Lanthanum oxide
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| IUPAC name
Lanthanum(III) oxide
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| Other names
Lanthanum sesquioxide
Lanthana | |
| Identifiers | |
3D model (JSmol)
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| ChemSpider | |
| ECHA InfoCard | 100.013.819 |
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PubChem CID
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CompTox Dashboard (EPA)
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| Properties | |
| La2O3 | |
| Molar mass | 325.808 g·mol−1 |
| Appearance | White powder, hygroscopic |
| Density | 6.51 g/cm3, solid |
| Melting point | 2,315 °C (4,199 °F; 2,588 K) |
| Boiling point | 4,200 °C (7,590 °F; 4,470 K) |
| Insoluble | |
| Band gap | 4.3 eV |
| −78.0·10−6 cm3/mol | |
| Structure | |
| Hexagonal, hP5 | |
| P-3m1, No. 164 | |
| Hazards | |
| Occupational safety and health (OHS/OSH): | |
Main hazards
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Irritant |
| GHS labelling: | |
 [1]
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| Warning[1] | |
| H315, H319, H335[1] | |
| P261, P280, P301+P310, P304+P340, P305+P351+P338, P405, P501[1] | |
| NFPA 704 (fire diamond) | |
| Flash point | Non-flammable |
| Safety data sheet (SDS) | External SDS |
| Related compounds | |
Other anions
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Lanthanum(III) chloride |
Other cations
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Cerium(III) oxide Actinium(III) oxide |
Related compounds
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Lanthanum aluminium oxide, LaSrCoO4 |
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Lanthanum(III) oxide, also known as lanthana, chemical formula 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
[edit]
Lanthanum oxide is a white solid that is insoluble in water, but dissolves in acidic solutions. La2O3 absorbs moisture from air, converting to lanthanum hydroxide.[2] Lanthanum oxide has p-type semiconducting properties and a band gap of approximately 5.8 eV.[3] Its average room temperature resistivity is 10 kΩ·cm, which decreases with an increase in temperature. La2O3 has the lowest lattice energy of the rare earth oxides, with very high dielectric constant ε = 27.
Structure
[edit]At low temperatures, La2O3 has an A-M2O3 hexagonal crystal structure. The La3+ metal atoms are surrounded by a 7 coordinate group of O2− 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.[4] On the other hand, at high temperatures lanthanum oxide converts to a C-M2O3 cubic crystal structure. The La3+ ion is surrounded by six O2− ions in a hexagonal configuration.[5][6]
Synthesis
[edit]Lanthanum oxide can crystallize in at least three polymorphs.[2]
Hexagonal La2O3 has been produced by spray pyrolysis of lanthanum chloride.[7]
- 2 LaCl3 + 3 H2O → La(OH)3 + 3 HCl
- 2 La(OH)3 → La2O3 + 3 H2O
An alternative route to obtaining hexagonal La2O3 involves precipitation of nominal 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:
- 2 LaCl3 + 3 H2O + 3 NH3 → La(OH)3 + 3 [NH4]Cl
Other routes include:
- 2 La2S3 + 3 CO2 → 2 La2O3 + 3 CS2
Reactions
[edit]Lanthanum oxide is used as an additive to develop certain ferroelectric materials, such as La-doped bismuth titanate (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.[8]
- 3 B2O3 + La2O3 → 2 La(BO2)3[clarification needed]
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.
Potential applications
[edit]Lanthanum oxide is most useful as a precursor to other lanthanum compounds.[9] 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 La2O3, as described below.
La2O3 forms glasses of high 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 in some piezoelectric and thermoelectric materials.
La2O3 has been examined for the oxidative coupling of methane.[10]
References
[edit]- ^ a b c d "Lanthanum Oxide". American Elements. Retrieved October 26, 2018.
- ^ a b Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. ISBN 978-0-08-037941-8.
- ^ Shang, G.; Peacock, P. W.; Robertson, J. (2004). "Stability and band offsets of nitrogenated high-dielectric-constant gate oxides". Applied Physics Letters. 84 (1): 106–108. Bibcode:2004ApPhL..84..106S. doi:10.1063/1.1638896.
- ^ Wells, A.F. (1984). Structural Inorganic Chemistry. Oxford: Clarendon Press. p. 546.
- ^ Wyckoff, R. W.G. (1963). Crystal Structures: Inorganic Compounds RXn, RnMX2, RnMX3. New York: Interscience Publishers.
- ^ Adachi, Gin-ya; Imanaka, Nobuhito (1998). "The Binary Rare Earth Oxides". Chemical Reviews. 98 (4): 1479–1514. doi:10.1021/cr940055h. PMID 11848940.
- ^ Kale, S.S.; Jadhav, K.R.; Patil, P.S.; Gujar, T.P.; Lokhande, C.D. (2005). "Characterizations of spray-deposited lanthanum oxide (La2O3) thin films". Materials Letters. 59 (24–25): 3007–3009. doi:10.1016/j.matlet.2005.02.091.
- ^ Vinogradova, N. N.; Dmitruk, L. N.; Petrova, O. B. (2004). "Glass Transition and Crystallization of Glasses Based on Rare-Earth Borates". Glass Physics and Chemistry. 30: 1–5. doi:10.1023/B:GPAC.0000016391.83527.44. S2CID 94177915.
- ^ "Lanthanum has also found modest uses." Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. p. 946. ISBN 978-0-08-037941-8.
- ^ Manoilova, O.V.; et al. (2004). "Surface acidity and basicity of La2O3, LaOCl, and LaCl3 characterized by IR spectroscopy, TPD, and DFT calculations". J. Phys. Chem. B. 108 (40): 15770–15781. doi:10.1021/jp040311m.