Yttria stabilized zirconia powder (YSZ) is a ceramic in which the cubic crystal structure of zirconium dioxide is made stable at room temperature by the addition of yttrium oxide. These oxides are commonly called "zirconia" (ZrO2) and "yttria" (Y2O3), hence the name. Yttria stabilized zirconia powder (YSZ) is used in the production of a solid oxide fuel cell (SOFC).

Yttria stabilized zirconia powder (YSZ) is used as the solid electrolyte, which enables oxygen ion conduction while blocking electronic conduction. In order to achieve sufficient ion conduction, an SOFC with a YSZ electrolyte must be operated at high temperatures (800 °C-1000 °C). While it is advantageous that YSZ retains mechanical robustness at those temperatures, the high temperature necessary is often a disadvantage of SOFCs. The high density of Yttria stabilized zirconia powder is also necessary in order to physically separate the gaseous fuel from oxygen, or else the electrochemical system would produce no electrical power.

Yttria-stabilized zirconia (YSZ) is a crystalline oxide which exists in three phases with different crystal structures depending on the temperature - monoclinic, tetragonal, and cubic. There is a significant volume change associated with the monoclinic-tetragonal transition, which can cause problems when processing the material. Yttria stabilized zirconia powder (YSZ) is renowned for its hardness and optical properties in monocrystal form (see "cubic zirconia"), it is used as jewelry.

Yttria stabilized zirconia powder is the most common oxygen ion conductive electrolyte used in Solid Oxide Fuel Cells15 and in gas sensors. Apart from its applications in the field of electrocatalysis, YSZ has been extensively used as electrolytic support in catalytic applications using solid electrolyte cell reactors as well as in the frame of the phenomenon of Electrochemical Promotion of Catalysis (EPOC).