Studies of Pyroelectric Dynamics of Polymers by means of Temperature Jump Spectroscopy

在几纳秒的脉冲激光作用下，当极化铁电聚合物的温度突然升高时，由于其热释电性，在很宽的时间范围内观察到了电荷响应。这项工作旨在通过对热释电响应曲线的定量分析来了解热释电的动力学。除了我们实验室的一台激光激光器Surelite-I和一台高速数字示波器TDS62O外，我们还购买了一颗二次谐波晶体。我们还开发了软件来测量和分析响应。因此，S在1 ns到10 ns的范围内的测量成为可能。我们使用的是偏氟乙烯VDF与三氟乙烯TrFE的共聚物，其含量为75/25摩尔%。用染料从溶液中浇铸得到一层膜。在高交流电场极化后，薄膜受到激光脉冲的影响，并连接到示波器。由此得到的热释电响应曲线表明，存在几种响应模式：瞬时模式、两个振荡模式和由于样品冷却而导致的渐变模式。振荡模式是由突变的热膨胀引起的机械振荡引起的。诱导了厚度伸缩和长度伸展模式的振荡，并观察到它们是由于与压电性耦合而引起的电荷响应的振荡。瞬时模式对应于热释电初级效应，仅占总响应的20%左右。还测量了高温下的响应曲线。响应量随着温度的升高而增加，直到略低于居里温度，然后随着极化的消失而减少。在居里温度下，振荡模先于瞬时模消失。

A charge response is observed for a wide range of time in a poled ferroelectric polymer due to its pyroelectricity when its temperature is raised suddenly by applying a YAG laser pulse with a duration of several nanoseconds. This work is aimed to understand the dynamics of pyroelectricity by analyzing quantitatively the pyroelectric response curves. In addition to a YAG laser Surelite-I and a high speed digitizing oscilloscope TDS62O in our laboratory, we bought a second-harmonics-generating crystal. We also developed software to measure and anaylize the respons. As a result, the measurement in a range of 1 ns to 10 s became possible. We used a copolymer of vinylidene fluoride VDF with trifluoroethylene TrFE of content of 75/25 mol%. A film was obtained by casting from solution with dye. After poled by a high ac field, the film was subjected to a laser pulse, being connected to the oscilloscope. The pyroelectric response curves thus obtained show that there are several modes of response : the instantaneous mode, two oscillating modes and a gradual decreasing mode which is due to cooling of the sample. Oscillating modes result from the mechanical oscillation induced by the abrupt themal expansion. The thickness extensional and the length extensional mode oscillations are induced and are observed as oscillations of charge response as a result of coupling with piezoelectricity. The instantaneous mode corresponds to the pyroelectric primary effect which is only ca. 20% of total response. The response curves were also measured at elevated temperatures. The amount of the response increases as the temperature is raised up to just below the Curie temperature, and then decreases as the polarization vanishes. The oscillatory modes are found to vanish prior to the instantaneous mode at the Curie temperature.