Effect of the valence state of ce ions on the phase stability and mechanical properties of the crystals of ZrO$_{2}$-based solid solutions

The structure and mechanical properties of the crystals of solid solutions of zirconium dioxide, which are stabilized by yttrium and cerium oxides, have been studied. The electron paramagnetic resonance technique has been used to identify Ce$^{3+}$ ions and to determine their relative concentration in the crystals. It is shown that the presence of Ce$^{3+}$ ions in the crystals is the main factor responsible for their high fracture toughness. The annealings carried out during investigations, which lead to a decrease in the concentration of Ce$^{3+}$ ions, show that a change in the valence state of cerium ions lowers the fracture toughness of the crystals.