Such a powder may have many more uses... But mixed-in yttria suggests your zirconia is meant for sintering ceramic parts.
That is, zirconia is well-known as a refractory ceramic, but its crystal changes twice with heat, making it break as it cools back. Yttria in it stabilizes at room temperature the crystal form that prevails at the highest temperature, allowing zirconia to go through temperature cycles without getting brittle.
Not only as massive parts: a present use and research topic is to coat refractory alloys with zirconia to protect them against corrosion in hot air or exhaust, at turbine blades, piston engines...
Hafnia is a sought refractory ceramic as well, but here it must be an impurity from yttria.