{{short description|Chemical compound}} {{chembox | Verifiedfields = changed | Watchedfields = changed | verifiedrevid = 459011566 | Name = Lanthanum(III) oxide | ImageFile = Oxyde de lanthane en poudre.jpg | ImageFile2 = La2O3structure.svg | ImageName = Lanthanum(III) oxide | IUPACName = Lanthanum(III) oxide | OtherNames = Lanthanum sesquioxide<br />Lanthana | data page pagename = <!--none--> |Section1={{Chembox Identifiers | CASNo_Ref = {{cascite|correct|CAS}} | CASNo = 1312-81-8 | RTECS = OE5330000 | PubChem = 150906 | ChemSpiderID_Ref = {{chemspidercite|correct|chemspider}} | StdInChI_Ref = {{stdinchicite|correct|chemspider}} | StdInChIKey_Ref = {{stdinchicite|correct|chemspider}} | ChemSpiderID = 2529886 | ChemSpiderID1 = 133008 | ChemSpiderID1_Ref = {{chemspidercite|correct|chemspider}} | UNII = 4QI5EL790W | EINECS = 215-200-5 | StdInChI=1S/2La.3O/q2*+3;3*-2 | StdInChIKey = MRELNEQAGSRDBK-UHFFFAOYSA-N | SMILES = [O-2].[O-2].[O-2].[La+3].[La+3] }} |Section2={{Chembox Properties | La=2|O=3 | Appearance = White powder, hygroscopic | Density = 6.51 g/cm<sup>3</sup>, solid | Solubility = Insoluble | MeltingPtC = 2315 | MeltingPt_notes = | BoilingPtC = 4200 | BoilingPt_notes = | BandGap = 4.3 eV | MagSus = −78.0·10<sup>−6</sup> cm<sup>3</sup>/mol }} |Section3={{Chembox Structure | CrystalStruct = Hexagonal, hP5 | SpaceGroup = P-3m1, No. 164 }} |Section7={{Chembox Hazards | GHSPictograms = {{GHS07}}<ref name=sds>{{cite web |title = Lanthanum Oxide |url = https://www.americanelements.com/lanthanum-oxide-1312-81-8 |publisher = American Elements |access-date = October 26, 2018}}</ref> | GHSSignalWord = Warning<ref name=sds /> | HPhrases = {{H-phrases|315|319|335}}<ref name=sds /> | PPhrases = {{P-phrases|261|280|301+310|304+340|305+351+338|405|501}}<ref name=sds /> | MainHazards = Irritant | NFPA-H = 1 | NFPA-F = | NFPA-R = | NFPA-S =W | FlashPt = Non-flammable }} |Section8={{Chembox Related | OtherAnions = Lanthanum(III) chloride | OtherCations = {{unbulleted list| * Cerium(III) oxide * Actinium(III) oxide }} | OtherCompounds = {{unbulleted list| * Lanthanum aluminium oxide * LaSrCoO<sub>4</sub> }} }} }}

'''Lanthanum(III) oxide''', also known as '''lanthana''', chemical formula {{chem2|La2O3}}, is an inorganic compound containing the rare-earth element lanthanum and oxygen. It is used in some ferroelectric materials, as a component of optical materials, and is a feedstock for certain catalysts, among other uses.

==Properties== thumb|left|upright=0.6|{{chem2|La2O3}} powder Lanthanum oxide is a white solid that is insoluble in water, but dissolves in acidic solutions. {{chem2|La2O3}} absorbs moisture from air, converting to lanthanum hydroxide.<ref name=G&E>{{Greenwood&Earnshaw2nd}}</ref> Lanthanum oxide has p-type semiconducting properties and a band gap of approximately 5.8&nbsp;eV.<ref>{{cite journal | last1 = Shang | first1 = G. | last2 = Peacock | first2 = P. W. | last3 = Robertson | first3 = J. | year = 2004| title = Stability and band offsets of nitrogenated high-dielectric-constant gate oxides | journal = Applied Physics Letters | volume = 84 | issue = 1 | pages = 106–108 | doi = 10.1063/1.1638896 | bibcode = 2004ApPhL..84..106S }}</ref> Its average room-temperature resistivity is 10&nbsp;kΩ·cm, which decreases with an increase in temperature. {{chem2|La2O3}} has the lowest lattice energy of the rare-earth oxides, with very high dielectric constant ε&nbsp;=&nbsp;27.

==Structure== At low temperatures, {{chem2|La2O3}} has an A-{{chem2|M2O3}} hexagonal crystal structure. The {{chem2|La(3+)}} metal atoms are surrounded by a 7-coordinate group of {{chem2|O(2−)}} atoms, the oxygen ions are in an octahedral shape around the metal atom, and there is one oxygen ion above one of the octahedral faces.<ref>{{cite book | author = Wells, A. F. | title = Structural Inorganic Chemistry |location = Oxford | publisher = Clarendon Press | year = 1984 | page = 546}}</ref> On the other hand, at high temperatures lanthanum oxide converts to a C-{{chem2|M2O3}} cubic crystal structure. The {{chem2|La(3+)}} ion is surrounded by six {{chem2|O(2−)}} ions in a hexagonal configuration.<ref>{{cite book | author = Wyckoff, R. W. G. | title = Crystal Structures: Inorganic Compounds RX''<sub>n</sub>'', R''<sub>n</sub>''MX<sub>2</sub>, R''<sub>n</sub>''MX<sub>3</sub> | location = New York | publisher = Interscience Publishers | year =1963}}</ref><ref>{{cite journal |doi=10.1021/cr940055h |title=The Binary Rare Earth Oxides |year=1998 |last1=Adachi |first1=Gin-ya |last2=Imanaka |first2=Nobuhito |journal=Chemical Reviews |volume=98 |issue=4 |pages=1479–1514 |pmid=11848940 }}</ref>

==Synthesis== Lanthanum oxide can crystallize in at least three polymorphs.<ref name=G&E/>

Hexagonal {{chem2|La2O3}} has been produced by spray pyrolysis of lanthanum chloride:<ref name=kale>{{cite journal |doi=10.1016/j.matlet.2005.02.091 |title=Characterizations of spray-deposited lanthanum oxide ({{chem|La|2|O|3}}) thin films |year=2005 |author1=Kale, S. S. |author2=Jadhav, K. R. |author3=Patil, P. S. |author4=Gujar, T. P. |author5=Lokhande, C. D. |journal=Materials Letters |volume=59 |issue=24–25 |pages=3007–3009}}</ref> : {{chem2|2 LaCl3 + 3 H2O → La(OH)3 + 3 HCl}} : {{chem2|2 La(OH)3 → La2O3 + 3 H2O}}

An alternative route{{cn|date=January 2026}} to obtaining hexagonal {{chem2|La2O3}} involves precipitation of nominal {{chem2|La(OH)3}} from aqueous solution using a combination of 2.5% {{chem2|NH3}} and the surfactant sodium dodecyl sulfate followed by heating and stirring for 24 hours at 80&nbsp;°C: : {{chem2|2 LaCl3 + 3 H2O + 3 NH3 → La(OH)3 + 3 [NH4]Cl}}

Other routes{{cn|date=January 2026}} include : {{chem2|2 La2S3 + 3 CO2 → 2 La2O3 + 3 CS2}}

==Reactions== Lanthanum oxide is used as an additive to develop certain ferroelectric materials, such as La-doped bismuth titanate ({{chem2|Bi4Ti3O12}}, "BLT"). Lanthanum oxide is used in optical materials; often the optical glasses are doped with {{chem2|La2O3}} to improve the glass' refractive index, chemical durability, and mechanical strength.<ref>{{cite journal |doi=10.1023/B:GPAC.0000016391.83527.44 |title=Glass Transition and Crystallization of Glasses Based on Rare-Earth Borates |year=2004 |author1=Vinogradova, N. N. |author2=Dmitruk, L. N. |author3=Petrova, O. B. |journal=Glass Physics and Chemistry |volume=30 |pages=1–5 |s2cid=94177915 }}</ref>

: {{chem2|3 B2O3 + La2O3 → 2 La(BO2)3}}{{Clarification needed|What this reaction stands for?|date=July 2022}}

The addition of the {{chem2|La2O3}} to the glass melt leads to a higher glass-transition temperature from 658&nbsp;°C to 679&nbsp;°C. The addition also leads to a higher density, microhardness, and refractive index of the glass.

==Potential applications== Lanthanum oxide is most useful as a precursor to other lanthanum compounds.<ref>"Lanthanum has also found modest uses." {{Greenwood&Earnshaw2nd|page=946}}</ref> Neither the oxide nor any of the derived materials enjoys substantial commercial value, unlike some of the other lanthanides. Many reports describe efforts toward practical applications of {{chem2|La2O3}}, as described below.

{{chem2|La2O3}}{{anchor|lanthanum_glass_anchor}} forms glasses of high density, refractive index, and hardness. Together with oxides of tungsten, tantalum, and thorium, {{chem2|La2O3}} improves the resistance of the glass to attack by alkali. {{chem2|La2O3}} is an ingredient in some piezoelectric and thermoelectric materials.<!-- untrue, that is cerium: Automobile exhaust-gas converters contain {{chem2|La2O3}}.<ref>{{cite journal |author1=Cao, J. |author2=Ji, H. |author3=Liu, J. |author4=Zheng, M. |author5=Chang, X. |author6=Ma, X. |author7=Zhang, A. |author8=Xu, Q. |year=2005 |title=Controllable syntheses of hexagonal and lamellar mesostructured lanthanum oxide |journal=Materials Letters |volume=59 |issue=4 |pages=408–411 |doi=10.1016/j.matlet.2004.09.034}}</ref> {{chem2|La2O3}} is also used in X-ray imaging intensifying screens, phosphors as well as dielectric and conductive ceramics. Gives off bright glow. {{chem2|La2O3}} films can be deposited by many different methods, including chemical vapor disposition, atomic layer deposition, thermal oxidation, sputtering, and spray pyrolysis. Depositions of these films occur in a temperature range of 250–450&nbsp;°C. Polycrystalline films are formed at 350&nbsp;°C.<ref name=kale/>

{{chem2|La2O3}} tungsten electrodes are replacing thoriated tungsten electrodes in gas tungsten arc welding (TIG) due to safety concerns with thorium's radioactivity. -->

{{chem2|La2O3}} has been examined for the oxidative coupling of methane.<ref>{{cite journal |author1=Manoilova, O.V. |display-authors=etal |year=2004 |title=Surface acidity and basicity of La2O3, LaOCl, and LaCl3 characterized by IR spectroscopy, TPD, and DFT calculations |journal=J. Phys. Chem. B |volume=108 |issue=40 |pages=15770–15781 |doi=10.1021/jp040311m}}</ref>

==References== {{reflist}}

{{Lanthanum compounds}} {{Oxides}}

{{DEFAULTSORT:Lanthanum(Iii) Oxide}} Category:Lanthanum compounds Category:Inorganic compounds Category:Sesquioxides