The development of lead-free piezoelectric materials for replacing lead zirconate titanate (PZT) has been a subject of intensive research for over twenty years. Several promising material systems have been identified, and since it is extremely difficult to match the versatility of doped PZT, it is quite unlikely that one single of these will be able to take over, meaning that the future market will be much more diverse than today. The most interesting lead-free piezoelectrics will be introduced, both well-known systems such as potassium sodium niobate (KNN), bismuth sodium barium titanate (BNT-BT) and barium calcium titanate zirconate (BCTZ), as well as less common systems such as tungsten bronze and Aurivillius structures. To simplify the comparison with PZT, a simplistic ”soft” and ”hard” classification will be used for these material systems. The second part of the talk will give an overview of applications of the lead-free piezoelectric materials, recalling the most relevant properties in each case. The main categories covered will be low-power applications including medical imaging, high-power applications including various industrial piezoelectric transducers and therapeutic ultrasound, and high-temperature applications. Representative examples will be given, either as results from literature or as more detailed cases. An important point for redesigning transducers with lead-free piezoelectrics is the need for detailed datasets enabling reliable modelling. Finally, the secondary obstacles for large-scale implementation of the new lead-free piezoelectric materials will be addressed, such as availability, reproducibility, and sample size.

DC link capacitors play a crucial role in various applications, including electric vehicle motor drives, power inverters, and industrial equipment. As active electronic components progress rapidly, passive components like capacitors need to keep up with advancements in power electronics. Our study focuses on the development of anti-ferroelectric MLCCs (Multi-Layer Ceramic Capacitors) for high-performance DC link capacitors. To meet the requirements of modern power electronics, DC link capacitors must withstand high voltages, exhibit low losses and parasitic parameters, and have high capacitance and energy density. Metallized film or electrolyte capacitors are commonly used, but their limitations have led to a growing interest in anti-ferroelectric MLCCs. Anti-ferroelectric dielectric materials, such as lead lanthanum zirconate titanate (PLZT), offer lower losses and longer service life compared to ferroelectric capacitors. The capacitance behavior of anti-ferroelectric MLCCs differs significantly, allowing for increased differential capacitance at the DC operating point. This characteristic reduces the space required for DC link capacitors, a critical factor considering they occupy a considerable portion of the inverter. By adjusting the composition and A-side doping of PLZT with Ba, we have successfully increased permittivity and switching field strength, resulting in higher capacitance and energy density for MLCCs operating at high bias voltages. Furthermore, the addition of dopants and optimization of thermal processes have improved the microstructure and performance. MLCC prototypes with 50 layers and sintered thickness of 45 µm were fabricated using the enhanced PLZT material and AgPd electrodes. These MLCCs exhibited nearly three times higher energy density compared to commercial anti-ferroelectric MLCC’s, making them suitable for applications with higher bias voltages, including electric vehicles. Ongoing investigations focus on losses, frequency, temperature, and voltage dependence, with further development steps planned for base metal electrodes, failure-tolerant designs, and reliability tests. The advancements in anti-ferroelectric MLCCs offer a promising solution for high-performance DC link capacitors, enabling miniaturization and improved performance in various power electronic applications. The presented results demonstrate the potential for enhancing the capabilities of DC link capacitors and contribute to the continuous development of power electronics.

Antiferroelectric materials are very attractive for high-power electronic applications needed in emerging green energy technologies and enhanced energy storage properties. Their exceptional functional properties are closely related to the electric field-induced antiferroelectric↔ferroelectric phase transition, which can be driven toward a critical end point by manipulation with an external electric field. The critical fluctuation of physical properties at the critical end point in ferroelectrics is a promising approach to improve their functional properties. We demonstrate the existence of two critical end points in antiferroelectric ceramics with a ferroelectric-antiferroelectric-paraelectric phase sequence, using the model system Pb0.99Nb0.02[(Zr0.57Sn0.43)0.92Ti0.08]0.98O3. The two critical end points terminate the lines of the first-order ferroelectric-to-antiferroelectric and antiferroelectric-to-paraelectric phase transitions. The exceptionally high dielectric tunability (221%), measured at the temperature of the antiferroelectric-paraelectric critical end point, was attributed to the divergent nature of the dielectric permittivity at the paraelectric phase transition and the proximity of the triple point with degenerate phases. On the other hand, the energy storage density revealed a maximum in the proximity of the ferroelectric-to-antiferroelectric critical end point. The enhanced energy storage density was related to the optimal ratio between the maximum polarization, critical electric field, and the slope of the polarization loop. These findings open up new possibilities for material design and will pave the way for the next generation of high-energy storage materials.

In recent years, there has been a surge in interest in antiferroelectric materials. Among several reasons behind this we can find the notable negative electrocaloric response near the antiferroelectric-ferroelectric transition. This underscores the pressing need for a comprehensive study of the phase diagram, examining the dependence of antiferroelectric materials on finite temperatures and applied electric fields. In this study, we employ a shell model fitted to PbZrO₃ first principles calculations to construct a temperature-electric field phase diagram. Utilizing molecular dynamics simulations, we investigate electric fields up to 5 MV/cm across different crystallographic directions, specifically [001]c, [-110]c, and [110]c. Additionally, we analyze the significant role of simulation supercell size in stabilizing certain phases. Facilitated by atomistic nature of the model, the interrelation of polarization rotation, octahedral tilting and other distortion modes is scrutinized along the switching paths.