Studies on Growth and Properties of Large Single Crystals of Ferroelectric Polymers

以PVDF（聚偏氟乙烯）、P（VDF-TrFE）（VDF和三氟乙烯的共聚物）和P（VDF-TeFE）（VDF和四氟乙烯的共聚物）为材料，研究了铁电聚合物的结晶和性能，旨在获得大单晶，阐明结晶机理，并将其应用于电子器件，特别是超声换能器。本研究的主要结果如下：1.大单晶的生长：将各种晶体生长方法应用于P（VDF-TrFE）和P（VDF-TeFE）。其中，我们发现在高压和高温下的晶化是最有效的，所得到的单晶是约0.2 μ m厚和10- 100 μ m宽的层状晶体，以及直径为10- 20 μ m的块状单晶。这些单晶是仅在顺电或旋转相生长的延伸链晶体，其中分子经历大振幅的旋转振动。精确相位 关于我们 得到了P（VDF-TrFE）的Se图。2. PVDF单晶：PVDF的延伸链β-形式单晶仅在2.4kb以上的高压和高温以及230 ℃下生长。该单晶体具有明显的铁电性和强的压电性，其压电性可持续到205 ℃.因此，在压电聚合物中，高压结晶PVDF膜可用于最高温度区域。3.高温下分子运动的研究：利用宽谱线NMR、介电和力学测量等手段研究了P（VDF-TrFE）的结晶和居里转变过程中的分子运动。发现在居里温度以上，链状分子沿分子链沿着是非常移动的。4.超声换能器的应用：高度结晶的P（VDF-TrFE）薄膜被应用于各种超声换能器。结果表明，该换能器工作温度范围宽（4K-450 K），工作频率范围宽（5- 1000 MHz）。少

Crystallization and properties of ferroelectric polymers were studied aiming to obtain large single crystals, to elucidate crystallization mechanisms, and to apply them to electronc devices, especially to ultrasonic transducers, using materials of PVDF (poly(vinylidene fluoride)), P(VDF-TrFE)(copolymers of VDF and trifluoroethylene), and P(VDF-TeFE)(copolymers of VDF and tetrafluoroethylene). The followings are the main results of the present studies.1. Growth of Large Single Crystals: Various methods for crystal growth were applied to P(VDF-TrFE) and P(VDF-TeFE). Among them, we found the crystallization under high pressures and high temperatures is most effective; the resulting single crystals were lamellar crystals about 0.2um thick and 10-100mum wide, and bulk single crystals with 10-20mum in diameter. These single crystals are extended chain crystals grown only in the paraelectric or rotational phase where the molecules undergo rotational vibration with large amplitude. Precise pha … More se diagram as a function of VDF content was obtained for P(VDF-TrFE). 2. Single Crystals of PVDF: Extended-chain beta-form single cystals of PVDF were grown only at high pressure and high temperatures above 2.4kb and 230 C. The single crystals exhibited conspicuous ferroelectricity and strong piezoelectricity which persist up to 205 C. Therefore, high-pressure crystallized PVDF film is usable at highest temperature region among piezoelectric polymers. 3. Studies on Molecular Motion at High Temperatures: The molecular motions correlating to crystallization and Curie transition were studied for P(VDF-TrFE) by means of broad line NMR and dielectric and mechanical measurements. It is found that chain molecules are very mobile along the molecular chains above the curie temperature. 4. Applications to Ultrasonic Transducers: Highly crystallized P(VDF-TrFE) films were applied to various ultrasonic transducers. It is found that these transducers can operate in the wide temperature range (4K-450K) and in the wide frequency range (5-1000MHz). Less