lanthanum oxide

File:La2O3powder.jpg

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.{{Greenwood&Earnshaw2nd}}

Lanthanum oxide has p-type semiconducting properties and a band gap of approximately 5.8 eV.{{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 }} Its average room temperature resistivity is 10 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 = 27.

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.{{cite book| author = Wells, A.F. | title = Structural Inorganic Chemistry|location = Oxford| publisher = Clarendon Press| year = 1984| page = 546}} 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.{{cite book| author = Wyckoff, R. W.G. | title = Crystal Structures: Inorganic Compounds RXn, RnMX2, RnMX3| location = New York| publisher = Interscience Publishers | year =1963}}{{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 }}

Lanthanum oxide can crystallize in at least three polymorphs.

Hexagonal {{chem2|La2O3}} has been produced by spray pyrolysis of lanthanum chloride.{{cite journal|doi=10.1016/j.matlet.2005.02.091|title=Characterizations of spray-deposited lanthanum oxide (La2O3) 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}}

:{{chem2|2 LaCl3 + 3 H2O → La(OH)3 + 3 HCl}}

:{{chem2|2 La(OH)3 → La2O3 + 3 H2O}}

An alternative route 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 °C:

:{{chem2|2 LaCl3 + 3 H2O + 3 NH3 → La(OH)3 + 3 [NH4]Cl}}

Other routes include:

:{{chem2|2 La2S3 + 3 CO2 → 2 La2O3 + 3 CS2}}

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.{{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 }}

:{{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 °C to 679 °C. The addition also leads to a higher density, microhardness, and refractive index of the glass.

Lanthanum oxide is most useful as a precursor to other lanthanum compounds."Lanthanum has also found modest uses." {{Greenwood&Earnshaw2nd|page=946}} 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.

{{chem2|La2O3}} has been examined for the oxidative coupling of methane.{{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}}

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{{Lanthanum compounds}}

{{Oxides}}

{{DEFAULTSORT:Lanthanum(Iii) Oxide}}

Category:Lanthanum compounds

Category:Inorganic compounds

Category:Sesquioxides