The mechanical properties, phase composition and luminescence of (ZrO2)1−x(Sm2O3)x (x = 0.02–0.06) crystals synthesized using directional melt crystallization were studied. The regularities of changes in the phase composition of the crystals depending on samaria concentration were analyzed. Optical spectroscopy showed that Sm ions were incorporated into the ZrO2 crystal lattice in the form of Sm3+. The microhardness of the crystals was shown to increase with Sm2O3 concentration and reached 12.45 GPa for (ZrO2)0.94(Sm2O3)0.06 crystals. The highest fracture toughness of 14.2 MPa∙m1/2 was observed for the crystals containing 3.7 mol.% Sm2O3. The experimental results were analyzed in order to understand the effect of phase composition on the mechanical properties of the crystals. The effect of ionic radii of stabilizing oxide cations (i.e., Y3+, Gd3+ and Sm3+) on the mechanical properties of the materials on the basis of partially stabilized zirconia was also discussed.
