- The stabilization of the tetragonal phase in zirconia ceramics is crucial for enhancing their mechanical properties, such as improved toughness and strength.
- Pure zirconia (ZrO₂) undergoes phase transformations at different temperatures which can lead to volume changes and cracking. To prevent this, certain dopants (stabilizing oxides) are added.

Among the options given:
- Yttria (Y₂O₃) is the most common dopant used to stabilize the tetragonal phase of zirconia at room temperature. It achieves this by substituting Zr⁴⁺ ions in the lattice with Y³⁺ ions, creating oxygen vacancies that help maintain the tetragonal structure.
- Other oxides like Calcia (CaO) and Magnesia (MgO) can also stabilize zirconia but are less commonly used or require higher concentrations.
- Alumina (Al₂O₃) is not a stabilizing agent for the tetragonal phase but is often used as a reinforcing phase in composite ceramics.

Thus, Yttria-stabilized zirconia (YSZ) is widely utilized in biomedical applications such as dental implants and prosthetics due to its superior mechanical performance.

Key Points:
- Yttria (Y₂O₃) effectively stabilizes the tetragonal phase of zirconia at room temperature.
- This stabilization prevents detrimental phase transformations and improves toughness.
- Yttria-doped zirconia is often referred to as Yttria-Stabilized Zirconia (YSZ).

Reference: Handbook of Biomaterials Properties, Volume 2, Chapter 5, Page 143-145