Editing Piezoelectricity (section)

===Lead-free piezoceramics===
* [[Sodium potassium niobate]] ((K,Na)NbO<sub>3</sub>). This material is also known as NKN or KNN. In 2004, a group of Japanese researchers led by Yasuyoshi Saito discovered a sodium potassium niobate composition with properties close to those of PZT, including a high ''T''<sub>C</sub>.<ref>{{cite journal |title=Lead-free piezoceramics |first1=Yasuyoshi |last1=Saito |last2=Takao |first2=Hisaaki |last3=Tanil |first3=Toshihiko |last4=Nonoyama |first4=Tatsuhiko |last5=Takatori |first5=Kazumasa |last6=Homma |first6=Takahiko |last7=Nagaya |first7=Toshiatsu |last8=Nakamura |first8=Masaya |journal=[[Nature (journal)|Nature]] |volume=432 |issue=7013 |pages=81–87 |doi=10.1038/nature03028 |pmid=15516921 |date=2004-11-04 |bibcode=2004Natur.432...84S }}</ref> Certain compositions of this material have been shown to retain a high mechanical quality factor (''Q''<sub>m</sub>&nbsp;≈&nbsp;900) with increasing vibration levels, whereas the mechanical quality factor of hard PZT degrades in such conditions. This fact makes NKN a promising replacement for high power resonance applications, such as piezoelectric transformers.<ref name="GurdalUral2011">{{cite journal|last1=Gurdal|first1=Erkan A.|last2=Ural|first2=Seyit O.|last3=Park|first3=Hwi-Yeol|last4=Nahm|first4=Sahn|last5=Uchino|first5=Kenji|title=High Power (Na<sub>0.5</sub>K<sub>0.5</sub>)NbO<sub>3</sub>-Based Lead-Free Piezoelectric Transformer|journal=Japanese Journal of Applied Physics|volume=50|issue=2|year=2011|page=027101 |doi=10.1143/JJAP.50.027101|bibcode = 2011JaJAP..50b7101G }}</ref>
* [[Bismuth ferrite]] (BiFeO<sub>3</sub>) &nbsp;– a promising candidate for the replacement of lead-based ceramics.
* Sodium niobate (NaNbO<sub>3</sub>)
* [[Barium titanate]] (BaTiO<sub>3</sub>)&nbsp;– Barium titanate was the first piezoelectric ceramic discovered.
* [[Bismuth titanate]] (Bi<sub>4</sub>Ti<sub>3</sub>O<sub>12</sub>)
* [[Sodium bismuth titanate]] (NaBi(TiO<sub>3</sub>)<sub>2</sub>)
The fabrication of lead-free piezoceramics pose multiple challenges, from an environmental standpoint and their ability to replicate the properties of their lead-based counterparts. By removing the lead component of the piezoceramic, the risk of toxicity to humans decreases, but the mining and extraction of the materials can be harmful to the environment.<ref>{{cite journal |last1=Ibn-Mohammed |first1=T. |last2=Koh |first2=S. C. L. |last3=Reaney |first3=I. M. |last4=Sinclair |first4=D. C. |last5=Mustapha |first5=K. B. |last6=Acquaye |first6=A. |last7=Wang |first7=D. |title=Are lead-free piezoelectrics more environmentally friendly? |journal=MRS Communications |date=March 2017 |volume=7 |issue=1 |pages=1–7 |doi=10.1557/mrc.2017.10 }}</ref> Analysis of the environmental profile of PZT versus sodium potassium niobate (NKN or KNN) shows that across the four indicators considered (primary energy consumption, toxicological footprint, eco-indicator 99, and input-output upstream greenhouse gas emissions), KNN is actually more harmful to the environment. Most of the concerns with KNN, specifically its Nb<sub>2</sub>O<sub>5</sub> component, are in the early phase of its life cycle before it reaches manufacturers. Since the harmful impacts are focused on these early phases, some actions can be taken to minimize the effects. Returning the land as close to its original form after Nb<sub>2</sub>O<sub>5</sub> mining via dam deconstruction or replacing a stockpile of utilizable soil are known aids for any extraction event. For minimizing air quality effects, modeling and simulation still needs to occur to fully understand what mitigation methods are required. The extraction of lead-free piezoceramic components has not grown to a significant scale at this time, but from early analysis, experts encourage caution when it comes to environmental effects.

Fabricating lead-free piezoceramics faces the challenge of maintaining the performance and stability of their lead-based counterparts. In general, the main fabrication challenge is creating the "morphotropic phase boundaries (MPBs)" that provide the materials with their stable piezoelectric properties without introducing the "polymorphic phase boundaries (PPBs)" that decrease the temperature stability of the material.<ref>{{cite journal |last1=Wu |first1=Jiagang |title=Perovskite lead-free piezoelectric ceramics |journal=Journal of Applied Physics |date=21 May 2020 |volume=127 |issue=19 |doi=10.1063/5.0006261 |bibcode=2020JAP...127s0901W |doi-access=free }}</ref> New phase boundaries are created by varying additive concentrations so that the [[phase transition]] temperatures converge at room temperature. The introduction of the MPB improves piezoelectric properties, but if a PPB is introduced, the material becomes negatively affected by temperature. Research is ongoing to control the type of phase boundaries that are introduced through phase engineering, diffusing phase transitions, domain engineering, and chemical modification.