The development of Piezoceramics which do not contain lead has been a main focus of universities and companies for at least the last two decades. This is mostly due to laws implemented in the EU to avoid certain substances, in this case lead, in the supply chain of electronic equipment and automotive applications.

In contrast to certain other applications, lead is not an addition, but the main constituent of the piezoelectric materials based on PZT and one of the main reasons for its unique properties. Despite the quite large research, no simple drop in substitution has been found so far.

The most promising materials are based on Potassium -Sodium-Niobate (KNN) and Bismuth–Sodium-Titanate-Barium-Titanate (BNT-BT). Still, the properties are inferior to PZT, especially the temperature dependance and the stability in application are still under development.

The powder processing routes are mostly more difficult due to solubility of some of the constituents in water, which makes the production more difficult. The use of KNN is, according to recent investigations into the Lifecycle (LCA) not beneficial to the environment either, in this case due to upstream issues, being more severe then even the raw materials for PZT.

Interestingly, some properties differ quite strong from PZT in a way, which could be used in some applications. BNT-BT based materials show a very strong anisotropy between the planar and longitudinal effect, which could be exploited in Ultrasonic measurement systems with higher frequencies (e.g. 500kHz and above) in addition to applications, where PZT seems to be mandatory.

In this presentation the current state of the art for leadfree piezoceramics will be presented. Comparisons are drawn with ultrasonic applications using PZT and the next steps to generate more data on reliability and reproducibility from a production point of view will be discussed.

Encouraged by environmental concerns and RoHS regulations, researchers have developed a range of lead-free alternatives to PZT. However, the comparison of performance parameters is not straightforward due to a non-linear response of both PZT and lead-free materials. As it is the case for PZT, lead-free formulations have to be adapted to specific applications, whether it is sensing or power ultrasonics. The focus of the present research is high-power ultrasound generation for medical handheld applications and the aim is to identify the challenges associated with the switch to lead-free materials, as well as to discuss the baseline for the comparison of materials. In this paper, two lead-free formulations, one NBT-based and one KNN-based, are tested as part of a bolted Langevin transducer. In the first part, the original transducer design using hard-doped PZT (Navy type III) is presented and simulated. Test samples have been manufactured using mentioned PZT and lead-free piezoelectric materials in a way that Lead-free piezoceramic rings were used as a direct substitution for PZT in the original design, without further dimensional adjustments. The impact of the preload level on the transducer impedance response was evaluated. Further testing of the samples included impedance response evaluation (small signal measurement) and high-power testing under different driving scenarios to observe transducer parameters and the relations between them in terms of input (driving) power, transducer impedance, vibration amplitude, resonance frequency, and self-heating of the transducer stack. All parameters were monitored over time to determine the maximum feasible driving conditions for each of the materials tested. Results indicate that lead-free alternatives can be used as a replacement for hard-doped PZT, though with certain performance trade-offs. Challenges associated with the direct re-placement of PZT by lead-free alternatives include changes in the electrical parameters (driving circuitry adjustments), shift of nodal point, and evolution of the frequency response affecting phase tracking. The applicability of the lead-free alternatives is further discussed, as well as necessary adjustments to the transducer assembly and driving.

Dielectric ceramics are playing increasing roles in pulsed-power electronics and smart grid technologies benefit from their outstanding energy storage properties such as higher power density, long cycle life, and excellent mechanical performance compared with other energy storage materials. (Ba,Sr)TiO3 (BST) based ceramics are the most widely studied and commercially attractive candidates.
0.9Ba0.6Sr0.4TiO3-0.1Bi(Nb1/3Mg2/3)O3（BST-BNM）ceramics with a core-shell grain structure have been prepared by a two-step synthesizing process. Back-scattering electron microscopy (BSE) in combination with energy dispersive spectroscopy (EDS) confirmed three distinct areas in the BST-BNM ceramic: a grain core, a grain shell, and gradient regions. The effect of chemical inhomogeneity of the grain including volume fractions of the grain core and compositional gradient which could be tuned by compositional design, synthesizing process, or post-annealing on the dielectric, electric, and energy storage properties were investigated in this chapter. Increasing Sr concentration leads to an increase in chemical inhomogeneity of the grain in BST-BNM ceramic. While the sample prepared by a two-step synthesizing process (BST-BNM(T) exhibits more core-shell grain structure in comparison to that from a one-step synthesizing process (BST-BNM(O) for a fixed composition. An increase in post-annealing temperature or time is effective in decreasing the chemical inhomogeneity of the grain, while over high temperature or long time would lead to the evaporation of Bi2O3. An increase in the chemical homogeneity of the grain is helpful to improve the dielectric loss and energy storage efficiency (η) due to a decrease in interfacial polarization, whereas it results in a decrease in dielectric temperature stabilities. The insulation of the sample is dominated by the resistance of grain boundaries, changing little with the variation in the chemical homogeneity of the grain. An increase in the volume fraction of the grain shell is useful to increase the BDS at the expense of εr. Improvement of BDS and εr simultaneously could be achieved by carefully regulating the compositional gradient and the core-shell grain structure through the post-annealing process. An optimized energy storage properties with BDS~415 kV/cm， Wrec~4.06 J/cm3, and η~88.5% could be attained for BST-BNM(T) ceramic after post-annealing at 1100℃/6h.