A. V. Kulebyakin

Structure and mechanical properties of crystals of partially stabilized zirconia after thermal treatment

The phase composition and morphology of the twin structure of the Y2O3-stabilized zirconia crystals (from 2.8 to 4.0 mol %) after the thermal treatment at 1600°C have been investigated by X-ray diffractometry and transmission electron microscopy. It is shown that as the concentration of the stabilizing Y2O3 impurity increases, the character of the twin structure changes, and the amount of the untransformed phase t′ increases. The dependence of the hardness and crack resistance of the crystals of partially stabilized zirconia on the Y2O3 concentration and the indenter orientation is investigated using the microindentation method. The sample with the lowest concentration of the stabilizing Y2O3 impurity turned out the most crack resistant. This can be explained by a high content of tetragonal phase t in it, which provides the transformation strengthening mechanism of the material, and by a more multilevel character of twinning.

Preparation and properties of Y2O3 partially stabilized ZrO2 crystals

We have studied the effect of composition and growth conditions on the structure and properties of 2.5–5 mol % Y2O3 partially stabilized ZrO2 crystals grown by directional solidification in a cold-wall crucible. The phase composition and density of the crystals have been determined. The crystals are shown to be uniform in composition, with local changes in Y2O3 content within ±0.5 mol %. The dimensions and quality of the single crystals are influenced by the growth conditions.

Mechanical properties of partially stabilized zirconia crystals studied by kinetic microindentation

Using kinetic microindentation, we have studied the strength and elastic characteristics of partially stabilized zirconia (PSZ) crystals. The results demonstrate that the mechanical properties of the crystals depend on yttria stabilizer concentration. Additional doping with ceria leads to an increase in the kinetic hardness, kinetic Young’s modulus, and plasticity of the crystals, thus improving their mechanical characteristics. The PSZ crystals have high plasticity for nonmetallic materials.

Structure, phase composition, and spectral-luminescent properties of ZrO2-Y2O3-Er2O3 crystals

This paper presents the results of investigations of the structure, phase composition, and spectral-luminescent properties of Er2O3-doped zirconia crystals with different Y2O3 concentrations: 99.7 mol % ZrO2-0.3 mol % Er2O3, 97.2 mol % ZrO2-1.0 mol % Y2O3-1.8 mol % Er2O3, 97.2 mol % ZrO2-2.0 mol % Y2O3-0.8 mol % Er2O3, 97.2 mol % ZrO2-2.5 mol % Y2O3-0.3 mol % Er2O3, 96.3 mol % ZrO2-3.4 mol % Y2O3-0.3 mol % Er2O3, and 86 mol % ZrO2-13.4 mol % Y2O3-0.6 mol % Er2O3. The transmission electron microscopy investigation has revealed the presence of twins in the 99.7 mol % ZrO2-0.3 mol % Er2O3 crystals with a monoclinic structure and in the 97.2 mol % ZrO2-2.5 mol % Y2O3-0.3 mol % Er2O3 and 96.3 mol % ZrO2-3.4 mol % Y2O3-0.3 mol % Er2O3 crystals with a tetragonal structure. No twins have been found in the 86 mol % ZrO2-13.4 mol % Y2O3-0.6 mol % Er2O3 crystals with a cubic structure. The phase composition of these crystals has been investigated using X-ray diffraction. It has been found that the 97.2 mol % ZrO2-1.0 mol % Y2O3-1.8 mol % Er2O3 crystals contain only the transformable tetragonal phase t, whereas the 97.2 mol % ZrO2-2.0 mol % Y2O3-0.8 mol % Er2O3, 97.2 mol % ZrO2-2.5 mol % Y2O3-0.3 mol % Er2O3, and 96.3 mol % ZrO2-3.4 mol % Y2O3-0.3 mol % Er2O3 crystals include two tetragonal phases with different degrees of tetragonality c/a: the transformable phase t and nontransformable phase t′. Specific features of the formation of Er3+ optical centers in zirconia crystals with different concentrations of stabilizing oxides have been revealed using the results of experiments on optical spectroscopy.

Phase composition and spectral-luminescent properties of yttrium partially stabilized zirconia crystals doped with Nd 2 O 3 and CeO 2

The phase composition and spectral-luminescent characteristics of yttrium partially stabilized zirconia (YSZ) crystals doped with Nd2O3 and CeO2 (ZrO2-Y2O3-Nd2O3-CeO2) are studied. X-ray diffraction shows that YSZ ZrO2-2.5 mol %Y2O3-0.2 mol %CeO2-0.1 mol %Nd2O3, ZrO2-2.03 mol %Y2O3-0.435 mol %CeO2-0.334 mol %Nd2O3, and ZrO2-2.03 mol %Y2O3-0.653 mol %CeO2-0.111 mol %Nd2O2 YSZ crystals contain two different tetragonal phases (transformable t and nontransformable ’t). The spectral-luminescent properties of these crystals indicate that Nd3+ ions occupy sites mainly in the transformable (t) phase.

Effect of Y 2 O 3 Stabilizer Content and Annealing on the Structural Transformations of ZrO 2

The structure of partially stabilized zirconia crystals has been studied by transmission electron microscopy before and after annealing. Structural characterization of Y2O3-doped (2.8 to 4 mol %) zirconia before annealing showed that all of the samples consisted of twin domains whose size was dependent on the stabilizer content. Annealing at 2100°C increased the domain size in the composition range 2.8–3.7 mol % Y2O3 and reduced it at 4 mol % Y2O3. These structural changes allowed us to determine the position of the representative point relative to the phase boundary in the equilibrium phase diagram of the system.

Structure and properties of the crystals of solid electrolytes (ZrO2)1 – x – y (Sc2O3) x (Y2O3) y (x = 0.035–0.11, y = 0–0.02) prepared by selective melt crystallization

Single crystals of solid electrolytes of the (ZrO2)1–x–y(Sc2O3)x(Y2O3)y (x = 0.035–0.11, y = 0‒0.02) system were grown by selective melt crystallization. Stabilization of ZrO2 only with Sc2O3 in the concentration range 9–11 mol % Sc2O3 did not afford crystals with a cubic structure, and only the introduction of additional Y2O3 stabilizers afforded uniform transparent single-phase cubic crystals. All the crystals under study had high microhardness, but low crack resistance. The ion conductivity of crystals with 6 and 9 mol % Sc2O3 (6ScZr and 9ScZr, respectively) is comparable to that of 8 mol % Y2O3-stabilized ZrO2 (8YSZ), which is the most suitable electrolyte in the ZrO2–Y2O3 binary system. The specific conductivity of crystals containing 8–10 mol % Sc2O3 and 1–2 mol % Y2O3 exceeds that of other materials including 8YSZ. The maximum conductivity in the given range of compositions is inherent in the cubic phase with 10 mol % Sc2O3 and 1 mol % Y2O3 (10Sc1YZr).

Study of the structural and physicochemical properties of nanostructured zirconia crystals for fabricating an innovative electrosurgical tool

To optimize the chemical composition of the crystals of nanostructured partially stabilized zirconium dioxide for fabricating cutting parts of an electrosurgical tool, the structural and strength properties of these crystals were investigated in dependence on the stabilizing impurity (Y2O3) content and the effect of additional dopants on the critical properties of the material was studied. It was established that in all the investigated crystals without additional doping, regardless of the stabilizing impurity content, there are two phases of zirconium dioxide tetragonal modification with different tetragonality factors, c/a = 1.006–1.007 and 1.014–1.015, the first being nontransformable and the second being transformable to a monoclinic phase. All the synthesized crystals are characterized by a pronounced twin domain structure, which forms upon cooling the single crystal during the transition of the cubic structure to the tetragonal one. It was established that the Y2O3 concentration in the range from 2.5 to 3.0 mol % is optimal for ensuring high values of the strength characteristics and fracture toughness of the material. Doping of the crystals with the rare-earth elements notice-ably affects their strength characteristics. One of the most promising materials for fabricating cutting blades of the electrosurgical tool is the crystals of partially stabilized zirconium dioxide doped with Ce2O3+Nd2O3, which are characterized by high fracture toughness and enhanced bending strength.

Investigation of the microstructure and nanostructure of partially stabilized zirconia crystals

This paper reports on the results of investigations into the dependence of the structure of partially stabilized zirconia crystals on the composition and technological conditions used for their growth. The zirconia crystals containing from 0 to 4 mol % Y2O3 are grown by directional crystallization in a cold container with the use of direct high-frequency heating. The microstructure and nanostructure of the grown crystals are examined using transmission and scanning electron microscopy. It is established that the formation of the structure depends directly on the composition of the crystals and the conditions of their growth.

Structure and Transport Properties of Zirconia-Based Solid Solution Crystals Co-Doped with Scandium and Cerium Oxides

The crystals of (ZrO2)1–x(Sc2O3)x(СeO2)0.01 solid solutions (x = 0.08–0.10) were obtained by directional crystallization. The crystals of the grown composites were semitransparent, opalescent, and without cracks and had varying microstructure in the bulk. In the range of compositions under study, it was impossible to obtain optically homogeneous, fully transparent crystals. The crystals grown at a growth rate of 10 mm/h had a nonuniform distribution of ceria along the length of the ingot. The introduction of ceria in an amount of 1 mol % increased the conductivity of the crystals, but the increase in the specific electric conductivity depended on the Sc2O3 content and the phase composition of the crystals. The highest conductivity was inherent in the (ZrO2)0.89(Sc2O3)0.10(CeO2)0.01 crystals.