The diverse properties and extensive applications of yttrium oxide

Yttrium oxide (Y2O3) is an important rare earth oxide, presenting a white or slightly yellowish powder-like appearance. This type of C-type rare earth hemihydrate has a unique body-centered cubic structure and is insoluble in water and alkalis but soluble in acids. In the air, it readily absorbs carbon dioxide and water, thus requiring sealed storage to prevent deterioration.
The molar mass of yttrium oxide is 282 g/mol, and its density is 0.1 g/cm³. This material not only has a melting point of up to 2410°C and a boiling point of 4300°C, demonstrating excellent thermal stability. Additionally, yttrium oxide exhibits outstanding performance in both physical and chemical aspects, with excellent corrosion resistance. Its thermal conductivity reaches 27 W/(m·K) at 300K, approximately twice that of yttrium aluminum garnet, giving it significant advantages when used as a laser working medium.
Furthermore, yttrium oxide has a wide optical transparency range, from 29 μm to 8 μm, with a theoretical transmittance exceeding 80% in the visible light region. At 1050 nm, its refractive index is as high as 89, providing high transparency. Its low-phonon energy characteristics, with the maximum phonon cutoff frequency approximately 550 cm⁻¹, effectively suppress non-radiative transitions and increase radiative transition probabilities, thereby enhancing the luminescence quantum efficiency. Below 2200°C, Y2O3 remains in the cubic phase, without birefringence, and at 1050 nm, its refractive index is 89. However, when the temperature exceeds 2200°C, it transforms into the hexagonal phase.
Moreover, the energy gap of Y2O3 is very wide, reaching 5 eV. The trivalent rare earth luminescent ion dopants are precisely located between the valence band and the conduction band of Y2O3, and above the Fermi level, forming discrete luminescent centers. As a matrix material, Y2O3 can accommodate high concentrations of trivalent rare earth ions doping and effectively replace Y3+ ions without causing structural changes.
Applications of yttrium oxide:
Yttrium oxide has widespread applications in various fields. For example, it can be used to synthesize yttrium-stabilized zirconia powder. Pure ZrO2 undergoes a phase transformation during high-temperature cooling, resulting in volume expansion. However, by stabilizing the t→m phase transformation to room temperature, stress-induced phase transformation can be utilized to absorb the fracture energy, thereby enhancing the fracture toughness and wear resistance of the material.
To achieve phase transformation toughening of zirconia, the key lies in adding appropriate stabilizers and through specific sintering conditions, stabilizing the stable phase - tetragonal phase to room temperature. Thus, the tetragonal phase transformation at room temperature can be achieved, enhancing the stability of zirconia. Among various stabilizers, Y2O3 has attracted much research attention due to its superior properties. Using Y2O3-stabilized zirconia, the sintered Y-TZP material exhibits excellent mechanical properties at room temperature, including high strength, excellent fracture toughness, and fine and uniform grain size. These characteristics make Y-TZP material stand out in numerous applications and attract much attention.
In the sintering process of special ceramics, fluxing agents play a crucial role. Their functions are diverse, typically including forming solid solutions with the sintered material, hindering crystal phase transformation, inhibiting grain growth, and generating liquid phases. Taking the sintering of alumina as an example, magnesium oxide (MgO) is often used as a microstructure stabilizer. It can refine the grains, significantly reducing the difference in grain boundary energy, thereby weakening the anisotropy of grain growth and inhibiting discontinuous grain growth. However, due to the high volatility of MgO at high temperatures, to ensure the best effect, it is usually considered to mix yttrium oxide (Y2O3) with MgO. The addition of Y2O3 not only helps further refine the grains but also promotes densification during the sintering process.