Lanthanum(III) oxide
2700960
223491779
2008-07-04T08:40:03Z
193.204.249.181
/* Properties */
{{Chembox new
| Name = Lanthanum(III) oxide
| ImageFile = Lanthanum(III) oxide.jpg
<!-- | ImageSize = 200px -->
| ImageName = Lanthanum(III) oxide
| IUPACName = Lanthanum(III) oxide
| OtherNames = Lanthanum sesquioxide<br />Lanthana
| Section1 = {{Chembox Identifiers
| CASNo = 1312-81-8
| RTECS = OE5330000
}}
| Section2 = {{Chembox Properties
| Formula = La<sub>2</sub>O<sub>3</sub>
| MolarMass = 325.81 g/mol
| Appearance = White powder, [[hygroscopic]].
| Density = 6.51 g/cm<sup>3</sup>, 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=<s>W</s>
| FlashPt = Non-flammable
| RPhrases = {{R36/37}}
| SPhrases = {{S26}}, {{S22}}, {{S37/39}}
}}
| Section8 = {{Chembox Related
| OtherCpds = [[Scandium(III) oxide]],<br />[[Yttrium oxide]],<br />[[Lanthanum aluminium oxide]],<br />LaSrCoO<sub>4</sub>
}}
}}
'''Lanthanum(III) oxide''' is La<sub>2</sub>O<sub>3</sub>, 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==
La<sub>2</sub>O<sub>3</sub> 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. La<sub>2</sub>O<sub>3</sub> 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 10<sup>3</sup> Ω cm.
==Structure==
At low temperatures, La<sub>2</sub>O<sub>3</sub> has an A-M<sub>2</sub>O<sub>3</sub> hexagonal crystal structure. The La<sup>3+</sup> metal atoms are surrounded by a 7 coordinate group of O<sup>2<nowiki>−</nowiki></sup>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 (Wells 546). On the other hand, at high temperatures the Lanthanum oxide converts to a C-M<sub>2</sub>O<sub>3</sub> cubic crystal structure. The La<sup>3+</sup> ion is surrounded by a 6 coordinate group of O<sup>2<nowiki>−</nowiki></sup> ions.
==Synthesis==
Different crystalline forms of lanthanum oxide have been prepared.
To produce hexagonal La<sub>2</sub>O<sub>3</sub>, a 0.1 M solution of LaCl<sub>3</sub> 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 LaCl<sub>3</sub> + 3 H<sub>2</sub>O → La(OH)<sub>3</sub> + 3 HCl
::2 La(OH)<sub>3</sub> + heat → La<sub>2</sub>O<sub>3</sub> + 3 H<sub>2</sub>O
An alternative route to hexagonal La<sub>2</sub>O<sub>3</sub> involves precipitation of nominally La(OH)<sub>3</sub> from aqueous solution using a combination of 2.5% NH<sub>3</sub> and the surfactant sodium dodecyl sulfate followed by heating and stirring for 24 hours at 80 °C:
::2LaCl<sub>3</sub>+ 3 H<sub>2</sub>O + 3 NH<sub>3</sub> → La(OH)<sub>3</sub> + 3 NH<sub>4</sub>Cl
::LaCl<sub>3</sub>.3H<sub>2</sub>O → La<sub>2</sub>O<sub>3</sub>
Other routes include:
::2La<sub>2</sub>S<sub>3</sub> + 3CO<sub>2</sub> → 2La<sub>2</sub>O<sub>3</sub> + 3CS<sub>2</sub>
::2La<sub>2</sub>(SO<sub>4</sub>)<sub>3</sub> + read heat → 2La<sub>2</sub>O<sub>3</sub> + 6SO<sub>3</sub>
==Reactions==
Lanthanum oxide is used to develop ferroelectric materials, such as La-doped Bi<sub>4</sub>Ti<sub>3</sub>O<sub>12</sub> (BLT).
Lanthanum oxide is used in optical materials, often the optical glasses are doped with La<sub>2</sub>O<sub>3</sub> to improve the glass’ refractive index, chemical durability, and mechanical strength.
::3B<sub>2</sub>O<sub>3</sub> + La<sub>2</sub>O<sub>3</sub> → 3La<sub>2</sub>O<sub>3</sub>•B<sub>2</sub>O<sub>3</sub>
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 La<sub>2</sub>O<sub>3</sub> 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==
La<sub>2</sub>O<sub>3</sub> 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]], La<sub>2</sub>O<sub>3</sub> improves the resistance of the glass to attack by alkali. La<sub>2</sub>O<sub>3</sub> is an ingredient for the manufacture of devices for [[piezoelectricity]], galvanothermy, and thermoelectricity material. Automobile exhaust-gas converters contain La<sub>2</sub>O<sub>3</sub> (Cao 408). La<sub>2</sub>O<sub>3</sub> is also used in X-Ray imaging intensifying screens, phophors as well as dielectric and conductive ceramics.
La<sub>2</sub>O<sub>3</sub> has been examined for the oxidative coupling of [[methane]] (Maoilova 15770).
La<sub>2</sub>O<sub>3</sub> 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).
==Sources==
* 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==
{{Unreferenced|date =September 2007}}
{{reflist}}
==External links==
* http://www.reade.com/Products/Oxides/lanthanum_oxide.html
* http://www.chemsoc.org/viselements/pages/data/lanthanum_data.html
[[Category:Lanthanum compounds]]
[[Category:Inorganic compounds]]
[[Category:Oxides]]
[[zh:氧化镧]]