Lanthanum(III) oxide, also known as lanthana, chemical formula , is an

inorganic compound In chemistry, an inorganic compound is typically a chemical compound that lacks carbon–hydrogen bonds, that is, a compound that is not an organic compound. The study of inorganic compounds is a subfield of chemistry known as '' inorganic che ...

containing the

rare earth element The rare-earth elements (REE), also called the rare-earth metals or (in context) rare-earth oxides or sometimes the lanthanides (yttrium and scandium are usually included as rare earths), are a set of 17 nearly-indistinguishable lustrous silv ...

lanthanum Lanthanum is a chemical element with the symbol La and atomic number 57. It is a soft, ductile, silvery-white metal that tarnishes slowly when exposed to air. It is the eponym of the lanthanide series, a group of 15 similar elements between lantha ...

and

oxygen Oxygen is the chemical element with the symbol O and atomic number 8. It is a member of the chalcogen group in the periodic table, a highly reactive nonmetal, and an oxidizing agent that readily forms oxides with most elements as ...

. It is used in some ferroelectric materials, as a component of optical materials, and is a feedstock for certain catalysts, among other uses.

Properties

Lanthanum oxide is a white solid that is insoluble in water, but dissolves in acidic solutions. absorbs moisture from air, converts to lanthanum hydroxide. Lanthanum oxide has p-type semiconducting properties and a band gap of approximately 5.8 eV. Its average room temperature resistivity is 10 kΩ·cm, which decreases with an increase in temperature. has the lowest lattice energy of the rare earth oxides, with very high

dielectric constant The relative permittivity (in older texts, dielectric constant) is the permittivity of a material expressed as a ratio with the electric permittivity of a vacuum. A dielectric is an insulating material, and the dielectric constant of an insulat ...

, ε = 27.

Structure

At low temperatures, has an A- hexagonal crystal structure. The metal atoms are surrounded by a 7 coordinate group of 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 lanthanum oxide converts to a C- cubic crystal structure. The ion is surrounded by six ions in a hexagonal configuration.

Synthesis

Lanthanum oxide can crystallize in at least three polymorphs. Hexagonal has been produced by spray pyrolysis of lanthanum chloride. : : An alternative route to obtaining hexagonal involves precipitation of nominal from aqueous solution using a combination of 2.5% and the surfactant

sodium dodecyl sulfate Sodium dodecyl sulfate (SDS) or sodium lauryl sulfate (SLS), sometimes written sodium laurilsulfate, is an organic compound with the formula . It is an anionic surfactant used in many cleaning and hygiene products. This compound is the sodium sa ...

followed by heating and stirring for 24 hours at 80 °C: : Other routes include: :

Reactions

Lanthanum oxide is used as an additive to develop certain ferroelectric materials, such as La-doped

bismuth titanate Bismuth titanate or bismuth titanium oxide is a solid inorganic compound of bismuth, titanium and oxygen with the chemical formula of Bi12TiO20, Bi 4Ti3O12 or Bi2Ti2O7. Synthesis Bismuth titanate ceramics can be produced by heating a mixture of ...

( - BLT). Lanthanum oxide is used in optical materials; often the optical glasses are doped with to improve the glass' refractive index, chemical durability, and mechanical strength. : The addition of the 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

Lanthanum oxide is most useful as a precursor to other lanthanum compounds. 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 , as described below. forms glasses of high density, refractive index, and hardness. Together with oxides of

tungsten Tungsten, or wolfram, is a chemical element with the symbol W and atomic number 74. Tungsten is a rare metal found naturally on Earth almost exclusively as compounds with other elements. It was identified as a new element in 1781 and first isola ...

tantalum Tantalum is a chemical element with the symbol Ta and atomic number 73. Previously known as ''tantalium'', it is named after Tantalus, a villain in Greek mythology. Tantalum is a very hard, ductile, lustrous, blue-gray transition metal that is ...

, and

thorium Thorium is a weakly radioactive metallic chemical element with the symbol Th and atomic number 90. Thorium is silvery and tarnishes black when it is exposed to air, forming thorium dioxide; it is moderately soft and malleable and has a high ...

, improves the resistance of the glass to attack by alkali. is an ingredient in some

piezoelectric Piezoelectricity (, ) is the electric charge that accumulates in certain solid materials—such as crystals, certain ceramics, and biological matter such as bone, DNA, and various proteins—in response to applied mechanical stress. The word ''p ...

and thermoelectric materials. has been examined for the oxidative coupling of methane.

References

{{DEFAULTSORT:Lanthanum(Iii) Oxide Lanthanum compounds Inorganic compounds Sesquioxides