What Is Lanthanum Oxide?
Lanthanum oxide is a white to almost white powder, an inorganic compound with the chemical formula La2O3, molecular weight 325.81, and CAS registration number 1312-81-8.
The main physical and chemical property of lanthanum oxide is a melting/freezing point of 4199 °F (2315 °C) and a boiling or first distillation point of 7592 °F (4200 °C). It is soluble in hydrochloric acid and nitric acid and is virtually insoluble in water.
Lanthanum oxide is also hygroscopic and easily absorbs carbon dioxide gas from the air. Lanthanum oxide is not subject to any major national laws and regulations.
Uses of Lanthanum Oxide
Lanthanum oxide is used in the optical field as a raw material for optical lenses. It is also known as a raw material for PLZT (lead lanthanum zirconate titanate), which is gaining attention for its use in PLCs (planar lightwave circuits). In the field of electronic components, it can be used as a raw material for ceramic capacitors and battery materials.
Lanthanum oxide is also used as a material for supporting zirconium (Zr) oxide, which is known as a support for automobile exhaust gas catalysts.
Properties of Lanthanum Oxide
Lanthanum oxide is an odorless white solid. Depending on the pH of the compound, different crystal structures can be obtained.
Lanthanum oxide is hygroscopic, meaning that it absorbs moisture over time in the air, transforming into lanthanum hydroxide. Lanthanum oxide has p-type semiconductor properties, with a band gap of approximately 5.8 eV.
The average room temperature resistivity is 10 kΩ-cm and decreases with increasing temperature. Lanthanum oxide has a very high dielectric constant of ε = 27 and the lowest lattice energy of the rare earth oxides.
Structure of Lanthanum Oxide
La2O3 at low temperatures has an A-M2O3 hexagonal structure of La3+ metal atoms surrounded by seven O2- atom coordination groups, with the oxygen ions around the metal atoms in an octahedral form. On one face of the octahedron, there is one oxygen ion.
In contrast, at high temperatures, La2O3 will change to a cubic structure of C-M2O3; the La3+ ions are surrounded by six O2- ions, in a hexagonal shape.
Other Information on Lanthanum Oxide
1. Synthesis of Lanthanum Oxide
Lanthanum oxide can be crystallized into polymorphs. To produce hexagonal La2O3, a preheated substrate, usually made of metal chalcogenides, is sprayed with 0.1M LaCl3 solution. In this process, two steps occur: hydrolysis and dehydration.
The surfactant sodium lauryl sulfate and 2.5% NH3 can also be combined to obtain hexagonal La2O3. A small amount of La(OH)3 is precipitated from this aqueous solution, which is then heated and stirred at 176 °F (80 °C) for 24 hours to produce La2O3.
2. Reaction of Lanthanum Oxide
Lanthanum oxide is used as an additive to develop certain ferroelectric materials, such as La-doped Bi4Ti3O12 (BLT). Optical glasses used for optical materials are often doped with La2O3 to improve the refractive index, mechanical strength, and chemical durability of the glass.
Mixing a 3:1 reaction of B2O3 and La2O3 into glass composites results in a lower melting point because the higher molecular weight of lanthanum increases the homogeneous melt mixture. The addition of La2O3 to the molten glass increases the glass transition temperature from 1216 to 1254 °F (658 °C to 679 °C). The addition of La2O3 can also increase the density, refractive index, and microhardness of the glass.
3. Elements Obtained Together With Lanthanum Oxide
The long-term analysis and decomposition of the ore gadolinite has led to the discovery of several elements. As the analysis of the gadolinite progressed, the residues were labeled first with ceria, then lanthanum oxide, followed by yttria and elvia.