View source for Barium titanate

{{chembox
| Verifiedfields = changed
| Watchedfields = changed
| verifiedrevid = 455377376
| Name = Barium titanate
| ImageFile = BaTiO3ceramics.JPG
| ImageCaption=Polycrystalline BaTiO<sub>3</sub> in plastic
| ImageName = Barium titanate ceramics in plastic package
| OtherNames =
|Section1={{Chembox Identifiers
| InChI = 1/2Ba.4O.Ti/q2*+2;4*-1;/r2Ba.O4Ti/c;;1-5(2,3)4/q2*+2;-4
| SMILES = [Ba+2].[Ba+2].[O-][Ti]([O-])([O-])[O-]
| InChIKey = JRPBQTZRNDNNOP-NXYSCRTKAD
| StdInChI_Ref = {{stdinchicite|correct|chemspider}}
| StdInChI = 1S/2Ba.4O.Ti/q2*+2;4*-1;
| StdInChIKey_Ref = {{stdinchicite|correct|chemspider}}
| StdInChIKey = JRPBQTZRNDNNOP-UHFFFAOYSA-N
| CASNo_Ref = {{cascite|correct|CAS}}
| CASNo = 12047-27-7
| UNII_Ref = {{fdacite|correct|FDA}}
| UNII = 73LKE302QO
| ChemSpiderID_Ref = {{chemspidercite|correct|chemspider}}
| ChemSpiderID =10605734
| PubChem = 6101006
| RTECS = XR1437333
| EINECS = 234-975-0
}}
|Section2={{Chembox Properties
| Formula = BaTiO<sub>3</sub>
| MolarMass = 233.192{{nbsp}}g/mol
| Appearance = White crystals
| Odor = Odorless
| BandGap = 3.2{{nbsp}}eV (300{{nbsp}}K, single crystal)<ref name=bandgap>{{cite journal|doi=10.1143/JJAP.44.2081|title=Optical Band Gap of Barium Titanate Nanoparticles Prepared by RF-plasma Chemical Vapor Deposition|journal=Jpn. J. Appl. Phys. |volume=44 |issue=4A|year=2005|pages=2081–2082|last1=Suzuki |first1=Keigo |last2=Kijima |first2=Kazunori |bibcode=2005JaJAP..44.2081S|s2cid=122166759 }}</ref>
| Density = 6.02{{nbsp}}g/cm<sup>3</sup>, solid
| Solubility = Insoluble
| SolubleOther = Slightly soluble in dilute mineral acids; dissolves in concentrated [[hydrofluoric acid]] 
| MeltingPtC = 1625
| MeltingPt_notes = 
| BoilingPt =
| RefractIndex=n<sub>o</sub> = 2.412; n<sub>e</sub> = 2.360<ref name="Tong2013">{{cite book|last=Tong |first=Xingcun Colin |title=Advanced Materials for Integrated Optical Waveguides|url=https://books.google.com/books?id=V1K6BAAAQBAJ&pg=PA357|date= 2013|publisher=Springer Science & Business Media|isbn=978-3-319-01550-7|page=357}}</ref>
}}
|Section3={{Chembox Structure
| CrystalStruct = [[Tetragonal]], [[Pearson symbol|tP5]] 
| SpaceGroup = P4mm, No. 99
}}
|Section7={{Chembox Hazards
| ExternalSDS = 
| GHSPictograms = {{GHS07}}
| GHSSignalWord = Warning
| HPhrases = {{H-phrases|302|332}}
| PPhrases = {{P-phrases|}}
}}
}}

'''Barium titanate''' ('''BTO''') is an [[inorganic compound]] with [[chemical formula]] BaTiO<sub>3</sub>. It is the barium salt of [[metatitanic acid]]. [[Barium]] titanate appears white as a powder and is transparent when prepared as large crystals.  It is a [[Ferroelectricity|ferroelectric]], [[Pyroelectricity|pyroelectric]], and [[Piezoelectricity|piezoelectric]] [[ceramic]] material that exhibits the [[photorefractive effect]].  It is used in [[capacitor]]s, [[electromechanical]] [[transducer]]s and [[nonlinear optic]]s.

==Structure==
{{Main|Perovskite (structure)}}
[[File:Perovskite.jpg|thumb|left|Structure of cubic BaTiO<sub>3</sub>. The red spheres are oxide centres, blue are Ti<sup>4+</sup> cations, and the green spheres are Ba<sup>2+</sup>.]]
The solid exists in one of four polymorphs depending on temperature. From high to low temperature, these crystal symmetries of the four polymorphs are [[Cubic crystal system|cubic]], [[Tetragonal crystal system|tetragonal]], [[Orthorhombic crystal system|orthorhombic]] and [[Trigonal crystal system|rhombohedral]] [[crystal structure]]. All of these phases exhibit the [[ferroelectric effect]] apart from the cubic phase.  The high temperature cubic phase is easiest to describe, as it consists of regular corner-sharing octahedral TiO<sub>6</sub> units that define a cube with O vertices and Ti-O-Ti edges.  In the cubic phase, Ba<sup>2+</sup> is located at the center of the cube, with a nominal [[coordination number]] of 12.  Lower symmetry phases are stabilized at lower temperatures and involve movement of the Ti<sup>4+</sup> to off-center positions.  The remarkable properties of this material arise from the cooperative behavior of the Ti<sup>4+</sup> distortions.<ref>Manuel Gaudon. Out-of-centre distortions around an octahedrally coordinated Ti4+ in BaTiO3. Polyhedron, Elsevier, 2015, 88, pp.6-10. <10.1016/j.poly.2014.12.004>. <hal-01112286></ref>

Above the melting point, the liquid has a remarkably different local structure to the solid forms, with the majority of Ti<sup>4+</sup> coordinated to four oxygen, in tetrahedral TiO<sub>4</sub> units, which coexist with more highly coordinated units.<ref>{{cite journal |author1=Alderman O L G |author2=Benmore C |author3=Neuefeind J |author4=Tamalonis A |author5=Weber R |year=2019 |title=Molten barium titanate: a high-pressure liquid silicate analogue |journal=Journal of Physics: Condensed Matter |volume=31 |issue=20 |page=20LT01 |doi=10.1088/1361-648X/ab0939 |pmid=30790768 |bibcode=2019JPCM...31tLT01A |osti=1558227 |s2cid=73498849 }}</ref>

==Production and handling properties==
[[File:Oxides particles.jpg|300px|left|thumb|Scanning Electron Microscopy (SEM) images showing particles of BaTiO<sub>3</sub>. The different morphologies depend on the synthesis conditions (precipitation, hydrothermal and solvothermal synthesis): size and shape can be varied by changing the concentration of precursors, the reaction temperature and the time. Color (if added) helps to emphasize the grayscale levels. In general, the synthesis of Barium titanate by precipitation from aqueous solution allows to produce particles with spherical shape with size that can be tailored from a few nanometers to several hundred nanometers by decreasing the concentration of reactants. At very low concentration the particles have the tendency to develop a dendritic-like morphology, as reported in the images.]]

Barium titanate can be synthesized by the relatively simple [[Hydrothermal synthesis|sol–hydrothermal]] method.<ref>{{cite journal|last1=Selvaraj |first1=M. |last2=Venkatachalapathy |first2=V. |last3=Mayandi |first3=J. |last4=Karazhanov |first4=S. |last5=Pearce |first5=J. M. |title=Preparation of meta-stable phases of barium titanate by Sol-hydrothermal method |journal=AIP Advances |volume=5 |issue=11 |pages=117119 |doi=10.1063/1.4935645|year=2015 |bibcode=2015AIPA....5k7119S |doi-access=free }}</ref> 
Barium titanate can also be manufactured by heating [[barium carbonate]] and [[titanium dioxide]].  The reaction proceeds via [[sintering#Liquid phase sintering|liquid phase sintering]]. Single crystals can be grown at around 1100&nbsp;°C from molten [[potassium fluoride]].<ref>{{cite book | last1 = Galasso | first1 = Francis S. | chapter = Barium Titanate, BaTiO <sub>3</sub> | year = 1973 | title = Inorganic Syntheses| volume = 14 | pages = 142–143 | doi = 10.1002/9780470132456.ch28 | isbn = 9780470132456 }}</ref>   Other materials are often added as [[doping (semiconductors)|dopants]], e.g., Sr to form solid solutions with [[strontium titanate]]. Barium titanate reacts with [[nitrogen trichloride]] and produces a greenish or gray mixture;<!--what's the chemical makeup of that mixture?--> the [[ferroelectric]] properties of the mixture are still present in this form.

Much effort has been spent studying the relationship between particle morphology and its properties. Barium titanate is one of the few ceramic compounds known to exhibit [[abnormal grain growth]], in which large faceted grains grow in a matrix of finer grains, with profound implications on densification and physical properties.<ref>[https://arxiv.org/ftp/arxiv/papers/1303/1303.2761.pdf#page=2 Journal of Crystal Growth] 2012, Volume 359, Pages 83-91, Abnormal Grain Growth </ref>   Fully dense nanocrystalline barium titanate has 40% higher [[permittivity]] than the same material prepared in classic ways.<ref>{{cite journal| doi=10.1021/jp7112818| title=Effect of Microwave Frequency on Hydrothermal Synthesis of Nanocrystalline Tetragonal Barium Titanate| year=2008 |last1=Nyutu |first1=Edward K.| journal=The Journal of Physical Chemistry C| volume=112| pages=9659| last2=Chen| first2=Chun-Hu| last3=Dutta| first3=Prabir K.| last4=Suib| first4=Steven L.| issue=26| citeseerx=10.1.1.660.3769}}</ref> The addition of inclusions of barium titanate to [[tin]] has been shown to produce a bulk material with a higher [[Viscoelasticity|viscoelastic]] [[stiffness]] than that of diamonds. Barium titanate goes through two phase transitions that change the crystal shape and volume. This phase change leads to composites where the barium titanates have a negative bulk modulus ([[Young's modulus]]), meaning that when a force acts on the inclusions, there is displacement in the opposite direction, further stiffening the composite.<ref>{{cite journal| doi = 10.1126/science.1135837| year=2007 |last1=Jaglinski |first1=T. |last2=Kochmann |first2=D. |last3=Stone |first3=D. |last4=Lakes |first4=R. S. | title = Composite materials with viscoelastic stiffness greater than diamond| volume = 315| issue = 5812| pages = 620–2| pmid = 17272714| journal = Science|bibcode=2007Sci...315..620J| citeseerx=10.1.1.1025.8289 | s2cid=25447870 }}</ref>

Like many [[oxide]]s, barium titanate is insoluble in water but attacked by [[sulfuric acid]]. It is also soluble in concentrated [[hydrochloric acid]], and [[hydrofluoric acid]].<ref>{{cite web |url=https://www.samaterials.com/content/barium-titanate-the-backbone-of-the-electronic-ceramic-industry.html |title=Barium Titanate - The Backbone of the Electronic Ceramic Industry |last=Trento |first=Chin |date=Dec 27, 2023 |website=Stanford Advanced Materials |access-date=Oct 15, 2024}}</ref> Its bulk room-temperature [[bandgap]] is 3.2 eV, but this increases to ~3.5 eV when the particle size is reduced from about 15 to 7&nbsp;nm.<ref name=bandgap/>

==Uses==
[[File:BaTiO3 ferro domains.jpg|thumb|[[Scanning transmission electron microscopy]] of the ferroelastic domains that form in BaTiO<sub>3</sub> on cooling through the [[Curie temperature]]. The vertex point, where domain bundles meet, moves from the center in isometric crystals (top) to off-center in oblongs (bottom).<ref>{{Cite journal | doi = 10.1088/1468-6996/16/3/036001| pmid = 27877812| title = Some current problems in perovskite nano-ferroelectrics and multiferroics: Kinetically-limited systems of finite lateral size| journal = Science and Technology of Advanced Materials| volume = 16| issue = 3| pages = 036001| year = 2015| last1 = Scott | first1 = J. F. | last2 = Schilling | first2 = A. | last3 = Rowley | first3 = S. E. | last4 = Gregg | first4 = J. M. |pmc=5099849| bibcode = 2015STAdM..16c6001S}}</ref>]]
Barium titanate is a [[dielectric]] ceramic used in [[capacitor]]s, with dielectric constant values as high as 7,000. Over a narrow temperature range, values as high as 15,000 are possible; most common ceramic and polymer materials are less than 10, while others, such as titanium dioxide (TiO<sub>2</sub>), have values between 20 and 70.<ref>{{Cite journal|title = Design solutions for DC bias in multilayer ceramic capacitors|last = Waugh|first = Mark D|date = 2010|journal = Electronic Engineering Times|url = http://www.compel.ru/wordpress/wp-content/uploads/2014/01/Mark-D.-Waugh.pdf|access-date = 2016-11-25|archive-date = 2020-11-02|archive-url = https://web.archive.org/web/20201102045630/http://www.compel.ru/wordpress/wp-content/uploads/2014/01/Mark-D.-Waugh.pdf|url-status = dead}}</ref>
High-purity barium titanate powder is reported to be a key component of new barium titanate capacitor energy storage systems for use in electric vehicles.<ref>{{cite web| url = http://gtresearchnews.gatech.edu/newsrelease/barium-titanate.htm| access-date=2009-06-06| title = Nanoparticle Compatibility: New Nanocomposite Processing Technique Creates More Powerful Capacitors|work=gatech.edu|date=April 26, 2007}}</ref>

It is a [[piezoelectric]] material used in [[microphone]]s and other [[transducer]]s, albeit largely replaced by [[lead zirconate titanate]]. 
The spontaneous polarization of barium titanate single crystals at room temperature range between 0.15{{nbsp}}C/m<sup>2</sup> in earlier studies,<ref>{{Cite journal| doi = 10.1103/RevModPhys.22.221| volume = 22| issue = 3| pages = 221–237| last = von Hippel| first = A.| title = Ferroelectricity, Domain Structure, and Phase Transitions of Barium Titanate| journal = Reviews of Modern Physics| date = 1950-07-01| bibcode=1950RvMP...22..221V}}</ref> and 0.26{{nbsp}}C/m<sup>2</sup> in more recent publications,<ref>{{Cite journal| doi = 10.1016/j.mseb.2008.11.046| issn = 0921-5107| volume = 161| issue = 1–3| pages = 50–54| last1 = Shieh| first1 = J.| last2 = Yeh| first2 = J. H.| last3 = Shu| first3 = Y. C.| last4 = Yen| first4 = J. H.| title = Hysteresis behaviors of barium titanate single crystals based on the operation of multiple 90° switching systems| journal = Materials Science and Engineering: B| series = Proceedings of the joint meeting of the 2nd International Conference on the Science and Technology for Advanced Ceramics (STAC-II) and the 1st International Conference on the Science and Technology of Solid Surfaces and Interfaces (STSI-I)| date = 2009-04-15}}</ref> and its [[Curie temperature]] is between 120 and 130&nbsp;°C. The differences are related to the growth technique, with earlier [[flux method|flux grown]] crystals being less pure than current crystals grown with the [[Czochralski process]],<ref>{{Cite journal| volume = base documentaire : TIB271DUO.| issue = ref. article : e1870| last = Godefroy| first = Geneviève| title = Ferroélectricité| journal = Techniques de l'Ingénieur Matériaux Pour l'Électronique et Dispositifs Associés| date = 1996| language = fr}}</ref> which therefore have a larger spontaneous polarization and a higher Curie temperature.

Barium titanate crystals find use in [[nonlinear optics]]. The material has high beam-coupling gain, and can be operated at visible and near-infrared wavelengths. It has the highest reflectivity of the materials used for self-pumped [[optical phase conjugation|phase conjugation]] (SPPC) applications. It can be used for continuous-wave [[four-wave mixing]] with milliwatt-range optical power. For photorefractive applications, barium titanate can be doped by various other elements, e.g. [[iron]].<ref>{{cite web| url = http://www.redoptronics.com/Fe-LiNbO3-crystal.html| title = Fe:LiNbO<sub>3</sub> Crystal|work=redoptronics.com}}</ref>
[[Thin film]]s of barium titanate display [[Electro-optic modulator|electrooptic modulation]] to frequencies over 40&nbsp;GHz.<ref>{{cite journal| doi = 10.1364/OPEX.12.005962| title = Electrooptic modulation up to 40 GHz in a barium titanate thin film waveguide modulator| year = 2004 |last1=Tang |first1=Pingsheng |journal=Optics Express |volume=12 |issue=24 |pages=5962–7 |pmid=19488237 |last2=Towner |first2=D. |last3=Hamano |first3=T. |last4=Meier|first4=A. |last5=Wessels |first5=B.|bibcode=2004OExpr..12.5962T |doi-access=free }}</ref>

The pyroelectric and ferroelectric properties of barium titanate are used in some types of uncooled sensors for [[thermal camera]]s.

Polycrystalline barium titanate has a positive [[temperature coefficient]] of resistance, making it a useful material for [[thermistor]]s and [[Positive temperature coefficient heating element|self-regulating electric heating systems]].  
For these applications, barium  titanate is manufactured with [[Doping (semiconductor)|dopants]] to give the material semiconductor properties. Specific applications include overcurrent protection for motors, ballasts for fluorescent lights, automobile cabin air heaters, and consumer space heaters.<ref>{{Cite book |url=https://www.tdk-electronics.tdk.com/download/539366/728d0d379187d1dfa0831555b8c93202/pdf-general-technical-information.pdf |title=PTC thermistors, general technical information |publisher=EPCOS AG |year=2016 |access-date=May 9, 2022}}</ref><ref>{{Cite web |title=Pelonis USA: Helpful Information |url=http://www.pelonis.com/hitech.htm |archive-url=https://web.archive.org/web/19981205114423/http://www.pelonis.com/hitech.htm |archive-date=December 5, 1998}}</ref>

Due to their elevated [[biocompatibility]], barium titanate [[nanoparticle]]s (BTNPs) have been recently employed as nanocarriers for [[drug delivery]].<ref>{{Cite journal| doi =10.1088/0957-4484/27/23/232001| pmid = 27145888  | issn = 0957-4484  | volume =27| issue = 23| pages =232001| last1 =Genchi | first1 = G.G.| last2 =Marino| first2 = A.| last3 =Rocca| first3 =A. | last4 =Mattoli | first4 = V. | last5= Ciofani| first5 = G.| title = Barium titanate nanoparticles: Promising multitasking vectors in nanomedicine | journal = Nanotechnology| date =5 May 2016| bibcode =2016Nanot..27w2001G| s2cid = 37287359 | hdl = 11586/470245| hdl-access = free}}</ref>

Magnetoelectric effect of giant strengths have been reported in thin films grown on barium titanate substrates.<ref>{{Cite journal|last1=Eerenstein|first1=W.|last2=Mathur|first2=N. D.|last3=Scott|first3=J. F.|date=August 2006|title=Multiferroic and magnetoelectric materials|journal=Nature|language=En|volume=442|issue=7104|pages=759–765|doi=10.1038/nature05023|pmid=16915279|issn=1476-4687|bibcode=2006Natur.442..759E|s2cid=4387694}}</ref><ref>{{Cite journal|last=Rafique|first=Mohsin|date=May 2017|title=Giant room temperature magnetoelectric response in strain controlled nanocomposites|journal=Applied Physics Letters|volume=110|issue=20|pages=202902|doi=10.1063/1.4983357|bibcode=2017ApPhL.110t2902R}}</ref>

==Natural occurrence==
Barioperovskite is a very rare natural analogue of BaTiO<sub>3</sub>, found as microinclusions in [[benitoite]].<ref>{{cite journal| year = 2008|last1=Ma |first1=Chi |last2=Rossman |first2=George R. |title=Barioperovskite, BaTiO<sub>3</sub>, a new mineral from the Benitoite Mine, California| volume = 93|issue=1 | pages = 154–157| journal = American Mineralogist| doi=10.2138/am.2008.2636|bibcode=2008AmMin..93..154M|s2cid=94469497 }}</ref>

==See also==
*[[Strontium titanate]]
*[[Lead zirconate titanate]]

==References==
{{reflist|30em}}

==External links==
{{Commons category|Barium titanate}}
*[http://gtresearchnews.gatech.edu/newsrelease/barium-titanate.htm Nanoparticle Compatibility: New Nanocomposite Processing Technique Creates More Powerful Capacitors]
*[http://blog.wired.com/gadgets/2007/09/instant-charge-.html EEStor's "instant-charge" capacitor batteries]

{{Barium compounds}}
{{Titanium compounds}}
{{Titanates}}

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{{DEFAULTSORT:Barium Titanate}}
[[Category:Titanates]]
[[Category:Barium compounds]]
[[Category:Ceramic materials]]
[[Category:Piezoelectric materials]]
[[Category:Ferroelectric materials]]
[[Category:Infrared sensor materials]]
[[Category:Nonlinear optical materials]]
[[Category:Perovskites]]