Editing Piezoelectricity (section)

===Discovery and early research===
{{See also|Physical crystallography before X-rays#Piezoelectricity}}
The [[pyroelectricity|pyroelectric effect]], by which a material generates an [[electric potential]] in response to a temperature change, was studied by [[Carl Linnaeus]] and [[Franz Aepinus]] in the mid-18th century. Drawing on this knowledge, both [[René Just Haüy]] and [[Antoine César Becquerel]] posited a relationship between [[Stress (mechanics)|mechanical stress]] and electric charge; however, experiments by both proved inconclusive.<ref>{{cite web|last=Erhart |first=Jiří |url=https://moodle.fp.tul.cz/nano/pluginfile.php/2476/mod_resource/content/3/FPM_Piezo_lecture1.pdf |title=Piezoelectricity and ferroelectricity: Phenomena and properties |publisher=Department of Physics, Technical University of Liberec |url-status=unfit |archive-url=https://web.archive.org/web/20140508030117/https://moodle.fp.tul.cz/nano/pluginfile.php/2476/mod_resource/content/3/FPM_Piezo_lecture1.pdf |archive-date=May 8, 2014 }}</ref>

[[File:Top view of Curie piezo electric compensator.jpg|thumb|View of piezo crystal in the top of a Curie compensator in the Museum of Scotland.]]
The first demonstration of the direct piezoelectric effect was in 1880 by the brothers [[Pierre Curie]] and [[Jacques Curie]].<ref>{{cite journal|first1=Jacques|last1=Curie|author1-link=Jacques Curie |first2=Pierre |last2=Curie|author2-link=Pierre Curie |date=1880 |title=Développement par compression de l'électricité polaire dans les cristaux hémièdres à faces inclinées |trans-title=Development, via compression, of electric polarization in hemihedral crystals with inclined faces |journal=Bulletin de la Société Minérologique de France |volume=3 |issue=4|pages=90–93|doi=10.3406/bulmi.1880.1564}}<br />
Reprinted in: {{cite journal |first1=Jacques |last1=Curie |author1-link=Jacques Curie |first2=Pierre |last2=Curie |author2-link=Pierre Curie |date=1880 |url=http://gallica.bnf.fr/ark:/12148/bpt6k30485/f296.image |title=Développement, par pression, de l'électricité polaire dans les cristaux hémièdres à faces inclinées |journal=Comptes Rendus |volume=91 |pages=294–295 |language=fr |url-status=live |archive-url=https://web.archive.org/web/20121205083302/http://gallica.bnf.fr/ark:/12148/bpt6k30485/f296.image |archive-date=2012-12-05 }}<br />
See also: {{cite journal|first1=Jacques|last1=Curie|author1-link=Jacques Curie|first2=Pierre|last2=Curie|author2-link=Pierre Curie|date=1880|url=http://gallica.bnf.fr/ark:/12148/bpt6k30485/f385.image|title=Sur l'électricité polaire dans les cristaux hémièdres à faces inclinées|trans-title=On electric polarization in hemihedral crystals with inclined faces|journal=Comptes Rendus|volume=91|pages=383–386|language=fr|url-status=live|archive-url=https://web.archive.org/web/20121205090430/http://gallica.bnf.fr/ark:/12148/bpt6k30485/f385.image|archive-date=2012-12-05}}</ref> They combined their knowledge of pyroelectricity with their understanding of the underlying crystal structures that gave rise to pyroelectricity to predict crystal behavior, and demonstrated the effect using crystals of [[tourmaline]], [[quartz]], [[topaz]], [[sugar cane|cane]] [[sugar]], and [[Rochelle salt]] (sodium potassium tartrate tetrahydrate). Quartz and [[Rochelle salt]] exhibited the most piezoelectricity.

[[Image:SchemaPiezo.gif|thumb|A piezoelectric disk generates a voltage when deformed (change in shape is greatly exaggerated).]]

The Curies, however, did not predict the converse piezoelectric effect. The converse effect was mathematically deduced from fundamental thermodynamic principles by [[Gabriel Lippmann]] in 1881.<ref>{{Cite journal|first=G.|last=Lippmann|title=Principe de la conservation de l'électricité|trans-title=Principle of the conservation of electricity|journal=[[Annales de chimie et de physique]]|volume=24|page=145|url=http://gallica.bnf.fr/ark:/12148/bpt6k348640|year=1881|language=fr|url-status=live|archive-url=https://web.archive.org/web/20160208081244/http://gallica.bnf.fr/ark:/12148/bpt6k348640|archive-date=2016-02-08}}</ref> The Curies immediately confirmed the existence of the converse effect,<ref>{{cite journal|first1=Jacques|last1=Curie|author1-link=Jacques Curie|first2=Pierre|last2=Curie|author2-link=Pierre Curie|date=1881|url=http://gallica.bnf.fr/ark:/12148/bpt6k3049g/f1131.image|title=Contractions et dilatations produites par des tensions dans les cristaux hémièdres à faces inclinées|trans-title=Contractions and expansions produced by voltages in hemihedral crystals with inclined faces|journal=Comptes Rendus|volume=93|pages=1137–1140|language=fr|url-status=live|archive-url=https://web.archive.org/web/20121205084840/http://gallica.bnf.fr/ark:/12148/bpt6k3049g/f1131.image|archive-date=2012-12-05}}</ref> and went on to obtain quantitative proof of the complete reversibility of electro-elasto-mechanical deformations in piezoelectric crystals.

For the next few decades, piezoelectricity remained something of a laboratory curiosity, though it was a vital tool in the discovery of [[polonium]] and radium by Pierre and [[Marie Curie]] in 1898. More work was done to explore and define the crystal structures that exhibited piezoelectricity. This culminated in 1910 with the publication of [[Woldemar Voigt]]'s ''Lehrbuch der Kristallphysik'' (''Textbook on Crystal Physics''),<ref>{{cite book |first=Woldemar |last=Voigt |author-link=Woldemar Voigt |url=https://books.google.com/books?id=SvPPAAAAMAAJ&pg=PR1 |title=Lehrbuch der Kristallphysik |location=Berlin |publisher=B. G. Teubner |date=1910 |url-status=live |archive-url=https://web.archive.org/web/20140421051401/http://books.google.com/books?id=SvPPAAAAMAAJ&pg=PR1 |archive-date=2014-04-21 }}</ref> which described the 20 natural crystal classes capable of piezoelectricity, and rigorously defined the piezoelectric constants using [[tensor analysis]].