Low-Hysteresis and Lineear Piezoelectric Actuator made from Ultra-fine Particles

当晶体的尺寸达到纳米数量级时，晶体通常表现出与体晶体不同的特性。我们多年来一直在研究铁电细颗粒中的这种“尺寸效应”，发现晶体尺寸影响畴壁运动或结晶过程，从而建立了一种合成超细颗粒的方法。在本工作中，我们试图改善压电陶瓷作动器中位移与外加电压之间的滞后现象或非线性关系。铅、钛和锆烷氧化物溶解在有机溶剂中。水解得到的PZT微粒仍处于无定形状态。在600℃的空气中加热5h可使非晶态细颗粒结晶。结晶温度远低于块状晶体（1280℃）的结晶温度。由于铅在这个温度下不会蒸发，所以降低的温度可以得到具有化学计量成分的陶瓷。获得的细颗粒通过HIP（热等静压）煅烧形成陶瓷圆盘。陶瓷形式的细颗粒表现出相当小的迟滞，约为1%，远小于传统陶瓷的迟滞（约10%）。通过扫描电镜观察发现，构成我们陶瓷的典型小颗粒尺寸为数百纳米。然而，其尺寸还不够小，不足以抑制畴壁运动。高分辨率透射电镜观察表明，颗粒中存在数纳米的精细结构。因此，精细结构似乎是起始粉末边界的“痕迹”，应该作为壁面运动的固定点。

Crystals generally show different characteristics from bulk crystals when their sizes become an order of nanometer. We have been studying this 'size effect' in ferroelectric fine particles for several years and found that the crystal size affects the domain wall movements or the crystallizing process,which establishes a method to synthesize ultra-fine particles. In the present work, we have attempted to improve the hysteresis phenomena or the non-linearity appeared in the relation between the displacement and the applied voltage in piezoelectric PZT actuators. Lead, titanium, and zirconium alkoxides are dissolved in an organic solvent. Hydrolyzing the solution gives PZT fine particles which are still in amorphous state. The amorphous fine particles can be crystallized through the heating at 600ﾟC in air for 5h. The crystallizing temperature is much lower than that of bulk crystals(1280 ﾟC). The lowered temperature enables to obtain ceramics of stoichiometric composition because lead does not evaporate at this temperature. Fine particles obtained are calcined through HIP(hot isostatic pressing) to form a ceramic disc. The ceramic form fine-particles shows quite small hysteresis of an order of 1%, much less than that of conventional ceramics(about 10 %). A typical size of the small particles composing our ceramics is found to be several hundreds nanometers by SEM observation. The size is not still enough small, however, to inhibit the domain wall movement. High resolution TEM observations suggest that fine structures of several nanometers exist in the particles. Thus, the fine structure seems to be 'traces' of boundary of starting powders and should act as pinning points of the wall movement.