Editing Piezoelectricity (section)

==History==
===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]].

===World War I and inter-war years===
The first practical application for piezoelectric devices was [[sonar]], first developed during [[World War I]]. The superior performance of piezoelectric devices, operating at ultrasonic frequencies, superseded the earlier [[Fessenden oscillator]]. In [[France]] in 1917, [[Paul Langevin]] and his coworkers developed an [[ultrasound|ultrasonic]] [[submarine]] detector.<ref>{{cite journal |title= Who knew piezoelectricity? Rutherford and Langevin on submarine detection and the invention of sonar |last= Katzir |first= S. |journal= Notes Rec. R. Soc. |date= 2012 |volume= 66 |issue= 2 |pages= 141–157 |doi= 10.1098/rsnr.2011.0049 |doi-access= free }}</ref> The detector consisted of a [[transducer]], made of thin quartz crystals carefully glued between two steel plates, and a [[hydrophone]] to detect the returned [[Echo (phenomenon)|echo]]. By emitting a high-frequency pulse from the transducer, and measuring the amount of time it takes to hear an echo from the sound waves bouncing off an object, one can calculate the distance to that object.

Piezoelectric devices found homes in many fields. Ceramic [[phonograph]] cartridges simplified player design, were cheap and accurate, and made record players cheaper to maintain and easier to build. The development of the [[ultrasonic transducer]] allowed for easy measurement of viscosity and elasticity in fluids and solids, resulting in huge advances in materials research. Ultrasonic [[time-domain reflectometer]]s (which send an ultrasonic pulse through a material and measure reflections from discontinuities) could find flaws inside cast metal and stone objects, improving structural safety.

===World War II and post-war===
During [[World War II]], independent research groups in the [[United States]], [[USSR]], and [[Japan]] discovered a new class of synthetic materials, called [[ferroelectricity|ferroelectrics]], which exhibited piezoelectric constants many times higher than natural materials. This led to intense research to develop [[barium titanate]] and later lead zirconate titanate materials with specific properties for particular applications.

One significant example of the use of piezoelectric crystals was developed by [[Bell Telephone Laboratories]]. Following World War I, Frederick R. Lack, working in radio telephony in the engineering department, developed the "AT cut" crystal, a crystal that operated through a wide range of temperatures. Lack's crystal did not need the heavy accessories previous crystal used, facilitating its use on the aircraft. This development allowed Allied air forces to engage in coordinated mass attacks through the use of aviation radio.

Development of piezoelectric devices and materials in the United States was kept within the companies doing the development, mostly due to the wartime beginnings of the field, and in the interests of securing profitable patents. New materials were the first to be developed—quartz crystals were the first commercially exploited piezoelectric material, but scientists searched for higher-performance materials. Despite the advances in materials and the maturation of manufacturing processes, the United States market did not grow as quickly as Japan's did. Without many new applications, the growth of the United States' piezoelectric industry suffered.

In contrast, Japanese manufacturers shared their information, quickly overcoming technical and manufacturing challenges and creating new markets. In Japan, a temperature stable crystal cut was developed by [[Issac Koga]]. Japanese efforts in materials research created piezoceramic materials competitive to the United States materials but free of expensive patent restrictions. Major Japanese piezoelectric developments included new designs of piezoceramic filters for radios and televisions, piezo buzzers and audio transducers that can connect directly to electronic circuits, and the [[piezo ignition|piezoelectric igniter]], which generates sparks for small engine ignition systems and gas-grill lighters, by compressing a ceramic disc. Ultrasonic transducers that transmit sound waves through air had existed for quite some time but first saw major commercial use in early television remote controls. These transducers now are mounted on several [[automobile|car]] models as an [[Acoustic location|echolocation]] device, helping the driver determine the distance from the car to any objects that may be in its path.