New lead-free piezoelectric composites for high-power applications

压电陶瓷可以实现电信号和机械信号之间的转换，在各种电子应用中得到了广泛的应用。高能量密度和低功耗使其在小电压互感器和超声波设备等大功率应用中不可或缺。此外，它们的小型化潜力使新的便携式电子设备和电子人体植入物的开发成为可能。高功率应用需要压电硬材料，从而硬化通常是通过用缺陷复合体钉扎铁电铁电畴壁来实现的。然而，这种硬化机制在高振动速度和高温下会导致机电性能退化，这大大限制了输出功率，因此是应用的一个重大缺陷。此外，最先进的压电材料含有大量有害铅，被列入许多环境法规的观察名单。该项目的主要目标是开发一种替代的硬化机制，这将导致一组新的无铅压电陶瓷具有更高和更稳定的大功率压电性能。不再使用传统的缺陷复合体强化方法，而是采用一种基于微观结构工程的新方法。为此，将利用弛豫体和各种刚性非钙钛矿夹杂物设计无铅(3-0)型压电复合材料。假设在这些复合材料中，可以通过机械应力和夹杂物中的带电载流子来获得磁畴壁的钉扎。为了解决不同的机制，将研究含有半导体夹杂物或绝缘夹杂物的复合材料。在较宽的频率和温度范围内，将评估小信号和大信号机电激励区域的钉扎强度。它的高功率性能和去极化性能将与最先进的硬铅(锆，钛)氧化物材料进行比较。为了了解宏观机电响应，该项目还将重点同时研究微观结构和结晶学参数。用X射线衍射仪、核磁共振和中子衍射仪研究了合金的晶体结构和残余应力。此外，使用高能X射线衍射的原位时间分辨测量将被用来确定畴壁和晶格应变的贡献。现场高功率测量的发展将提高对硬压电体非线性行为的总体理解。综上所述，本项目将引入一类新型的可持续硬压电材料，为新的硬化机理提供基本的科学理解，并为利用复合方法设计其他硬质压电材料提供指导。

Piezoelectric ceramics enable conversion between electrical and mechanical signals and are widely used in various electronic applications. High energy density and low power consumption make them indispensable in high-power applications, such as small voltage transformers and ultrasonic devices. Moreover, their miniaturization potential enables the development of new portable electronic devices and electronic body implants. High-power applications require piezoelectrically hard materials, whereby the hardening is conventionally achieved by pinning the ferroelectric domain walls with defect complexes. This hardening mechanism, however, suffers degradation of electromechanical properties at high vibration velocities and elevated temperatures, which considerably limits the output power and therefore represents a vital drawback for applications. Moreover, the state-of-the-art piezoelectrics contain large amounts of hazardous lead, placing them on the watch list of many environmental regulations. The main goal of the proposed project is to develop an alternative hardening mechanism, which will result in a new group of lead-free piezoceramics with higher and more stable high-power piezoelectric properties. Instead of using classical hardening with defect complexes, a new approach based on engineering the microstructure will be utilized. To this end, lead-free (3-0)-type piezoelectric composites will be designed using relaxor matrix and various rigid non-perovskite inclusions. It is hypothesized that in these composites the pinning of domain walls can be obtained by mechanical stresses and charged carriers from inclusions. To resolve the different mechanisms, composites with either semiconductive or insulating inclusions will be investigated. The pinning strength will be evaluated for small- and large-signal electromechanical excitation regimes over a broad frequency and temperature range. The high-power properties and depolarization behaviour will be compared to the state-of-the-art hard Pb(Zr,Ti)O3 materials. To understand the macroscopic electromechanical response, the project will additionally focus on simultaneous investigation of microstructural and crystallographic parameters. The crystallographic structure and residual stresses will be investigated using X-ray diffraction, nuclear magnetic resonance, and neutron diffraction. Moreover, in situ time-resolved measurements using high-energy X-ray diffraction will be utilized to determine the contributions from domain walls and lattice strains. Development of in situ high-power measurements will improve the general understanding of the non-linear behaviour of hard piezoelectrics. In summary, this project will introduce a new class of sustainable hard piezoelectric materials, provide basic scientific understanding of the novel hardening mechanism, and give guidelines for the design of other hard piezoelectrics utilizing the composite approach.