Lanthanum(III) oxide
Encyclopedia
Lanthanum oxide is La2O3, an inorganic compound
containing the rare earth element
lanthanum
and oxygen
. It is used to develop ferroelectric materials, and in optical materials.
of the rare earth oxides at 4.3 eV, while also having the lowest lattice energy, with very high dielectric constant
, ε = 27. 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. La2O3 is hygroscopic; Under atmosphere, lanthanum oxide absorbs moisture over time and converts to lanthanum hydroxide. Lanthanum oxide has p-type semi-conducting properties because its resistivity decreases with an increase in temperature, average room temperature resistivity is 10 kΩ·cm.
s.
To produce hexagonal La2O3, a 0.1 M solution of LaCl3 is sprayed onto a preheated substrate, usually made of metal chalcogenides. The process can be viewed as occurring in two steps – hydrolysis followed by dehydration:
An alternative route to 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:
Other routes include:
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.
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. 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.
, tantalum
, and thorium
, La2O3 improves the resistance of the glass to attack by alkali. La2O3 is an ingredient for the manufacture of piezoelectric and thermoelectric materials. Automobile exhaust-gas converters contain La2O3. 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
.
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 250–450 °C. Polycrystalline
films are formed at 350 °C.
Inorganic compound
Inorganic compounds have traditionally been considered to be of inanimate, non-biological origin. In contrast, organic compounds have an explicit biological origin. However, over the past century, the classification of inorganic vs organic compounds has become less important to scientists,...
containing the rare earth element
Rare earth element
As defined by IUPAC, rare earth elements or rare earth metals are a set of seventeen chemical elements in the periodic table, specifically the fifteen lanthanides plus scandium and yttrium...
lanthanum
Lanthanum
Lanthanum is a chemical element with the symbol La and atomic number 57.Lanthanum is a silvery white metallic element that belongs to group 3 of the periodic table and is the first element of the lanthanide series. It is found in some rare-earth minerals, usually in combination with cerium and...
and oxygen
Oxygen
Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...
. It is used to develop ferroelectric materials, and in optical materials.
Properties
La2O3 has largest band gapBand gap
In solid state physics, a band gap, also called an energy gap or bandgap, is an energy range in a solid where no electron states can exist. In graphs of the electronic band structure of solids, the band gap generally refers to the energy difference between the top of the valence band and the...
of the rare earth oxides at 4.3 eV, while also having the lowest lattice energy, with very high dielectric constant
Dielectric constant
The relative permittivity of a material under given conditions reflects the extent to which it concentrates electrostatic lines of flux. In technical terms, it is the ratio of the amount of electrical energy stored in a material by an applied voltage, relative to that stored in a vacuum...
, ε = 27. 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. La2O3 is hygroscopic; Under atmosphere, lanthanum oxide absorbs moisture over time and converts to lanthanum hydroxide. Lanthanum oxide has p-type semi-conducting properties because its resistivity decreases with an increase in temperature, average room temperature resistivity is 10 kΩ·cm.
Structure
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. 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.Synthesis
lanthanum oxide crystallizes as several polymorphPolymorphism (materials science)
Polymorphism in materials science is the ability of a solid material to exist in more than one form or crystal structure. Polymorphism can potentially be found in any crystalline material including polymers, minerals, and metals, and is related to allotropy, which refers to chemical elements...
s.
To produce hexagonal La2O3, a 0.1 M solution of LaCl3 is sprayed onto a preheated substrate, usually made of metal chalcogenides. 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 → La2O3 + 3 H2O
An alternative route to 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
Sodium dodecyl sulfate
Sodium dodecyl sulfate , sodium laurilsulfate or sodium lauryl sulfate is an organic compound with the formula CH311OSO3Na). It is an anionic surfactant used in many cleaning and hygiene products...
followed by heating and stirring for 24 hours at 80°C:
- 2 LaCl3+ 3 H2O + 3 NH3 → La(OH)3 + 3 NH4Cl
- LaCl3·3H2O → La2O3
Other routes include:
- 2 La2S3 + 3 CO2 → 2 La2O3 + 3 CS2
- 2 La2(SO4)3 + heat → 2 La2O3 + 6 SO3
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.
- 3 B2O3 + La2O3 → 2 La(BO2)3
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. 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 and applications
La2O3 is used to make optical glasses, to which this oxide confers increased density, refractive index, and hardness. Together with oxides of tungstenTungsten
Tungsten , also known as wolfram , is a chemical element with the chemical symbol W and atomic number 74.A hard, rare metal under standard conditions when uncombined, tungsten is found naturally on Earth only in chemical compounds. It was identified as a new element in 1781, and first isolated as...
, tantalum
Tantalum
Tantalum is a chemical element with the symbol Ta and atomic number 73. Previously known as tantalium, the name comes from Tantalus, a character in Greek mythology. Tantalum is a rare, hard, blue-gray, lustrous transition metal that is highly corrosion resistant. It is part of the refractory...
, and thorium
Thorium
Thorium is a natural radioactive chemical element with the symbol Th and atomic number 90. It was discovered in 1828 and named after Thor, the Norse god of thunder....
, La2O3 improves the resistance of the glass to attack by alkali. La2O3 is an ingredient for the manufacture of piezoelectric and thermoelectric materials. Automobile exhaust-gas converters contain La2O3. 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
Oxidative coupling of methane
The oxidative coupling of methane is a type of chemical reaction discovered in the 1980s for the direct conversion of natural gas, primarily consisting of methane, into value-added chemicals. Direct conversion of methane into other useful products is one of the most challenging subjects to be...
.
La2O3 films can be deposited
Deposition (chemistry)
In chemistry, deposition is the settling of particles or sediment from a solution, suspension and mixture or vapor onto a pre-existing surface...
by many different methods, including: chemical vapor disposition, thermal oxidation
Thermal oxidation
In microfabrication, thermal oxidation is a way to produce a thin layer of oxide on the surface of a wafer. The technique forces an oxidizing agent to diffuse into the wafer at high temperature and react with it. The rate of oxide growth is often predicted by the Deal-Grove model...
, sputtering
Sputtering
Sputtering is a process whereby atoms are ejected from a solid target material due to bombardment of the target by energetic particles. It is commonly used for thin-film deposition, etching and analytical techniques .-Physics of sputtering:...
, and spray pyrolysis. Depositions of these films occur in a temperature range of 250–450 °C. Polycrystalline
Polycrystalline
Polycrystalline materials are solids that are composed of many crystallites of varying size and orientation. The variation in direction can be random or directed, possibly due to growth and processing conditions. Fiber texture is an example of the latter.Almost all common metals, and many ceramics...
films are formed at 350 °C.
External links
- http://www.chemsoc.org/viselements/pages/data/lanthanum_data.html
- External MSDS 1
- External MSDS 2