Pure zirconium dioxide undergoes a phase transformation from monoclinic (stable at room temperature) to tetragonal (at about 1173 °C) and then to cubic (at about 2370 °C), according to the scheme
: monoclinic (1173 °C) ↔ tetragonal (2370 °C) ↔ cubic (2690 °C) ↔ melt.
Obtaining stable sintered zirconia ceramic products is difficult because of the large volume change, about 5%, accompanying the transition from tetragonal to monoclinic. Stabilization of the cubic polymorph of zirconia over wider range of temperatures is accomplished by substitution of some of the Zr ions (ionic radius of 0.82 Å, too small for ideal lattice of fluorite characteristic for the cubic zirconia) in the crystal lattice with slightly larger ions, e.g., those of Y (ionic radius of 0.96 Å). The resulting doped zirconia materials are termed stabilized zirconias.
Materials related to YSZ include calcia-, magnesia-, ceria- or alumina-stabilized zirconias, or partially stabilized zirconias (PSZ). Hafnia-stabilized zirconia has about 25% lower thermal conductivity, making it more suitable for thermal barrier applications.
Although 8–9 mol% YSZ is known to not be completely stabilized in the pure cubic YSZ phase up to temperatures above 1000 °C. 
Commonly used abbreviations in conjunction with yttria-stabilized zirconia are:
* Partly stabilized zirconia ZrO:
** PSZ – partially stabilized zirconia
** TZP – tetragonal zirconia polycrystal
** 4YSZ: with 4 mol% YO partially stabilized ZrO, yttria-stabilized zirconia
* Fully stabilized zirconias ZrO:
** FSZ – fully stabilized zirconia
** CSZ – cubic stabilized zirconia
** 8YSZ – with 8 mol% YO fully stabilized ZrO
** 8YDZ – 8–9 mol% YO-doped ZrO: the material is not completely stabilized and decomposes at high application temperatures, see next paragraphs)