Precipitation hardening in piezoceramics

压电陶瓷在大功率应用中的应用要求最小化介电损耗和压电陶瓷损耗。否则，陶瓷将在使用中升温并去极。这种最小化是使用受主掺杂实现的，其将氧空位引入晶格中。这些形成偶极子，稳定畴结构并钉扎畴壁。然而，高温和高功率（加热材料）会促使氧空位的流动并破坏硬化效果。高功率应用，如超声波焊接和超声波电机，因此需要一种机制，钉域壁。由于这些是非线性变形的载体，因此源于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，位错钉畴壁。我们最近还发表了，第二相，这是混合到基体粉末，稳定域结构。在该项目中，考虑了沉淀物对畴结构的硬化。这种选择提供了相当大的灵活性和晶格中的钉扎中心的上级分布（并且不仅在像混合的第二相的晶界处）。此外，预计沉淀硬化在高温和高振动速率下稳定。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，以及更常见的属性，如压电系数和获得的应变。除了电硬化的机械硬化，通过铁弹行为的调查计划。探索性的调查，通过引入位错在高温下，随后沉淀在相同的位错沿着位错网络也被认为是。一个新的机制的基本调查，设想使用原位TEM实验作为温度的函数（初步工作提供）和作为电场的函数。同样，原位压电力显微镜也计划。这些方法提供了潜在的可视化畴壁的形成在位错作为温度的函数和钉扎的畴壁的位错作为电场的函数。这些调查是考虑无铅压电陶瓷，因为他们的突破，预计硬压电陶瓷。然而，所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.