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.     

Structure and phase composition studies of partially stabilized zirconia

Zirconia single crystals doped with 2.8, 3.2, 3.7, and 4.0 mol % of Y₂O₃ have been studied. The phase composition and structure have been studied by X-ray diffraction analysis and transmission electron microscopy. It has been established that all investigated samples has two ZrO₂ tetragonal phases with tetragonality c/a = 1.006–1.007 and c/a = 1.014–1.015 independent of the stabilizing impurity content. The former phase is not transformed, whereas the latter is transformed into a monoclinic one. In all cases the samples have a developed twin structure. Twinning hierarchy is observed: there are first-, second-, third-order, etc., twins, each of them containing the next-order twins inside them. Elastic stress relaxation occurs by twinning rather than by generation of dislocations. The stabilizing impurity content affects the structure nonmonotonically; the minimum dimensions of the twin lamellas refer to the Y₂O₃ concentration of 3.2 mol %.     

Microscopic mechanism of stability in yttria-doped zirconia

The relaxed configurations of yttria-stabilised zirconia (YSZ) between 3 and 10 mol % of Y₂O₃ were modeled using the pseudopotential technique. In the displacive limit of a double-well potential model, the vibrational mode corresponding to the soft phonon in pure c-ZrO₂ was calculated for each Y₂O₃ composition. These anharmonic vibrations, associated with the stabilization of YSZ, were investigated within the self-consistent phonon approximation making obtainable the fine structure in spectral density. In studying the phonon dynamics, we use the displacement probability density, which can quantify very accurately the transition temperature necessary for stabilizing the YSZ cubic phase.     

Structure,phase composition,and spectral luminescence properties of partially stabilized zirconium dioxide crystals doped with Yb<Superscript>3+</Superscript> ions

Investigation of partially stabilized zirconium dioxide crystals via transmission electron microscopy has revealed a developed twin structure therein. The following compositions of the above crystals have been selected for this study: 97.2 mol % ZrO₂–1.0 mol % Y₂O₃–1.8 mol % Yb₂O₃; 97.2 mol % ZrO₂–2.0 mol % Y₂O₃–0.8 mol % Yb₂O₃; 97.2 mol % ZrO₂–2.5 mol % Y₂O₃–0.3 mol % Yb₂O₃; and 96.3 mol % ZrO₂–3.4 mol % Y₂O₃–0.3 mol % Yb₂O₃. X-ray diffraction analysis of these crystals indicate the presence of transformable (t) and nontransformable (t') tetragonal phases. Optical spectroscopy measurements of ZrO₂–Y₂O₃–Yb₂O₃ crystals with tetragonal and cubic structures have highlighted in Yb³⁺-doped zirconium dioxide samples the formation of the optical centers of the Yb³⁺ ions is observed, whose crystal surrounding is similar to those in cubic zirconium dioxide crystals.     

Structure, properties, and formation models of optical ceramics

The structure, properties, and formation mechanisms of Y₃Al₅O₁₂, Y₂O₃, and Lu₂O₃ laser ceramics are investigated. Their microhardness and fracture toughness are determined. It is shown that the change in mechanical properties is related both to the grain size and grain boundary structure. Processes of plastic deformation of crystals by mechanical twinning are considered. Mechanisms of formation and motion of twins in crystals with FCC structure are determined. It is shown that the realization of similar mechanisms in crystals with HCP structure results in the phase transformations. Models of the formation and motion of twin boundaries are proposed which result in pore healing when preparing monolithic samples of highly transparent ceramics.     

Composition dependence of the ionic diffusion coefficients in yttria-stabilized zirconias

The diffusion coefficient of the O²⁻ ions in yttria-stabilized zirconia (1−x)ZrO₂·xYO_1.5 has been investigated as a function of the concentration of Y³⁺ ion over a range x = 0.131–0.261 by using quasielastic light scattering. The diffusion coefficients were deduced from the analysis of the temperature dependence of the scattering intensity at 3 GHz. It is concluded that the diffusion coefficient reaches its maximum value at x = 0.165. The composition dependence of the scattering intensity suggests that the concentration of the moving carrier decreases as the Y³⁺ content increases in spite of an increase of the oxygen vacancies.     

Electrochemical transient investigations on the diffusion of minority charge carriers in YSZ doped by transition metal oxides

The voltage relaxation of galvanic cells with zirconia based electrolytes polarised between an inert Pt electrode and a Pt/air electrode is analysed to obtain the diffusion coefficients of holes and electrons. The hole diffusion coefficient can be reduced by replacing zirconium with guest ions of different size, e.g. Nb⁵⁺ and Ti⁴⁺. The TZP phase with 3 mol% Y₂O₃ of dopant has a higher hole diffusion coefficient than the CYZ phase doped with 8 mol% Y₂O₃. 1 and 3 mol% p-type MnO_1.5 doping increases the conductivity of holes in CYZ to a large extend, but does not influence the diffusivity. This indicates that the doping increases the hole conductivity through an increased concentration of holes. In the case of 10 and 15 mol% MnO_1.5 doped Z3Y, the electronic conductivity is dominant. The chemical diffusion coefficients which are related to the oxygen vacancies were determined by GITT. The results show that the chemical diffusion coefficient of oxygen vacancies is much larger than that for holes in zirconia.     

Luminescence and scintillation properties of Y<Subscript>3</Subscript>A<Subscript>l5</Subscript>O<Subscript>12</Subscript>:Ce single crystals and single-crystal films

Luminescence and scintillation properties of Y₃A_l5O₁₂:Ce single crystals grown from the melt by the Czochralski and horizontal directed crystallization methods in various gas media and Y₃A_l5O₁₂:Ce single-crystal films grown by liquid-phase epitaxy from a melt solution based on a PbO-B₂O₃ flux have been comparatively analyzed. The strong dependence of scintillation properties of Y₃A_l5O₁₂:Ce single crystals on their growth conditions and concentrations of Y_Al antisite defects and vacancy defects has been established. Vacancy defects are involved in Ce³⁺ ion emission excitation as the centers of intrinsic UV luminescence and trapping centers. It has been shown that Y₃A_l5O₁₂:Ce single-crystal films are characterized by faster scintillation decay kinetics than single crystals and a lower content of slow components in Ce³⁺ ion luminescence decay during high-energy excitation due to the absence of Y_Al antisite defects in them and low concentration of vacancy defects. At the same time, the light yield of Y₃A_l5O₁₂:Ce single-crystal films is comparable to that of single crystals grown by directed crystallization due to the quenching effect of the Pb²⁺ ion impurity as a flux component and is slightly lower (∼25%) than the light yield of single crystals grown by the Czochralski method.     

Effect of Y2O3 additive on the microstructure and high-frequency properties of Z-type hexaferrites

In order to improve the high-frequency electromagnetic properties of Z-type hexaferrites such as high cut-off frequency and low dielectric constant, Y₂O₃ was introduced. The influence of Y₂O₃ additive on the phase composition, densification, microstructural and electromagnetic properties of the ceramics with composition of Ba₃(Co_0.4Zn_0.6)₂Y_xFe_24−xO₄₁ (x=0−1) was investigated. The results show that as the amount of Y₂O₃ additive increased, the major phase changed to Z-phase; simultaneously, a small amount of garnet phase appeared. With increasing Y₂O₃ content, the garnet phase separated out on grain boundaries as a secondary phase restraining grain growth. When x was varied from 0 to 1, the dielectric constant decreased and the ferroelectric resonance peak shifted toward a higher frequency. Meanwhile, the initial permeability increased at first, and then decreased with further increasing x, which could be mainly attributed to the change of phase composition and sintering density. With increasing Y₂O₃ content, the minimum reflection point of the samples shifted toward a higher frequency.     

Local structure analysis of YSZ by Y-89 MAS-NMR

The local coordination structure around Yttrium ions in yttria stabilized zirconia (YSZ) has been investigated by ⁸⁹Y MAS-NMR. The NMR spectrum showed multiple peaks corresponding to yttrium ions in different coordination numbers. The compositional dependence of spectra was observed. Yttrium ions of different oxygen coordination number were quantified. The oxygen vacancy concentration around the cations was determined. It was found that the vacancies were distributed around Zirconium ions in lower Y₂O₃ concentrations, and the vacancy concentration located to Yttrium began increasing at concentrations above 10 mol% Y₂O₃. The local structure change was able to be directly observed by ⁸⁹Y NMR measurements.     

Spectroscopic characteristics of the Nd3+ ions in garnet crystals

The article deals with the research of oscillator strengths and the Ω_t (t=2,4,6) intensity parameters of Nd³⁺ doped garnet crystals. It has been found that the absorption intensity of the ⁴I_9/2→⁴G_5/2, ²G_7/2 hypersensitive transition in the Ca₃(NbGa)₅O₁₂ crystals doped with Nd³⁺ is considerably higher than the corresponding values in the following garnet crystals: Y₃Al₅O₁₂:Nd, (GdY)₃(ScAl)₅O₁₂:Nd, Gd₃(ScAl)₅O₁₂:Nd and (GdСa)₃(GaZr)₅O₁₂:Nd. It has been established also that the Ω₂ intensity parameter of the Ca₃(NbGa)₅O₁₂:Nd crystals is one order of magnitude higher compared to the same parameter for the other garnet crystals. These effects in the Ca₃(NbGa)₅O₁₂:Nd crystals are explained by the presence of the Nd³⁺ ions optical sites with a symmetry of local environment C₂, C_2v, C₁.     

Regularities of formation of cubic zirconia stabilized with calcium,yttrium, and indium oxides under mechanochemical treatment

An effect of the composition of reacting components during mechanochemical activation on the ZrO₂ structure stabilized with additives of In₂O₃, CaO, and Y₂O₃ oxides has been revealed. It is established that mechanochemical activation of oxide mixtures leads to the formation of dispersed solid solutions based on cubic zirconia. It is shown that interaction depth of the components during mechanochemical activation increases in the series of oxides In₂O₃ < CaO < Y₂O₃.     

Comparative analysis of the twin and heterophase structures in (1−x)Pb(Mg1/3Nb2/3)O3−xPbTiO3 crystals

The specific features of the coexistence of phases in heavily twinned crystals of the (1?x)Pb(Mg_1/3Nb_2/3)O₃?xPbTiO₃ system in the vicinity of the morphotropic phase boundary (0.30≤x≤0.40) are investigated. The phase transformations in crystals at x = const during cooling are considered at electric field strengths E=0 and 0.1 MV/m. The conditions of the formation of interphase boundaries (zero net strain planes) are determined for different first-order phase transitions. The results of calculating the tetragonal-monoclinic M _C and monoclinic-monoclinic (M _C –M _A ) phase transitions are represented in the form of “twin state-interphase boundary” diagrams. The effect of a 90° domain (twin) structure of the tetragonal phase on the heterophase state associated with the presence of monoclinic phases is analyzed.     

Luminescence properties of solid solutions of borates doped with rare-earth ions

The structural and luminescence properties of Lu _x Y_{1 ? x} BO₃ solid solutions doped with Ce³⁺ or Eu⁺³ have been investigated. It has been found that the solid solutions crystallize in the vaterite phase with a lutetium concentration x < 0.5. For a higher lutetium concentration x, the solid solutions contain an additional calcite phase with a content less than 5 wt %. The luminescence spectra are characterized by intensive impurity emission under excitation with the synchrotron radiation in the X-ray and ultraviolet spectral ranges. It has been shown that, as the lutetium concentration x in the Lu _x Y_{1 ? x} BO₃: Ce³⁺ solid solutions increases, the emission intensity smoothly decreases, which is associated with a gradual shift of the Ce³⁺ 5d(1) level toward the bottom of the conduction band, as well as with a decrease in the band gap. It has been established that, in the Lu _x Y_{1 ? x} BO₃: Eu³⁺ solid solutions with intermediate concentrations x, the efficiency of energy transfer to luminescence centers increases. This effect is explained by the limited spatial separation of electrons and holes in the solid solutions. It has been demonstrated that the calcite phase adversely affects the luminescence properties of the solid solutions.     

Ionic conductivity and point defects in pure and doped MnF2 and MgF2 single crystals

Conductivity, σ, of MnF₂ and MgF₂ single crystals, pure and doped (with Li⁺, Na⁺, Y³⁺, Gd³⁺), has been measured, from room temperature to 500°C. Further, some crystals were contaminated with O^2? as an additional impurity. These tetragonal (rutile structure) crystals both behave like typical ionic conductors. Of particular interest is the existence of a large anisotropy, σ being largest when measured parallel to the c-axis. Study of the conductivity isotherms and anisotropy as functions of impurity concentration allows identification of the conduction mechanism in terms of the migration of two mobile defects: the fiuorine-ion vacancy, V_F, and interstitial, F_i. A value of 1.44 eV was obtained for the enthalpy of formation of the intrinsic anion Frenkel defect, 0.80 eV for the migration enthalpy of a V_F and 0.88 eV for an F₁ in MnF₂ parallel to the c-axis. Similar values were obtained for MgF₂. This work shows that more information about point defects can be obtained from conductivity measurements in non-cubic cyrstals than in cubic ionic crystals, because of the additional information from conductivity anisotropy.     

Structure and spectral-luminescence properties of yttrium-stabilized zirconia crystals activated with Tm<Superscript>3+</Superscript> ions

Yttrium-stabilized zirconia crystals (ZrO₂-13.8 mol % Y₂O₃-0.2 mol % Tm₂O₃ and ZrO₂-12 mol % Y₂O₃-2 mol % Tm₂O₃) have been grown by directed crystallization from a melt in a cold container using direct high-frequency melting. The crystals have been analyzed by X-ray diffraction. The spectral-luminescence properties have been studied, and the cross-relaxation efficiency for Tm³⁺ ions (³ H ₄ → ³ F ₄, ³ H ₆ → ³ F ₄) in these crystals has been estimated.     

Conductivity of Fe2O3-doped YSZ

Effect of 2 mol.% Fe₂O₃ addition on conductivity of yttria stabilized zirconia ceramics (YSZ, 6–12 mol.% Y₂O₃) was established. For Fe doped material, it was shown that conductivity demonstrates maximum at 10 mol.% Y₂O₃, and its value increases by 1.4 times. Conductivity maximum corresponds with the minimal volume of crystal lattice. Discussion of results was performed in terms of the model that assumes the control effect of hydrostatic pressure on oxygen ions diffusion.     

Ionic and electronic conduction of oxygen ion conductors in the Bi2O3−Y2O3 system

The ionic conduction of sintered samples of Bi₂O₃?Y₂O₃ containing 20–30 mol% Y₂O₃ has been investigated by means of ac conductivity experiments and EMF measurement of an oxygen concentration cell using the specimen tablet as electrolyte. Ac conductivity was measured at a frequency of 10 kHz under oxygen partial pressures ranging from 1 to 10^-21 atm. The results show that these materials possess high ionic conduction. The conductivities for samples containing 22.5–30 mol% Y₂O₃ are many times higher than those of stabilized zirconia-based solid electrolyte at corresponding temperatures. The ratio of E_meas./E_calc. of an oxygen concentration cell Pt∣O₂(air)∣Bi₂O₃?Y₂O₃∣O₂(pure oxygen)∣Pt is close to 1 which shows that the materials containing 22.5 to 30 mol% Y₂O₃ are nearly pure ionic conductors. The p-type conductivity is negligible at higher P_O2 values. The n-type conduction for a sample containing 27.5 mol% Y₂O₃ was investigated using the Coulomb titration technique in which the following cell was used: Pt Rh∣O₂(air)∣Bi₂O₃?Y₂O₃∣[O]_sn∣W.log P_é=-767000/T+665. P_é is equal to 2.6×10^-61 atm at 800°C. The n-type conductivity is also very small. Thus these materials are good oxygen ionic conductors.     

EPR Spectroscopy of Impurity Thulium Ions in Yttrium Orthosilicate Single Crystals

The frequency-field and orientation dependences of the electron paramagnetic resonance (EPR) spectra are measured for impurity Tm³⁺ ions in yttrium orthosilicate (Y₂SiO₅) single crystals by stationary EPR spectroscopy in the frequency range of 50–100 GHz at 4.2 K. The position of the impurity ion in the crystal lattice and its magnetic characteristics are determined. The temperature dependences of the spin–lattice and phase relaxation times are measured by pulse EPR methods in the temperature range of 5–15 K and the high efficiency of the direct single-phonon mechanism of spin–lattice relaxation is established. This greatly shortens the spin–lattice relaxation time at low temperatures and makes impurity Tm³⁺ ions in Y₂SiO₅ a promising basis for the implementation of high-speed quantum memory based on rare-earth ions in dielectric crystals.     

Various types of photoactive behavior of the Y<Subscript>3</Subscript>Fe<Subscript>5</Subscript>O<Subscript>12</Subscript> ferrimagnetic insulator

The photomagnetic behavior of single-crystal yttrium iron garnet Y₃Fe₅O₁₂ doped with iridium, substituting the cation of iron in the octahedron, is investigated upon illumination at room temperature. It is shown that the photomagnetic properties of Y₃Fe_4.97Ir_0.03O₁₂ samples are to a large degree related to the impurity distortion of the sublattice of iron atoms in octahedral coordination, rather than solely to the possible presence of Fe⁴⁺ cations, which are inactive at room temperature and may even be lacking in single crystals doped with iridium. It is concluded that the photoinduced change in the magnetic parameters of this material is determined by the location of impurity cations and increased surface imperfection of the material. The reasons for the different photoactive behavior of this promising material for spintronics, that is, a singlecrystal yttrium iron garnet, are summarized.