion data. The calculated local polarization and the measured reversible spontaneous polarization were compared and the relaxor behavior of the PIN-PT compositions was analyzed.     

Electric-field-induced redistribution of polar nano-regions in a relaxor ferroelectric

Relaxor ferroelectrics, with their strong dependence of polarization on the applied electric field, are of considerable technological importance. On a microscopic scale, however, there exists competition as well as coexistence between short-range and long-range polar order. The conventional picture is that the polar nano-regions (PNRs) that appear at high temperatures beyond the Curie transition, form nuclei for the field-induced long-range order at low temperatures. Here, we report high-energy X-ray diffuse-scattering measurements on the relaxor Pb(Zn(1/3)Nb(2/3))O(3) (PZN) to study the short-range polar order under an electric field applied along the [111] direction. In contrast to conventional expectations, the overall diffuse-scattering intensity is not suppressed. On the other hand, the field induces a marked change on the shape of the three-dimensional diffuse-scattering intensity pattern, corresponding to a redistribution of PNRs in real space. We show that these surprising results are consistent with a model in which the PNRs with [110]-type polarizations, orthogonal to that of the surrounding environment, are embedded and persist in the [111]-polarized ferroelectric order of the bulk.     

高居里温度弛豫基铁电单晶的研究进展

传统压电铁电材料已不能满足工业发展的需要,高居里温度弛豫基铁电单晶将是下一步铁电压电材料发展的趋势.PINT、PYNT、BSPT和BS-BG-PT单晶等几种高居里温度弛豫基铁电单晶的研究已经开展,它们均表现出优良的性能;但其研究仍处于初步阶段,存在很多问题有待解决,如晶体尺寸小,性能研究不完善,材料成本高等.大尺寸高质量单晶的生长、结构性能的深化研究以及新体系的探索将是下一步高居里温度弛豫基铁电单晶的研究重点.     

O.92PZN-0.08PT晶体的缺陷与畴结构研究

应用环境扫描电子显微术(ESEM)、原子力扫描显微术(AFM)、同步辐射白光形貌术(SRWBT)等形貌成像技术研究了0.92PZN-0.08PT晶体的表面缺陷形态与铁电畴结构.通过对畴结构动态演化的同步辐射形貌观察,可揭示出该晶体的结构相变过程.     

Characterization of lead-based relaxor ferroelectric crystals by acoustic emission

The acoustic emission (AE) method is presented as a useful complementary tool for nondestructive characterization of selective relaxor ferroelectrics. Combined measurements of the dielectric permittivity and AE activity as a function of temperature and externally applied electric fields have been carried out using Pb(Mg_1/3Nb_2/3)O₃–33%PbTiO₃ (PMN-0.33PT) single crystals and Pb(Sc_0.5Ta_0.5)O₃ (PST) single crystals. Anomalous behavior in the electric field dependencies of the characteristic temperatures, T_m (diffuse permittivity maximum in PMN-PT) and T_n (formation of incommensurate antiferroelectric domains in PST), and the associated AE intensities has been observed. Both T_m and T_n exhibit minima coinciding with the AE activities maxima at critical values of the applied dc electric fields, 0.5 and 0.13 kV respectively. These phenomena are discussed mainly in terms of the interaction of the external field with the random electric fields originating from the polar nanoregions in relaxor ferroelectrics.     

Fatigue-less relaxor ferroelectric thin films with high energy storage density via defect engineer

Thin film capacitors with excellent energy storage performances,thermal stability and fatigue endurance are strongly desired in modern electrical and electronic industry.Herein,we design and prepare lead-free 0.7Sr0.7Bi0.2TiO3-0.3BiFeO3-x％Mn(x=0,0.5,1.5,2,3)thin films via sol-gel method.Mn ions of divalent valence combine with oxygen vacancies,forming defect complex,which results in marked decline in leakage current and obvious enhancement in breakdown strength.A high energy storage density～47.6 J cm-3 and good efficiency～65.68％are simultaneously achieved in 2％Mn doped 0.7Sr0.7Bi0.2TiO3-0.3BiFeO3 thin film capacitor.Moreover,the 2％Mn-doped thin film exhibits excellent thermal stability in wide operating temperature range(35-115℃)and strong fatigue endurance behaviors after 108 cycles.The above results demonstrate that 2％Mn-doped 0.7Sr0.7Bi0.2TiO3-0.3BiFeO3 thin film capacitor with superior energy storage performances is a potential candidate for electrostatic energy storage.     

弛豫铁电体基陶瓷薄膜的溶胶-凝胶制备和电性能研究

采用溶胶-凝胶工艺成功地制备了纯钙钛矿结构的Pb(Mg1/3Nb2/3)0.65Ti0.35O3(简称PMNT)弛豫型铁电陶瓷薄膜,分析了溶胶先驱体中铅含量对PMNT薄膜钙钛矿结构稳定性的影响规律,表明热退火过程的氧化铅气氛层覆盖技术对获得纯钙钛矿结构PMNT薄膜材料至关重要,系统测试了纯钙钛矿PMNT薄膜材料的铁电和介电性能,提出弛豫型铁电PMNT陶瓷薄膜制备中晶粒自由结晶和异常生长动力学机制.     

Piezoelectric properties and equivalent circuits of ferroelectric relaxor single crystals

Temperature dependent piezoelectric properties of ferroelectric relaxor single crystals, particularly the cerium-doped strontium barium niobate compositions (SBN60: Ce), were investigated by resonance and anti-resonance technique. Characteristic resonant frequencies (f_r−f_a, f_s−f_p, and f_m−f_n) were studied using equivalent circuit simulation. Piezoelectric resonance in a relaxor resonator persists into temperatures much higher than Tm (the temperature at which dielectric constant, κ, has a maximum at 1 kHz) in comparison with the normal ferroelectrics such as TGS. The parameters in an equivalent circuit, however, are phenomenally different from a normal resonator like a TGS, near and above the transition temperature region. The significance and understanding of the piezoelectric resonance characteristics in ferroelectric relaxor are discussed. This revised version was published online in November 2006 with corrections to the Cover Date.     

Reaction sintering and characterization of lead magnesium niobate relaxor ferroelectric ceramics

The formation and densification of Pb(Mg_1/3Nb_2/3)O₃ ceramics prepared by reaction sintering have been investigated. Two kinds of lead sources. PbO and Pb₃O₄ are used as the starting materials for Pb(Mg_1/3Nb_2/3)O₃. During heating processes, the specimens first expand while the pyrochlore phase is formed. At elevated temperatures, the formation and rapid sintering of Pb(Mg_1/3\Nb_2/3)O₃ occur simultaneously. The starting materials of the Pb₃\O₄ system exhibit better reactivity and sinterability than those of the PbO system. With Pb₃\O₄ as the starting material, monophasic Pb(Mg_1/3\Nb_2/3)O₃ ceramics with high sintering density are successfully achieved by reaction sintering at as low as 900 °C. While for the PbO system, pure perovskite phase could not be synthesized because of the existence of residual pyrochlore phase, and the ceramics obtained have low sintering density. The dielectric permittivity of the Pb(Mg_1/3Nb_2/3)O₃ ceramics obtained in the Pb₃O₄ system is higher than that in the PbO system. This is attributed to the formation of pure perovskite phase and high sintering density in the former system.     

Phase instability induced by polar nanoregions in a relaxor ferroelectric system

Relaxor ferroelectrics are a special class of material that exhibit an enormous electromechanical response and are easily polarized with an external field. These properties make them attractive for applications as sensors and actuators. Local clusters of randomly oriented polarization, known as polar nanoregions (PNRs), are specific to relaxor ferroelectrics and play a key role in governing their dielectric properties. Here, we show through neutron inelastic scattering experiments that the PNRs can also significantly affect the structural properties of the relaxor ferroelectric Pb(Zn(1/3)Nb(2/3))O(3)-4.5%PbTiO(3) (PZN-4.5%PT). A strong interaction is found between the PNRs and the propagation of acoustic phonons. A comparison between acoustic phonons propagating along different directions reveals a large asymmetry in the lattice dynamics that is induced by the PNRs. We suggest that a phase instability induced by this PNR-phonon interaction may contribute to the ultrahigh piezoelectric response of this and related relaxor ferroelectric materials. Our results naturally explain the emergence of the various observed monoclinic phases in these systems.     

Sintering characteristics and dielectric properties of silver-doped PMN-PZN-PT relaxor ferroelectric ceramics

The effects of silver doping on PMN-PZN-PT relaxor ferroelectric ceramics were investigated in order to demonstrate the roles of the inner electrodes in the cofiring of MLCCs, because silver could diffuse from an electrode layer into a dielectric layer. Even if the addition of silver promoted the sintering of ceramics, the insulation resistance and the dielectric properties were changed to a certain extent so that they had a great influence on the reliability of MLCCs. Defect chemistry principles were used to analyze the mechanism of action of silver doping. The relationship of silver migration and microstructural formation was also discussed     

Orientation dependence of electromechanical properties of relaxor based ferroelectric single crystals

The orientation dependence of electromechanical properties of relaxor based ferroelectric single crystals Pb(Zn_1/3Nb_2/3)O₃–(6–7)%PbTiO₃ and Pb(Mg_1/3Nb_2/3)O₃–33%PbTiO₃ has been calculated by coordinate transformation. Different from previous studies, the optimum cutting orientations have been predicted in terms of their piezoelectric responses in the corresponding crystal planes. The calculation results indicated that the anisotropic piezoelectric effects of [001] _c and [011] _c poled multi-domain crystals mainly come from the intrinsic contribution. However, the strong dielectric anisotropy of [001] _c poled multi-domain crystals mainly comes from extrinsic domain and domain wall contributions. For [011] _c poled multi-domain crystals, the intrinsic orientation effect enhances the dielectric anisotropy.     

Enhanced energy storage in Sn-doped sodium bismuth titanate lead-free relaxor ferroelectric ceramics

Journal of Materials Science: Materials in Electronics - SnO2-doped (Bi0.5Na0.5)0.93Ba0.07TiO3 (BNT7BT) ceramics were prepared via a conventional solid-state reaction method. Their phase...     

Characterization of lead-based relaxor ferroelectric ceramics sintered in a 2.45 GHz microwave radiation

Microwave processing of relaxor ferroelectric ceramics was investigated in a 2.45 GHz multimode cavity. The microwave-sintered samples were densified more rapidly and in a shorter time than the conventional sintered sample. A much smaller grain size and more uniform microstructure was developed in microwave heating. Dielectric measurement showed microwave sintered samples could obtain comparable dielectric properties (high pemittivity of 20,000) to the conventional. It was found that a high breakdown strength of 10 kV/mm and mechanical strength of 90 MPa can be achieved by the microwave method. It shows the potential to improve the figure of merit for the materials. The results reveal that microwave processing is a promising method for sintering the high dielectric ceramics.     

A Monte Carlo simulation on domain pattern and ferroelectric behaviors of relaxor ferroelectrics

The domain configuration and ferroelectric property of mode relaxor ferroelectrics (RFEs) are investigated by performing a two-dimensional Monte Carlo simulation based on the Ginzburg-Landau theory on ferroelectric phase transitions and the defect model as an approach to the electric dipole configuration in relaxor ferroelectrics. The evolution of domain pattern and domain wall configuration with lattice defect concentration and temperature is simulated, predicting a typical two-phase coexisted microstructure consisting of ferroelectric regions embedded in the matrix of a paraelectric phase. The diffusive ferroelectric transitions in terms of the spontaneous polarization hysteresis and dielectric susceptibility as a function of temperature and defect concentration are successfully revealed by the simulation, demonstrating the applicability of the defect model and the simulation algorithm. A qualitative consistency between the simulated results and the properties of proton-irradiated ferroelectric copolymer is presented.