Editing Ferroelectricity (section)

==Applications==
The nonlinear nature of ferroelectric materials can be used to make capacitors with adjustable capacitance. Typically, a [[ferroelectric capacitor]] simply consists of a pair of electrodes sandwiching a layer of ferroelectric material. The permittivity of ferroelectrics is not only adjustable but commonly also very high, especially when close to the phase transition temperature. Because of this, ferroelectric capacitors are small in physical size compared to dielectric (non-tunable) capacitors of similar capacitance.

The spontaneous polarization of ferroelectric materials implies a [[hysteresis]] effect which can be used as a memory function, and ferroelectric capacitors are indeed used to make [[ferroelectric RAM]]<ref name=Scott>{{Cite book|author=J.F. Scott |title= Ferroelectric Memories |publisher=Springer |year=2000|isbn=978-3-540-66387-4}}</ref> for computers and [[RFID]] cards. In these applications thin films of ferroelectric materials are typically used, as this allows the field required to switch the polarization to be achieved with a moderate voltage. However, when using thin films a great deal of attention needs to be paid to the interfaces, electrodes and sample quality for devices to work reliably.<ref name=Dawber>{{Cite journal|author1=M. Dawber |author2=K.M. Rabe|author2-link= Karin M. Rabe |author3=J.F. Scott |title= Physics of thin-film ferroelectric oxides |journal=Reviews of Modern Physics |volume=77 |page= 1083 |year=2005|arxiv = cond-mat/0503372 |bibcode = 2005RvMP...77.1083D |doi = 10.1103/RevModPhys.77.1083|issue=4 |s2cid=7517767}}</ref>

Ferroelectric materials are required by symmetry considerations to be also piezoelectric and pyroelectric. The combined properties of memory, [[piezoelectricity]], and [[pyroelectricity]] make ferroelectric capacitors very useful, e.g. for sensor applications. Ferroelectric capacitors are used in medical ultrasound machines (the capacitors generate and then listen for the ultrasound ping used to image the internal organs of a body), high quality infrared cameras (the infrared image is projected onto a two dimensional array of ferroelectric capacitors capable of detecting temperature differences as small as millionths of a degree Celsius), fire sensors, sonar, vibration sensors, and even fuel injectors on diesel engines.

Another idea of recent interest is the ''[[ferroelectric tunnel junction]]'' (''FTJ'') in which a contact is made up by nanometer-thick ferroelectric film placed between metal electrodes.<ref name=ftj>{{Cite journal
|doi=10.1103/PhysRevLett.94.246802
|author1=M.Ye. Zhuravlev |author2=R.F. Sabirianov |author3=S.S. Jaswal |author4=E.Y. Tsymbal |title=Giant Electroresistance in Ferroelectric Tunnel Junctions
|journal=Physical Review Letters
|volume=94
|pages=246802–4
|year=2005
|bibcode=2005PhRvL..94x6802Z|arxiv = cond-mat/0502109
|issue=24 |s2cid=15093350 }}</ref> The thickness of the ferroelectric layer is small enough to allow tunneling of electrons. The piezoelectric and interface effects as well as the depolarization field may lead to a giant electroresistance (GER) switching effect.

Yet another burgeoning application is [[multiferroics]], where researchers are looking for ways to couple magnetic and ferroelectric ordering within a material or heterostructure; there are several recent reviews on this topic.<ref name=ferroics>{{Cite journal|first1=R.|last1=Ramesh|first2=N.A|last2=Spaldin|author2-link=Nicola Spaldin|journal= Nature Materials |volume= 6 |year=2007|bibcode = 2007NatMa...6...21R |doi = 10.1038/nmat1805 |pmid=17199122|issue=1|pages=21–9|title=Multiferroics: Progress and prospects in thin films}}{{Cite journal|author1=W. Eerenstein |author2=N.D. Mathur |author3=J.F. Scott |journal= Nature |volume= 442 |year=2006|bibcode = 2006Natur.442..759E |doi = 10.1038/nature05023 |pmid=16915279 |issue=7104|pages=759–65 |title=Multiferroic and magnetoelectric materials|s2cid=4387694 }}, {{Cite journal|first1=N.A.|last1=Spaldin|author1-link=Nicola Spaldin|first2=M.|last2=Fiebig |journal= Science |volume= 309 |issue=5733|pages=391–2 | doi=10.1126/science.1113357  |year=2005|title=The renaissance of magnetoelectric multiferroics |pmid=16020720|s2cid=118513837}} {{Cite journal|author=M. Fiebig |journal= Journal of Physics D: Applied Physics|title=Revival of the magnetoelectric effect |volume=38 |issue= 8|page=R123 |year=2005|doi=10.1088/0022-3727/38/8/R01|bibcode = 2005JPhD...38R.123F |s2cid= 121588385}}</ref>

[[Catalysis|Catalytic]] properties of ferroelectrics have been studied since 1952 when Parravano observed anomalies in CO oxidation rates over ferroelectric sodium and potassium niobates near the [[Curie temperature]] of these materials.<ref>{{cite journal |last1=Parravano |first1=G. |title=Ferroelectric Transitions and Heterogenous Catalysis |journal=The Journal of Chemical Physics |date=February 1952 |volume=20 |issue=2 |pages=342–343 |doi=10.1063/1.1700412 |bibcode=1952JChPh..20..342P }}</ref> Surface-perpendicular component of the ferroelectric polarization can dope polarization-dependent charges on surfaces of ferroelectric materials, changing their chemistry.<ref>{{Cite journal|title=Ferroelectrics: A pathway to switchable surface chemistry and catalysis|pages=302–316|journal=Surface Science|volume=650|doi=10.1016/j.susc.2015.10.055|date=August 2016|bibcode=2016SurSc.650..302K|last1=Kakekhani|first1=Arvin|last2=Ismail-Beigi|first2=Sohrab|last3=Altman|first3=Eric I.|doi-access=free}}</ref><ref>{{Cite journal|last1=Kolpak|first1=Alexie M.|last2=Grinberg|first2=Ilya|last3=Rappe|first3=Andrew M.|date=2007-04-16|title=<nowiki>Polarization Effects on the Surface Chemistry of ${\mathrm{PbTiO}}_{3}$-Supported Pt Films</nowiki>|journal=Physical Review Letters|volume=98|issue=16|pages=166101|doi=10.1103/PhysRevLett.98.166101|pmid=17501432}}</ref><ref>{{cite journal |last1=Yun |first1=Yang |last2=Altman |first2=Eric I. |title=Using Ferroelectric Poling to Change Adsorption on Oxide Surfaces |journal=Journal of the American Chemical Society |date=December 2007 |volume=129 |issue=50 |pages=15684–15689 |doi=10.1021/ja0762644 |pmid=18034485 }}</ref> This opens the possibility of performing catalysis beyond the limits of the [[Sabatier principle]].<ref name=":0">{{cite journal |last1=Kakekhani |first1=Arvin |last2=Ismail-Beigi |first2=Sohrab |title=Ferroelectric-Based Catalysis: Switchable Surface Chemistry |journal=ACS Catalysis |date=29 June 2015 |volume=5 |issue=8 |pages=4537–4545 |doi=10.1021/acscatal.5b00507 |bibcode=2015APS..MARY26011K |doi-access=free }}</ref> Sabatier principle states that the surface-adsorbates interaction has to be an optimal amount: not too weak to be inert toward the reactants and not too strong to poison the surface and avoid desorption of the products: a compromise situation.<ref>{{cite journal |last1=Laursen |first1=Anders B. |last2=Man |first2=Isabela Costinela |last3=Trinhammer |first3=Ole L. |last4=Rossmeisl |first4=Jan |last5=Dahl |first5=Søren |title=The Sabatier Principle Illustrated by Catalytic H<sub>2</sub>O<sub>2</sub> Decomposition on Metal Surfaces |journal=Journal of Chemical Education |date=December 2011 |volume=88 |issue=12 |pages=1711–1715 |doi=10.1021/ed101010x |bibcode=2011JChEd..88.1711L }}</ref> This set of optimum interactions is usually referred to as "top of the volcano" in activity volcano plots.<ref>{{cite journal |last1=Seh |first1=Zhi Wei |last2=Kibsgaard |first2=Jakob |last3=Dickens |first3=Colin F. |last4=Chorkendorff |first4=Ib |last5=Nørskov |first5=Jens K. |last6=Jaramillo |first6=Thomas F. |title=Combining theory and experiment in electrocatalysis: Insights into materials design |journal=Science |date=13 January 2017 |volume=355 |issue=6321 |pages=eaad4998 |doi=10.1126/science.aad4998 |pmid=28082532 |s2cid=217918130 |url=https://backend.orbit.dtu.dk/ws/files/131069434/aad4998_Review_Article_Manuscript.pdf }}</ref> On the other hand, ferroelectric polarization-dependent chemistry can offer the possibility of switching the surface—adsorbates interaction from strong [[adsorption]] to strong [[desorption]], thus a compromise between desorption and adsorption is no longer needed.<ref name=":0" /> Ferroelectric polarization can also act as an [[Energy harvesting|energy harvester]].<ref>{{cite journal |last1=Zhang |first1=Yan |last2=Xie |first2=Mengying |last3=Adamaki |first3=Vana |last4=Khanbareh |first4=Hamideh |last5=Bowen |first5=Chris R. |title=Control of electro-chemical processes using energy harvesting materials and devices |journal=Chemical Society Reviews |date=2017 |volume=46 |issue=24 |pages=7757–7786 |doi=10.1039/c7cs00387k |pmid=29125613 |doi-access=free }}</ref> Polarization can help the separation of photo-generated [[electron-hole pairs]], leading to enhanced photocatalysis.<ref>{{cite book |doi=10.1002/9783527807505.ch9 |chapter=Ferroelectrics in Photocatalysis |title=Ferroelectric Materials for Energy Applications |year=2018 |last1=Fang |first1=Liang |last2=You |first2=Lu |last3=Liu |first3=Jun-Ming |pages=265–309 |isbn=9783527807505 |s2cid=104740681 }}</ref> Also, due to [[Pyroelectricity|pyroelectric]] and [[Piezoelectricity|piezoelectric]] effects under varying temperature (heating/cooling cycles)<ref>{{cite journal |last1=Benke |first1=Annegret |last2=Mehner |first2=Erik |last3=Rosenkranz |first3=Marco |last4=Dmitrieva |first4=Evgenia |last5=Leisegang |first5=Tilmann |last6=Stöcker |first6=Hartmut |last7=Pompe |first7=Wolfgang |last8=Meyer |first8=Dirk C. |title=Pyroelectrically Driven •OH Generation by Barium Titanate and Palladium Nanoparticles |journal=The Journal of Physical Chemistry C |date=30 July 2015 |volume=119 |issue=32 |pages=18278–18286 |doi=10.1021/acs.jpcc.5b04589 }}</ref><ref>{{cite journal |last1=Kakekhani |first1=Arvin |last2=Ismail-Beigi |first2=Sohrab |title=Ferroelectric oxide surface chemistry: water splitting via pyroelectricity |journal=Journal of Materials Chemistry A |date=2016 |volume=4 |issue=14 |pages=5235–5246 |doi=10.1039/C6TA00513F }}</ref> or varying strain (vibrations) conditions<ref>{{cite journal |last1=Starr |first1=Matthew B. |last2=Shi |first2=Jian |last3=Wang |first3=Xudong |title=Piezopotential-Driven Redox Reactions at the Surface of Piezoelectric Materials |journal=Angewandte Chemie International Edition |date=11 June 2012 |volume=51 |issue=24 |pages=5962–5966 |doi=10.1002/anie.201201424 |pmid=22556008 |doi-access=free }}</ref> extra charges can appear on the surface and drive various [[Chemical reaction|(electro)chemical reactions]] forward.

[[Photoferroelectric imaging]] is a technique to record optical information on pieces of ferroelectric material. The images are nonvolatile and selectively erasable.<ref name="land">{{cite encyclopedia |title=Photoferroelectric imaging |encyclopedia= McGraw-Hill Concise Encyclopedia of Science and Technology |edition=5 |date= |year=2004 |last=Land |first=Cecil |publisher=McGraw-Hill |location=New York |id= |url= |access-date= }}</ref>