Here's why:

* Electro negativity difference: Zirconium (Zr) is a metal with a low electronegativity, while oxygen (O) is a non-metal with a high electronegativity. The large difference in electronegativity between these two elements leads to the transfer of electrons from zirconium to oxygen.

* Formation of ions: Zirconium loses its valence electrons to form a positively charged Zr⁴⁺ ion, while oxygen gains electrons to form a negatively charged O²⁻ ion.

* Electrostatic attraction: The oppositely charged ions (Zr⁴⁺ and O²⁻) attract each other through strong electrostatic forces, resulting in an ionic bond.

While ZrO2 exhibits ionic bonding, it can also exhibit some degree of covalent character due to the relatively high electronegativity of oxygen. However, the predominant bonding type in ZrO2 is ionic.