Lanthanum(III) oxide


Lanthanum(III) oxide

Chembox new
Name = Lanthanum(III) oxide
ImageFile = Lanthanum(III) oxide.jpg
ImageName = Lanthanum(III) oxide
IUPACName = Lanthanum(III) oxide
OtherNames = Lanthanum sesquioxide
Lanthana
Section1 = Chembox Identifiers
CASNo = 1312-81-8
RTECS = OE5330000

Section2 = Chembox Properties
Formula = La2O3
MolarMass = 325.81 g/mol
Appearance = White powder, hygroscopic.
Density = 6.51 g/cm3, solid.
Solubility = Insoluble
MeltingPt = 2315°C (2590 K)
BoilingPt = 4200°C (4500 K)

Section3 = Chembox Structure
Coordination = Monocapped octahedral
CrystalStruct = Hexagonal and cubic

Section7 = Chembox Hazards
ExternalMSDS = [http://physchem.ox.ac.uk/MSDS/LA/lanthanum_oxide.html External MSDS]
MainHazards = Irritant
NFPA-H = 1
NFPA-F =
NFPA-R = 1 | NFPA-O=W
FlashPt = Non-flammable
RPhrases = R36/37
SPhrases = S26, S22, S37/39

Section8 = Chembox Related
OtherCpds = Scandium(III) oxide,
Yttrium oxide,
Lanthanum aluminium oxide,
LaSrCoO4

Lanthanum(III) oxide is La2O3, a chemical compound containing the rare earth element lanthanum and oxygen. It is used to develop ferroelelectric material, and in optical materials. Production is on laboratory scale, mostly.

Properties

La2O3 has largest band gap of the rare earth oxides at 4.3 eV, while also having the lowest lattice energy, with very high dielectric constant, ε = 27 pF/m. La2O3 is widely used in industry as well as in the research laboratory. Lanthanum oxide is an odorless, white solid that is insoluble in water, but soluble in dilute acid. Depending on the pH of the compound, different crystal structures can be obtained. Lanthanum oxide has p-type semi-conducting properties because its resistivity decreases with an increase in temperature, average room temperature resistivity is 103 Ω cm.

tructure

At low temperatures, La2O3 has an A-M2O3 hexagonal crystal structure. The La3+ metal atoms are surrounded by a 7 coordinate group of O2atoms, the oxygen ions are in an octahedral shape around the metal atom and there is one oxygen ion above one of the octahedral faces (Wells 546). On the other hand, at high temperatures the Lanthanum oxide converts to a C-M2O3 cubic crystal structure. The La3+ ion is surrounded by a 6 coordinate group of O2 ions.

ynthesis

Different crystalline forms of lanthanum oxide have been prepared.

To produce hexagonal La2O3, a 0.1 M solution of LaCl3 is sprayed onto a preheated substrate, usually made of metal chalcogenides (Kale 3007). The process can be viewed as occurring in two steps - hydrolysis followed by dehydration:

::2 LaCl3 + 3 H2O → La(OH)3 + 3 HCl::2 La(OH)3 + heat → La2O3 + 3 H2OAn alternative route to hexagonal La2O3 involves precipitation of nominally La(OH)3 from aqueous solution using a combination of 2.5% NH3 and the surfactant sodium dodecyl sulfate followed by heating and stirring for 24 hours at 80 °C:::2LaCl3+ 3 H2O + 3 NH3 → La(OH)3 + 3 NH4Cl::LaCl3.3H2O → La2O3

Other routes include: ::2La2S3 + 3CO2 → 2La2O3 + 3CS2::2La2(SO4)3 + read heat → 2La2O3 + 6SO3

Reactions

Lanthanum oxide is used to develop ferroelectric materials, such as La-doped Bi4Ti3O12 (BLT).Lanthanum oxide is used in optical materials, often the optical glasses are doped with La2O3 to improve the glass’ refractive index, chemical durability, and mechanical strength.

::3B2O3 + La2O3 → 3La2O3•B2O3

When this 1:3 reaction is mixed into a glass composite, the high molecular weight of the lanthanum causes an increase of the homogeneous mixture of the melt which leads to a lower melting point (Vinogradova 1). The addition of the 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.

Uses & Applications

La2O3 is used to make optical glasses, to which this oxide confers increased density, refractive index, and hardness. Together with oxides of tungsten, tantalum, and thorium, La2O3 improves the resistance of the glass to attack by alkali. La2O3 is an ingredient for the manufacture of devices for piezoelectricity, galvanothermy, and thermoelectricity material. Automobile exhaust-gas converters contain La2O3 (Cao 408). La2O3 is also used in X-Ray imaging intensifying screens, phophors as well as dielectric and conductive ceramics.

La2O3 has been examined for the oxidative coupling of methane (Maoilova 15770).

La2O3 films can be deposited by many different methods, including: chemical vapor disposition, thermal oxidation, sputtering, and spray pyrolysis. Depositions of these films occur in a temperature range of 523–723 K (Kale 3007). Polycrystalline films are formed at 623 K (Kale 3008).

ources

* Maoilova, O. V. “Surface Acidity and Basicity of La2O3, LaOCl, and LaCl3 Characterized by IR Spectroscopy, TPD, and DFT Calculations.” Journal of Physical Chemistry. 180 (1980):15770-16781.
* Bedoya, C. “MOCVD of Lanthanum Oxides from La(tmhd)3 and La(tmod)3 Precursors: A Thermal and Kinetic Investigation.” Chemical Vapor Deposition. 12 (2006): 46-53.
* Vinogradova, L. N. “Glass Transition and Crystallization of Glasses Based on Rare-Earth Borates.” Glass Physics and Chemistry. 30 (2004): 1-5.
* Kale, S.S. “Characterizations of spray-deposited lanthanum oxide (La2O3) thin films.” Materials Letters. 59 (2005): 3007-3009.
* Imanaka, Nobuhito. “Preparation of the cubic-type La2O3 phase by thermal decomposition of LaI3.” Journal of Solid State Chemistry. 178 (2005): 395-398.
* Cao, Jieming. “Controllable syntheses of hexagonal and lamellar mesostructured lanthanum oxide.” Materials Letters. 59 (2005): 408-411.
* Wyckoff, R. W.G. Crystal Structures: Inorganic Compounds RXn, RnMX2, RnMX3. New York: Interscience Publishers (1963).
* “Lanthanum oxide.” The Merck Index: An Encyclopedia of Chemicals, Drugs, and Biological. 11th ed. 1989.
* Veldurthy, B. “Magnesium-Lanthanum Mixed Metal Oxide: A Strong Solid Base for the Michael Addition Reaction.” Adv. Synth. Catal. 347 (2005): 767-771.
* Wells, A.F. Structural Inorganic Chemistry. Oxford: Clarendon Press, 1984.
*"Lanthanum oxide." Encyclopedia of Chemical Reactions. 1951.
* [http://camel.conncoll.edu/offices/envhealth/MSDS/botany/L/Lanthanum-oxide.html| R and S data source] .

References

External links

* http://www.reade.com/Products/Oxides/lanthanum_oxide.html
* http://www.chemsoc.org/viselements/pages/data/lanthanum_data.html


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