The expected piezoelectric market size is over $50 Billion by 2022 and most of them contain more than 60 wt % lead in their structure. Only 150000 kilograms of lead is emmitted from cell phone wastes annually.
Risks of using and manufacturing Lead based ceramics for workplace and environment:
- Exposure to lead vapor and dusts while manufacturing (mixing, calcining, machining etc.)
- Failure of dust filtering and increase of airborne and topsoil lead concentration.
- Failure of process liquid filtering and unplanned increase of lead concentration entering water treatment plants
Development of lead free ferroelectrics is a very crucial topic to eliminate the usage of poisonous lead based systems such as Pb(Zr0.52Ti0.48)O3 (PZT), Pb(Mg1/3Nb2/3)O3-PbTiO3 (PMN-PT) etc. Lead free studies have gained momentum after Saito et al., 2004*. Their results proved that controlled chemical composition and crystallographic orientation could give high ferroelectrical performances to K0.5Na0.5NbO3 (KNN) based systems which are comparable with PZT based ferroelectrics. If we focus on crystallographic orientation, the critical inputs to the “Templated grain growth -TGG” process are ceramic templates.
TGG process is lead by Ostwald ripening process which is based on the growth of larger grains (templates) at the expense of finer grains (matrix particles). The difference in surface free energies between templates and matrix grains cause a driving force for growth. So the templates must have lattice match with desired final composition and high aspect ratio to be oriented mechanically with doctor blade equipment. Thermodynamic stability is another necessity of templates. If a liquid phase former used in the system to prevent constrained sintering, templates mustn’t react with the liquid and/or secondary phases. The higher aspect ratio of templates (platelet, whisker, needle etc.) lead easy orientation.
The available pathways for developing lead free piezoceramics to replace lead based ones
Crystal structure engineering by changing chemical composition (Limits have been reached when applied alone).
Microstructure engineering by producing textured ceramics and obtaining increased performances from multi crystalline structures like single crystals. (ENTEKNO’s plate like particles (templates) play critical role in this pathway…)
Sodium Niobate (NaNbO3) platelets are basic components for texturing lead free piezoelectric ceramics. Desired morphological properties with high aspect ratio, damage free features etc. can be improved by controlling synthesis conditions. Single phase Sodium Niobate NaNbO3 platelets with 5-25 µm particle size, with high aspect ratio can be synthesized in ENTEKNO Laboratories. You can choose ENTEKNO templates which are good candidates for your TGG process. Lets see selection criteria below for your help:
- Lattice parameter mismatch between template and the desired phase should be less than 15%,
- The templating phase must be able to nucleate and grow from the oriented template particle at elevated temperature
- The template particle must have a suitably high aspect ratio morphology so that it can be oriented readily
- The template should not react or dissolve into the matrix before, stable oriented nuclei form and grow.
* Saito, Y., Takao, H., Tani, T., Nonoyama, T., Takatori, K., Homma, T., Nagaya, T., Nakamura, T., “Lead- Free Piezoceramics,” Nature, 432  84-87, 2004.