Thermal behavior of ferroelectric Polyamide 11 in relation to pyroelectric properties

The pyroelectric properties of oriented thin films of ferroelectric Polyamide 11 have been studied in the temperature range of −100°C up to +140°C. The temperature dependence of the experimental pyroelectric coefficient has been analyzed. Three changes of slope of the pyroelectric coefficient are observed at −20, +50, and +100°C. The origin of the lower temperature event has not yet been defined. The upper transition is attributed to chain movements in crystalline regions, and more precisely, to a crystalline phase transition. The intermediate event is close to the glass transition temperature T_g observed by DSC. It is attributed to the manifestation of the glass transition. Below T_g, the variations of the pyroelectric coefficient are very small. For higher temperatures, it increases rapidly, attesting to a major contribution of secondary pyroelectricity and dimensional effects above T_g. The breaking of hydrogen bonds occurring at the glass transition temperature observed on DSC thermograms does not affect pyroelectric properties. Pyroelectric properties are mildly reduced after annealing at temperatures up to +140°C. A comparative study of oriented ferroelectric films prepared by quenching from the melt and nonoriented slowly cooled samples has been carried out by means of DSC. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 715–723, 1999     

Ferroelectric ceramics by sol–gel methods and applications: a review

New advances in the sol?Cgel processing of ferroelectric ceramic powders and thin films and recently, scientific and technological interests in ferroelectric ceramics have been focused particularly on thin films. This is mainly due to their great potential applications in integrated electronics as passive components and as non-volatile ferroelectric memories, optoelectronic devices, etc. Special attention has been paid to the effects of the microstructure and composition on the piezoelectric properties of ferroelectric ceramic powders and thin films, and various characterization techniques are reported. This paper introduces the basic principles governing ferroelectricity and lists the various materials which exhibit these properties. The processing of ferroelectric ceramics and thin films in general and sol?Cgel processing in particular, with some examples are described. Finally, important applications of ferroelectric films and microstructure examination as well as powerful techniques are briefly discussed.     

Effects of plasticizer on the mechanical and ferroelectric properties of uniaxially oriented β-phase PVF2

The ferroelectric, piezoelectric, and dynamic mechanical properties of uniaxially oriented films of poly(vinylidene fluoride) PVF₂, undoped and doped with a plasticizer, tricresyl phosphate (TCP), were investigated. X-ray diffraction studies were carried out and show that for uniaxially oriented films, as dopant concentration increased, the percentage of nonpolar α-phase increased. These results also confirmed previous studies that indicate that the dopant resides in the amorphous regions. The piezoelectric coefficients (d₃₁ and e₃₁), pyroelectric coefficient (p_y), and remanent polarization (P_r) were observed to be enhanced by doping with TCP. Measurements of the pyroelectric coefficient, p_y, showed that the dopant produced a large increase in p_y from 19.6 to 28.5 μC/m²/K, suggesting an increase in the thermal expansion coefficient, α₃. The data also suggest that a small amount of dopant in the noncrystalline regions greatly enhanced the high-temperature stability of the remanent polarization. © 1996 John Wiley & Sons, Inc.     

非晶态与晶态的压电热电铁电高聚物

本文综述了晶态与非晶态两类高聚物的压电性,热释电性和铁电性。这些现象近年来研究得愈来愈广泛。文中以聚氯乙烯作为非晶态高聚物的例子;以PVDF及其共聚物,还有尼龙11作为晶态高聚物的例子。按照偶极子模型,高聚物一般假定需具备四个条件,就可显示出较大的压电性,热释电性和铁电性。本文探讨了上述高聚物的结构与性能,这些对识别材料是很重要的。最后,列举了PVDF及其它材料的压电常数,热释电系数和介电常数,以供读者参考。     

Dielectric and Ferroelectric Properties of Sol-Gel Derived YMnO3 Films

There has been considerable interest in ferroelectric (FE) films especially for non-volatile memories and ultra high density DRAM applications. Such FE films typically consist of lead zirconate titanate (PZT) with novel oxide contacts, or layered perovskite such as Sr2Bi2TaO9. Recently, there have been reports of sputtered YMnO3 films which exhibit a single polarization axis and do not contain any volatile species of Pb or Bi. Single crystal YMnO3 exhibits satisfactory polarization (6 C/cm2) and low coercive field (<20 kV/cm). Additionally, the dielectric constant of YMnO3 is quite low (<30) which should facilitate ferroelectric switching. In this study, sol-gel derived YMnO3 films were prepared on platinized Si wafers and their dielectric and ferroelectric properties were characterized. Their electrical properties will be discussed with respect to Y/Mn stoichiometry ratio, hexagonal phase development and processing conditions. The potential of YMnO3 as a material in non-volatile memories is evaluated.     

Dependence of dielectric,ferroelectric, and piezoelectric properties on crystalline properties of p(VDF‐co‐TrFE) copolymers

Thermal processing at various temperatures has been used to fabricate poly(vinylidene fluoride‐co‐trifluoroethylene) [P(VDF‐co‐TrFE)] films with varied crystalline properties in an attempt to improve their piezoelectric properties. Although the dielectric constant of the films annealed at higher temperature is smaller than that of cooled and quenched ones, it has been shown that the annealed films possess larger crystallinity and stacked lamellar crystal grain size. The ferroelectric domains deriving from crystal region in all the samples are effectively improved by hot polarization. As a result, the remnant polarizations (P_r) and coercive electric field (E_c) of the corresponding films are improved at a low frequency due to the response of dipoles in crystal phase, and the largest piezoelectric constant in the longitudinal thickness mode (d₃₃=?25 pC/N) is obtained in an annealed copolymer film. The results illustrate improving the crystal structure of P(VDF‐co‐TrFE) is an effective way to realize high electromechanical properties, which provides broadly applied scenery for this kind of copolymer in piezoelectric components. © 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2012     

金属β－二酮化合物用于MOCVD法生长铁电氧化物薄膜

对用于MOCVD法生长铁电氧化物薄膜的金属β－二酮化合物的制备、结构及性质进行了评述，对它们在生长铁电薄膜中的应用现状进行了介绍，并对它们的应用前景作了展望。     

Ferroelectric and piezoelectric properties of a quenched poly(vinylidene fluoride-trifluoroethylene) copolymer

The ferroelectric and piezoelectric properties of melt-quenched unoriented poly(vinylidene fluoride-trifluoroethylene) (73 : 27) copolymer films as a function of the number of poling cycles have been studied. The investigation revealed that quenched films exhibit a decrease in D-E hysteresis behavior as the number of poling cycles increases when the samples are poled at room temperature. Corresponding decreases in remanent polarization, Pr, as well as small increases in the coercive field, Ec, were observed as the material was subjected to successive poling cycles. The piezoelectric coefficients, d₃₁ and e₃₁, also decreased as the number of poling cycles increased. In addition, a clear reduction in the “apparent” Curie transition temperature between unpoled and poled material was observed. Preliminary evidence indicates that films quenched from the melt to below T_c do not form a stable ferroelectric crystal phase as previously believed. © 1997 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 35: 2671–2679, 1997     

Past and future impact of electroactive polymers on the electronics sector

A broad review of the field of applications of electroactive polymers, defined as inherently conductive, charged, piezoelectric and pyroelectric, and systems made electroactive by addition of conductive additives, in the field of electronics and microelectronics. Applications mentioned include the use of polymers for electrodes for rechargeable batteries, electret microphones, hydrophones, vidicons, EMI and ESD protection, and conductor and resistor tracks as thick films on printed circuit boards. Future trends as the development of supermolecular assemblies for parallel processing are also highlighted.     

Micropatterning of the Ferroelectric Phase in a Poly(vinylidene difluoride) Film by Plasmonic Heating with Gold Nanocages

Polymer thin films with patterned ferroelectric domains are attractive for a broad range of applications, including the fabrication of tactile sensors, infrared detectors, and non‐volatile memories. Herein, we report the use of gold nanocages (AuNCs) as plasmonic nanostructures to induce a ferroelectric–paraelectric phase transition in a poly(vinylidene fluoride) (PVDF) thin film by leveraging its photothermal effect. This technique allows us to generate patterned domains of ferroelectric PVDF within just a few seconds. The incorporation of AuNCs significantly enhances the pyroelectric response of the ferroelectric film under near‐infrared irradiation. We also demonstrate the use of such patterned ferroelectric films for near‐infrared sensing/imaging.     

MOCVD生长铁电氧化物薄膜MO源研究进展

高性能铁电氧化物薄膜是当今功能材料的研究热点之一.随着新型MO源的不断研究与开发,利用MOCVD技术制备高质量铁电薄膜材料得到了快速的发展.本文在分析金属醇盐和金属β-二酮化合物等MO源的结构与其物性依赖关系基础上,分类综述了近年来在用于MOCVD方法生长铁电氧化物薄膜的新型MO源研究和开发方面的发展动态与趋势,为MOCVD方法制备铁电薄膜材料MO源的选择提供有用的参考与借鉴.     

LaNiO3衬底上Pb(ZrxTi1－x)O3铁电薄膜及梯度薄膜的制备和研究

报道了在镍酸镧 (LaNiO₃, 简称LNO)衬底上锆钛酸铅 [Pb(Zr_xTi_1－x)O₃, 简称PZT]铁电薄膜及其成分梯度薄膜的结构、介电性能、铁电性能以及热释电性能. 首先通过金属有机化合物热分解(MOD)法在Si(100)基片上制备出LaNiO₃, 薄膜, 再通过溶胶-凝胶(sol-gel)法, 在LNO/Si(100)衬底上制备出Pb(Zr_0.80Ti_0.20)O₃, [PZT(80/20)]和Pb(Zr_0.20Ti_0.80)O₃, [PZT(20/80)]铁电薄膜及其成分梯度薄膜. 经俄歇微探针能谱仪(AES)对制备的梯度薄膜进行了成分深度分析, 结果证实成分梯度的存在. 经XRD分析表明, 制备的梯度薄膜为四方结构和三方结构的复合结构, 但其晶面存在一定的结构畸变. 经介电频谱测试表明, 梯度薄膜的介电常数比每个单元的介电常数要大, 但介电损耗相近. 在10 kHz下, 梯度薄膜的介电常数和介电损耗分别为317和0.057. 经电滞回线的测试表明, 梯度薄膜的剩余极化强度比每个单元都大, 而矫顽场却明显较小. 梯度薄膜的剩余极化强度和矫顽场分别为29.96 μC•cm^-2 和54.12 kV•cm^－1. 经热释电性能测试表明, 室温下梯度薄膜的热释电系数为5.54×10-8 C•cm^－2•K^－1, 高于每个单元的热释电系数.     

Ferroelectricity in solid state chemistry

This article discusses some state-of-the-art aspects of solid state chemistry within the context of ferroelectric materials such as oxides, fluorides and oxyfluorides, whose crystalline networks include octahedra. Structural considerations make it possible to determine the origin of the ferroelectricity and to predict the existence of polar properties in new families. Crystallographic distortions of different nature lead to highly variable transition sequences. Ferroelectricity is often associated with ferroelasticity. The Curie temperature is linked to the composition and to the chemical bond. In this respect, several factors are to be considered, e.g. size, coordination and configuration of the cations, covalence of bonds, order-disorder, etc. Physical studies are very useful: first, the dielectric characteristics and their variations with temperature, frequency and electric field are typical of ferroelectrics; second, the pyroelectric, piezoelectric, electro-optical and non-linear optical properties are among the most effective. Various types of materials (single crystals, ceramics, thin films) are used nowadays in a wide range of applications. © 2000 Académie des sciences / Éditions scientifiques et médicales Elsevier SASferroelectricity / solid state chemistry     

The Solgel Preparation and Electric Properties of MnO2-doped PbTiO3 Ceramics

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Ferroelectric PZT Thin Films by Sol-Gel Deposition

Sol-gel spin coating has a low thermal budget, is cheap compared to vacuum-based techniques and is now routinely used to produce dense, pore-free ferroelectric films. PbZrx Ti(1 – x)O3 (PZT) is utilized in most applications because it has a large remanent polarization, high piezo- and pyroelectric coefficients and optimized electromechanical coupling factors, depending on precise composition. This paper will review some of the principles and applications of PZT films and highlight using transmission electron microscopy some of the basic problems and solutions involved in producing device-quality material on Si-substrates.     

Comparative Solution Synthesis of Mn Doped (Na,K)NbO3 Thin Films

(K_0.5Na_0.5)NbO₃ (KNN) is a promising lead-free alternative for ferroelectric thin films such as Pb(Zr,Ti)O₃. One main drawback is its high leakage current density at high electric fields, which has been previously linked to alkali non-stoichiometry. This paper compares three acetate-based chemical solution synthesis and deposition methods for 0.5 mol % Mn-doped KNN film fabrication, using lower crystallization temperature processes in comparison to the sintering temperatures necessary for fabrication of KNN ceramics. This paper shows the crucial role of the A site homogenization step during solution synthesis in preserving alkali chemical homogeneity of Mn doped KNN films. Chemically homogeneous films show a uniform grain size of 80 nm and a leakage current density under 2.8×10⁻⁸ A cm⁻² up to electric fields as high as 600 kV cm⁻¹, which is the highest breakdown strength reported for KNN thin films. Solution synthesis involving two-step pyrolysis resulted in films with dense, columnar microstructures, which are interesting for orientation control and enhancement of piezoelectric properties. This study reports detailed solution synthesis and deposition processes with good dielectric, ferroelectric and breakdown field properties. An optimized fabrication method that should couple low leakage current density with dense and oriented microstructures is proposed.     

Ferroelectric liquid crystalline elastomers: from the analysis of the molecular dynamics to the design of nanomachines

In ferroelectric liquid crystalline elastomers (FLCE) the properties of ferroelectric liquid crystals are combined with that of polymeric networks. With use of refined synthetic techniques, it is possible to align the chiral mesogenic groups in FLCE on a macroscopic scale (∼cm²). By employing that set of methods, the development of a new class of materials has been achieved having an extraordinary profile of features, among them the following: (1) FLCE are piezoelectric because of the ferroelectric order of the chiral mesogens and because of the fact that the polymeric network prevents flow. (2) Due to a photochemically or thermally induced cross‐linking reaction the viscoelastic properties of FLCE can be adjusted over a wide range. (3) The coupling between the elastomeric network and the (polar) chiral mesogens can be modified by chemical engineering, hence offering the possibility to tailor the piezoelectric as well as the viscoelastic properties of FLCE. (4) It is possible to prepare thick (∼ 100 μm), thin (∼ μm), and ultrathin (∼ nm) films of macroscopically oriented FLCE, as self‐supporting or as transferred samples. With this combination of properties FLCE have made a strong technological impact as basic materials for sensors and soft actuators in the area of microsystems technology. The present contribution is focused on the piezoelectric effect in FLCE and its molecular interpretation.     

Control of microstructure and functional properties of PZT thin films via UV assisted pyrolysis

The influence of ultraviolet (UV) light during pyrolysis of sol-gel fabricated Pb(Zr_0.52Ti_0.48)O₃ thin films on (111)Pt/Ti/SiO₂/Si substrates has been investigated. The UV treated films show a homogeneous fine grain structure with (100) preferential orientation, whereas a bimodal grain structure and (111) preferential orientation were found for the untreated film. This is explained in terms of specific template layers formed during pyrolysis. The ferroelectric, dielectric and piezoelectric properties are also reported for both films. It is shown that while the ferroelectric properties are higher for the (111) films, the (100) films show better dielectric and piezoelectric properties with an effective piezoelectric coefficient, d _33eff, of 183 pm/V vs. 101.8 pm/V for the (111) films.     

Anisotropic networks, elastomers and gels

Anisotropic networks, elastomers and gels exhibit piezoelectric, pyroelectric, ferroelectric and NLO properties of potential interest for use communication and processing technologies. The formation, properties and applications of such anisotropic, mainly liquid crystalline, networks are described. If some of the molecules in a liquid mixture contain at least two reactive groups which can be either photochemically or thermally polymerized, then crosslinked, anisotropic networks, elastomers and gels can be produced. Solid macroscopically aligned elastomers or networks can be formed as required beforehand or simultaneously by orientation of the sample. Anisotropic gels consist of a solid anisotropic network and non-covalently bonded, but strongly oriented domains of low molar mass liquid crystals. Anisotropic networks, elastomers preformed amorphous or liquid crystalline polymers incorporating additional reactive groups, which can be macroscopically oriented in the additional crosslinking reactions. Reversible networks, elastomers and gels can be prepared either non-covalently or covalently by thermally side group polymers and low molar mass molecules, liquid crystalline properties in the pure state. in many electro-optic devices for optical and gels can be prepared from liquid crystalline state and then fixed by reversible linkages between, for example, neither of which necessarily exhibit     

Relaxation processes at the glass transition in polyamide 11: from rigidity to viscoelasticity

Relaxation processes associated with the glass transition in nonferroelectric and ferroelectric polyamide (PA) 11 are investigated by means of differential scanning calorimetry, dynamic mechanical analysis, and dielectric relaxation spectroscopy (DRS) in order to obtain information about the molecular mobility within the amorphous phase. In particular, the effects of melt quenching, cold drawing, and annealing just below the melting region are studied with respect to potential possibilities and limitations for improving the piezoelectric and pyroelectric properties of PA 11. A relaxation map is obtained from DRS that shows especially the crossover region where the cooperative alpha relaxation and the local beta relaxation merge into a single high-temperature process. No fundamental difference between quenched, cold-drawn, and annealed films is found, though in the cold-drawn (ferroelectric) film the alpha relaxation is suppressed and slowed down, but it is at least partly recovered by subsequent annealing. It is concluded that there exists an amorphous phase in all structures, even in the cold-drawn film. The amorphous phase can be more rigid or more viscoelastic depending on preparation. Cold drawing not only leads to crystallization in a ferroelectric form but also to higher rigidity of the remaining amorphous phase. Annealing just below the melting region after cold drawing causes a stronger phase separation between the crystalline phase and a more viscoelastic amorphous phase.