Precipitation hardening in piezoceramics

压电陶瓷在高功率应用中的应用要求将介电损耗和压电陶瓷损耗降到最低。否则，陶瓷会在使用过程中受热而脱落。这种最小化是通过受体掺杂实现的，它在晶格中引入了氧空位。它们形成偶极子，稳定畴结构并固定畴壁。然而，高温和高功率（加热材料）会促使氧空位的迁移，破坏硬化效果。因此，高功率应用，如超声波焊接和超声波电机，需要一种固定畴壁的机制。由于这些是非线性变形的载体，源自金属物理学的方法可能是有用的。事实上，理论（和我们的第一个实验）证实，例如，位错固定了畴壁。我们最近还发表了一篇文章，第二相与基体粉末混合，稳定了畴结构。在这个项目中，考虑了由析出物引起的畴结构硬化。这种选择提供了相当大的灵活性和优越的钉钉中心在晶格中的分布（而不仅仅是在晶界上，如混合的第二相）。此外，沉淀硬化有望在高温和高振动速率下保持稳定。我们建议利用钛酸钡从根本上研究压电陶瓷的硬化。这需要包括烧结和时效处理在内的加工技术。需要在温度和振动速率下进行复杂的性能评估。这特别适用于机电质量和耦合系数，其次是更常见的特性，如压电系数和获得的应变。除了电硬化外，还计划通过铁弹性行为的研究进行机械硬化。还考虑了通过在高温下引入位错，然后沿着位错网络在相同位错上沉淀的探索性研究。考虑利用原位透射电镜实验作为温度（提供了初步工作）和电场的函数，对新机制进行基础研究。同样，原位压电力显微镜也在计划中。这些方法提供了将位错处畴壁的形成作为温度的函数和位错对畴壁的固定作为电场的函数可视化的潜力。无铅压电陶瓷的研究有望在硬质压电陶瓷领域取得突破性进展。然而，获得的基本理解可以类似地应用于含铅压电陶瓷，然后可以在比以前更高的温度下使用。

The application of piezoceramics for high-power applications demands a minimization of dielectric and piezoceramic losses. Otherwise, the ceramic will heat up in service and depole. This minimization is achieved using an acceptor doping, which introduces oxygen vacancies into the lattice. These form dipoles, which stabilize the domain structure and pin the domain walls. However, high temperatures and high power (heating up the material) prompt a mobility of the oxygen vacancies and destroy the hardening effect. High-power applications such as ultrasconic welding and ultrasonic motors therefore demand a mechanism, which pins domain walls. As these are the carriers of non-linear deformation, methods stemming from metal physics may be useful. Indeed, theory (and our first experiments) verify that, for example, dislocations pin domain walls. We also published recently, that a second phase, which is mixed to the matrix powder, stabilizes the domain structure. In this project the hardening of the domain structure by precipitates is contemplated. This option offers considerable flexibility and superior distribution of pinning centers in the lattice (and not only at grain boundaries like the admixed second phase). Further, precipitate hardening is expected to be stable at high temperature and high vibration rates. We propose to utilize barium titanate to fundamentally investigate the hardening of piezoceramics. This entails the processing technology including sintering and aging treatment. A complex property evaluation at temperature and vibration rate is required. This holds specifically for electromechanical quality and for the coupling factor next to more common properties such as piezocoefficient and obtained strains. In addition to electrical hardening the mechanical hardening through an investigation of the ferroelastic behavior is planned. Explorative investigations through introduction of dislocations at high temperature followed by precipitation at same dislocations along the dislocation networks are also considered. A fundamental investigation of the new mechanism is contemplated using in-situ TEM experiments as function of temperature (preliminary work provided) and as function of electric field. Similarly, in-situ piezo force microscopy is also planned. These methods offer the potential to visualize the formation of domain walls at dislocations as function of temperature and pinning of domain walls by dislocations as function of electric field. The investigations are contemplated on lead-free piezoceramics as their breakthrough is expected for hard piezoceramics. The obtained fundamental understanding, however, can similarly be applied to lead-containing piezoceramics, which then could be utilized at higher temperatures than before.